Responses of grass productivity traits to bush clearing in semi-arid rangelands in North-West Province of South Africa

Abstract

Woody plant encroachment threatens herbaceous plant productivity in many rangelands globally. We evaluated the impact of bush clearing on grass tiller, leaf and biomass production, and tuft sizes in the Kgomo-kgomo and Makapaanstad rangelands in North-West Province, South Africa. In each rangeland, the number of tillers and leaves, tuft sizes and biomass of eight dominant grass species were recorded in bush-cleared and uncleared treatments. The treatment and species interacted significantly (P < 0.001) for tiller and leaf production and tuft sizes. Bush clearing increased tiller production of bunch grasses but not stoloniferous grasses. At Kgomo-kgomo, bunch grasses (Panicum maximum (Jacq.) and Urochloa mosambicensis (Hack.) Dandy] had three to six times more tillers and leaves per plant in the cleared than uncleared treatment. At Makapaanstad, only annual bunch grasses [Brachiaria eruciformis (Sibth. & Sm.) Griseb and Tragus berteronianus (Schult.)] attained twice as many tillers and leaves per plant in the cleared compared to uncleared treatment. Biomass was 1776 ± 159 and 696 ± 159 g m−2 in cleared and uncleared treatments respectively at Kgomo-kgomo and 1358 ± 258 and 1089 ± 258 g m−2 at Makapaanstad. The tufts of bunch grasses were nearly twice as large in the cleared compared with the uncleared treatment at Kgomo-kgomo, whereas only stoloniferous grass tufts increased at Makapaanstad. Overall, bush clearing improved grass productivity and performance, but the responses varied by species.