Disentangling the effects of compositional and structural diversity on forest productivity

TitleDisentangling the effects of compositional and structural diversity on forest productivity
Publication TypeJournal Article
Year of Publication2017
AuthorsM. Pedro S, Rammer W., Seidl R.
JournalJournal of Vegetation Science
KeywordsEcosystemfunctioning, Forest productivity, Forest successional development, iLand model, Net primary production, Structural diversity, Tree species diversity

Questions: Tree species diversity is widely reported to positively influence forest
productivity. Yet, a consistent attribution of productivity effects is complicated
by the fact that compositional and structural diversity are often related in
forest ecosystems. Here, our objective was to disentangle the effects of diversity
in species and structures on forest productivity.We further assessed whether the
influence of structure and composition on productivity changes over the course
of forest development.
Location: Hainich National Park, central Germany.
Methods:We conducted a factorial simulation experiment in which 63 unique
combinations of six different tree species were studied over 500 yr of forest
development. Themodel used was iLand, a process-based simulator operating at
individual tree resolution. The indicators of compositional diversity considered
included species richness, entropy, evenness and identity, while structural
diversity was characterized by indicators describing vertical and horizontal stand
structure. Net primary production (NPP) was studied as the response variable,
and randomforest analysis was used to synthesize simulation output.
Results: We found positive effects of both compositional and structural diversity
on productivity, but their influence changed distinctly over the course of forest
development. In early-seral stages, diversity effects on NPP were dominated by
aspects of tree species composition, and displayed a strong positive selection
effect for European beech (Fagus sylvatica L.). In later stages of forest development,
diversity effects on NPP were dominated by structural diversity, with productivity
increasing with increased variation in tree diameter and canopy
Conclusion: To better understand the effects of diversity on ecosystem functioning,
both the compositional and structural dimensions of diversity in forest
ecosystems (and their changes over time) need to be considered. In the context
of ecosystem management our results suggest that the reduction in productivity
associated with the loss of a canopy tree species (e.g. due to the invasion of an
alien pest species) can to some degree be compensated through increased structural
diversity. Fostering both compositional and structural diversity are important
means to increase the robustness of forest ecosystemfunctioning.


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