by Michael Gallagher, Science & Technology committee
Monitoring fire effects is important for evaluating ecological outcomes of fire management efforts and refining silvicultural methods for maintaining and restoring healthy forests. While monitoring fire effects is conceptually straightforward (i.e. making observations of change due to fire), selecting the indicators of ecological change and measuring them at appropriate spatial and temporal scales is difficult and time consuming to the extent that such monitoring is rarely conducted. However, new indices for rapidly assessing burn severity are helping managers and ecologists improve their fire monitoring.
The term fire effects describes the collection of direct and indirect ecological impacts of wildland fire (e.g. prescribed fire or wild fire). Direct fire effects, known as first order fire effects, are those that occur during a fire event as a direct result of the chemical and physical processes of fire, such as the consumption of biomass, the girdling of cambium of flora, and the alteration of chemical and physical properties of soil (Reinhardt, Keane and Brown 2001). Second order fire effects, on the other hand, refer to those effects that require additional actions beyond the fire itself, such as the dispersal of smoke created by fire, blow downs of dead trees, and soil erosion. Regeneration, reinvasion, and new invasions of species are heavily dependent on these changes, inherent site conditions, and the conditions of the surrounding mosaic of vegetation patches.
Many studies — from across the country — have found that these difficult-to-monitor effects actually tend to be correlated with other fire effects that can easily be assessed using visual methods, or with satellite imagery. In these studies, effects that are difficult to measure are compared with visually-assessed burn severity indices, which are generated from observations of indicators such as soil, vegetation, and downed woody material (Key and Benson 2006). Outcomes of such studies have demonstrated rapid burn severity assessments can be used to predict changes in bird species occurrence (Rose et al. 2016), ungulate browsing habits (Bailey and Whitham 2002), and spatial patterns in regeneration of fire-dependent plants (Chambers et al. 2016, Lentile, Smith and Shepperd 2005).
The most common approach to rapidly assessing burn severity in the field is the Composite Burn Index method, which uses a field sheet to quantify qualitative change among indicators. This method is most useful in relatively small management units such as those managed by consulting foresters, where landscape-level change may not be a focus. Using this approach, initial assessments that are conducted in the days to weeks following fires are best for capturing first order fire effects, while extended assessments that are conducted in the months to years following fire are best suited for capturing second order fire effects. Where landscape-level fire effects are more important, remote sensing indices may provide the best results. While these indices don’t work in every vegetation type (such as grasslands), recent work by US Forest Service and West Virginia University found that both field- and remote-sensing methods produced very similar results in the NJ Pinelands, suggesting their utility there (Warner, Skowronski and Gallagher 2017). Although burn severity studies have not yet been published for other forest types in the northeast, the range of forest types that have been studied using burn severity indices suggest a strong potential for wider use.
Most recently the North Atlantic Fire Science Exchange hosted a 3-day workshop at the Albany Pine Bush Preserve in Albany, NY, where forest managers from around the region learned techniques for fire effects monitoring including the Composite Burn Index. In doing so, attendees observed how first order fire effects were best evaluated immediately after fire, while second order fire effects were more easily evaluated the following season after fire. Coverage and resources from this workshop are available online at the North Atlantic Fire Science Exchange’s website: http://firesciencenorthatlantic.org/. Likewise, the original USFS General Technical Report describing the Composite Burn Index and associate field sheet is from the US Forest Service at: https://www.fs.fed.us/rm/pubs/rmrs_gtr164/rmrs_gtr164_13_land_assess.pdf.
Bailey, J. K. & T. G. Whitham (2002) Interactions among fire, aspen, and elk affect insect diversity: reversal of a community response. Ecology, 83, 1701-1712.
Chambers, M. E., P. J. Fornwalt, S. L. Malone & M. A. Battaglia (2016) Patterns of conifer regeneration following high severity wildfire in ponderosa pine–dominated forests of the Colorado Front Range. Forest Ecology and Management, 378, 57-67.
Gallagher, M. R. In preparation. Monitoring Fire Effects in the New Jersey Pine Barrens with Burn severity Indices. Rutgers University Graduate School, New Brunswick.
Key, C. H. & N. C. Benson (2006) Landscape assessment (LA). FIREMON: Fire effects monitoring and inventory system. Gen. Tech. Rep. RMRS-GTR-164-CD, Fort Collins, CO: US Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Lentile, L. B., F. W. Smith & W. D. Shepperd (2005) Patch structure, fire-scar formation, and tree regeneration in a large mixed-severity fire in the South Dakota Black Hills, USA. Canadian Journal of Forest Research, 35, 2875-2885.
Reinhardt, E. D., R. E. Keane & J. K. Brown (2001) Modeling fire effects. International Journal of Wildland Fire, 10, 373-380.
Rose, E. T., T. R. Simons, R. Klein & A. J. McKerrow (2016) Normalized burn ratios link fire severity with patterns of avian occurrence. Landscape Ecology, 1-14.
Warner, T. A., N. S. Skowronski & M. R. Gallagher (2017) High spatial resolution burn severity mapping of the New Jersey Pine Barrens with WorldView-3 near-infrared and shortwave infrared imagery. International Journal of Remote Sensing, 38, 598-616.