The occurrence of C3 and C4 grasses in fynbos and allied shrublands in the South Eastern Cape, South Africa.

There are roughly equal numbers of C3 and C4 grass species in fynbos and allied shrublands of the warm temperate coastal regions of the south eastern Cape. Subtropical-tropical C4 species have the highest relative cover in all shrubland types, particularly in renosterveld communities on moderately fertile soils. Physiological characteristics of C3 and C4 grasses predict that C3 species will be most abundant in cool, shaded sites. This prediction, and the hypothesis that relative C3 grass cover would be highest on infertile soils, were tested by correlation and regression analyses. Results show that C3 grass cover is significantly correlated with increased post-disturbance vegetation age, low intensity grazing, high litter cover and cool, steep, poleward slopes. All these factors contribute to lower growing season temperatures, favouring the competitive growth of C3 species. Amongst the soil variables, high sand content and low levels of total nitrogen emerged as predictors of high relative C3 grass cover.