Reconciling timber extraction with biodiversity conservation in tropical forests using reduced-impact logging

Abstract

Over 20% of the world's tropical forests have been selectively logged, and large expanses are allocated for future timber extraction. Reduced-impact logging (RIL) is being promoted as best practice forestry that increases sustainability and lowers CO₂ emissions from logging, by reducing collateral damage associated with timber extraction. RIL is also expected to minimize the impacts of selective logging on biodiversity, although this is yet to be thoroughly tested.We undertake the most comprehensive study to date to investigate the biodiversity impacts of RIL across multiple taxonomic groups. We quantified birds, bats and large mammal assemblage structures, using a before-after control-impact (BACI) design across 20 sample sites over a 5-year period. Faunal surveys utilized point counts, mist nets and line transects and yielded >250 species. We examined assemblage responses to logging, as well as partitions of feeding guild and strata (understorey vs. canopy), and then tested for relationships with logging intensity to assess the primary determinants of community composition.Community analysis revealed little effect of RIL on overall assemblages, as structure and composition were similar before and after logging, and between logging and control sites. Variation in bird assemblages was explained by natural rates of change over time, and not logging intensity. However, when partitioned by feeding guild and strata, the frugivorous and canopy bird ensembles changed as a result of RIL, although the latter was also associated with change over time. Bats exhibited variable changes post-logging that were not related to logging, whereas large mammals showed no change at all.Indicator species analysis and correlations with logging intensities revealed that some species exhibited idiosyncratic responses to RIL, whilst abundance change of most others was associated with time.Synthesis and applications. Our study demonstrates the relatively benign effect of reduced-impact logging (RIL) on birds, bats and large mammals in a neotropical forest context, and therefore, we propose that forest managers should improve timber extraction techniques more widely. If RIL is extensively adopted, forestry concessions could represent sizeable and important additions to the global conservation estate - over 4 million km².

Keywords: BACI; Guyana; RIL; bat; before-after control-impact; bird; feeding guild; forest disturbance; forestry; sustainable forest management.

Figure 1

Sample sites in Iwokrama Forest, Guyana, for birds and bats, and large mammal transects, logging roads and watercourses after reduced‐impact logging. Lower left: location of logging sites in relation to control sites. Lower right: bat and bird mist net and point‐count spatial survey design at each sample site.

Figure 2

Bird NMDS ordinations for all species (a), by feeding guild (b, c) and forest‐use strata (d, e) at each site before and after reduced‐impact logging. Each pre‐logging and pre‐control site is rescaled to zero and represented by the centroid (unfilled circle). The direction of the point from the centre indicates the change in assemblage composition at that site, and the magnitude of change is represented by the distance from the centroid.

Figure 3

Bat NMDS ordinations for all species (a), by feeding guild (b, c) at each site before and after reduced‐impact logging. Each pre‐logging and pre‐control site is rescaled to zero and represented by the centroid (unfilled circle). The direction of the point from the centre indicates the change in assemblage composition at that site, and the magnitude of change is represented by the distance from the centroid.

Figure 4

Relationship between the change in abundance pre‐ and post‐logging, and the difference in correlation coefficient (r _tau) with Axis 1 and Axis 2 of the assemblage ordinations, for every species of bird (a) and bat (b). Darker points show the indicator species as identified by indval (see Table S2, Supporting information), and labelled species are those mentioned in the text. Only the indicator species exhibited significant differences pre‐ and post‐logging. Species furthest from the zero centre (in the corners) show the greatest differences pre‐ and post‐logging, which for birds are explained by either turnover (above zero line) or logging intensity (below zero line). The bat ordination axes were not strongly correlated with any of the logging variables measured.