Seasonal variation of grassland basal cover

Abstract

Preliminary results of a long-term study of seasonal variation in grassland basal cover are presented. Seasonal stability appears to have been taken for granted but has not yet been shown experimentally. The experimental area is situated in the National Botanic Gardens, Pretoria, at 28 degrees 18' E and 25 degrees 44' S on a gentle, southwest-facing slope with an annual rainfall of 630 mm. The vegetation cover is an open, bunch grassland. The construction of a portable bridge for establishing 1100 relocatable points is described. Basal cover, measured by wheel-point and bridge-point methods, showed a statistically significant seasonal increase through summer and a decrease again after the rainfall began decreasing with the onset of winter. An initial small rise and fall in basal cover at the beginning of spring was shown by the wheel-point survey only. Inspection of individual species behaviour showed that the seasonal changes in basal cover are a result of small changes in basal cover of many species. Possible sources of error in the application of the point technique which were revealed during the study are given.

Keywords: bunchgrass|species lists|methods|techniques|plant species|wheel point methods|Pretoria|long term studies|basal covers|grasslands|seasonal variations|vegetation cover|bridge point methods (ill)