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Boulder City, NV, United States

Abella S.R.,National Park Service | Abella S.R.,Natural Resource Conservation LLC
Invasive Plant Science and Management

The United States created national parks to conserve indigenous species, ecological processes, and cultural resources unimpaired for future generations. Curtailing impacts of exotic species is important to meeting this mission. This synthesis identified 56 studies reported in 60 publications that evaluated effects of exotic plant treatments on National Park Service lands. Studies encompassed 35 parks in 20 states and one U.S. territory and included 157 exotic plant species. Eighty-seven percent of studies reported that at least one treatment reduced focal exotic species. Of 30 studies evaluating response of native vegetation, 53% reported that natives increased, 40% reported neutral responses, and 7% reported that natives decreased. For at least some of the neutral cases, neutrality was consistent with management objectives. In other cases, insufficient time may have elapsed to thoroughly characterize responses, or restoration might be needed. Nonfocal exotic species increased in 44% of the 16 studies evaluating them, but the other 56% of studies reported no increase. Results suggest that: (1) a range of exotic species spanning annual forbs to trees have been effectively treated; (2) developing effective treatments often required extensive experimentation and balancing nontarget impacts; (3) presence of multiple exotic species complicated treatment efforts, highlighting importance of preventing invasions; and (4) placing treatment objectives and outcomes in context, such as pretreatment condition of native vegetation, is important to evaluating effectiveness. Attaining the goal in national parks of conserving native species and ecological processes minimally influenced by exotic species will likely require comprehensive management strategies inclusive of treatment interactions with focal exotic species, other potential invaders, and native species. © 2013 Weed Science Society of America. Source

Abella S.R.,Natural Resource Conservation LLC | Chiquoine L.P.,University of Nevada, Las Vegas | Newton A.C.,National Park Service | Vanier C.H.,University of Nevada, Las Vegas
Journal of Arid Environments

Effective restoration techniques are needed in many arid lands for reversing degradation and desertification. In the Mojave Desert of the American Southwest, we tested experimental techniques for enhancing survival of salvaged perennial plants and their establishment on severely disturbed sites. Rooting hormone, slurry, and soaking treatments were ineffective at enhancing plant survival of salvage. Survival of salvaged plants after one year of nursery care was 48% (1017 of 2105 plants). Of these survivors, 50% survived 27mo after transplanting back to field restoration sites. On restoration sites, irrigation increased transplant survival by 50% (DRiWATER, a slow-release gel) and 79% (hand watering), compared to no irrigation (35% survival). Providing salvaged topsoil as a growth medium, without irrigation, doubled survival, nearly equivalent to irrigating plants. Survival varied by an order of magnitude across 23 species, and species amenable to salvage also generally survived transplanting to field sites (r=0.82 between salvage and transplant survival). Selecting species amenable to restoration and identifying treatments effective at enhancing survival can reestablish native perennial plants, often considered a first step in restoring desert ecosystems. © 2015 Elsevier Ltd. Source

Abella S.R.,University of Nevada, Las Vegas | Abella S.R.,Natural Resource Conservation LLC | Chittick K.L.,University of Nevada, Las Vegas
Journal of the Botanical Research Institute of Texas

Woodlands of Acacia greggii, Prosopis glandulosa, and Prosopis pubescens are of conservation-priority in the Mojave Desert because of their wildlife and watershed values. We measured plant community composition, environmental variables (e.g., slope gradient, soil), and ecological condition (e.g., tree recruitment) in 50, 0.1-ha woodland plots within 449, 000-ha Lake Mead National Recreation Area in the eastern Mojave Desert in Arizona-Nevada. We classified community types, analyzed vegetation-environment relationships, developed ecological species groups (species sharing similar distributions), and evaluated woodland condition. Cluster analysis identified 5 community types at the finest hierarchical level, which were quite distinct floristically (53% mean Sorensen similarity within communities), and included an A. greggii community occupying dry washes, 2 P. glandulosa communities, a mixed community, and a P. pubescens community inhabiting drainage outflows of springs. We recorded a total of 201 taxa. Mean species richness varied significantly among communities from 10 in P. pubescens to 35 species/0.1 ha in mixed communities. Environmental variables such as soil texture and cations were related to community gradients, distributions of tree species, and frequency of the tree parasite desert mistletoe (Phoradendron californicum). We classified 73 species into 14 species groups, ranging from groups characteristic of uplands (e.g., Larrea tridentata group) to those most frequent in lowlands (e.g., Allenrolfea occidentalis group). Ecological condition of the woodlands was characterized by well-distributed tree density among size classes (except for P. pubescens communities which were dominated by large trees), dominance by native species (94% of total taxa were native), mistletoe infection on 66% of plots, and infrequent evidence of perceived threats (e.g., woodcutting). Source

Abella S.R.,Natural Resource Conservation LLC | Crouse J.E.,Northern Arizona University | Covington W.W.,Northern Arizona University | Springer J.D.,Northern Arizona University
Restoration Ecology

A major challenge to advancing the science and practice of ecological restoration is working across large landscapes containing diverse sites that may respond differently to restoration. We conducted a 5-year restoration experiment, replicated across 9 sites spanning 3 soil parent material types within a 9,000-ha Pinus ponderosa forest landscape. We evaluated plant community response to restoration Pinus thinning, grazing, and aqueous smoke application. We measured vegetation before (2003) and 3 (2006) and 5 (2008) years after treatment. Plant community responses of species richness, cover, and composition were diverse, ranging from increases, decreases, or no change depending on soil parent material, tree thinning, and presence or exclusion of grazing. Restoration outcomes were under hierarchical control: soil parent material constrained response to Pinus thinning, which in turn influenced grazing effects. On limestone-derived soil, responses included no change in species richness but increased plant cover with Pinus thinning. Both plant richness and cover increased on benmorite soil after thinning, and cover generally increased more without grazing. On rocky, basalt soil, plant richness increased but cover did not after any treatment. Diversity of responses to restoration has implications for: (1) setting goals or monitoring indicators tailored to inherent soil capability; (2) identifying where grazing most affects restoration outcomes; and (3) forecasting responses to restoration across landscapes. Diverse responses to restoration along physiographic gradients such as soil parent material warrant consideration when developing restoration across degraded landscapes. © 2014 Society for Ecological Restoration. Source

Abella S.R.,Natural Resource Conservation LLC | Springer J.D.,Northern Arizona University
Forest Ecology and Management

Mixed conifer forests of western North America are challenging for fire management, as historical fire regimes were highly variable in severity, timing, and spatial extent. Complex fire histories combined with site factors and other disturbances, such insect outbreaks, led to great variation in understory plant communities, and management activities influence future dynamics of both overstory and understory communities. This variation needs to be considered as part of ecosystem-scale efforts to influence future fires and restore the composition and structure of mixed conifer forests. We undertook a systematic review of published studies evaluating effects of tree cutting and fire on understory vegetation in western North American mixed conifer forests. Forty-one studies, published in 50 articles, met inclusion criteria and encompassed projects in seven states in the USA and British Columbia in Canada. Total understory plant abundance (cover, biomass, or density) commonly declined in the short term within 4years after treatment. This may result from damage to plants during tree cutting operations or fire, heavy loadings of slash, little change or even expansion of tree canopies after low-intensity treatments, herbivory, or drought. In contrast, all 7 studies measuring understories longer than 5years since treatment reported increases in understory metrics. Treatments in these long-term studies also persistently decreased tree canopy cover. Most or all native species endured (even if reduced in abundance) through cutting operations or fire. A model of understory response has emerged that treatments generally do not eliminate species, and often benefit species absent or uncommon in untreated forest. Groups of native species (e.g., Epilobium spp.) appear fire-dependent, because they are uncommon or absent in unburned mixed conifer forests and after tree cutting alone. Cutting and prescribed fire applied together resulted in the greatest invasion of non-native plants, but non-native cover was minimal compared to native cover. Few studies examined influences of intensity of tree cutting or severity of prescribed fire, but overstory-understory relationships suggest that treatments must substantially reduce overstory density from maximum values (which can exceed 3000stemsha-1 and 80m2ha-1 basal area) and tree canopy cover to <30-50% cover to elicit appreciable responses from the forest understory. Few studies examined understory dynamics after wildfire relative to unburned forest, and further work is warranted because wildfire is a likely eventual outcome of passive management in these forests. Across a broad region from the southwestern United States into Canada, prescribed fire and tree cutting consistently increased disturbance-promoted native species in the short term and total understory abundance in the long term. Active management using tree cutting and fire will likely benefit both biodiversity conservation and fire management in current mixed conifer forests. © 2014 Elsevier B.V. Source

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