Slope aspect of a mountainous grassland landscape shapes the structure of an encroaching shrub (Euryops floribundus N.E. Br): insights from communal grazing sites located at varying distances from rural homesteads

Abstract

Mountainous grassland landscapes are severely threatened by the proliferation of shrub encroachment. So far, it remains unclear though how slope aspect coupled with land disturbances linked to the proximity of homesteads to communal grazing sites affects the distribution, density and structure of the encroaching shrubs in these grassland ecosystems. In this study, we investigated the role that slope aspect plays in determining the density and structure of an encroaching shrub species Euryops floribundus N.E. Br in three communal grazing sites located at varying distances from rural homesteads in a semi-arid mountainous grassland in the Eastern Cape Province of South Africa. Three sites were strategically chosen in Cala communal grazing lands in an encroached mountainous grassland landscape that depicted north and south-facing slope aspects. The selected sites were Tsengiwe; a site located in close proximity to homesteads at a distance of less than 100 m, Upper Mnxe situated at an intermediate distance ranging from 200 to 800 m away from homesteads and Manzimdaka, which was located furthest from homesteads at a distance greater than 1600 m. In each site and corresponding slope aspect, the density and structure of the shrub E. floribundus were evaluated on 36 randomly distributed plots, yielding a total of 108 plots across all sites. We found that shrub density was significantly higher (50%) on the north-facing slope compared to the south-facing slope in Tsengiwe, the site located near homesteads. Shrub height was significantly higher (53 and 17%) on the north-facing slope compared to the south-facing slope at Upper Mnxe and Manzimdaka, which were located at intermediate and furthest distances from the homesteads. Notably, shrub height was significantly lower (37%) in the north-facing slope compared to the south-facing slope in Tsengiwe. Following a similar pattern to shrub height, total stem number was significantly higher (20 and 85%) in the north-facing slope compared to the south-facing slope at Upper Mnxe and Tsengiwe, respectively. Shrub crown area was higher (33 and 11%) in the north-facing slope compared to the south-facing slope at Upper Mnxe and Manzimdaka, respectively. A strong positive relationship was established between the height of shrubs and their longest crown diameter, shortest crown diameter and shrub crown area across all sites, suggesting that the investigated shrub species E. floribundus employs its structural characteristics to survive, and thrive and this was more evident in the north-facing slope. The results highlight the importance of considering the proximity of homesteads into account in ecological studies, and puts emphasis on improved understanding of the vegetation patterns shaped by shrub encroachment in mountainous grasslands, which is crucial in the development of effective land management strategies.