Die invloed van gesimuleerde beweiding op die produksie van enkele efemeerplantspesies van Namakwaland

Abstract

The effect of various simulated grazing and water stress treatments were studied in three winter ephemeral species, namely Dimorphotheca sinuata, Grielum humifusum and Osteospermum hyoseroides by means of pot trials. The intensity of water stress, the intensity and frequency of grazing, as well as the phenophase of the plant, determined the reaction of plants to grazing. Grazing had a large effect on the production of the plants of all three species. Dimorphotheca sinuata and Osteospermum hyoseroides are strict ephemeral species and reacted similarly to grazing, while the reaction of Grielum humifusum, a facultative perennial species, differed considerably from the above-mentioned species. Grazing, in general, led to a decrease in the total biomass of D. sinuata and 0. Hyoseroides plants. High intensity grazing of mature plants led to a decrease in plant production. Frequent grazing of leaves, stems and reproductive organs led to delayed phenological development of plants. Light grazing before and at the time of bud formation, as well as high intensity grazing before bud formation, had the least disadvantage for D. sinuata and 0. hyoseroides. Weekly or continuous grazing on the other hand disadvantage D. sinuata and 0. hyoseroides plants. Grielum humifusum was not affected negatively by grazing. A single high or low intensity grazing treatment during bud formation or a weekly grazing treatment during the bud formation and flowering stages, in various ways benefitted G. humifusum plants. Grazing of G. humifusum led to higher reproductive allocation, whereas it led to a decrease in the fruit production of D. ,sinuata and 0. hyoseroides. Moderate water stress had no negative effect on the total production of Dimorphotheca sinuata plants. Grazing of moderately water stressed plants, should be limitted to the early phenological stages. For optimum utilization of D. sinuata and to ensure a good flowering display, it is therefore recommended that a moderate water stress treatment is combined with a single high intensity grazing during the earlier phenophases. Fieldwork, by means of exclusion plots, was done on the Goegap Nature Reserve in Namaqualand. Ephemeral plant species were utilized during the winter, as well as during summertime. The abundance of showy plant species was decreased under circumstances of high grazing intensities. Antelope preferred plant species such as grasses, Foveolina albida, Galenia sarcophyla, Arctotis fastuosa and Mesembryanthemum karrooense. In general to ensure the survival of the plant species; for maximum fruit production and a spectacular floral display, the ephemeral plants of Namaqualand should not be grazed intensively.