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University of Toronto (2002)

Dynamics of woody vegetation under grazing by domestic goats in the Tamaulipan matorral of northeastern Mexico .

Manzano-Camarillo, Mario Guadalupe

Titre : Dynamics of woody vegetation under grazing by domestic goats in the Tamaulipan matorral of northeastern Mexico .

Auteur : Manzano-Camarillo, Mario Guadalupe

Université de Soutenance : University of Toronto

Grade : Doctor of Philosophy (PhD) 2002

Résumé
Following a static temporal approach, three different goat grazing regimes were studied on two landscape units with different morphology, and soil type (Regosols on medium slopes and Vertisols in low plains) in the Tamaulipan matorral of northeastern Mexico. Vegetation attributes and surface soil properties were measured at the site level to identify effects of browsing and trampling on the dynamics of this plant community. Results provided evidence that the degradation of rangelands in the Tamaulipan matorral occurred through changes in major plant community attributes. These included shifts in floristic composition, structure, reproduction potential and perpetuation, as well as changes in functional soil properties, mainly those affecting soil water content. Soil moisture emerged as the most influential soil factor and was tightly associated with different soil properties at each unit. In the Regosol unit decreased soil moisture was apparently explained by high soil stoniness and low organic matter content. In the Vertisol unit, changes in moisture content were highly correlated with compaction, increased bulk density and low infiltration. Soil feedbacks were important to either enhance or overcome the effects of browsing on plants, which depended largely on the soil type. Degradational phases, represented by grazed sites, are considered transitional stages within the context of state-and-transition models. Although differences amongst grazing regimes were significant, they did not involve substantial physiognomic changes. The community still persists as a matorral ( sensu lato ), particularly in the Regosol unit, though rather disturbed, simpler and more open on grazed sites of the Vertisol unit. Therefore, no evident floristic and physiognomic thresholds were identified. These results provided descriptions of the degradation status and predictions of the pattern of trends in dynamics of this plant community under grazing. Management implications within the socioeconomical and political framework of the Mexican ejido are also discussed. This study provides a scientific and practical basis to infer on vegetation dynamics in grazing systems of the Tamaulipan matorral from original site-level field measurements.

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Page publiée le 12 février 2004, mise à jour le 9 septembre 2019