A Preliminary Study of the Temporal and Spatial Biomass Patterns of Herbaceous Vegetation Consumed by Mountain Gorillas in an Afromontane Rain Forest

Abstract

Although many animal species consume herbaceous vegetation found in African tropical forests, little is known of the temporal and spatial availability of these plants. From September 2004 to August 2005 we conducted a study that quantified the temporal and spatial biomass availability of 20 species of herbs frequently consumed by endangered mountain gorillas at two locations (Buhoma and Ruhija) in Bwindi Impenetrable National Park, Uganda. In general, the biomass of herbs varied over the study period, but these changes were relatively small. For 12 of 18 and nine of 11 species in Buhoma and Ruhija, respectively, herb biomass differed significantly among habitat types. Of the nine species found in both locations, seven species had a higher biomass at Ruhija, one species had a higher biomass at Buhoma, and one species showed no difference. These results demonstrate that herb biomass varied little temporally but spatial differences in herb biomass were more pronounced. Future studies should investigate the variables that may influence herb phenological patterns such as rainfall, light, soil quality, previous disturbance regimes, and animal foraging and trampling damage.

Factors Influencing Ranging on Community Land and Crop Raiding by Mountain Gorillas

“…Against our predictions, the availability of food resources inside the park had no influence on the number of days groups ranged outside the park or crop raided. Hence, there appears to be no need for gorillas to supplement their diet with crops in times of low fruit availability as abundant and high‐quality herbaceous vegetation is available throughout the year (Nkurunungi et al ., ; Ganas et al ., ). In sum, what was available along the park boundary was driving gorilla foraging outside the park and crop raiding, not a lack of food resources within the forest.…”

“…Ten nested quadrats on alternate sides along each transect in intervals of 20 m were sampled. For herbs, we measured stem length and counted leaves in 1 m 2 plots, shrubs were counted in 5 m 2 and trees were sampled in 10 m 2 plots by measuring diameter at breast height (for more details, see Ganas et al ., ).…”

“…We calculated an average herb biomass g m −2 per group using only the transects included in a group's home range. Because of the low temporal variability of herb biomass in Bwindi (Ganas et al ., ), we used one estimate per group for the whole study period.…”

“…To reduce the frequency of gorillas ranging outside the park and crop raiding, it is necessary to relate these patterns to the availability of resources outside and inside the protected area, both of which vary over time and space (Ganas, Nkurunungi & Robbins, ; Seiler, unpubl. data).…”

Assessing the role of megafauna in tropical forest ecosystems and biogeochemical cycles – the potential of vegetation models

“…Rodents can sometimes cause higher seedling mortality than elephants (Piiroinen et al 2017). Additionally, some processes such as trampling and uprooting have only been studied sporadically (Ganas et al 2009, Kurten 2013, Omeja et al 2014, while other processes such as the impact on soil and the transport of digested biomass have not been evaluated (Wing and Buss 1970, but see also Braithwaite et al 1984). For example, Wing and Buss (1970) estimated that 413 forest elephants in Kibale could move roughly 22 500 t of material per year, and that trampling of herbaceous vegetation could protect the soil and reduce runoff.…”