Usala Forest

Central Africa > Democratic Republic of the Congo > Usala Forest

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Summary

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• Eastern chimpanzees (Pan troglodytes schweinfurthii) & Grauer's gorillas (Gorilla beringei graueri) are present in Usala Forest.
• In 2007, the gorilla population was estimated to range between 240 to 410 individuals. The chimpanzee population is unknown.
• The gorilla population trend is stable; the chimpanzee population trend is unknown.
• The site has a total size of 3,500 km².
• Important threats to great apes include illegal mining and the presence of armed groups.
• Conservation activities are not documented.

Site characteristics

Usala forest lies to the east of Maiko National Park, in the Democratic Republic of the Congo. It is among the most remote, intact, and inaccessible blocks of tropical rainforest remaining in Africa (Kümpel et al. 2015). The site is also important for the conservation of okapis (Kümpel et al. 2015).

Table 1. Basic site information for Usala Forest

Species	Gorilla beringei graueri
Area	3,500 km²
Coordinates	Lat: -0.5275 , Lon: 28.2898
Type of site	Non-protected area
Habitat types	Subtropical/tropical moist lowland forest
Type of governance

Types of sites Governance types Habitat types

Ape status

Survey results suggest that between 2007 and 2014, the gorilla population in Usala remained relatively stable (Nixon et al. 2015).

Table 2. Ape population estimates reported for Usala Forest

Species	Year	Occurrence	Encounter or vistation rate (nests/km; ind/day)	Density estimate [ind./ km²] (95% CI)	Abundance estimate (95% CI)	Survey area	Sampling method	Analytical framework	Source	Comments	A.P.E.S. database ID
Gorilla beringei graueri	2014	Present				Usala Forest (340 km²)​	Reconnaissance walk		Nixon et al. 2015	Survey effort: 200 km. 28 nest sites were encountered.
Gorilla beringei graueri	2007				240-410	Usala Forest (850 km²)​	Reconnaissance walk		Nixon et al. 2015	Assessment led by the Dian Fossey Gorilla Fund International. 34 nest sites and large gorilla groups were encountered. Abundance estimate is tentative. Survey effort: 240 km.

Sampling methods Analytical frameworks

Threats

Table 3. Threats to apes reported for Usala Forest

Category	Specific threats	Threat level	Description	Year of threat
3 Energy production & mining	3.2 Mining & quarrying	High (more than 70% of population affected)	Presence of armed groups involved in illegal mining activities (Kümpel et al. 2015).	Ongoing (2015)

Threats

Challenges

Widespread presence of armed groups and illegal mining operations present serious challenges for the implementation of conservation activities (Kümpel et al. 2015).

Table 5. Challenges reported for Usala Forest

Challenges	Specific challenges	Source	Year(s)
6 Safety and stability	6.3 Civil unrest/war	Kümpel et al. 2015

Challenges

Enablers

Table 6. Enablers reported for Usala Forest

Enablers	Specific enablers	Source	Year(s)
1 Site management
2 Resources and capacity
3 Engaged community
4 Institutional support
5 Ecological context
6 Safety and stability

Enablers

Research activities

Nixon, S.C., Mufabule, K., Eliba, A. & Patule, I.M. 2007. A prospection survey of the Usala Forest and proposed Usala Community Reserve, Democratic Republic of Congo. Unpublished report submitted to DFGI, Dian Fossey Gorilla Fund International, Goma, DRC. Available at http://fondationkumu.files.wordpress.com/2012/05/usalaprospection-2007.pdf

Documented behaviours

Table 7. Behaviours documented for Usala Forest

Category	Behavior	Observation type	Prevalence	Observation dates	Source	Habituation	Species	Comment
	Not reported

Behaviours

Exposure to climate change impacts

As part of a study on the exposure of African great ape sites to climate change impacts, Kiribou et al. (2024) extracted climate data and data on projected extreme climate impact events for the site. Climatological characteristics were derived from observation-based climate data provided by the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP, www.isimip.org). Parameters were calculated as the average across each 30-year period. For 1981-2010, the EWEMBI dataset from ISIMIP2a was used. For the two future periods (2021-2050 and 2071-2099) ISIMIP2b climate data based on four CMIP5 global climate models were used. For future projections, two Representative Concentration Pathways (RCP) were used. RCP 2.6 is a scenario with strong mitigation measures in which global temperatures would likely rise below 2C. RCP 6.0 is a scenario with medium emissions in which global temperatures would likely rise up to 3C by 2100. For the number of days with heavy precipitation events, the 98th percentile of all precipitation days (>1mm/d) was calculated for the 1979-2013 reference period as a threshold for a heavy precipitation event. Then, for each year, the number of days above that threshold was derived. The figures on temperature and precipitation anomaly show the deviation from the mean temperature and mean precipitation for the 1979-2013 reference period.

The estimated exposure to future extreme climate impact events (crop failure, drought, river flood, wildfire, tropical cyclone, and heatwave) is based on a published dataset by Lange et al. 2020 derived from ISIMIP2b data. The same global climate models and RCPs as described above were used. Within each 30-year period, the number of years with an extreme event and the average proportion of the site affected were calculated (Kiribou et al. 2024).

Table 8. Estimated past and projected climatological characteristics in Usala Forest

Value	1981-2010	2021-2050, RCP 2.6	2021-2050, RCP 6.0	2071-2099, RCP 2.6	2071-2099, RCP 6.0
Mean temperature [C]	22.8	24	23.7	24.2	25.3
Annual precipitation [mm]	1648	1637	1699	1599	1729
Max no. consecutive dry days (per year)	5.8	11.4	12	15.5	13.1
No. days with heavy precipitation (per year)	7.1	7.5	8.3	8.1	11.8

Table 9. Projected exposure of apes to extreme climate impact events in Usala Forest

Type	No. of years with event (2021-2050, RCP 2.6)	% of site exposed (2021-2050, RCP 2.6)	No. of years with event (2021-2050, RCP 6.0)	% of site exposed (2021-2050, RCP 6.0)	No. of years with event (2070-2099, RCP 2.6)	% of site exposed (2070-2099, RCP 2.6)	No. of years with event (2070-2099, RCP 6.0)	% of site exposed (2070-2099, RCP 6.0)
Crop failure	4	0	3.5	0	5	0	16.5	0
Drought	0	0	0	0	0	0	0	0
Heatwave	0	0	0	0	0	0	1.5	100
River flood	2	1.04	2.75	2.04	1.75	1	5.5	2.4
Tropical cyclone	0	0	0	0	0	0	0	0
Wildfire	30	0.39	30	0.38	29	0.47	29	0.28

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  Precipitation anomaly in Usala Forest

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  Temperature anomaly in Usala Forest

References

Kümpel, N. F., Quinn, A., Queslin, E., Grange, S., Mallon, D. & Mapilanga, J-J. (2015). Okapi (Okapia johnstoni): Conservation Strategy and Status Review. Gland, Switzerland: IUCN and Institut Congolais pour la Conservation de la Nature (ICCN). pp. 58

Nixon, S., Kaghoma, C. & Vyalengerera, M. (2015). The status of Grauer’s gorilla in the Usala Forest. Gorilla Journal (Journal of Berggorilla and Regenwald Direkthilfe) 50. link

Kiribou, R., Tehoda, P., Chukwu, O., Bempah, G., Kühl, H. S., Ferreira, J., …, & Heinicke, S. (2024). Exposure of African ape sites to climate change impacts. PLOS Climate, 3(2), 1-19. doi:10.1371/journal.pclm.0000345

Page created by: APES Atlas Team Date: 2020-12-29