Grass species composition under and outside tree canopies in a semi-arid savanna rangeland in Zimbabwe.
1996
Moyo, C. S. | Campbell., B. M. | Mushove, P. T. | Shumba, E. M. | Matose, F.
A study was conducted to evaluate the impact of widely spaced leguminous and non-leguminous trees on their understorey herbaceous composition. The trees studied were Acacia karoo on vertisols, red soils and sandveld and Terminalia sericea on sandveld. Grass species presence and density relative to a tree bole was measured in 15m x 0,2m transects. Grass samples were harvested, on a species basis, from 1 square meter quadrats under tree canopies (1m away from tree bole) and in open grasslands (20m away from tree bole). Ordination of the herbaceous vegetation using density and biomass as indices showed species dispersed without pattern along the first axis and same scores forming distinct groups according to soil type, respectively This suggests that there is no strong grass species association with undercanopy or grassland environments. Semi-arid savannas are sensitive to disturbances, such as heavy grazing and drought, which may have long term effects and override the impact of tree canopies on their understorey herbage. Trees, in disturbed systems, may still have positive effects on yield and quality of the similar grass species occurring under canopy and in grassland areas. short-term studies in semi-arid savanna must consider disturbance factors for the current and previous seasons.
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