Forest Snow and Landscape Research ISSN 1424-5108

Volume 79, Issue 3, 2005 195–415

Growth Rings in Herbs and Shrubs: life span, age determination and stem anatomy

Fritz Hans Schweingruber and Peter Poschlod

Publishers Swiss Federal Research Institute WSL, Birmensdorf Haupt, Berne, Stuttgart, Vienna Cerastium semidecandrum L., Caryophyllaceae. Collected April 6th 2005 in a vineyard in Fully, Valais, Switzerland. Transverse section of a 0.9 mm thick root collar stained with Astrablue and Safranin. Magnification 120x. The xylem in the center is surrounded by a cambium, a phloem, a cortex, an exodermis and an epidermis. The xylem is characterized by a rayless, unlignified parenchymatic tissue (blue), in which slightly lig nified vessels are embedded (reddish). The concentration of vessels at the periphery of the xylem indicates that the annual herb germinated in fall, stopped growth in winter and finished its life period in spring. The cambium is one to two cells wide. Typical for the phloem is the composition of very small sieve elements and the small parenchymatic cells. The thick belt with large cells represents the cortex (dark blue). It is surrounded by the exodermis, where the cell walls are intensively lignified (red). The outermost thin- walled cells represent the epidermis. For. Snow Landsc. Res. 79, 3: 195–415 (2005) 197

Growth Rings in Herbs and Shrubs: life span, age determination and stem anatomy

Fritz Hans Schweingruber1 and Peter Poschlod2 1 WSL Swiss Federal Research Institute, Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland. [email protected] 2 Institute of Botany, Faculty of Biology and Preclinical Medicine, University of Regensburg, D-93040 Regensburg, Germany. [email protected]

Revised manuscript accepted 17 October, 2005

Abstract

Growth Rings in Herbs and Shrubs: life span, age determination and stem anatomy Can the age of herbs, dwarf shrubs and shrubs be determined, and if so, how old can they get? And what possibilities exist for answering ecological questions about plants and populations using the ages of such plants? These and many more questions prompted us to analyse the growth rings observed in central European herbs, dwarf shrubs and shrubs, and also, more generally, to review the state of the art for classifying and determining the age of plants. We also explore how the knowl- edge of the presence of growth rings can be applied to ecological and biological conservation ques- tions, and which factors may limit the lifespan of plants. We present techniques and prerequisites for identifying growth rings and for validating that they are actually annual rings. The limitations of growth-ring analysis are discussed. The anatomy of the root collars of about 800 central European species is given. The methods of age classification/determination reviewed include: annual ring and other chrono- logical methods, growth form analysis, permanent plot research, and historical and genetic analy- ses. The application of growth-ring analysis to describe population structures allows the current status of a population to be assessed. Several examples are given. Physiological and environmental factors that may limit a plant’s lifespan are reviewed. Preliminary results evaluating our data set show that lifespan may be limited by temperature and nutrients.

Keywords: life span, growth-ring analysis, annual rings, plant anatomy, ontogeny, herbs, dwarf shrubs, shrubs, plant population structure, temperature, nutrients, moisture

For. Snow Landsc. Res. 79, 3 (2005) 199

Preface

Life span is a key trait in the life history of plants. What determines a plant’s survival under specific environmental conditions? Many factors affect a plant’s life span and help us ident- ify its age, such as: morphological, anatomical, ontogenetic, physiological and ecological fac- tors, and even the structure of populations. Until now, there has been no overview taking into account all these aspects and only a few studies of the life span of non-trees. Such an overview would, we thought, be an exciting challenge in which we could draw on our experience in dif- ferent fields. For the first author this has been in dendrochronology and wood anatomy, and for the second in population biology and vegetation ecology. This overview is, in our opinion, long overdue. Until recently ecologists seem to have largely ignored the fact that the age of non-woody plants can also be determined, and plant physiologists still cite MOLISCH (1929, 1938) when they discuss the life span of a whole plant or plant ageing. Our main aim is to encourage scientists from different disciplines to ask new questions by offering them not only a catalogue of species whose annual rings can be analysed, but also to encourage a state-of-the-art overview of how to measure the life span and persistence of a number of plant species. In the future we hope that it will be possible to determine the life span and persistence of plants with primary roots possessing growth rings, as well as to analyse the short-term demography of perennial species. Where annual growth rates and vegetation carbon storage can be measured in the herb and shrub layer, it should also be possible to examine issues such as the extent to which plant life span depends on habitat quality or the effect of different environmental conditions on population structures. Analyses of population structures should also help us to evaluate the success, or otherwise, of conservation or resto- ration management treatments. Finally, we hope that this overview and review will encourage plant physiologists to give further thought not just to the death of a cell or an organ such as a leaf, but also to the whole plant and various related aspects. Meeting this challenge would not have been possible without the help of many colleagues and friends: Stephan Krebs (LEL, Schwäbisch Gmünd, Germany) introduced us to Ernst Rieger (Blaufelden, Germany), without whose generous support we would not have been able to prove that annual rings in herbs are really annual rings. He let us dig in the fields where he cultivates an innumerable number of “wild species”, with exact sowing dates recorded for individuals of about 30 species. Anne-Kathrin Jackel (Regensburg, Germany) provided data on growth forms from the BioPop database and “managed” the “Swiss data”. Christine Römermann (Regensburg, Germany) put together data on vegetation types and life forms. During the literature search we found a huge amount of material in Russian on these topics, which was translated from Russian into German by Wioletta Moggert (Regensburg, Germany). Her telephone calls to Russia are already legendary: they made it possible for us to consult missing volumes of the Biological Flora of Moscow. Frantisek Krahulec (Prague and Pruhonice, Czechia), from the Institute of Botany at the Czech Academy of Sciences, provided the first paper by Rabotnov on the ontogenetic classification of species, which was available neither in Germany nor in Switzerland. Nina Ulanova (Moscow) also sent some Russian literature. The discussions we had with her (by e-mail) on the ontogenetic concepts of Rabotnov were very helpful. We also thank Bertil Krüsi, who provided unpublished data from studies on the growth rate and age of Brachypodium pinnatum patches and Jeremy Flower-Ellis, who provided a copy of his thesis. Tanja Donaubauer, Oliver Geuss, Isabel Hoffmann, John Hoffmann (all Regensburg, Germany), Claudia Baumberger (Biel, Switzerland), Marion and Richard Joss-Petersdorf (Schlatt, Winterthur, Switzerland), Andrea Münch and Ruth Schwarz (Würzburg, Germany) and Yvonne Steiner (Basel, Switzerland) provided unpublished data from their theses and research work. Karl-Friedrich Schreiber helped Tanja Donaubauer and the second author in the field to dig up individuals for annual- 200 ring analysis. Special thanks go to the Swiss Federal Institute for Snow and Avalanche Research (SLF) in Davos and the Swiss Federal Institute WSL in Birmensdorf. Both insti - tutions have allowed the first author to work in their laboratories since his retirement. The Swiss National Science Foundation supported the first author for 15 years in his collection of plant material and preparation of slides. Finally, we have to thank Vanessa Winchester (Oxford, UK), and Silvia Dingwall (Nussbaumen, Switzerland), who have patiently corrected our English. Their nice comments have been refreshing and stimulating. We are also grateful for the helpful feedback from two anonymous reviewers. Many thanks also to Ruth Landolt for editing the large manuscript and to Sandra Gurzeler, Margrit Wiederkehr, and Jacqueline Annen for their careful layout.

Birmensdorf and Regensburg, October 2005 Fritz Schweingruber and Peter Poschlod For. Snow Landsc. Res. 79, 3 (2005) 201

Contents

Abstract 197

Preface 199

1 Introduction 203

2 Age classification and determination of herbs, dwarf shrubs and shrubs – 205 the state of the art 2.1 Soft classifications 205 2.2 Hard classifications 208 2.3 Age determination 211

3 Determining the age and growth dynamics of herbs and shrubs by the analysis 223 of growth rings 3.1 Are annual rings annual rings? 223 3.2 Limitations on using ring counting to estimate the age of an individual 228 3.3 Crossdating 231

4 Morphological pre-requisites of growth-ring analysis 233

5 Analysis and anatomy of growth rings 237 5.1 Preparation and microscopic techniques 237 5.2 Stem anatomy 240 5.3 Growth-ring characteristics in the xylem and phloem 250

6 Age structure of Central European herbs and dwarf shrubs 263

7 Population age structure: examples of the application of growth-ring analysis 265 to issues in ecological and biological conservation 7.1 Age structure of populations and successional stage 268 7.2 Age structure of populations and management 270 7.3 Age structure of populations and restoration management 273 7.4 Age structure and reconstruction of landscape history 275

8 What restricts the life span of a plant? State of the art and analysis of 277 our data set 8.1 Physiological factors 277 8.2 Ecological/environmental factors 278

9 Conclusions 285

10 Summary 287

11 References 289

Appendices 301 Glossary 302 Table A 1 306 Atlas 315 For. Snow Landsc. Res. 79, 3 (2005) 203

1 Introduction

Life span is one of the most important characteristics in the life history of an organism, ani- mal or plant (WEIHER et al. 1999). This characteristic is central to theoretical concepts such as r- and K-selection (MACARTHUR and WILSON 1967; PIANKA 1970) and C-S-R selection (GRIME 1979, 2001). However, data on the age of a plant or even the potential maximum age of a plant species as a whole are one of the least accessible parameters in the life history of plants (DIETZ and SCHWEINGRUBER 2002). The age of non-trees is almost completely ignored in the floras of the world, except for data on the (maximum) age of few species, given in the first biological flora, the “Lebensgeschichte der Blütenpflanzen” (KIRCHNER et al. 1908ff), The Biological Floras of the British Isles (SALISBURY 1928; British Ecological Society 1941; CLAPHAM et al. 1958), The Biological Flora of Moscow (RABOTNOV 1974ff; PAVLOV et al. 1990ff; PAVLOV and TIKHOMIROV 1995ff; PAVLOV 2000ff) and Central Europe (MATTHIES and POSCHLOD 2000). A bibliographical overview of these Biological Floras is given in POSCHLOD et al. (1996). To date, exact data on the individual age of a limited number of plants have been pro- vided by growth-form analysis based on annual morphological markers (e.g. TROLL 1937), the analysis of annual rings in woody plants (e.g. SCHWEINGRUBER 1990), or permanent plot research (e.g. TAMM 1948ff.). Less detailed information on individual age has been based either on the ontogenetic stage of an individual or its size (e.g. LINKOLA 1935, RABOTNOV 1950). The presence of annual growth rings in herbaceous plants, described by MOLISCH (1929, 1938), VIDAL (1906), ZOLLER (1949), and KERSTER (1968), was summarized by HARPER (1977) in the context of ecological studies. However, this knowledge was neglected or even ignored until it was “rediscovered” recently (DIETZ and ULLMANN 1997; SCHWEINGRUBER and DIETZ 2001; DIETZ and SCHWEINGRUBER 2002)1. The identification and analysis of growth rings requires however, a detailed knowledge of the anatomy of the respective species (SCHWEINGRUBER 2001). Until now, there has been no overview of the anatomy of growth rings in non-trees. HARPER (1977 p. 557) states that it would be “a snare and delusion to believe that age structures offer an easy short cut to understanding population dynamics”. Nevertheless, the population dynamics of long-living perennials can be analysed if details of a population’s age structure are added to other demographic data collected over several years. In addition, exact data on life spans can also be used to validate the results of predictive approaches to life span modelling (EHRLÉN and LEHTELÄ 2002). RABOTNOV (1950ff) developed an alternative approach describing population structures based on the ontogenetic analysis of plants. However, this approach has still been almost completely ignored outside Russian-speaking countries, apart from a reference to the Russian school in HARPER (1977), several papers in English (GATSUK et al. 1980), several chapters in WHITE (1985) and the translation of a textbook in German (RABOTNOV 1995).

1 DIETZ and ULLMANN (1997) created a new term for the study of annual rings in herbaceous species – “herbchronology” in contrast to “dendrochronology”. This term is correct as long as studies con- centrate exclusively on herbs. However, the Greek term dendros means only “tree”, whereas the Latin name herba means “herbs” and also “plants”. Thus we should really find new terms for shrubs and dwarf shrubs as well, as the terms are too broad. And what about the chronology of grass-like species which also have clear annual morphological markers? We would prefer to use a term that is clear to everybody, e.g.: chronology of herbs, dwarf shrubs, etc. Where annual growth rings are used to determine the age of an individual, we suggest the term should be chronology or age determi - nation by growth-ring analysis. We do not propose changing the term dendrochronology since it is already well established. 204 Fritz Hans Schweingruber, Peter Poschlod

This Russian approach is, therefore, also included in our review. To date, correlations between age and fecundity in herbs and dwarf shrubs have been little studied. Nor do we know much which factors affect life span (THOMAS 2002). Do these plants have an internal clock or is their life span strongly affected by environmental factors and, if so, by which environmental factors (LARSON 2001)? Since herbs often occupy habi- tats where trees never grow, analyses of annual growth rings in herbs should allow us not only to examine theories that were initially developed for tree species but also to develop new theories.

Objectives In summary, we know little about the age and anatomy of the shoots of dicotyledonous herbs, while our corresponding knowledge about dwarf shrubs and shrubs is also limited. This review, therefore, has five principal aims: 1 To provide an overview of possible ways of determining the individual age of a plant, including the ontogenetic approach. 2 To provide an anatomical overview and to demonstrate the enormous variability of the xylem seen in transverse sections of hundreds of native central European herbs and dwarf shrubs. 3 To evaluate whether growth rings are sufficiently distinct to be suitable for age determi- nation in root collars and plant rhizomes. 4 To explore the factors limiting the life span of herbs and shrubs. 5 To provide data on the age structure of plant populations and to show, with examples, the application of growth-ring analysis in ecological and population studies.

Nomenclature The nomenclature is based on the original names in the relevant literature. In chapters 3 to 5, as well as in the Atlas part of this book we use the nomenclature of LAUBER and WAGNER (2001). For. Snow Landsc. Res. 79, 3 (2005) 205

2 Age classification and determination of herbs, dwarf shrubs and shrubs – the state of the art

Age determination of plants other than trees, namely shrubs, dwarf shrubs, herbs and mono- cotyledonous plants including gramineous or liliaceous species, has been carried out both in the past and more recently (SCHLAGINTWEITH und SCHLAGINTWEITH 1850, ROSENTHAL 1904, KANNGIESSER 1907ff, MOLISCH 1929, RAUH 1937, TROLL 1937, ZOLLER 1949, STEINGER et al. 1996, DIETZ and ULLMANN 1997). Previously, methods of age determination included life and growth-form analysis, age-state analysis, dendrochronology and the moni- toring of individuals on permanent plots. Recently, the combination of growth rates and genetic analysis has even allowed the ageing of clones. In the following, the possibilities as well as the limitations of these different methods are described.

2.1 Soft classifications Life form The classification of life forms is a rough, but very common method for describing the life span of a plant species. Life forms were first described by WARMING (1895, 1909). He dis- tinguished hapaxanthous (monocarpic) plants, including annuals and biennials reproducing only once, from pollacanthous (polycarpic) plants, which reproduce repeatedly and are, therefore, always perennials (Table 1).

Table 1. Life-form types according to flowering frequency (WARMING 1909). Only the main groups are distinguished. Flowering frequency Life span Type Monocarpic annual Annuals Monocarpic biennial Biennials Monocarpic perennial Pluriennials, hapaxanthous Polycarpic perennial Pollacanthous

RAUNKIAER (1910, 1934) developed another approach focusing on environmentally adapt- ive mechanisms for plant survival during unsuitable growing periods, such as snowy winters in temperate regions. Raunkiaer’s classification of buds and seeds was based on the position of the regenerative organs (Fig. 1): phanerophytes (regenerative buds above ground and more than 30 cm above the soil surface); chamaephytes (regenerative buds above ground and less than 30 cm above the soil surface); hemicryptophytes (regenerative buds above ground and at the soil surface); crypto- or geophytes (regenerative buds below ground – rhi- zomes, bulbs, onions etc.), and therophytes (annuals which survive as seeds on the soil sur- face or below ground). In many floras, all species have already been classified according to their life forms. Furthermore, differentiations are made between annuals, biennials and perennials (e.g. the central European flora: ELLENBERG et al. 1992). Annual plants are plants that complete their life cycle and die within 12 months, although the life spans may overlap two calendar years (winter annuals in contrast to summer annuals, HARPER 1977). Perennials may live for two or more years. Biennials are those that form vegetative rosettes in the first year, and flower and die in the second year. However, HARPER (1977) also states “there are no natural breaks in the continuum of plant life cycles (and that) separation into the categories of annual, biennial and perennial is rather arbitrary”. He also adds “it is, however, very doubt- ful whether this category of behaviour is clearly defined in nature: the biennial habit is only an extension of the phenology of the winter-germinating annual which also makes some 206 Fritz Hans Schweingruber, Peter Poschlod growth in the late autumn of one calendar year and resumes and completes its growth cycle in the spring of the second year”. JÄGER (2000) noted that most of the so-called biennials, which are able to live more than two years but which die after first flowering, are mono- carpic perennials or so-called hapaxanthous or semelparous plants (in contrast to the polla- canthous or polycarpic or iteroparous perennials). Despite a certain plasticity, there are only a few species where ecotypes are different in life form or life span: life forms are species specific. Therefore, life forms provide a suitable basis for describing the “age structure” of phytogeographic regions, ecosystems (e.g. RAUNKIAER 1910, 1934; WALTER 1973) or plant communities (BRAUN-BLANQUET 1964; DIERSCHKE 1994), but they are not suitable for describing plant populations (Table 2 to 4). Table 2 gives an overview of life forms in phytogeographic zones or biomes. Long-lived life forms, such as phanerophytes, dominate in tropical zones and hemicryptophytes dominate in nemoral, arctic or alpine zones, whereas short-lived life forms such as therophytes are most frequent in deserts and the meridional zone. Proportionally, the life forms in central European plant formations or communities favour short-lived life forms in arable weeds, ruderal formations/communities or pioneer communities (Table 3, 4). This bias reflects the role of the disturbance factor in the pro- portion of short-lived life forms. The more intense or the more frequent the disturbance is, the lower is the proportion of long-lived life forms (see also the r/K concept, CSR-concept etc.; PIANKA 1970; GRIME 1979, 2001).

Table 2. Life-form spectra of selected phytogeographic zones, belts or ecosystems (WALTER 1973). P – phanerophytes, Ch – chamaephytes, H – hemicryptophytes, C – cryptophytes = geophytes, T – thero- phytes.

Zone/ecosystem Site P Ch H C T Tropical zone Seychelles 61 6 12 5 16 Deserts Libya 12 21 20 5 42 Cyrenaika 9 14 19 8 50 Meridional zone Italy 12 6 29 11 42 Nemoral zone Paris basin 8 6.5 51.5 25 9 Swiss midland 10 5 50 15 20 Denmark 7 3 50 22 18 Arctic zone Spitsbergen 1 22 60 15 2 Alpine belt Alps – 24.5 68 4 3.5

Fig. 1. Life-forms according to RAUNKIAER (1937). 1 – phanerophyte, 2a and 2b – chamaephytes, 3a to c – hemicryptophytes, 4a and 4b – crypto- or geophytes, 5 – therophyte. For. Snow Landsc. Res. 79, 3 (2005) 207

Table 3. Life-form spectra of selected central European plant formations, according to ELLENBERG (1996). No. – Number of species; P – phanerophytes, NP – nanophanerophytes, wCh – woody chamae- phytes, hCh – semi-woody chamaephytes, H – hemicryptophytes, C – cryptophytes = geophytes, T – therophytes; Hyd – hydrophytes.

Plant formations No. P NP wCh hCh H C T Hyd Freshwater and mire vegetation 281 0.2 0.0 2.0 3.5 37.0 12.6 3.5 41.2 Seawater and saltmarsh vegetation 296 0.0 0.0 0.0 5.0 42.5 11.3 33.8 8.8 Arable weed and ruderal vegetation 471 0.0 0.0 0.0 2.1 35.5 6.7 54.4 1.1 Rocks and alpine vegetation 732 0.0 0.3 2.9 22.4 64.1 6.3 4.2 0.0 Heaths and grasslands 280 0.0 0.0 3.1 8.3 60.6 13.0 15.1 0.0 Tall perennial herb and shrub veget. 93 1.2 6.6 3.6 3.0 75.3 7.8 3.0 0.0 Coniferous forests 208 5.3 11.7 25.5 10.6 27.7 13.8 4.3 0.0 Deciduous forests 99 19.2 33.3 2.7 6.9 49.0 29.5 2.7 0.4

Table 4. Life-form spectra of selected central European plant communities, according to KORNECK et al. (1996). No. – Number of species; P – phanerophytes, NP – nanophanerophytes, wCh – woody chamae- phytes, hCh – semi-woody chamaephytes, H – hemicryptophytes, C – cryptophytes = geophytes, T – therophytes; Hyd – hydrophytes. communities

Plant communities No. P NP wCh hCh H C T Hyd Saltmarsh communities 77 0.0 0.0 0.0 5.2 46.8 10.4 37.7 14.3 Coastal dune communities 14 0.0 21.4 21.4 0.0 50.0 21.4 7.1 0.0 Rock, wall and scree communities outside the alpine mountains 93 0.0 0.0 1.1 21.5 72.0 5.4 9.7 0.0 Grassland, rock and scree communities of the alpine mountains 265 0.0 0.0 4.2 21.9 71.3 6.0 4.5 0.0 Bidens pioneer communities on nutrient-rich soils 37 0.0 0.0 0.0 0.0 18.9 0.0 89.2 2.7 Arable weed and annual ruderal communities 302 0.0 0.0 0.0 0.7 19.2 5.6 93.0 0.3 Tall herb and perennial ruderal communites of nutrient-rich soils 323 0.0 0.9 0.3 5.6 81.4 13.9 17.6 0.0 ruderal grasslands and Agrostis stolonifera communities 116 0.0 0.0 0.0 8.6 71.6 12.9 29.3 5.2 Semi-ruderal grasslands 112 0.0 0.0 0.0 7.1 76.8 19.6 15.2 0.0 Oligotrophic mires 174 2.9 5.7 6.9 8.6 57.5 25.3 2.9 9.8 Oligotrophic lakes and rivers 49 0.0 0.0 0.0 2.0 24.5 2.0 18.4 79.6 Annual pioneer communities on mud 48 0.0 0.0 0.0 2.1 18.8 0.0 87.5 18.8 Eutrophic lakes and rivers 159 0.0 0.0 0.0 1.3 42.8 16.4 5.7 69.2 Springs 40 0.0 0.0 0.0 17.5 85.0 2.5 12.5 15.0 Wet meadows 242 0.0 0.4 0.8 3.3 80.2 19.4 3.3 1.7 Meadows and pastures 171 0.0 0.0 0.6 5.3 80.7 15.8 11.7 0.0 Heathlands and nard grasslands 212 0.0 2.4 8.5 9.0 69.8 14.6 8.5 0.0 Dry grasslands 468 0.0 0.2 4.9 9.2 62.0 16.5 19.9 0.0 Fringes 148 0.0 1.4 4.1 7.4 78.4 13.5 6.1 0.0 Tall herb and shrub communities of the mountains 184 2.2 10.9 8.2 4.9 71.2 11.4 1.6 0.0 Swamp and floodplain forests 200 13.0 13.0 2.0 3.5 53.0 25.5 1.5 7.0 Deciduous and coniferous forests 324 8.6 13.6 2.2 5.9 50.6 24.4 3.1 0.0 Deciduous and coniferous forests of acid and oligotrophic soils 175 8.6 10.3 9.1 7.4 53.1 17.1 4.0 0.0 Forests and shrublands of dry and warm habitats 200 10.5 23.5 5.5 5.0 46.0 18.5 3.5 0.0 208 Fritz Hans Schweingruber, Peter Poschlod

2.2 Hard classifications

Size and age state classification As an alternative to classifying plant species according to life form, some authors have tried to divide species according to certain morphological or biological criteria. These represent states of life-cycle development as shown by their size-class stages as seedlings, juveniles, vegetative adults and generative adults (e.g. GASSER 1986; HUTCHINGS 1991; JENSCH et al. 2001; COLLING et al. 2002; LIENERT et al. 2002). These stages have also been called “biologi- cal age classes” (ROBBINS 1957; LEVIN 1966), “physiological age classes” (SCHAF FALITZKY DE MUCKADELL 1959; GRUBB 1977) or “ontogenetic age classes” (RABOTNOV 1950; URANOV 1975; PASSECKER 1977, GATSUK et al. 1980). The differentiation of these size or age classes enables a rapid analysis of a population’s age structure (KAWANO 1985). This approach is, therefore, often used in monitoring schemes where many populations are studied (HUTCHINGS 1991; JENSCH et al. 2001). LINKOLA (1935), who was among the first to try correlating size class with plant age, culti- vated individuals over various time periods to assess the age structure of plant populations in meadows (e.g. Trollius europaeus, Fig. 2). He showed that 1-year-old plants were the most common individuals in each of the study species (with one exception). The proportion of these 1-year-old plants in different populations were as follows: Polygonum viviparum 67% and 81 %, Ranunculus auricomus 67 % and 75 %, Trollius europaeus 48 % and less than 10%, Ranunculus acris 37 %, and Geum rivale 27 %. WAGER (1938) developed another method for age determination by estimating the size and weight of plants and counting leaves in permanent plots in the Arctic over a two-year period. He differentiated 0, 1, 2, 3, 4, 5, “a” and “A” year-old plants. “The ‘0’-year plants were

Fig. 2. Juvenile stages of the age classes “I” to “VIII” of Trollius europaeus (LINKOLA 1935). For. Snow Landsc. Res. 79, 3 (2005) 209 those grown from seed in the current year; the ‘1’-year were plants in their second year, etc. ‘a’ plants were larger than the ‘5’-year class, yet still small and generally non-flowering, with ages varying from about 5 to 10 years; ‘A’ were those plants that could be called adult and flowered freely” (WAGER 1938). However, he was unable to date individuals older than five years. As he himself states, the method is difficult and “It is obvious that mistakes will be made, but by dealing with large numbers, some 2000 plants were mapped twice over, these will tend to average out”. Similar to the approach differentiating size or age classes is the differentiation of socalled age states or ontogenetic classes according to the Russian school initiated by RABOTNOV (1950, 1978, 1985). Many other Russian ecologists such as URANOV (1975), URANOV et al. (1977) and SMIRNOVA et al. (1976) have also applied this very detailed classification of ontogenetic stages or so-called “age states” for perennial plants (Table 5; Figs. 3, 4). An overview of this approach is given in GATSUK et al. (1980).

Table 5. Age states and ontogenetic periods of plants, according to GATSUK et al. (1980).

Age states Ontogenetic period Symbol 1 Seed I. Latent se 2 Seedling II. Pre-reproductive (pre-generative) pl 3 Juvenile j 4 Immature im 5 Virginal v

6 Young III. Reproductive (generative) g1 7 Mature g2 8 Old g3 9 Subsenile IV. Post-reproductive (post-generative) ss 10 Senile s

Fig. 3. Ontogeny and age-states in Festuca beckeri (given in VORONTZOVA and ZAUGOLNOVA 1985). For abbrevations of age states see Table 5. 210 Fritz Hans Schweingruber, Peter Poschlod

The Russian school described the ontogeny of many grasses and herbs besides that of trees ans shrubs. They studied the life spans of certain age states of a small number of plants in permanent plots. The duration of the full ontogeny or total life span was calculated by adding the life span of each age-state (Table 6). The maximum age of plants is given for some species, for instance of grasses aged between 10 and >100 years (KURCHENKO 1985; VORONTZOVA and ZAUGOLNOVA 1985; Table 6); several Plantago species where P. major was said to reach a maximum age of 15 to 20 years and P. lanceolata >12 years (ZHUKOVA 1983a, b, c). However, the method showing how the age states and classification were derived has only been clearly described in one paper, which deals only with trees (SMIRNOVA et al. 1999). A comparison of all the Russian papers on classification shows that the age states of all trees, shrubs, grasses and herbs are the same (Table 5). Astonishingly, the last stage is always a senile stage (Table 5, 6; Figs. 3, 4). However, in all our studies of herbs we have never observed senile stages as described by the Russian authors. We determined the oldest of two herb individuals, Lotus corniculatus and Sanguisorba minor and a dwarf shrub, Helianthemum nummularium by counting the annual rings in about 1000 individuals of each species. GATSUK et al. (1980, Table 5) would have classified these individuals as “mature” or “old”. However, in all the available Russian literature, woody species as well as herbaceous species in which generative reproduction has ceased have been described as senile, for example, SMIRNOVA et al. (1999), writing on the senile stage of trees says: “A senile plant has living shoots in the secondary crown only, and the leaves may be of the juvenile type. The upper parts of the crown and trunk are lost; the root system is destroyed. Seeds do not appear at all. Trees of g3- and s-stages show suppressed growth”. Several gardeners growing perennial plants have confirmed our observations concerning the lack of senile stages in the above-mentioned species (e.g. Rieger, pers. comm.). The viewpoint held by one representative of the Russian “school”, Dr. Nina Ulanova studying Rubus idaeus, is that herbaceous specimens die when they reach a “mature” or “old” stage. However, she stated: “We found subsenile and senile plants only in non optimal ecological conditions. For example, Rubus idaeus shrubs in senile states are very common in forests under the canopy. There, you will find flowering shoots, as after virginal states shrubs change to subsenile states without generative states. This is a rule for all perennial plants. That is why in gardens you will never find senile states” (Ulanova, pers. comm.). However, our view is that suffering from suboptimal conditions does not necessarily equate with senility. Nevertheless, the approach per se is interesting and enables the descrip- tion of population structures. Subsenile or senile stages have to be individually defined – if they exist.

Table 6. Duration (years) of the age-states and duration of full ontogeny in some steppe grasses (VORONTZOVA and ZAUGOLNOVA 1985). For abbreviations of age-states, see Table 5.

Species Habitat Age states Duration

jimVg1 g2 g3 + ss s of full ontogeny Stipa pennata Dry steppes 3 3 8 8 9 14 + 20 10 75 Northern steppes 1–4 2–3 20–25 10 45 Festuca valesica Semidesert 1 2 5 10 6 5 30 ssp. sulcata Northern steppes 0.1–0.6 1–2 2-4 18–19 5–8 5 40 Festuca beckeri Dry steppes 2–3 3 5 2 6 11 + 8 4 40 For. Snow Landsc. Res. 79, 3 (2005) 211 ab

c

Fig. 4. Ontogeny and age-states of Plantago major, P. media and P. lanceolata (ZHUKOVA 1983a, b, c). For abbreviations of age-states, see Table 5.

2.3 Age determination

Growth form analysis There is a long tradition of age determination by growth form analysis, not only of woody but also of non-woody species, e.g. ferns, grasses and herbs (RAUH 1937; TROLL 1937). In many studies it has been found that plants show specific seasonal growth patterns in above- ground shoots or stolons and particularly in belowground shoots, such as rhizomes. Annual increments may be clearly defined by markers that allow the estimation of rhizome age not only in spermatophytes but also in pteridophytes. However, a realistic age for an individual can only be obtained if rhizomes are long-lived (KLIMES et al. 1997). Where stolons or rhi- zomes are short-lived, or where older parts of the rhizome have already decayed or clones have disintegrated, only part of the life span can be reconstructed. For example in the pteri- dophytes group, lycopods show changes in leaf density along the main axis (PRIMACK 1973; CALLAGHAN 1980; Fig. 5). A point of higher density reflects the end of an annual increment (arrows in Fig. 5), whereas lower density after this point represents the start of a growing season. 212 Fritz Hans Schweingruber, Peter Poschlod

Fig. 5. Growth form of Lycopodium annotinum. H = horizontal segments, V = vertical segments, S = strobili. Numbers refer to ages in years, while arrows denote morphological markers of annual growth (CALLAGHAN 1980).

In many monocotyledonous species, the scars of buds (Figs. 6, 7) or shoots may supply clear annual markers. Polygonatum species are often shown as typical examples of this, with a growing season defined by the scar of a shoot or ramet (Figs. 6, 7; TROLL 1937). Several orchids produce similar rhizomes, with buds each representing one year. KULL and KULL (1991) calculated the age of Cypripedium calceolus clones by analysing the num- ber of buds in a rhizome (Fig. 8).

Fig. 7. Photograph of a 13-year-old rhizome of Polygonatum multi- florum (photo by Fritz Schweingruber).

Fig. 6. Rhizome of Polygonatum multiflorum seen from above (TROLL 1937). J – the cut shoot of the year 1935; N – scars of the shoots from former years (one shoot per year); S1 – “sympodial sections” of the rhizome, B – scars of the bracts; S2 – S4 – lateral branches of the rhizome. For. Snow Landsc. Res. 79, 3 (2005) 213

Fig. 8. Rhizome of Cypripedium calceolus from a pine forest in Estonia (KULL and KULL 1991). Numbers mark the remaining buds of the aboveground shoot in the respective year. Age >26 years (1962–1988).

In dicotyledonous species, indications of an individual’s age are the thickened bases of aboveground shoots on the rhizome and the scars on shoots and leaves, often combined with clear indentations in the rhizome resulting from growth retardation in autumn and winter. Although age determination often needs a detailed knowledge of the growth and growth form of a species, Euphorbia dulcis supplies one clear example of a thickened base of an aboveground shoot on a rhizome. One shoot per year is produced and, before the shoot dies, nutrients are shifted to the base of the aboveground shoot for storage, resulting in sym podial growth (Fig. 9; TROLL 1937). Another example is provided by the rhizome of Dictamnus albus, which shows visible annual growth recognizable from the scars on shoots, often combined with branching at the beginning of the season (JÄGER et al. 1997; Fig. 10). Bud-scale scars may supply clear age markers for dwarf shrubs (CALLAGHAN and COLLINS 1976) such as Salix (WIJK 1980), Empetrum (EMANUELSSON 1980) and Vaccinium species (KARLSSON 1980). The age of gramineous plants in cold habitats may be determined by the number of leaves produced since birth, combined with knowledge of annual leaf production rates. This approach is also valid for the early growth stages of dicotyledons (WAGER 1938; SHAVER and BILLINGS 1975; CALLAGHAN 1976, 1977, 1984). Beside growth form analysis, the age of clonal species can be estimated by analysing annual growth rates and genet size (COOK 1983, 1985). Bylebyl (unpubl. data) measured a growth rate of 0.69cm/year for Iris sibirica populations in wet meadows in Estonia, where the average diameter of a clone was 80 cm, resulting in a calculated age of about 58 years (80/0.69 = 116 yrs/2 = 58) 214 Fritz Hans Schweingruber, Peter Poschlod

Fig. 9. Four- (I) and eight-year- (II) old individ - Fig. 10. Twelve annual increments clearly visible uals of Euphorbia dulcis (TROLL 1937). W – main in Dictamnus albus (JÄGER et al. 1997). Indi - root; hy – hypocotyl; ek – resting bud for the fol- vidual with five flowering shoots (B) and one lowing year; annual increments, visible from the vegetative shoot (V). thickened bases of the aboveground shoot, are marked with Roman figures.

Chronological analysis There is a vast literature on dendrochronology, especially on the subject of maximum tree age (Table 7).

Table 7. Selected records of oldest known trees: as estimated by dendrochronology. There are hardly any exactly dated ages of European trees in the literature, but some estimations have been made (not included in the table).

Species Age Location Reference 4000+ years Pinus longaeva 4844 Treeline White Mountains, SCHULMAN 1958, BROWN 1996 Nevada, USA 3000+ years Fitzroya cupressoides 3622 Chile LARA and VILLALBA 1993 Sequoiadendron giganteum 3220 Sierra Nevada, California BROWN 1996 2000+ years Juniperus occidentalis 2675 Sierra Nevada, California MILES and WORTHINGTON 1998 Pinus aristata 2435 Central Colorado BRUNSTEIN and YAMAGUCHI 1992 1000+ years Larix lyalli 1917 Kananaskis, Alberta WORRALL 1990 Pinus flexilis 1659 Ketchum, Idaho SCHULMAN 1956 Thuja occidentalis 1653 Ontario, Canada KELLY and LARSON 1997 Taxodium distichum 1622 Bladen Co., North Carolina STAHLE et al. 1988 Pinus albicaulis 1267 Central Idaho PERKINS and SWETNAM 1996 Lagarostrobus franklinii 1089 Tasmania COOK et al. 1991 in BROWN 1996 For. Snow Landsc. Res. 79, 3 (2005) 215

At the beginning of the 20th century, annual rings were already known to occur not only in woody species like trees and shrubs but also in dwarf shrubs and herbaceous species. SCHLAGINTWEIT and SCHLAGINTWEIT (1850), ROSENTHAL (1904), KANNGIESSER (1906, 1907, 1909, 1914) and KANNGIESSER and JACQUES (1917) showed that annual rings are very common in dwarf shrubs. Extensive studies of the clonal Calluna vulgaris and Vaccinium myrtillus were carried out by FLOWER-ELLIS (1971), who found annual rings in rhizomes and tillers. He found tillers with a maximum age of 10 to 17 years (with one aged 34 yrs) and rhizomes attaining an age of 28 years. Clone age, calculated from diameters and average radial growth rates, was found to be between 40 and 100 years. MOLISCH (1929) was the first to mention annual rings in herbs with woody bases such as Globularia cordifolia or Teucrium chamaedrys (Table 8). ZOLLER (1949) carried out a more extensive study, while KERSTER (1968) and LEVIN (1973) used the occurrence of annual rings in Liatris species and BOGGS and STORY (1987) in Centaurea maculosa to analyse population structure. HARPER (1977 p. 553), citing the corms of Cyclamen and Liatris as examples, stated that “in a very few cases herbaceous perennials develop annual growth rings”. DIETZ and ULLMANN (1997), with no reference to the previous study at all, “re - visited” this phenomenon in greater detail and called it “herbchronology”. However, accord- ing to findings from our study and others (SCHWEINGRUBER and DIETZ 2001; DIETZ and FATTORINI 2002, DIETZ and SCHWEINGRUBER 2002), the development of annual growth rings is not exceptional, but is a frequent occurrence in perennial dicotyledonous herbs. Table A 1 in the Appendix gives an overview of the state of the art before our study. A detailed description of the chronological analysis of shrubs, dwarf shrubs and herbs is given in the next chapter.

Permanent plot research The famous studies of TAMM (1948ff) showed that permanent plot research is particularly appropriate for dating the age of individuals, especially geophytes such as orchids that may disappear from above ground in one year and reappear in another. TAMM (1948ff), and later INGHE and TAMM (1985), used permanent plots to show that orchids and other geophytes can become 20 or even 30 years old (Fig. 11). Many Russian scientists used permanent plot research, particularly in dating studies of grasses with a tussock-growth form (Table 6). A recent example is the study of Brachypodium pinnatum. On Alp Stabelchod, an aban- doned subalpine pasture in the Swiss National Park, 10 colonies of the clonal grass Brachypodium pinnatum L. have been permanently marked and monitored for up to 65 years (BÄRLOCHER et al. 2000; Stüssi unpubl.; Krüsi et al. unpubl.). One of the colonies dis- appeared between 1980 and 1993. In 2004 the remaining nine colonies ranged in diameter from 2.04 to 15.84 m. Long-term data show that radial growth follows in all colonies a linear pattern (Fig. 12), even though each colony has a different radial growth rate (range of the long-term average: 2.58–6.74 cm/year). Based on the individual growth rates, the age of the colonies in 2004 was estimated to be between 25 and 147 years. Given the almost circular shapes and the close to linear radial growth, it was assumed that each of the colonies was formed or at least dominated by one single genet. The considerable differences among the colonies with regard to size, age, radial growth and vitality of Brachypodium pinnatum L. (cover, growth height and flowering intensity) also suggested that all the colonies would be genetically different. Both assumptions could be confirmed by the application of extensive isozyme analysis (Krüsi et al. unpubl. data). 216 Fritz Hans Schweingruber, Peter Poschlod

Fig. 11. Fate of individuals of Hepatica nobilis within a forest site plot. Flowering ramets are marked in bold; non-flowering ramets in thin solid lines. Branched lines indicate that the ramet has ramified. Broken lines show that the ramet/plant was not observed in that year. In years where all lines are bro- ken, no inspection of the permanent plot was made (INGHE and TAMM 1985).

However, as INGHE and TAMM (1985) state, it is sometimes difficult to follow a marked indi- vidual, especially if the shoot disappears during the winter period. Our own experiences with Dactylorrhiza maculata (Staab unpubl. data) showed that, over a four-year period, “individuals” may migrate more than a centimetre a year. This was confirmed in another permanent plot study of vegetation dynamics in dry grasslands (Poschlod unpubl. data). VAN DER MAAREL and SYKES (1993) studied, on a very small scale (10 × 10 cm), the dynam- ics of a number of species and found out that they appear to “turn around”, being present in one year but absent in the next within the same quadrate (Fig. 13). They interpreted this phenomenon as competition avoidance and proposed a “carousel model”. Thus, it seems that a spatial record can only specify that an individual is the nearest neighbour to its former position. This situation may be mitigated by extreme long-term records, such as those of INGHE and TAMM (1985), which minimize the likelihood that a nearest neighbour could be a dormant bulb or rhizome. For. Snow Landsc. Res. 79, 3 (2005) 217

Since not only recruitment but also mortality rates within populations of some species can be quantified by demographic studies in permanent plots, population dynamics may also be predicted. INGHE and TAMM (1985) did so for Hepatica nobilis and Sanicula europaea, two typical species of deciduous forests in the temperate region. In this study they predicted the half-life as well as the potential maximum age of an individual (Figs. 14, 15).

5 R2 = 0.9946

4.5

4

3.5

(m) 3 s

2.5

2 mean radiu 1.5

1

0.5

0 1940 1950 1960 1970 1980 1990 2000 2010 year Fig. 12. Radial growth of a colony of Brachypodium pinnatum on Alp Stabelchod, Swiss National Park, 1950 m a.s.l. (Krüsi, unpubl. data).

Fig. 13. Small-scale population dynamics of two “circulating” species on an alvar limestone grassland in 40 1-dm2 quadrats, each situated in two rows 80cm apart in the plot (from VAN DER MAAREL and SYKES 1993). Dots: presence; filled squares: presence with cover >12.5%; open circles (1991): absence, but earlier presence. 218 Fritz Hans Schweingruber, Peter Poschlod

Fig. 14. Survival of the “old guards” (= genets existing at the beginning of a permanent survey of popu- lations in 1943 and flowering at least once between 1943 and 1946: each was assumed to be a separate genet in 1943). Regression lines predict half-lives. A: Hepatica nobilis, b: Sanicula europaea (from INGHE and TAMM 1985). For. Snow Landsc. Res. 79, 3 (2005) 219

Fig. 15. Predicted survival of the “old guards” (see Fig. 14) of different populations of Hepatica nobilis and Sanicula europaea according to data from permanent plot research applied to a simulation model (from INGHE and TAMM 1985).

Historical analysis (clonal plants) OINONEN (1967 a, b) reconstructed the age of Pteridium aquilinum (bracken) clones from an analysis of site history. He correlated the diameter and position of clones with the dates of battles in various Russian-Finnish wars by assuming that bracken spores only germinate in ash after fire has destroyed existing vegetation. Later the results were confirmed by genetic or molecular analysis of the size of clones (PAGE 1986; SHEFFIELD et al. 1989; PARKS and WERTH 1993). Lycopodium species also germinate following spore exposure to fire. Oinonen provided ages of several hundred years for three species (L. complanatum – OINONEN 1967c, L. annotinum, L. clavatum – OINONEN 1968) and showed that the age- dependent size of the clones of the three Lycopodium species and Pteridium aquilinum was strongly correlated (OINONEN 1968). Finally, Oinonen also correlated the clone sizes of Calamagrostis epigejos and Convallaria majalis with the clone sizes of Pteridium aquilinum and the Lycopodium species (OINONEN 1969). Other examples are reviewed by COOK (1983).

Genetic analysis (clonal plants) Whereas the results of a historical or any other type of morphological and dendrochrono- logical analysis of clones (Table 8) may be doubtful or not cover the total size of the clone, genetic methods allow a better estimation of clone size if the annual growth rate is known. However, in many cases the results of traditional approaches have been confirmed. For example, in Picea mariana (black spruce), a species that spreads vegetatively by branch lay- ering, morphological and dendrochronological analysis supplied an age of at least 300 years (LEGÈRE and PAYETTE 1981). Molecular studies confirmed this estimation and proved that the age of a genet could even be over 1800 years (LABERGE et al. 2000). Specimens of Lomatia tasmanica are the oldest genets discovered to date. Genetic studies of about 500 shoots of this species in a single world-wide population, extending over a 1.2 km-wide area, showed a complete lack of genetic variability, suggesting that this “population represents a single individual” (LYNCH et al.1998). Fossilised leaves identified as L. tasmanica by JORDAN et al. (1991) were dated as being at least 43600 years old and this, therefore, could represent the minimum age of this genet. 220 Fritz Hans Schweingruber, Peter Poschlod

Table 8. Size and estimated age of plant clones.

Species Size of the Annual Estimated Method to estimate Reference clone growth age (years) the size of the clone (diameter in m rate or area in m2) (cm/year) Pteridophytes Pteridium up to 489m – 1.400+ Comparative analysis of Oinonen 1967 aquilinum site history and clone size Pteridium 390 m – “considerable Isozyme analysis Sheffield et al. 1989 aquilinum antiquity” Pteridium 1015m 43 1180 Allozyme analysis Parks and Werth 1993 aquilinum Lycopodium up to 250m – 850 Comparative analysis of Oinonen 1967c complanatum site history and clone size Spermatophytes, gymnosperms Picea mariana 14m – 300+ Morphological and Legère and dendrochronological Payette 1981 analysis, statistical analysis Picea mariana up to 691.3m2 – > 1800 Genetic (RAPD) and Laberge et al. 2000 dendrochronological analysis Spermatophytes, angiosperms, monocotyledons Calamagrostis 50m – 400+ Comparative analysis of Oinonen 1969 epigejos site history and clone size

Festuca ovina 10m 1/8inch 1000+? Morphological analysis, Harberd 1962 (10 yards) cross-pollination tests Festuca rubra 220m 9 inch 1000+? Morphological analysis, Harberd 1961 (240 yard) (exp. field) cross-pollination tests Holcus mollis 880m (at least ? 1000+? Morphological and Harberd 1967 100yard across, phenological analysis, 1/2mile) chromosome analysis Sasa senanensis 300m – – Genetic (AFLP) analysis Suyama et al. 2000 Carex curvula 1.6m 0.04 2000 Genetic (RAPD) analysis Steinger et al. 1996 Convallaria majalis 83m – 670+? Comparative analysis of site history and clone size Spermatophytes, angiosperms, dicotyledons Anemone 12m 1.9–3.1 190–320 Allozyme analysis Stehlik and nemorosa Holderegger 2000 Gaylusaccia 1.980m 13000 Wherry 1972 brachycerium Larrea tridentata 11m 9170 Growth rings, radiocarbon Vasek 1980 dating of old wood samples Larrea tridentata 15.6m 0.066 11700 Isozyme analysis, growth Sternberg 1976 recal- rings, radiocarbon dating culated by Vasek 1980 Lomatia 1.200m 43600 Isozyme analysis, Lynch et al. 1998 tasmanica chromosome counts, dating of fossilised leaves (Jordan et al. 1981) Populus 510m ? 10000+? Morphological analysis, Kemperman and tremuloides aerial photographs Barnes 1976 Rhododendron ? 2.6 300 genetic (AFLP) analysis Escaravage et al. 1998 ferrugineum Teucrium scorodonia ? ? 50–100 ? Hutchinson 1968 For. Snow Landsc. Res. 79, 3 (2005) 221

Recent molecular studies have been carried out in alpine and arid habitats. Clones of the shrub Rhododendron ferrugineum were shown to be at least 300 years old (ESCARAVAGE et al. 1998; Table 3, PORNON and DOCHE 1996), whereas the age of a single ramet was found not to exceed more than about 100 years (KANNGIESSER and JAQUES 1917). STEINGER et al. (1996) showed that clones of Carex curvula in alpine grasslands reached a size of 1.6 m. Taking the annual growth rate as 0.04 cm/yr they calculated a minimum age of about 2000 years. Many other molecular studies have only estimated the size of a clone by means of genetic or molecular markers. However, these approaches also support the assertion that clonal species can reach a great age. WU et al. (1975) used isozymes to show that an extensive lawn population of Agrostis stolonifera originated from only two genets, while SUYAMA et al. (2000) applied AFLP analysis to show that clones of a little bamboo, Sasa senanensis, could cover areas up to 300 m in diameter. For. Snow Landsc. Res. 79, 3 (2005) 233

4 Morphological pre-requisites of growth-ring analysis

One of the major aims of our study is the determination of the real age of plants instead of assessing the ontogenetic stage. To do this we count growth rings in the root-stem transition zone of primary roots, termed the root collar, whose anatomical principles were established by STRASBURGER in 1958 (Fig. 18). A root is theoretically characterized by the absence and the shoot by the presence of a pith. In reality the transition zone is often difficult to identify because: a it may be buried by litter fall; b vertical soil movements, caused by organisms, often bury the stem of the seedling below the surface; c the vegetation point may be continuously pulled below ground by contractile roots (Lilium martagon, Fig. 19).

In old plants, the root/shoot transition zone is especially deep below the surface. We found an approx. 30-year-old shoot of Gentiana punctata 25 cm below the surface on a pasture in the subalpine zone. The contractile roots created a heavily wiggled periderm.

apex

adventitious shoots

cotyledon cotyledon

hypocotyl hypocotyl root collar

adventitious shoots

seedling

primary root older plant

Fig 18. Schematic representation of a dicotyledonous plant (STRASBURGER 1958) showing a seedling with two cotyledons and an older plant with a shoot, leaves, latent and adventitious shoots and roots. 234 Fritz Hans Schweingruber, Peter Poschlod

12 3 4

soil surface

contractile roots Fig 19. The effect of Lilium marta- gon contractile roots. Root short- ening depends mainly on changes in the shape of the inner cortical cells that expand radially and con- tract longitudinally (ESAU 1977). Contractile roots pull the veg- etation point deep below the sur- face. 1) Germination; 2) plant after its second vegetation period; 3) plant in its descendent period; 4) plant at its lowest position (STRAS - BURGER 1936).

The boundary between root and shoot is sometimes shown by differences in colour, rough- ness of bark and the presence of leaf scars or leaf remains, but in many cases the primary growth zone is unrecognizable. When a shoot is buried, it forms adventitious roots and, in older individuals with a high density of such roots, it may be impossible to differentiate between root and stem from external appearances. In herbs, almost the only safe indicator of a shoot or root is the presence (shoot) or absence (root) of a pith (Fig. 20). We confirmed the existence of abrupt anatomical changes in the root/shoot zones (Fig. 20) by making longitudinal sections of 10 species belonging to 9 families (Barbarea vulgaris, Cicerbita muralis, Dianthus carthusianorum, Echium vulgare, Galium mollugo, Geum urbanum, Geranium robertianum, Hypericum maculatum, Rhinanthus alectorolophus, Senecio vulgaris). A small pith area was present in the root of Sanguisorba minor, but this was much reduced in size compared with that in the shoot. However, various dicotyledonous tree species do possess a pith, e.g. Acer pseudoplantanus, Fagus sylvatica, Fraxinus excelsior and Quercus robur. In these species it is impossible to detect differences between shoots and roots based on presence or absence of a pith alone. For. Snow Landsc. Res. 79, 3 (2005) 235

Various morphological types demonstrate these principles: e. g. plants with short or long, vertical, oblique or horizontal, monopodial or sympodial rhizomes (Fig. 21). Growth-ring counts made in the root collars of taproot plants indicate the real age (Fig. 21). However, only the maximum age of remaining tissue can be determined in plants with rotten primary roots and long rhizomes. In both cases, it is possible to reconstruct average annual longitudinal growth by determining the age of the oldest and the youngest part of the rhizome. The average annual longitudinal growth can be calculated by dividing the total length of the rhizome by the number of growth rings. Ring boundaries are most clearly expressed in the root collar zone, just above or below the point where the pith disappears (Fig. 25), but rings are hard to recognize in the youngest part of the root, which is usually deep in the soil.

cortex and phellem phloem pith xylem phloem

cortex and phellem

shoot with pith

leaf base scar

xylem pith cortex and phellem phloem

xylem root without pith

Fig. 20. Echium vulgare: semi-schematic representation of transverse sections through the shoot, the root and a longitudinal section from the root to the shoot. The pith disappears in the longitudinal direc- tion in a zone two to three millimeters wide. The root begins below leaf scars. 236 Fritz Hans Schweingruber, Peter Poschlod

abcd e f

Fig. 21. Morphology of rhizomes and their positiones in relation to the soil surface. The dot indicates the transition between root and shoot and short lines mark leaf base scars. a–c Plants with preserved primary roots with vertical and oblique monopodial rhizomes. d Plant with a preserved primary root and a sympodial rhizome. e Plant with a decayed primary root and a preserved rhizome. f Plant with a bulb and a decayed primary root. For. Snow Landsc. Res. 79, 3 (2005) 237

5 Analysis and anatomy of growth rings

5.1 Preparation and microscopic techniques

Age determination is based on various techniques. It begins with the collection and labelling of plants, and continues with the sectioning and microscopic preparation before the final photographing. Here we describe several simple techniques which can be used by people not specialized in wood anatomy.

Digging out specimens For age determination, the most important part of a plant is the root collar (the transition zone between root and germination stem) or the ends of rhizomes. A small trowel or axe, depending on soil density and plant size, is used for exposing the transition zone between the root and stem.

Labeling, transport and storage Plastic bags are suitable for transportation. Thick-walled plastic bags are best since thin plas- tic bags are alcohol-permeable. For final storage, we use plastic boxes like those used for storing frozen fruits. Plants are labelled with a very soft pencil e.g. Stabilo – Aquarellable, on thick paper. The following characteristics should be noted: a Latin name and its author. b Part of plant (e.g. rhizome, primary root-shoot transition). c Life form. d Phenological stage of the plant, stem deformations. e Site conditions, e.g. dry slope, beech forest, grazed, etc. f Locality, region, country. g Altitude, collection date.

Carefully washed plants or their parts can be conserved for long periods in thick small plas- tic bags, e.g. 10 × 15 cm, in 40 % ethanol or any commercial alcohol such as whisky or vodka.

Sample preparation for microtome sectioning How the samples are prepared depends on the size of the plants: Approximately one- centimeter long cuboid sections are cut from large stems or whole stems. Very thin stems are clamped in styropor. Samples are held by the movable holder of the microtome (Fig. 22). 238 Fritz Hans Schweingruber, Peter Poschlod

Sample preparation for episcopic microscopic examination Cross-sections of samples are first planed with a knife or a razor blade for microscopic examination, and the sample stuck in grafting wax (Fig. 22) and stored in petri cups. Ring boundaries can, in many cases, be clearly seen without any treatment under a stereomicroscope. Ring structures in brownish wood may be highlighted by rubbing chalk into the vessels. Ring-structure visibility in very light wood with fairly big vessels may be improved by staining the surface with a green or red permanent marker and rubbing chalk into the vessels. Alternatively, ring visibility may be improved by staining the surface with Safranin and paring away half a millimeter of the surface. Improvements in ring-boundary visibility are due to differential absorption of the stain by earlywood vessels as a result of differing capillarity intensities below the stem surface (Fig. 23; ISELI and SCHWEINGRUBER 1989).

Fig. 23. Ring boundary staining due to variable tis- sue capillarity: Vaccinium uliginosum 30:1.

Making thin sections It is only possible to make thin sections for microscopic inspection if you have a very steady hand. For high-quality sections, a sliding microtome is mandatory. The best instrument is an old sliding microtome from REICHERT. Today the company EUROMEX offers both smaller and larger models. The smaller one is suitable for some herbs, but the large one is suitable for both herbs and wood. Well-sharpened knifes are a prerequisite for good sections (Type C). The expensive knife sharpener from LEICA produces very sharp blades, but sharpening by hand is possible with a cheap sharpening tool from EUROMEX. Disposal blades (available from LEICA) or paper knife blades (NT) can be used for small wood pieces and soft herbs. For. Snow Landsc. Res. 79, 3 (2005) 239

With a few rules even beginners can produce good sections: set the microtome knife to take thin sections between 10 to 60 microns thick (ring boundaries may be visible even on thick sections). Place a drop of alcohol (100%) on the flat surface of the samples; lightly wet the sample with an aquarelle brush and pull the knife across. This procedure prevents the sec- tion curling. The knife should be angled so that at least one quarter of the blade is used when taking a section, and it also helps if the blade’s contact point is wetted. The section can then be slid off the blade onto a wetted microscope slide using the brush. If the section is covered by a drop of glycerol, it is possible to store it on its slide for hours or days.

Preparation of thin sections for permanent slides Once the section is placed on a slide, sample preparation procedures can begin. Liquids are dropped directly on to the section with pipettes while holding the slide at an oblique angle so that surplus liquid runs off into a container (Fig. 24). Before staining, wash glycerol off with water. A naturally dark-coloured sample on a slide can be microscopically observed without preliminary staining. There are a number of different staining methods (GERLACH 1969). Commonly used products are Astrablue (Astrablue 0.5 g; acetic or tartaric acid 2 gr aqua dest.100 ml) and Safranin (Safranin 1 % water soluble). Astrablue is mixed with Safranin at a ratio of 1:1 and a drop of the solution is placed on the section for two to three minutes. After this the sample is first washed several times with 95% alcohol until it runs clear, then alcohol (100%) is used to dehydrate it. Staining makes unlignified cells appear blue and lignified cells red. Gelatinous fibres of tension wood appear blue. Dehydration is achieved with absolute alcohol. Replace the very hydrophile absolute alcohol with 95 % alcohol mixed with 5 % 2,2 Dimethoxypropane Aceton-dimethlyacetat (FLUKA). The slide is rinsed several times with alcohol and then a drop of Xylol is placed on the section to test for the presence of water. Dehydration is incomplete if the Xylol turns milky, indicating more absolute alcohol washing is required. When the Xylol runs clear, a small drop of Canada Balsam is placed on the section and a cover slip pressed on top. In our experience Canada Balsam is the best and most permanent embedding resin. To prevent the thin section from buckling, which makes examination difficult, the slide and cover slip are sandwiched between PVC strips with two small magnets placed on either side to keep the sandwich together and keep air bubbles out while drying in an oven (Fig. 25). The oven is set at 60°C for 8 hours. After drying, any hard resin remaining outside the cover slip can be scraped off with razor blades.

HR5

HR5 HR6

Fig. 24. Staining and dehydration procedures. Fig. 25. Microslides between two plastic strips The whole staining and dehydration process loaded with magnets on an iron plate. occurs on the slide. 240 Fritz Hans Schweingruber, Peter Poschlod

Preparation for impermanent slides A mixture of 2 ml Phloroglucin, 94 ml alcohol 96 % and 2ml hydrochloric acid 10 % is dropped onto the section for 20 seconds. All lignified tissues appear red. Species containing a lot of slime (muscilage) or starch are difficult to examine. In such cases the section is first soaked in a drop of bleach (calcium hypochlorite, CaO2Cl2 = Eau de Javelle) for five to ten minutes to destroy cell contents, e.g. nuclei and starch. The section is then rinsed with water until the smell of bleach has disappeared, after which it is ready for staining and dehydration.

Microscopic observation Microscopes with objective magnifications of 2, 4, 10, 20 and 40 are all well suited for obser- vations. Cells with and without secondary walls can be distinguished under polarized light. All cells with secondary walls appear bright (birefringence), while all others remain dark.

Photography We use commercial laboratory microscopes with analog (film) or digital equipment. Dark green filters enhance pale tissues on black and white photographs.

5.2 Stem anatomy

The distinctiveness of growth rings and intra-annual growth characteristics is determined by the plant’s anatomical structure and stem morphology. Most important are the size and dis- tribution of vessel fibres and parenchyma cells. Below we explain some details to help inter- prete the photographs.

Cylindrical stems The root collars of gymnosperms (conifers) and dicotyledonous angiosperms are a product of primary and secondary thickening (ESAU 1977). Shoots are characterized by the presence of a pith, a relict of primary growth, while roots mostly do not have a pith (Figs. 26, 27). The cambium, a secondary meristem, produces xylem and phloem. A tertiary meristem, originat- ing in the parenchyma cells of the phloem, forms phellogen (cork cambium), which produces phellem (Figs. 28–30). The proportions of pith, xylem, phloem and bark vary greatly. Some stems are mainly “pith stems” e.g. Corydalis cava; some are “xylem stems” e.g. Calluna vul- garis; whereas others are “phloem stems” e.g. Taraxacum officinale or “phellem stems”, e.g. some Saxifragaceae. Most plants show a continuous cambial bilateral function (Figs. 28–30) and a few have successive cambia, e.g. Caryophyllaceae, Amaranthaceae and Chenopodiaceae (Figs. 37, 38). Only one monocotyledoneous angiosperm, Tamus communis (Dioscoreaceae), grows in annual radial increments. For. Snow Landsc. Res. 79, 3 (2005) 241

pith

without pith

Fig. 26. Shoot with pith: Teucrium Fig. 27. Root without pith, Teu cri um chamaedrys, 25:1. chamaedrys 25:1.

Fig. 28. Tree (phanerophyte): sapling Fig. 29. Dwarf shrub (chamaephyte): root collar with a pith, Acer pseudopla- root collar. Characteristic is the pith. tanus, 40:1. Calluna vulgaris, 40:1. 242 Fritz Hans Schweingruber, Peter Poschlod

Fig. 30. Herb (hemicryptophyte): root collar. Silene vul- garis, 40:1.

Fluted stems Stems are usually round, although many different forms exist. For example, lobed stems are common in dwarf shrubs, shrubs and trees, and more particularly, in specific taxonomic units, e.g. Labiatae. Lateral irregular cambial activity produces stem forms with irregular cross sec- tions. In the simplest case, cambial growth can be a localized feature halted by large rays, below dying branches or injured parts of stems (Fig. 31). The cambium of plants exposed to direct stress may remain active only in protected spots, resulting in irregular growth forms (Fig. 32). Stem reorganization occurs due to the formation of new cambium and phellogen by living parenchyma cells in the xylem. So-called strip-bark stems grow only on the most localized, protected side of the stem (Fig. 33). For. Snow Landsc. Res. 79, 3 (2005) 243

Fig. 31. A uniform lobed stem in an annual plant. Root collar: Myosotis arvensis 20:1.

Fig. 32. Periodically lobed stem in a perennial plant. Stem base: Satureja montana 20:1. 244 Fritz Hans Schweingruber, Peter Poschlod

Fig. 33. Reorganized stem. A new cam- bium has been formed around the stem on the lateral side of the growth zones. Lotus corniculatus, 40:1.

pith

Alternating xylem-phloem structure The most usual growth form is continuous bilateral cambial activity around stem circumfer- ences. However, this is not the case for some bulbs whose cambial activity stops soon after the formation of vascular bundles. Single bundles remain around the circumference in the parenchyma tissue (Figs. 34, 35). Stem construction in the genus Primula provides an example of this (Fig. 36). Other species that we examined lacked secondary growth with closed vascular bundles, produced by the primary meristem, irregularly dispersed in the cross section (Fig. 36). In a few cases, bilateral cambial activity begins by developing nor- mally but later changes mode and forms cambium in the phloem. The result is a stem in which phloem is periodically included (Figs. 37, 38). For. Snow Landsc. Res. 79, 3 (2005) 245

vascular bundle

Fig. 34. Perennial plant with closed vas- Fig. 35. Perennial plant with open vascu- cular bundles arranged in a circle. Stem lar bundles. Bulb of Polygonum vivipa- base of Ranunculus nemorosus, 40:1. rum, 20:1.

Fig. 36. Perennial plant with single closed Fig. 37. Perennial plant with phloem vascular bundles (arrow) distributed included periodically (arrow). Stem of across the whole cross section: Primula the cushion plant Silene acaulis, 20:1. latifolia, 40:1 246 Fritz Hans Schweingruber, Peter Poschlod

cambium phloem

xylem

phloem parenchyma

xylem

parenchyma

Fig. 38. Annual plant with included phloem produced by successive cambia. Stem of Amaranthus cruentus, 40:1.

Modifications by mechanical stress and injuries There is no difference between herbs, dwarf shrubs, shrubs and trees in their anatomical responses to mechanical stress produced by imbalances, wounding, cell collapse, and dis- turbances in the crown and root systems. Imbalances trigger eccentric growth, including wedging rings (Fig. 39), compression wood-like libriform fibre zones (Fig. 40), and tension wood (Fig. 41). They have long pointed ends and live for many years. Some contain starch. The cell wall has very small simple pits with slit-like apertures along the macrofibrils and is slightly lignified, showing intense birefringence in polarized light. Such tissues have mainly been found in the families of Brassicaceae, Caryophyllaceae and Fabaceae. Extreme dense cork belts (phelloderm) trigger tissue collapse (Fig. 42). Few families produce true tension wood (fibre cells with unlignified gelatinous internal walls). We observed tension wood in herbs of the families of Euphorbiaceae and Hypericaceae. Eccentric growth is the most common response to one-sided mechanical stress, as shown, for example, by the families of Rosaceae and Ericaceae. Eccentricity also occurs when tissues have insufficient space to expand due to intensive compression of the xylem or the phloem and the xylem by strong phellem (cork) belts. As a consequence, unlig- nified tissues in the xylem (particularly in the family of Campanulaceae) collapse, with thin- walled tissue unable to resist the pressure becoming irregularly folded. Wounding triggers compartmentalization. Living cells excrete phenols around injured zones (Figs. 43 to 45). The consequences of mechanical or physiological damage to the crown, e.g. by pruning, defoliation or destruction of the root system, are abrupt radial growth reductions, structural changes and reduced cell-wall growth (Fig. 46). For. Snow Landsc. Res. 79, 3 (2005) 247

Fig. 39. Eccentric stem caused by oblique Fig. 40. Bands of thick-walled libriform root growth of a dwarf shrub: Thymus fibres (arrow) in a herb: Dianthus seguieri, serpyllum, 20:1. 100:1.

Fig. 41. Tension wood (arrow) in an Fig. 42. Crushed xylem, vessel/fibre annual herb: Euphorbia helioscopia. stripes in a herb, revealed by polarized 200:1. light: Campanula trachelium, 40:1. 248 Fritz Hans Schweingruber, Peter Poschlod

Fig. 43. Overgrown wound on the root of Fig. 44. Overgrown wound on the root of an annual herb: Arabidopsis thaliana, a dwarf shrub: Helianthemum appen- 40:1. ninum, 40:1.

Fig. 45. Callus tissue (arrow) in the root Fig. 46. Abrupt growth reduction (arrow) of a herb: Viola tricolor, 100:1. in the stem of a dwarf shrub: Chamaecy - tisus purpureus, 20:1. For. Snow Landsc. Res. 79, 3 (2005) 249

Modifications by environmental stress Different growing conditions can modify the stem morphology and the anatomical struc- ture. Here we describe some findings from samples of Lotus corniculatus, taken from the primary root collar a few millimeters below the first leaf scars. The samples were taken from free-standing plants with similar anatomical structures, growing on newly cleared land under optimal environmental conditions (Figs. 47 to 49). The findings show that plants growing on extreme sites, e.g. on windy ridges in the sub- alpine zone, do not form circular stems (Fig. 32) or parenchymatic bands in the latewood (Fig. 50). Plants growing in rock crevices possess tissues with extremely large rays and few vessels (Fig. 51). Such specimens have lost their “typical” anatomical structure and cannot be identified.

Fig. 47. Lotus corniculatus, Fig. 48. Lotus corniculatus, Fig. 49. Lotus corniculatus, perennial dicotyledonous herb: perennial dicotyledonous herb: perennial dicotyledonous herb: Optimal growth, 3000 m a.s.l., Optimal growth, 400 m a.s.l. Optimal growth, 600 m a.s.l. nival zone. abandoned crop field. semi-arid climate.

Fig. 50, left. Lotus corniculatus, perennial dicotyledonous herb: Extreme site, 2600 m a.s.l. windy ridge. (arrow = parenchymatic band)

Fig. 51, right. Lotus cornicu- latus, perennial dicotyledonous herb: Extreme site, 400 m a.s.l. rock crevice. (arrow = ray) 250 Fritz Hans Schweingruber, Peter Poschlod

5.3 Growth-ring characteristics in the xylem and phloem

The xylem of most dicotyledonous plants contains parenchyma cells in rays, axial tissues in vessels and tracheids, fibre tracheids and libriform fibres. There are differences in vessel size in earlywood and latewood cells, frequency differences between latewood and earlywood cells and differences in cell size. Wall thickness between latewood and earlywood cells and intra-annual cell-wall thickness vary greatly during annual wood formation. Although it is normally impossible to draw a definite boundary between earlywood and latewood due to intra-annual variations, annual growth increments can be defined.

Earlywood vessel size in herbs and dwarf shrubs Vessels in herbs and dwarf shrubs are normally small, with diameters mostly varying between 10 and 50 microns (Figs. 52, 53), although the vessels in lianas are larger (Fig. 55). There is a tendency towards reduction of vessel elements in dwarf shrubs (BAAS 1976), e.g. very short stems have very small vessels, whereas those with longer stems have larger vessels. However, we found many exceptions (Fig. 54). The herbaceous liana Bryonia dioica (Fig. 55), Humulus lupulus (root stock) and the lignified Clematis show earlywood vessels with diameters up to 250 microns. Vessel size seems to be a taxonomic characteristic in herbs and dwarf shrubs as it is in trees (SCHWEINGRUBER 1990).

Fig. 52. Vessel diameter 10 to 20 microns Fig. 53. Vessel diameter up to 50 microns in a short rhizom: Senecio incanus, 100:1. in a short rhizom: Salvia pratensis, 100:1. For. Snow Landsc. Res. 79, 3 (2005) 251

Fig. 54. Vessel diameter up to 100 Fig. 55. Vessel diameter up to 250 microns in a long rhizom: Petasites para- microns in a long annual shoot: Bryonia doxus, 100:1. dioica, 100:1.

Differences in latewood and earlywood vessel size The growth rings in the xylem of trees and shrubs (CARLQUIST 1988) and herbs are com- monly characterized by vessel size and frequency. Most frequent in herbs are semi-porous rings where latewood vessels are normally a little smaller than earlywood vessels (Figs. 57 to 59). Ring porosity, as defined in tree-stem xylem, is absent and pure diffuse porosity is extremely unusual in the xylem of dwarf shrubs and herbs. Vessel sizes can vary greatly around the circumference. 252 Fritz Hans Schweingruber, Peter Poschlod

Fig. 56. Diffuse porous. Almost no differ- Fig. 57. Semi-ring porous: 120 vessels per ence in vessel size between earlywood mm2 in the vessel/fibre zone: Cardamine and latewood: 300 vessels per mm2: alpina, 100:1. Calluna vulgaris, 40:1.

Fig. 58. Semi-ring porous: 200 vessels per Fig. 59. Semi-ring porous: 180 vessels per mm2 : Thesium pyrenaicum, 40:1. mm2 in the vessel/fibre zone: Centranthus angustifolius, 40:1. For. Snow Landsc. Res. 79, 3 (2005) 253

Vessel frequency: differences between latewood and earlywood In stems, vessel density is usually high (GREGUSS 1945), but vessel frequency in species with vessels varies mostly between 100 per mm2 to 1000 per mm2. In herbs, semi-ring porous structures are very abundant, (Figs. 61–63). Species without any vessels are rare (Fig. 60). Low vessel frequency in earlywood and absent vessels in latewood is uncommon (Fig. 61); high-vessel frequency in earlywood and low-vessel density in latewood is the more usual arrangement (Fig. 62). However, continuous, very high vessel density can be observed in some alpine dwarf shrubs (Fig. 63).

Fig. 60. Vessels are mostly absent in the Fig. 61. Few small vessels in the early- root of the herb Lythrum salicaria, 100:1. wood, vessels are absent in the latewood. Approx. 200 vessels per mm2: Antennaria dioica, 40:1. 254 Fritz Hans Schweingruber, Peter Poschlod

Fig. 62. Many vessels in the earlywood, Fig. 63. High vessel density over the few or no vessels in the latewood, whole section. Over 500 vessels per mm2: approx. 160 pores per mm2: Silene dioica, Loiseleuria procumbens, 40:1. 40:1.

Fibre size and fibre form differences between latewood and earlywood The demarcation of growth zones is often based on structural differences in fibre tissue. Since it is impossible to distinguish fibres from parenchyma in cross sections, the term “fibres” is used for both. Latewood and earlywood fibres show little or no differences in many species (Figs. 64–66). However, many species have also intra-annual, radial, flat fibres around either the whole or part of their circumference (Fig. 67). Growth-ring visibility is excellent when there are several marginal rows of flat fibres (Fig. 68). For. Snow Landsc. Res. 79, 3 (2005) 255

Fig. 64. No size differences between Fig. 65. Little size differences between earlywood and latewood fibres: Taraxa - earlywood and latewood fibres: Buph - cum alpinum, 100:1. thalmum salicifolium, 100:1.

Fig. 66. No size differences between earlywood and latewood fibres: Silene dioica, 40:1. 256 Fritz Hans Schweingruber, Peter Poschlod

Fig. 67. One row of marginal, radial, flat Fig. 68. Many rows of marginal flat fibres fibres: Vaccinium uliginosum, 100:1. It is (arrows): Artemisia absinthium, 100:1. difficult to distinguish annual ring boundaries from intra-annual tangential fibre zones. See also Fig. 23.

Differences in fibre-cell wall thickness between latewood and earlywood There is great variety in the intra-annual appearance of fibres with thin and thick cell walls and growth zones can often be demarcated as a result. When primary fibre cell walls (S1 layer) are very fragile, rings fall apart (ring shake Fig. 69). Some species have thin-walled, marginal parenchyma bands (Fig. 70). And, as is well known, tree-stem latewood fibres have thicker secondary walls than those in earlywood (Fig. 71). The thickened zones are often interrupted by ray-like zones (Fig. 72). In many cases, little patches of fibres with thick cell walls characterize latewood (Figs. 72, 73). For. Snow Landsc. Res. 79, 3 (2005) 257

Fig. 69. Single rings fall apart (ring Fig. 70. Marginal parenchymatic band shake): Saxifraga bryoides, 100:1. (arrows) (polarized light): Artemisia val - le siaca, 40:1.

Fig. 71. Slightly thickened fibres in the Fig. 72. Tangential discontinuous mar- latewood (arrows): Campanula trache- ginal patches of thick-walled libriform lium, 40:1. fibres (arrows): Helleborus foetidus, 100:1. 258 Fritz Hans Schweingruber, Peter Poschlod

Fig. 73. Groups of thick-walled fibres in the latewood (arrows): Peucedanum ostruthium, 100:1.

Intra- and inter-annual tangential bands The recognition of ring boundaries in many plants can be complicated by intra-annual tan- gential bands. In some taxonomic units, fast-growing individuals make rhythmic tangential vessel bands (Fig. 74). We found more or less rhythmic tangential bands of thin- and thick- walled fibres (Fig. 75) and patches of thick-walled fibres in the families of Fabaceae (Fig. 76) and Asteraceae. Growth rings in individuals with such features (Fig. 74) can normally be recognized by a degree of semi-ring porosity or distinct changes in fibre forms on the late- wood-earlywood boundary. Plants growing on shallow soils in a dry climate with aperiodic rainfall often have discontinuous or even false rings (Fig. 77), which makes cross dating diffi- cult since it is not always possible to distinguish annual growth rings. Since pollarding a tree’s photosynthetically active crown results in false rings or density variations (SCHWEINGRUBER 2001), it can be hypothesised that intra-annual irregularities are also produced by mowing and grazing of herbs. We confirmed this hypothesis in a study of Sanguisorba minor and Capsella bursa-pas- toris growing on undisturbed and mown sites. A meadow was mown at Birmensdorf (450 m a.s.l.) on June 15th 2000 and again in August and October 2000. We harvested the plants at the beginning of the growing season, 29 March 2001. The study showed that undisturbed perennial individuals produce distinct growth rings (Figs. 78, 80). Mown plants show intra- annual variations in vessel frequency and fibre structure (Figs. 79, 81) and, consequently, it is not always possible to age such plants. For. Snow Landsc. Res. 79, 3 (2005) 259

Fig. 74. Tangential vessel bands (arrows), Fig. 75. Tangential bands of thick- and Senecio inaequalis, 40:1. thin-walled fibres (arrows) in an annual plant: Lepidium densi florum, 40:1.

Fig. 76. Patches of thick-walled fibre Fig. 77. Discontinuous rings and false (arrows): Anthyllis vulneraria, 40:1. rings in the latewood (arrows): Thymus serpyllum, 40:1. 260 Fritz Hans Schweingruber, Peter Poschlod

Fig. 78. Sanguisorba minor growing in an Fig. 79. Sanguisorba minor growing on a undisturbed bed rock. The rings are mown pasture. Four fibre zones formed semi-ring porous without intra-annual during one growing season. 40:1. disturbances. 25:1. Polarized light.

Fig. 80. Capsella bursa-pastoris, growing on an undisturbed site harvested Fig. 81. Capsella bursa-pastoris growing 15.5.2000. Only one growth zone was on a mown site. Three growth zones formed. 25:1. formed during one growing season. 40:1. For. Snow Landsc. Res. 79, 3 (2005) 261

Growth-ring classification in the phloem Tangential structures, well known in tree bark, occur in the phloem (HOLDHEIDE 1951). Changes between bands of parenchyma, sieve cells and fibres produce growth-ring-like structures. Such phenomena also occur frequently in herb phloem (Figs. 83, 84). A compari- son of the numbers of xylem rings and phloem rings clearly shows that phloem rings mostly do not represent annual productions. Phloem rings are rhythmically produced in bands and the numbers of phloem and xylem rings are only equal on sites with very short vegetation periods. Many species in the family of Apiaceae and Asteraceae show tangential rows of oil ducts in the phloem (Fig. 82). The rows might represent annual growth zones in slow-growing indi- viduals, but since many species do not form distinct growth rings in the xylem, it is difficult to prove the annuality of oil-duct zones. We also observed several tangential rows of oil ducts in one-year-old individuals of e.g. the perennial Pimpinella major.

Fig. 82. Tangential rows of oil ducts in the Fig. 83. Tangential bands of dark sieve phloem (arrows): Laserpitium latifolium, cells and light parenchyma in the 40:1. phloem: Taraxacum alpinum, 40:1. 262 Fritz Hans Schweingruber, Peter Poschlod

Fig. 84. Tangential bands of dark sieve cells and light parenchyma in the phloem: Capsella bursa-pastoris, 100:1. For. Snow Landsc. Res. 79, 3 (2005) 263

6 Age structure of Central European herbs and dwarf shrubs

Since the ages of perennial herbs are almost unknown and the age determinations given in a number of publications are very heterogeneous and incomplete (Table A 1), it was our goal to determine the chronological ages of a great number of central European herbs and dwarf shrubs. We prepared 2547 microscopic thin sections and evaluated the distinctiveness of the ring structure and the age. Finally we selected the maximum age of each species. Here we present for the first time an overview of 914 analysed species. 80 perennial herbs do not show annual rings due to indistinct ring boundaries, missing secondary growth (Ranunculus sp.) or included phloem (successive cambia in Amaranthaceae and Chenopodiaceae). Therefore it was not possible to date them. In 603 of the analysed species, we also analysed the root collars of primary roots and in 231 species the oldest parts of living rhizomes (Fig. 85). We included all species that show very distinct, distinct and indistinct rings. Definitions are given in the “Explanations of legends in Atlas” (see Appendix). The results for 834 species are given in Figure 85. Young plants aged one to four years dominate the flora. 39.6 % of the plants had primary roots and 41.1 % of the plants rhizomes. Approximately 60 % of all species are younger than four years. The age decrease is intensive in the first ten years. Later it decreases more slowly. Only 8.1 % of plants with primary roots and 9.5 % of plants with rhizomes of all the species analysed are older than 20 years. The oldest individuals from herbs, dwarf shrubs and shrubs

120 Maximum ages primary roots rhizoms 100

80 s pecie

s 60 Nr. of Nr. 40

20

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21– 31– >50 30 50 Age (years)

Fig. 85. Maximum ages of Central European herbs and dwarf shrubs. Shown are the number of species with primary roots (603 species, black colums) and with rhizomes (231 species, gray colums). 264 Fritz Hans Schweingruber, Peter Poschlod from species with primary roots or rhizomes are shown in Table 16. Dwarf shrubs with inten- sively lignified stems live longer than herbs. The oldest shrub is 352 years old, the oldest dwarf shrub 202, and the oldest herb 50. Most of the oldest herbs grow in the subalpine and alpine zone at mostly dry sites. Only Potentilla micrantha grows at dry sites in the hill zone. The short vegetation period in a cold climate seems to promote longevity (see chapter 8.2). The determination of the real age of species with rhizomes is impossible because the transition zone between the primary roots and rhizome part is rotten. We have to assume that the ages are higher than shown in Figure 85. The maximum ages of the species shown are not absolute numbers. Individuals at very extreme sites might be older, e.g. Dryas octopetala 108 years (SCHRÖTER 1926). Shiyatov (oral communication) found an individual of Juniperus communis ssp. sibirica (little shrub) with 840 rings in the Polar Ural. Our data show clear differences not only in the taxonomic system, but also along environ- mental gradients (see section 8.2). Some families contain many old species and some mainly young species, e.g. the average age of the Apiaceae is in our material only 4.6 years and that of the Ericaceae 106 years. There are also large differences between species in some genera. In later studies we plan to provide more details.

Table 16. Maximum ages of herbs, dwarf shrubs and shrubs with primary roots or rhizomes in central Europe. H = hemicryptophyte, DS = dwarf shrub, S = shrub, LI = liana, * = approximate age; not clearly identifiable due to the occurrence of intra-annual growth rings.

Species with primary roots Life/ Age Species with rhizomes Life/ Age growth (years) growth (years) form form Trifolium alpinum H50 Geum reptans H 40* Draba aizoides H43 Alchemilla alpina H34 Minuartia sedoides H40 Scutellaria alpina H28 Oxytropis campestre H38 Potentilla micrantha H26 Eritrichium nanum H32 Achillea erba-rotta H23 Rhododendron ferrugineum DS, S 202 Loiseleuria procumbens DS 110 Rhododendron hirsutum DS 132 Arctostaphylos alpina DS 93 Erica carnea DS 82 Dryas octopetala DS 76 Globularia cordifolia DS 60 Vaccinium myrtillus DS 76 Helianthemum nummularium DS 55 Empetrum nigrum DS 63 Rhamnus pumila DS 50 Salix retusa DS 62 Helianthemum canum DS 42 Arctostaphylos uva-ursi DS 60 Juniperus communis spp. nana S 352 Vaccinium vitis-idaea DS 52 Crataegus monogyna S97 Salix reticulata DS 47 Lonicera coerulea S97 Salix herbacea DS 43 Cornus sanguinea S35 Vitis vinifera (cultivated) LI >160 For. Snow Landsc. Res. 79, 3 (2005) 265

7 Population age structure: examples of the application of growth-ring analysis to issues in ecological and biological conservation

The analysis of a plant population’s chronological or age-state is a good way to investigate the habitat quality of the species and its management. In forestry, such analyses are often used to assess the “quality” of a forest stand or to reconstruct historical events. So far, however, other ecological and biological conservation questions have seldom been addressed in this way and applications to shrubs, dwarf shrubs or even herbs are limited to single examples. LINKOLA (1935) was one of the first to describe herb population structures, classifying them into so-called size-classes (see section 2.2.). He showed that mortality among seedlings and juvenile plants is high, but reduced in older-age classes (Fig. 86). In another study, RABOTNOV (1950) analysed both the ontogenetic and the population age structure of species with clearly defined annual increments. He was probably the first to state that some herbs’ life spans can be shorter on both favourable sites and less favourable nutrient-poor sites (e.g. Libanotis transcaucasica, Fig. 87). KERSTER (1968) and LEVIN (1973) were the first to count annual rings to describe the age structure of herbaceous plant populations. KERSTER (1968) wrote a short report on the population age structure of Liatris aspera, a prairie herb to “demonstrate … the con- venience of such organisms for study from the viewpoint of the animal population ecologist”. He sampled seven populations in which four showed apparent obsolescence (Fig. 88). Others have shown increasingly successful recruitment in more recent years (Fig. 89), as the mean age indicates (Table 17). However, he did not interpret his population structures in detail but noted only a “depressant effect on generation span of a fire” (in 1945) and he concluded that the evidence of resurgent and senescent populations “raise(s) interesting questions”.

A 70 B 70 60 60 50 50 40 40 30 30 20 20 Proportion (%) Proportion (%) 10 10 0 0 I II III IV V VI VII VIII I II III IV V VI VII VIII C 70 “Year classes” “Year classes” 60 50 40 30 20 Fig. 86. Proportion of “year classes” (I – Proportion (%) seedlings to VIII – flowering individuals) 10 in three different plant populations in 0 meadows in Finland (from LINKOLA 1935). I II III IV V VI VII VIII A – Trollius europaeus, B – Potentilla erec- “Year classes” ta, C – Polygonum viviparum. 266 Fritz Hans Schweingruber, Peter Poschlod

A 50 B 50

40 40

30 30

20 20

Proportion (%) 10 Proportion (%) 10

0 0 6– 11– 16– 21– 26– 31– 36– 41– 46– 6– 11– 16– 21– 26– 31– 36– 41– 46– 10 15 20 25 30 35 40 45 50 10 15 20 25 30 35 40 45 50 Age classes (years) Age classes (years) C 50 D 50

40 40

30 30

20 20

Proportion (%) 10 Proportion (%) 10

0 0 6– 11– 16– 21– 26– 31– 36– 41– 46– 6– 11– 16– 21– 26– 31– 36– 41– 46– 10 15 20 25 30 35 40 45 50 10 15 20 25 30 35 40 45 50 Age classes (years) Age classes (years) Fig. 87. Proportion of flowering individuals in each age class of populations of Libanotis transcaucasica in four different habitats (from RABOTNOV 1950). A – short-grass steppe, B – Stipa steppe, C – Bromus/Carex meadow, D – Festuca meadow.

25

1945 fire 20

s idual

v 15

10 Number of indi

5

0 1357911131517192321 25 27 29 31 33 35 Age in years Fig. 88. Structure of a “senescent population” of Liatris aspera in the Zion Sand Prairie, Illinois, USA (from KERSTER 1968). Black columns – non flowering individuals; white columns – flowering individuals. For. Snow Landsc. Res. 79, 3 (2005) 267

100

1945 fire 80

s idual

v 60

40 Number of indi

20

0 1357911131517192321 25 27 29 31 33 35 Age in years Fig. 89. Structure of a “resurgent population” of Liatris aspera in the Zion Sand Prairie, Illinois, USA (from KERSTER 1968). Black columns – non flowering individuals; white columns – flowering individ - uals.

LEVIN (1973) compared the age structure of three Liatris species and three hybrids. He found that the attainment of adult status is more rapid in hybrids, but life spans are longer in non-hybrid species (Table 18). KAY and HARRISON (1970) published some data on the age structure of Draba aizoides, a rosette chamaephyte growing on rocky cliffs. They estimated the age by counting internodes in the branching stem-system below the rosette (Figs. 90, 91). Recently, several authors have studied the effect of habitat quality and management on the population structure, using a classification into ontogenetic stages or size classes (OOSTERMEIJER et al. 1994, 1996, VALVERDE and SILVERTOWN 1998, BÜHLER and SCHMID 2001, COLLING et al. 2002, LIENERT et al. 2002, BISSELS et al. 2004, ENDELS et al. 2004).

Table 17. Some characteristics of the age-structure analysis of Liatris aspera populations in Zion Sand prairie, Illinois, USA (from KERSTER 1968). Type of population: r – “resurgent”, s = “senescent”.

Sample Number of Type of Average Maximum Average age of Age of youngest individuals population age age flowering plants flowering plant 1 117 s 13.04 30 only flowering 8 2 259 s 14.87 34 17.40 8 3 134 s 9.81 18 11.10 2 4 149 r 8.84 24 13.53 8 5 243 r 5.21 23 13.16 4 6 100 s 13.74 29 16.26 8 7 159 s 15.58 34 17.97 9 268 Fritz Hans Schweingruber, Peter Poschlod

Table 18. Matrix of mean age differences between Liatris species and hybrids in Zion Sand Prairie, Illinois, USA (from LEVIN 1973). *, ** - significant differences between the means: * - p < 0.5, ** - p < 0.01. L. aspera x L. spicata x L. aspera x L. spicata L. cylindracea L. spicata L. cylindracea L. cylindracea L. spicata x L. cylindracea 1.74 L. aspera x L. cylindracea 2.48 0.74 L. spicata 2.06* 0.32 0.42 L. cylindracea 3.08** 1.34 1.02 0.60 L. aspera 5.13** 3.39 3.07** 2.65 2.03

5

s 4 idual v

3

Fig. 90. Age structure of a

Number of indi 1 Draba aizoides subpopu - lation in Ramsgrove, UK (from KAY and HARRISON 1970). Black columns – non 0 flowering individuals; white 13579111315171921 columns – flowering individ- Age in years uals. 5

s 4 idual v

3

Fig. 91. Age structure of a 1 Draba aizoides subpopu lation Number of indi in Knave, UK (from KAY and HARRISON 1970). Black 0 columns – non flowering indi- 13579111315171921 viduals; white columns – flow- Age in years ering individuals.

7.1 Age structure of populations and successional stage

WATT (1955) described the age structure of Calluna vulgaris populations growing on heath- lands on podsol soils in the UK. He differentiated four successional stages, “pioneer”, “building”, “mature” and “degenerate”. He defined the so-called “building” and “mature” phases (Table 19) and clearly showed that mean age increases as Calluna heath succession develops, with seedling regeneration apparently absent in the three older stages. For. Snow Landsc. Res. 79, 3 (2005) 269

Table 19. Age structure (minimum and maximum age, Ø – mean age) of Calluna vulgaris populations (annual ring analysis) in different successional stages of Calluna heathlands (from WATT 1955 and Geuss unpubl. data).

Callunetum phases Pioneer Building Mature Degenerate UK (Lakenheath Warren) – 4–13 (Ø 7.4) 15-24 (Ø 18.6) Germany (Neumarkt, Bavaria) 1–9 (Ø 2.8) 1–22 (Ø 8.3) 10-36 (Ø 17.9)

Similar results were found in a comparative study by Geuss (unpubl. data) on inland dunes in south-eastern Germany. He compared the age structure of Calluna populations in the pioneer phase (Corynephoretum); the mature phase (Callunetum) and the degenerate phase (former Callunetum, overgrown by Pinus sylvestris). In his detailed analysis, Geuss found that seed regeneration only occurs in the pioneer phase (Fig. 92). Age structure on heathland was comparable to the “building” and/or “mature” phase of WATT (1955), and

40 a s 35 30 idual v 25 20 15 10 5 Number of indi 0 121311579 13 15 17 19 23 25 27 29 31 33 35 37 39 Number of annual rings

100 b s 80 idual v 60

40

20 Number of indi 0 121311579 13 15 17 19 23 25 27 29 31 33 35 37 39 Number of annual rings

5 c s 4 Fig. 92. Age structure of Calluna idual

v vulgaris populations in different 3 successional stages of inland 2 dunes in southeast Germany (Geuss, unpublished data). a – 1 open pioneer community (Co - rynephoretum), n = 118, b – Number of indi 0 heathland (Callunetum), n = 602, 121311579 13 15 17 19 23 25 27 29 31 33 35 37 39 c – former heathland grown over Number of annual rings by Pinus sylvestris, n = 42. 270 Fritz Hans Schweingruber, Peter Poschlod maximum seed regeneration occurred seven to eight years previously. In a population over- grown by pines there was no peak, but the youngest individual was nine years old, whereas the oldest was 36 years, suggesting a clear pattern of population obsolescence. However, patterns of increasing mean population age cannot be generalised. KUEN and ERSCHBAMER (2002) showed on a glacier foreland in the Central Alps that the mean age of populations on moraines of different ages did not differ significantly from each other. The maximum age of individuals even decreased with increasing successional age of the moraines (Table 20).

Table 20. Mean age of the population and the largest individuals of Trifolium pallescens on moraines of different ages in a glacier foreland of the Central Alps, Switzerland (from KUEN and ERSCHBAMER 2002).

Age of the moraines 1971 1923 1858 Mean age Ø 3.1 Ø 2.5 Ø 2.9 Average age of the largest individuals > 8 (max. 11) 6 > 4

RIXEN et al. (2004) studied the age structure and biomoass production of the dwarf shrub Vaccinium myrtillus and the hemicryptophytic herb Potentilla aurea on a ski piste which had been graded 25 years previously and on an ungraded piste which had been under the influ- ence of artificial snow for the previous 7 years with neighboring undisturbed sites. Vaccinium myrtillus reacts negatively to both treatments, and aboveground shoots are younger and produce less biomass than those on control sites. The age structure of Potentilla aurea populations is comparable on all sites, but the annual biomass production is higher on disturbed sites. The small plants benefit from the lack of competition from blueberries.

7.2 Age structure of populations and management

DIETZ and ULLMANN (1998) studied the age structure of two ruderal species in central Europe, Bunias orientalis an invasive neophyte and Rumex crispus an indigenous species, along an increasing disturbance gradient. Using dendroecological analysis, they showed that, in habitats where disturbance events were rare, Bunias orientalis individuals over 4 years old were over-represented, whereas in frequently disturbed habitats one- and two-year-old indi- viduals dominated (Fig. 93). Furthermore, the analysis revealed that reproductive individuals were younger on fre- quently disturbed sites than on those with low disturbance rates. Comparing the population structures of Bunias orientalis and Rumex crispus on a recently disturbed site showed that Bunias orientalis had a narrow age distribution due to the marked decline of seedling estab- lishment as vegetation density increased, whereas Rumex crispus was less affected by canopy closure (Fig. 94). To assess the effect of management and even fragmentation on population structures, analyses of age states or size classes were also often performed (OOSTERMEIJER et al. 1994; 1996: VALVERDE and SILVERTOWN 1998; BÜHLER and SCHMID 2001; COLLING et al. 2002; LIENERT et al. 2002; BISSELS et al. 2004; ENDELS et al. 2004). The advantage of these is that they supply a non-destructive assessment of the age structure. A case study is presented in Table 21 showing a binary assessment of the proportion of two age states of Trollius europaeus populations (containing generatively reproducing juvenile and adult individuals) For. Snow Landsc. Res. 79, 3 (2005) 271

OF (lower limit)

OF (upper limit)

FS

RV Frequency (%) Frequency Increasing disturbance

GV

Plant age (years)

Fig. 93. Age structure of older Bunias orientalis stands at sites differing in type and frequency of disturbance: OF, old fallow; FS, fertile slope; RV, road verge; GV, grassland vegetation; vegetative plants (black columns); generative plants (white columns); vegetative and generative plants (grey columns) (from DIETZ and ULLMANN 1998). 272 Fritz Hans Schweingruber, Peter Poschlod

Fig. 94. Developing age structure of relatively young stands of Bunias orientalis and co-occurring Rumex crispus on different sites following recent disturbances. R. crispus was missing from MSS. RW, Roadside wasteland; DSS, dry soil spoil; MSS, moist soil spoil. Black bars, B. orientalis ; white bars, R. crispus (from DIETZ and ULLMANN 1998). For. Snow Landsc. Res. 79, 3 (2005) 273 growing on different types of managed and abandoned grasslands. This binary assessment clearly shows that abandonment results in a loss of juveniles. Fallow studies in Baden-Württemberg, running since 1975, have also shown how different conservation-management treatments of grassland can affect population structures. Treatments include grazing, mowing, mulching (different frequencies), burning and aban- donment.

Table 21. Proportion of juvenile to adult, generatively reproducing individuals of Trollius europaeus populations on differently managed and abandoned grasslands in the Hochsauerland, Hessen, Germany (Kowarsch and Poschlod, unpubl. data).

Management (site) Size of the studied Number of Proportion of population (m2) individuals juveniles to adult, of the studied reproducing population individuals Nutrient poor meadow (NSG “Liesetal”) 25 60 14 Hay pasture (Ahretal) 25 61 1.8 Hay pasture (Bremkebachtal) 180 171 0.3 Abandoned meadow/fallow (Sonneborn) 336 49 0.7 Abandoned meadow/fallow (Orketal) 390 58 0.9 Abandoned meadow/fallow (NSG “Trolliuswiese”) 25 57 0 Abandoned meadow/fallow (NSG “Im Boden”) 650 113 0

The age structure of Sanguisorba minor in the grazing plot (Fig. 95) provides an example of an insufficiently intensive grazing regime over the two years prior to the study: seedlings and one- and two-year-old individuals are almost completely lacking. Alternatively, in the suc- cession plot there is no clear pattern of population except low-density variations. However, the oldest individuals were 16 and 17 years old, whereas on the mown plot the oldest individ- uals were only eight years old. Mowing and burning produce a typical age structure: there are many seedlings and juveniles and a decreasing number of older individuals. In contrast to mowing where there is a constant decrease in the number of individuals on the age axis, the burning plot shows a sudden decrease between two- and three-year-old individuals, but from thence on the decrease is minimal. This pattern might result from competition with the dom- inant Brachypodium pinnatum, a herb producing a very dense rooting horizon in the upper 20 centimetres. Alternatively, Sanguisorba minor with its deep central root, survives once it has broken through this horizon to the deeper layers where there is no competition.

7.3 Age structure of populations and restoration management

Geuss (unpublished data) assessed the effect of rewetting management on the “Wurzacher Ried”, a bog in Southwest Germany. Here he analysed the population structure of Calluna vulgaris populations on a natural site in peat land and on two other sites subject to the rewetting regime. He found that on the natural site and on one of the rewetted sites, there were nearly no new individuals due to lack of seed recruitment three years after rewetting. However, on the other site, a typical population structure with many young and few old indi- viduals had developed, indicating that the rewetting management was unsuccessful. 274 Fritz Hans Schweingruber, Peter Poschlod

2 10 Grazing /m s 8 idual v 6

4

2 Number of indi 0 021 34567891011121314151617 Age (years)

2 30 Mowing /m s 25

idual 20 v 15 10 5 Number of indi 0 021 34567891011121314151617 Age (years)

2 0.4 Succession /m s 0.3 idual v 0.2

0.1 Number of indi 0 021 34567891011121314151617 Age (years)

2 10 Burning /m s 8 idual v 6 Fig. 95. Age structure of Sangui - sorba minor populations in a cal- 4 careous grassland with different management treatments (grazing n 2 = 175 individuals, succession n = 50, Number of indi 0 mowing n = 391, burning n = 254) 021 34567891011121314151617 (from Donaubauer and Poschlod, Age (years) unpubl. data). For. Snow Landsc. Res. 79, 3 (2005) 275

7.4 Age structure and reconstruction of landscape history

Population-age-structure analysis has been used to document the history of river-, lake- and sea-level fluctuations e.g. by BÉGIN and PAYETTE (1991) and glacier retreat in a number of studies (e.g. Bleuler unpublished in SCHWEINGRUBER 1996). One case study of glacier fore- lands in Switzerland (Münch unpubl. data, Schwarz unpubl. data) shows that continuous glacier retreat results in continuous invasion of plants on newly exposed land. Both Münch (unpubl. results) and Schwarz (unpubl. data) showed that, on land un - covered in 1960 by the Morteratschgletscher in the eastern Swiss Alps, species’ age reaches a maximum after a few years (Fig. 96) at which point primary roots can no longer be differen- tiated from adventitious roots due to primary-root decay. The maximum age of the primary roots for Lotus corniculatus was found to be 6 years, for Sempervivum arachnoideum and

a 35 Salix daphnoides 30

) 25 s 20

e (year 15 g

A 10 5 0 1995 1990 1985 1980 1975 1970 1965 1960 Year of the glacier retreat b 30 Rumex scutattus 25 )

s 20

15 e (year g

A 10

5

0 1995 1990 1985 1980 1975 1970 1965 1960 Year of the glacier retreat c 16 Achillea erba-rotta 14 12 ) s 10 8 Fig. 96. Maximum ages of the e (year

g 6 shrub Salix daphnoides (a) A and the herbs Rumex scutatus 4 (b) and Achillea erba-rotta (c) 2 in relation to dated glacier 0 retreat stages (from Münch, 1995 1990 1985 1980 1975 1970 1965 1960 unpubl. data) and Schwarz Year of the glacier retreat (unpubl. data). 276 Fritz Hans Schweingruber, Peter Poschlod

Hieracium statisticifolium 8 years, for Oxyria digyna 9 years, for Trifolium pallescens and Epilobium fleischeri 13 years, for Achillea erba-rotta 15 years (Fig. 96 c) (23 years in rock crevices) and for Rumex scutatus 28 years (Fig. 96 b). Of the shrubs Myricaria germanica had a maximum age of 19 and Salix daphnoides 29 years (Fig. 96 a). Recolonization episodes on newly exposed land can, therefore, only be reconstructed over the first two decades (first stage of the invasive phase). Another case study in Austria on the Rotmoosferner glacier foreland exposed in 1856 (KUEN and ERSCHBAMER 2002) supplies absolute dates for moraines and retreat stages. The dating of Trifolium pallescens revealed changes in population structure (see Table 20). The maximums age varied there between 6 to >8 years, whereas it is 13 years in the fore- land of the Morteratschglacier. It seems to be possible to date glacier retreats only on undisturbed sites. WINCHESTER and HARRISON (2000) came to the conclusion that erosion in the glacier forefield creates herb and shrub regeneration periods which are not related to ice retreat. For. Snow Landsc. Res. 79, 3 (2005) 277

8 What restricts the life span of a plant? State of the art and analysis of our data set

What restricts the age of a plant?2 Different aspects of ageing have been discussed in a num- ber of reviews (HILDEBRAND 1882, KÜSTER 1921, MOLISCH 1929, 1938, WANGERMANN 1965, HARPER 1977, LEOPOLD 1980, NOODÉN 1980, THIMANN 1980, NOODÉN 1988a, c, d, NOODÉN and LEOPOLD 1988, RODRIGUEZ et al. 1990, LARSON 2001, and THOMAS 2002), but there is almost no literature from an ecological viewpoint. Trying to find studies of plants that reproduce either by gametes or clonally, where anything other than the immortality of organisms, (LARSON 2001), is like looking “for a needle in a haystack”. In a recent book enti- tled “Aging. A natural history” by RICKLEFS and FINCH (1995) only two pages are devoted to plants and these contain almost no information beyond that provided by MOLISCH 60 years ago (1929, 1938). Even the most recent review by THOMAS (2002) refers only to “old” theories that, from a physiological point of view, range from death by exhaustion (MOLISCH 1929, 1938) to programmed senescence (LEOPOLD et al. 1959). Indeed, most recent studies in this field refer only to parameters of senescence in a cell, tissue or organ, and not to the entire plant (e.g. THOMAS et al. 2003, ZENTGRAF et al. 2004), with the chlorophyll content or leaf longevity used as a measure of senescence (NOODÉN 1988a, THOMAS and HOWARTH 2000, NOODÉN and PENNEY 2001). Summaries of the reasons for the death of a cell or tissue are provided by THOMAS (1994) and THOMAS et al. (2000). For further reading, the excellent reviews by LEOPOLD (1980), NOODÉN (1980, 1988a, c) and LARSON (2001) are still relevant.

8.1 Physiological factors

“Senescence in plants is an internally regulated and orderly degeneration leading to the death of single cells, organs or even whole plants during their life cycle” state NOODÉN and PENNEY (2001) in the first sentence of the introduction to their article on the control of senescence and death in the plant Arabidopsis thaliana, which is probably the best known plant at least from a molecular biological and genetic point of view. Senescence seems to be well understood in monocarpic plants where it is hormonally controlled (NOODÉN 1980, 1988b). As soon as flowering is initiated, the growth rate of monocarpic plants starts to decrease (NOODÉN 1984, 1988c). “Reproductive growth recipro- cally replaces vegetative growth” (NOODÉN and PENNEY 2001). This links longevity to flower ing and fruiting (LEOPOLD 1980). MOLISCH (1929, 1938) noted, that the removal of reproductive structures prolongs the life of a plant; a fact also recently observed in Arabidopsis thaliana. It is not surprising that NOODÉN and PENNEY (2001) were able to con- firm this fact since it is commonly known to gardeners that, “preventing seed set by, for example, removing flower buds as they appear greatly promotes vegetative growth and extends the longevity of monocarpic species” (THOMAS 2002). The development of seeds requires a certain amount of nutrition. If this is insufficient, then the plant may suffer what MOLISCH (1929, 1938) called “death by exhaustion”. More recently, this has been termed “exhaustion death” (NOODÉN 1988) or the “death-by-starvation hypothesis” (THOMAS 2002). This hypothesis is, however, too superficial, as THOMAS (2002) points out. He claims firstly, that in monocarpic species the whole plant is senescent and secondly, that this is invalid for dioecious plant species. Despite the absence of seeds, male plants die at the same

2 We focus here on the longevity of ramets or of non-clonal plants. The longevity of clones is briefly reviewed in chapter 2, but is not otherwise within the scope of this book. 278 Fritz Hans Schweingruber, Peter Poschlod

age as female plants (LEOPOLD et al. 1959). Therefore, THOMAS and SADRAS (2001) have argued that delayed senescence in sterile plants is favoured by the influence of herbivory and internal competition between organs. Senescence can be followed by death in cells, tissues and organs but not, necessarily, by death of the whole plant individual. Therefore, senescence does not have to be a consequence of ageing or the death process. THOMAS (2002) stresses the fact that in plants there are many examples of death without senescence, and of senescence without death. Senescence is even reversible in many species (THOMAS and DONNISON 2000). Therefore, programmed senescence alone cannot explain the maxi- mum age of plants. Genetic damage is another argument for imposing restrictions on the maximum age of plants. In contrast to animals, where genetic damage accumulates and leads finally to the death of the organism, somatic mutations in plant meristems may even be an important source of adaptive fitness (GILL et al. 1995; SALOMONSON 1996; PINEDA-KRCH and FAGERSTRÖM 1999; THOMAS 2002). Plants have developed strategies, “to resist, avoid and pre-empt ageing” (THOMAS 2002). Therefore, THOMAS (2002) claims “plants can hardly be said to age at all in any sense recognisable in animals. Ageing is a fate that probably awaits all organisms: it is just that plants are organised so that they are not there when it happens”. A further important factor restricting plant life spans could be the specific resistance of some plant species to pathogens (LARSON 2001). This hypothesis is derived from tree studies in which LOEHLE (1988, 1996) studied resistance in detail. However, there are no studies relating to other vascular plants such as dwarf shrubs or herbs. Despite the arguments focusing on genetic damage, the problem of ageing and sen - escence in polycarpic plants remains unsolved. In contrast to short-lived plants such as annuals, biennials or most monocarpic perennials, polycarpic perennials have less precise limits to longevity (LEOPOLD 1980; NOODÉN 1988c). This is especially true for clonal plants, but also for non-clonal plants. WAREING and SETH (1967) claim that the root system is import - ant for longevity in polycarpic plants (see also NOODÉN 1988c). Although NOODÉN (1988c) claims that longevity seems to be genetically determined, there are many factors, especially environmental ones, which may influence the age of non-clonal, polycarpic perennial plants. In conclusion, the ageing of plants is not yet fully understood and a unified effort is needed by cell biologists, plant physiologists and ecologists to understand the phenomenon of plant ageing and death. Many more studies are needed of the non-monocarpic, non-clonal and non-woody plants that make up a great part of our flora.

8.2 Ecological/environmental factors

MOLISCH (1929, 1938) already recognised in the 1930s that the maximum age of an individ- ual plant depends on the “intensity of assimilation and dissimilation processes”. Comparing the proportion of annuals in different vegetation types along an altitudinal gradient, Bonnier and Flahault (in MOLISCH 1929) showed that the proportion of annuals becomes smaller as altitude increases. From this, MOLISCH (1929, 1938) concluded that an individual life span depends on environmental conditions, in this case temperature. The fact that environmental stress extends individual life spans as a result of reduced growth was first recognised in alpine and arctic habitats, where growth is not only restricted by an extremely short growing season and cold temperatures, but also by desiccation and mineral nutrient stress (SCHRÖTER 1926; HAAG 1974; WARD 1982; KLÖTZLI 1991; SONESSON and CALLAGHAN 1991; KÖRNER 2003). A longer life span may be ecologically interpreted as compensating for erratic and hazardous seed production in these habitats (BILLINGS and MOONEY 1968; GRIME 2001). For. Snow Landsc. Res. 79, 3 (2005) 279

LARSON (2001) tried to prove the hypothesis that environmental stress might be a restricting factor at the ecosystem level. He took values for standing crops in different ecosystems stud- ied by the IBP (International Biological Program; WHITTAKER and LIKENS 1973; LIETH and WHITTAKER 1975) and divided these by the annual increase in biomass to calculate a turnover rate for the ecosystem involved. This measure of turnover rate was assumed to represent an average age for all organisms in these ecosystems. The highest “mean age” was found in temperate deciduous forest and boreal forest. However, it was not much less in tropical rain forests and, in open areas without trees, the highest values were found in deserts, rock, ice, and arctic and alpine tundras (Table 22). In many cases, longevity should depend on a combination of factors. This fact is under- lined by the striking example of Thuja occidentalis, a pioneer species on fallow land. It also occurs (rarely) in wet marshes, fens and bogs or rocky, waste places and rock outcrops. Whereas, as a pioneer tree it reaches on average 80 (maximum 400) years old, individuals on cliffs have a normal life span of 500 years with a maximum age recorded to date of 1890 years (LARSON 2001). In the following section we focus on single environmental variables that may affect the maximum age of an individual plant.

Table 22. Average organism ages of certain terrestrial and aquatic ecosystems calculated from the standing crop and annual productivity (LARSON 2001).

Ecosystem Standing crop Annual productivity Mean age (years) (kg m-2) (kg m-2 year-1) Terrestrial ecosystems Tropical rain forest 45 2.2 20.5 Temperate deciduous forest 30 1.2 25.0 Boreal forest 20 0.8 25.0 Savanna 4 0.9 4.4 Temperate grassland 1.6 0.6 2.6 Tundra (arctic + alpine) 0.6 0.14 4.3 Desert and scrub 0.7 0.09 7.8 Extreme desert/rock/ice 0.02 0.003 6.7 Cultivated land 1.0 0.65 1.5 Mean terrestrial 12.3 0.78 15.9 Aquatic ecosystems Swamp and marsh 15 2.0 7.5 Open ocean 0.003 0.125 0.024 (8.7d) Upwelling zones 0.02 0.5 0.04 (15d) Alagal forests/reefs 2.0 2.5 0.8 Mean aquatic 0.01 0.152 0.066 (24.d) Mean global 3.6 0.333 10.8 280 Fritz Hans Schweingruber, Peter Poschlod

Temperature The proportion of annual to perennial species is lower the higher the altitude (MOLISCH 1929, 1938). This is probably not related to the length of vegetation season since DIETZ et al. (2004) found no differences in the life span of two species in the centre (long snow cover) and periphery (shorter snow cover) of a snow bank. To test this idea of MOLISCH (1929, 1935), we correlated the quantitative age data of all the sampled species (except shrubs) with the height above sea level where they were collected. The correlation was not very strong, but still significant (Fig. 97). Comparative studies have been made of tree and shrub species along a temperature or altitudinal gradient, but none for dwarf shrubs, herbs and grasses. Therefore, we selected species where more than ten samples were available over an altitude gradient of at least 1000 m. The results varied from species to species. Although in many cases there was no age/height correlation, in others there was. For example there was no correlation for Calluna vulgaris, but there was one for Erica carnea (Fig. 98). A significant correlation was also found for Helianthemum nummularium (Fig. 99). The data had, however, to be carefully interpreted since firstly, most correlations were not very strong. Secondly, only single individuals within a population were sampled, although the collector tried to find the oldest individual within a population. And thirdly, at higher altitudes soils may be different, e.g. they may contain less fine material resulting in drier conditions and this may also affect species growth. The lack of a general correlation for most of the study species is unexpected. However, the hypothesis should be tested using a stronger sampling design that links the mean age of each population with specific altitudes, while holding all other environmental factors constant at all sites.

120 R2 = 0.1482*

100

80 ) s

60 e (year g A 40

20

0 0 500 1000 1500 2000 2500 3000 3500 Altitude (m) Fig. 97. Correlation between the ages of the studied herbs and dwarf shrubs (no shrubs included) and height above sea level (altitude in m). * = p<0.05, Pearson correlation coefficient. For. Snow Landsc. Res. 79, 3 (2005) 281

2500 a

2000

1500

1000 Altitude (m)

500

0 0 1020304050 Age (years) 3000 R2 = 0.6634* b 2500

2000

1500

Altitude (m) 1000 Fig. 98. Correlation between age (in years) of individuals of Calluna vul- 500 garis (a) and Erica carnea (b) and height above sea level (altitude in 0 0 20406080100m). * = p< 0.05, Pearson correlation Age (years) coefficient.

3000 a R2 = 0.2314* 2500

2000

1500

Altitude (m) 1000

500

0 0204060 Age (years) 3500 b R2 = 0.201* 3000 2500 2000 1500 Altitude (m) 1000 Fig. 99. Correlation between age (in years) of Helianthemum num- 500 mularium (a) and Lotus cornicula- 0 tus (b) and height above sea level 01051520(altitude in m). * = p< 0.05, Pearson Age (years) correl ation coefficient. 282 Fritz Hans Schweingruber, Peter Poschlod

Nutrients As already mentioned, growth rates may also be affected by lack of nutrients. We found no literature explicitly testing the hypothesis that lower nutrient levels result in longer life spans. We found a significant relationship when we correlated the quantitative-age data of all the sampled species (except shrubs) with the Ellenberg nitrogen or nutrient indicator values. The correlation was not very strong, but still significant (Fig. 100). However, a striking finding was that there was only one species, with a mean age of more than 10 years, growing in habitats which are more or less nutrient-rich (nitrogen indicator value > 4). Since we had no data on the nutrient status of the habitats where the single individuals were collected, we could not test the hypothesis at the species level.

70 R2 = 0.2362*

60

50 ) s 40

e (year 30 g A 20

10

0 0246810 Nitrogen (nutrient) value Fig. 100. Correlation between the mean ages of all studied herbs and dwarf shrubs (no shrubs included) and nitrogen indicator values, according to ELLENBERG et al. (1992). * = p< 0.05, Pearson correlation coefficient.

Moisture, wetness CALLAGHAN and EMANUELSSON (1985) stated that longer life spans are attained in dry rather than in wetter areas, i.e. in so-called fell-fields (tundra habitats). However, they failed to refer to a specific species or even study. In contrast, SANO et al. (1980) found that popu- lations of the annual Oryza perennis occur where there are dry conditions in the dry season and only shallow flooding in the rainy season. Populations of perennial individuals, on the other hand, were found where there are moist conditions during the dry season and deep flooding during the rainy season (Table 23). They interpreted this result as due to the fact that shallow or temporary swamps may be too dry in the dry season for plants to survive. They argue that, where reproduction depends on seed, it is probably safer to survive in the seed bank than to rely on vegetative propagation. A similar interpretation is given by BEATLEY (1970) for high plasticity in the life span of Tridens pulchellus (Poaceae) and Astragalus lentiginosus (Fabaceae) in the Mojave desert community in Nevada (USA). Perennial populations were restricted to those sites with a relatively constant precipitation throughout the year. For. Snow Landsc. Res. 79, 3 (2005) 283

Table 23. Relationship between water conditions, disturbances and life span of individuals in Oryza perennis populations in Thailand (SANO et al. 1980).

Dry season condition Rainy season flooding Habitat disturbance by man High Low Dry Shallow Annual Annual (?) Moist Deep Intermediate Perennial

Our data clearly show that the average species life span is highest at an intermediate level of (soil) moisture (Fig. 101). The mean age of a species diminishes where soil moisture is wetter or drier. However, it should be noted that an average age is, in many cases, only true for ramets and not for genets. Many species in, for example, wet habitats produce clonal growth and, therefore, have a potentially longer life span.

80

70

60

50 ) s 40 e (year g

A 30

20

10

0 0246810 Moisture value (F)

Fig. 101. Correlation between the mean ages of all species and the moisture indicator value, according to ELLENBERG et al. (1992). 284 Fritz Hans Schweingruber, Peter Poschlod

Intra- and interspecific competition LAW et al. (1977) showed that individuals of Poa annua selected for density-dependency have longer life spans than those selected for density-independency. In contrast, the latter have shorter pre-reproductive periods and a higher seed output earlier in life than the former.

Disturbance Disturbances may also affect the age of plants. It is obvious that any kind of disturbance may lead to the death of a specific individual. However, it could also be shown that, in some bien- nials or short living perennials, frequent disturbances may lead to the evolution of annual individuals. Adaptation to disturbance in relation to longevity has been studied in detail in annuals, particularly in weeds (MAHN 1989). Annual plants have high variability in relation to pheno- and genotypic plasticity, enabling rather rapid establishment in new niches. Plants have two ways of reacting to disturbances related to life span. The first is by reducing the duration of flowering. For example, natural populations of Lapsana communis in forest habitats flower over a longer time span than populations of the same species in arable fields (BERKEFELD 1988). The second is by reducing the whole life cycle. Examples are Galium aparine and Polygonum lapathifolium, where populations in arable fields have a shortened life cycle, which is not the case for populations in natural habitats such as floodplains (GROLL and MAHN 1986; KONOPATZKY in MAHN 1989). The reduction of the life cycle is here related to the vegetative phase. These adaptations could be shown to be genetically fixed by common garden experiments. Life-span plasticity is also reported for other species (HARPER 1977). For. Snow Landsc. Res. 79, 3 (2005) 285

9 Conclusions

“After an individual becomes established, it must persist. There are many traits that enhance population persistence, but the most basic trait is the life span of the individual” (WEIHER et al. 1999). Here we demonstrate that it is possible to quantify “life span” in months, in years or even in calender dates. We found that hundreds of perennial herbs and dwarf shrubs among the central European flora form growth rings. Analyses of plants with known sowing dates have confirmed that these growth rings represent annual growth rings. Annual plants form one ring, whereas perennial plants form several rings. Ring formation is based on secondary growth. It occurs in annual and perennial plants of all growth forms, and in tiny annual herbs as well as in large, long-living trees in all climatic zones. It is important to note that principal anatomical differences between different growth forms do not occur. Cell elements, as well as growth reactions to environmental factors, are identical. Annual growth rings are most distinct in the transition zone between root and shoot (root collar). This observation makes it possible to determine the age of whole plants with just the primary roots and the age of the oldest preserved tissue of plants with rhizomes. There are some exceptions: Many perennial plants form indistinct growth rings. In this case only an estimation of the age can be made. Some species do not show ring boundaries, and others produce internal bark layers. In such cases it is impossible to determine their age. However, we can still classify ontogenetic stages or size classes. In half of the herb species studied, the average life span is between one and five years. Maximum life spans decrease from trees to herbs. The “oldest living tree” (Pinus longaeva) is about 4900 years old, the oldest shrub 352 (Juniperus communis ssp. nana), the oldest dwarf shrub 202 (Rhododendron ferrugineum) and the oldest herb 50 (Trifolium alpinum). However, clonal plants may grow to be even older, for instance Larrea tridentata, Gaylusaccia brachycerium can be more than 10000 years old and Lomatia tasmanica more than 40000 years old. The principal of seasonal ring formation is identical in shrubs and trees. Hardly anything is known, however, about the dynamics of the radial growth of herbs and dwarf shrubs. It is technically easy to identify, count and measure the growth rings of many species. Analysing the anatomical features of the xylem and phloem of herbs and dwarf shrubs is also based on simple and well-known microscopic techniques. Therefore, we are now in a position to begin to address new questions. For example, ecological processes in plant com- munities can only be understood if we know the age of each individual. By analysing growth rings, it is possible to reconstruct retrospectively the dynamics of plant populations under different environmental conditions, e.g. on poor or rich soil, and under natural, polluted or discontinuous conditions. Our results show that both the maximum age of a species and its population structure differ from habitat to habitat and are also affected by management practices. The science of wood and bark anatomy can be dramatically expanded by taking into account “unlignified” plants. In addition to the approximately 200 tree species, 7000 dicotyledonous species of shrubs, dwarf shrubs and herbs can be studied in European Flora. As the cross-sections in the Atlas show (pg. 317–415), anatomical structures of the xylem and the phloem contain import ant taxonomic characteristics. Vessel size, distribution and frequency, ray presence, distri bution and construction as well as the distribution of fibres and parenchymatic cells characterize whole families, genera or sometimes single species. Anatomical features are also related to ecophysiological conditions. Different life and growth forms have different anatomical structures. It is obvious that vessel size and fre - quency is related to the size of plants, e.g. small plants such as cushion plants, contain numer- 286 Fritz Hans Schweingruber, Peter Poschlod ous very small vessels (diameter 20–50 microns) and several metre-long lianas show vessels with diameters of 100 to 250 microns. Anatomical features are also related to climatic con- ditions. We found that the sizes and numbers of vessels in alpine plants of the Brassicaceae are definitely larger than in plants of the alpine hill zone (SCHWEINGRUBER 2006). An anatomical survey in relation to taxonomy, growth forms and ecology will be presented in later studies. In summary: age determination and anatomical studies of xylem and bark open up vast new fields of research in plant taxonomy, wood anatomy, plant physiology and ecology in general. For. Snow Landsc. Res. 79, 3 (2005) 287

10 Summary

Using growth-ring analysis to classify and determine plant age Classifications of plant age may be soft or hard, based on, for example, life form, ontogen etic age or size classification. It is possible to determine the age of plant individuals not only by analysing growth forms, but also by analysing growth rings. This is based on the observation that annual plants and annual shoots always show one growth ring. Perennial plants have several growth rings. We found that the number of growth rings following harvesting perfectly reflected sowing dates. The number of growth rings is best seen in the transition zone between the shoot and root collar. The number of growth rings expresses the real age for plants with primary roots, but for plants with rhizomes it only indicates the age of the oldest preserved part. There are many limitations on ring counting. Age determination may be impossible because of minimal anatomical differences between latewood and earlywood, intra-annual tangential fibre- and vessel bands, wedging rings or alternating phloem-xylem structures (Chenopodiaceae, Amaranthaceae, Caryophyllaceae) or the absence of secondary growth in some genera of the families Ranunculaceae and Primulaceae. Tangential growth structures in the bark (oil ducts, groups of phloem cells) normally do not correspond with the number of xylem rings and are therefore not annual rings. Annual xylem growth rings in herbs and dwarf shrubs occur in all regions with seasonal climates. Plants in subtropical regions often show intra-annual tangential bands. Growth rings in arid regions may correspond with acyclic rainfall. In both regions dendrochronologi - cal age determination is problematic.

Anatomy of growth rings We present the microscopic growth-ring structures of herbs and dwarf shrubs of 781 species from 62 families from central Europe. Longevity varies greatly, with 40% of all analysed plants reaching ages of one to four years and 60% growing to be older than four. Herbs with primary roots reach an age of approximately 50 years and dwarf shrubs of 200 years. Seasonal growth-ring formation in shrubs corresponds with that of trees. The dates of the beginning and the end of radial growth vary, as does the relationship to phenological stages. There are no principal anatomical differences between the xylem of herbs and trees. Vessels, fibres, axial parenchyma and rays are the principal cell elements. The size, the number and the intra-annual distribution of cell types vary. Plants’ reaction mechanisms to environmental changes are identical in all growth forms. We found growth changes, cell collapses, and callus and tangential cracks in herbs as well as in trees.

Application of growth ring analysis to ecological issues We use several examples to illustrate how the age structure of plant populations differs depending on the successional age of plant communities and also on management. The age structure also allows us to reconstruct habitat and landscape history. Growth-ring analysis also enables us to study the mechanisms in herbs that restrict the life span of individual plants, which tend to vary, depending on the specific environmental conditions. Lower tem- peratures, high altitudes and a low nutrient status all seem to result in older individuals, whereas with moisture average life spans were highest at an intermediate level.

For. Snow Landsc. Res. 79, 3 (2005) 289

11 References

BAAS, P., 1976: Some functional and adaptive aspects of vessel member morphology. Leiden, Botanical Series 3: 157–181. BAKSHI, T.S.; COUPLAND, R.T., 1960: Vegetative propagation in Linaria vulgaris. Can. J. Bot. 38: 243–249. BANNISTER, P., 1965: Biological Flora of the British Isles: Erica cinerea L. J. Ecol. 53: 527–542. BANNISTER, P., 1966: Biological Flora of the British Isles: Erica tetralix L. J. Ecol. 54: 795–813. BÄRLOCHER, A.; SCHÜTZ, M.; KRÜSI, B.O.; GRÄMIGER, H.; SCHNELLER, J.J., 2000: Development of species richness in mono-dominant colonies of tor grass (Brachypodium pinnatum) – an indicator of the impact of grazing upon subalpine grassland? In: SCHÜTZ, M.; KRÜSI, B.O.; EDWARDS, P. (eds) Succession Research in the Swiss National Park. From Braun-Blanquet’s permanent plots to models of long-term ecological change. Natl.park-Forsch. Schweiz 89: 89–105. BEATLEY, J.C., 1970: Perennation in Astragalus lentiginosus and Tridens pulchellus in relation to rainfall. Madroño 20: 326–332. BEDANOKOVA, O.A.; VORONTZOVA, L.I.; MIKHAILOVA, N.F., 1975: Some specific biological fea- tures of Stipa pennata L. in the steppes of Naurzum reserve (in Russian). Bull. Mosk. obsch. isp. prir. otd. biolog. 80, 2: 77–91. BÉGIN, Y.; PAYETTE, S., 1991: Population structure of lakeshore willows and ice-push events in Subarctic Quebec, Canada. Holarct. Ecol. 14: 9–17. BELL, J.N.B.; TALLIS, J.H., 1973: Biological Flora of the British Isles: Empetrum nigrum L. J. Ecol. 61: 289–305. BENEDICT, J.B., 1989: Use of Silene acaulis for dating: The relationship of cushion diameter to age. Arct., Antarc., Alp. Res. 21: 91–96. BERKEFELD, K., 1988: Untersuchungen zur Ökotypenbildung bei Galium aparine L. (Rubiaceae) und Lapsana communis L. (Compositae). Flora 181: 111–130. BESCHEL, R.E., 1963: Observations on the time factor in interactions of permafrost and vegeta- tion. Permafrost Tech. Mem. (Ottawa) 76: 43–56. BILLINGS, W.D.; MOONEY, H.A., 1968: The ecology of arctic and alpine plants. Biol. Rev. 43: 481–529. BISHOP, G.F.; DAVY, A.J., 1991: Biological Flora of the British Isles: Triglochin maritimum L. J. Ecol. 79: 531–555. BISSELS, S.; HÖLZEL, N.; OTTE, A., 2004: Population structure of the threatened perennial Serratula tinctoria in relation to vegetation and management. Appl. Veg. Sci. 7: 267–274. BOGGS, K.W.; STORY, J.M., 1987: The population age structure of Spotted Kanpweed (Centaurea maculosa) in Montana. Weed Science 35: 194–198. BRAUN-BLANQUET, J., 1964: Pflanzensoziologie. 3rd ed. Wien, Springer. 865 pp. BRELOER, J., 1974: 1000 Jahre? Rosenstock am Dom zu Hildesheim. Hildesheim, Bernward Verlag. 39 pp. BRIGHTMORE, D.; WHITE, P.H.F., 1963: Biological Flora of the British Isles: Lathyrus japonica Willd. J. Ecol. 51: 795–801. British Ecological Society, 1941: Biological Flora of the British Isles. J. Ecol. 29: 356–357. BROWN, P.M., 1996: OLDLIST: A database of maximum tree ages. In: DEAN, J.S.; MEKO, D.M.; SWETNAM, T.W. (eds) Tree Rings, Environment, and Humanity. Radiocarbon 1996. Tucson, Department of Geosciences, The University of Arizona. 727–731. BRUNSTEIN, F.C.; YAMAGUCHI, D.K., 1992: The oldest known Rocky Mountain bristlecone pines (Pinus aristata Engelm.). Arct., Antarc., Alp. Res. 24: 253–256. BÜHLER, C.; SCHMID, B., 2001: The influence of management regime and altitude on the popula- tion structure of Succisa pratensis: implications for vegetation monitoring. J. Appl. Ecol. 38: 689–698. BURDON, J.J., 1983: Biological Flora of the British Isles: Trifolium repens L. J. Ecol. 71: 307–330. BURKILL, I.H., 1944: Biological Flora of the British Isles: Tamus communis L. J. Ecol. 32: 121–129. BUTCHER, R.W., 1947: Biological Flora of the British Isles: Atropa belladonna. J. Ecol. 34: 345–353. 290 Fritz Hans Schweingruber, Peter Poschlod

BYLOVA, A.M., 1976: Centaurea scabiosa L. In: RABOTNOV, T.A. (ed) Biological flora of the Moscow region 7 (in Russian). Moscow, Izdatel’stvo Moskovskogo universiteta. 151–161. CALLAGHAN, T.V., 1973: A comparison of the growth of tundra plant species at several widely separated sites. Institute of Terrestrial Ecology, Merlewood Research and Development Paper 53: 1–52. CALLAGHAN, T.V., 1976: Growth and population dynamics of Carex bigelowii in an alpine envi- ronment. Strategies of growth and population dynamics of tundra plants. III. Oikos 35: 402–413. CALLAGHAN, T.V., 1977: Adaptive strategies in the life cycles of South Georgian graminoid species. In: LLANO, G.A. (ed) Adaptations within Antarctic Ecosystems. Houston, Gulf. Pub. Co. 981–1002. CALLAGHAN, T.V., 1980: Age-related patterns of nutrient allocation in Lycopodium annotinum from Swedish Lapland. Strategies of growth and population dynamics of tundra plants. V. Oikos 35: 373–386. CALLAGHAN, T.V., 1984: Growth and translocation in a clonal southern hemisphere sedge, Uncinia meridensis. J. Ecol. 72: 529–546. CALLAGHAN, T.V.; COLLINS, N.J., 1976: Introduction. Strategies of growth and population dynam- ics of tundra plants. I. Oikos 27: 383–388. CALLAGHAN, T.V.; COLLINS, N.J., 1981: Life cycles, population dynamics and the growth of tundra plants. In: BLISS, L.C.; HELA, O.W.; MOORE, J.J. (eds) Tundra Ecosystems: a Comparative Analysis. Cambridge, Cambridge University Press. 257–284. CALLAGHAN, T.V.; EMANUELSSON, U., 1985: Population structure and processes of tundra plants and vegetation. In: WHITE, J. (ed) The Population Structure of Vegetation. Handbook of Vegetation Science 3. Dordrecht, Boston, Lancaster, Kluwer. 399–439. CARLQUIST, S., 2001: Comparative wood anatomy. 2nd ed. Springer Series in Wood Science. Berlin, Heidelberg, Springer. 448 pp. CAVERS, P.B.; HARPER, J.L., 1964: Biological Flora of the British Isles: Rumex obtusifolius L. and R. crispus L. J. Ecol. 52: 737–766. CLAPHAM, A.R.; COOMBE, D.E.; PIGOTT, C.D.; RICHARDS, P.W., 1958: The Biological Flora of the British Isles. J. Ecol. 46: 495–506. CLAPHAM, A.R.; TUTIN, T.G.; WARBURG, E.F., 1962: Flora of the British Isles. Cambridge, Cambridge University Press. 1269 pp. COKER, P.D., 1962: Biological Flora of the British Isles: Corrigiola litoralis L. J. Ecol. 50: 833–840. COKER, P.D., 1966: Biological Flora of the British Isles: Sibbaldia procumbens L. J. Ecol. 54: 823–831. COLLING, G.; MATTHIES, D.; RECKINGER, C., 2002: Population structure and establishment of the threatened, long-lived perennial Scorzonera humilis in relation to environment. J. Appl. Ecol. 39: 310–320. COOK, R.E., 1983: Clonal plant populations. American Scientist 71: 244–253. COOK, R.E., 1985: Growth and development in clonal plant populations. In: JACKSON, J.B.C.; BUSS, L.W.; COOK, R.E. (eds) Population Biology and Evolution of Clonal Organisms. New Haven, Yale University Press. 259–296. CROWDER, A.A.; PEARSON, THE LATE M.C.; GRUBB, P.J.; LANGLOIS, P.H., 1990: Biological Flora of the British Isles: Drosera rotundifolia L. J. Ecol. 78: 233–252. DALLIMORE, W., 1908: Holly, Yew and Box with Notes on Other Evergreens. London, John Lane. 284 pp. DIERSCHKE, H., 1994: Pflanzensoziologie. Stuttgart, Ulmer. 683 pp. DIETZ, H.; FATTORINI, M., 2002: Comparative analysis of growth rings in perennial forbs grown in an alpine restoration experiment. Ann. Bot. 90: 663–668. DIETZ, H.; SCHWEINGRUBER, F.H., 2002: Annual rings in native and introduced forbs of lower Michigan, U.S.A. Can. J. Bot. 80: 642–649. DIETZ, H.; ULLMANN, I., 1997: Age-determination of dicotyledonous herbaceous perennials by means of annual rings: exception or rule? Ann. Bot. 80: 377–379. DIETZ, H.; ULLMANN, I., 1998: Ecological application of “Herbchronology”: Comparative stand age structure analyses of the invasive plant Bunias orientalis L. Ann. Bot. 82: 471–480. For. Snow Landsc. Res. 79, 3 (2005) 291

DIETZ, H.; VON ARX, G.; DIETZ, S., 2004: Growth increment patterns in the roots of two alpine forbs growing in the center and at the periphery of a snowbank. Arct., Antarc., Alp. Res. 36: 591–597. DODDS, J.G., 1953: Biological Flora of the British Isles: Plantago coronopus L. J. Ecol. 41: 467–478. EHRLÉN, J.; LEHTELÄ, K., 2002: How perennial are perennial plants? Oikos 98: 308–322. ELKINGTON, T.T., 1963: Biological Flora of the British Isles: Gentiana verna L. J. Ecol. 51: 755–767. ELKINGTON, T.T., 1964: Biological Flora of the British Isles: Myosotis alpestris F.W. Schmidt. J. Ecol. 52: 709–722. ELKINGTON, T.T., 1971: Biological Flora of the British Isles: Dryas octopetala L. J. Ecol. 59: 887–905. ELKINGTON, T.T.; WOODELL, S.R.J., 1974: Biological Flora of the British Isles: Potentilla fruticosa L. J. Ecol. 51: 78–87. ELLENBERG, H., 1954: Naturgemäße Anbauplanung Melioration und Landschaftspflege. Landwirtschaftliche Pflanzensoziologie 3. Stuttgart, Ulmer. 109 pp. ELLENBERG, H., 1996: Vegetation Mitteleuropas mit den Alpen. Stuttgart, Ulmer. 1095 pp. ELLENBERG, H.; MUELLER-DOMBOIS, D., 1967: A key to Raunkiaer plant life forms with revised subdivisions. Ber. Geobot. Inst. Eidgenöss. Tech. Hochsch., Stift. Rübel 37: 56–73. ELLENBERG, H.; WEBER, H.E.; DÜLL, R., 1992: Zeigerwerte von Pflanzen in Mitteleuropa. 2nd ed. Scr. Geobot. 18: 1–258. EMANUELSSON, U., 1980: Mechanical impact on vegetation in the Torneträsk area (in Swedish). Fauna Flora Uppsala 75: 37–42. EMANUELSSON, U., 1984: Ecological effects of grazing and trampling on mountain vegetation in northern Sweden. PhD-thesis, Univ. Lund, Sweden, Dept. of Plant Ecology. 157 pp. ENDELS, P.; JACQUEMYN, H.; BRYS, R.; HERMY, M., 2004: Impact of management and habitat on demographic traits of Primula vulgaris in an agricultural landscape. Appl. Veg. Sci. 7: 171–182. ESAU, K., 1977: Anatomy of seed plants. 2nd ed. New York, Chichester, Brisbane, Toronto, Singapore, Wiley and Sons. 550 pp. ESCARAVAGE, N.; QUESTIAU, S.; PORNON, A.; DOCHE, B.; TABERLET, P., 1998: Clonal diversity in a Rhododendron ferrugineum L. (Ericaceae) population inferred from AFLP markers. Mol. Ecol. 7: 975–982. FAHN, A., 1977: Plant anatomy. 3rd ed. New York, NY, Pergamon Press. 611 pp. FAHN, A.; WERKER, E.; BAAS, P., 1986: Wood anatomy and identification of trees and shrubs from Israel and adjacent regions. Jerusalem, Israel Acad. Sciences and Humanities. 221 pp. FARREL, L., 1985: Biological Flora of the British Isles: Orchis militaris L. J. Ecol. 73: 1041–1053. FEARN, G.M., 1973: Biological Flora of the British Isles: Hippocrepis comosa L. J. Ecol. 61: 915–926. FLAMM, E., 1922: Zur Lebensdauer und Anatomie einiger Rhizome. Sitzungsberichte der mathe- matisch-naturwissenschaftlichen Klasse in Wien Abt. I, 131: 7–23. FLOWER-ELLIS, J.G.K., 1971: Age structure and dynamics in stands of bilberry (Vaccinium myr- tillus L.). Rapporter och Uppatser Avdelningen för Skogsekologi (Research Notes of the Department of Forest Ecology and Forest Soils, SLU) 9: 1–108. GASSER, M., 1986: Genetical-ecological investigations in Biscutella laevigata L. Veröff. Geobot. Inst. Eidgenöss. Tech. Hochsch., Stift. Rübel Zür. 86: 1–86. GATSUK, L.E.; SMIRNOVA, O.V.; VORONTZOVA, L.I.; ZAUGOLNOVA, L.B.; ZHUKOVA, L.A., 1980: Age states of plants of various growth forms: A review. J. Ecol. 68: 675–696. GERLACH, D., 1969: Botanische Mikrotechnik. Stuttgart, Georg Thieme. 298 pp. GILBERT, H.; PAYETTE, S., 1982: Écologie des populations d’aulne vert (Alnus crispa [Ait.] Pursh) à la limite des forêts, Québec nordique. Géogr. Phys. Quat. 36: 109–124. GILBERT, O.L., 1970: Biological Flora of the British Isles: Dryopteris villarii Bell. J. Ecol. 58: 301–313. GILL, D.E.; CHAO, L.; PERKINS, S.L.; WOLF, J.B., 1995. Genetic mosaicism in plants and clonal ani- mals. Annual Review of Ecology and Systematics 26: 423–444. GIMINGHAM, C.H., 1960: Biological Flora of the British Isles: Calluna vulgaris L. J. Ecol. 48: 455–483. 292 Fritz Hans Schweingruber, Peter Poschlod

GOOD, R.C.R., 1927: The genus Empetrum L. J. Linn. Soc. Bot. 47: 489–523. GRÉGOIRE, M.; BÉGIN, Y., 1993: The recent development of a mixed shrub and conifer community on a rapidly emerging coast (eastern Hudson Bay, subarctic Québec). J. Coast. Res. 9: 924–933. GREGUSS, P., 1945: Holzanatomie der europäischen Laubhölzer und Sträucher. Budapest, Akademia Kiado. 501 pp. GRIFFITH, M.E.; PROCTOR, M.C.F., 1956: Biological Flora of the British Isles: Helianthemum canum L. J. Ecol. 44: 677–682. GRIGGS, G.F., 1956: Competition and succession on a rocky mountain fell field. Ecology 37: 8–20. GRIME, J.P., 1979: Plant strategies and vegetation processes. Chichester, Wiley. 222 pp. GRIME, J.P., 2001: Plant strategies, vegetation processes and ecosystem properties. 2nd ed. Chichester, Wiley. 456 pp. GROLL, U.; MAHN, E.G., 1986: Zur Entwicklung ausgewählter Populationen des Kletten- Labkrautes (Galium aparine L.). Flora 178: 93–110. GRUBB, P.J., 1977: Maintenance of species-richness in plant communities: the importance of the regeneration niche. Biol. Rev. 52: 107–145. HAAG, R.W., 1974: Nutrient limitations to plant production in two tundra communities. Can. J. Bot. 52: 103–116. HARBERD, D.J., 1961: Observations on population structure and longevity of Festuca rubra L. New Phytol. 60: 184–206. HARBERD, D.J., 1962: Some observations on natural clones in Festuca ovina L. New Phytol. 61: 85–100. HARBERD, D.J., 1963: Observations on natural clones of Trifolium repens L. New Phytol. 62: 198–204. HARBERD, D.J., 1967: Observations on natural clones in Holcus mollis. New Phytol. 66: 401–408. HARPER, J.L., 1977: Population Biology of Plants. London, New York, San Francisco, Academic Press. 892 pp. HESLOP-HARRISON, Y., 1955a: Biological Flora of the British Isles: Nuphar lutea (L.) DC. J. Ecol. 43: 344–355. HESLOP-HARRISON, Y., 1955b: Biological Flora of the British Isles: Nymphaea alba L. J. Ecol. 43: 722–734. HILDEBRAND, F., 1882: Die Lebensdauer und Vegetationsweise der Pflanzen, ihre Ursachen und Entwicklung. Botanisches Jahrbuch 2: 51–135. HOLDHEIDE, W., 1951: Anatomie mitteleuropäischer Gehölzrinden. In: FREUND, H. (ed) Handbuch der Mikroskopie in der Technik. V/I. Frankfurt a.M., Umschau-Verlag. 193–367. HOLLÄNDER, K.; JÄGER, E.J., 1998: Wuchsform und Lebensgeschichte von Globularia bisnagari- ca L. (G. punctata Lapeyr., Globulariaceae). Hercynia N.F. 31, 2: 143–171. HOWARD, H.W.; LYON, A.G., 1952a: Biological Flora of the British Isles: Nasturtium officinale R. Br. (Rorippa nasturtium-aquaticum). J. Ecol. 40: 228–238. HOWARD, H.W.; LYON, A.G., 1952b: Biological Flora of the British Isles: Nasturtium microphyllum Boenningh. ex. Rchb. (Nasturtium uniseratum Howard and Manton, Rorippa microphylla [Boenn. Hyl.]). J. Ecol. 40: 239–245. HUISKES, A.H.L., 1979: Biological Flora of the British Isles: Ammophila arenaria (L.) Lk. J. Ecol 67: 363–382. HUMULUM, C., 1981: Age distribution and fertility of populations of the arctic-alpine species Oxyria digyna. Holarct. Ecol. 4: 238–244. HUTCHINGS, M.J., 1991: Monitoring plant populations: census as an aid to conservation. In: GOLDSMITH, F.B. (ed) Monitoring for Conservation and Ecology. London, Chapman and Hall. 61–76. HUTCHINSON, T.C., 1968: Biological Flora of the British Isles: Teucrium scorodonia L. J. Ecol. 56: 901–911. INGHE, O.; TAMM, C.O., 1985: Survival and flowering of perennial herbs. IV. The behaviour of Hepatica nobilis and Sanicula europaea on permanent plots during 1943–1981. Oikos 45: 400– 420. ISELI, M.; SCHWEINGRUBER, F.H., 1989: Sichtbarmachen von Jahrringen für dendrochronologis- che Untersuchungen. Dendrochronologia 7: 145–154. For. Snow Landsc. Res. 79, 3 (2005) 293

JACOB, M., 1995: Dendrochronology to measure average movement rates of gelifluctuation lobes. Dendrochronologia 13: 141–146. JÄGER, E., 1986: Grundlagen der pflanzlichen Entwicklung. In: SCHUBERT, R. (Hrsg.) Lehrbuch der Ökologie. Jena, Fischer. JÄGER, E.K., 1991: Grundlagen der Pflanzenverbreitung. In: SCHUBERT, R. (Hrsg.) Lehrbuch der Ökologie. 3. Aufl. Jena, Gustav Fischer. 159–165. JÄGER, E., 2000: A database on biological traits of the German flora – state of the art and need of investigation of the vegetative structures. Z. Ökol. Nat.schutz 9: 53–59. JÄGER, E.J.; JOHST, A.; LORENZ, H., 1997: Wuchsform und Lebensgeschichte von Dictamnus albus L. (Rutaceae). Hercynia 30: 217–226. JENSCH, D.; POSCHLOD, P.; SCHOSSAU, C., 2001: Überlegungen zur Zustandsbewertung und zu einem Monitoring von Pflanzenpopulationen im Rahmen der FFH-Richtlinie. In: FARTMANN, T.; GUNNEMANN, H.; SALM, P.; SCHRÖDER, E. (eds) Berichtspflichten in Natura-2000- Gebieten. Empfehlungen zur Erfassung der Arten des Anhangs II und Charakterisierung der Lebensraumtypen des Anhangs I der FFH-Richtlinie. Angewandte Landschaftsökologie 42: 46–64. JOLLS, C.L., 1982: Plant population biology above timberline: biotic selective pressures and plant reproductive success. In: HALFPENNY, J.C. (ed) Ecological Studies in the Colorado Alpine. A Festschrift for John W. Marr. Univ. Colorado, Institute of Arctic and Alpine Research, Occasional Paper 37: 83–95. JONG DE, T.J., 1990: Biological Flora of the British Isles: Cynoglossum officinale L. J. Ecol. 78: 1123–1144. JORDAN, G.J.; CARPENTER, R.J.; HILL, R.S., 1991: Late Pleistocene vegetation and climate near Melaleuca Inlet, south-western Tasmania. Aust. J. Bot. 39: 315–333. KAENNEL, M.; SCHWEINGRUBER, F.H., 1995: Multilingual glossary of dendrochronology. Bern, Stuttgart, Wien, Haupt. 467 pp. KANNGIESSER, F., 1906: Einiges über Alter und Dickenwachstum von Jenenser Kalksträuchern. Jenaische Zeitschrift für Naturwissenschaften 41: 472–482. KANNGIESSER, F., 1907: Über die Lebensdauer der Sträucher. Flora 97: 401–420. KANNGIESSER, F., 1909: Zur Lebensdauer der Holzpflanzen. Flora 99: 414–435. KANNGIESSER, F., 1914: Über Lebensdauer von Zwergsträuchern aus hohen Höhen des Himalaya. Vierteljahrsschr. Nat.forsch. Ges. Zür. 58: 198–202. KANNGIESSER, F.; JAQUES, A., 1917: Ein Beitrag zur Kenntnis der Lebensdauer von Zwergsträuchern aus hohen Höhen der Schweiz. Ber. Schweiz. bot. Ges. 26: 87–94. KARLSSON, S., 1980: Evergreen or deciduous – what does this mean to a plant in the mountains? (in Swedish). Fauna Flora Uppsala 75: 25–31. KAWANO, S., 1985: Life history characteristics of temperate woodland plants in Japan. In: WHITE, J. (ed) The Population Structure of Vegetation. Handbook of Vegetation Science 3. Dordrecht, Boston, Lancaster, Kluwer. 515–549. KAY, Q.O.N.; HARRISON, J., 1970: Biological Flora of the British Isles: Draba aizoides L. J. Ecol. 58: 877–888. KELLY, P.E.; LARSON, D.W., 1997: Dendroecological analysis of the population dynamics of an old-growth forest on cliff-faces of the Niagara Escarpment, Canada. J. Ecol. 85: 467–478. KEMPERMAN, J.A.; BARNES, B.V., 1976: Clone size in American aspens. Can. J. Bot. 54: 2603–2607. KERSHAW, K.A., 1960: Cyclic and pattern phenomena as exhibited by Alchemilla alpina. J. Ecol. 48: 443–453. KERSTER, H.W., 1968: Population age structure in the prairie forb Liatris aspera. BioScience 18: 430–432. KIHLMAN, A.O., 1890: Pflanzenbiologische Studien aus Russisch-Lappland. Acta Soc. Fauna Flora Fenn. 6: 1–263. KIRCHNER, O.; LOEW, E.; SCHROETER, C., 1908ff: Lebensgeschichte der Blütenpflanzen Mitteleuropas. Stuttgart, Ulmer. KLIMES, L.; KLIMESOVÁ, J.; HENDRIKS, R.; VAN GROENENDAL, J., 1997: Clonal plant architecture: a comparative analysis of form and function. In: DE KROON, H.; VAN GROENENDAL, J. (eds) The Ecology and Evolution of Clonal Plants. Leiden, Backhujs Publishers. 1–29. 294 Fritz Hans Schweingruber, Peter Poschlod

KLÖTZLI, F., 1991: Niches of longevity and stress. In: ESSER, G.; OVERDIECK, D. (eds) Modern Ecology. Basic and Applied Aspects. Amsterdam, London, New York, Tokyo, Elsevier. 97–110. KÖRNER, C., 1984: Auswirkungen von Mineraldünger auf alpine Zwergsträucher. Verh. Ges. Ökol. 12: 123–136. KÖRNER, C., 2003: Alpine Plant Life. Functional Plant Ecology of High Mountain Ecosystems. 2nd ed. Berlin, Springer. 344 pp. KÖRNER, C.; HILSCHER, H., 1978: Wachstumsdynamik von Grünerlen auf ehemaligen Almflächen an der zentralalpinen Waldgrenze. Ökologische Analysen von Almflächen im Gasteiner Tal. Veröff. Österr. MaB-Hochgebirgsprogramm Hohe Tauern 2: 187–193. KORNECK, D.; SCHNITTLER, M.; KLINGENSTEIN, F.; LUDWIG, G.; TAKLA, M.; BOHN, U.; MAY, R., 1998: Warum verarmt unsere Flora? Auswertung der Roten Liste der Farn- und Blüten - pflanzen Deutschlands. Schr.reihe Veg.kd. 29: 299–444. KRAUS, G., 1873: Über Alter und Wachstumsverhältnisse ostgrönländischer Holzgewächse. Bot. Ztg. 33: 513–518. KUEN, V.; ERSCHBAMER, B., 2002: Comparative study between morphology and age of Trifolium pallescens in a glacier foreland of the Central alps. Flora 197: 379–384. KULL, T.; KULL, K., 1991: Preliminary results from a study of populations of Cypripedium calceo- lus in Estonia. In: WELLS, T.C.E.; WILLEMS, J.H. (eds) Population Ecology of Terrestrial Orchids. The Hague, SPB Academic Publishing. 69–76. KURCHENKO, E.I., 1985: Coenopopulation structure of Agrostis species. In: WHITE, J. (ed) The Population Structure of Vegetation. Handbook of Vegetation Science 3. Dordrecht, Boston, Lancaster, Kluwer. 207–224. KÜSTER, E., 1921: Botanische Betrachtungen über Alter und Tod. Abhandlungen zur theoretis- chen Biologie 10. Berlin, Bornträger. 1–44. LABERGE, M.-J.; PAYETTE, S.; BOUSQUET, J., 2000: Life span and biomass allocation of stunted black spruce clones in the subarctic environment. J. Ecol. 88: 584–593. LARA, A.; VILLALBA; R., 1993: A 3620-year temperature record from Fitzroya cupressoides tree rings in southern South America. Science 260: 1104–1106. LARSON, D.W., 2001: The paradox of great longevity in a short-lived tree species. Experimental Gerontology 36: 651–673. LARSON, P.R., 1994: The vascular cambium. Development and structure (Series in Wood Anatomy). Berlin, Heidelberg, New York, London, Paris, Tokyo, Hong Kong, Barcelona, Budapest, Springer. 725 pp. LAUBER, K.; WAGNER, G., 2001: Flora Helvetica. 3rd ed. Bern, Stuttgart, Wien, Haupt. 1616 pp. LAW, R.; BRADSHAW, A.D.; PUTWAIN, P.D., 1977: Life history variation in Poa annua. Evolution 31: 233–246. LEFÈBVRE, C.; CHANDLER-MORTIMER, A., 1984: Demographic characteristics of the perennial herb Armeria maritima on zine-lead mine works. J. Appl. Ecol. 21: 255–264. LEGÈRE, A.; PAYETTE, S., 1981: Ecology of a black spruce (Picea mariana) clonal population in the hemiarctic zone, northern Quebec: Population dynamics and spatial development. Arct., Antarc., Alp. Res.13: 261–276. LEOPOLD, A.C., 1980: Ageing and senescence in plant development. In: THIMANN, K.V. (ed) Senescence in plants. Boca Raton, Florida, CRC Press. 1–12. LEOPOLD, A.C.; NIEDERGANAG-KAMIEN, E.; JANICK, J., 1959: Experimental modification of plant senescence. Plant Physiol. 34: 570–573. LEVIN, D.A., 1973: The age structure of a hybrid swarm in Liatris (Compositae). Evolution 27: 532–535. LEVIN, G.G., 1966: Age changes in plants (in Russian). Botanicheskij zhurnal SSSR 51: 1774–1795. LEWIS, M.C.; CALLAGHAN, T.V.; JONES, G.E., 1972: International Biological Programme, tundra biome, bipolar botanical project, Arctic research programme phase II. Report to the Royal Society, London. 34 pp. LIENERT, J.; DIEMER, M.; SCHMID, B., 2002: Effects of habitat fragmentation on population struc- ture and fitness components of the wetland specialist Swertia perennis L. (Gentianaceae). Basic and Applied Ecology 3: 101–114. LIETH, H.; WHITTAKER, R.H., 1975: Primary Productivity in the Biosphere. Ecol. Studies 14: 339 pp. For. Snow Landsc. Res. 79, 3 (2005) 295

LINKOLA, K., 1935: Über die Dauer und Jahresklassenverhältnisse des Jungenstadiums bei eini- gen Wiesenstauden. Acta For. Fenn. 42: 1–56. LOEHLE, C., 1988: Tree life history strategies: the role of defences. Can. J. For. Res. 18: 209–222. LOEHLE, C., 1996: Optimal defensive investment in plants. Oikos 75: 299–302. LOOMAN, J., 1976: Biological Flora of the Canadian Prairie Provinces IV. Triglochin L., the genus. Can. J. Plant Sci. 56: 725–732. LUFF, M.L., 1965: The morphology and microclimate of Dactylis glomerata tussocks. J. Ecol. 53: 771–787. LYNCH, A.J.J.; BARNES, R.W.; CAMBECÈDES, J.; VAILLANCOURT, R.E., 1998: Genetic evidence that Lomatia tasmanica (Proteaceae) is an ancient clone. Aust. J. Bot. 46: 25–33. MACARTHUR, R.H.; WILSON, E.O., 1967: The theory of island biogeography. Monographs in Population. Ecology 1. Princeton, New Jersey, Princeton Univ. Press. 203 pp. MAHN, E.G., 1989: Anpassungen annueller Pflanzenpopulationen an anthropogen veränderte Umweltvariable. Verh. Ges. Ökol. 18: 655–663. MATTHIES, D.; POSCHLOD, P., 2000: The Biological Flora of central Europe – aims and concepts. Flora 195: 116–122. MCCARTHY, D.P., 1992: Dating with cushion plants: Establishment of a Silene acaulis growth curve in the Canadian Rockies. Arct., Antarc., Alp. Res. 24: 50–55. MEREDITH, T.C.; GRUBB, P.J., 1993: Biological Flora of the British Isles: Peucedanum palustre (L.) Moench. J. Ecol. 81: 813–826. MEYERSCOUGH, P.J., 1980: Biological Flora of the British Isles: Epilobium angustifolium L. J. Ecol. 68: 1047–1074. MILES, D.H.; WORTHINGTON, M.J., 1998: Sonora Pass junipers from California USA: Construction of a 3500-year chronology. In: STRAVINSKIENE, V.; JUKNYS, R. (eds) Dendrochronology and Environmental Trends. Proceedings of the International Conference 17–21 June 1998, Kaunas, Lithuania. Vytautas Magnas University Department of Environmental Sciences, Kaunas. MITCHELL, N.D.; RICHARDS, A.J., 1979: Biological Flora of the British Isles: Brassica oleracea ssp. Oleracea L. J. Ecol. 67: 1087–1096. MITSCHERLICH, G., 1975: Wald, Wachstum und Umwelt. Eine Einführung in die ökologischen Grundlagen des Waldwachstums. Band 3: Boden, Luft und Produktion. Frankfurt a.M., Sauerländer. 352 pp. MOLISCH, H., 1929: Die Lebensdauer der Pflanze. Jena, Gustav Fischer. 168 pp. MOLISCH, H., 1938: The Longevity of Plants. Lancaster, PA, Science Press. 226 pp. MORK, E., 1946: Om skogsbunnens lyngvegetasjon. Meddelser fra det Norske Skogforsøksvesen 33: 274–356. MOSS, E.H., 1936: The ecology of Epilobium angustifolium with particular reference to rings of periderm in the wood. Am. J. Bot. 23: 114–120. MUELLER-DOMBOIS, D.; ELLENBERG, H., 1974: Aims and methods of vegetation ecology. New York, Wiley. 547 pp. NEUMANN, K.; SCHOCH, W.; DÉTIENNE, P.; SCHWEINGRUBER, F.H., 2001: Wood of the Sahara and the Sahel. Bern, Stuttgart, Wien, Haupt. 465 pp. NICKSTADT, A.; JÄGER, E.J., 2000: Beiträge zur Populationsbiologie der Silberdistel (Carlina acaulis L.). Hercynia N.F. 33: 245–256. NOODÉN, L.D., 1980: Senescence in the whole plant. In: THIMANN, K.V. (ed) Senescence in Plants. Boca Raton, Florida, CRC Press. 219–258. NOODÉN, L.D., 1984: Integration of soybean pod development and monocarpic senescence. Physiol. Plant. 62: 273–284. NOODÉN, L.D.; LEOPOLD, A.C., 1988: Senescence and aging in plants. San Diego, CA, Academic Press. 526 pp. NOODÉN, L.D.; PENNEY, J.P., 2001: Correlative controls of senescence and plant death in Arabidopsis thaliana (Brassicaceae). J. Exp. Bot. 52: 2151–2159. NOODÉN, L.V., 1988a: The phenomena of senescence and ageing. In: NOODÉN, L.D.; LEOPOLD, A.C. (eds) Senescence and Aging in Plants. San Diego, CA, Academic Press. 1–50. NOODÉN, L.V., 1988b: Abscisic acid, auxin, or other regulators of senescence. In: NOODÉN, L.D.; LEOPOLD, A.C. (eds) Senescence and Aging in Plants. San Diego, CA, Academic Press. 367–397. 296 Fritz Hans Schweingruber, Peter Poschlod

NOODÉN, L.V., 1988c: Whole plant senescence. In: NOODÉN, L.D.; LEOPOLD, A.C. (eds) Senescence and Aging in Plants. San Diego, CA, Academic Press. 391–439. NOODÉN, L.V., 1988d: Postlude and prospects. In: NOODÉN, L.D.; LEOPOLD, A.C. (eds) Senescence and Aging in Plants. San Diego, CA, Academic Press. 499–517. OINONEN, E., 1967a: The correlation between the size of Finnish bracken (Pteridium aquilinum [L.] Kuhn.) clones and certain periods of site history. Acta For. Fenn. 83: 1–51. OINONEN, E., 1967b: Sporal regeneration of bracken (Pteridium aquilinum [L.] Kuhn) in Finland in the light of the dimensions and the age of its clones. Acta For. Fenn. 83: 1–96. OINONEN, E., 1967c: Sporal regenation of ground pine (Lycopodium complanatum L.) in south- ern Finland in the light of the dimensions and age of its clones. Acta For. Fenn. 83: 76–85. OINONEN, E., 1968: The size of Lycopodium clavatum L. and L. annotinum L. stands as compared to that of L. complanatum L. and Pteridium aquilinum (L.) Kuhn stands, the age of the tree stand and the dates of fire on the site. Acta For. Fenn. 87: 1–53. OINONEN, E., 1969: The time table of vegetative spreading in the Lily-of-the-Valley (Convallaria majalis L.) and the Wood Small-Reed (Calamagrostis epigeios [L.] Roth.) in southern Finland. Acta For. Fenn. 97: 1–35. OOSTERMEIJER, J.G.B.; BRUGMAN, M.L.; DE BOER, E.R.; DEN NIJS, J.C.M., 1996: Temporal and spatial variation in the demography of Gentiana pneumonanthe, a rare perennial herb. J. Ecol. 84: 153–166. OOSTERMEIJER, J.G.B.; VAN’T VEER, R.; DEN NIJS, J.C.M., 1994: Population structure of the rare, long-lived perennial Gentiana pneumonanthe in relation to vegetation and the management in the Netherlands. J. Appl. Ecol. 31: 428–438. OVINGTON, J.D.; SCURFIELD, G., 1956: Biological Flora of the British Isles: Holcus mollis L. J. Ecol. 44: 272–280. PAGE, C.N., 1986: The strategies of bracken as a permanent ecological opportunist. In: SMITH, R.T.; TAYLOR, J.A. (eds) Bracken: Ecology, Land Use and Control Technology. Lancs, The Parthenon Publishing Group Limited. 173–181. PARKS, J.C.; WERTH, C.R., 1993: A study of spatial features of clones in a population of bracken fern, Pteridium aquilinum (Dennstaedtiaceae). Am. J. Bot. 80: 537–544. PARNELL, J.A.N., 1985: Biological Flora of the British Isles: Jasione montana L. J. Ecol. 73: 341–358. PASSECKER, F., 1977: Theorie der ontogenetischen Evolution und Alterung holziger Gewächse. Bodenkultur 28: 277–294. PAVLOV, V.N., 2000ff: Biological flora of the Moscow region (in Russian). Vol. 14 (2000), Vol. 15 (2003). Moscow, Grif & K. PAVLOV, V.N.; RABOTNOV, T.A.; TIKHOMIROV, V.N., 1990ff: Biological flora of the Moscow region (in Russian). Vol. 8 (1990), Vol. 9 (1993). Moscow, Izdatel’stvo Moskovskogo universiteta. PAVLOV, V.N.; TIKHOMIROV, V.N., 1995ff: Biological flora of the Moscow region (in Russian). Vol. 10 (1995), Vol. 11 (1995), Vol. 12 (1996), Vol. 13 (1997). Moscow, Argus, Poliex. PEARSON, M.C.; ROGERS, J.A., 1962: Biological Flora of the British Isles: Hippophae rhamnoides L. J. Ecol. 50: 501–513. PELTON, J., 1953: Studies on the life-history of Symphoricarpos occidentalis Hook. in Minnesota. Ecol. Monogr. 23: 17–39. PERKINS, D.; SWETNAM, T.W., 1996: A dendroecological assessment of whitebark pine (Pinus albi- caulis) in the Sawtooth-Salmon river region of Idaho. Can. J. For. Res. 26: 2123–2133. PERSIKOVA, Z.I., 1959: The formation and life cycle of some tussock grasses (in Russian). Biolog. Nauk. 3. PIANKA, E.R., 1970: On r- and K-selection. Am. Nat. 104: 592. PIGOTT, C.D., 1955: Biological Flora of the British Isles: Thymus L. J. Ecol. 43: 365–387. PIGOTT, C.D., 1956: The vegetation of upper Teesdale in the North Pennines. J. Ecol. 44: 545–586. PIGOTT, C.D., 1958: Biological Flora of the British Isles: Polemonium caeruleum L. J. Ecol. 46: 507–525. PIGOTT, C.D., 1968: Biological Flora of the British Isles. Cirsium acaulon (L.) Scop. J. Ecol. 56: 597–612. For. Snow Landsc. Res. 79, 3 (2005) 297

PINEDA-KRCH, M.; FAGERSTRÖM, T., 1999: On the potential for evolutionary change in meristem- atic cell lineages through intraorganismal selection. Journal of Evolutionary Biology 12: 681–688. PORNON, A.; DOCHE, B., 1996: Age structure and dynamics of Rhododendron ferrugineum L. pop- ulations in northwestern French Alps. J. Veg. Sci. 7: 265–272. POSCHLOD, P.; MATTHIES, D.; JORDAN, S.; MENGEL, C., 1996: The biological flora of Central Europe – an ecological bibliography. Bull. Geobot. Inst. ETH 62: 89–108. PRIMACK, R.B., 1973: Growth patterns of five species of Lycopodium. American Fern Journal 63: 3–7. QUANTIN, A., 1935: L’évolution de la végétation à l’étage de la chênaie dans le Jura méridional. Thèse Paris, Comm. SIGMA (Montpellier) 37: 1–382. RABOTNOV, T.A., 1950: The life cycle of perennial herbaceous plants in meadow coenoses (in Russian). Trudy bot. Inst. Akad. Nauk SSSR, Ser. III, 6: 7–204. RABOTNOV, T.A., 1974ff: Biological flora of the Moscow region (in Russian). Vol. 1 (1974), Vol. 2 (1975), Vol. 3 (1976), Vol. 4 (1978), Vol. 5 (1980), Vol. 6 (1980), Vol. 7 (1983). Moscow, Izdatel’stvo Moskovskogo universiteta. RABOTNOV, T.A., 1978: On coenopopulations of plants reproducing by seeds. In: FREYSEN, A.H.J.; WOLDENDORP, J.W. (eds) Structure and Functioning of Plant Populations. Amsterdam, Oxford, New York, North-Holland Publishing Company. 1–26. RABOTNOV, T.A., 1985: Dynamics of coenotic populations. In: WHITE, J. (ed) The Population Structure of Vegetation. Handbook of Vegetation Science 3. Dordrecht, Boston, Lancaster, Kluwer. 121–142. RABOTNOV, T.A., 1995: Phytozönologie. Stuttgart, Ulmer. 243 pp. RAUH, W., 1937: Die Bildung von Hypokotyl- und Wurzelsprossen und ihre Bedeutung für die Wuchsformen der Pflanzen. Nova Acta Leopoldina N.F. 4: 395–553. RAUNKIAER, C., 1910: Statistik der Lebensformen als Grundlage für die biologische Pflanzen - geographie. Beiheft zum Botanischen Centralblatt 27: 171–206. RAUNKIAER, C., 1934: The life forms of plants and statistical plant geography. Being the collected papers of C. Raunkiaer. Oxford, Clarendon Press. 632 pp. RAUNKIAER, C., 1937: Plant life forms. Oxford, Clarendon Press. 104 pp. RICKLEFS, R.E.; FINCH, C.E., 1995: Aging: A Natural History. New York, Scientific American Library. 209 pp. RIXEN, E.; CASTELLER, KA.; SCHWEINGRUBER, F.H.; STOECKLI, V., 2004: Age analysis helps to estimate plant performance on ski pistes. Bot. Helv. 114: 127–138. ROBBINS, W.I., 1957: Physiological aspects of ageing in plants. Am. J. Bot. 44: 289–294. RODRIGUEZ, R.; SÁNCHEZ TAMÉS, R.; DURZAN, D.J., 1990: Plant Aging. Basic and applied Approaches. NATO ASI Series Vol. 186. New York, London, Plenum Press. 462 pp. ROSE, F., 1948: Biological Flora of the British Isles: Orchis purpurea Huds. J. Ecol. 36: 366–377. ROSENTHAL, M., 1904: Ueber die Ausbildung der Jahrringe an der Grenze des Baumwachstums in den Alpen. Diss. Univ. Berlin. 24 pp. RUTTER, A.J., 1955: The composition of wet-health vegetation in relation to the water-table. J. Ecol. 43: 407–440. SALOMONSON, A., 1996: Interaction between somatic mutations and plant development. Vegetatio 127: 71–75. SANO, Y.; MORISHIMA, H.; OKA, H.-I., 1980: Intermediate perennial-annual populations of Oryza perennis found in Thailand and their evolutionary significance. Bot. Mag. Tokyo 93: 291–305. SCHAFFALITZKY DE MUCKADELL, M., 1959: Investigation on ageing of apical mersitems in woody plants and its importance in silviculture. Forstlige Forsogsvacsen I Danmark 4: 307–455. SCHLAGINTWEITH, H.; SCHLAGINTWEITH, A., 1850: Untersuchungen über die physikalische Geographie der Alpen. Leipzig. 582 pp. SCHMELTER, A., 1998–1999: The temperature-growth relationship of Discaria trinervis in the cen- tral Andes of Argentina and the influence of local site factors. Dendrochronologia 16–17: 87–98. SCHROETER, C., 1926: Das Pflanzenleben der Alpen. 2nd ed. Zürich, Albert Baustein. 1288 pp. 298 Fritz Hans Schweingruber, Peter Poschlod

SCHULMAN, E., 1956: Dendroclimatic Changes in Semiarid America. Tucson, University of Arizona Press. 142 pp. SCHULMAN, E., 1958: Bristlecone pine, oldest known living thing. Nat. Geogr. 113: 355–372. SCHWEINGRUBER, F.H., 1990: Anatomy of European woods. Bern, Haupt. 800 pp. SCHWEINGRUBER, F.H., 1992: Annual growth rings and growth zones in woody plants in Southern Australia. IAWA Bull N.S. 13: 359–379. SCHWEINGRUBER, F.H., 2001: Dendroökologische Holzanatomie. Anatomische Grundlagen der Dendrochronologie. Bern, Stuttgart, Haupt. 472 pp. SCHWEINGRUBER, F.H., 2006: Anatomiocal characteristics and ecological trends in the xylem and phloem of Brassicaceae and Resedaceae. IAWA J. (in press) SCHWEINGRUBER, F.H.; DIETZ, H., 2001: Annual rings in the xylem of dwarf shrubs and perennial dicotyledonous herbs. Dendrochronologia 19: 115–126. SCOTT, G.A.M., 1963: Biological Flora of the British Isles: Glaucium flavum Crantz. J. Ecol. 51: 743–754. SHAVER, G.R.; BILLINGS, W.D., 1975: Root production and root turnover in a wet tundra ecosys- tem, Barrow, Alaska. Ecology 56: 401–409. SHEFFIELD, E.; WOLF, P.G.; HAUFLER, C.H., 1989: How big is a bracken plant? Weed Research 29: 455–460. SHIRREFFS, D.A., 1985: Biological Flora of the British Isles: Anemone nemorosa L. J. Ecol. 73: 1005–1020. SHORINA, N.I.; SMIRNOVA, O.V., 1985: The population biology of ephemeroids. In: WHITE, J. (ed) The Population Structure of Vegetation. Handbook of Vegetation Science 3. Dordrecht, Boston, Lancaster, Kluwer. 225–240. SIMMONDS, N.W., 1946: Biological Flora of the British Isles: Gentiana pneumonanthe L. J. Ecol. 33: 295–307. SMIRNOVA, O.V.; CHISTYAKOVA, A.A.; ZAUGOLNOVA, L.B.; EVSTIGNEEV, O.I.; POPADIOUK, R.V.; ROMANOVSKY, A.M., 1999: Ontogeny of a tree. Botan. Zhur. 84: 8–20. SMIRNOVA, O.V.; ZAUGOLNOVA, L.B.; ERMAKOVA, I.M., 1976: Plant Coenopopulations (Basic Concept and Structure) (in Russian). Moscow, Nauka. 216 pp. SONESSON, M.; CALLAGHAN, T.V., 1991: Strategies of survival in plants of the Fennoscandian tun- dra. Arctic 44: 95–105. SPARLING, J.H., 1968: Biological Flora of the British Isles: Schoenus nigricans L. J. Ecol. 56: 883–899. STAHLE, D.W.; CLEAVELAND, M.K.; HEHR, J.G., 1988: North Carolina climate changes recon- structed from tree rings: A.D. 372 to 1985. Science 240: 1517–1519. STEHLIK, I.; HOLDEREGGER, R., 2000: Spatial genetic structure and clonally diversity of Anemone nemorosa in late successional deciduous woodlands of Central Europe. J. Ecol. 88: 424–435. STEINGER, T.; KÖRNER, C.; SCHMID, B., 1996: Long-term persistence in a changing climate: DNA analysis suggests very old ages of clones of alpine Carex curvula. Oecologia 105: 94–99 STERNBERG, L., 1976: Growth forms of Larrea tridentata. MadroÀo 23: 408–417. STRASBURGER 1936 – Zitat von Fritz; und Strasburger 1958 (s. Leg. Abb. 4.1) SUGORKINA, N.S., 1995: Geranium sylvaticum L. In: RABOTNOV, T.A. (ed) Biological flora of the Moscow region 7 (in Russian). Moscow, Izdatel’stvo Moskovskogo universiteta. 189–197. SUMMERFIELD, R.J., 1972: Biological inertia – an example. J. Ecol. 60: 793–798. SUMMERFIELD, R.J., 1974: Biological Flora of the British Isles: Narthecium ossifragum (L.) Huds. J. Ecol. 62: 325–339. SUYAMA, Y.; OBAYASHI, K.; HAYASHI, I., 2000: Clonal structure in a dwarf bamboo (Sasa senanen- sis) population inferred from amplified fragment length polymorphism (AFLP) fingerprints. Mol. Ecol. 9: 901–906. TAMM, C.O., 1948: Observations on reproduction and survival of some perennial herbs. Botaniska Notiser 3: 305–321. TAMM, C.O., 1956: Further observations on the survival and flowering of some perennial herbs. Oikos 7: 274–292. TAMM, C.O., 1972a: Survival and flowering of some perennial herbs. II. The behaviour of some orchids on permanent plots. Oikos 23: 23–28. For. Snow Landsc. Res. 79, 3 (2005) 299

TAMM, C.O., 1972b: Survival and flowering of some perennial herbs. III. The behaviour of Primula veris on permanent plots. Oikos 23: 159–166. THIMANN, K.V. (ed) 1980: Senescence in Plants. Boca Raton, CRC Press. 276 pp. THOMAS, H., 1994: Aging in the plant and animal kingdoms – the role of cell death. Rev. Clin. Geront. 4: 5–20. THOMAS, H., 2002: Ageing in plants. Mechanisms of Ageing and Development 123: 747–753. THOMAS, H.; DONNISON, I., 2000: Back from the brink: plant senescence and its reversibility. In: BRYANT, J.; HUGHES, S.G.; GARLANT, J.M. (eds) Programmed Cell Death in Animals and Plants. Oxford, Bios. 149–162. THOMAS, H.; HOWARTH, C.J., 2000: Five ways to stay green. J. Exp. Bot. 51: 329–337. THOMAS, H.; OUGHAM, H.J.; WAGSTAFF, C.; STEAD, A.D., 2003: Defining senescence and death. J. Exp. Bot. 54: 1127–1132. THOMAS, H.; SADRAS, V.O., 2001: The capture and gratuitous disposal of resources by plants. Funct. Ecol. 15: 3–12. THOMAS, H.; THOMAS, H.M.; OUGHAM, H., 2000: Annuality, perenniality and cell death. J. Exp. Bot. 51: 1781–1788. TROLL, W., 1937: Vergleichende Morphologie der höheren Pflanzen. Erster Band: Vegetations - organe. Erster Teil. Berlin, Bornträger. 955 pp. URANOV, A.A., 1975: Age spectrum of the phytocoenopopulation as a function of time and ener- getic wave processes (in Russian). Biologicheskie Nauki 2: 7–34. URANOV, A.A.; ZAUGOLNOVA, L.B.; SMIRNOVA, O.V., 1977: Plant Coenopopulations (Development and Interaction) (in Russian). Moscow, Nauka. 133 pp. VALVERDE, T.; SILVERTOWN, J., 1998: Variation in the demography of a woodland understorey herb (Primula vulgaris) along the forest regeneration cycle: projection matrix analysis. J. Ecol. 86: 545–562. VAN DER MAAREL, E.; SYKES, M., 1993: Small-scale plant species turnover in a limestone grass- land: the carousel model and some comments on the niche concept. J. Veg. Sci. 4: 179–188. VASEK, F.C., 1980: Creosote bush: long lived clones in the Mohave Desert. Am. J. Bot. 67: 246–255. VERDCOURT, B., 1948: Biological Flora of the British Isles: Cuscuta europaea L. J. Ecol. 36: 358–365. VIDAL, M.L., 1906: Anatomie de la racine et de la tige de l’Eritrichium nanum. Notes et mémoires de l’association française pour l’avancement des sciences fusionnée avec l’association scien- tifique de France 1905: 472–475. VON LAZNIEWSKI, W., 1896: Beiträge zur Biologie der Alpenpflanzen. Flora 82: 224–267. VON MÖRS, I.; BÉGIN, Y., 1993: Shoreline shrub population extension in response to recent isosta- tic rebound in Eastern Hudson Bay, Quebec, Canada. Arct., Antarc., Alp. Res. 25: 15–23. VORONTZOVA, L.I.; ZAUGOLNOVA, L.B., 1985: Population Biology of Steppe Plants. In: WHITE, J. (ed) The Population Structure of Vegetation. Handbook of Vegetation Science 3. Dordrecht, Boston, Lancaster, Kluwer. 143–178. WAGER, H.G., 1938: Growth and survival of plants in the Arctic. J. Ecol. 26: 390–410. WALTER, H., 1973: Allgemeine Geobotanik. Stuttgart, Ulmer. WALTER, H.; LIETH, H., 1960–1967: Klimadiagramm-Weltatlas. 3 vol. Jena, VEB Gustav Fischer. WANGERMANN, E., 1965: Longevity and ageing in plants and plant organs. In: RUHLAND, W. (ed) Handbuch der Pflanzenphysiologie Vol. 15/2. Berlin, Springer. 1037–1057. WARD, L.K., 1982: The conservation of juniper: longevity and old age. J. Appl. Ecol. 19: 917–928. WAREING, P.F.; SETH, A.K., 1967: Ageing and senescence in the whole plant. Symp. Soc. Exp. Biol. 21: 543–558. WARMING, E., 1895: Plantesamfund. Grundtræk af den økologiske Plantegeografi. Copenhague, Philipsen. 335 pp. WARMING, E., 1909: Oecology of Plants. An Introduction to the Study of Plant Communities. Oxford, Oxford Univ. Press. 422 pp. WARREN WILSON, J., 1964: Annual growth of Salix arctica in the High Arctic. Ann. Bot. 28: 71–76. WATT, A.S., 1955: Bracken versus heather, a study in plant sociology. J. Ecol. 43: 490–506. 300 Fritz Hans Schweingruber, Peter Poschlod

WEIHER, E.; VAN DER WERF, A.; THOMPSON, K.; RODERICK, M.; GARNIER, E.; ERIKSSON, O., 1999: Challenging Theophrastus: A common core list of plant traits for functional ecology. J. Veg. Sci. 10: 609–620. WEIN, R.W., 1973: Biological Flora of the British Isles: Eriophorum vaginatum L. J. Ecol. 61: 601–618. WELCH, D., 1966: Biological Flora of the British Isles: Juncus squarrosus L. J. Ecol. 54: 535–548. WHEELER, E.A.; BAAS, P.; GASSON, P.E., 1989: IAWA list of microscopic features for hardwood identification. IAWA Bull. N.S. 10: 219–332. WHERRY, E.T., 1972: Box-huckleberry as the oldest living protoplasm. Castanea 37: 94–95. WHITE, J., 1985: The population structure of vegetation. Handbook of Vegetation Science Part III. Dordrecht, Boston, Lancaster, Dr. W. Junk Publishers. 669 pp. WHITTAKER, R.H.; LIKENS, G.E., 1973: The primary production of the biosphere. Hum. Ecol. 1: 299–369. WIJK, S., 1980: Plants and the snow cover (in Swedish). Fauna Flora Uppsala 75: 32–36. WILLIAMS, O.B., 1970: Population dynamics of two perennial grasses in Australian semiarid grass- land. J. Ecol. 58: 869–875. WINCHESTER, V.; HARRISON, S., 2000: Dendrochronology and lichenometry: an investigation into colonization, growth rates and dating on the east side of the North Patagonian Icefield, Chile. Geomorphology 34: 181–194. WOODCOOK, H.; BRADLEY, R., 1994: Salix arctica (Pall.) Its potential for dendroclimatological studies in the High Arctic. Dendrochronologia 12: 11–23. WORBES, M., 1990: Site and sample selection in tropical forests. In: COOK, E.R.; KAIRIUKSTIS, L.A. (eds) Methods of Dendrochronology: Applications in the Environmental Sciences. Boston, MA, Kluwer. 35–40. WORRALL, J., 1990: Subalpine larch: oldest trees in Canada? The Forestry Chronicle: 478–479. WU, L.; BRADSHAW, A.D.; THURMAN, D.A., 1975: The potential for evolution of heavy metal tol- erance in plants. III. The rapid evolution of copper tolerance in Agrostis stolonifera. Heredity 34: 165–187. ZENTGRAF, U.; JOBST, J.; KOLB, D.; RENTSCH, D., 2004: Senescence-related gene expression pro- files of rosette leaves of Arabidopsis thaliana: Leaf age versus plant age. Plant Biol. 6: 178–183. ZHUKOVA, L.A., 1983a: Plantago major L. In: RABOTNOV, T.A. (ed) Biological Flora of the Moscow region 7 (in Russian). Moscow, Izdatel’stvo Moskovskogo universiteta. 189–197. ZHUKOVA, L.A., 1983b: Plantago media L. In: RABOTNOV, T.A. (ed) Biological Flora of the Moscow region 7 (in Russian). Moscow, Izdatel’stvo Moskovskogo universiteta. 197–202. ZHUKOVA, L.A., 1983c: Plantago lanceolata L. In: RABOTNOV, T.A. (ed) Biological Flora of the Moscow region 7 (in Russian). Moscow, Izdatel’stvo Moskovskogo universiteta. 203–209. ZOLLER, H., 1949: Beitrag zur Altersbestimmung von Pflanzen aus der Walliser Felsensteppe. Ber. Geobot. Inst. Eidgenöss. Tech. Hochsch., Stift. Rübel für das Jahr 1948: 61–68.