ACTA PHYTOGEOGRAPHICA SUECICA 80 EDIDIT SVENSKA VAXTGEOGRAFISKA SALLSKAPET Martin Diekmann Deciduous forest vegetation in Boreo-nemoral Scandinavia UPPSALA 1994 ACTA PHYTOGEOGRAPHICA SUECICA 80 EDIDIT SVENSKA VAXTGEOGRAFISKA SALLSKAPET Martin Diekmann Deciduous forest vegetation in Boreo-nemoral Scandinavia OPULUS PRESS AB UPPSALA 1994 Doctoral thesis at Uppsala University ISBN 91-721 0-080-X (paperback) ISBN 91-7210-480-5 (cloth) ISSN 0084-5914 Editor: Erik Sj ogren Editorial Board: A. W .H. Darnman, Storrs, CT F.J.A. Daniels, MUnster L. Ericson, Umea D. Glenn-Lewin, Ames, lA 0. Hamann, Copenhagen H. Sj ors, Uppsala H. Trass, Tartu Technical Editor: Marijke van der Maarel-Versluys © Martin Diekmann 1994 Cover illustration: Reno Lottmann Edidit: Svenska VaxtgeografiskaSallskapet Villavagen 14, S-752 36 Uppsala DTP: OPULUS PRESS AB Printed in Sweden, 1994 by Eklundshof Grafiska AB, U ppsala Acta Phytogeogr. Suec. 80 Deciduous fo rest vegetation in Boreo-nemoral Scandinavia 3 Abstract. Martin Diekrnann. 1994. Deciduous forest vegetation The underlying environmental factors for the vegetational in Boreo-nemoral Scandinavia - Acta Phytogeogr. Suec. 80, differentiation on the forest type level were a complex-gradient Uppsala. 112 pp. ISBN 91-7210-080-X. (91-7210-480-5). in nutrient status, connected with variation in light conditions, and a moisture gradient. On the community level, mainly geo­ This study aimed at an investigation of the vegetation ecology of graphic-climatic factors were operating, in particular an East­ deciduous hardwood forests in the Boreo-nemoral zone of Scan­ West and a humidity gradient. Anthropogenic factors were less dinavia. Different community types were described with regard important. to their species composition and structure, differentiation, geo­ Ellenberg's central-European indicator values for light, graphic distribution, ecological conditions and dynamics, as moisture, nitrogen and reaction proved to be useful in character­ well as their affinities to community types in other vegetation izing the Scandinavian forests, although some species seem to zones in northern and central Europe. occur under environmental conditions which differ from those Field work was conducted in S Sweden and SE Norway. In in central Europe. The Boreo-nemoral forests are as species-rich total 367 releves were made. In each stand, structural character­ as the Nemoral forests; the absence of several southerly distrib­ istics as well as cover-abundance values of all vascular plants uted taxa is 'compensated' for by comparatively higher frequen­ and bryophytes were recorded. The releves were analyzed by cies of other species. Community types on soils with an interme­ means of cluster analysis (program TWINSPAN) and ordination diate to moderately high fertility have the highest species rich­ (program Correspondence Analysis from the program package ness. CANOCO). Vegetation-environment relationships were analyzed Most stands have been influenced strongly by human activ­ by correlating the explanatory variables with releve scores on ity and are compositionally unstable. In eutrophic elm-ash for­ the ordination axes. ests, Quercus spp. and Fraxinus excelsior were better repre­ In 69 stands of two areas (Oland and the mainland of eastern sented with larger size classes, whereas Acer platanoides and Sweden), tree size was analyzed in order to reveal the population Ulmus spp. had higher frequencies in smaller size classes. It is structure of the most important tree species in the main forest suggested that this patterncan be interpreted in terms of a future types. Successional trends were inferred from the relative densi­ replacement series: in a succession following termination of ties of species in different DBH (diameter at breast height) human impact, Quercus and Fraxinus will be partly replaced by classes. Ulmus and Acer. The population structure in mesotrophic for­ Environmental studies were carried out in 17 stands of ests revealed that Quercus will decrease, whereas Ulmus and mesotrophic and eutrophic forests in the vicinity of Uppsala, Fraxinus and, in particular, Acer and Tilia, will increase. In including inclination, heat index, maximum temperature, mini­ oligotrophic forests, however, Quercus will maintain a domi­ mum temperature, temperature range, evaporation, wind expo­ nant position, while Picea may increase in importance. The tree sure, canopy cover, light, dry bulk density, organic matter, species dynamics will also lead to increasing canopy closure moisture, pH(H20), pH(KCl) and nitrogen. Canonical Corre­ and, subsequently, compositional changes in the other vegeta­ spondence Analysis (CANOCO program package) and correla­ tion layers. tion analysis were used to reveal the relationships between The environmental studies in the selected forest stands re­ vegetation and environment. vealed that pH (together with nutrients) and light were the Four forest types were described, with in total nine commu­ primary factors related to vegetational variation in the field and nities: (1) oligotrophic oak forests: Quercus petraea-Frangula bottom layers. Other properties of the soil and the climate of the alnus community, Quercus robur-Betula pendula community; forest as well as physiographic factors, were of minor signifi­ (2) mesotrophic mixed deciduous fo rests: Quercus robur-Tilia cance. Mesotrophic forests had significantly lower soil reaction, cordata community, Quercus robur-Euonymus europaeus com­ higher light intensities and higher maximum temperatures than munity, Quercus robur-Fraxinus excelsior community; (3) eutrophic forests. They also tended to have a lower soil mois­ eutrophic elm-ash forests: Ulmus glabra-Fraxinus excelsior ture, a wider temperature range, lower minimum temperatures community, Ulmus minor-Fraxinus excelsior community; (4) and a higher evaporation. eutrophic alder-ash forests: Fraxinus excelsior-Prunus padus As a whole, deciduous hardwood forests in Boreo-nemoral community, Fraxinus excelsior-Alnus glutinosa community. Scandinavia have become rare and threatened, particularly the Mesotrophic forests represent the most widespread and charac­ eutrophic forests. Existing forests, especially those with a long, teristic forest type of the Boreo-nemoral zone, without floristically uninterrupted history, should therefore be maintained and pro­ similar counterparts in the Nemoral zone. tected. Martin Diekmann, Department of Ecological Botany, Uppsala University, Villaviigen 14, S-752 36 Uppsala, Sweden. Acta Phytogeogr. Suec. 80 Contents 1 Introduction 5 1.1 Aims 5 1.2 Nature conservation aspects 5 1.3 Deciduous hardwood forests in northern Europe: a brief literature review 6 1.4 Vegetation and forest history 8 2 Study area 12 2.1 The Boreo-nemoral zone and its delimitation 12 2.2 Geology and Soils 13 2.3 Climate 15 3 Analysis of vegetation and vegetation-environment relations 18 3.1 General 18 3.2 Sampling procedure 18 3.3 Data treatment 18 3.4 Tables 20 3.5 Nomenclature of fo rest communities 20 3.6 Nomenclature of species and comments on difficult taxa 20 4 Forest communities 22 4.1 Introduction: Survey of clusters 22 4.2 Oligotrophic oak fo rests 23 4.3 Mesotrophic mixed deciduous fo rests 32 4.4 Eutrophic elm-ash fo rests 48 4.5 Eutrophic alder-ash forests 55 4.6 Syntaxonomy 64 5 The population structure of trees and fo rest dynamics 69 5.1 Introduction 69 5.2 Methods 70 5.3 Results 71 5.4 Discussion 74 6 Environmental studies 79 6. 1 Introduction 79 6.2 Soil analysis and climatic measurements 80 6.3 Results 82 6.4 Discussion 89 7 General discussion and conclusions 95 7. 1 Species 95 7.2 Communities and environment 98 7.3 Geographic distribution of communities and the Boreo-nemoral zone 10 1 7.4 Structure and dynamics 102 7.5 Implications for nature conservation 103 8 Acknowledgements 104 9 References 105 1 Introduction 1.1 Aims composition in order to reveal the primary causes for community differentiation. The Boreo-nemoral commu­ This study aims at a floristicand ecological description of nities will also be discussed with respect to their central deciduous forest communities in the Boreo-nemoral zone and western European counterparts. of Scandinavia. Field investigations have mainly been carried out in Sweden, partly for practical reasons but also because the deciduous forests in Sweden are less well 1.2 Nature conservation aspects known than their Norwegian counterparts. The study deals with forests of a type called 'adellovskog' in Swedish Climatic deterioration as well as millennia of cultivation (broad-leaved hardwood forest), composed of Acer and exploitation have diminished the area of deciduous platanoides, Fraxinus excelsior, Quercus spp., Tilia forest in Scandinavia to a small fraction of its prehistoric cordata and Ulmus spp. The term 'adel' ('noble') refers to size. The majority of sites suitable for deciduous forest are the species' relatively high demands for nutrients and now covered by arable land and spruce plantations. The temperature, as well as their greater economic importance remaining stands have been influenced and changed by and higher status, compared with 'trivial' species such as land use practises such as logging, pollarding and grazing, Betula spp. and Populus tremula. Also Fagus sylvatica earlier also thinning for haymaking in wooded meadows. and Carpinus betulus are often treated as 'noble' tree Deciduous forests seem to be common in many parts of species. However, forests composed of these two species southernand central Sweden. However, this impression