The Manica Highlands, spanning Zimbabwe and Mozambique, are a birding paradise characterised by exceptional levels of floral and faunal endemism. This region serves as a vital habitat for several iconic species, including the samango monkey, Blue Swallow, and blue duiker. Among these species, the Blue Swallow stands out as a critically endangered intra-African migratory bird, endemic to sub-Saharan Africa, with a particular preference for breeding in montane grasslands. Nyanga National Park, located within the Manica Highlands, is one of the last known breeding grounds for the Blue Swallow, supporting approximately 200 breeding pairs. However, the ecological balance of this crucial habitat is under severe threat. Invasive alien plants, notably Australian acacias (wattles) and pines, are altering the landscape, leading to localised extinctions of the Blue Swallow. This situation poses a significant risk of irreversible decline to the species’ population. Immediate action is imperative to mitigate these threats and safeguard the long-term survival of the Blue Swallow.
To preserve the remaining breeding sites, targeted conservation interventions, including the sustainable management of the invading wattles in montane grasslands and habitat restoration is required. Current efforts to manage invasive alien plants have been localised and based on mechanical clearing. In addition to being costly and logistically challenging, these interventions have had little impact due to the plants having rapid seedling recruitment from the long-lived seed banks and fast growth rates. Zimbabwe currently has limited resources especially to put towards conservation efforts. Thus, a cost-effective self-perpetuating management initiative would be the most appropriate solution to manage these woody invaders. Biological control is a weed management technique that involves the use of living organisms to prevent or reduce the losses or harm caused by pest organisms. It is species-specific, meaning that natural enemies are selected based on their ability to effectively target and control the weed species of concern while having very little to no negative impacts to non-target organisms.
Pioneering work by the University of Cape Town Scientists led by Professor John Hoffmann and Fiona Impson has resulted in the implemented one of the most successful and globally recognised biological control programmes for Australian wattles (see Hoffman, Impson 2023 references). The programme is based on highly effective host-specific seed-feeding biological control agents, including Melanterius weevils and flower-galling Dasineura midges. The insects reduce the reproductive abilities of the target tree species through a reduction in the soil seed bank of the trees and seedling recruitment, ultimately slowing their spread into remaining patches of native vegetation.
The Centre for Biological Control Rhodes University is in the process of seeking permission to expand this successful biological control programme into the Manica highlands. In order to do that they are working with Kundai Dube – no stranger to birdlife, being the terrestrial ecologist from Nyanga National Park and National Coordinator for Ornithology. Kundai is currently conducting comprehensive pre-release studies to assess wattle population demographics and their reproductive ecology (seedling recruitment, number of seeds produced and size of the soil seed bank) as well as impacts on native vegetation and Blue Swallow habitats. This data will provide a baseline for evaluation of proposed interventions. Another key aspect will be stakeholder consultations to determine any potential conflicts of interest associated with the management of the invasive wattles. Dr Gerald Chikowore (CBC Zimbabwe) is currently working with the Department of Agricultural Research, Innovation and Specialist Services to obtain the required authorisations. Gerald has actively been promoting and implementing biological control in Zimbabwe for the last four years with the successful recent releases of the water hyacinth hopper Megamelus scutellaris against water hyacinth and the Salvinia weevil Cyrtobagous salviniae against Kariba weed.
The introduction of biological control measures in the Manica Highlands grasslands presents a promising avenue for sustainable, long-term invasive alien plant management. This approach not only supports the conservation efforts of the endangered Blue Swallow but also aids in preserving other endemic species, thereby contributing significantly to the overall integrity and functionality of the ecosystem. It is important to note that biological control programs are not immediate solutions, the initiative targeting Australian acacias in South Africa took over twenty years to yield significant results. The investment into this program has proven to be worthwhile, given the sustained and widespread suppression of acacias. With the enormous benefits observed in South Africa, prioritising the implementation of similar biological control measures in the Manica Highlands is crucial. While other control methods will continue to play a role, the expectation is that the long-term advantages experienced in South Africa will eventually be realised in Zimbabwe as well.
If you are interested in learning more about this initiative or wish to offer support—especially considering its current operation on limited resources—please feel free to contact Grant Martin or Gerald Chikowore.
