Research

:: BETAMPONA THREATENED BY INVASIVE EXOTIC SPECIES

Quick Links

While habitat loss remains the primary cause driving species extinctions, the problem of invasive species has grown to such an extent that it is now considered to be the second or third leading cause of extinctions worldwide. The extent of ecological damage invasives can bring about in isolated habitat patches can result in their complete loss.

The IUCN recognizes the extreme threat invasive species represent and have therefore ranked control of invasives as a priority objective for conserving the world's biodiversity. In their guidelines they write: "When a potentially alien invasive species is first detected, mobilize and activate sufficient resources and expertise quickly". They recommend total eradication whenever possible but warn that a well designed management plan must be in place because: "procrastination markedly reduces the chances of success" (IUCN Guidelines for the Prevention of Biodiversity Loss Caused by Alien Invasive Species, 2002).

Optimizing Resources

Accomplishing multiple goals in the course of a single project stretches what can be accomplished with limited funds. In 2009 the MFG initiated research to assess the most effective and least environmentally damaging method to control guava in a rainforest habitat.This work provided an opportunity to offer Lala Randiatavy Manager of Ivoloina's Conservation and Training Center, advanced training in natural resource management. Lala is now enrolled in a PhD program at the University of Antananarivo . Our Research Director, Dr. Karen Freeman oversees his research and is a member of his Ph.D. committee. Focusing his work on a significant conservation challenge, Lala's graduate studies will prepare him to become one of the well educated professionals Madagascar requires to tackle the complex issues inherent in conserving the island's rich but highly threatened biodiversity.

The Status of Invasive Plant Species in Betampona Natural Reserve

The problem of invasive plant species within the borders of Betampona Natural Reserve was already recognized when the MFG first began working in the forest. Vast monospecific stands of wild ginger (Afromomum) flourished in the northwestern quadrant of the Reserve that had been used for tavy before Betampona was designated a protected area. That the burned area never recovered suggests that wild ginger blocks all regeneration of natural primary forest.

Over the years, the highly invasive strawberry guava (P. cattleianum) has been encroaching into the Reserve along its southern border. The same species that occurs in Betampona is considered to be one of the worst invasive exotics in Reunion, Mauritius and other neighboring islands. The ecological damage that a related guava species (P. guajava) can cause has been well documented in the Galapagos Islands where it too out-competed endemic flora.

A characteristic shared by guava and wild ginger is that the fruit is not only edible but highly preferred by some lemur species. A four month study that focused on the feeding ecology of the of the white-fronted brown lemur, Eulemur fulvus albifrons found that during this period the study groups were observed feeding on 38 plant species. Guava was found to be preferred, not only by those individuals within the study group that resided in the secondary forest but also individuals whose home range was in the primary forest. Observations showed that after feeding extensively on guava along the forest periphery, the lemurs dispersed guava seeds through their feces when they returned to the forest interior. Lemur feces serves as an excellent germination medium for the seeds; indeed, E. f. albifrons' feces was found with seeds of guava germinating in the crooks of trees, an alarming indication that guava can grow almost anywhere!

Betampona 1957

Yidy and Justin collecting data

Betampona 1997

The above maps shows forest loss from 1957 to 1997. Invasive exotic plant species have spread from the forest's edge further into the Reserve and now represent a major threat to native flora and the diversity of fauna species dependant on them.

To obtain an understanding of the extent to which guava and wild ginger had taken hold within Betampona, the MFG supported the Master's thesis research of graduate student Yedidya Ratovonamana from the University of Madagascar Antananarivo. Using GPS Yidy mapped the distribution of the two exotics in the Reserve and showed that guava had already overtaken approximately 365 hectares of natural forest. As part of his research, Yidy also investigated the he regenerative abilities of native tree species by establishing a series of study plots with and without guava. The results clearly showed that guava inhibits the growth of native tree seedlings and thereby can profoundly change the nature and structure of a forest. This research may be one of the very few datasets available to Madagascar National Parks that quantifies the impact that an invasive plant can have on Madagascar's forests. Such evidence was important in gaining approval to carry out the next stage of our research, to assess which of four trial methods is the most effective and least environmentally damaging to control guava in a rainforest habitat.

The above figure from Ratovonamana's thesis shows the relationship between the diversity of species and density of invasive exotics on 10 study plots. Invasive species changed the soil PH and, by blocking light from penetrating to the forest floor, prevented the germination of native species.