title: Does one model fit all? Patterns of beech mortality in natural forests of three European regions.
abstract: Large uncertainties characterize forest development under global climate change. Although recent studies have found widespread increased tree mortality, the patterns and processes associated with tree death remain poorly understood, thus restricting accurate mortality predictions. Yet, projections of future forest dynamics depend critically on robust mortality models, preferably based on empirical data rather than theoretical, not well-constrained assumptions. We developed parsimonious mortality models for individual beech (Fagus sylvatica L.) trees and evaluated their potential for incorporation in dynamic vegetation models (DVMs). We used inventory data from nearly 19,000 trees from unmanaged forests in Switzerland, Germany, and Ukraine, representing the largest dataset used to date for calibrating such models. Tree death was modelled as a function of size and growth, i.e., stem diameter (dbh) and relative basal area increment (relBAI), using generalized logistic regression accounting for unequal re-measurement intervals. To explain the spatial and temporal variability in mortality patterns, we considered a large set of environmental and stand characteristics. Validation with independent datasets was performed to assess model generality. Our results demonstrate strong variability in beech mortality that was independent of environmental or stand characteristics. Mortality patterns in Swiss and German strict forest reserves were dominated by competition processes as indicated by J-shaped mortality over tree size and growth. The Ukrainian primeval beech forest was additionally characterized by windthrow and a U-shaped size-mortality function. Unlike the mortality model based on Ukrainian data, the Swiss and German models achieved good discrimination and acceptable transferability when validated against each other. We thus recommend these two models to be incorporated and examined in DVMs. Their mortality predictions respond to climate change via tree growth, which is sufficient to capture the adverse effects of water availability and competition on the mortality probability of beech under current conditions.
authors: Research Unit Forest Resources and Management, WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Zürcherstrasse 111, 8903, Birmensdorf, Switzerland.|Forest Ecology, Institute of Terrestrial Ecosystems, ETH Zurich, Universitätstrasse 16, 8092, Zürich, Switzerland.
authors: Lisa
authors: L
authors: Hülsmann
authors: Forest Ecology, Institute of Terrestrial Ecosystems, ETH Zurich, Universitätstrasse 16, 8092, Zürich, Switzerland.
authors: Harald K M
authors: HK
authors: Bugmann
authors: Research Unit Forest Resources and Management, WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Zürcherstrasse 111, 8903, Birmensdorf, Switzerland.
authors: Brigitte
authors: B
authors: Commarmot
authors: Sachgebiet Waldnaturschutz/Naturwald, Nordwestdeutsche Forstliche Versuchsanstalt NW-FVA, Grätzelstrasse 2, 37079, Göttingen, Germany.
authors: Peter
authors: P
authors: Meyer
authors: Research Unit Forest Soils and Biogeochemistry, WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Zürcherstrasse 111, 8903, Birmensdorf, Switzerland.
authors: Stephan
authors: S
authors: Zimmermann
authors: Research Unit Forest Resources and Management, WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Zürcherstrasse 111, 8903, Birmensdorf, Switzerland.
authors: Peter
authors: P
authors: Brang
mesh_terms: D057231:Climate Change; D017753:Ecosystem; D029964:Fagus; D065928:Forests; D013557:Switzerland
keywords: 
  Fagus sylvatica
  ; climate change; dynamic vegetation models; external validation; forest inventory data; forest reserves; generalized logistic regression; individual tree mortality