Woody vegetation in grasslands and savannas has increased worldwide over the past 100-200 years. This phenomenon of "woody plant encroachment" (WPE) has been documented to occur at different times but at comparable rates in rangelands of the Americas, Australia, and southern Africa. The objectives of this chapter are to review (1) the process of WPE and its causes, (2) consequences for ecosystem function and the provision of services, and (3) the effectiveness of management interventions aimed at reducing woody cover. Explanations for WPE require consideration of multiple interacting drivers and constraints and their variation through time at a given site. Mean annual precipitation sets an upper limit to woody plant cover, but local patterns of disturbance (fire, browsing) and soil properties (texture, depth) prevent the realization of this potential. In the absence of these constraints, seasonality, interannual variation, and intensity of precipitation events determine the rate and extent of woody plant expansion. Although probably not a triggering factor, rising atmospheric CO 2 levels may have favored C 3 woody plant growth. WPE coincided with the global intensification of livestock grazing that by reducing fine fuels, hence fire frequency and intensity, facilitated WPE. From a conservation perspective, WPE threatens the maintenance of grassland and savanna

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To assess the consequences of increased recreational activity in wilderness areas, we studied the effects of human activity on breeding behavior of Bald Eagles (Haliaeetus leucocephalus) in interior Alaska. Activity budgets of breeding eagles changed considerably when humans were camped for 24 h at a distance of 100 m from nests (treatment) compared to when they were camped 500 m from nests (control) (P ϭ 0.0036). With humans near nests, adult eagles decreased the time they preened (percentage change from control to treatment ϭ Ϫ53%), slept (Ϫ56%), maintained nests (Ϫ50%), and fed themselves and their nestlings (Ϫ30%) and increased the time they brooded nestlings (ϩ14%). Further, overall activity (total number of behaviors performed by adults at nests per day) decreased by 27% with humans near nests, as did the amount of prey adults consumed (Ϫ26%) and fed to nestlings (Ϫ29%). In contrast, nest attendance did not change with humans near nests (percentage change ϭ 0.3%, P ϭ 0.9); however, the time adults were absent from the nest area (Ն200 m from nests) increased by 24% with humans near nests (P ϭ 0.013). Throughout 24-h treatments, eagle responses to nearby humans diminished, suggesting that eagles habituated to the disturbance. During the last 4 h of treatment, however, adults still vocalized twice as frequently as controls, indicating continued agitation. Human activity near nests caused clear and consistent changes in behaviors of breeding eagles, suggesting that frequent human activities near nests could adversely affect nestling survival, and therefore reproductive success.

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Contrast in vegetation composition and structure between 2 nearby areas of semi-desert grassland, 1 dominated by native grasses (top) and 1 dominated by a nonnative grass, Eragrostis lehmanniana (bottom). Photo by our friend and colleague, Eric Albrecht, who studied songbirds on these grasslands as part of his M.S. degree, and who died in 2004.ABSTRACT Invasions by nonnative plants have changed the structure of many terrestrial ecosystems and altered important ecological processes such as fire, the dominant driver in grassland ecosystems. Reestablishing fire has been proposed as a mechanism to restore dominance of native plants in grasslands invaded by nonnative plants, yet fire may function differently in these altered systems, potentially affecting animals in novel ways. To assess whether invasions by nonnative plants alter the effects of fire on animals, we performed a manipulative experiment in semi-desert grasslands of southeastern Arizona that have been invaded by a perennial, nonnative grass from Africa, Lehmann lovegrass (Eragrostis lehmanniana). We applied fire to 36 of 54 1-ha plots established along an invasion gradient where dominance of E. lehmanniana ranged from 0% to 91% of total live plant biomass. Over the 5-year period from 2000 to 2004, we used mark-recapture methods to assess how population and community attributes of small mammals varied along the gradient of nonnative grass and in response to fire. We quantified changes in presence of 17 species, abundance of 9 species, total abundance of all species combined, species richness, and species composition. Based on 11,226 individual mammals from 24 species, we found that effects of nonnative-grass dominance varied with habitat preferences of each species, resulting in composition of the small-mammal community changing predictably along the invasion gradient. As dominance of nonnative grass increased, presence and abundance of granivorous heteromyids and insectivores (e.g., Chaetodipus, Perognathus, Onychomys; pocket mice and grasshopper mice) decreased, whereas presence and abundance of omnivorous and herbivorous murids (e.g., Reithrodontomys, Sigmodon; harvest mice and cotton rats) increased. Species richness of the small-mammal community averaged 8.4 species per plot and was highest at intermediate levels of nonnative-grass dominance where vegetation heterogeneity was greatest. Abundance of all small mammals combined averaged 26.9 individuals per plot and did not vary appreciably with nonnative-grass dominance. During the 4-to 8-week period immediately after fire, abundance of 6 of the 9 most common species changed, with 5 species decreasing and 1 species increasing on burned plots relative to unburned plots. During this same time period, species richness of small mammals decreased by an average of 3 species (38%) and total abundance of all species combined decreased by an average of 16 individuals (61%) on burned plots relative to unburned plots. Effects of fire on vegetation biomass, on presence of 9 of 17 mammalian species, and on abundance...

Human activity in caves can affect bats adversely, especially bats that assemble in maternity colonies where appropriate roosts are restricted to areas with a narrow range of microclimates necessary to raise young. We assessed behavioral responses of a maternity colony of about 1 , 000 cave myotis (Myotis velifer) to experimental cave tours by manipulating 3 factors: size of tour groups, whether tour groups talked, and a combination of light intensity and color used to illuminate trails. We also considered the effects of distances between bat roosts and the tour group as well as season. We measured 4 behavioral responses of bats: number of takeoffs, number of landings, activity level, and vocalization intensity. Light intensity affected bat behavior most; all bat responses were highest in trials with high-intensity white light and lowest in trials with no light. When tour groups talked, takeoffs, landings, and activity level increased. Size of tour groups and treatment interactions did not affect bat behaviors. When bats roosted near the tour route, takeoffs and activity level increased. In addition, all behavioral responses increased as the maternity season progressed. Designing cave tours to minimize short-term effects on bats will require careful consideration of cave lighting and tour frequency, route location, and noise levels.

Effective conservation requires strategies to monitor populations efficiently, which can be especially difficult for rare or elusive species where field surveys require high effort and considerable cost. Populations of many reptiles, including Sonoran desert tortoises (Gopherus agassizii), are challenging to monitor effectively because they are cryptic, they occur at low densities, and their activity is limited both seasonally and daily. We compared efficiency and statistical power of 2 survey methods appropriate for tortoises and other rare vertebrates, linetransect distance sampling and site occupancy. In 2005 and 2006 combined, we surveyed 120 1-km transects to estimate density and 40 3-ha plots 5 times each to estimate occupancy of Sonoran desert tortoises in 2 mountain ranges in southern Arizona, USA. For both mountain ranges combined, we estimated density to be 0.30 adult tortoises/ha (95% CI 5 0.17-0.43) and occupancy to be 0.72 (95% CI 5 0.56-0.89). For the sampling designs we evaluated, monitoring efforts based on occupancy were 8-36% more efficient than those based on density, when contrasting only survey effort, and 17-30% more efficient when contrasting total effort (surveying, hiking to and from survey locations, and radiotracking). Occupancy had greater statistical power to detect annual declines in the proportion of area occupied than did distance sampling to detect annual declines in density. For example, we estimated that power to detect a 5% annual decline with 10 years of annual sampling was 0.92 (95% CI 5 0.75-0.98) for occupancy and 0.43 (95% CI 5 0.35-0.52) for distance sampling. Although all sampling methods have limitations, occupancy estimation offers a promising alternative for monitoring populations of rare vertebrates, including tortoises in the Sonoran Desert.

Like all grasslands across North America, the distribution of desert grasslands has been reduced markedly, and remnants have been altered extensively by humans. In Arizona, New Mexico, Texas, USA, and in Mexico, desert grasslands have been invaded by dozens of non‐native plants, especially perennial grasses that evolved in arid systems with similar climate and disturbance regimes. In desert grasslands invaded by non‐native plants, biomass, richness, and diversity of native plants typically decrease, whereas plant density, biomass, and litter typically increase. These changes in composition and structure of the plant community affect animals that inhabit grassland ecosystems, with the direction and magnitude of effects reflecting the resource needs of each species, the degree of plant invasion, and the contrast in structure between invading and native plants. When non‐native plants present similar structural cues but provide different levels of resources than native plants, cues that trigger habitat selection by animals may be decoupled from the resources linked evolutionarily to that cue, creating the potential for an ecological trap. Plant invasions also influence the ecological drivers that maintain grasslands in an open condition, which will alter the long‐term dynamics of plant and animal populations. Specifically, by increasing fuel load and continuity, fires in invaded grasslands increase in frequency and intensity relative to those in native grasslands. Although eradication is unlikely once a non‐native plant has naturalized, retaining patches of native vegetation within a matrix of non‐native plants may provide a strategy to reduce effects of plant invasions on wildlife in grasslands. © 2013 The Wildlife Society.