Browsing Journal of Range Management, Volume 44, Number 6 (November 1991) by Subjects
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Economic feasibility and management considerations in range revegetationAlthough range researchers and managers involved in range revegetation often have little economics training, economic analysis is usually a crucial step in range revegetation decisions. This synthesis paper is intended to provide a useful background in economic analysis for teachers, students, and natural resource professionals who deal with range revegetation. First, 3 economic standards by which all revegetation projects must be judged are described and interpreted: (1) economic feasibility, (2) economic efficiency, and/or (3) cost effectiveness. Next, the information required for economic analysis and the analytical procedures used to evaluate range revegetation projects are described. A detailed reseeding example is then used to describe the following information requirements: project costs, benefits, value of benefits, interest rate (including real vs. nominal rates), risk, project life (including life extension and grazing deferment), and range site selected for revegetation. Last, procedures for determining optimal vegetation conversion and use are reviewed, emphasizing the vegetation response function as the key to balancing the 3 determinants of long-term net returns: initial vegetation conversion, grazing intensity, and project life.
Perspectives and processes in revegetation of arid and semiarid rangelandsRange revegetation research has been dominated by empirical studies that provide some information about what works or does not work under a given set of conditions, but tell us little or nothing about the underlying ecological processes. Research has emphasized the establishment of vigorous exotic grasses on specific sites rather than the establishment of persistent, biologically diverse plant communities. A more mechanistic research approach is needed to better understand factors governing germination, seedling establishment, and plant community development in natural and synthetic systems to guide revegetation toward biological diversity. This paper evaluates selected aspects of the present knowledge of revegetation science on arid and semiarid lands, and attempts to identify areas for future research direction. Specific concepts and aspects of succession and plant community development, such as seedbed ecology, temporal and spatial patterns of resource availability and use, species life history traits, and species interactions are important areas of research. Continuous measurement of detailed environmental and biological data at the appropriate scale (down to the size of small seeds) will allow development of mechanistic models which can be used to predict plant establishment and community development for different environmental conditions.
Plant-animal interactions affecting plant establishment and persistence on revegetated rangelandThe role of ungulate grazing in shaping rangeland ecosystems is well known relative to other important plant-animal interactions such as pollination, seed dispersal, granivory, and belowground herbivory. Successful rangeland revegetation may be enhanced by strategies that favor certain groups of animals and discourage others. Many perennial forbs and shrubs require animals for successful pollination, reproduction, and subsequent maintenance of species on a site; however, pollination biology of many rangeland plants and pollinator abundances at potential revegetation sites are largely unknown. Granivory may be significant in some locations and planning and design of revegetation areas may be improved by implementing principles of seed escape mechanisms, such as predator satiation, seed escape in space (low perimeter-to-area ratio for revegetation site), and seed escape in time (synchronous or staggered timing for nearby revegetation sites). Seedling establishment may be associated with invertebrate population levels which need to be considered in future revegetation projects. Timing and site preparation are important in limiting belowground herbivory. Animals can serve as dispersal agents of seeds. Livestock dosed with desirable seeds can disperse them in their dung across the landscape, thereby creating patches of desirable plants. If revegetation sites will be grazed by livestock, then managers should choose plant species that tolerate rather than avoid grazing and should apply adequate management to establish and maintain plant populations. Seeds inoculated with mutualistic species such as mycorrhizae, nitrogen-fixing bacteria, or actinomycetes may enhance establishment, productivity, and nutrient quality of rangeland species while increasing rates of succession.
Plant-plant interactions affecting plant establishment and persistence on revegetated rangelandRestoration and revegetation of rangeland ecosystems is based on knowledge of abiotic and biotic interactions that affect plant establishment. Once plants become autotrophic, interactions within and between plant species may occur and then interactions may range from antagonistic to mutualistic. This full range of potential interactions needs to be considered to ensure successful revegetation. At the intraspecific level, we propose the development and use of density-yield diagrams for rangeland species. These diagrams would be based on the self-thinning principle, that aboveground biomass is related to plant density and to the dynamic process of density-dependent mortality. The proposed approach would be used to determine optimum seeding rates, and to predict future biomass of revegetated rangeland. At the interspecific level, competitive relationships of species used to reseed rangelands need to be identified to enhance the probability that species will coexist and thereby facilitate greater species diversity on the site. A diversity of species and growth forms may provide a more stable cover and productivity than a monoculture on sites characterized by environmental variability while potentially enhancing nutrient status for the site.