Action: Use selective logging instead of clear-cutting
- One site comparison in Sierra Leone found that primate densities were higher in forest that had been logged at low intensity than in a forest logged at high intensity.
- One before-and-after study in Madagascar found that the number of lemurs increased following selective logging.
- One site comparison study in Uganda found that primate densities were similar in forest that had been logged at low intensity and forest logged at high intensity.
Logging is the third greatest threat to primates in all regions worldwide (Estrada et al. 2017). Selective logging is a more ecologically sustainable practice than clear-cutting, which entails removing all trees at the same time. The idea behind selective logging is to maintain an uneven or all-aged forest of trees varying not only in age, but in size and species as well. Selectively logged areas can sustain primates at varying densities, depending on the logging intensity and history (e.g. Bortolamiol et al. 2014). Although several correlative studies have shown that high logging intensity spatially correlates with low primate density (e.g. Weisenseel et al. 1993) and local extinction in very heavily-logged or clear-cut areas (e.g. Ancrenaz et al. 2010), in some moderately-logged areas, densities of some primate species, including eastern chimpanzees Pan troglodytes schweinfurthii and western gorilla Gorilla gorilla gorilla for example, were reported to be relatively high (e.g. Bortolamiol et al. 2014, Stokes et al. 2010). For orangutans Pongo pygmaeus morio, a simulation study by Wilson et al. (2014) has suggested that reduced-impact logging practices, coupled with additional protection may be a strategy that could even outperform habitat protection.
For best ‘Best Practice Guidelines for Reducing the Impact of Commercial Logging on Great Apes in Western Equatorial Africa’ published by the IUCN SSC Primate Specialist Group (PSG), please refer to Morgan & Sanz (2007).
Ancrenaz M., Ambu L., Sunjoto I., Ahmad E., Manokaran K., Meijaard E. & Lackman I. (2010) Recent surveys in the forests of Ulu Segama Malua, Sabah, Malaysia, show that orang-utans (P. p. morio) can be maintained in slightly logged forests. PLoS ONE, 5, e11510.
Bortolamiol S., Cohen M., Potts K., Pennec F., Rwaburindore P., Kasenene J., Seguya A., Vignaud Q. & Krief S. (2014) Suitable habitats for endangered frugivorous mammals: small-scale comparison, regeneration forest and chimpanzee density in Kibale National Park, Uganda. PLoS ONE, 9, e102177.
Estrada A., Garber P.A., Rylands A.B., Roos C., Fernandez-Duque E., Di Fiore A., Nekaris K.A.-I., Nijman V., Heymann E.W., Lambert J.E., Rovero F., Barelli C., Setchell J.M., Gillespie T.R., Mittermeier R.A., Verde Arregoitia L., de Guinea M., Gouveia S., Dobrovolski R., Shanee S., Shanee N., Boyle S.A., Fuentes A., MacKinnon K.C., Amato K.R., Meyer A.L.S., Wich S., Sussman R.W., Pan R., Kone I. & Li B. (2017) Impending extinction crisis of the world’s primates: why primates matter. Science Advances, 3, e1600946.
Morgan D. & Sanz C. (2007) Best Practice Guidelines for Reducing the Impact of Commercial Logging on Great Apes in Western Equatorial Africa. Gland, Switzerland: IUCN SSC Primate Specialist Group (PSG), 32 pp.
Stokes E.J., Strindberg S., Bakabana P.C., Elkan P.W., Iyenguet F.C., Madzoke B., Malanda G.A.F., Mowawa B.S., Moukoumbou C., Ouakabadio F.K. & Rainey H.J. (2010) Monitoring great ape and elephant abundance at large spatial scales: measuring effectiveness of a conservation landscape. PLoS ONE, 5, e10294.
Weisenseel K., Chapman C.A. & Chapman L.J. (1993) Nocturnal primates of Kibale forest: effects of selective logging on prosimian densities. Primates, 34, 445–450.
Wilson H.B., Meijaard E., Venter O., Ancrenaz M. & Possingham H.P. (2014) Conservation strategies for orangutans: reintroduction versus habitat preservation and the benefits of sustainably logged forest. PLoS ONE, 9, e102174.
Supporting evidence from individual studies
A site comparison in 1984-1985 in rainforest in Gola Forest Reserves, Sierra Leone found that group densities of three out of six primate species were lower in selectively logged than in unlogged forests. Diana monkeys Cercopithecus diana, spot-nosed monkeys Cercopithecus petaurista, and Campbell's monkeys Cercopithecus campbelli had similar group densities in low-intensity selectively logged and unlogged forest patches. In contrast, group densities of red colobus Procolobus badius, black-and-white colobus Colobus polykomos, and olive colobus Procolobus verus appeared lower in selectively logged than in unlogged forests. Group densities of all species were lower in heavily selectively logged forest than in unlogged or low-intensity selectively logged forests. Group densities for Campbell's monkeys were similar in unlogged and logged forests. Hunting rate was highest in high-intensity selectively logged forests, moderate in selectively logged forests and low in unlogged forests. However, no statistical tests were carried out to determine whether this difference was significant. Sample sizes were small and ranged from one to seven groups. Selective logging involved the cutting of commercial tree species with a girth larger than 2-2.6 m. Three unlogged sites, one low-intensity selectively logged site (eight logged trees/8 ha plot), and one heavily selectively logged site (51 logged trees/8 ha plot) were surveyed by walking a rectangular 2 km trail and mapping primate groups and their calls.
A before-and-after trial in 1990-1992 in tropical dry forest in Fôret de Kirindy, western Madagascar found that lemur encounter rates increased two years after low-intensity selective logging (<or=10% of crown area removed) for the fat-tailed dwarf lemur Cheirogaleus medius, the mouse lemurs Microcebus spp., and the Masoala fork-marked lemur Phaner furcifer. Encounter rates did not change for the brown lemur Eulemur fulvus, Verreaux's sifaka Propithecus verreauxi, Lepilelur mustelinus, and Coquerel's giant mouse lemur Mirza coquereli. Encounter rates increased from 0 to 2.8 sightings/km for the mouse lemurs Microcebus spp., from 1.5 to 4.1 sightings/km for the western fat-tailed dwarf lemur Cheirogaleus medius and from 0.5 to 0.9 sightings/km for the Masoala fork-marked lemur Phaner furcifer. However, the authors speculated that the increase was a consequence of a shift in home ranges between surveys, rather than population growth, as most of the species reproduce too slowly to cause a noticeable effect within two years. The same site was surveyed during the day and at night repeatedly and along the same trails in 1990 before logging and in 1992 after low-intensity selective logging. Authors also surveyed two additional sites, one logged in 1985-1986 and one unlogged area to control for potential year-to-year population variation.
A site comparison in 1968-1996 in three evergreen forests in Uganda found that light selective logging (5.1 stems/ha) did not affect average primate group densities and group sizes of blue monkey Cercopithecus mitis, redtail monkey Cercopithecus ascanius, Ugandan red colobus Procolobus tephrosceles, and grey-cheeked mangabey Lophocebus albigena when compared to populations in heavy selected logging (7.4 stems/ha) areas. However, group density of eastern black-and-white colobus (BWC) Colobus guereza was lower in the light selective logging area in 1980-1981 (3.31 vs 4.81 groups/km2) and in 1996-1997 (4.83 vs 9.12 groups/km2) than in the heavily logged area. BWC had higher group densities in the light selective logging area than in the unlogged area (1980/81: 3.31 vs 0.89 groups/km2; 1996/97: 4.83 vs 2.00 groups/km2). Heavy selective logging resulted in lower group densities compared to unlogged and light selective logging for red colobus (1980-1981: 3.08 vs 5.46 and 5.78 groups/km2) and redtail monkeys (1980-1981: 2.21 vs 5.58 and 7.03 groups/km2; 1996-1997: 1.04 vs 4.83 and 11.48 groups/km2). Relative abundance (number of groups seen/ km surveyed) in heavy selective logging decreased between surveys conducted in 1980-1981 to 1996-1997 for red colobus (0.567 vs 0.292), BWC (1.144 vs 0.542), redtail monkey (0.589 vs 0.094), and blue monkey (0.337 vs 0.021), but only for red colobus in lightly logged forests (0.710 vs 0.459) over the same period. BWC relative abundance decreased in unlogged areas from 0.23 in 1970-1972 to 0.11 in 1974-1967 and 0.11 in 1980-1981 but increased for grey-cheeked mangabeys (1970-1972: 0.12; 1980-1981: 0.16). Surveys used line transect methods to assess primate densities across three forestry compartments with heavy-, light- and no selective logging in the late 1960s. The unlogged area was surveyed in 1970-1976. Survey effort and data collection methods were comparable.
- Davies A.G. (1987) Conservation of primates in the Gola Forest Reserves, Sierra Leone. Primate Conservation, 8, 151-153
- Ganzhorn J.U. (1995) Low-Level Forest Disturbance Effects on Primary Production, Leaf Chemistry, and Lemur Populations. Ecology, 76, 2084-2096
- Chapman C.A., Balcomb S.R., Gillespie T.R., Skorupa J.P. & Struhsaker T.T. (2000) Long-Term Effects of Logging on African Primate Communities: a 28-Year Comparison From Kibale National Park, Uganda. Conservation Biology, 14, 207-217