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

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. --