Includes our current knowledge of the invasion or encroachment and cause of population growth and spread of some dry land, arid zone woody legumes. Community structure, population growth, and competition of these woody legumes will also be examined. These species and ecosystems are both extensive and dynamic. They occur worldwide, but mainly in the arid zones of the tropics and sub-tropics. The cause of the growth and spread of these species and communities has long been claimed to be caused by distal factors rather than proximal ones. However, these species appear to be influenced and perhaps controlled by anthropogenic factors, specifically grazing and fire or lack of fire. Their overall worldwide distribution has probably changed little in the recent past, but their populations have expanded into grasslands and their density has increased in many places. Some associated communities have shown dramatic changes in response to recent large-scale droughts and the loss of most of the dominant overstory species. However, changes in the woody legume communities and their species are generally unknown. ​

This book is open access under a CC BY-NC 2.5 license. This book provides an unprecedented synthesis of the current status of scientific and management knowledge regarding global rangelands and the major challenges that confront them. It has been organized around three major themes. The first summarizes the conceptual advances that have occurred in the rangeland profession. The second addresses the implications of these conceptual advances to management and policy. The third assesses several major challenges confronting global rangelands in the 21st century. This book will compliment applied range management textbooks by describing the conceptual foundation on which the rangeland profession is based. It has been written to be accessible to a broad audience, including ecosystem managers, educators, students and policy makers. The content is founded on the collective experience, knowledge and commitment of 80 authors who have worked in rangelands throughout the world. Their collective contributions indicate that a more comprehensive framework is necessary to address the complex challenges confronting global rangelands. Rangelands represent adaptive social-ecological systems, in which societal values, organizations and capacities are of equal importance to, and interact with, those of ecological processes. A more comprehensive framework for rangeland systems may enable management agencies, and educational, research and policy making organizations to more effectively assess complex problems and develop appropriate solutions.

An advanced textbook adopting a theoretical modeling approach to review and discuss the current range and distributions of alien species, their rates of spread, and their impact in human-dominated ecosystems.

Woody plant encroachment is a globally-prevalent vegetation change phenomenon that has shifted grass-dominated ecosystems to mixed grass and woody plant matrices over the last century. In the Rio Grande Plains of Texas, the introduction of N-fixing woody legumes has increased above- and belowground primary productivity and changed the litter chemistry of the system, accelerating rates of belowground biogeochemical processes. The purpose of this study was to assess the impact of grassland to woodland transition on i) P concentrations in soil physical fractions that differ in their organic matter turnover rates, ii) P availability within the soil over the course of woody encroachment and across the landscape, and iii) microbial community composition and diversity. Soil samples were collected in remnant grasslands and four woody landscape elements (clusters, groves, drainage woodlands, and playas) along a 135-yr chronosequence of woody plant encroachment. P was fractionated by the Hedley method and P concentrations were determined by alkaline oxidation and lithium fusion coupled with ascorbic acid colorimetry. Bacterial and fungal communities were characterized by molecular methods. Whole soil P concentrations were 2-5X greater in woody landscape elements than in grasslands, and nutrient concentrations increased linearly with time following woody plant invasion in all but the slowest-cycling physical fractions. Plant-available P and organic P increased dramatically with time following encroachment. Changes in P availability were more pronounced in drainages and playas than in upland clusters and groves. Analysis of the bacterial and fungal communities demonstrated that microbial communities in grasslands differ at both phylum and genus level from the flora of the wooded landscape elements. This study demonstrates that woody encroachment strongly influences the distribution and availability of soil P and indicates that nutrient cycles in the soil are closely linked and similarly affected by increased woody plant abundance. Microbial communities under woody species differ in composition from those of the grasslands, and are likely contributing to the observed changes in nutrient availability. Since N and P are generally the most limiting nutrients in terrestrial ecosystems, increased stores of P are likely to alter rates of microbial processes, plant-microbe and plant-plant interactions, and successional dynamics in this ecosystem and similar landscapes around the world.

Invasion ecology is the study of the causes and consequences of the introduction of organisms to areas outside their native range. Interest in this field has exploded in the past few decades. Explaining why and how organisms are moved around the world, how and why some become established and invade, and how best to manage invasive species in the face of global change are all crucial issues that interest biogeographers, ecologists and environmental managers in all parts of the world. This book brings together the insights of more than 50 authors to examine the origins, foundations, current dimensions and potential trajectories of invasion ecology. It revisits key tenets of the foundations of invasion ecology, including contributions of pioneering naturalists of the 19th century, including Charles Darwin and British ecologist Charles Elton, whose 1958 monograph on invasive species is widely acknowledged as having focussed scientific attention on biological invasions.