For four years, during missions that were spread over several months in the forest, the young researcher set about finding gorilla nests, harvesting their faeces (taking advantage of the abundant amount of fecal matter in the nest sites), in order to examine the seeds contained in the faeces and identifying and testing their germination conditions in various types of substrates and environments. This type of work, which is both laborious and somewhat adventurous, is facilitated by the partnership approach developed by the Forestry Laboratory of Tropical and Subtropical Regions of Gembloux, which is today an integral part of the Forestry Management Axis of Gembloux Agro-Bio Tech: in exchange for specialised scientific support (particularly for management plans designed in the context of certification frameworks like the “Forest Stewardship Council”, FSC), the researchers and doctoral students from the university benefit from logistical facilities within vast field study areas which are relatively well-preserved. In the present case, Barbara Haurez was able to complete her study in a forestry concession of some 600,000 hectares, managed by the Swiss company Precious Woods.  

“I became familiar with the tropical forest in Cameroon while doing a course to prepare my Master thesis which was on the subject of seed dispersal by the lowland gorillas of Gabon. In Cameroon, I had accompanied research teams in monitoring gorilla trails between nesting sites and had participated in the creation of a tree nursery. In Gabon, the main difficulty I faced at the outset was the same as the one I experienced in Cameroon: finding a sufficient quantity of excrement. It was like looking for a needle in a haystack! I found it helpful to use the traditional method of linear transects”. These grid systems (arranged in straight lines) covering vast territories are put in place by forestry prospectors in order to establish an inventory of tree species used in the timber industry. These systems enabled the young researcher to methodically cover an area of nearly 13,500 hectares, within which she counted slightly fewer than 150 nesting sites built by the gorillas. “I was able to calculate the density of nests using a computer software programme and to convert this into the density of animals using conversion factors”.

Washing dung in clear water

Once the dung were collected (making up about one kilo per unit and carried on the back…) they were washed in river water using sieves that are normally used for cooking. The purpose of this was to gather the seeds and begin the work of identifying them, mostly visually, with the help of a botanist. “During the twenty months spent gathering the seeds, I counted 59 plant species dispersed by the gorillas. One third of these species were of economic interest because of their use in the timber industry or non-timber forest products (Omvong - Dialium pachyphyllum; Ossabel - Dacroydes normandii; Adjouba - Dacroydes klaineana; etc.). The dung contained several dozen or even several hundred intact seeds (up to 500). But on average, they contained two different species. The most common were the Ebo (Santiria trimera), which is a small tree (ten to twenty metres in height) varying in colour from grey to a shade of yellow and whose fruit, is also eaten by humans, the Longhi (Chrysophyllum lacourtianum) and the Omvong (Dialium pachyphyllum), a larger species (up to 30 metres) whose larger individuals are generally indicative of older forests. The fruit of the Longhi and the pulp surrounding the seed of the Omvong are enjoyed by gorillas and humans alike. I also found a large quantity of Aframomum sp. or wild ginger. The fruit of this herbaceous plant is consists in a softish red shell containing seeds in a slightly sweet and spongy tissue”.  The dispersion of these four types of seeds by the gorillas is good for the local communities because, apart from crops such as the banana or the cassava, the villagers stock up on forest fruits both for food and traditional medicine. The gorillas clearly participate in the regeneration of species that supply fruit, roots and wood to human populations.

The second step involved studying the impact of the passage of the seeds through the digestive tract. For methodological reasons, two species were chosen:  the Ebo and the red Longhi (whose wood is occasionally used for industrial timber). “For these two species, I compared the rate of germination of four categories of seeds: those harvested in fruits and left as they were, those harvested in fruits but with the pulp removed, those harvested in excrement and cleaned, and finally, those harvested in excrement but covered in fecal matter. All of these were grown in the nursery. It became evident that the seeds that passed through the digestive system of the animal systematically showed an improved rate of germination. I also observed that the fecal matter contributed to the development of the seedling”. Barbara Haurez considers that this positive conclusion is probably valid for seeds other than those of the Ebo and the Longhi but this remains to be proven. The physico-chemical processes at work in the digestive tract have not yet been identified. It is clear, however, that passage through the digestive tract of the gorilla nullifies the negative impact of a fungus (still in the process of being identified) on the germination of Longhi seeds.