Disturbance legacies have a stronger effect on future carbon exchange than climate in a temperate forest landscape

Abstract

<p><strong>Abstract.</strong> Forest ecosystems play an important role in the global climate system, and are thus intensively discussed in the context of climate change mitigation. Over the past decades temperate forests were a carbon (C) sink to the atmosphere. However, it remains unclear to which degree this C uptake is driven by a recovery from past disturbances vs. ongoing climate warming, inducing high uncertainty regarding the future temperate forest C sink. Here our objectives were (i) to investigate legacies within the natural disturbance regime by empirically analyzing two disturbance episodes affecting the same landscape 90 years apart, and (ii) to unravel the effects of past disturbances and future climate on 21st century forest C uptake by means of simulation modelling. We collected historical data from archives to reconstruct vegetation and disturbance history of a forest landscape in the Austrian Alps from 1905 to 2013. The effect of past legacies and future climate was determined by simulating 32 different combinations of past disturbances (including natural disturbances and management) and future climate scenarios. We found only moderate spatial overlap between two episodes of wind and bark beetle disturbance affecting the landscape in the early 20th and 21st century, respectively. The future forest C sink was driven by past disturbances, while climate change reduced forest C uptake. Historic management (and its cessation) had a considerably stronger influence on the future C balance than the natural disturbance episodes of the past. We conclude that neglecting disturbance legacies can substantially bias assessments of future forest dynamics.</p>