Influences of Prior Wildfires on Vegetation Response to Subsequent Fire in a Reburned Southwestern Landscape

Abstract

Abstract. Large and severe wildfires have raised concerns about the future of forested landscapes in the southwestern United States, especially under repeated burning. In 2011, under extreme weather and drought conditions, the Las Conchas fire burned over several previous burns as well as forests not recently exposed to fire. Our purpose was to examine the influences of prior wildfires on plant community composition and structure, subsequent burn severity, and vegetation response. To assess these relationships, we used satellite-derived measures of burn severity and a nonmetric multidimensional scaling of pre-and post-Las Conchas field samples. Earlier burns were associated with shifts from forested sites to open savannas and meadows, oak scrub, and ruderal communities. These non-forested vegetation types exhibited both resistance to subsequent fire, measured by reduced burn severity, and resilience to reburning, measured by vegetation recovery relative to forests not exposed to recent prior fire. Previous shifts toward non-forested states were strongly reinforced by reburning. Ongoing losses of forests and their ecological values confirm the need for restoration interventions. However, given future wildfire and climate projections, there may also be opportunities presented by transformations toward fire-resistant and resilient vegetation types within portions of the landscape.

Characterizing Spatial Neighborhoods of Refugia Following Large Fires in Northern New Mexico USA

“…The species we observed included both forest and non-forest species that hold important traditional uses among Pueblo peoples, including Colorado barberry, Carruth's sagewort (Artemisia carruthii), ragleaf bahia (Bahia dissecta) and many others [37]. Grass and shrub species, present across the RG (Appendix A), are often found in the surrounding burned matrix and tend to persist through multiple fire events by rebounding quickly [18]. Where meadows and shrublands are protected from severe fire, these communities may harbor legacies, including seedbanks of obligate seeders (including the conifer trees found in the region), and may provide habitat for animal seed dispersers [34,76].…”

“…Progress of Las Conchas was rapid in the first day of burning (c; area shaded gray). We used field plot data from Coop et al (2016; c; red dots). Projection is the Albers Equal Area (units = m).…”

“…To characterize refugial plant communities, we used field data compiled in a recent study of upland vegetation patterns on the Las Conchas landscape [18]. Field data collection was done using sampling protocols in Muldavin et al [39]; cover was recorded in 20 × 20-m plots by species and strata (tree, woody plants ≥5 m; shrub, woody plants <5 m, including tree seedlings and saplings; graminoid; and forb).…”

“…For Dome and Cerro Grande, dNBR images were downloaded from the Monitoring Trends in Burn Severity website (http://mtbs.gov/). Details for La Mesa image processing (change in Normalized Difference Vegetation Index from pre-to post-fire (dNDVI)) are described in [18] and from Lisa Holsinger, US Forest Service, pers. com.…”

“…Dome and Cerro Grande RGs were derived using the same methods as Las Conchas, described above ( Table 2). Because La Mesa pre-dated Landsat Thematic Mapper, dNBR was predicted from Normalized Difference Vegetation Index (dNDVI) values derived using Multispectral Scanner Bands 3 and 4 [18]. We sampled the RGs within the older burn perimeters randomly, and at the 57 field plot locations and used this information to interpret the ordination results relative to past burn event.…”