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)

“Liaisons dangereuses”: The invasive red-vented bulbul ( Pycnonotus cafer ), a disperser of exotic plant species in New Caledonia

International audienceThe biodiversity hotspot of New Caledonia hosts high levels of endemism (74% of flora) that is threatened increasingly by climate change, habitat reduction, and inva-sive species. The fruit-eating red-vented bulbul (Pycnonotus cafer) is currently invading the main island of the archipelago, and its recent dispersal out of urbanized habitats raises questions about its potential to disperse noxious plant seeds along urban corridors and beyond. Indeed, the red-vented bulbul is considered a vector of several introduced plant species in its alien range including Miconia calvescens, Lantana camara, and Schinus terebinthifolius. We conducted a quantitative assessment of the bulbul's fruits consumption by analyzing the gut contents of shot birds. We estimated gut passage times for four species of fruit found in gut contents (S. terebin-thifolius, Myrtastrum rufopunctatum, Passiflora suberosa, and Ficus prolixa) and tested the effects of bird digestion on seed germination rates for two species. Finally, we monitored the movements of individual VHF radio-tagged red-vented bulbuls. All of the consumed fruit species we identified here have red fleshy diaspore, including fruit of the shrub M. rufopunctatum that occurred frequently (9.6%) in bulbul gut samples. Median gut passage times were short (15-41 min), corresponding to short-distance seed transportation (77-92 m). The effect of gut passage was positive for the germination of the invasive S. terebinthifolius and negative for the endemic M. ru-fopunctatum, suggesting a potential bias in the contribution to the dispersal toward alien species. This study provides the first integrated assessment of mechanisms involved in the seed dispersal effectiveness of this high-concern invasive bird species that is expected to face similar plant communities in most of its alien range in tropical islands. More generally, our results enhance knowledge of synergies between non-native frugivores and plant species dispersal

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