Living on the Edge: Effectiveness of Buffer Strips in Protecting Biodiversity in Boreal Riparian Forests

Living on the edge: effectiveness of buffer strips in protecting biodiversity in boreal riparian forests

Kristoffer Hylander

Umeå 2004

Landscape Ecology Group Department of Ecology and Environmental Science Umeå University SE-901 87 Umeå Sweden

AKADEMISK AVHANDLING

kommer med vederbörligt tillstånd av rektorsämbetet vid Umeå Universitet, för erhållande av filosofie doktorsexamen i ekologi, offentligen försvaras fredagen den 7 maj 2004, kl. 10.00 i P.O. Bäckströms sal, Sveriges lantbruksuniversitet, Umeå

Examinator: Professor Christer Nilsson

Opponent: Professor Ellen Macdonald, Department of Renewable Resources, University of Alberta, Edmonton, Canada Organisation Document name Umeå University Doctoral Dissertation Dept. of Ecology and Environmental Science Date of Issue SE-901 87 Umeå, Sweden May 2004

Author Kristoffer Hylander

Title Living on the edge - effectiveness of buffer strips in protecting biodiversity in boreal riparian forests

Abstract The objective of this thesis is to evaluate the ecological consequences of buffer strip retention on riparian and terrestrial biodiversity. Earlier studies on forest buffer strips have evaluated their effectiveness in relation to water quality and aquatic biota. However, forests along streams are species rich habitats for many organism groups. Buffer strip management is assumed to be important also for protecting such species. Current approaches to biodiversity- oriented forest management practices need to be scientifically evaluated. In this thesis the effects on bryophytes and land snails have been evaluated. A before-and-after experiment along 15 small streams in northern Sweden showed that buffer strips of 10 m on each side of the stream moderated the negative effects exhibited at the clear-cuts. The number of land snail species remained similar as to before logging and the number of vanished bryophyte species was lower in the buffer strips than in the clear-cuts. The ground moisture influenced the survival rate of land snails at the clear-cuts. At mesic sites many species vanished but at wet sites the snail fauna was unaffected by the logging. Many bryophyte species, most of them liverworts, decreased or disappeared in the buffer strips. These were mostly growing on substrates elevated from the forest floor, such as logs, stumps and tree-bases. A number of nationally red-listed species, sensitive for changes in microclimate, were among those decreasing most. Thus, for the species in most need of protection the buffer strips were too narrow. An experiment with bryophyte transplants followed over a season showed that wet ground moisture moderated the negative edge effects in narrow buffer strips. On the other hand, the growth in mesic and moist sites was almost as low as in comparable clear-cuts. Microclimatic edge effects are stronger at south facing than north-facing edges of forest clear-cuts. This was shown in an experiment using bryophyte growth as an indicator of differences in microclimate. However, the depth of edge influence seemed to be similar between north- and south-facing forest edges, >30 m for one species. An explanation for this could be that wind penetrates deeper into edges than solar radiation and has a more variable direction. In conclusion, narrow buffer strips consist entirely of edge habitat. For many species the environment in buffer strips is good enough for persistence. For others, most notably bryophyte species on convex substrates, wider buffer strips are needed to ensure long-term survival.

Key words boreal forest, bryophyte, buffer strip, ecological boundary, edge effect, headwater stream, land snail, liverwort, moss, phytometer, riparian forest, substrate, terrestrial gastropod

Language English ISBN 91-7305-611-1 Number of pages 35

Signature Date 2004-03-26

Till Eva, May, Ruben och Lydia

Phd thesis Dissertation 2004 ISBN 91-7305-611-1 © Kristoffer Hylander Printed by VMC, KBC, Umeå University, Sweden Sammanfattning

Syftet med avhandlingen är att utvärdera nyttan av att vid avverkning lämna kantzoner längs bäckar för skogslevande arter. Tidigare studier har fokuserat på kantzoners effektivitet att skydda vattenkvalitet och organismer i den akvatiska miljön. Strandskogar är emellertid artrika miljöer för många organismgrupper. Man har ansett att lämnande av kantzoner kan vara en bra metod att också skydda sådana arter. Det är dock viktigt att vetenskapligt utvärdera metoder för naturvårdshänsyn. I avhandlingen har effekterna på mossor och landsnäckor studerats då de tidigare har visats påverkas negativt av kalavverkning. Ett före-efter experiment genomfördes längs 15 små skogsbäckar i norra Sverige. Resultatet visar att kantzoner om 10 m på varje sida av bäcken väsentligt motverkar de negativa effekterna av kalavverkning. I kantzonerna var antalet snäckarter oförändrat efter avverkningen och antalet försvunna mossarter var färre jämfört med de kalavverkade ytorna. Överlevnaden hos snäckor på de kalavverkade platserna påverkades av markfuktigheten. På frisk mark minskade både abundans och artrikedom medan snäckfaunan i blöta skogar inte påverkades av avverkningen. Ganska många mossarter, särskilt levermossarter, minskade eller försvann i kantzonerna. De flesta av dessa växte på upphöjda substrat såsom lågor, stubbar och trädbaser. Bland de arter som drabbades hårdast, som en konsekvens av det förändrade mikroklimatet, var ett antal nationellt rödlistade arter. Kantzonen var således för smal för att kunna skydda de känsligaste och mest hotade arterna. Ett experiment där tillväxten av transplanterade mossor följdes över en säsong på kalhyggen, kantzoner och i referenser visade att på blöt mark mildrades de negativa effekterna av kantzonerna. Å andra sidan var tillväxten av mossorna i kantzoner på frisk till fuktig mark nästan lika låg som på de kalavverkade ytorna. Mikroklimatrelaterade effekter är kraftigare i sydexponerade jämfört med nordexponerade skogskanter. Detta visades i ett experiment där mossors tillväxt användes som indikator på ett förändrat mikroklimat. Djupet på kanteffekten, det vill säga hur långt in i skogen förändringar kunde detekteras, verkade dock vara lika, >30 m för en av arterna. En förklaring skulle kunna vara att tillväxtminskningen i de inre delarna av skogen berodde på ökad vindhastighet och i mindre utsträckning på direkt solljus. Vind når djupare in i skogen och har en mer varierad riktning än solinstrålning. Huvudslutsatsen i avhandlingen är att smala kantzoner helt och hållet påverkas av mikroklimatiska kanteffekter. För många arter av både landsnäckor och mossor är dock denna miljö ett avsevärt bättre alternativ än att ingen kantzon lämnas. För andra, tydligast observerat för mossor på konvexa substrat, skulle dock bredare kantzoner behövas för deras långsiktiga överlevnad i dessa miljöer. Contents

List of papers______2 Introduction ______3 Habitat loss and fragmentation______3 Edge effects______4 Buffer strip management ______5 Study system ______6 Forests along small streams ______6 Bryophytes ______7 Land snails ______8 Objectives ______9 Study areas and sites ______9 Methodological approaches______11 Before-and-after experiment (I, II)______11 Bryophyte growth as microclimate indicator (paper III, IV) ______12 Major results and discussion______12 Effects of clear-cutting ______12 Effectiveness of buffer strips ______14 Exploration of edge effects______15 Concluding remarks and future perspectives ______19 Buffer strip management – considerations for practitioners_____ 20 Results relevant to buffer strip management ______20 Reviewing buffer strip management along small streams ______22 Acknowledgements______25 References ______25 Tack (In Swedish)______34

List of papers

This thesis is based on the following papers, which will be referred to in the text by their Roman numerals.

I Hylander, K., Dynesius, M., Jonsson, B. G, and Nilsson, C.: Lie low: substrate form determines the fate of bryophytes in riparian buffer strips – Submitted manuscript.

II Hylander, K., Nilsson, C. and Göthner, T.: Effects of buffer strip retention and clearcutting on land snails in boreal riparian forests – Conservation Biology, in press.

III Hylander, K., Jonsson, B. G. and Nilsson, C. 2002: Evaluating buffer strips along boreal streams using bryophytes as indicators – Ecological Applications 12:797-806.

IV Hylander, K.: North- vs. south-facing edge effects: different magnitudes but equal spatial extent – Submitted manuscript.

Papers II and III are reproduced with the kind permission from the publishers.

2 Introduction

One important motive for this thesis could be found in the political goal to conserve the world’s biodiversity that most countries have agreed on (Glowka et al. 1994). This is, however, a delicate task in a world increasingly modified by humans. Much research has been devoted to develop strategies and guidelines for ecosystem management including restoration and management for biodiversity (e.g., Franklin 1989, Hunter 1999, Burton et al. 2003). In the boreal forest ecosystem the conceptual basis for the proposed modified management practices has been natural variability emphasising disturbance dynamics in natural forests as well as structural and functional heterogeneity (Fries et al. 1997, Angelstam 1998, Kuuluvainen 2002). In Fennoscandia, biodiversity-oriented management practices such as green tree retention, prescribed burning, creation of artificial snags, and retention of buffer strips are nowadays used extensively (Larsson and Danell 2001). There is an increasing need of scientific evaluation of these new forestry practices to judge if they reach the goal of better accommodation of biodiversity in the managed forest landscape (Simberloff 1999, Larsson and Danell 2001).

Habitat loss and fragmentation The boreal forest biome (which is the context in which the studies in this thesis were carried out) is managed for timber production to an increasing extent. Fennoscandia is one of the areas where this transformation has gone furthest (Anon. 1987). The natural boreal landscape of Fennoscandia had a large proportion of multi-aged stands created either by recurrent wild fires (often not stand replacing) and by internal dynamics in areas that had escaped fires for a long time (Esseen et al. 1997). Today the landscape is instead dominated by even-aged stands with a high proportion of clear-cuts and young stands (Östlund et al. 1997). This transformation of the landscape has heavily affected biodiversity. According to the Swedish red-list, approximately 2000 forest species are considered threatened or care-demanding, and 115 have gone extinct (Gärdenfors 2000). Isolation of populations due to habitat fragmentation will eventually drive species with restricted dispersal capacities to extinction, even if they can linger on in remnant patches for a while (Tilman et al. 1994). Thus, even if habitat destruction ceases many species are presumed to go extinct in the future due to an extinction debt (Hanski 2000, Siitonen 2001, Berglund 2004, but cf. Honnay et al. 1999). 3 In much research inspired by the equilibrium theory of island biogeography (MacArthur and Wilson 1967) and its succeeding theories, fragments of old-growth forests have been considered to function as islands surrounded by a hostile matrix unimportant for the long-term survival of the forest interior species (Brotons et al. 2003). However, for many forest species this is not the case unless the surrounding areas are not transformed into for example urban areas or agricultural land. Recently, Brotons et al. (2003) showed for forest birds that forest fragments did not function as true islands because of compensatory effects of the surrounding matrix of managed forest. Few studies have, however, studied the quality of the managed forest and its effects on core areas of high habitat quality (Hansson 1998). Improving the quality of the matrix has been suggested to be an important action to protect biodiversity in the managed forest landscape and to reduce the dependence on reserves (Saunders et al. 1991, Angelstam and Andersson 2001, also cf. Bengtsson et al. 2003). Retaining trees in different ways either as single trees or as groups of trees on the clear- cuts or in riparian areas has been one practice to improve the quality for biodiversity in the managed forest landscape (Vanha-Majamaa and Jalonen 2001).

Edge effects Different kinds of edge effects are a consequence of fragmentation and may greatly impact ecosystems (Saunders et al. 1991). When a more or less continuous forest cover is fragmented into patches with much smaller grain size the amount of edges increases dramatically (Franklin and Forman 1987). In addition to the positive effects of matrix on forest patches previously mentioned there is, however, also much evidence that many species and ecological processes are negatively affected at edges created by silviculture (e.g., Esseen and Renhorn 1998, Chen et al. 1999, Harper and Macdonald 2002). Such edge effects could consist of many different environmental or biological effects such as e.g., altered microclimate, increased predation, and invasion of exotic species (Murcia 1995). There is evidence from some studies that edge effects occur over large spatial scales (Laurance 2000), but for most species or processes interior conditions are attained within 10 to 100 meters from the edge (Murcia 1995). Edge orientation, topography, canopy height and many other factors can affect the extent and magnitude of microclimatic edge effects (Chen et al. 1999), which are the kind of effects that are discussed most frequently in this thesis. The gradients in microclimatic variables such as light, wind, temperature, and moisture 4 through forest–clear-cut edges are well documented (e.g., Chen 1995, Brosofkse 1997). Studies on ecological responses that can directly be coupled to these gradients are, however, fewer (Chen et al. 1999). Lichens, bryophytes, and other poikilohydric organisms, i.e., organisms that lack effective mechanisms for regulating uptake or loss of water (Proctor 1990), should be more directly and rapidly influenced by an altered microclimate at forest–clear-cut edges than for example most animals and vascular plants (cf. Palmqvist and Sundberg 2000). Such organisms would thus be interesting to study and use as indicators of changed microclimatic conditions at edges (cf. Renhorn et al. 1997, Esseen and Renhorn 1998, Kivistö and Kuusinen 2000).

Buffer strip management The practice of leaving buffer strips along streams when the rest of the stand is logged is nowadays common in North America, Europe and Australia (Bergquist 1999, Blinn and Kilgore 2001). The focus has in most cases been on water quality and the aquatic biota, and the purposes with the buffer strips have been to reduce nutrient leakage, sediment input, and temperature fluctuations in the water (Castelle et al. 1994, Blinn and Kilgore 2001). The role of buffer strip retention as a means of protecting riparian forest biodiversity has more recently come into focus (e.g., Hannon et al. 2002, Cockle and Richardson 2003, Goebel et al. 2003) along with the more widely acknowledged concerns about biodiversity losses due to silviculture. The effectiveness of buffer strips in this respect has, however, been little evaluated, except for birds where the knowledge is steadily accumulating (e.g., Darveau et al. 1995, Pearson and Manuwal 2001, Whitaker and Montevecchi 1999). Swedish legislation is not very precise regarding buffer strip management. It only states that buffer strips should be retained to the extent that is needed with respect to values of plants, animals, culture and the landscape (Anon. 1993). In other places, for example several states in USA and provinces of Canada, there are more strict guidelines with fixed buffer widths (in the interval of 7.5–50 m) for different types of streams (Blinn and Kilgore 2001). In the Pacific Northwest region many buffer strips, however, are considered “management zones” where harvest of the largest trees is permitted (Young 2000). According to Young (2000) long-term consequences are a degradation of the riparian zone since the source of large woody debris is continuously removed. Most studies on microclimatic edge effects find the depth of edge influence to be much deeper than 10 m (Murcia 1995), which is a commonly used buffer width, if any, along small streams in Sweden 5 (Anon. 2002). One could thus presume that such buffer strips consist entirely of edge habitat. It is, however, not the same as to say that a buffer strip is a worthless habitat for protection of riparian species. The response of the biota in the buffer strips must be investigated directly. Different riparian sites could differ in the pre-logging conditions regarding species composition and species richness. When the effectiveness of buffer strips is evaluated this inherent variation in species composition should be taken into account.

Study system

Forests along small streams Despite their modest area compared to the rest of a watershed riparian forests play an important ecological role. Riparian areas link terrestrial and aquatic ecosystems at both local and regional scales, and function both as boundaries and corridors in the landscape (Naiman and Décamps 1997). The gradients in for example moisture, nutrients, shade, microclimate, and micro-topography that characterise the riparian zone are considered to be a major explanation for the high diversity of species of many different organism groups often found within this habitat (Gregory et al. 1991, Naiman et al. 1993). Even in situations where the numbers of species do not differ there can be a considerable change in species composition along the gradient from uplands to riparian forests with unique species occurring in both upland and riparian habitats (e.g., Jonsson 1997, Whitaker and Montevecchi 1997, Goebel et al. 2003). As an example of the opposite, riparian forests along lakes in Alberta were not a unique forest habitat, and hence not preferred before any other forest stand as a site for protection of old forest values (Hannon et al. 2002). The riparian zone is often (narrowly) defined as the zone of regular inundation or (more widely) the zone where the vegetation could be influenced by the hyporheic water (i.e., the water in the ground flowing along with the stream) (Naiman and Décamps 1997). This has led to the view that headwater streams often have narrow riparian zones. Brosofske et al. (1997) have, however, shown that a moist microclimate could reach >50 m from small streams in rather steep terrain. For organisms relying on a moist microclimate this zone of influence from the stream could be important for the distribution of the species. How these microclimatic gradients influence patterns of biodiversity and ecological processes is, however, mostly unknown (Naiman et al. 2000). 6 Bryophytes In this thesis I have chosen to study bryophytes (mosses and liverworts). Bryophytes are an important component of the boreal forest ecosystem both in terms of abundance and species diversity (Hallingbäck 1992). However, species richness is not evenly distributed over the landscape. A study in spruce forests in mid Norway demonstrated a main gradient in bryophytes species richness that followed a productivity gradient, reflecting coincidence gradients in water, nutrients and pH (Frisvoll and Prestø 1997). A similar gradient in bryophyte community composition in boreal forest coupled to water and nutrients has also been demonstrated in other studies in both Europe (Kuusipalo, 1985, Økland, 1993) and North America (Carleton, 1990, Robinson et al., 1989). Recently, Dynesius (2001) showed that both young and old forests along small streams house 2-3 times mores bryophyte species compared to upland forests (randomly located less than 1 km from the stream site) of the same age in northern Sweden (grain size 0.1 ha). These results conform to the mentioned results of Frisvoll and Prestø (1997), as forests along small streams often are both moister and have a higher productivity than most upland forests. However, Dynesius (2001) also pointed out that forests along small streams exhibit wide habitat gradients within short distances, in for example moisture and pH, increasing the number of bryophyte niches (Dynesius, 2001). The poikilohydric nature of bryophytes (i.e., that they lack mechanisms for regulating uptake and loss of water) has the consequence that the growth is confined to temporal windows where the shoots are moist and there is sufficient light (Proctor 1990). Species with different "life forms" or species growing on different substrates could be expected to differ regarding their sensitivity to an altered microclimate (cf. Bates 1998). One could hypothesise that a species on a convex surface should be more dependent of a moist microclimate than a species growing on wet forest floor. On the other hand, one could assume that species on surfaces that often dry out should be more tolerant to desiccation and hence be less sensitive to edge effects. Indeed, the capacity to withstand periods of desiccation is characteristic for most bryophyte species (Proctor 1990). Studies on the initial effect of forestry on bryophytes in non-riparian sites provide important background information for this thesis as specific studies in riparian sites are lacking. The general view is that bryophytes are sensitive to the altered microclimate brought about by logging. Many studies report strong declines of cover and species richness as an initial response to clear-cutting, mostly studied at small spatial scales (0.25-2 m2) (e.g., 7 Hannerz and Hånell 1997, Jalonen and Vanha-Majamaa 2001). Several studies on bryophytes also find that young managed forests have an impoverished flora compared to old-growth forests, especially for epixylic species (species growing on dead wood) (Andersson and Hytteborn 1991, Frisvoll and Prestø 1997, Kruys et al. 1999).

The leaves of most bryophyte species are composed of a single cell layer without a protecting cuticula. Here part of a leaf of Lophozia longidens (Lindb.) Macoun in mag-nification. (Photo: Niklas Lönnell)

Land snails The other organism group, which I studied in this thesis, is land snails (also called terrestrial gastropods). I studied litter dwelling species, which constitute the major part of the approximately 120 species recorded from Sweden (Falkner et al. 2001). In boreal forests the highest species richness and abundance are found in deciduous forests and most notably in aspen stands (Kralka 1985, Suominen et al. 2003). There are generally more snails in sites with higher pH and calcium content (Wäreborn 1970). Calcium is needed for shell formation and is a limiting factor in many sites (e.g., Gärdenfors 1992). There are, however, shelled land snails also in coniferous forests on entirely acidic bedrock (Wäreborn 1970). From a conservation perspective land snails are interesting as a model organism group because of their limited dispersal capacity compared to many other organism groups (Baur and Baur 1988). This implies that the short-term effect of a disturbance can be of great importance for the long-term survival. In other words, local extinctions could lead to extended periods of absence. Regarding land snails the knowledge of the effect of disturbance is very incomplete. Karlin (1961) reports on severe declines after wildfire and von Proschwitz (1993) mentions several species that are considered to be sensitive to human disturbance, including forestry. However, a study in north-eastern USA did not find any clear pattern of species richness and stand age for land snails, even if there seemed to be an initial decline in abundance and species richness just after clear-cutting (Strayer et al. 1986). 8 Objectives

The main objective of this thesis is to evaluate the ecological consequences of buffer strip retention on the riparian and terrestrial portion of the biodiversity. The focus is on small streams and the study organisms are bryophytes and land-snails. Specific objectives (with the papers addressing them referred to in roman numerals) are:

• To study the initial effects of clear-cutting on species richness and composition in riparian forests. (I, II) • To describe the initial effects on species richness and community composition in buffer strips after adjacent logging (I, II) • To investigate if bryophyte growth could be used as an indicator for changed microclimate in buffer strips and other forest–clear-cut edges. (III, IV) • To describe the effects on growth of bryophytes under different ground moisture conditions in buffer strips. (III) • To investigate microclimatic edge effects in forest–clear-cut edges, and how these effects differ between north- and south-facing edges. (IV)

Study areas and sites

The studies in this thesis have all been conducted in the mid-boreal zone (sensu Ahti et al. 1968) in northern Sweden (Fig. 1). The field work for papers I and II was done in the provinces of Medelpad and Jämtland [62°40' N and 16°05' E (midpoint of the area)] and the field work for papers III and IV in Västerbotten (63°55' N and 20°05' E). The whole region has been subjected to repeated glaciations and most of the parent material in the till is derived from rather acidic granitic and metamorphic rocks (Fredén 1994). The pH in the till is, however, slightly higher in Medelpad-Jämtland compared to Västerbotten. The study sites in the Medelpad-Jämtland area are situated above the post- glacial highest coastline while the area in Västerbotten is below this boundary. A consequence of this is that clay, silt and sand are more common substrates in low topographical positions in Västerbotten. The two areas are climatologically similar. The yearly precipitation is ~700 mm and the growing season is approximately 155 d (Raab and Vedin 1995). The distribution of the precipitation over the year is, however, 9 slightly different with higher summer rainfall and lower winter precipitation in the Medelpad-Jämtland area. The most abundant tree species in the canopy of the mature forests are Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.), with scattered birches (Betula pubescens Ehrh. and Betula pendula Roth) and aspen (Populus tremula L.) occurring in both areas. Along lakeshores and riverbanks grey alder [Alnus incana L. (Moench)] is common. The productivity of the forest is slightly higher in the Medelpad-Jämtland area with ~5 m3ha-1 versus 4-5 m3ha-1 in the Västerbotten area (Nilsson 1990). The forests in these areas have been logged for industrial purposes for about 150 years with clear-cutting being the prevalent method the last 50 years (Esseen et al. 1997). In collaboration with the forest company SCA (Svenska Cellulosa Aktiebolaget), I selected 15 mature forest stands with intersecting small (0.5 – 2 m wide) streams in Medelpad and Jämtland. In each stand, two plots were established along the stream. During the summer of 1998 bryophytes and land snails were inventoried. In the winter of 1998/1999 the forests were logged according to my specifications. The stands were clear-cut all the way down to the stream along half of the stretch, and along the other half, buffer strips of 10 m were left on both sides of the stream (see e.g., Fig. 2b in paper I). One plot was located in each of these two treatments at each site. In 2001, the third summer after the logging event the plots were inventoried a second time. In addition to these stands, 10 reference stands of mature forest along small streams in nature reserves were selected (results reported in papers I and II).

Field sites for papers III and IV

65° Umeå Östersund

Gulf of Field sites for 60° Bothnia papers I and II Sundsvall

0 10 km Fig. 1. Location of the field sites for the different experiments in northern Sweden. Papers I and II are based on data collected in the southern area and papers III and IV on data collected in the northern area (paper III filled circles, paper IV open circles). 10 In Västerbotten two different sets of field sites were used (Fig. 1). The experiment reported in paper III consisted of 36 different sites along small streams: 12 clear-cuts, 12 buffer strips and 12 reference sites. Finally, the experiment reported in paper IV was conducted in eight north-facing and eight south-facing forest–clear-cut edges.

Methodological approaches

Before-and-after experiment (I, II) I conducted a before-and-after experiment in order to analyse the effects of buffer strip retention on species richness and community composition. In a before-and-after experiment the statistical power can be high even if there is a lot of variation between sites. This makes the need of stratification low and the generality at the landscape scale will be high. For bryophytes I used large plots (200–1000 m2) compared to most studies on community composition and species richness in this group (cf. e.g., Økland et al. 2003, Vellak and Paal 1999, but see Frisvoll and Prestø 1997). The advantage of this is that it was possible to get a better understanding of the species composition and richness at the stand level, since infrequent species on patchily distributed substrates such as crevices, logs, uprootings, and boulders were more likely to be included in the plot. The use of large plots also reduces the between-site variation since most substrates are present in all plots. Small plots tend to emphasise differences within stands rather than differences between stands (Økland et al. 1990, Mills and Macdonald 2004). If the focus is on species survival on the stand scale large sampling plots should be used. Getting good data on litter dwelling land snail species composition at a site is a laborious task. There is a trade off between precision regarding the completeness of the species list and reliable estimates of the abundance of different species (cf. Hawkins 1998, McCoy 1999). I chose to use a “semi-quantitative” method proposed and described by Valovirta (1996), where litter is collected from systematically placed quadrats. The litter is sieved and later on gone through for snails with a magnifying glass. This method allowed me to compare both species lists and abundance data between sites and years. However, a more complete species list would likely have been obtained if litter was collected at many different small sites subjectively chosen throughout the stand (Waldén 1981). 11 Bryophyte growth as microclimate indicator (paper III, IV) I made use of the poikilohydric nature of bryophytes in field experiments to assess edge effects. By following the growth of transplanted forest bryophytes in pots over a vegetation period in forests far from edges reference values were obtained with which the growth in edges could be compared. A reduction in growth was interpreted as caused by an altered microclimate. In this way it was possible to get an estimate of microclimatic edge effects relevant to an organism and summarised over a whole vegetation season. A benefit of this approach is also that it is cheap and easy to apply to large numbers of sites, which increases the generality of the obtained results.

Major results and discussion

Effects of clear-cutting The initial effect of clear-cutting on bryophytes was drastic since the cover decreased from 85% to 27% and the species composition changed significantly (paper I). The reasons for the decline were both direct disturbances such as piles of slash and wheel-tracks as well as an altered microclimate. The clear-cuts along streams were, however, far from “deserts” for most of the species, and many bryophytes were retrieved in small pockets of shade and moisture. As a consequence of this, a larger proportion of the species was retrieved at the larger scale (1000 m2) than at the smaller scale (200 m2). Liverworts were generally more negatively affected than mosses in the clear-cuts. There were virtually no liverwort species that were favoured by the logging, while there were several mosses that increased in frequency and even a number of new species that were found frequently after the logging at disturbed patches. When sub-groups of the bryophytes (according to their main substrate association) were analysed separately, important differences were revealed. Species growing on substrates that were elevated from the forest floor such as logs, stumps and boulders decreased significantly. In contrast, the number of lost species with main substrate on moist and wet forest floor did not differ significantly from the situation in the references at the larger scale of 1000 m2. Even if most bryophytes can stand desiccation for periods (Proctor 1990) the drought or the high irradiance at the elevated substrates was lethal. Many species on wet ground were less affected. For those species the sun exposure by itself obviously was not detrimental. This could be due to the fact that the water prevented desiccation and that many of these species actually 12 have their main occurrences on open mires and thus are adapted to high light levels. The ground moisture was also very important for the survival of land snails at the clear-cuts (paper II). At the wet clear-cuts no decrease in either abundance or species richness could be found. On moist and mesic sites, on the other hand, the number of species declined by 20– 70%. There was a clear connection between wet ground and change in bryophyte cover. It is therefore possible that the survival of the snails had to do with the intact cover of bryophytes and not the wetness per se. Vertigo ronnebyensis (Westerlund) which is on the Swedish red-list (Gärdenfors 2000) was among the species with strongest decline. It was only retrieved in five out of 13 sites.

Vertigo ronnebyensis (Westerlund) has a shell that is approximately 2.3 mm high. (Photo: Niklas Lönnell)

The reason for a depauperate bryophyte flora in managed stands compared to more old-growth like states has often been attributed to the relatively young phase in the succession that the managed stands represent (Andersson and Hytteborn 1991). It is often almost tacitly implied that the bottleneck in the successional development of forests for many species is the clear-cut (or wild fire) (Hannerz and Hånell 1997). It could, however, be hypothesised that there are bottlenecks in later seral stages. One such stage could be when the vascular flora becomes very dense so that it could out-compete some species. Another scenario is if the young stands of coniferous trees grow very dense. The shade and litter-fall in these sites can constitute a harsh environment for many bryophyte species (cf. Johansson and Dynesius 1999 and for a similar discussion on snails Shikov 1984). If other stages in the succession are more important for the long-term outcome of species composition (e.g., the similarity of a managed stand to an old-growth stand) the importance of survival of species in small pockets at the clear-cuts should not be overemphasised. If, on the other hand the clear-

13 cut indeed is the bottleneck the survival in small pockets can be very important. The spatial scale for this survival is important for the probability of recolonising the previous places. For bryophytes there should be good opportunities for future survival if a species that occurred in every segment (200 m2) before logging also could be retrieved there after logging, even if it decreased in abundance (supposing that the logging or the years after was the bottleneck as discussed earlier). An indication that the survival of species in situ after clear-cutting is important in riparian forests is that Dynesius (2001) found a high similarity in bryophyte species composition between old-growth riparian forests and young stands (30-50 years after clear-cutting). The species that were sparser in the young stands than in the old stands in the study by Dynesius (2001) were mostly the same species that decreased much in my study (e.g., several liverworts on convex substrates, paper I). However, before this conclusion could be confirmed it must be known what is happening in the temporal window between my studies (0-3 years after clear-cutting) and Dynesius’ studies (30-50 years after clear- cutting). The discussion of the importance of survival in pockets during the most severe phase of sun and wind exposure at the clear-cut (or a patch hit by a natural disturbance event) can apply very well to land snails as well. Since ground moisture was such a strong predictor of survival at the site level in my study, wet or moist forest floors probably serve as refugia even at smaller spatial scales, such as shallow hollows and crevices beside boulders and stumps (cf. Prior 1985). Given that land snails are generally poor dispersers (e.g., Baur and Baur 1990) the short- term effects of a disturbance should be very important for their survival in the long term. The spatial distribution of refugia is probably important for long term-survival, but available data do not provide any answers to these questions.

Effectiveness of buffer strips In both of the studies on the effectiveness of buffer strips (papers I, II, and III) it was clear that the buffer strips mitigated the negative effects shown in the clear-cuts. From this the conclusion is that the quality of a matrix that contains buffer strips probably is better for many species than a matrix without buffer strips. The resilience of the ecosystem is probably also better maintained (cf. Bengtsson et al. 2003). The figures in papers I, II and III show that the buffer strips lay in between the references and the clear-cuts for most of the measured variables. 14 However, the effectiveness of buffer strips in mitigating changes in species composition was variable and depended on certain environmental variables and differed between different groups of species. Generally the land snail community was rather well protected in the buffer strips even if the general abundance declined (Table 1, paper II). An important explanation to this could be that the bryophyte cover was mostly intact in the buffer strips compared to the clear-cuts. Many of the bryophyte species that were negatively affected at the clear-cuts displayed a similar direction of response in the buffer strips even if the magnitude was smaller (Fig. 3 in paper I). This indicates that the mechanism that caused the decrease was the same in the clear-cuts as in the buffer strips. The generally negative response of species growing on convex surfaces (e.g., logs, stumps, and tree-bases) showed that the changed microclimate was a hazard for these species (Fig. 6 in paper I). For example only 50 % of the occurrences of red-listed species (that mostly were found on logs) survived in the buffer strips (Fig. 8 in paper I). The occurrence of wind-throws brought about further changes in species composition through changing the microclimate even more and through creating large areas of exposed mineral soil. Foresters hesitate to leave buffer strips because of the great risk of wind-throws (cf. Esseen 1994 who reported high proportions of uprooted and stem- broken trees in small fragments on a clear-cut). My study (papers I and II) showed that many trees indeed blew down, but that most of the buffer strips were rather intact 2.5 years after the logging. The proportion of standing trees could significantly predict the number of retrieved species of both bryophytes and land snails. If wind-throws could be avoided narrow buffer strips of 10 m on each side would probably be enough to maintain the snail fauna. However, for bryophytes this would not be enough since the microclimate would still be much different from pre-logging conditions. From another perspective, the addition of logs in this system should be very valuable for many organisms both in the stream and on land, in both a long and a short time perspective (Naiman et al. 2000).

Exploration of edge effects In paper III the influence of forest floor moisture on the magnitude of edge effects was explored through an experiment using bryophyte transplants. Because bryophytes are sensitive to desiccation and there is a large variation in forest floor moisture among different sites of riparian forest this was considered an important question. The general 15 guidelines for buffer strip management also consider the wetness of the forest as an important factor, where wider buffers are recommended at wet sites (e.g., SCA 1998, Henrikson 2000). My results showed that the wet forest floor mitigated the negative effects seen in moist/mesic sites (measured as differences in bryophyte growth) (Fig. 2, paper III). My result thus showed that the studied species were more affected by microclimatic edge effects in mesic and moist sites (compared to wet). The investigated species [Hylocomiastrum umbratum (Hedw.) Fleisch., Calypogeia integristipula Steph. and Tritomaria quinquedentata (Huds.) Buch] naturally grow in moist riparian forests. The results from the study on land snails (paper II) also showed that the soil moisture mitigated negative effects of logging, and the bryophytes of concave substrates were almost unaffected in the buffer strips (paper I). This taken together indicates that for the studied organism groups more care has to be taken on moist and mesic sites than on wet, contrary to the guidelines. An exception could be if a site with wet forest floor contains many convex substrates protruding above the ground. The experimental species of paper III were all evaluated in the logging experiment as well (reported in paper I). It is thus possible to put the results from paper III into a broader context where also the results on population persistence and not only growth parameters were evaluated (paper I). H. umbratum and C. integristipula were both clearly negatively affected in the buffer strips, while T. quinquedentata was unaffected in both studies (see paper III and Appendix to paper I). There were, however, 31 species that had a stronger negative pRDA score (results from an ordination method) in the buffer strip than C. integristipula and 43 species that were more negatively affected than H. umbratum. The results reported in paper III for H. umbratum and C. integristipula are thus not examples of the response of extremely sensitive species, but rather of intermediately sensitive species.

Base of spruce in a buffer strip with a zone of dead liverworts indicated. (Photo: K.H)

16 Besides moisture, lateral slope was found to be an important factor influencing the response in the buffer strips. The change in bryophyte species composition was generally smaller in sites with a marked valley than at level ground (not reported in paper I). There are many things that can influence the magnitude of the edge effects resulting from a changed microclimate in a buffer strip or a stand (cf. Chen et al. 1993). Field observations in the sites studied in paper I and II drew my attention to the seemingly large effect of edge orientation. I made regular observations in the buffer strips that the bryophytes were dead at the south-facing side but vigorous at the north-facing side of logs, boulders and hummocks. To assess the magnitude and spatial extent of microclimatic edge effects in edges with different orientation a field experiment in eight north- and eight south-facing edges was conducted (reported in paper IV). Using the same technique as in paper III the growth of mosses placed in pots were followed in forest–clear-cut edges and the reduction in growth was interpreted as a result of a changed microclimate. The magnitude of the edge effect was much larger at the south-facing edges compared to the north-facing edges in both of the used species showing that the direct solar radiation heavily affected the growing conditions. Growth increased exponentially from edge to interior and a model could be used to estimate the spatial extent of the edge influence. At 90% (arbitrarily chosen level) of the interior value the distance of edge influence was rather similar in the north- and south-facing edges. For Hylocomium splendens (Hedw.) Schimp. this value was around 15 m, while it was >30 m for H. umbratum. The result makes sense since the latter species is found in moister forest sites than the former. Direct studies on microclimate have shown that wind effects penetrate much deeper than direct solar radiation (Chen et al. 1995). This might be the explanation for the pattern found in my study, since the wind direction was much more variable than solar radiation. It is important to separate the magnitude of edge effects and the spatial extent because different mechanisms (e.g., wind or sun effects) can account for part of the difference and the prevailing orientation of the effects do not need to be the same. My study, however, shows that if interior forests (or stream habitats) should be protected by buffer zones these need to be much wider at the south side of the reserve, unless they are very wide (>40 m in the case of H. umbratum according to this study). The application to buffer strip management along small streams is obvious. In the case of a stream flowing along an east-westerly axis the best growing condition for H. umbratum is near the north-facing edge 17 (see Fig. 9 in paper IV). Consider that the goal is to create a buffer strip that protects microclimatic conditions in a 10 m wide area on each side of the stream allowing a relative growth of 80% of that in the interior forest (for H. umbratum). Applying the regression curves from this study it would imply that 21 m need to be retained at the north-facing side and 30 m on the south-facing side additional to the area in focus (Fig. 2). The total width of the buffer strip would then be 71 m. Corresponding buffers for H. splendens would be 38 m.

Edge effect from north Edge effect from south Combined effect

100

20 Relative growth(%)

North-facing edge South-facing edge 20 m riparian zone

0 -60 -40 -20 0 20 40 60 Distance from stream Stream Distance from stream to north (m) to south (m)

Fig. 2. Estimated growth of Hylocomiastrum umbratum (Hedw.) Fleisch. in a 71 m wide buffer strip along a stream flowing along an east-westerly axis. The growth in the 20 m wide zone closest to the stream is estimated to be >80% of interior values. Data from regression lines in paper IV.

18 Concluding remarks and future perspectives

Large scale disturbances are characteristic of the boreal forest (Esseen et al. 1997, Engelmark 1999). Some species survive the disturbance in situ and many have to move across the landscape. My thesis provides important data on the actual in situ persistence of species in forests along small streams after such a heavy disturbance that clear-cutting is. I showed that at the spatial scale of 200 to 1000 m2 many bryophyte species survived in pockets although the overall cover declined (paper I). Also for snails many species were found at the clear-cuts, albeit in lower numbers (paper II). The used plot size for the bryophyte study (paper I) was relevant for uncommon species as they seldom occurred in more than one patch per 200 m2. This spatial scale is also relevant for the long-term persistence of more abundant species since they likely will regain their former cover in a 200 m2 plot if they survive in any part of it. The in situ surviving species are important components for the resilience of the ecosystem (Bengtsson et al. 2003). My data also provide information on which species that will need to disperse from outside the clear-cut in order to re-build the same community structure. This group was rather large for the bryophytes and also some snail species exhibited stronger declines than others. Future studies on in situ survival should continue on two tracks. The first is to further investigate the in situ survival at non-riparian sites. One could hypothesise that the survival of populations in riparian sites in the long run could be important sources for colonisation for upland forests if the in situ survival rate is lower there. A second and important step is to follow sites over time (or to make chronosequence studies). It could be the lack of suitable substrates or lack of small-scale disturbance (e.g., windthrows) in dense young stands that is the real bottleneck for many mature forest species and not the clear-cut phase (cf. Johansson and Dynesius 1999). In such a case, the initial survival has little to do with resilience in the long term. These questions could be addressed for bryophytes and land snails as well as for many other organisms. Narrow buffer strips could be considered as consisting of edge habitat throughout. Results reported in this thesis (papers I and II), however, showed that narrow buffer strips significantly moderated the negative effects displayed at clear-cuts. The number of snail species was for example almost the same in the buffer strips after the logging and they could probably serve as important refugia. Most species of 19 bryophytes also seemed to thrive well in the buffer strips. The other side of the coin is, however, that there was indeed a group of bryophyte species that were strongly negatively affected by the changed microclimate, not only at the clear-cuts but also in the buffer strips. Many of these species are species that already have declined in the landscape and should need the protection of the riparian forests most. Hence, for the long-term survival of the most disfavoured bryophyte species in the landscape buffer strip retention with narrow buffers will probably not contribute much. This thesis provides knowledge on which species that are sensitive to edge effects and on which substrate they have their main occurrences (Appendix in paper I). Furthermore, the more detailed understanding of how ground moisture (paper III) and edge orientation (paper IV) affect microclimatic edge effects can be used to make buffer strip management more effective. As time elapses it will be possible to evaluate the ecological effects of the different biodiversity-oriented management practices in a more long-term perspective. The plots used in the before-and-after experiment (reported in papers I and II) are permanently marked up in the field ready for a re- inventory.

Buffer strip management: considerations for practitioners

Results relevant to buffer strip management With a wise management the potential of using riparian forests for bryophyte and land snail protection in the landscape is good. This is because the habitats are species-rich and interspersed throughout the landscape. In the studies reported in this thesis the effectiveness of a buffer strip was measured as the capacity of moderating species loss or growth decline of the experimental species. The following list summarises results relevant to buffer strip management.

(1) The proportion of standing trees in the buffer strips (not wind- thrown or cut) was a good predictor of buffer strip effectiveness for both bryophytes and land snails. (2) Marked valleys protected the microclimate in the bottom making 10 m wide buffer strips more effective there than on level ground for bryophytes. (3) Aspect (i.e. north- vs. south-facing) was extremely important for the magnitude of the microclimatic edge effect. 20 (4) No edge effect could be detected further than 40 m into the forest. Similarly, Moen and Jonsson (2003) found an edge effect of 50 m on epixylic liverworts. This indicates how wide the buffer should be on each side of the habitat that should be protected. (5) Bryophytes on convex substrates (e.g., logs and tree-bases) were more sensitive to an altered microclimate than species on concave substrates (e.g., crevices and wet ground). (6) The snail fauna at sites with a wet forest floor was mostly unaffected by logging.

Buffer strip guidelines generally stress the importance of leaving wider buffer strips on wet sites and when the stream is situated in a ravine or marked valley (SCA 1998, Henrikson 2000). The results from this thesis, however, point in the opposite direction, that the microclimatic effects generally are stronger in mesic sites and on level ground. For bryophytes and land snails there is nothing in my data (not reported in the papers in this thesis) showing that sites in marked valleys or on wet ground are more species rich or more important for red-listed species (Hylander and Dynesius unpublished). For bryophytes instead many sites on moist and mesic ground with much coarse woody debris and boulders exhibited both high species richness and/or many red- listed species (Hylander and Dynesius unpublished). The latter kind of sites are thus the most vulnerable habitats and must be protected from strong edge effects if many bryophyte species on convex substrates should be able to persist there (paper I). Land snail communities exhibited nestedness (i.e., species at species poor sites were subsets of the community at species rich sites) with highest species numbers and abundance in sites with high pH and an element of deciduous trees in the canopy (Hylander et al. unpublished). There was no correlation (either positive or negative) between species richness and sensitivity to edge effects in the buffer strips. One of the species that declined most at the clear-cuts was Vertigo ronnebyensis (paper II). It was one of the species which abundance was least correlated with the overall species richness (Hylander et al. unpublished). For this species moist and mesic sites were the most favoured (i.e., the sites with the most heavy decline of land snails as seen in paper II).

21 Reviewing buffer strip management along small streams There could be many motives for retaining trees along a stream when the adjacent stand is clear-cut. In most cases the objective has been to moderate negative effects on water quality and stream biota (Castelle et al. 1994). In recent years buffer strip retention has been motivated also from the fact that riparian areas are species rich for terrestrial and riparian species and contain unique species in a landscape context (e.g., Henrikson 2000, Hansson 2001). In the following discussion I leave water quality and nutrient retention aspects and focus on the terrestrial and aquatic biota in the buffer strips. An evaluation of buffer strip retention along streams in central Sweden revealed large differences between streams of different sizes (Anon. 2002). Generally, streams narrower than 3 m had buffers only at 50% of the stretches. In the interval 3–10 m wide streams 70 % of the streams at recent clear-cuts had buffer strips, but only half of these had buffers wider than 10 m. In the light of this thesis the current situation regarding protection of riparian forests in Sweden seems to be very insufficient. Turning all riparian forests into wide (e.g., >100 m) buffer strips that are left for development into late successional stages is neither economically feasible nor motivated from a conservation point of view. Such an approach does not take into account that natural large scale disturbances are an integral part of the ecology of boreal forests, sometimes disturbing also riparian sites (Macdonald et al. 2004). Leaving buffer strips at sites, which have experienced regular disturbance could, however, still be motivated from a conservation perspective, as the age distribution in the landscape is so biased towards young successional stages (Östlund et al. 1997). Furthermore a narrow buffer strip (e.g., 10 m) is probably more similar to a wild fire disturbance along a stream than a clear-cut, since natural processes shaping a varied microtopography such as production of dead trees and uprootings can continue (cf. Meleason et al. 2003). Under limited resources there will be a trade off between connectivity and width of buffer strips. For riparian and aquatic biota, connectivity has been emphasised as important (e.g., Jansson et al. 2000). This corridor integrity may, however, not necessarily need to include the riparian forest for all organisms. It has for example been shown that temperature changes in streams due to increased sun- exposure at clear-cuts are not affecting the fish fauna negatively in boreal streams (Murphy et al. 1986) in contrast to the situation in temperate regions (e.g., Barton et al. 1985). The value of corridors for 22 terrestrial organisms has been questioned (Gustafsson and Hansson 1997, Niemelä 2001). Instead, the quality of the buffer strip or the area per se of the habitat, has been shown to be of great importance for birds in riparian forests (Darveau et al. 1995, Whitaker and Montevecchi 1999, Groom and Grubb 2002). This thesis also highlights that buffer strips of 10 m on each side of the stream are too narrow to maintain the microclimate needed for certain bryophyte species. To achieve a core area of undisturbed microclimate there needs to be a shift from the focus on the stream to a focus on the whole habitat. A buffer zone then needs to be retained additional to the area that shall be protected (cf. Götmark et al. 2000). Ten randomly chosen topographic maps (1:50 000) from mid-boreal Sweden were analysed with respect to stream density and mean distance from average points in the landscape. Preliminary results show that if 20 m buffer strips should be retained on both sides along all streams (shown on these maps) it would cover on average 3.6% of the forested land. Integrating knowledge from research on different species (or habitats) into management guidelines for an ecologically sound forestry is a challenge. If the accumulated costs of all recommendations become too high, there will be a trade off between different actions. In practical forestry this is probably more rule than exception. The development of a sustainable forestry where ecosystem functions and species diversity are retained is therefore a process where researchers, forest owners and forest authorities all are important actors (c.f. Niemelä 1999). For now, assume that the 3.6% of the forested land mentioned above is a realistic figure to be used for riparian buffer strip management. The next question is how this area should be partitioned along the streams. Even buffer strips of 20 m on each side of a stream are likely to experience microclimatic edge effects though out (i.e., paper IV). Also studies on birds in Canada show that buffer strips need to be considerably wider (>40 m on each side) in order to maintain a pre- logging bird community (Darveau et al. 1995, Whitaker and Montevecchi 1999). For the protection of many organisms it is thus better to concentrate the efforts to certain places than to have fixed buffers throughout the landscape. For example the hypothesised 20 m buffers could be partitioned like this: 20% 5 m, 40% 10 m, 20% 25 m, and 20% 50 m on each side of the stream. In that way the connectivity of water and riparian habitat will be maintained along with the protection of important riparian forest habitats at some of the stretches. But even in the case of the widest buffer strips in this scenario the core area with no edge influence is likely to be small. The effectiveness of 23 the buffer strips could also be improved by avoiding logging on both sides of the stream at the same time and by adjusting the width with respect to topography and aspect. Selective logging of valuable trees is not recommended since it will reduce the input of coarse woody debris into the system. Logs are an important structural component and habitat in both the aquatic and terrestrial part of riparian forests (Hilderbland et al. 1997, Lindström 2003). The long-term consequences of selective logging in riparian forest could be a degradation of the riparian zone (Young 2000). I want to emphasise three types of sites, which I think deserve special protection with wider buffer strips or riparian reserves.

(1) Sites with erosion prone fine sediments. Several studies have shown that input of fine sediment is a threat to the fish fauna as it destroys the spawning habitat (e.g., Scrivener and Brownlee 1989). Retaining wide buffer strips could be one practice to avoid sediment input. Wide buffers could, however, be of limited value if for example the wheel-tracks from a tractor cross the stream upstream the buffer strip (see discussion in e.g., Nyberg and Eriksson 2001). (2) Wet and moist sites. According to the results presented in this thesis wet sites should not be considered as places where extra care should be taken. However, along stretches with wet and moist ground the hydrology is easily disturbed if the soil is disturbed or compacted by machines (Nugent et al. 2003). There is also evidence from studies on other organism groups than studied in this thesis (e.g., lichens) that wet forest types contain many species favoured by old-growth conditions (Kuusinen 1996, Ohlson et al. 1997, Hörnberg et al. 1998). Variation in species composition among different types of wet sites for these organisms deserves further investigation. (3) Sites with woody debris and boulders. For many organisms in riparian forests the moist microclimate is essential for persistence. Under these circumstances convex surfaces could be colonised by more species, which probably is the explanation for the denser populations of for exampleepixylic bryophytes near streams than only 100 m away from it in similar forest types (Dynesius 2001, Lindström 2003). Shaded boulders, logs and tree-bases in a moist microclimate are rather unique features of small stream forests. This recommendation is valid on sites with both wet, moist, mexic and dry ground. 24 These suggestions assume that the riparian forest in focus has some ecological values to protect. However, in heavily managed landscapes many watercourses are canalised or have an altered hydrology in some way. Another unnatural situation is when the riparian zone is covered with a dense and homogeneous spruce plantation. In such cases, buffer strip retention has to involve restoration actions such as actively creating canopy gaps (for allowing deciduous trees to regenerate), logs, and uprootings along with a hydrological restoration of the stream channel. These restoration actions will be beneficial for both terrestrial and aquatic biodiversity, and could preferably start already in the thinning phase of young stands.

Acknowledgements

I would like to thank Christer Nilsson, Bengt Gunnar Jonsson, Nic Kruys, Eva Hylander, and Torleif Eriksson for thoroughly reading and commenting upon the text. Thanks to Karin Aune for doing the GIS- calculations on stream density and to Niklas Lönnell for the photos on bryophytes and snails. Financial support for this study has been provided by The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (to Christer Nilsson) and by J. C. Kempe and Ruth and Gunnar Björkman’s foundations.

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33 Tack!

Det gick ju fort att bläddra förbi alla sidor för att hitta hit! Att smyga in några intressanta resultat på den här sidan vore smart. Lika bra att börja på en gång. Mossfloran i kantzoner utmed vattendrag är ….. OK, OK, OK, till sak:

De här åren som doktorand har varit väldigt roliga och utvecklande för mig. Det beror förstås på många olika saker. Jag tänker t.ex. på att jag har haft en arbetsplats med kollegor med liknande intressen, kombinationen av fältarbete, tänkande, undervisning och skrivande, och att jag fått internationella utblickar. Inte minst månaderna i Sydafrika, mötena i BRYOPLANET (nordiskt mossekolognätverk) och konferensresorna till Finland och Kanada har tillfört mycket till både forskningen och det övriga livet. Nyvunna vänner i Umeå och ett engagemang i Carlskyrkan har hjälpt mig att fokusera på viktigare saker här i livet än mossor och P-värden. Här skulle jag dock vilja lyfta fram några personer som på olika sätt har sin del i att jag skrivit denna avhandling.

Tack: Mina handledare Christer Nilsson och Bengt Gunnar (Bege) Jonsson. Ni har alltid ställt upp för att lyssna, bolla idéer, läsa och uppmuntra. Tack för stor frihet att utforma studier och experiment. Christer, tack för att du gav mig möjlighet att doktorera. Din snabbhet och noggrannhet i manuskripthaterandet har varit mycket peppande och du har utmanat mig att sikta högt bland tidskrifterna. Hoppas du inte har ”avmossat” mig alltför mycket. Bege, förutom mycket värdefull handledning på många sätt har det varit lite extra kul att lägga ut astroturf (dvs dörrmattor) i skogen i Vitvattnet och konka garanterat sporfri lera ut på myrarna i Bodbyn (det s.k. sabbatsbrottsprojektet).

Mats Dynesius för att du anlitade mig den där myggiga sommaren 1995 och på så sätt lockade in mig i forskningen. Sedan dess har du varit en stor inspiratör och hjälpt mig med mycket. Snart är du en fullfjädrad bryolog! Tack också Roland Jansson och Jim Helfield för stor hjälp med bl.a. manuscript, Tuss för inte minst den skojiga Kanadaexkusionen, Mats Johansson, Lenita Lindblom, Elisabeth Carlborg, och Martina Kluge för hjälp med många saker mellan himmel och jord. Carl-Johan för att du ville inventera lavar i mina provytor. Tack också Tove Göthner, utan ditt exjobb ingen snäckartikel i denna volym! Tack också alla ni andra i Landskapsekologigruppen inklusive somrarnas fältarbetare. Tack vare er finns det en positiv stämning av hjälpsamhet och uppmuntran som gör det till en fantastisk arbetsplats. Jag vill också tacka alla ni andra på storinstitutionen som gjort dessa år så bra: undervisningskollegor, medresenärer till Mexiko, innebandylirare m.fl. Tack Kicki Palmqvist, Jon Moen och Frank Johansson för vägledning i er roll som handledargrupp.

34 Per Simonsson med kollegor på SCA för gott samarbete kring fältstudien i Medelpad och Jämtland. David Rönnblom med kollegor på Holmen AB samt personal på SVS i Umeå och Bjurholm som hjälpt till att ta fram kartunderlag till många av objekten i studierna i Västerbotten. Jag hoppas att mina resultat kommer att bidra till en effektivare naturvård i det praktiska skogsbruket.

Lars Hedenäs som lärde mig känna igen de första 100 mossarterna på en kurs på Stockholms universitet och betytt mycket för att jag skulle fortsätta med mossor. Tack för hjälp med många skumma ”ekologiska” kollekter och uppmuntran att skriva ihop mina små tidiga upptäckter till Myrinia och Lindbergia. Tack också Kell Damsholt och Ted von Proschwitz för hjälp med kontrollbestämning av levermossor respektive snäckor.

Niklas Lönnell. Utan dig som trogen vän hade nog inte mosseriet blivit en så långvarig och allvarlig åkomma.

Alla ni som uppmuntrat och inspirerat mig i mina naturstudier: mossvännerna i föreningen Mossornas Vänner, kursare på Biogeo-utbildningen, Ekbackens fältbiologer och min högstadielärare Gudrun Lindvall.

Dr. Magnus Karlsson och Dr. Mattias Öberg för att ni gått före och visat vägen, för vänskap och allmänt ”forskningsgrubbleri”.

Alla ni som hjälpt till med praktiska saker mot slutet när det körde ihop sig med bebis och foglossning. Mamma, Pappa, May-Britt och Bengt Gustafsson, Birgitta Sundqvist, Kicki Blomberg, Siv och Anders Törnell, Cathy Reidy, Jim Helfield, Anna Thorén, Christina Bohman och Hans och Kristine Lindetorp.

Mamma, Pappa, Lina och Samuel. Ni finns alltid där och säger de saker jag behöver för stunden och omsluter mig med bön. Tack Pappa för att du uppmuntrat mitt naturintresse från barnsben. Om farfar hade levt nu hade han också varit glad över (och kunna ta åt sig lite ära för) att jag fått möjlighet att tränga på djupet i botaniken. Tack Mamma för ditt 100%-iga stöd i alla lägen, även när det handlade om att flytta 78 mil norrut med ditt första barnbarn.

May, Ruben och Lydia. Tack för er fantastiska förmåga att påminna mig om att jag i första hand är pappa, kock, monster och klätterträd.

Eva! Helst skulle jag vilja stanna så för det blir fånigt att lyfta fram något litet av vad du gjort. Jag måste dock tacka en extra gång för alla snäckbestämningar som gjorde artikel II möjlig. Det var ingen medveten kupp att inspirera dig att börja med snäckor. Du hade kunnat vara medförfattare till den artikeln, men ville hellre finnas med i tacket med vad du gjort. En referee tyckte dock det var märkligt ”Varför är den som gjort det mesta av arbetet inte författare?” 35