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Brachiaria brizantha (Hochst ex. A. Rich) Stapf apresenta boa adaptação às condições edafoclimáticas brasileiras e é muito utilizada como planta forrageira em pastagem na produção de bovinos. Apesar de seu potencial na produção de ovinos, ainda são necessárias novas investigações para aperfeiçoar o seu manejo. Objetivou-se com esta pesquisa avaliar as características produtivas, fisiológicas e bromatológicas de um pasto formado por Brachiaria brizantha cv. Marandu, fertilizada com doses de nitrogênio (N) e sob pastejo ovino. O delineamento experimental foi em blocos completos casualizados com 04 repetições e 05 tratamentos experimentais: 0; 90; 180; 270; 360 kg de N.ha-1, totalizando 20 parcelas experimentais. O método de pastejo foi o rotativo, com ciclo de pastejo de 30 dias, sendo 25 dias de descanso e 5 dias de ocupação, como forma de rebaixar o pasto à altura de resíduo de 6 cm. As medições no pasto foram feitas a cada 3 dias em 3 ciclos de pastejo, quando se avaliou: o fluxo de tecidos, a dinâmica de perfilhamento, a produção e a composição bromatológica da planta forrageira. Para massa seca de forragem verificou-se comportamento quadrático nas doses crescentes de N, atingindo o platô em 246 kg.ha-1. As variáveis taxas de senescência foliar, peso médio e densidade populacional de perfilhos não foram influenciados (P>0,05) pela adubação nitrogenada enquanto que a taxa de alongamento e de aparecimento de folhas, a taxa de alongamento de colmo, o número de folhas vivas, o comprimento final de folhas foram influenciados pela adubação nitrogenada (P<0,05). O filocrono e a duração de vida da folha foram mais curtos na presença do N. Em relação às características bromatológicas, o N afetou positivamente nos teores de FDA, FDN, e PB. Pelo manejo imposto aos pastos, a utilização do N teve efeito positivo nas características fisiológicas, produtivas e nutritivas do capim-marandu. / Brachiaria Brizantha (Hochst ex. A. Rich) Stapf is well adapted to Brazilian climatic conditions, and is widely used as a forage grass on pasture production in cattle. Despite its potential for use in the present sheep production, further research studies are still needed to optimize their management. The objective of this research was evaluate yield, physiological and chemical characteristics of a pasture of Brachiaria brizantha cv. Marandu, fertilized with nitrogen and grazing sheep. The experimental design was a randomized complete block with 04 replications and 05 experimental treatments: 0, 90, 180, 270 and 360 kg N.ha-1 totaling 20 experimental plots. The grazing method was rotating with cicle of grazing of 30 days, 25 days of rest and 5 days of occupancy to reach height of pasture residue of 6 cm. Measurements were made in the pasture every 3 days, at,three grazing cycle evaluated. Thus analyzing the flow of plant tissue, the dynamics of tillering, yield and composition chemical of forage. For dry herbage mass there was a quadratic behavior in increasing doses. The increase of N, there was a quadratic behavior, reaching a plateau where the best dose was 270 kg.ha-1. The variables leaf senescence rate, average weight and tiller density were not affected (P>0.05) by use of N, while the variables leaf elongation rate and appearance, stem elongation rate, number of living leaves, final length of leaves were influenced by nitrogen fertilization (P<0.05), Phyllochron and lifetime leaves were shorter in the presence of N. Regarding the chemical caracteristics, the presence of N affected positively the levels of the ADF, NDF and CP, The grazing management imposed, the use of N had a positive effect on the physiological, productive and chemical characteristics of Marandugrass.

The objective of this study was to evaluate the influence of cow age on grazing distribution relative to mountain riparian areas. In each of two years, sixty cow-calf pairs were stratified by age into the following treatments: 1) thirty first calf heifers (442 kg, body condition score (BCS)=4.5), and 2) thirty mature cows (5-7 years of age; 569 kg, BCS=5.0). From late July to early September, treatments were randomly assigned to four pastures with treatments reversed in Year 2. Analysis of hourly cattle locations observed during 4-d periods early (d 15 to d 18) and late (d 36 to d 39 in Year 1; d 29 to d 32 in Year 2) during the grazing bout revealed a three-way interaction between cow age, time of day, and grazing bout (P<0.01). In the morning hours of the early grazing bout, mature cows distributed farther from the stream (P<0.10), and occupied the riparian vegetation type less (P<0.10) than first calf heifers. No differences (P>0.10) in distribution occurred between age classes from 1300 h until dark. Similarly, during the late grazing bout, no differences were observed (P>0.10) between the distribution of the age classes. While no difference (P=0.20) occurred between age classes in total minutes spent grazing, first calf heifers foraged longer during the morning and evening bouts (P<0.10). The forage utilization pattern and the fecal deposits within 1-m of the stream were not different (P>0.10) between age classes. While mature cows tended (P=0.17) to have higher dry matter intake (DMI), first calf heifers consumed more feed per unit of body weight (BW) (P=0.08). Though first calf heifers tended (P=0.13) to gain more BW, no differences occurred between age classes in BCS change (P=0.69), or calf average daily gain (ADG) (P=0.34). In summary, mature cows distributed farther from water and spent more time outside the riparian vegetation zones during the morning hours early (d 15 to d 18) in the trial compared to first calf heifers. / Graduation date: 2003

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2007. / Thesis documentation sheet inserted. Appendix reproduces four papers and manuscripts, three co-authored with others. Includes bibliographical references. Also issued electronically via World Wide Web in PDF format; online version lacks appendix paper 4.

Reforesting harvested lands in southwestern Oregon has been difficult because of low rainfall, high evaporative demand, and competitive understory vegetation. Herbicides have been a preferred method to control competing vegetation but herbicide use on federal lands was curtailed in 1984. As a result, interest in livestock grazing as a vegetation control method has increased. I used prescribed cattle grazing from 1986-1990 to assess effects on reforestation. Treatments were established on a low-elevation (670 m) site to evaluate seedling survival and growth of Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco.) and ponderosa pine (Pinus ponderosa Dougl.). Treatments were: a) seeding of palatable forage species (SU); b) seeding with grazing (SG); c) no seeding with grazing (NG); and d) no seeding or grazing, with paper mulch applied on Douglas-fir only (PM/C). Year 5 mortality among treatments ranged from 57 to 87% for Douglas-fir and 11 to 25% for ponderosa pine. Porcupine girdling and late-spring frost were major causal factors in ponderosa pine and Douglas-fir mortality, respectively. Competition from understory vegetation, browsing, and trampling were only minor causal factors in seedling mortality. Cumulative growth of both species was best in NG. Severe browsing by cattle in year 2 on SG resulted in reduced year 3 relative growth for ponderosa pine. However, year 2 browsing did not reduce long-term relative growth. By year 5, relative growth for ponderosa pine was greatest in SG and lowest in SU. During years 1-3, soil moisture availability was not enhanced on the grazed vs. ungrazed treatments. However, by year 4, xylem potentials and soil moisture indicated seedlings in SG were less water-stressed than those in SU. Reduced water stress probably resulted from reductions in roots of orchardgrass (Dactylis glomerate L.) because of defoliation. Sampling with a root periscope indicated roots were reduced for defoliated (SG) plants compared with undefoliated (SU) plants. Leaf area and root growth reductions were apparent mechanisms permitting increased soil moisture availability. These results suggested that prescribed cattle grazing can facilitate reforestation. / Graduation date: 1992

Increased knowledge of plant interactions is important for our understanding of how ecosystems will respond to climate changes. Using four common low-herb and three tall- herb species as phytometers I measured the net outcome of plant interactions in an alpine environment by a neighbour removal experiment. Grazing and climate were tested as explanatory factors for differences in the outcome of plant interactions, with two altitudes representing different climates. The most important finding in this experiment is that competition is the dominating interaction among plants in this habitat, regardless of plant size, climate and grazing. Climatic exposure and grazing only influenced tall-herb species while low-herbs were mainly limited by competition, presumably for light. These results are important since facilitative interactions and net facilitation in plant communities are often reported to become more common in severe climates.

The wetlands of the semi-arid savanna ecosystem of Amboseli are the critical dry-season range for a diverse wildlife population, as well as for livestock and humans. Changes in the migratory patterns and increases in the population of the elephants in the ecosystem, as well as a shift in the lifestyle of the growing human population from predominantly nomadic pastoralist society to a sedentary agrarian community, has had far-reaching effects on the ecosystem and the wetlands. In this thesis, the current status of the wetlands and the changes in vegetation over the last four decades were examined using satellite imagery and long-term census data. Studies were also conducted to determine the impact of grazing by elephants and other large mammals on wetland vegetation, and the flooding patterns and extents of some of the wetlands were examined. <br /><br /> Long-term aerial count data indicated that the wetlands that are currently protected by the Amboseli National Park have been under increasing use year-round by elephants since 1975. These wetlands showed a rapid increase in extent between 1950 and 1976. This corresponds to the elephant-driven decline in <I>Acacia xanthophloea</I> woodlands, which may have changed the hydrology of the area. Since then, only one of the wetlands, Longinye, has shown dynamic changes in extent. This is either the effect of the blockage of water flow by vegetation or the creation of new channels by elephants and hippopotami. The wetlands had a diverse range of wetland habitat from areas of open water with scattered tall <I>Cyperus papyrus</I> communities in the centre of one wetland to large expanses of seasonally inundated <I>C. laevigatus</I> and <I>Cynodon dactylon</I> dominated habitats fringing the wetlands. Most of the wetland habitats were composed of short sedges and grasses, which was shown to be the direct result of elephant grazing. Elephants tended to keep the vegetation of a control wetland short and of low biomass during both wet and dry seasons, whereas the vegetation in a treatment wetland, where elephants were excluded, showed a rapid increase in biomass and height. Other herbivores were shown to maintain conditions of short vegetation of low biomass through grazing pressure in the dry season. The impact of natural and simulated grazing on growth of the vegetation was studied and only under simulated grazing pressure was growth increased in the seasonally inundated <I>C. dactylon</I> grasslands, as well as the floating mat communities dominated by <I>C. laevigatus</I> that occur in the shallow water wetlands. This indicates that natural grazing may be detrimental either to the plants or the soil. <br /><br /> The wetlands that are under human use had predominantly shallow water and seasonal wetland habitat. Deep water habitat with <I>C. papyrus</I> communities was only present in one of these wetlands, Kimana, which is also the only wetland outside the park that is used by livestock and wildlife, as well as to irrigate a large area of land around the wetland. Two other wetlands, Namelok and Lenkir that were predominantly used for irrigated agriculture, were largely composed of seasonally inundated wetland habitat. A fourth wetland, Esoitpus, has been almost completely drained and this has most likely resulted in the development of <I>A. xanthophloea</I> and <I>C. dactylon</I> dominated riverine and <I>C. laevigatus</I> / <I>C. dactylon</I> dominated seasonally inundated wetland communities. <br /><br /> Overall, the wetlands in the park provide a measure of habitat diversity that may be useful for various invertebrate and vertebrate communities. However, the present lack of tall sedges may negatively impact the bird community. This state can be reversed by the exclusion of elephants from some wetlands for short periods of time. On the other hand, the wetlands outside the park appear to be facing rapid draw-down. Hence, there is an urgent need for sound water management practices for these wetlands.