Shifting fire regimes in Africa
In West Africa, fire regimes range from savannas that experience annual, low-intensity fires to wet tropical forests that rarely burn (Dwomoh and Wimberly 2017). Patterns of satellite active fire detections and burned area are mainly influenced by vegetation, whereas the seasonality and intensity of fires are more strongly associated with climate. Between 2003-2015, fire activity generally decreased in the savanna ecoregions and increased in the forested ecoregions. Forest fires were widespread during the regional drought of the 1980’s and resurged again in Ghana during an ENSO-associated drought event in 2016. (Dwomoh and Wimberly 2019). Forest degradation caused by fire and other disturbances increases the risk of subsequent fire (Dwomoh et al. 2017, Dwomoh and Wimberly 2019), raising concerns that increasing droughts resulting from climate change will catalyze new cycles of wildfire and forest loss. We are continuing to study the determinants and consequences fire in African ecosystems by using satellite remote sensing to characterize burned areas, vegetation moisture status, and forest structure.
- Dwomoh, F. K., M. C. Wimberly, M. A. Cochrane, and I. Numata. 2019. Forest degradation promotes fire during drought in moist tropical forests of Ghana. Forest Ecology and Management 440: 148-168.
- Dwomoh, F. K., and M. C. Wimberly. 2017. Fire regimes and their drivers in the Upper Guinean Region of West Africa. Remote Sensing 9: 1117.
Global change and fire in the western U.S.
Wildfires in western North America have increased in size and intensity over the past several decades because of climate change and landscape alterations that have affected ignitions and fuels. The EcoGRAPH group has studied the effects of climate, vegetation, and forest management on wildfire in the western United States (Liu and Wimberly 2015) and developed models to project the effects of climate change on future fire regimes (Liu and Wimberly 2016). These studies projected increased burned area and showed that the indirect effects of shifting vegetation types in response to climate change will be as important as the direct effects of climate change on fire weather and fuel moisture. We also projected the combined effects of climate change and wildland-urban interface (WUI) expansion on fire risk in the Colorado Front Range (Liu et al. 2014). The combined effect of these two factors was non-linear, with climate change exacerbating the risks from expansion of low-density homes into fire-prone vegetation types.
Fuel treatments, such as thinning and prescribed burning, are a potentially valuable tool for adapting to changing fire regimes. We have used satellite remote sensing data and fire behavior models to analyze the effects of different types of fuel treatments on wildfire size and severity (Wimberly et al. 2009, Cochrane et al. 2012). In general treatments that combined reduction of canopy fuels by thinning with reduction of surface fuels by prescribed burning or mastication were most effective at reducing fire severities and sizes. We also explored the influences of forest roads on fire ignitions, the locations of fire boundaries, and fire severity (Narayanaraj and Wimberly 2011, 2012, 2013). Both human and lightning ignitions were more frequent close to roads, but fires also had lower fire severities and were more likely to stop spreading close to roads.
- Liu, Z., M. C. Wimberly. 2016. Direct and indirect effects of climate change on projected future fire regimes in the western United States. Science of the Total Environment 542: 65-75.
- Liu, Z., M. C. Wimberly. 2015. Climatic and landscape influences on fire regimes from 1984 to 2010 in the western United States. PLoS One 10(10): e0140839.
- Narayanaraj, G., and M. C. Wimberly. 2013. Influences of forest roads and their edge effects on the spatial pattern of burn severity. International Journal of Applied Earth Observation and Geoinformation 23: 62-70.
- Cochrane, M. A., C. J. Moran, M. C. Wimberly, A. D. Baer, M. A. Finney, K. L. Beckendorf, J. Eidenshink, and Z. Zhu. 2012. Estimation of wildfire size and risk changes due to fuels treatment. International Journal of Wildland Fire 21: 357-367.
- Narayanaraj, G., and M. C. Wimberly. 2012. Influences of forest roads on the spatial patterns of human-and lightning-caused wildfire ignitions. Applied Geography 32: 878-888.
- Narayanaraj, G., and M. C. Wimberly. 2011. Influences of forest roads on the spatial pattern of wildfire boundaries. International Journal of Wildland Fire 20: 792-803.
- Wimberly, M. C., M. A. Cochrane, A. D. Baer, and K. Pabst. 2009. Assessing fuel treatment effectiveness using satellite imagery and spatial statistics. Ecological Applications 19: 1377-1384.
Historical fire regimes and landscapes in the Pacific Northwest
Old-growth forests in the Pacific Northwest region of the United States are characterized by large tree sizes, accumulations of dead wood, and complex horizonal and vertical structure. The extent of old growth forests was greatly reduced by logging during the 20th century (Wimberly and Ohmann 2004). However, large wildfires occurred in the region prior to European settlement, raising the question how current levels of old growth compare to those under pre-settlement fire regimes. To answer this question, we developed the LAndscape Dynamics Simulator (LADS) to simulate wildfires and the dynamics of old growth forests in historical landscapes (Wimberly et al. 2000, Wimberly 2002). Despite the occurrence of large wildfires, we found that old growth was historically the most prevalent age class, covering 29-52% of the total forest area. The current area of old- growth forest is considerably lower than this historical range of variability (Wimberly et al. 2004). More recent versions of LADS have been modified to better model the dynamics of mixed-severity fire regimes (Wimberly and Kennedy 2008, Kennedy and Wimberly 2009). In the future, a warmer and drier climate will likely result in increased fire frequencies and severities that will push landscapes even further outside the range of historical variability (Wimberly and Liu 2014).
- Wimberly, M. C., and Z. Liu. 2014. Interactions of climate, fire, and management in future forests of the Pacific Northwest. Forest Ecology and Management 327: 270-279.
- Kennedy, R. S. H., and M. C. Wimberly. 2009. Historical fire and vegetation dynamics in dry forests of the interior Pacific Northwest, USA and relationships to Northern Spotted Owl (Strix occidentalis caurina) habitat conservation. Forest Ecology and Management 258: 554-566.
- Wimberly, M. C., and R. S. H. Kennedy. 2008. Spatially explicit modeling of mixed-severity fire regimes and landscape dynamics in the interior Pacific Northwest. Forest Ecology and Management 254: 511-523.
- Wimberly, M. C., and J. L. Ohmann. 2004. A multi-scale assessment of human and environmental constraints on forest land cover change on the Oregon (USA) Coast Range. Landscape Ecology 19: 631-646.
- Wimberly, M. C., T. A. Spies, and E. Nonaka, 2004. Using criteria based on the natural fire regimes to evaluate forest management in the Oregon Coast Range. Page 146-157 In: Perera, A. H., L. J. Buse, and M. G. Weber, editors. Emulating Natural Forest Landscape Disturbances: Concepts and Applications. Columbia University Press, New York.
- Wimberly, M. C. 2002. Spatial simulation of historical landscape patterns in coastal forests of the Pacific Northwest. Canadian Journal of Forest Research 32: 1316-1328.
- Wimberly, M. C., T. A. Spies, C. J. Long, and C. Whitlock. 2000. Simulating Historical Variability in the Amount of Old Forests in the Oregon Coast Range. Conservation Biology 14: 167-180.