A GIS Habitat Map for the Kagwene Gorilla Sanctuary, Cameroon
The Cross River gorilla is the most endangered of all great ape taxa,
and its rare and increasingly fragmented populations continue to be threatened
by habitat loss and, to a lesser degree, hunting for the bushmeat trade.
The 11 or so sites in which the Cross River gorilla is still known are
spread across approximately 12,000 km² of extremely rugged and forested
terrain spanning the Nigeria-Cameroon border region, with remaining populations
estimated at 70-90 individuals in Nigeria, and 150 individuals in Cameroon
(Oates et al. 2003).
In the last decade a concerted effort has been mounted to learn more about
the Cross River gorilla, and to implement conservation action in both
Nigeria and Cameroon. As outlined in the Regional Action Plan for the
Cross River Gorilla (Oates et al. 2007), this has been spearheaded
by the Wildlife Conservation Society (WCS), working in collaboration
with host governments and other partners. Considerable success has been
achieved on a number of fronts, but efforts have been hindered by a lack
of understanding of both the areas in which remaining populations are
found, and the current and potential basic habitat requirements of the
subspecies. Moreover, site-specific conservation plans are hampered by
an absence of knowledge about habitats remaining in the area, as well
as their current usage by gorilla populations.
With this in mind, we have recently undertaken a project to produce a
habitat map for the newly formed (by Decree No. 2008/0634/PM issued 3
April, 2008) Kagwene Gorilla Sanctuary in Cameroon, in addition to an
analysis of gorilla nesting preferences within the sanctuary. Such knowledge
is essential to help guide practical field-based management activities
linked to the protection, and possible expansion, of the current population.
The Kagwene Gorilla Sanctuary (KGS) covers an area of 19.44 km2, and reaches
altitudes of roughly 2,000 m, lying between 06° 05' 55" and 06°
08' 25" North and between 09° 43' 35" and 09° 46' 35"
East. It is divided by a provincial boundary, and encompasses the northern
part of South West Province, and the southern part of North West Province,
of the Republic of Cameroon.
Nine villages surround the KGS, and villagers have historically utilized
land within the sanctuary boundary for farming and hunting to varying
degrees. Bororo settlements (settled grazers) are dotted within and surrounding
the sanctuary, and these pastoralists graze their cattle on areas of open
grassland adjacent to the Kagwene Mountain forests. Much of this land
is burned each year to encourage the growth of new grasses, often resulting
in the unplanned burning of forest. Currently, farmers also continue to
cultivate crops within the boundaries of the sanctuary, especially in
the southern sector of the reserve, with cocoyams the crop most commonly
grown beneath the forest canopy. WCS operates a research camp from within
the KGS, which has a permanent staff presence.
To produce a working GIS habitat map for the KGS, we undertook fieldwork
from mid-March to the end of May 2008. We aimed to map areas of farmland
and grassland within the sanctuary, and then to determine the variety
and distribution of vegetation within the undisturbed forested sections.
Using GPS units set to track-log, we walked around the edge of farms and
grassland patches. Farm areas were so numerous within the reserve that
we mapped a sample of them in this way, while the remaining farm distribution
was determined through conversations with gorilla trackers familiar with
the area, resulting in the creation of a second habitat category for our
map of "presumed farm under canopy". To assess habitat types
in the remaining forested zones of the sanctuary we undertook "recce
walks" (White & Edwards 2000), which involved using GPS to record
movements through the sanctuary, documenting vegetation changes as and
when they occurred. We recorded both top storey and understorey vegetation,
in addition to other information, such as understorey density, the slope
of the ground, and canopy cover. Data collected during this fieldwork
were downloaded into ArcGIS 9.1 and manipulated in order to generate habitat
maps for the forested areas, overlaying GPS points measured around farms
and grassland patches. To investigate nesting habitat preferences of gorillas
at KGS, data were used from WCS records collected between January 2006
and March 2008, and we re-visited these nest sites to reassess the top
storey and understorey type and density. This assessment relies on the
assumption that little change has occurred in the habitat between the
time of construction and re-finding the nest, which seems likely. We also
recorded a number of other aspects of the nest area, including measures
of visibility, aspect, slope and canopy cover, using the same methods
as were used during habitat mapping.
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Kagwene botanical survey Photo: Marion Rawson |
A preliminary analysis of the habitat map has shown that only a little
over half of the sanctuary is forested (i.e. under tree cover and not
farmland), and therefore potentially available to the gorillas. The other
half of the sanctuary is roughly split between farmland under canopy and
grassland patches. By overlaying nest site locations, we found that the
gorillas at Kagwene do not nest in either farmed or grassland areas. As
they are not known to crop-raid, farmland prevalent in the southern sector
of the sanctuary is clearly avoided by the gorillas, while grasslands
in the northern sector can be seen to fragment forest potentially suitable
for the gorillas.
Further analysis and dissemination of gorilla nesting habitat preferences
at the KGS are ongoing. This involves a full analysis of how the gorillas
nest with respect to available top storey and understorey habitats in
the sanctuary, and we hope to disseminate our results widely by publishing
them in a scientific journal. These analyses will add valuable insight
to our understanding of Cross River gorilla ecology. The habitat map will
provide an extremely useful tool for the WCS, who are assisting the government
with elaborating management strategies for the sanctuary, as well as for
gorilla trackers working on a daily basis within the sanctuary. Thanks
to the ongoing support of organizations such as the US Fish & Wildlife
Service, WWF, The Gorilla Organization, and Margot Marsh
Biodiversity Foundation, the conservation of the Cross River gorillas
of the Kagwene Gorilla Sanctuary is increasingly assured. However, further
support is needed to implement site-based action in all 11 known Cross
River gorilla sites (including parks, forest reserves, sanctuaries and
unclassified areas of forest), as well as in habitat corridors that provide
connectivity between these core areas.
Ruth Wiseman, Ymke Warren, Aaron Nicholas, Mary Mackenzie and James P. Higham
Ruth Wiseman is interested in the
research and conservation of endangered apes. She undertook GIS habitat
mapping of the Kagwene Gorilla Sanctuary, Cameroon, as part of the MRes
Primatology programme at Roehampton University, London.
Dr. Ymke Warren is the Research Coordinator for the Wildlife Conservation
Society's Takamanda-Mone Landscape Project with responsibilities that
include overseeing ongoing research in the Kagwene Gorilla Sanctuary and
field surveys in general.
Aaron Nicholas is the Director of the Wildlife Conservation Society's
Takamanda-Mone Landscape Project, with the core focus of conserving the
Cross River gorilla in Cameroon.
Mary Mackenzie is the Technical Manager at Roehampton University.
Her responsibilities include operational management of the Life Sciences
laboratories, GIS and cartography, and ecological and environmental fieldwork
support.
Dr. James P. Higham is a Post-Doctoral Researcher at The University
of Chicago. His research has included projects on baboon ecology at Gashaka-Gumti
National Park, Nigeria, and drill endocrinology with Pandrillus, Nigeria.
References
Oates, J. F. et al. (2003): The Cross River Gorilla: Natural History and
Status of a Neglected and Critically Endangered Subspecies. Pp. 472-497
in: Taylor, A. B. & Goldsmith, M. L. (eds.) Gorilla Biology. Cambridge
(Cambridge University Press)
Oates, J. F. et al. (2007): Regional Action Plan for the Conservation
of the Cross River Gorilla (Gorilla gorilla diehli). Arlington,
VA, USA (IUCN/SSC Primate Specialist Group and Conservation International)
White, L. & Edwards A. (2000): Methods for assessing the status of
animal populations. In: White, L. & Edwards A. (eds.): Conservation
Research in the African Rain Forests: A Technical Handbook. New York (The
Wildlife Conservation Society)