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Ecological patterns and importance of forest understory herbs in a tropical forest site in southeast Cameroon

Gorillas depend on herbaceous plants that constitute an important source nest-building materials and food. The ecological patterns and the use of herbaceous plants were studied in a tropical forest site of south-east Cameroon to assess the influence of ecological factors on these resources and establish a link between environmental variables and herbaceous plants availability and use by gorillas. Species diversity and stem density were determined by identifying and counting herb stems in a series of plots distributed in different habitat types. Soil fertility parameters and other abiotic variables were recorded in a set of plots, and herbaceous plants were monitored in these plots to investigate possible influences of environmental factors on their availability. Nests built by gorillas were seasonally monitored during an extended period to identify the plant species used in their construction and classify them in terms of preference. Preferred herb stems and gorilla nest sites were inventoried in different habitat types to describe the relationship between herb availability and gorilla distribution. Herbaceous plants of the families Marantaceae and Zingiberaceae were preferentially used by gorillas. Abiotic factors such as light and organic matter had stronger effects on herbs and mostly explained spatial variations in their availability. The spatial variability in the magnitude of abiotic factors translated to spatial variations in diversity and stem biomass, dispersion and density of herbaceous plants. These environmental gradients influenced gorilla ranging patterns, as they commonly built nests and harvested their herb foods in habitats with high herb species diversity, many large-size herb stems, more pronounced herb clumps and high herb stem density. Stem density and species diversity were high in the study site, and gorillas used a high diversity of plant species to build nests compared to other sites, emphasizing variability in the availability of nest building materials and habitat differences across their range. At the temporal scale, climatic variables such as rainfall, temperature and air humidity did not appear to influence total herb density, as there were only little variations in the number of stem recorded throughout the year. As a result, temporal changes in the plant composition in gorilla nests were not important despite seasonal changes in the use of nesting habitats by gorillas. Recently disturbed forest areas and less-accessible swamps which are characterized by a limited visibility and a high density of forest herbs can play a crucial role in the ecology and conservation of gorillas as they provide abundant and clumped nest-building materials, year-round nutrient-rich herbs and natural protection from hunters. Although light appears to be an important factor of herb availability, soil properties and climatic variables potentially represent important drivers. Conservation-applied research efforts should therefore focus on issues such as climate change effects on gorilla plant resources and the impact of logging-induced alterations of canopy and forest soil properties on herbaceous plants.
Datum:1 jan 2008  →  1 dec 2012