Browsing Journal of Range Management, Volume 54, Number 4 (July 2001) by Subjects
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Carbon and nitrogen dynamics in elk winter rangesRecent increases in elk (Cervus elaphus L.) herbivory and changes in hydrology towards drier conditions have contributed to declines in willow (Salix spp. L.) communities in the winter ranges for elk in Rocky Mountain National Park. In 1994, we constructed 12 large elk exclosures in 2 watersheds of the winter range for elk in the park, and conducted field experiments from 1995 to 1999 to investigate the effects of herbivory and proximity to surface water on the dynamics of C and N. Litterfall biomass averaged 65.6 and 33.0 g m(-2) inside and outside the exclosures, respectively. Elk herbivory increased (P < 0.05) N concentration of willow litter from 1.25 to 1.49%, but there were no differences in losses of C and N from litterbags placed in grazed and ungrazed plots in any of the growing seasons. Carbon losses from litterbags were higher in lower landscape positions (P = 0.001), in comparison to upper landscape positions. Shoot biomass of willow plants fertilized with N averaged 27.3 g and was higher (P < 0.05) than that of unfertilized plants, which averaged 20.2 g, indicating that N availability limits plant growth in our study sites. Elk herbivory had no effect on soil inorganic N availability, even though we estimated that the return of N to the soil in grazed plots could be as much as 265% of the N return in exclosed plots. In the long-term, greater return of N to the soil combined with increased litter quality in the grazed plots could contribute to increases in N cycling rates and availability, and these changes could affect ecosystem structure and function in the winter range for elk in Rocky Mountain National Park.
Endophytic fungi in Canada wild rye in natural grasslandsSome grasses harbor endophytic fungi living in intercellular spaces in the leaves, stems and reproductive organs. The fungi can dramatically affect the physiology and ecology of plants. For example, fungi may produce toxins that deter herbivores and they may alter the water status of the plant to increase drought tolerance. The distribution of fungal infection in natural plant populations is unknown for many host species. We investigated the occurrence of endophytic fungi in Elymus canadensis L. (Canada wild rye) from 13 remnant prairie sites in the midwest and 23 sites in the southern Great Plains. Collections of plant tissue came from Nebraska, Kansas, Minnesota, Iowa, Missouri, Illinois, Oklahoma, and Texas. All midwest plants were grown in a common garden site in eastern Nebraska. Seeds collected from Oklahoma and Texas accessions were planted in the greenhouse. At least 3 tillers from 2 plants of each accession were screened for endophytes, using light microscopy. The endophytic fungus was found in seed of all accessions and in plants from all but 4 accessions. The functional significance of the fungus is unclear, but it may affect plants by enhancing productivity or deterring herbivores. The widespread occurrence of endophytic fungi in natural populations of E. canadensis suggests that the plant-fungal association may be long-standing and important in the evolution and success of this native prairie species.
Herbivore response to anti-quality factors in foragesPlants possess a wide variety of compounds and growth forms that are termed "anti-quality" factors because they reduce forage value and deter grazing. Anti-quality attributes can reduce a plant's digestible nutrients and energy or yield toxic effects. Herbivores possess several adaptive mechanisms to lessen the impacts of anti-quality factors. First, herbivores graze selectively to limit consumption of potentially harmful plant compounds. Grazing animals rely on a sophisticated system to detect plant nutritional value or toxicity by relating the flavor of a plant to its positive or negative digestive consequences. Diet selection skills are enhanced by adaptive intake patterns that limit the deleterious effects of plant allelochemicals; these include cautious sampling of sample new foods, consuming a varied diet, and eating plants in a cyclic, intermittent, or carefully regulated fashion. Second, grazing animals possess internal systems that detoxify or tolerate ingested phytotoxins. Animals may eject toxic plant material quickly after ingestion, secrete substances in the mouth or gut to render allelochemicals inert, rely on rumen microbes to detoxify allelochemicals, absorb phytochemicals from the gut and detoxified them in body tissues, or develop a tolerance to the toxic effects of plant allelochemicals. Understanding the behavioral and metabolic abilities of herbivores suggests several livestock management practices to help animals contend with plant anti-quality characteristics. These practices include offering animals proper early life experiences, selecting the appropriate livestock species and individuals, breeding animals with desired attributes, and offering nutritional or pharmaceutical products to aid in digestion and detoxification.