Shrub-layer dominance by Leucosidea sericea (Rosaceae) in eastern Zimbabwe: evidence of native woody encroachment in Nyanga National Park

Native woody encroachment is transforming open ecosystems globally, yet its impact on Zimbabwe’s high-altitude montane grasslands remains poorly quantified. This study evaluated the ecological impacts of Leucosidea sericea Eckl. & Zeyh. (Rosaceae) encroachment in Nyanga National Park, Zimbabwe. We established 21 plots representing varying levels of encroachment: unencroached, moderately encroached, and heavily encroached. Shrub density increased sharply, exhibiting a threshold effect. Heavily encroached sites supported almost three-times more shrubs and were characterised by near-dominance of L. sericea. Tree height declined markedly along the encroachment gradient, indicating suppression of the tree layer, whereas grass richness and cover remained broadly stable. However, a pronounced functional shift occurred as shade-intolerant, fire-prone Eragrostis acraea was replaced by shade-tolerant Hyparrhenia rufa, implying reduced flammable fuels and dampened fire intensity. These patterns suggest a self-reinforcing transition towards a stable shrub-thicket state that may be resistant to traditional fire management. We recommend early intervention in moderately encroached zones and propose H. rufa dominance as an early-warning indicator of the impacts of native woody encroachment on montane grasslands. Recognising native woody encroachment as a conservation threat on par with invasive alien plants is essential for maintaining the integrity of Zimbabwe’s montane grasslands.