The interplay between disturbance and diversity in Central European forest ecosystems

Rupert Seidl, Cornelius Senf and Werner Rammer, School of Life Sciences, Technical University of Munich, Freising, Germany, Rupert Seidl, Berchtesgaden National Park, Berchtesgaden, Germany

Background/Question/Methods
In ecosystems, disturbance and diversity are intricately linked. Disturbances are important drivers of diversity, and diversity in turn modulates disturbance regimes. Yet, quantifying this important interaction often remains challenging, because of the multiple spatio-temporal scales involved. Furthermore, it is unclear how the interplay between disturbance and diversity will change in the future as global change progressively alters disturbance regimes. Here we focus on two national parks in Central Europe (Bavarian Forest National Park and Berchtesgaden National Park) to explore the links between disturbance and diversity in forest ecosystems. Focusing on structural diversity, our objectives were (1) to quantify the effect of disturbance on diversity, (2) to investigate how this effect changes as disturbance rates increase, and (3) to assess the buffering capacity of diversity on future forest disturbance regimes. We used a combination of active and passive remote sensing information to address our first two research objectives, and employed an individual-based forest landscape model to simulate future ecosystem trajectories for our third research objective.
Results/Conclusions
Disturbance is a strong driver of structural diversity in Central European forest ecosystems. Structural diversity showed an unimodal response with disturbance rate, which emerged from contrasting disturbance effects across scales, i.e. decreasing alpha diversity and increasing beta diversity with increasing disturbance rate. This relationship was consistent across study landscapes, spatial scales and diversity indicators. Diversity was highest for disturbance rates between 0.5% and 1.5% of the forest area disturbed per year, which suggests that the disturbances of the past decades (affecting forests at a rate of 0.7-1.1% per year) increased the structural diversity of Central European forests. However, a climate-induced increase in disturbance could result in a tipping point being crossed, leading to substantial structural homogenization. Using scenario simulations to test potential future trajectories we show that the climatic changes expected for the 21st century could substantially increase disturbance rates by up to 221%. Although not being able to fully compensate the amplifying effect of climate change, disturbance-mediated changes in forest structure and composition reduced future disturbance activity. Our results suggest that increased diversity provides an important dampening feedback on changing forest disturbance regimes. We conclude that forest management should harness disturbance-created diversity and prevent the homogenization of disturbed areas (e.g., via the eradication of disturbance legacies through salvage logging) to foster the future resilience of forest ecosystems.