Will forest dynamics continue to accelerate throughout the 21st century in the Northern Alps?

Abstract

Observational evidence suggests that forests in the Northern Alps are changing at an increasing rate as a consequence of climate change. Yet, it remains unclear whether the acceleration of forest change will continue in the future, or whether downregulating feedbacks will eventually decouple forest dynamics from climate change. Here we studied future forest dynamics at Berchtesgaden National Park, Germany by means of a process-based forest landscape model, simulating an ensemble of 22 climate projections until the end of the 21st century. Our objectives were (i) to assess whether the observed acceleration of forest dynamics will continue in the future, (ii) to analyze how uncertainty in future climate translates to variation in future forest disturbance, structure, and composition, and (iii) to determine the main drivers of future forest dynamics. We found that forest dynamics continue to accelerate in the coming decades, with a trend towards denser, structurally more complex and more species rich forests. However, changes in forest structure leveled off in the second half of the 21st century regardless of climate scenario. In contrast, climate scenarios caused trajectories of tree species change to diverge in the second half of the 21st century, with stabilization under RCP 2.6 and RCP 4.5 scenarios and accelerated loss of conifers under RCP 8.5. Disturbance projections were 3 to 20 times more variable than future climate, whereas projected future forest structure and composition varied considerably less than climate. Indirect effects of climate change via alterations of the disturbance regime had a stronger impact on future forest dynamics than direct effects. Our findings suggest that dampening feedbacks within forest dynamics will decelerate forest change in the second half of the 21st century. However, warming beyond the levels projected under RCP 4.5 might profoundly alter future forest disturbance and composition, challenging conservation efforts and ecosystem service supply.

Increasing aridity causes larger and more severe forest fires across Europe

“…Furthermore, climate change will also alter the forest vegetation of Europe, and could lead to a reassembly towards broadleaved communities in some areas (e.g. Thom et al, 2022), which could alter flammability. Such dynamic feedbacks between climate, vegetation, and fire were not considered here and should be the focus of future research.…”

“…The climate sensitivity reported here is thus a conservative estimate, as the effects of increasing VPD in spring and fall were not considered. Furthermore, climate change will also alter the forest vegetation of Europe, and could lead to a reassembly towards broadleaved communities in some areas (e.g Thom et al, 2022),. which could alter flammability.…”

Climate change accelerates ecosystem restoration in the mountain forests of Central Europe

“…iLand was extensively evaluated at BGNP in a previous study, successfully testing the ability of the model to reproduce individual tree dimensions and natural forest dynamics (Thom et al, 2022). Here version 1.1 of iLand was used.…”

“…by reducing the competitiveness of some species over others, which could hamper restoration to historic conditions. At the same time climate change also increases disturbance frequency and severity (Seidl et al, 2017), which in turn accelerates forest dynamics (Thom et al, 2022) and creates opportunities for restoration (e.g. by post‐disturbance tree planting).…”

“…Specifically, we asked (i) “Can restoration goals be met within the 21st century?” and (ii), “How much better are active restoration strategies compared to passive restoration?”. We hypothesised that despite the expected future acceleration of forest dynamics (Thom et al, 2022), neither restoration strategy will be able to meet the restoration targets during the 21st century, due to today's large deviation from target conditions. We, however, expected that active restoration will speed up the development towards restoration targets compared to passive restoration, and that this effect is already visible in the empirical data (e.g.…”