The frying pan and the fire: Megadisturbances are threatening the resilience of forest ecosystems to climate change
Millar, C.I., and Stephenson, N.L. Temperate forest health in an era of emerging megadisturbances. Science 349, 6250. 823 – 826. (2015). PDF
Summary
Temperate forest ecosystems have shown remarkable resilience to human disturbances and climate change over recent decades. However, increases in the frequency and severity of climatic events, and the interaction of climate events with other disturbances (e.g., impacts of invasive species), can reduce the resilience of forests (i.e., prevent them from rebounding back to their original state). These unprecedented ‘megadisturbances’, as described by Millar and Stephenson (2015), are threatening to push ecosystems past the threshold of natural resilience and into alternative states. This is happening more frequently in the western and southern U.S., whereas eastern and northern forests are still relatively resilient.
Forests that have shifted into alternative states show major, often irreversible transformations in ecological health, biodiversity, and ecosystem services. For example, increased temperatures over past decades have contributed to increased severity of droughts. These extreme droughts both directly affect forest health via increasing water stress and indirectly affect forest health by making forest ecosystems more vulnerable to the effects of invasive pests and pathogens.
In the short-term, the authors suggest many temperate forests will continue to be resilient to megadisturbance events associated with climate change. However, in the long-term, most temperate forests are likely to change in condition, catalyzed by megadistrubances, with changes in forest structure and species composition on the one end to novel ecosystems at the other extreme. Proactive management (e.g., thinning trees to minimize competition for water or translocating climate-adapted species) will likely be necessary to facilitate a gradual transition in forest structure and composition. Such proactive management might help guide the trajectory of inevitable forest changes to minimize potential shifts or losses in ecosystem services.
Take home points
Climate change disturbances have increased in severity and frequency, resulting in megadisturbance events that threaten the natural resilience of temperate forest ecosystems.
Megadisturbances can cause forests to shift into alternative states, characterized by major or irreversible changes in forest structure, biodiversity, or ecosystem services.
Megadisturbance events (e.g., severe, reoccurring droughts coupled with high temperatures) can interact with other disturbances (e.g., impacts of invasive species) to drive major ecological changes that threaten the resilience of temperate forest ecosystems.
Temperate forests will likely remain resilient to megadisturbances in the short term; however, proactive management will be needed long-term to facilitate gradual transitions in forest ecosystems, which might minimize losses of ecosystem services.
Management implications
Identifying vulnerable and/or high priority forest ecosystems for management intervention is necessary to strategically allocate management time and money.
Early and proactive management (e.g., thinning trees to minimize water stress or human-assisted movement and establishment of climate-adapted species) might enable gradual transitions in forest structure, health, and ecosystem services.
Integrated and coordinated efforts among institutes, agencies, and governments are needed to improve the likelihood that short- and long-term forest management actions are successful.
Keywords
Climate change and resilience, Climate extremes, Impact studies, Megadisturbance, Forest ecosystem health