The dominant habitat-type of Omo National Park (ONP), Ethiopia, is grassland. 111 This grassland supports a variety of wild herbivores and indigenous people; the latter hunt large herbivores for subsistence or graze their domestic livestock in the Park. Therefore, an understanding of grassland dynamics is a high priority for ONP management. Grazing and fire are major factors influencing species composition and vegetation change in East African grasslands . Rainfall regime, in tum, can influence both grassland response to grazing and fire. The ONP grasslands occur along a rainfall gradient ranging from subhumid to semiarid. Research objectives were to: (1) test the Milchunas, Sala, and Lauenroth grazing response model at three sites along the rainfall gradient; (2) determine how basal cover for dominant perennial grasses along the rainfall gradient was influenced by an extended period of intensive defoliation; and (3) determine if current distribution of grassland species associations was related to fire frequency. Species composition changes associated with defoliation were consistent with predictions of the Milchunas, Sala, and Lauenroth model; large changes occurred in subhumid grasslands while minimal changes occurred in semiarid sites . Furthermore, an intermediate response was found at the site that received an intermediate level of rainfall. Basal cover of dominant grasses was not adversely affected by intensive defoliation, and this tolerance was expressed under all three moisture regimes. Significant reductions in basal cover were found, however, in >50% of dominant grasses as a result of protection from grazing and fire . Estimated fire frequency pattern was unrelated to the distribution of species associations within grasslands. Conceptual models of vegetation change were developed for the three grasslands using research results. At the current level of management these models provide information that can be used to improve relations between Park staff and local pastoralists . Given the tolerance of most perennial grasses to intensive defoliation, ONP managers could modify the current policy of no grazing within the Park to one of limited grazing . If management capabilities were to improve, conceptual models could guide an active approach to grassland management.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-09-03T15:08:48Z No. of bitstreams: 1 ALDINETE BEZERRA BARRETO - TESE PPGMET 2012..pdf: 6263495 bytes, checksum: 1008afd187e39f22ffed865972093dbc (MD5) / Made available in DSpace on 2018-09-03T15:08:48Z (GMT). No. of bitstreams: 1 ALDINETE BEZERRA BARRETO - TESE PPGMET 2012..pdf: 6263495 bytes, checksum: 1008afd187e39f22ffed865972093dbc (MD5) Previous issue date: 2012-05-08 / CNPq / O objetivo deste estudo é caracterizar o regime de chuvas de Salvador em várias escalas de tempo, com foco em eventos extremos de chuva, e identificar padrões da circulação atmosférica de grande escala relacionados com tais eventos. O período de estudo é de 1964 a 2009. Métodos matemático-estatísticos (Percentil, Correlação Linear, Análise de Ondeletas, Análise de Componentes Principais (ACP) e Análise de Agrupamento) foram aplicados a dados observacionais de precipitação e dados em ponto de grade de reanálise. A técnica do percentil aplicada à série temporal dos dados diários de precipitação possibilitou classificar como eventos extremos os totais diários com valor igual ou maior do que 50 mm. O principal período chuvoso, abril a julho, detém 61% de todos os eventos da série. A análise de correlação linear mostrou uma relação direta entre a ocorrência dos eventos extremos e total mensal de chuva acima da média. A análise de ondeletas indicou que os eventos estão relacionados com, pelo menos, três tipos de oscilação na escala intrassazonal: de até 12 dias, de 12-24 dias e de 48-96 dias, o que sugere a contribuição de sistemas de escala sinótica como os distúrbios de leste e os sistemas frontais, e de circulações de escala planetária como a Oscilação de Madden-Julian. A ACP aplicada a dados de reanálise identificou padrões nos baixos níveis com configuração indicativa da presença do cavado equatorial/ZCIT, ondas de latitudes médias austrais e ZCAS, essa última relacionada com eventos dos meses de verão (dezembro-janeiro-fevereiro). O padrão do principal período chuvoso tem estrutura ondulatória no escoamento de oeste do hemisfério sul. Todos os padrões apresentam um cavado invertido no leste do Nordeste e área oceânica próxima, resultante da propagação/interação de sistemas atmosféricos da área tropical-extratropical. Nos altos níveis (200 hpa), o padrão relacionado com os eventos de verão mostra a Alta da Bolívia deslocada para nordeste, e o cavado de ar superior posicionado sobre o Atlântico tropical. A estrutura dominante nos padrões de inverno (junho-julho-agosto) é: (a) ondas de latitudes médias austrais com propagação em latitudes baixas, ou (b) uma área de difluência próxima ao equador relacionada com a ZCIT. / The objective in this study is to characterize the rainfall regime of Salvador on various time scales, with a focus on extreme rainfall events, and to identify large scale atmospheric circulation patterns related to such events. The period of study is from 1964 to 2009. Mathematical-statistical methods (Percentiles, Linear Correlation, Wavelet Analysis, Principal Component Analysis (PCA), Cluster Analysis) were applied to observational precipitation and gridpoint reanalysis data. The percentile technique applied to daily precipitation time series allowed to classify as extreme events daily rainfall totals equal to or greater than 50 mm. The main rainy period, from April to July, has 61% of all events. The linear correlation analysis identified a direct relation between the occurrence of extreme events and above-normal monthly rainfall totals. The wavelet analysis indicated that the events are related to, at least, three types of oscillations on the intraseasonal time scale: up to 12 days, 12-24 days and 48-96 days, suggesting the contribution of synoptic scale systems such as easterly disturbances and frontal systems, and planetary scale circulations as the Madden-Julian Oscillation. The PCA applied to reanalysis data identified low level patterns depicting the equatorial trough/ITCZ, southern mid-latitude waves and SACZ, the last one related to summer month events (December-January-February). The pattern of the main rainy period has a wavelike structure in the southern westerlies. All patterns show an inverted trough in eastern Northeast and the nearby oceanic area, a result of the propagation /interaction of tropical-extratropical atmospheric systems. At high levels (200 hpa), the summer pattern shows the Bolivian high displaced northeastward, and the upper level trough located over the tropical Atlantic. The dominating structure in the winter patterns (June-July-August) is: (a) southern mid-latitude waves propagating toward low latitudes, or (b) a difluence area close to the equator related to the ITCZ.