Tamm Review: Management of mixed-severity fire regime forests in Oregon, Washington, and Northern California

Abstract

a b s t r a c tIncreasingly, objectives for forests with moderate-or mixed-severity fire regimes are to restore successionally diverse landscapes that are resistant and resilient to current and future stressors. Maintaining native species and characteristic processes requires this successional diversity, but methods to achieve it are poorly explained in the literature. In the Inland Pacific US, large, old, early seral trees were a key historical feature of many young and old forest successional patches, especially where fires frequently occurred. Large, old trees are naturally fire-tolerant, but today are often threatened by dense understory cohorts that create fuel ladders that alter likely post-fire successional pathways. Reducing these understories can contribute to resistance by creating conditions where canopy trees will survive disturbances and climatic stressors; these survivors are important seed sources, soil protectors, and critical habitat elements. Historical timber harvesting has skewed tree size and age class distributions, created hard edges, and altered native patch sizes. Manipulating these altered forests to promote development of larger patches of older, larger, and more widely-spaced trees with diverse understories will increase landscape resistance to severe fires, and enhance wildlife habitat for underrepresented conditions.Closed-canopy, multi-layered patches that develop in hot, dry summer environments are vulnerable to droughts, and they increase landscape vulnerability to insect outbreaks and severe wildfires. These same patches provide habitat for species such as the northern spotted owl, which has benefited from increased habitat area. Regional and local planning will be critical for gauging risks, evaluating trade-offs, and restoring dynamics that can support these and other species. The goal will be to manage for heterogeneous landscapes that include variably-sized patches of (1) young, middle-aged, and old, closedcanopy forests growing in upper montane, northerly aspect, and valley bottom settings, (2) a similar diversity of open-canopy, fire-tolerant patches growing on ridgetops, southerly aspects, and lower montane settings, and (3) significant montane chaparral and grassland areas. Tools to achieve this goal http://dx

Tree Regeneration Spatial Patterns in Ponderosa Pine Forests Following Stand-Replacing Fire: Influence of Topography and Neighbors

“…If managers choose to augment natural regeneration, patterns of naturally recovering landscapes can inform efforts to address deficiencies [58] and enhance recovery [59]. Plantings should reinforce local patterns of fine-scale heterogeneity [12], such as those we found, leveraging both topographic gradients and presence of facilitatory woody plants [16].…”

“…The mixture and frequency of severities were significantly spatially variable over landscapes, influenced by complex topography, and over decades, influenced by broad-scale climatic oscillations [28]. Though there is some debate as to the relative historical portion and patch sizes of fire severities across these landscapes [31], it is generally accepted that high-severity fires were not historically as common in extent or occurrence as today [12].…”

Effects of accelerated wildfire on future fire regimes and implications for the United States federal fire policy

“…Although areas of dense multilayered forests were preserved under historical fire regimes because of their topographic positions and climate (Camp et al 1997), accelerated wildfire scenarios we simulated burned through these areas. Refining the simulations to increase the frequency of lower severity fire specifically could lead to the development of forest structure and composition that is resilient to fire and climate change (Hessburg et al 2016). Although Davis et al (2016) found that NSO habitat in the eastern Cascades of Oregon actually increased by 13% between 1993 and 2012, a single large fire within the study area could reverse this trend.…”

Bridging the Divide: Integrating Animal and Plant Paradigms to Secure the Future of Biodiversity in Fire-Prone Ecosystems

“…In Australia, South Africa, and increasingly in Europe and South America, patch-mosaic burning or planned burning have been implemented [3,6]. In North America, there has been a strong focus on restoration of fire regimes to historical conditions [1,16], and, more recently, on encouraging natural patterns of ignitions that result in mixed-severity fires [17]. The fire mosaic paradigm and pyrodiversity hypothesis have been criticized for their simplistic representation of fire regimes and animal habitat [2,3].…”

“…Under the EBVs framework, six dimensions of biodiversity have been identified-including genetic composition, species population, species traits, community composition, ecosystem function, and ecosystem structure-to assess biodiversity change [20]. As a first step, essential variables used to inform knowledge of species persistence in fire-prone landscapes could include the occurrence and abundance of animals and plants at key life stages [13], traits that mediate fire responses at different levels of ecological organization [15], and elements of habitat structure, such as tree size and density [17]. Systematic measures of species occurrence or abundance could be pooled to provide multi-species indicators of biodiversity, and models used to extrapolate observations from sites to landscapes.…”