Direct And Indirect Effects Of Livestock Grazing Intensity On Processes Regulating Grassland Bird Populations

In grasslands, grazing by large ungulates can influence vegetation structure, composition, primary productivity, and ultimately, ecosystem functioning. While grazing represents a complex disturbance, grazing intensity largely determines the effects of grazing on vegetation. Structural and compositional changes in the plant community caused by grazing could have bottom-up effects on species and interactions at higher trophic levels. Thus, particular management strategies for domestic livestock in rangeland systems could exert a strong affect on grassland wildlife. Grassland-dependent songbirds may be particularly susceptible to the effects of domestic grazers because they depend on grassland vegetation for foraging and nesting. Domestic livestock may influence grassland-breeding bird populations by affecting settlement decisions, resource availability, or reproductive success. We investigated the effects of grazing intensity on grassland vegetation structure and songbird demography in a northwestern bunchgrass prairie using paddocks with experimentally-manipulated cattle stocking rates. We compared effects of four stocking rates (0, 14.4, 28.8, and 43.2 animal unit months) on songbirds using a randomized complete block design with four replicates of each stocking rate to address hypotheses regarding demography of grassland songbirds. Overall paddock-level vegetation structure decreased and structural heterogeneity of vegetation increased with higher stocking rates, and those effects carried over one-year post-grazing. However, most bird species were able to locate nesting sites with similar vegetation structure regardless of paddock-level effects of stocking rate. The exceptions were western meadowlarks and vesper sparrows; nests of these species in paddocks with higher stocking rates had less vegetative cover. Apparent nest density for grasshopper sparrows was negatively affected by higher stocking rates. Grazing treatment effects on songbird population density were restricted to negative effects of higher stocking rates on savannah sparrows, but this relationship was not observed until the post-treatment year. Songbird community composition differed between control and heavily-grazed paddocks, but diversity was not affected by stocking rate. Nest fates were evaluated to determine whether stocking rate influenced nest survival or cause-specific nest failure. Other variables such as vegetation structure and predator community, date, year, and nest age were included to help clarify which mechanisms might be responsible for differences in nest survival or failure rates among treatments. For our analysis, we introduce the use of a novel software package, McNestimate, to estimate the daily probability of nest survival and failure from specific causes. McNestimate estimates the probability of nest failure from competing causes when the exact dates of failure are unknown using a Markov Chain framework, and incorporates a model selection approach which allows the use of covariates to help identify variables important in explaining variation in the daily probability of nest failure. Nest predation rates increased with the age of the nest and throughout the breeding season, but were not affected by stocking rate. The probability of nest failure from adverse weather declined throughout the season, but the rate of decline depended on year. Nest failure rates due to trampling were higher in paddocks with higher stocking rates, but also depended on the number of days cattle were present during the nesting period. Patterns of overall probability of nest success were driven by predation patterns in the first year, but in the second year were strongly influenced by the chances of weather-related nest failure. Although starvation was not identified as a significant source of nest failure, grazing-induced changes to vegetation structure and composition could influence food availability for breeding songbirds, ultimately affecting the composition of nestling diets and nestling condition. To better understand the relationship between grazing intensity, nestling diet composition, and subsequent effects on nestling condition, we examined the invertebrate composition of nestling fecal samples. All species showed strong preferences for Lepidoptera (moths and butterflies) larvae, and partial preferences for Coleoptera (beetles) and Araneae (spiders). The proportion of preferred prey items was not affected by stocking rate. There were effects of bird species on the proportion of Araneae and Coleoptera and the proportion of Acrididae (short-horned grasshoppers) in the diet of western meadowlark nestlings decreased with high stocking rates. Growth rates for western meadowlarks and vesper sparrows were negatively affected by higher stocking rates. These results suggest that stocking rates can have variable effects on grassland songbird population and nest density depending on each species' habitat requirements. However, negative effects of high stocking rates on nest survival and nestling condition could have consequences for juvenile survival and recruitment. Overall, low-to-moderate stocking rates are likely compatible with many grassland bird species in northwest bunchgrass prairie, and although heavier livestock grazing may help create suitable vegetation structure for some songbird species, high stocking rates may influence grassland songbird diet quality, or have negative effects on nestling condition. We hypothesized that grazing intensity could influence the grassland songbird community through "bottom-up" effects on vegetation, but effects of grazing at different intensities did not translate directly through the food web to influence songbird populations as strongly as lower trophic levels. Processes responsible for changes in community composition such as immigration or emigration may not have had time to ensue during our short-term experiment; alternatively, sufficient spatial or temporal heterogeneity remained in the system, even at the highest grazing intensity, such that grazing-induced changes in lower trophic levels were irrelevant for most songbird species. Our results contribute to understanding grassland songbird demographic responses to different grazing intensities and identify specific mechanisms by which conservation measures for declining grassland bird populations can be improved.

Key researchers present newly emerging approaches to computer simulation models of large, forest landscapes.

"The assessment builds on the work of the Livestock, Environment and Development (LEAD) Initiative"--Pref.

This book contains 28 chapters with emphasis on the interactive nature of the relationships between the soil, plant, animal and environmental components of grassland systems, both natural and managed. It analyses the present knowledge and the future trends of research for combining the classical view of grasslands, as a resource for secure feeding of an increasing human population, with the more recent perspective of the contribution of grasslands to the mitigation of environmental impacts and biodiversity erosion as consequences of human society activities. The chapters are organized within five sections dealing with the different functions and the main ecosystem services expected from grasslands: (i) domestic herbivore feeding and animal production; (ii) the regulation of biogeochemical cycles and its consequences for the environment; (iii) dynamics of biodiversity hosted by grasslands; (iv) integration of grasslands within sustainable animal production systems; and (v) interactions of grassland areas with other land use systems at the landscape level.

Funded by and written during theEuropean Multisward project, this open access ebook presents an inventory of grasslands and forage crops in Europe by placing them in the production system in which they are embedded, and studying the technical, economic and regulatory determinants of past and present trends. Profusely illustrated with maps, it also features many case studies in all European regions and interviews of farmers and key stakeholders.

This volume investigates how large herbivores not only influence the structure and distribution of the vegetation, but also affect nutrient flows and the responses of associated fauna. The mechanisms and processes underlying the herbivores' behavior, distribution, movement and direct impact on the vegetation are discussed in detail. It is shown that an understanding of plant/animal interactions can inform the management of large herbivores to integrate production and conservation in terrestrial systems.

This book begins with a brief account of the extraordinary sequence of events that led to emergence of grasslands as major vegetation formations that now occupy some of the driest and hottest and the highest and coldest on earth as well as vast steppes and prairies in more temperate climes. It is the story of grasses successfully competing with forests and woodlands, aided and abetted by grazing herbivores and by humans and their use of fire as a tool. It is a story of adaptation to changing climates and the changing biophysical environments. A major focus of the book is the Palaearctic biogeographic realm that extends over some 45 million km2 and thus more than 1/3 of the terrestrial ice-free surface on Earth. It comprises extensive grasslands of different types and origin, which can be subdivided into (1) natural grasslands with (1a) steppes (climatogenic in dry climates), (1b) arctic-alpine grasslands (climatogenic in cold climates) and (1c) azonal and extrazonal grasslands (pedogenic and topogenic) as well as (2) secondary grasslands created and sustained by human activities, such as livestock grazing, mowing or burning. Grasslands of the Palaearctic do not only form a major basis for the agriculture of the region and thus its food supply, but are also crucial for other ecosystem services and host a supra proportional part of the realm’s plant and animal diversity. To reflect that suitability of grasslands for biodiversity strongly depends on their state, we apply the term High Nature Value grassland to those natural grasslands that are not degraded (in good state) and those secondary grasslands that are not intensified (semi-natural). The situation in a variety of countries where grasslands are evolving under the influence of global climate change is also considered. Case studies are presented on Southern Africa, Eastern Africa, India, China, South America, North America and Australia. The concluding chapter examines a set of themes arising from the chapters that make up the bulk of this book. The following provide a focus: recent history of grassland biomes – brief recap of current thinking and recent trends with special reference to dry grasslands in the Palearctic regions; the current status of grasslands and germplasm resources (biodiversity) – an overview; management systems that ensure sustainability; how to recover degraded grasslands; socio-economic issues and considerations in grassland management; the impacts of environmental problems in grasslands such as future climate change and intensification and the problems/prospects facing pastoralists and other grassland-based livestock producers.

The Clean Water Act (CWA) requires that wetlands be protected from degradation because of their important ecological functions including maintenance of high water quality and provision of fish and wildlife habitat. However, this protection generally does not encompass riparian areasâ€"the lands bordering rivers and lakesâ€"even though they often provide the same functions as wetlands. Growing recognition of the similarities in wetland and riparian area functioning and the differences in their legal protection led the NRC in 1999 to undertake a study of riparian areas, which has culminated in Riparian Areas: Functioning and Strategies for Management. The report is intended to heighten awareness of riparian areas commensurate with their ecological and societal values. The primary conclusion is that, because riparian areas perform a disproportionate number of biological and physical functions on a unit area basis, restoration of riparian functions along America's waterbodies should be a national goal.