Spatial and Temporal Dynamics of Plant Populations in Salt-Desert Shrub Vegetation Grazed by Sheep

I studied the effect of moderate sheep grazing on a shadscale plant community at the Desert Experimental Range, southwestern Utah, USA, using a 61-yr data set with two grazing treatments (yes vs. no), two seasons (spring vs. winter), and two soil types (loamy-skeletal vs. coarse-loamy). I studied precipitation, total species cover, annuals, shrub survival, seedling recruitment, plant succession, and plant spatial relationships./p\u3e Precipitation showed high variability (CV=31%) masking on short-term cycles, resulting in study intervals with average (1935-58), dry (1958-69), driest (1969-75), and wet (1980-94[5]) regimes. Total cover in both grazed and ungrazed pastures increased between 1935 and 1975 before decreasing to 1994. Treatments diverged with time, however, so cover was higher in ungrazed pastures in 1975 and 1994. Individually, Atriplex confertifolia decreased from 1958-94 and Ceratoides lanata from 1975-94. Artemisia spinescens increased in ungrazed pastures from 1935-94, while remaining very low in grazed pastures. Grasses increased from 1935-94 with little grazing effects. Annuals increased from absence in 1935 to 63% frequency in 1994; precipitation may be related to this increase. Grazing and soil type had few long-term or short effects on shrub survival. Similarly, only C. lanata showed a microhabitat effect, with greater seedling survival in vegetated than open patches. Seedling recruitment was positively correlated with precipitation. Only A. confertifolia recruitment responded to grazing; it was higher in grazed pastures. A fuzzy graph analysis showed a moderate grazing effect on succession. Clumped distributions were common and were unaffected by grazing but increased in wet years. Plant establishment occurred disproportionally in sites occupied or formerly occupied by plants, suggesting facilitation. Negative interference, however, was suggested by new recruitment occurring further from larger existing individuals. Moderate grazing had little effect on spatial relationships. In conclusion, the multivariate approach yielded broader conclusions than any individual factors. Although some factors showed more grazing effects than others, grazing could not completely explain observed changes; climate and inherent plant attributes must also be considered. Management at moderate grazing levels may only play a limited role in shadscale communities

Chapter 02: National, Regional and Local Context

To better understand today’s constraints and opportunities for improving small ruminant production systems on the Bolivian Altiplano, it is important to first consider the broader contexts of environment and social history. This chapter provides an introductory overview of secondary information concerning major ecological regions of Bolivia, constituent agroecosystems and how ecological regions are interrelated in terms of climate, geography, macro-economics and agricultural policy. Key aspects of cultural change and political history are also reviewed. These are important because present-day values and behaviours of Andean campesinos, as well as their use of agricultural technologies, have been profoundly shaped by forces including the indigenous Aymara culture, Incan occupation, Spanish colonialism, the initial Republican Period and contemporary policies of the Bolivian government.https://digitalcommons.usu.edu/sustaining_agropastoralism/1001/thumbnail.jp

Chapter 03: Ecology and Natural Resources of San Jose Llanga

Development and change in traditional societies is strongly affected by interactions between humans and their natural environments. Management practices used by most low-input, rural societies represent an amalgamation of technologies, social rules and organisational structures that have been tested over time and found suitable for sustainable exploitation of resources. In many cases, however, changes in population, social values, market opportunities, government policies or technology alter a delicate balance between humans and sustainable resource use. Given these critical relationships, a thorough knowledge of the biophysical environment is essential to comprehend and attempt to improve low-input production systems such as SJL. Our overall purpose in this chapter is to characterise the environment and natural resources of the Cantón of SJL. This is accomplished in two steps. First the climate, surficial geology, hydrology, soils and vegetation are described. Descriptions include brief accounts of land use (i.e., cultivation, grazing, fuel wood collection, etc.) for broadly defined geomorphic units. Second, an analysis is presented concerning selected aspects of ecosystem dynamics at various spatial and temporal scales.https://digitalcommons.usu.edu/sustaining_agropastoralism/1002/thumbnail.jp

Chapter 05: The Grazing Livestock of San José Llanga: Multiple-species Resource Use and the Management and Productivity of Sheep

The main objective of the joint IBTA/SR-CRSP project in Bolivia was to assess the overall role of small ruminants in the ecological and economic sustainability of an agropastoral system. Prominent was a mandate for us to investigate: (1) Whether small ruminants were important contributors to environmental degradation; and (2) whether there were feasible improvements in management that could mitigate negative impacts of small ruminants on natural resources and increase efficiency of animal production (see Chapter 1: Project objectives and research approach). These issues are important in light of recent controversy concerning environmental degradation of the world’s rangelands. On one hand people and livestock are blamed (Sinclair and Fryxell 1985; Cloudsley-Thompson 1988) while on another hand climate, or change in climate, is cited as a key factor (Rasmusson 1987; Ellis and Swift 1988). If livestock are not to blame then efforts to de-stock traditional pastoral systems could be in error (Behnke and Scoones 1991).https://digitalcommons.usu.edu/sustaining_agropastoralism/1004/thumbnail.jp