Trends in spatial distribution of alien woody species and primary production on invaded sites in Nyanga National Park, Zimbabwe

Abstract

The study sought to establish trends in spatial distribution of the invasive plants, Acacia mearnsii (black wattle) and Pinus spp (pines) and assess their impact on primary production in Nyanga National Park, Zimbabwe, over the past three decades. A stratified random sampling procedure, with three different strata, namely open montane grassland, sparsely wooded grassland and heavily invaded sites, was adopted. Digital imagery from ArcGIS was used in stratifying sampling units, followed by ground truthing. Results showed that the spatial extent of invasion increased over the years, reaching its greatest extent in 2010, while that of pines decreased during later years of the study period. The area occupied by montane grassland and natural woodland consequently decreased over the study period. The study also showed that soil pH and total phosphorus contributed the most to the differences between invaded and uninvaded sites. There was no significant difference in soil moisture and total nitrogen between invaded and uninvaded sites. The increased primary production that is attributed to dominance of woody species on invaded sites is associated with decreased species diversity.