Pyrodiversity and Biodiversity in the Sierra
May 4, 2021
By Dr. Grant Ballard, Chief Science Officer
Point Blue has monitored California’s iconic Sierra Nevada ecosystems since the 1970’s, with a particularly extensive study of birds and vegetation covering thousands of locations across the entire mountain range beginning in 2009. This long-term study serves as a witness to the transformation of Sierra ecosystems that is currently underway, and reveals key insights to mitigating the negative consequences of climate change and other disturbances. Some of our study sites have burned, been logged, and been subject to drought stress and pine-boring beetle outbreaks, while others remain relatively undisturbed.
Many species are adapted to exploit disturbance in order for their populations to thrive, and in the Sierra, fire is the biggest form of natural disturbance. After many decades of fire-suppression, some of these species have dwindling populations, but might have new opportunities as fire has become more common in the Sierra since the mid-1980’s (Westerling et al. 2006). Recent work by our Sierra team utilized information from 71 different bird species that breed in Sierra forests, and showed that more species had their highest abundances in habitats that had burned at moderate and high severity, compared with habitats that had experienced low-severity fires or logging, and especially compared with habitats that have had no recent disturbances (Roberts et al. 2021).
Several Sierra bird species are fire-specialists, utilizing habitat that has burned at moderate to high-severity within the first several years following the fire, and then moving on to newly available post-fire locations (for example: Black-backed Woodpecker, Western Bluebird, Lazuli Bunting), while other species that have evolved to capitalize on the increasingly tall shrubs and young-trees take their place years later (Fox Sparrow, House Wren, and Green-tailed Towhee). Because of the large number of study locations we are monitoring, we are able to also identify species that are more likely to thrive after low-severity fires (Red-breasted Sapsucker, Chipping Sparrow, Black-throated Gray Warbler in the short term; White-breasted Nuthatch, Western Wood-Pewee, Gray Flycatcher in the longer term). The authors concluded that fire can’t be replicated by logging or fuels treatments in the Sierra because the ecosystem, including the bird community, has evolved over millions of years to respond with specific sensitivity to a diversity of fire intensities and histories.
The word “pyrodiversity” was introduced in 1992 in a paper titled “Fires as agents of biodiversity; pyrodiversity promotes biodiversity” (Martin and Sapsis 1992) and has been gaining usage in recent years. It is important to understand that fire is a natural part of the ecosystem but also that it has been manipulated for thousands of years and that it interacts in complex ways with the effects of climate change, invasive species, and of course human use including habitation and recreation. Point Blue’s long-term studies of bird populations across the Sierra are the definitive reference for ecosystem responses to all of these factors during this time of rapidly shifting baselines. Our findings suggest that forest managers should prescribe and allow fires of varying intensities to burn in the Sierra in order to maximize biodiversity, when it is safe to do so.
References
Martin RE, Sapsis DB. 1992. Fires as agents of biodiversity: pyrodiversity promotes biodiversity. In Proc. of the Symp. on Biodiversity in Northwestern California, 1991 (ed. Kerner HM), pp. 150–157. Berkeley, CA: Wildland Resources Centre, University of California.
Roberts, L.J., Burnett, R.D., Fogg, A.F. 2021. Fire and Mechanical Forest Management Treatments Support Different Portions of the Bird Community in Fire Suppressed Forests. Forests 12, 150.
Westerling, A.L.; Hidalgo, H.G.; Cayan, D.R.; Swetnam, T.W. 2006. Warming and earlier spring increase western US forest wildfire activity. Science 313, 940–943