INVASIVE SPECIES REMOVAL AND BIOLOGICAL MONITORING, ZIMBABWE

To eradicate invasive alien plant species in Victoria Falls National Park


The ecosystem of Victoria Falls National Park is a relic of a rainforest that closely resembles that of a true equatorial rainforest; the vegetation being supported by a seasonal spray of water from the Falls.  These conditions have supported the growth of invasive alien plant species (IAPS) over at least the last 30 years, such as lantana camara, ageratum houstonianum, nephrolepsis cordifolia, ipomea carica and solanum seaforthianum. These plants have been known to invade and replace indigenous vegetation that might result in the local extinction of some indigenous species.  Our hope is to completely eradicate IAPS in the Victoria Falls National Park area.  At present eradication efforts have been limited to mechanical methods.

To complement the eradication effort, a biological monitoring programme has been embarked upon, aimed at mapping eradicated areas, evaluating eradication efforts and measuring vegetation change directly resulting from eradication activities.  Various parameters are measured seasonally and trends are monitored to depict change.  Our plan is to enhance this study and monitor changes using high resolution satellite images.  Various vegetation indices can be used to estimate the changes in biomass.

Lantana camara with higher standing biomass than the other IAPS in the Victoria Falls rainforest and environs has been of particular concern.  It was first sited in the Victoria Falls National Park in the 1970s though very little was done to control it.

The first eradication exercise was implemented between 1975 and 1980. Eradication by the Zimbabwe Parks and Wildlife Management Authority (ZPWMA) was stopped between the years 1980 and 1999 and invasion over this period of neglect became serious.  Eradication resumed in 1999 and results are starting to show by way of evidence of mass regeneration of tree species in eradicated areas.  Lantana camara has now also invaded the gorges.  These places are largely inaccessible and have acted as reservoirs for seed.  Lantana camara - the wicked weed - is now a major issue in many regions of the Palaeotropics where it invades natural and agricultural ecosystems.  The plants can grow individually, in clumps or as dense thickets, crowding out indigenous species. It can become the dominant under-storey species, disrupting succession and decreasing biodiversity. Its allelopathic qualities can reduce vigour of plant species nearby and at some sites Lantana infestations have been so persistent that they have completely stalled the regeneration of some rainforests for decades.  Lantana can also greatly alter fire regimes in natural systems.  Lantana has many secondary impacts, especially in tropical countries where it can harbour several serious pests such as malarial mosquitoes and tsetse flies causing serious health problems.

Both ALERT and Environment Africa are working to enhance direct management intervention to undertake mechanical control of the weeds where uprooting and burning of the residue after drying is done.  Volunteers are joined by local sourced labourers that are hired to dig up the weeds.  The equipment used includes mattocks, hoes, rubber gloves and gumboots.  Through further funding we will be able to employ a greater number of labourers and source additional and more effective equipment in order improve the efficiency of the eradication undertaking.  We will also be seeking specialist equipment to attempt to deal with IAPS that have now infiltrated the less accessible Batoka Gorge.


Milestones:

2010:  4950 man / hours undertaken on the eradication effort during the course of the year

2012:  The program was suspended by the Government due to technical issues

2013:  120 man/hours have been undertaken in the eradication during the course of the year

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