Synthesis of Knowledge on the Effects of Fire and Thinning Treatments on Understory Vegetation in U.S. Dry Forests

A century of fire exclusion in dry forests across the United States has resulted in high fuel loads and increasing dominance by fire-intolerant vegetation. Federal, state, and private agencies have adopted a goal of managing forests to reduce the risk of high-severity wildfire. Forest managers use a variety of tools to create desired conditions within forests; the most common are prescribed fire and mechanical thinning. These two treatments may be used separately or in combination, depending on restoration goals for the forest stand. Before these treatments can be applied, managers must justify their choice by documenting the effects of the treatment on other ecosystem components, such as understory vegetation. Understory vegetation in fire-dominated landscapes often has adapted to regrowing in frequent, low-severity fire regimes. Because fire releases nutrients and, by opening the canopy, allows light to the forest floor, the understory response is positive (e.g., increased growth or reproduction). Scientific reviews of the literature document the effect of fire (prescribed and wildfire) on both native and exotic understory vegetation. However, no synthesis is available on the effects of thinning treatments on understory vegetation. One goal of this document is to synthesize the literature on the effects of mechanical thinning on understory plant species. A second goal is to document the effect of prescribed burning on rare, threatened, or endangered species. We review current literature on studies that address effects of prescribed fire and thinning treatments on understory vegetation. The studies’ outcomes are presented in two sets of tables: (1) functional group results, and (2) species-specific results. Managers often are interested in and need to report the effects of treatments on species; functional group responses can provide a clue to how a species might respond if no other information is available. In general, fire and thinning treatments increased response of understory species. More intense treatments, such as combined thin+burn treatments and greater thinning intensity, had the highest increases in cover and production. Thin-only and burn-only treatments had more moderate increases. In addition, most studies found exotic plants’ response increased as disturbance intensity increased; however, most studies report very low invasive presence even after the treatments. If one of the goals of the forest management plan is to increase presence or cover of understory species in general, then prescribed fire and thinning treatments may be a viable option to restore forest understory. Rare, threatened, and endangered species in dry forest environments often respond favorably to prescribed fires. Many of the species reported in this document increased in abundance or reproduction or were unaffected by fire, indicating that prescribed fire is compatible with (or beneficial for) restoration of these species. The results of this synthesis illustrate several important lessons. First, current forest structure is the result of decades of fire-suppression activities, and so restoration will require multiple treatments to bring forests to within the range of historic variation. Second, while the treatments discussed in this document generally increased native plant responses, the same treatments also increased exotic plant response. Therefore, to avoid spread of exotic plant species, it is important to consider the context of the treatment area, (e.g., nearby roads, wildland urban interface, previous exotic plant invasions) before applying the treatments. Third, applying thinning and prescribed burning treatments in a mosaic pattern of treatment time and type across the landscape will help to maintain a diversity of vegetation (e.g., early-, mid-, and late-successional species across the landscape)

Synthesis of knowledge on the effects of fire and thinning treatments on understory vegetation in U.S. dry forests

"... One goal of this document is to synthesize the literature on the effects of mechanical thinning on understory plant species. A second goal is to document the effect of prescribed burning on rare, threatened, or endangered species. We review current literature on studies that address effects of prescribed fire and thinning treatments on understory vegetation ... The results of this synthesis illustrate several important lessons. First, current forest structure is the result of decades of fire-suppression activities, and so restoration will require multiple treatments to bring forests to within the range of historic variation. Second, while the treatments discussed in this document generally increased native plant responses, the same treatments also increased exotic plant response. Therefore, to avoid spread of exotic plant species, it is important to consider the context of the treatment area, (e.g., nearby roads, wildland urban interface, previous exotic plant invasions) before applying the treatments. Third, applying thinning and prescribed burning treatments in a mosaic pattern of treatment time and type across the landscape will help to maintain a diversity of vegetation (e.g., early-, mid-, and late-successional species across the landscape)."--Summary.Published September 2009. Reviewed December 2013. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalo

Stable occupancy by breeding hawks (Buteo spp.) over 25 years on a privately managed bunchgrass prairie in northeastern Oregon, USA

Potential for large prairie remnants to provide habitat for grassland-obligate wildlife may be compromised by nonsustainable range-management practices. In 1979–1980, high nesting densities of 3 species of hawks in the genus Buteo—Ferruginous Hawk (Buteo regalis), Red-tailed Hawk (B. jamaicensis), and Swainson’s Hawk (B. swainsoni)—were documented on the Zumwalt Prairie and surrounding agricultural areas (34,361 ha) in northeastern Oregon, USA. This area has been managed primarily as livestock summer range since it was homesteaded. Unlike in other prairie remnants, land management on the Zumwalt Prairie was consistent over the past several decades; thus, we predicted that territory occupancy of these 3 species would be stable. We also predicted that territory occupancy would be positively related to local availability of nesting structures within territories. We evaluated these hypotheses using a historical dataset, current survey and habitat data, and occupancy models. In support of our predictions, territory occupancy of all 3 species has not changed over the study period of ~25 yr, which suggests that local range-management practices are not negatively affecting these taxa. Probability of Ferruginous Hawk occupancy increased with increasing area of aspen, an important nest structure for this species in grasslands. Probability of Swainson’s Hawk occupancy increased with increasing area of large shrubs, and probability of Red-tailed Hawk occupancy was weakly associated with area of conifers. In the study area, large shrubs and conifers are commonly used as nesting structures by Swainson’s Hawks and Red-tailed Hawks, respectively. Availability of these woody species is changing (increases in conifers and large shrubs, and decline in aspen) throughout the west, and these changes may result in declines in Ferruginous Hawk occupancy and increases in Swainson’s Hawk and Red-tailed Hawk occupancy in the future.Keywords: Historical data, Grassland birds, Redtailed Hawk, Raptor, Occupancy modeling, Ferruginous Hawk, Nesting habitat, Swainson’s Haw

Effects of Landscape Characteristics on Annual Survival of Lesser Prairie-Chickens

Agriculture and development have caused landscape change throughout the southwestern Great Plains in the range of the lesser prairie-chicken (Tympanuchus pallidicinctus). Landscape alteration within the lesser prairie-chicken range may contribute to range contraction and population losses through decreases in survival rates. Our objectives were to determine if: (1) landscape configuration (i.e., the spatial arrangement of habitat) or composition (i.e., the amount of habitat), at the study-site scale, affected annual survival of females, (2) relationships exist between landscape context (i.e., landscape configuration and composition) and weekly survival to assess effects of landscape composition and configuration on lesser prairie-chicken populations, and (3) anthropogenic features influenced daily mortality risk. We captured 170 female lesser prairie-chickens and used very-high-frequency and GPS (Global Positioning System) transmitters to track their movement and survival for 2 y. We used known-fate survival models to test if landscape configuration or composition within three sites in Kansas were related to differences in female survival among sites. In addition we tested for relationships between weekly survival and landscape configuration or composition within home ranges. Finally, we used Andersen-Gill models to test the influence of distance to anthropogenic features on daily mortality risk. Differences in survival were evident between sites with differing landscape compositions as annual survival in Northwestern Kansas (ˆS ¼ 0.27) was half that of Clark County, Kansas (ˆS ¼0.56), which corresponded with 41.9% more grassland on the landscape in Clark County; landscape configuration did not measurably differ among sites. Survival was greater for prairie-chickens with home-ranges that had greater patch richness and in areas with 30% crop and 57% grassland. Female lesser prairie-chickens also experienced greater mortality risk closer to fences at patch edges. Further conversion of grassland landscapes occupied by lesser prairie-chickens should be avoided to reduce habitat loss and fragmentation thresholds that could affect survival. We suggest continued encouragement of Conservation Reserve Program enrollment in western areas of the lesser prairie-chicken range to maintain or increase the amount of grassland to increase annual survival.acceptedVersio