Tree cover at fine and coarse spatial grains interacts with shade tolerance to shape plant species distributions across the Alps.
The role of competition for light among plants has long been recognised at local scales, but its importance for plant species distributions at larger spatial scales has generally been ignored. Tree cover modifies the local abiotic conditions below the canopy, notably by reducing light availability, and thus, also the performance of species that are not adapted to low-light conditions. However, this local effect may propagate to coarser spatial grains, by affecting colonisation probabilities and local extinction risks of herbs and shrubs. To assess the effect of tree cover at both the plot- and landscape-grain sizes (approximately 10-m and 1-km), we fit Generalised Linear Models (GLMs) for the plot-level distributions of 960 species of herbs and shrubs using 6,935 vegetation plots across the European Alps. We ran four models with different combinations of variables (climate, soil and tree cover) at both spatial grains for each species. We used partial regressions to evaluate the independent effects of plot- and landscape-grain tree cover on plot-level plant communities. Finally, the effects on species-specific elevational range limits were assessed by simulating a removal experiment comparing the species distributions under high and low tree cover. Accounting for tree cover improved the model performance, with the probability of the presence of shade-tolerant species increasing with increasing tree cover, whereas shade-intolerant species showed the opposite pattern. The tree cover effect occurred consistently at both the plot and landscape spatial grains, albeit most strongly at the former. Importantly, tree cover at the two grain sizes had partially independent effects on plot-level plant communities. With high tree cover, shade-intolerant species exhibited narrower elevational ranges than with low tree cover whereas shade-tolerant species showed wider elevational ranges at both limits. These findings suggest that forecasts of climate-related range shifts for herb and shrub species may be modified by tree cover dynamics.
Departamento de Botánica, Universidad de Granada, Avenida Fuentenueva, E-18071 Granada, Spain ; Section for Ecoinformatics & Biodiversity, Department of Bioscience, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark.
Diego
D
Nieto-Lugilde
Section for Ecoinformatics & Biodiversity, Department of Bioscience, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark ; Ecologie et Dynamique des Systèmes Anthropisés (EDYSAN, FRE 3498 CNRS-UPJV), Plant Biodiversity Lab, Jules Verne University of Picardie, 1 rue des Louvels, FR-80037 Amiens Cedex 1, France.
Jonathan
J
Lenoir
Domaine de Charance, Conservatoire Botanique National Alpin, Gap, 05000, France.
Sylvain
S
Abdulhak
Laboratoire de Systématique végétale et Biodiversité, Conservatoire et Jardin botaniques, 1 Chemin de l'Impératrice, CH-1292 Chambésy, Switzerland.
David
D
Aeschimann
Faculty Centre for Biodiversity, Department of Conservation Biology, Vegetation and Landscape Ecology, University of Vienna, Vienna, Austria ; Vienna Institute for Nature Conservation and Analyses, Vienna, Austria.
Stefan
S
Dullinger
AgroParisTech, Unité Mixte de Recherche 1092, AgroParisTech-Institut National de la Recherche Agronomique (INRA), Laboratoire d'Etude des Ressources Forêt-Bois (LERFoB), Nancy, France.
Jean-Claude
JC
Gégout
Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
Antoine
A
Guisan
Institute for Interdisciplinary Mountain Research (IGF) of the Austrian Academy of Sciences, c/o Department of Conservation Biology, Vegetation and Landscape Ecology, University of Vienna, Vienna, Austria.
Harald
H
Pauli
Laboratoire d'Ecologie Alpine, UMR CNRS 5553, University Joseph Fourier, Grenoble 1, BP 53, 38041 Grenoble Cedex 9, France.
Julien
J
Renaud
Centre alpien de Phytogéographie Fondation J.-M. Aubert, CH-1938 Champex-Lac, Switzerland and Section of Biology, University of Geneva, Case postale 60, CH-1292 Chambésy, Switzerland.
Jean-Paul
JP
Theurillat
Laboratoire d'Ecologie Alpine, UMR CNRS 5553, University Joseph Fourier, Grenoble 1, BP 53, 38041 Grenoble Cedex 9, France.
Wilfried
W
Thuiller
Domaine de Charance, Conservatoire Botanique National Alpin, Gap, 05000, France.
Jérémie
J
Van Es
Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
Pascal
P
Vittoz
Vienna Institute for Nature Conservation and Analyses, Vienna, Austria.
Wolfgang
W
Willner
Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland.
Thomas
T
Wohlgemuth
Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland.
Niklaus E
NE
Zimmermann
Section for Ecoinformatics & Biodiversity, Department of Bioscience, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark.
Jens-Christian
JC
Svenning
biotic interactions; biotic modifiers; facilitation; light competition; plant-plant interactions; shade tolerance; spatial grain; species distribution models