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What you need to know about Alnus viridis an exotic plant eating up the vegetation of Mgahinga Gorilla National Park-Uganda

This is an article written by Ms Alice Mbayahi from International Gorilla Conservation Program

“If not aggressively eliminated, this exotic fast-growing tree Alnus viridis will eat up the entire natural park vegetation, threaten the survival of the wildlife therein and the integrity of the unique and beautiful Mgahinga gorilla national park”. Samuel Amanya – Senior Warden In-Charge of MGNP.

Covering 33.7km2 Mgahinga gorilla national park is the smallest national park in Uganda. It is known for its striking three dormant volcanic peaks with superb crater lakes, swamps and gorges. Mgahinga gorilla national park is a home to 76 species of mammals ( but specifically it is the only place where golden monkeys are found in Uganda and also part of the trans boundary Virunga Massif and its population of mountain gorillas. The park’s other conservation values include preserving of the Batwa/Pygmies cultural values and the critical water catchment island surrounded by highly porous volcanic soils. According to the Senior Warden In-Charge of Mgahinga, the park collects about 4-5 billion Uganda shillings as tourism revenue annually directly and indirectly.

Unfortunately, this outstanding natural heritage is being threatened by rapidly multiplying exotic species that are displacing plants which the wild animals feed on. The invasive plants which include Alnus viridis (85%), Black wattle (10%) and Eucalyptus spp. (5%) have covered about 62.45 hectares (0.625Km2) of the park in Muremure area, according to a concept note on Eradication of Invasives in Muremure area (2019) written by the Ecological Monitoring and Research department of BMCA.
A field assessment done by UWA in 2013 established that the exotics had covered about 19 hectares then, and in 2015 UWA working with a community based organization, Gitenderi Protect Environment Group (GPEG) with support from the Greater Virunga Trans-boundary Collaboration (GVTC) embarked on eliminating the exotics within the park boundary. However, the elimination method used then wasn’t effective as the tree stumps and roots later sprouted and continued to grow.
It is sad, alarming and dangerous that in less than four years the invasive species have rapidly multiplied from 19 to 62 hectares. At this rate if nothing is effectively done, all the indigenous vegetation of the park will be no more in the coming years – what a threat, what a loss!

A part covered by alnus whose underneath has completely been eaten up. Photo credit: UWA

Alnus viridis is a light-demanding, fast-growing plant that grows well on poorer soils and in mountainous/hilly landscapes. Its seeds spread so easily wide and fast by wind. Alnus was introduced in the region as an agro forestry tree for soil fertility improvement.
According to Joseph Arinaitwe, (who spearheaded the recent invasive species assessment of Mgahinga gorilla national park in July 2019), Alnus viridis has overwhelmingly invaded the indigenous vegetative species, grossly interfered with the habitat for wildlife and affected the foraging patterns of fauna since most of the invasive flora species are not palatable and usually out compete and most times totally eliminate the indigenous vegetation mix. Joseph regrets to add that the only habituated trans-boundary mountain gorilla group in MGNP – Nyakagezi, and the golden monkeys previously living in this area seem to have migrated from the affected area.

“Mgahinga is a very small park, at this rate there isn’t much left apart from saving the situation. We need a strong coordinated approach to eradicate this stubborn exotic plant completely” Dr. Andrew Seguya, Executive Secretary GVTC notes.

Eradication of the invasive species should be done as soon as possible before the newly sprouted invasives mature enough to effectively disperse more seeds to the surrounding area. Mgahinga being rocky makes mechanical measures almost impossible to apply, future elimination methods however need to be clearly researched and thought out to ensure complete elimination of the invasive species. Commenting on future interventions Joseph says elimination of the invasives should never again be a single intervention but a series which allows for periodic monitoring and uprooting of any sprouting remnant roots and complete elimination of any germinating seedlings until the exotic plants are completely eradicated.

The removal of the exotic species allows for regeneration of the native species and herbage, promotes biodiversity conservation and ensures the ecological integrity of the protected area.

Given the trans-boundary nature of the protected area and the fast spreading nature of the invasive specie the problem needs not to be looked at as a Mgahinga problem but rather a problem for all. “The three countries/park authorities need to look at this exotic invasion as a challenge for all which requires joint assessment, planning, resource mobilization and implementation of the eradication exercise” Mr. Samuel Amanya states.

Mr. Amanya adds that although UWA is committed to eliminating the exotic species, it is continuously limited by both financial resources and technical expertise, for example this year’s budget allocated for the elimination of invasive species in MGNP is less than 10% of the total amount needed for this exercise. Probably more support from conservation partners can help save the situation, secure the habitat and its wildlife and also allow MGNP acquire its status as a UNESCO World Heritage Site that it is currently undergoing preparations for.

About GVTC

Greater Virunga Transboundary Collaboration is a framework for strategic, transboundary, collaborative management of the Greater Virunga Landscape


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