Impact of Lantana Camara invasion on a cattle/wildlife ranch: A case of Imire Ranch, Wedza District, Zimbabwe

Abstract

The impact of Lantana camara invasion in a mixed game/cattle ranch was assessed at Imire Ranch using remote sensing and ground truthing techniques. Vegetation communities of the ranch were classified and mapped as a way of determining the pattern and extent of L. camara invasion. NDVI was used as a proxy for net primary productivity to assess the impact of invasion on primary production. LandSat images from 2001 to 2013 were used to assess the spatial extent and trends in L. camara invasion over a twelve-year period. Differences in key edaphic variables among invaded, managed and non-invaded sites were determined as a means of assessing impacts of invasion on floristic composition, abundance and diversity. Nine vegetation types were distinguished and described floristically and physiognomically. Five woodland communities constitute the primary vegetation components of the range, namely: Brachystegia spiciformis woodland, Brachystegia spiciformis-Julbernardia globiflora woodland, Julbernardia globiflora-Brachystegia spiciformis mixed woodland, Acacia sieberiana –L. camara woodland and Mixed Acacia woodland. Two grassland communities were distinguished where Aristida sp. or wetland grasses and sedges dominated. The only natural grassland community in the ranch is the wetland grassland as the other grassland community represents former cultivated lands. An Acacia nilotica- Combretum molle bush land was also distinguished as well as small Eucalyptus plantations. The highest cover and abundance of L. camara was observed in a section of the ranch occupied by A. sieberiana where nitrogen enriched soils present a conducive environment for the invasive species. L. camara also tended to be confined to nutrient rich termite mounds in B. spiciformis woodlands and in wetland grasslands with higher water and nutrient content. The invasive species also occurred on open sandy soils and mesic conditions in Eucalyptus plantations. Though it only occupied a small section of the ranch, the invasive species appeared to be highly adaptable, with the potential to spread into other vegetation types as observed in several vegetation communities, though in small isolated patches. L. camara invasion had lowered the diversity of herbaceous species. The area occupied by L. camara indicated a persistent decline in NDVI between 2002 and 2013. The invasion also appeared to have impacted on soil physico-chemical properties, raising soil pH and N, P, K levels.