Wild fire hd drivers#
In seasonally dry western forests, fire severity (defined here as basal area mortality from fire) and frequency are major drivers of plant community structure and forest successional patterns (Diaz-Delgado et al. Forest managers need to understand what limits and promotes natural conifer regeneration in the postfire environment, especially following high severity fires, so that forests might be better managed for long-term sustainability and resilience in a changing world (Brown et al.
2012), potentially altering tree and woody shrub responses. 2011, Miller and Safford 2012, Safford et al. However, the frequency, size, and severity of wildfires across much of the western United States are increasing (Lenihan et al. Many plants in western US forests have evolved traits that allow them to persist in a variety of fire regimes, including fire-resistant bark, self-pruning limbs, and sexual and/or asexual regeneration (i.e., seeder and/or resprouter species Pausas et al. We developed a second model specifically for forest managers and restoration practitioners who work in yellow pine and mixed conifer forests in the central NAMCZ to assess potential natural regeneration in the years immediately following a fire, allowing them to prioritize which areas may need active postfire forest restoration and supplemental planting.įire plays an important ecological role in many forest ecosystems, including creation and maintenance of landscape structure, recycling of nutrients, biodiversity regulation, and both consumption and production of forest fuels (Agee 1993, Covington and Moore 1994, Sugihara et al. Seedling densities of conifer species were lowest in sites that burned at high severity, principally due to the biotic consequences of high severity fire, for example, increased distances to live seed trees and competition with fire-following shrubs. When regeneration did occur, it was dominated by shade-tolerant but fire-sensitive firs ( Abies spp.), Douglas-fir ( Pseudotsuga menziesii) and incense cedar ( Calocedrus decurrens). Ten of the 14 fires had median conifer seedling densities that did not meet Forest Service stocking density thresholds for mixed conifer forests.
Across all fires, 43% of all plots had no conifer regeneration. We specified a zero-inflated negative binomial mixed model with random effects to understand the importance of each measured variable in predicting conifer regeneration. We measured site characteristics, seedling densities, woody shrub, and tree growth. We established 1490 survey plots in 14 burned areas on 10 National Forests across a range of elevations, forest types, and fire severities in the central and northern NAMCZ to provide insight into factors that promote natural tree regeneration after wildfires and the differences in postfire responses of the most common conifer species. This is especially the case in the North American Mediterranean-climate zone (NAMCZ), which supports the highest precipitation variability in North America and a 4- to 6-month annual drought, and has seen greater-than-average increases in air temperature and fire activity over the last three decades. To a great extent, the future status of western US forests will depend on tree species’ responses to patterns and trends in fire activity and fire behavior and postfire management decisions. Due to fire suppression policies, timber harvest, and other management practices over the last century, many low- to mid-elevation forests in semiarid parts of the western United States have accumulated high fuel loads and dense, multi-layered canopies that are dominated by shade-tolerant and fire-sensitive conifers.
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