Natural disturbances as drivers of tipping points in forest ecosystems under climate change - implications for adaptive management

As climate continues to change, disturbances may increasingly navigate forest ecosystems towards tipping points, causing irreversible state shifts and a loss of biodiversity and ecosystem services. In this review, I elaborate the Special Issue topic 'Natural disturbances as tipping points of forest ecosystems under climate change' featured by Forestry and suggest a suit of adaptive measures to mitigate increasing disturbances and their impacts on forest ecosystems. The Special Issue contains seven case studies assessing drought, fire, wind and bark beetle disturbances in Europe, North America and Africa. Despite high severities and/or frequencies, disturbances have not yet induced a shift of the investigated forest ecosystems towards an alternative state. Instead, forests have shown high resistance, resilience or both. For instance, one case study reveals that short-interval fires in European beech forests may not even significantly alter tree species composition due to the high resprouting ability of beech. Yet, other case studies identify distinct differences in resilience amongst ecoregions, and indicate that climate change and disturbance interactions might tip the future carbon balance of forests from sink to source. Many forest ecosystems are likely able to cope with future increases in disturbance activity to some degree. However, tipping points might vary across ecosystems dominated by different disturbance agents. While wind and bark beetles mainly affect canopy trees, fire and drought also directly impair tree regeneration, thus reducing the capacity of ecosystems to recover and reorganize. Hence, forest ecosystems in which fire and drought are the dominant disturbance agents might approach tipping points earlier than forests dominated by other agents if disturbance activity continues to increase. Several proactive and reactive adaptive measures are available to mitigate increasing disturbances, but more research is needed to develop robust and region-specific strategies to prevent tipping points in forest ecosystems.