The role of alpha and beta diversity in buffering the effects of intensifying natural disturbance regimes

Forests are strongly affected by climatic changes, but impacts vary between tree species and prevailing site conditions. A number of studies suggest that increasing tree species diversity is a potent management strategy to decrease climate change impacts in general, and increase the resilience of forest ecosystems to changing disturbance regimes. However, most studies to date have focused on stand-level diversity in tree species (alpha diversity), which is often difficult to implement in operational forest management. Inter-species competition requires frequent management interventions to maintain species mixture and complicates the production of high-quality stemwood. An alternative option to increasing alpha diversity is to increase tree species diversity between forest stands (beta diversity). Here we quantify the effects of alpha and beta diversity on the impact of forest disturbances under climate change. We conducted a simulation experiment applying two forest landscape models (i.e. iLand and LandClim) in two landscapes with strongly contrasting environmental conditions in Central Europe. Simulations investigate different levels of tree species diversity (no diversity, low diversity and high diversity) in different spatial arrangements (alpha diversity, beta diversity). Subsequently a standard forest management regime and a series of prescribed disturbances are applied over 200 years. By analyzing biomass values relative to a no-disturbance run, variation in biomass over time and the number of trees > 30 cm dbh per hectare, we isolate the effect of tree species diversity on the resistance of forests to disturbances.