Sustainable forest management is vital for the persistence of sun bear Helarctos malayanus populations in Sabah, Malaysian Borneo

Highlights

• Sun bears can thrive in production forests without heavy poaching pressure.

• Well-managed production forests are better habitat than degraded protected areas.

• Anti-poaching measures are integral sustainable forest management practices.

Abstract

With large mammals in Southeast Asia facing a host of threats such as forest loss and poaching, one important strategy in supporting conservation interventions is to understand local trends in species distributions. In Sabah, Malaysian Borneo, selective logging has both historically (conventional selective logging) and currently (reduced impact logging) impacted large areas of forest. Furthermore, the impact of poaching remains difficult to assess, potentially leading forest managers to underestimate its effects on large mammals. Our study focused on the sun bear (Helarctos malayanus), a forest dependent species threatened by poaching across its range. We used camera trap data collected in 2014 and 2018 from 127 camera trap stations in two adjacent forest blocks in Sabah. One of these blocks is a complex of degraded protected areas (formerly logged using conventional selective logging), interspersed with two areas of forest plantations (Tangkulap), while the other block is an active production forest logged using reduced impact logging techniques (Deramakot). We ran single-season occupancy models using covariates representing both habitat quality and poaching pressure to understand what factors most influenced sun bear habitat use and projected their distribution over the study area. We found that sun bear habitat selection was most strongly influenced by a dynamic covariate representing habitat quality, Normalised Difference Moisture Index (NDMI) from Landsat satellite data. Sun bear occupancy marginally increased from 2014 to 2018, in response to forest regeneration in Deramakot and Tangkulap. Overall, sun bear distribution was higher in the reduced impact logged and sustainably managed Deramakot compared to Tangkulap. Our proxies for poaching pressure had very minor effects on sun bear occupancy, suggesting that the population in this study area may not be subject to intense poaching. We highlight that sun bear populations can in fact better persist in well-managed production forests as compared to degraded protected areas.

Introduction

Biodiversity across Southeast Asia is declining due to unsustainable levels of poaching (especially snaring; Gray et al., 2018, Tilker et al., 2019) as well as habitat loss and degradation (Curtis et al., 2018). In particular, large parts of the island of Borneo have seen staggering levels of forest loss and degradation over just four decades (Gaveau et al., 2014). In the same period, the state of Sabah, part of Malaysian Borneo, saw a large area (60%) of its remaining natural forests undergoing degradation, mostly due to conventional selective logging activities (Bryan et al., 2013, Gaveau et al., 2014). Certain areas (~17,000 km²) of degraded forest have now been clear-cut and replaced with oil palm or forest plantations (Bryan et al., 2013), in some cases creating mosaics of natural forest interspersed with plantations. However, since 1997 Sabah began to gradually implement sustainable forest management in its logging concessions (Sabah Forestry Department, 2018). This put a heavy emphasis on local community engagement, silvicultural treatment, timber stand improvement and strictly regulated timber harvest via reduced impact logging (Sabah Forestry Department, 2015). Reduced impact logging is a form of selective logging that involves extensive pre-harvest planning to identify harvest trees while protecting high conservation value assets and riparian buffers. As opposed to conventional selective logging, reduced impact logging has been shown to result in a lower net loss of tropical biodiversity (Bicknell et al., 2014).

Besides habitat loss and degradation, the Southeast Asia poaching crisis has had a tremendous impact on biodiversity in the region (Harrison et al., 2016). Levels of poaching (particularly widespread snaring for commercial purposes) in Sabah may have been low in the past. Alarmingly, poaching pressure has been shown to be the prime driver of local species extirpations in pristine forest landscapes in Vietnam and Laos, even having a stronger negative impact compared to forest degradation (Tilker et al., 2019). The intensity of poaching and its long-term impacts on species is still poorly understood in Sabah. However, based on trends observed elsewhere in Southeast Asia (Gray et al., 2018) it is conceivable that levels of poaching in Sabah have increased over time and will continue to increase in the future.

Currently, Sabah’s large area of logged forest (both formerly and actively logged) and plantation-forest matrices are still inhabited by large mammals such as Bornean orangutan (Pongo pygmaeus), Sunda clouded leopard (Neofelis diardi) and sun bear (Helarctos malayanus; Brodie et al., 2015, Deere et al., 2018, Mohamed et al., 2019). Given the threats to large mammals in Sabah, it is imperative that we are able to track species population trends. For most low density large mammals in the tropics, occupancy, rather than abundance, has been shown as a useful metric in monitoring trends over time (Rasphone et al., 2019, Wong et al., 2012). Robust monitoring of population trends is especially urgent as Sabah’s large mammals are faced with a triple threat: forest degradation via selective logging, forest loss via plantation expansion and poaching. A clearer understanding of these threats on large mammal persistence will be useful for identifying appropriate conservation interventions before it is too late (Tilker et al., 2020), and for further evaluating the outcome of specific conservation interventions (Duangchantrasiri et al., 2016, Marescot et al., 2019).

The sun bear is considered to be a forest dependent species (Scotson et al., 2017), and while negatively impacted by forest loss, is somewhat tolerant of the degradation caused by selective logging activities (Brodie et al., 2015, Jati et al., 2018). Sun bears are threatened by commercially driven poaching throughout their range, primarily due to the value of their body parts in the illegal wildlife trade (Crudge et al., 2019). Poaching is further compounded by selective logging and plantation expansion, as these allow for easier access to remaining forests (Crudge et al., 2019).

To date, few studies have examined changes to sun bear distributions or populations across time. Such studies are more suitable in examining the impacts of forest degradation (caused by selective logging), forest loss (caused by plantation expansion) and poaching on population trends compared to surveys that only capture a single moment in time (Wong et al., 2012). In this study, we assessed the area occupied by sun bears in two adjacent forests with different management histories over a five year period. Our aim was to test the following hypotheses: 1) Sun bear occupancy declined due to poaching; 2) Sun bear occupancy declined in areas that were reduced impact logged during the study period; 3) Sun bear occupancy remained low in forest plantation areas; and 4) Sun bear occupancy increased in regenerating forests.