Chad T. Hanson

Examining historical and current mixed-severity fire regimes in ponderosa pine and mixed-conifer forests of Western North America

There is widespread concern that fire exclusion has led to an unprecedented threat of uncharacteristically severe fires in ponderosa pine (Pinus ponderosa Dougl. ex. Laws) and mixed-conifer forests of western North America. These extensive montane forests are considered to be adapted to a low/moderate-severity fire regime that maintained stands of relatively old trees. However, there is increasing recognition from landscape-scale assessments that, prior to any significant effects of fire exclusion, fires and forest structure were more variable in these forests. Biota in these forests are also dependent on the resources made available by higher-severity fire. A better understanding of historical fire regimes in the ponderosa pine and mixed-conifer forests of western North America is therefore needed to define reference conditions and help maintain characteristic ecological diversity of these systems. We compiled landscape-scale evidence of historical fire severity patterns in the ponderosa pine and mixed-conifer forests from published literature sources and stand ages available from the Forest Inventory and Analysis program in the USA. The consensus from this evidence is that the traditional reference conditions of low-severity fire regimes are inaccurate for most forests of western North America. Instead, most forests appear to have been characterized by mixed-severity fire that included ecologically significant amounts of weather-driven, high-severity fire. Diverse forests in different stages of succession, with a high proportion in relatively young stages, occurred prior to fire exclusion. Over the past century, successional diversity created by fire decreased. Our findings suggest that ecological management goals that incorporate successional diversity created by fire may support characteristic biodiversity, whereas current attempts to “restore” forests to open, low-severity fire conditions may not align with historical reference conditions in most ponderosa pine and mixed-conifer forests of western North America.

Overestimation of Fire Risk in the Northern Spotted Owl Recovery Plan

The U.S. Fish and Wildlife Services recent recovery plan for one of the most carefully watched threatened species worldwide, the Northern Spotted Owl (Strix occidentalis caurina), recommended a major departure in conservation strategies in the northwestern United States. Due to concern about fire, the plan would switch from a reserve to a no-reserve strategy in up to 52% of the owls range. Fuel treatments (e.g., thinning) at regular intervals also would occur on up to 65-70% of dry forests in this area. Estimations of fire risk, however, were based on less than a decade of data and an anecdotal assessment of a single, large fire. We found that decadal data are inherently too short, given infrequent large fires, to accurately predict fire risk and trends. Rates of high-severity fire, based on remote-sensing data, are far lower than reported in the plan and in comparison with the rate of old-forest recruitment. In addition, over a 22-year period, there has been no increase in the proportion of high-severity fire. Our findings refute the key conclusions of the plan that are the basis for major changes in conservation strategies for the Spotted Owl. The best available science is needed to address these strategies in an adaptive-management framework. From the standpoint of fire risk, there appears to be ample time for research on fire and proposed treatment effects on Spotted Owls before designing extensive management actions or eliminating reserves.

Complex Early Seral Forests of the Sierra Nevada: What are They and How Can They Be Managed for Ecological Integrity?

ABSTRACT: Complex early seral forests (CESFs) occupy potentially forested sites after a stand-replacement disturbance and before re-establishment of a closed-forest canopy. Such young forests contain numbers and kinds of biological legacies missing from those produced by commercial forestry operations. In the Sierra Nevada of California, CESFs are most often produced by mixed-severity fires, which include landscape patches burned at high severity. These forests support diverse plant and wildlife communities rarely found elsewhere in the Sierra Nevada. Severe fires are, therefore, essential to the regions ecological integrity. Ecologically detrimental management of CESFs, or unburned forests that may become CESFs following fire, is degrading the regions globally outstanding qualities. Unlike old-growth forests. CESFs have received little attention in conservation and reserve management. Thus, we describe important ecological attributes of CESFs and distinguish them from early serai conditions created by logging. We recommend eight best management practices in CESFs for achieving ecological integrity on federal lands in the mixed-conifer region of the Sierra Nevada.

Postfire Woodpecker Foraging in Salvage-Logged and Unlogged Forests of the Sierra Nevada

Abstract In forests, high-severity burn patches—wherein most or all of the trees are killed by fire—often occur within a mosaic of low- and moderate-severity effects. Although there have been several studies of postfire salvage-logging effects on bird species, there have been few studies of effects on bird species associated with high-severity patches in forests that have otherwise burned at lower severities. From 2004 to 2006, we investigated the foraging presence or absence of three woodpecker species, the Black-backed (Picoides arcticus), Hairy (P. villosus), and White-headed (P. albolarvatus) Woodpeckers, within four different forest habitat conditions in Sierra Nevada conifer forests: unburned; moderate-severity and unlogged; high-severity and unlogged; and high-severity and logged. We found Black-backed Woodpecker foraging was restricted to unlogged high-severity patches. Hairy Woodpeckers foraged most in unlogged high-severity patches, and White-headed Woodpeckers showed no significant difference in presence among conditions. These results suggest that unlogged, high-severity forest is important habitat for the Black-backed and Hairy Woodpeckers.

Is fire severity increasing in the Sierra Nevada, California, USA?

Research in the Sierra Nevada range of California, USA, has provided conflicting results about current trends of high-severity fire. Previous studies have used only a portion of available fire severity data, or considered only a portion of the Sierra Nevada. Our goal was to investigate whether a trend in fire severity is occurring in Sierra Nevada conifer forests currently, using satellite imagery. We analysed all available fire severity data, 1984-2010, over the whole ecoregion and found no trend in proportion, area or patch size of high-severity fire. The rate of high-severity fire has been lower since 1984 than the estimated historical rate. Responses of fire behaviour to climate change and fire suppression may be more complex than assumed. A better understanding of spatiotemporal patterns in fire regimes is needed to predict future fire regimes and their biological effects. Mechanisms underlying the lack of an expected climate- and time since fire-related trend in high-severity fire need to be identified to help calibrate projections of future fire. The effects of climate change on high-severity fire extent may remain small compared with fire suppression. Management could shift from a focus on reducing extent or severity of fire in wildlands to protecting human communities from fire.

Influence of Pre-Fire Tree Mortality on Fire Severity in Conifer Forests of the San Bernardino Mountains, California

High tree mortality due to drought and insects often is assumed to increase fire severity once ignition occurs. In 2002-2003, coniferous forests in the San Bernardino Mountains, California experienced a significant tree mortality event due to drought and an outbreak of western pine beetles (Dendroctonus brevicomis). In October 2003, fire burned approximately 5,860 ha of conifer forest types in many beetle- and drought-affected stands where most pre-fire dead trees had retained needles. We used pre- and post-fire GIS data to examine how fire severity was affected by pre-fire tree mortality, vegetation characteristics, and topography. We found no evidence that pre-fire tree mortality influenced fire severity. These results indicate that widespread removal of dead trees may not effectively reduce higher-severity fire in southern Californias conifer forests. We found that sample locations dominated by the largest size class of trees (>61 cm diameter at breast height (dbh)) burned at lower severities than locations dominated by trees 28-60 cm dbh. This result suggests that harvesting larger-sized trees for fire-severity reduction purposes is likely to be ineffective and possibly counter-productive.

Projecting Impacts of Fire Management on a Biodiversity Indicator in theSierra Nevada and Cascades, USA: The Black-Backed Woodpecker

In the Sierra Nevada and southern Cascade ranges of California and Oregon, a genetically distinct population of the black-backed woodpecker has become rare due, in part, to fire suppression. This species is considered an indicator species for its primary habitat: early successional burned forests with an abundance of standing dead trees. Fuel reduction treatments such as post-fire logging, and forest thinning prior to fire (by creating insufficient snag density and enhancing fire suppression), may further reduce this habitat, but this has not been quantified. Our goal here is to address this information gap. Specifically, we first quantified the impacts of fire suppression and fuel treatments on primary habitat for the black-backed woodpecker. Our objective in this paper was to address how fire management affects the primary habitat of the black-back woodpecker and associated species in the Sierra Nevada and Cascades. We found that fire suppression was associated with a dramatic reduction in stand-initiation processes, a proxy for tree mortality, since the 1930s on public lands. We additionally found that thinning and post-fire clear cutting each exacerbated the effects of fire suppression by reducing primary habitat at an approximately 1:1 ratio with area treated. A scenario based on thinning 20 percent of mature forests over a 20 year period, and post-fire logging in 33% of potential habitat created by fire, reduced the amount of primary habitat after 27 years to 30%of the amount that would occur without these treatments, assuming that modeled effects of the fuel treatments in controlling fire may be realized. Our results indicate that conserving the distinct population of black-backed woodpeckers in the southern Cascades and Sierra Nevada and the biodiversity for which they are an indicator will require that more unthinned area be burned by wildfires and protected after fire as critical habitat. Our results also show that restoration of fire to an extent closer to historical levels would considerably increase black-backed woodpecker habitat and have minimal tradeoff with conservation of mature forest.

Historical Forest Conditions within the Range of the Pacific Fisher and Spotted Owl in the Central and Southern Sierra Nevada, California, USA

ABSTRACT: There is significant debate about restoration targets for ponderosa pine (Pinus ponderosa) and mixed-conifer forests in the Sierra Nevada, California, USA. On one side are recommendations to create both extensive open and park-like pine forests, and to reduce high-severity fire occurrence by mechanical thinning of forests. These recommendations drive current management. On the other side are recommendations to manage landscapes for both dense, old forest, and complex early-seral forest that is created by both high-severity and moderate-severity fires characteristic of historical fire regimes. Our research suggests that the latter approach may best maintain forest associated with two imperiled species that are top management concerns of federal agencies in the Sierra Nevada: the California Spotted Owl (Strix occidentalis occidentalis) and the Pacific Fisher (Pekania pennanti). We used spatially extensive US Forest Service forest survey data from 1910 and 1911, and synthesized research from other parts of this region for comparison, to assess reference conditions in low/mid-elevation Sierra Nevada forests. We found that historical ponderosa pine and mixed-conifer forests had a mixed-severity fire regime, with an average of 26% high-severity fire effects, and varied more widely in species composition and density than suggested by previous research. Our findings are contrary to other reports using a very small subset (∼6%) of the available data from these same 1910 and 1911 surveys. Therefore, we suggest that historical reference conditions of forests in the Sierra Nevada range of these species are not like that reported previously in other studies, and that mixed-severity fire, and forests defined by strong contrasts and dynamic natural processes, were characteristic of historical ponderosa pine and mixed-conifer forests of the western Sierra Nevada. Our analysis indicates that managing for both dense, old forests, and protecting complex early-seral forest created by high-severity fire, will likely advance conservation and recovery of the Spotted Owl and Pacific Fisher, while current management direction may exacerbate threats.

Habitat Use of Pacific Fishers in a Heterogeneous Post-Fire and Unburned Forest Landscape on the Kern Plateau, Sierra Nevada, California

The Pacific fisher (Martes pennanti) is a rare forest carnivore strongly associated with dense, old forest with high canopy cover for denning and resting. The Sierra Nevada population is very small, genetically distinct, and isolated. Mixed-severity wildland fire is assumed to be a potentially greater threat than logging, and land managers are conducting large-scale forest thinning operations under the hypothesis that it is needed to reduce fire spread and severity. However, the relationship between fishers and fire has not been tested previously. I investigated this question with teams of dogs specially trained to detect the scat of Pacific fishers and, thus, their concentration of movements and habitat use. All scat samples were genetically verified. In surveys on the Kern Plateau in the southwestern Sierra Nevada, within unlogged post-fire forests with mixed-severity effects from large fires, and in unburned forests, I found that fishers selected Sierran mixed-conifer forests in both post-fire and unburned areas, and selected closed-canopied, mature/old forest in unburned forests, as well as burned forests that had this structure in the pre-fire condition. When fishers were near burned/unburned edges, they selected the within-fire side. Fishers used dense, mature/old forest that experienced moderate/high-severity fire at the same level as unburned dense, mature/old forest, and both males and females were found deep inside large fires—several km from the fire perimeter. These results indicate that fishers may benefit from the structural complexity of such post-fire habitat for foraging. This suggests mixed-severity wildland fire could be restored through managed wildland fire in these forests.

Sierra Nevada fire severity conclusions are robust to further analysis: a reply to Safford et al.

Safford et al. (this issue) question our earlier findings that fire severity has not increased in Sierra Nevada conifer forests 1984–2010, hypothesising that an increasing trend might have appeared had we restricted our analysis to wildland fire in frequent-fire forest types on US Forest Service lands. Here, we tested that hypothesis and again found no trend of increasing severity.