Soil loss and run-off in Umfolozi Game Reserve and the implications for game reserve management.

Abstract

Two management blocks were set aside in Umfolozi Game Reserve

(UGR) to compare different management approaches. In one, the

non-cull block, a noninterventionist policy was followed and no

large mammals were removed, while the other, the cull block was

subjected to the same game removal treatment as the remainder of

the reserve. The main objectives of this study were to determine

the relationships between vegetation, soil surface variables and

both soil loss and rainfall run-off, to derive predictive models

for run-off and soil loss based on vegetation and soil surface

variables, to determine the relationship between different levels

of soil erosion and the production potential of soils, and to

determine the relationship between different levels of soil

erosion and herbaceous species diversity.

Rainfall simulator trials and natural run-off plots were used to

collect quantitative data on soil loss and run-off. Bivariate

scattergrams showed that the relationship between soil surface

and vegetation variables plotted against soil loss was

curvilinear. "Susceptibility to erosion" showed the highest

positive correlation, and "surface cover" the highest negative

correlation with soil loss. The relationship between annual

run-off and both the soil surface and vegetation variables was

also curvilinear, with "soil capping" showing the highest

positive and "litter cover" the highest negative correlation with

run-off. Using multiple regression analysis it was found that

"susceptibility to erosion" and

predictors of annual soil loss.

"surface cover" were the best

"Soil capping" and "percentage

contribution of

run-off.

forbs" were the best predictors of annual

No clear relationship between either soil loss and stocking rate,

or run-off and stocking rate was apparent in the two experimental

blocks, and the differences in soil loss and run-off could not be

explained by differences in stocking rate alone. There were

however defects in the experimental design which invalidated the assumption that the stocking ~ate diffe~entia1

management blocks would inc~ease with time.

between the two

Because of the above deficiency, an a1te~native study a~ea on the

weste~n bounda~y fence, which allowed fo~ pai~ed sampling sites

on eithe~ side of the fence, was chosen. Ge~lach t~oughs we~e

used to measu~e soil loss. The g~eatest va~iabi1ity in soil loss

was explained by the position of the plots on the slope ~athe~

than whethe~ the plots we~e in UGR o~ in adjacent KwaZu1u.

Simi1a~ly, diffe~ences in topog~aphy, ~athe~ than diffe~ences in

1anduse, exe~ted an ove~~iding effect on A-ho~izon depth, he~bage

accumulation and g~ass species ~ichness. Conside~ing the ~esu1ts

obtained, the opinion that a noninte~ventionist policy would lead

to a decline in vegetation p~oductivity and to a 10ng-te~m

~eduction in species dive~sity appea~s to be unfounded.

Finally, based on the data collected and on a ~eview of cu~~ent

scientific 1ite~atu~e, changes to the Natal Pa~ks Boa~d soils

policy and objectives a~e suggested, and the objectives a~e

t~ans1ated into ope~ationa1 management goals.