Psidium guajava: Spatial distribution of invasive guava along roadways and trail ways within the Dwesa-Cwebe Nature Reserve

Background/Question/Methods

Under the South Africa National Biodiversity Act, the Eastern Cape Park and Tourism Board (ECPTA) is required to implement management plans to control invasive species within its nature reserves. The Dwesa-Cwebe nature Reserve, the location of this study site, is recognized by Conservation International for having the highest tree richness of all temperate forests on the planet, for it is part of the Maputaland-Pondoland-Albany biodiversity hotspot. The historically frequent anthropogenic disturbances related to the establishment of a hotel within the Cwebe side of the twin nature reserve, have facilitated the establishment of many non-native and invasive plant species including the Psidium guajava (common guava). Psidium guajava is fruit-bearing, facilitating rapid dispersal and is widely tolerant of drought, heat, frost, sea spray, and poor soil composition, suggestive of its potential to become invasive and out-compete native species. The aim of this research was to create a comprehensive map of Psidium guajava shrub distribution within Cwebe to (a) facilitate the removal and/or control of the shrub by the ECPTA, and to (b) document the patterns of guava distribution in the unique context of Cwebe, which is located in close proximity to rural and impoverished networks of communities, that are denied access to forest resources within the reserve boundaries. To map the species distribution in Cwebe, Trimble GeoXM GPS software was used to locate all Psidium guajava shrubs along 7 km of roadways. Transects were used to investigate the intrusion of guava in forest interiors, and a detailed literature review was used to explore the primary agents of dispersal (i.e humans, vervet monkeys, birds, cattle).

Results/Conclusions

In total, more than 5,142 shrubs were recorded. As expected, guava was restricted to roadways and was not found in adjacent forests. The abundance of guava along roadways frequented by people and animals suggests the importance of dispersal in its dominated distribution, but also highlights the potentially critical role of the fruit as a diet supplement for both humans and wildlife. Given that Dwesa-Cwebe is a critical case-study for exploring post-Apartheid conservation and land management issues, the removal of the shrubs likely would have complex socio-ecological implications.