Forest Refugia
Clark's nutcracker eatings seeds from whitebark pine.
Photo by Frank D. Lospalluto / Flickr CC BY-NC-ND 2.0
Forest Refugia
Warmer temperatures, changing drought patterns, increasing pressure from pests and pathogens, and altered fire regimes associated with climate change, threaten many important natural and cultural resources in the Northwestern U.S. However, not all places on the landscape are changing in the same way. Climate change refugia are areas relatively buffered from contemporary climate change over time that enable persistence of valued physical, ecological, and socio-cultural resources (Morelli et al. 2016). Across the Northwest, many different types of refugia are being defined, mapped, and evaluated. These diverse approaches to studying refugia provide the scientific foundation for meeting regional management needs, such as preserving old-growth forests, protecting high priority species (e.g., marbled murrelet), and conserving the threatened whitebark pine ecosystem. Here, we highlight recent climate change refugia research efforts and discuss their importance to developing a regional climate change adaptation strategy.
Iconic white bark pine trees are keystone species in high elevation forests, providing critical habitat for wildlife.
Credit: Famartin (CC-BY-SA-3)
Refugia may promote conservation of whitebark pine forests
Of all Northwest forests, whitebark pine (Pinus albicaulis)-dominated forests are one of the most threatened due to interactions between white pine blister rust (Cronartium ribicola), bark beetles, drought, changing fire regimes, and climate change. Scientists at the U.S. Forest Service and the University of Idaho, have developed new methods for mapping “genetic refugia” in whitebark pine forests. By using spatial datasets of white pine blister rust resistance, drought tolerance, late winter cold hardiness, and genetic diversity, they are able to identify populations with favorable genetic attributes that are more likely to persist, despite changing environmental conditions. The areas, identified as genetic refugia, are priorities for active conservation and restoration efforts. However, only 1% of the mapped refugia currently exist in protected wilderness areas.
Unburned or lightly-burned islands of vegetation (white outline) that persist during fire events can provide important seed sources and critical habitat for animals. Unburned/lightly-burned islands like this one have recently been mapped for 2300 fires across the Northwest.
Photo credit: Medden et al. 2016
Fire refugia are integral to fire management in northwest forests
With an average of 4,100 wildfires burning nearly 758,000 acres annually, fire is a common element of the Northwest landscape. In every fire, there are islands of vegetation that remain unburned or burn at a lower severity—i.e., fire refugia. These fire refugia serve as important resources in the post-fire forest environment. Scientists at the University of Idaho have employed remote-sensing techniques to identify unburned islands by examining 2300 fires occurring between 1984-2014 in the interior Northwest. New research at Oregon State University has resulted models predicting fire refugia by classifying areas dependent on their fire weather conditions and topographic complexity. These new models suggest that many fire refugia are created by an area of a landscape that endures through repeated fire events and assists in the development and maintenance of forest ecosystems, including old-growth. However, current fire management, aiming to reduce diversity in burn severity, may be altering or removing fire refugia needed for the establishment, persistence, and movement of organisms. Identification and management of fire refugia needs to be an integral part of maintaining ecosystem resilience to future fire conditions.
Researchers at OSU have developed a conceptual and modeling framework for predicting refugia as a function of these persistent landscape features.
Chart credit: Krawchuk et al. 2016
A NW CASC research collaboration on fire refugia has produced a very helpful website containing several key fire refugia findings (click here for more detailed summary):
Ecoregional refugia dynamics can vary greatly
Old forest and large tree habitat are important sources of refugia
Non-stand-replacing severity fire is an important source of large tree habitat
Past timber harvest has resulted in multi-decadal depressions in fire refugia probability, and increases in high-severity fire
Fire management strategies can promote (or diminish) fire refugia
Extreme fire growth trumps extreme fire weather
Some fire refugia are able to persist even under extreme fire conditions
Infographic illustrating the species composition, contrasting spatial patterns and drivers of fire refugia revealed by researchers’ models, sensitivity to fire weather and growth conditions, and relationships between fire dynamics and the creation or maintenance of mature and old forest structure for three major forest types (wet, cold, and dry forest) in the Pacific Northwest. The upper banner is a graphical representation of the different spatial patterns of fire refugia and their sensitivity (or resistance) to fire weather conditions across the three forest types. For each forest type, more detailed descriptions of the composition, distribution, and response to fire weather are provided in the infographic text.
Hydrologic refugia buffer northwest forests from intensifying disturbances
Illustration of different types of hydrologic refugia and the landscape features that create them.
Illustration by: McLaughlin et al. 2017
As with other types of refugia, wetter micro-environments that maintain relatively high water availability—i.e., hydrologic refugia—may help species persist in the face of changing climate conditions. Hydrologic refugia may be especially important in buffering forest species from interacting disturbances like drought and insect outbreaks. Researchers at the USGS and the University of Washington are developing new methods of identifying hydrologic refugia. These methods have recently been applied to identify potential refugia in dry mixed-conifer forests in southern Oregon by studying recent drought events in the region. The persistent landscape features that create hydrologic refugia, allow their continued functioning in the face of climate change. Therefore, their identification and management is an important strategy for conserving old-growth forests and other high priority forest resources.
Preliminary identification of refugia from drought and mountain pine beetle mortality in the Gearhart Mountain Wilderness in southern Oregon in 2009. Refugia were identified using a novel remote sensing approach based on the Normalized Difference Moisture Index.
Image credit: Cartwright 2017
Refugia are complex, connected landscapes
The Nature Conservancy (TNC) is taking a different approach to mapping climate change refugia in the northwest. By focusing on two persistent landscape factors —topographic climate diversity and connectedness of the landscape —TNC has developed maps of areas that are likely to be resilient to climate change (Buttrick et al. 2015). These resilient landscapes maps are available for the entire northwest region and offer a starting place for developing adaptation strategies and guiding future conservation investments in the face of uncertain future conditions.
relevant rrc publications
Shuman, J.K., Balch, J.K., Barnes, R.T., Higuera, P.E., Roos, C.I., Schwilk, D.W., Stavros, E.N., Banerjee, T., Bela, M.M., Bendix, J. and Bertolino, S., 2022. Reimagine fire science for the anthropocene. PNAS Nexus, 1(3), p.pgac115. https://doi.org/10.1093/pnasnexus/pgac115
Downing, W.M., Meigs, G.W., Gregory, M.J. & Krawchuk, M.A. 2021. Where and why do conifer forests persist in refugia through multiple fire events? Global Change Biology. https://doi.org/10.1111/gcb.15655.
Cartwright, J.M., Littlefield, C.E., Michalak, J.L., Lawler, J.J. & Dobrowski, S.Z. 2020. Topographic, soil, and climate drivers of drought sensitivity in forests and shrublands of the Pacific Northwest, USA. Scientific Reports. https://doi.org/10.1038/s41598-020-75273-5.
Downing, WM, Johnston, JD, Krawchuk, MA, Merschel, AG, & Rausch, JH. 2020. Disjunct and decoupled? The persistence of a locally endemic, fire-sensitive conifer species in a historically frequent fire landscape. Nature Conservation. https://doi.org/10.1016/j.jnc.2020.125828
Downing, WM, Krawchuk, MA, Coop, JD, Meigs, GW, Haire, SL, Walker, RB, Whitman, E, Chong, G, Miller, C, &Tortorelli, C. 2020. How do plant communities differ between fire refugia and fire-generated early-seral vegetation? Journal of Vegetation Science 31:26-39. https://doi.org/10.1111/jvs.12814
Krawchuk et al. 2020. Disturbance refugia within mosaics of forest fire, drought, and insect outbreaks. https://doi.org/10.1002/fee.2190
Krawchuk MA, Meigs GW, Cartwright J, et al. 2020. Disturbance refugia within mosaics of fire, drought, and insect outbreaks enable forest persistence. Front Ecol Environ. https://doi.org/10.1002/fee.2190
Meigs, GW, Dunn, CJ, Parks, SA, & Krawchuk, MA. 2020. Influence of topography and fuels on fire refugia probability under varying fire weather in forests of the US Pacific Northwest. Canadian Journal of Forest Research. https://doi.org/10.1139/cjfr-2019-0406
Coop, JD, DeLorty, TJ, Downing, WM, Haire, SL, Krawchuk, MA, Miller, C, Parisien, M-A, & Walker, RB. 2019. Contributions of fire refugia to resilient ponderosa pine and dry mixed-conifer forest landscapes. Ecosphere 10(7) https://doi.org/10.1002/ecs2.2809
Downing, WM, Krawchuk, MA, Meigs, GW, Haire, SL, Coop, JD, Walker, RB, Whitman, E, Chong, G, & Miller, C. 2019. Influence of fire refugia spatial pattern on post-fire forest recovery in Oregon's Blue Mountains. Landscape Ecology 34: 771-792 https://doi.org/10.1007/s10980-019-00802-1
Cartwright, J. 2018. Landscape topoedaphic features create refugia from drought and insect disturbance in a lodgepole and whitebark pine forest. Forests, 9(11), 715. https://doi.org/10.3390/f9110715
Meddens, AJH, Kolden, CA, Lutz, JA, Smith, AMS, Cansler, CA, Abatzoglou, JT, Meigs, GW, Downing, WM, & Krawchuk, MA. 2018. Fire Refugia: What Are They, and Why Do They Matter for Global Change? BioScience, 68(12), https://doi.org/10.1093/biosci/biy103
Meigs, G, and Krawchuk, MA. 2018. Composition and structure of forest fire refugia: what are the ecosystem legacies across burned landscapes. Forests 2018, 9(5), 243; https://doi.org/10.3390/f905024
Krawchuk MA, Haire SL, Coop J, Parisien M-A, Whitman E, Chong G, Miller C. 2016. Topographic and fire weather controls of fire refugia in forested ecosystems of northwestern North America. Ecosphere 7:12. https://doi.org/10.1002/ecs2.1632
Millar CI &Stephenson NL. 2015. Temperate forest health in an era of emerging megadisturbance. Science (80- ) 349: 823 LP – 826. https://doi.org/10.1126/science.aaa9933
Millar CI, Stephenson NL, and Stephens SL. 2007. Climate change and forests of the future: Managing in the face of uncertainty. Ecol Appl 17: 2145–51. https://doi.org/10.1890/06-1715.1