Are Namibia's grasslands desertifying?

We compared the herbage standing crop on 31 farms along a rainfall gradient in Namibia (southwestern Africa) in 1997 with the results attained for the same gradient by Waiter (1939), We found that the slope for the regression of herbage yield on mean annual rainfall in 1997 was 5.93, i.e. 5.93 kg he rbage was produced per hectare for every 1 mm increase in rainfall along th e gradient, This regression slope is considerably lower than that in Waiter 's (1939) study (slope = 10.34). Thus, current grassland productivity per u nit of rainfall in Namibia is about half that of 50 years ago. There is no evidence of a change in annual rainfall over this period, nor is there any evidence that either short-term (current) or longer-term (11 years) stockin g densities affect current herbage yield, We conclude that, while desertifi cation has taken place, grazing over the last decade has not been the cause of this reduced productivity.