The work of Barbara Haurez, a researcher at the Forestry Laboratory of Tropical and Subtropical Regions of Gembloux Agro-Bio Tech (University of Liege), shows that western lowland gorilla populations, which might be resilient to the practice of selective deforestation common in Central Africa, play a vital role in seed dispersal both from a quantitative and qualitative point of view. By dropping the majority of ingested seeds in its nest site, the gorilla contributes to the regeneration of certain plant species: liana, herbaceous plants, trees etc. This can only be beneficial for the forest and all the different species that dwell in it (including humans!).
The mountain gorilla (Gorilla beringei beringei) is probably one of the most emblematic animals in the Congo Basin, particularly in Virunga National Park in the Democratic Republic of Congo. Less known to the wider public but nonetheless spectacular, the western lowland gorilla (Gorilla gorilla gorilla) frequents the more western part of Central Africa. Even though its name does not suggest it, the western lowland gorilla likes the forest habitat, particularly dense humid forest typical of Gabon, Cameroon, the Central African Republic and Equatorial Guinea etc. Despite its relatively low population (estimates vary between 100,000 and 200,000 individuals), this species has been classed as being “in critical danger of extinction” by the International Union for the Conservation of Nature (UICN). In barely twenty years, this species with low fertility levels and delayed sexual maturity has seen its numbers fall by nearly 50%. The different factors threatening the survival of this species (deforestation, poaching…) have led the UICN to predict that the population of this species will fall by 80% over the next forty years, a very worrying statistic.
Like its mountain cousin, the lowlands gorilla lives in groups dominated by an adult male (or “silverback”). However, unlike the mountain gorilla, it is essentially frugivorous. It is also diurnal and generally covers up to two or three kilometres per day in search of fruit, seeds, leaves, tree bark and occasionally insects. Being able to observe the animal in its natural environment which is dense and impenetrable is a daunting prospect. The animal is also shy and will retreat at the slightest hint of an unusual odour or suspicious noise. Every evening, the gorillas chose a nesting site, under a somewhat open canopy, where they build nests (mostly on the ground) made of grass stems, lianas or tree branches. There they spend the night, the females share their nest with unweaned youngsters.
Does the combination of the gorilla’s diet and daily movements play a role in the dynamics of the dense tropical rainforest? This question is central to the work conducted by Barbara Haurez who was recently awarded a doctorate in Agronomic Sciences and Biological Engineering at Gembloux Agro-Bio Tech (ULg). “For twenty years, research teams have been interested in the role played by various animals in seed dispersal (elephants, monkeys etc.) by means of their excrement. In particular, they have demonstrated the phenomenon of “directed dispersal: certain “dispersing” animals drop the seeds in places that are particularly favourable for the germination of seeds and the growth of seedlings. This is the case with the gorilla which, by dropping most of the seeds in the nest site, contributes to the regeneration of certain plant species: lianas, herbaceous plants and trees”, she explains.
Tracking the gorillas’ nests
It is still necessary to distinguish the beneficial species according to the region in question. For example, the question arises as to whether this phenomenon of seed dispersal could benefit certain species of trees or plants that are intended for human use in the form of food, pharmacopeia products or the timber industry. In the context of the exploitation of central African forests for timber production, it is also interesting to examine the impact of timber harvesting on gorilla populations and, conversely, the impact of the gorillas themselves on forest regeneration following the activities of lumberjacks and loggers.