A Broader View of Disturbance Refugia in a Changing Climate

Students from UW Professor Brian Harvey’s Lab conduct research following the 2017 Norse wildfire in the Snoqualmie National Forest.
Source: University of Washington

Many natural disturbances, like wildfires, which have helped to maintain ecosystem processes and biodiversity in the past, are worsening under climate change and are threatening biodiversity. There is increasing recognition of the role of disturbance refugia — locations disturbed less severely or less frequently than the surrounding landscape — as legacies important to sustaining species under rapid ecological change. Although previous research on disturbance refugia in forests has primarily focused on fire, a new Northwest Climate Adaptation Science Center-funded study by Meg Krawchuk (Oregon State University), Garrett Meigs (now at Washington DNR) and colleagues, synthesized research on multiple types of disturbances in forests and how they interact and influence refugia.

Although it may be easiest to classify refugia as either present or not present in a given area, this study recommends taking a broader view of disturbance refugia by considering the spectrum of types and qualities of refugia across landscapes. Because they can take on many different forms over spatial and time scales, disturbance refugia should be considered at a range of scales, from individual organisms to entire landscapes. The quality of refugia also differs, since disturbances occur at different levels of severity. For example, fire refugia are not simply locations that are unburned. Instead, there is a broader range of fire effects that can contribute to persistence as a refugium. Additionally, refugia provide a range of ecological functions, from providing seed sources for tree regeneration to critical resources for wildlife during and after a disturbance. This makes it helpful to ask the questions “refugia from what disturbance?” and “refugia for what ecological attribute?” when identifying refugia and their ecological roles.

This study provides a disturbance refugia framework that goes beyond fire and recognizes single and overlapping disturbance events — like fire, drought and insect outbreaks — and describes how they might interact in supporting forest biodiversity. Interactions in forest ecosystems can either improve or reduce refugia functionality through negative (stabilizing) and positive (amplifying) feedbacks. Because positive feedbacks between fire, drought and insects are expected to become more common under climate change, it’s likely that refugia will be less abundant and less functional in areas where these positive feedbacks occur. For this reason, it will be increasingly important to better understand underlying causes of disturbance refugia and how they are affected by interacting disturbances. This more comprehensive view of forest disturbance refugia provides insights for forest management in North America under climate change that can also be translated to forest management strategies to benefit forests globally.

In addition to providing and illustrating the disturbance refugia framework, this study also highlights advances in methods and tools for understanding disturbance refugia. It emphasizes that using multiple techniques for identifying refugia can provide an effective toolbox for understanding the potential of disturbance refugia to conserve biodiversity. A case study focusing on fire refugia in late successional/old-growth forest of the Pacific Northwest and conservation for the northern spotted owl (Strix occidentalis caurina), provides an illustrative example of refugia science dovetailing with management application.

The disturbance refugia framework emphasizes that disturbance refugia represent one component in a complex patchwork created by disturbances in forests. Although this study focuses on three natural disturbances in North American forests, the disturbance refugia framework is relevant to ecosystems across the world. Continued research that considers the range and complexity of disturbance refugia will be critical to informing management of disturbance refugia under climate change.

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Snoqualmie National Forest
Source: University of Washington