Tree diversity and environmental context predict herb species richness and cover in Germany's largest connected deciduous forest

Abstract In temperate deciduous forests, the herb layer contributes most to total vascular plant species richness. The diversity of the tree layer can influence herb layer diversity by modifying resource availability and environmental conditions relevant to herb layer plants. Here, we explore the relationship between tree layer diversity and herb layer species richness and cover. Also, we address the question how different environmental factors that are potentially modified by the tree layer influence herb layer characteristics. Our study area is located in the Hainich National Park, one of the largest continuous stretches of broad-leaved deciduous forest in Central Europe. We recorded herb and tree layer composition on 79 plots selected along a tree diversity gradient ranging from two to nine tree species. In addition, canopy cover, soil pH, mass of the humus layer, soil C:N ratio, soil moisture and distance to the forest edge were determined. We used generalized least square models to analyse effects of tree diversity, environmental variables, and spatial plot positions on herb layer species richness and cover. Species richness and cover of the herb layer increased with increasing tree diversity. In addition, both species richness and cover showed a negative response to increasing canopy cover and mass of the humus layer. Herb layer species richness was also positively related to increasing soil pH and the distance to the forest edge. The proportion of forbs increased with increasing tree diversity, whereas the proportion of tree saplings decreased and the proportion of graminoids was not affected. The proportion of true forest species increased with increasing canopy cover. We conclude that forest stands with a high tree diversity feature a more diverse herb layer and a higher herb cover. Furthermore, the environmental variables humus layer mass, light availability and pH also strongly affect herb layer species richness and cover.

[1]  J. Ewald.  Multiple controls of understorey plant richness in mountain forests of the Bavarian Alps , 2002 .

[2]  Christine J. Small,et al.  Relationship of understory diversity to soil nitrogen, topographic variation, and stand age in an eastern oak forest, USA , 2005 .

[3]  C. Leuschner,et al.  Acidity, nutrient stocks, and organic‐matter content in soils of a temperate deciduous forest with different abundance of European beech (Fagus sylvatica L.) , 2009 .

[4]  R. D. Waal,et al.  Effects of tree species composition on within‐forest distribution of understorey species , 2005 .

[5]  A. Hagen-Thorn,et al.  The impact of six European tree species on the chemistry of mineral topsoil in forest plantations on former agricultural land , 2004 .

[6]  M. Bernhardt‐Römermann,et al.  Forest ecosystem research in Hainich National Park (Thuringia): first results on flora and vegetatio , 2006 .

[7]  W. Härdtle,et al.  The effects of light and soil conditions on the species richness of the ground vegetation of deciduous forests in northern Germany (Schleswig-Holstein) , 2003 .

[8]  M. Pärtel,et al.  Relationships between species richness patterns in deciduous forests at the north Estonian limestone escarpment , 2003 .

[9]  Z. Dzwonko,et al.  Influence of litter and weather on seedling recruitment in a mixed oak-pine woodland. , 2002, Annals of botany.

[10]  Gordon C. Tucker,et al.  Quercus robur L. , 2002 .

[11]  A. Magurran,et al.  Measuring Biological Diversity , 2004 .

[12]  F. Borchsenius,et al.  Vegetation structure and diversity of an ancient temperate deciduous forest in SW Denmark , 2004, Plant Ecology.

[13]  H. Bugmann,et al.  Predicting Understorey Vegetation Cover from Overstorey Attributes in Two Temperate Mountain Forests , 2003, Forstwissenschaftliches Centralblatt vereinigt mit Tharandter forstliches Jahrbuch.

[14]  I. Mölder.  Diversity and tree neighborhood effects on the growth dynamics of European beech and the stand seed bank in temperate broad-leaved forests of variable tree diversity , 2009 .

[15]  S. Pickett,et al.  Influence of canopy opening on the environment and herb layer in a northern hardwoods forest , 1987, Vegetatio.

[16]  S. Fleck,et al.  Functional role of forest diversity: Pros and cons of synthetic stands and across-site comparisons in established forests , 2009 .

[17]  D. Binkley,et al.  Impact of several common tree species of European temperate forests on soil fertility , 2002 .

[18]  A. Gazol,et al.  Variation of plant diversity in a temperate unmanaged forest in northern Spain: behind the environmental and spatial explanation , 2010, Plant Ecology.

[19]  D. Alard,et al.  Effect of tree mixture on the humic epipedon and vegetation diversity in managed beech forests (Normandy, France) , 2004 .

[20]  Ken A. Elliott,et al.  The effects of partial harvest on the understory vegetation of southern Ontario woodlands , 2008 .

[21]  P. Balandier,et al.  Influence of tree species on understory vegetation diversity and mechanisms involved—A critical review for temperate and boreal forests , 2008 .

[22]  Jacques Ranger,et al.  Effects of tree species on understory vegetation and environmental conditions in temperate forests , 2003 .

[23]  U. Nordén.  Influence of tree species on acidification and mineral pools in deciduous forest soils of South Sweden , 1994 .

[24]  D. J. Hicks.  Intrastand Distribution Patterns of Southern Appalachian Cove Forest Herbaceous Species , 1980 .

[25]  G. Tyler,et al.  Herb layer vegetation of south Swedish beech and oak forests—effects of management and soil acidity during one decade , 1996 .

[26]  G. Houle.  Determinants of fine-scale plant species richness in a deciduous forest of northeastern North America , 2007 .

[27]  E. Veldkamp,et al.  Calibration of a Frequency Domain Reflectometry Sensor for Humid Tropical Soils of Volcanic Origin , 2000 .

[28]  Axel Don,et al.  Exploring the functional significance of forest diversity: A new long-term experiment with temperate tree species (BIOTREE) , 2007 .

[29]  K. Puettmann,et al.  Overstory Composition and Stand Structure Influence Herbaceous Plant Diversity in the Mixed Aspen Forest of Northern Minnesota , 2000 .

[30]  M. Hermy,et al.  Diverging effects of overstorey conversion scenarios on the understorey vegetation in a former coppice-with-standards forest , 2008 .

[31]  D. Buchori,et al.  Temperature and a dominant dolichoderine ant species affect ant diversity in Indonesian cacao plantations , 2010 .

[32]  C. Leuschner,et al.  Nutrient release from decomposing leaf litter of temperate deciduous forest trees along a gradient of increasing tree species diversity , 2009 .

[33]  S. Ladet,et al.  Relative contribution of edge and interior zones to patch size effect on species richness: An example for woody plants , 2010 .

[34]  D. Sheil,et al.  Assessing forest canopies and understorey illumination: canopy closure, canopy cover and other measures , 1999 .

[35]  J. Hošek,et al.  The influence of light and nutrient availability on herb layer species richness in oak-dominated forests in central Bohemia , 2009, Plant Ecology.

[36]  M. Jacob,et al.  Leaf litter decomposition in temperate deciduous forest stands with a decreasing fraction of beech (Fagus sylvatica) , 2010, Oecologia.

[37]  H. Ellenberg.  Vegetation Mitteleuropas mit den Alpen : in ökologischer ,dynamischer und historischer Sicht , 2010 .

[38]  T. Hiura,et al.  Effects of disturbance history and environmental factors on the diversity and productivity of understory vegetation in a cool-temperate forest in Japan , 2009 .

[39]  G. Houle,et al.  Response of herbaceous plant diversity to reduced structural diversity in maple-dominated (Acer saccharum Marsh.) forests managed for sap extraction , 2006 .

[40]  D. M. Newbery,et al.  M. A. Huston, Biological Diversity: the coexistence of species on changing landscapes . Cambridge University Press. ISBN 0-521-36930-4 (pbk). 681 + xix. pages. £24.95. , 1995, Journal of Tropical Ecology.

[41]  S. Macdonald,et al.  Understory plant communities of boreal mixedwood forests in western Canada: Natural patterns and response to variable-retention harvesting , 2007 .

[42]  Sari C. Saunders,et al.  Edge Influence on Forest Structure and Composition in Fragmented Landscapes , 2005 .

[43]  M. Wulf.  Preference of plant species for woodlands with differing habitat continuities , 2003 .

[44]  K. Klinka,et al.  Diversity of the understory vascular vegetation in 40 year‐old and old‐growth forest stands on Vancouver Island, British Columbia , 1997 .

[45]  F. Gilliam,et al.  The Ecological Significance of the Herbaceous Layer in Temperate Forest Ecosystems , 2007 .

[46]  G. Balent,et al.  Woody plant composition of forest layers: the importance of environmental conditions and spatial configuration , 2009, Plant Ecology.

[47]  B. Graae,et al.  A comparison of understorey vegetation between untouched and managed deciduous forest in Denmark , 1997 .

[48]  T. Naaf,et al.  Herb layer response to broadleaf tree species with different leaf litter quality and canopy structure in temperate forests , 2009 .

[49]  I. Király,et al.  The effect of light conditions on herbs, bryophytes and seedlings of temperate mixed forests in Őrség, Western Hungary , 2009, Plant Ecology.

[50]  S. Pickett,et al.  Indirect effects of litter on woody seedlings subject to herb competition , 1991 .

[51]  Han Y. H. Chen,et al.  FIRE, LOGGING, AND OVERSTORY AFFECT UNDERSTORY ABUNDANCE, DIVERSITY, AND COMPOSITION IN BOREAL FOREST , 2008 .

[52]  Currie.  The responsive C and N biogeochemistry of the temperate forest floor. , 1999, Trends in ecology & evolution.

[53]  J. Dupouey,et al.  Does the effect of forest roads extend a few meters or more into the adjacent forest? A study on understory plant diversity in managed oak stands , 2010 .

[54]  P. Wardle.  Fraxinus Excelsior L. , 1961 .

[55]  C. Mabry,et al.  Seasonal storage of nutrients by perennial herbaceous species in undisturbed and disturbed deciduous hardwood forests , 2008 .

[56]  C. Murcia.  Edge effects in fragmented forests: implications for conservation. , 1995, Trends in ecology & evolution.

[57]  A. Gazol,et al.  Different response to environmental factors and spatial variables of two attributes (cover and diversity) of the understorey layers , 2009 .

[58]  J. Neirynck,et al.  Impact of Tilia platyphyllos Scop., Fraxinus excelsior L., Acer pseudoplatanus L., Quercus robur L. and Fagus sylvatica L. on earthworm biomass and physico-chemical properties of a loamy topsoil , 2000 .

[59]  David R. Anderson,et al.  Model selection and multimodel inference : a practical information-theoretic approach , 2003 .

[60]  J. P. Grime,et al.  EFFECTS OF TREE LEAF LITTER ON HERBACEOUS VEGETATION IN DECIDUOUS WOODLAND , 1981 .

[61]  D. Whigham.  Ecology of woodland herbs in temperate deciduous forests , 2004 .

[62]  A. Magurran,et al.  Biological diversity : the coexistence of species on changing landscapes , 1994 .

[63]  J. Yarie.  THE ROLE OF UNDERSTORY VEGETATION IN THE NUTRIENT CYCLE OF FORESTED ECOSYSTEMS IN THE MOUNTAIN HEMLOCK BIOGEOCLIMATIC ZONE , 1980 .

[64]  P. White,et al.  The influence of carbon - nutrient balance on herb and woody plant abundance in temperate forest understories , 2006 .

[65]  D. Bates,et al.  Mixed-Effects Models in S and S-PLUS , 2001 .

[66]  Christian Wirth,et al.  Is forest diversity driving ecosystem function and service , 2010 .

[67]  D. Peterson,et al.  Nutrient Dynamics of Herbaceous Vegetation in Upland and Floodplain Forest Communities , 1982 .

[68]  B. Graae,et al.  The impact of forest continuity and management on forest floor vegetation evaluated by species traits. , 2000 .

[69]  R. Wisskirchen,et al.  Standardliste der Farn- und Blütenpflanzen Deutschlands , 1998 .

[70]  W. Schmidt,et al.  Herb-layer diversity in deciduous forests: Raised by tree richness or beaten by beech? , 2008 .

[71]  Gordon C. Tucker.  Acer pseudoplatanus L. , 2005 .

[72]  A. Kooijman.  Litter quality effects of beech and hornbeam on undergrowth species diversity in Luxembourg forests on limestone and decalcified marl , 2010 .