Effects of intensity and height of shading on the tiller initiation of six grass species from the Highland sourveld of Natal

Grass species of the conservation areas of the Natal Drakensberg are divided into two ecological groups. Decreaser species are those which decrease with over- or under-utilization, while increaser I species are those which increase with under-utilization. The effect of intensity and height of shading on decreaser species (Themeda triandra, Heteropogon contortus and Trachypogon spicatus) and increaser species (Tristachya leucothrix, Harpochloa falx and Alloteropsis semialata) was determined in potted plant trials. Results of this study support the hypothesis that decreaser species were more sensitive to low light intensities (30% full sunlight) than increaser species. These two species groups did not, however, differ in their response to height of shading. The results suggest that different fire regimes resulting in changes in canopy cover and light quality are important mechanisms in regulating tiller initiation in perennial grasses. Grassoorte van die Natalse Drakensberg word in twee ekologiese groepe verdeel. Afnemerspesies verminder met oor- of onderbenutting, terwyl toenemer-I-spesies vermeerder met onderbenutting. Die effek van digtheid en hoogte van beskaduwing op afnemerspesies (Themeda triandra, Heteropogon contortus en Trachypogon spicatus) en toenemerspesies (Tristachya Ieucothrix, Harpocloa falx en Alloteropsis semialata) is met behulp van potproewe vasgestel. Die resultate van hierdie studie ondersteun die veronderstelling dat afnemerspesies meer gevoelig is vir lae ligsterkte (30% volle sonlig) as toenemerspesies. Hierdie twee ekologiese groepe het egter nie in hulle reaksie ten opsigte van die hoogte van beskaduwing verskil nie. Die resultate dui daarop dat verskillende veldbrandstelsels wat veranderings in kroonbedekking en ligkwaliteit tot gevolg het, ’n belangrike meganisme in die regulering van spruitontwikkeling is.