Logging Concessions Research Articles

Unveiling spatial variations of high forest live biomass carbon stocks of Gabon using advanced remote sensing techniques

Gabon is one of 11 high-forest, low-deforestation (HFLD) countries in the world. It has the highest proportion of preserved forests in the Congo Basin and is the first country to create large forest carbon offset credits in the market. However, about 60% of forests in Gabon is allocated to logging concessions, causing concerns for forest degradation and the sustainability of carbon credits. Here, we use a combination of air- and space-borne remote sensing data and the-state-of-the-art gradient boosted regression trees to estimate forest structure and aboveground biomass carbon density (ACD) of trees at 100 m resolution for the year circa 2020. Mapping spatial variations of ACD across floristically diverse landscapes, we estimate average density and total living carbon storage of trees at the national and sub-national levels. The estimated ACD of trees in forestlands within the country was 142.12 ± 7.3 Mg C ha−1 with the highest values found in central Gabon (150.08 ± 5.8 Mg C ha−1) and on highlands (161.18 ± 6.7 Mg C ha−1). On average, in every region, ACD of forests found within logging concessions (149.89 ± 6.1 Mg C ha−1) was higher than unmanaged forests of unprotected areas (122.81 ± 4.4 Mg C ha−1), indicating the combined effects of logging in carbon-rich forests and increased productivity due to management. The country’s total estimated biomass carbon for trees (above and belowground) stored within the forests was 4.14 ± 0.3 Pg C with 68% found within logging concessions and 14% within protected areas. The map provides high precision and comprehensive assessment of carbon stocks of trees in Gabon’s forests, significantly improving the country’s prospects to implement climate mitigation policies and to participate in carbon markets.

FSC-certified forest management benefits large mammals compared to non-FSC

More than a quarter of the world’s tropical forests are exploited for timber1. Logging impacts biodiversity in these ecosystems, primarily through the creation of forest roads that facilitate hunting for wildlife over extensive areas. Forest management certification schemes such as the Forest Stewardship Council (FSC) are expected to mitigate impacts on biodiversity, but so far very little is known about the effectiveness of FSC certification because of research design challenges, predominantly limited sample sizes2,3. Here we provide this evidence by using 1.3 million camera-trap photos of 55 mammal species in 14 logging concessions in western equatorial Africa. We observed higher mammal encounter rates in FSC-certified than in non-FSC logging concessions. The effect was most pronounced for species weighing more than 10 kg and for species of high conservation priority such as the critically endangered forest elephant and western lowland gorilla. Across the whole mammal community, non-FSC concessions contained proportionally more rodents and other small species than did FSC-certified concessions. The first priority for species protection should be to maintain unlogged forests with effective law enforcement, but for logged forests our findings provide convincing data that FSC-certified forest management is less damaging to the mammal community than is non-FSC forest management. This study provides strong evidence that FSC-certified forest management or equivalently stringent requirements and controlling mechanisms should become the norm for timber extraction to avoid half-empty forests dominated by rodents and other small species.

Early detection of human impacts using acoustic monitoring: An example with forest elephants.

The impacts of human activities and climate change on animal populations often take considerable time before they are reflected in typical measures of population health such as population size, demography, and landscape use. Earlier detection of such impacts could enhance the effectiveness of conservation strategies, particularly for species with slow population growth. Passive acoustic monitoring is increasingly used to estimate occupancy and population size, but this tool can also monitor subtle shifts in behavior that might be early indicators of changing impacts. Here we use data from an acoustic grid, monitoring 1250 km2 of forest in northern Republic of Congo, to study how forest elephants (Loxodonta cyclotis) assess risk associated with human impacts across a landscape that includes a national park as well as active and inactive logging concessions. By quantifying emerging patterns of behavior at the population level, arising from individual-based decisions, we gain an understanding of how elephants perceive their landscape along an axis of human disturbance. Forest elephants in relatively undisturbed forests are active nearly equally day and night. However, they become more nocturnal when exposed to a perceived risk such as poaching. We assessed elephant perception of risk by monitoring changes in the likelihood of nocturnal vocal activity relative to differing levels of human activity. We show that logging is perceived to be a risk on moderate time and small spatial scales, but with little effect on elephant density. However, risk avoidance persisted in areas with relatively easy access to poachers and in more open habitats where poaching has historically been concentrated. Increased nocturnal activity is a common response in many animals to human intrusion on the landscape. Provided a species is acoustically active, passive acoustic monitoring can measure changes in human impact at early stages of such change, informing management priorities.

Natural regeneration in tropical forests along a disturbance gradient in South-East Cameroon

The dynamics of tropical forests are highly dependent on the forest understorey. Understanding its diversity and composition is essential to ensure sustainable management of forest ecosystems. In this study, following a gradient of human disturbance, we analysed the density, diversity and floristic composition of the forest understorey in three land use types of south-eastern Cameroon: a protected area, a selective logging concession and community forests. Vegetation was inventoried in thirty-three permanent one-hectare plots. Woody individuals (tree, shrub, liana) were classified in four strata depending on their diameter: seedling (dbh < 1 cm), sapling (1–9.9 cm), small trees (10–29.9 cm), large tree (≥30 cm). A total of 4,159 individuals (dbh < 10 cm) belonging to 418 species and 232 genera were recorded. They mainly represent tree species (65%) and shade tolerant plants (77%), with diaspores disseminated by animals (74%). Life forms and modes of dissemination were significantly different between land use types. Abundance, species richness and diversity of juveniles varied significantly between strata and land use types: they were globally the highest in plots that have been logged less than five years before inventory. In terms of species composition, the different land use types were not clearly separated, indicating some resilience to disturbance. A low similarity between strata was observed. In all types, most canopy species are light demanding and cannot regenerate in the understorey. This indicates a natural evolution of the forest stands in the absence of silviculture. The presence of species that currently dominate the canopy of these forests will be gradually reduced without human intervention.

Extending the conservation impact of great ape research: Flagship species sites facilitate biodiversity assessments and land preservation.

To inform regional conservation planning, we assessed mammalian and avian biodiversity in the Djéké Triangle, which is an intact forest with long-term research and tourism focused on western lowland gorillas (Gorilla gorilla gorilla). This critical region serves as a conservation conduit between the Nouabalé-Ndoki National Park (NNNP) in the Republic of Congo and the Dzanga-Ndoki National Park in Central African Republic. Wildlife inventories were conducted to determine if biodiversity in the Djéké Triangle (initially part of a logging concession) was equivalent to the NNNP. Camera traps (CTs) were deployed to estimate species richness, relative abundance, naïve occupancy, and activity patterns of medium-to-large species in mixed species and monodominant Gilbertiodendron forests that comprise the majority of regional terra firma. Species inventories were collected from CTs positioned on a grid and at termite nests throughout the Djéké Triangle and compared to CTs placed in the Goualougo Triangle located within the NNNP. From 10,534 camera days at 65 locations, we identified 34 mammal and 16 bird species. Allaying concerns of wildlife depletion, metrics of species richness in the Djéké Triangle surpassed those of the Goualougo Triangle. Many species were observed to occur across habitats, while others showed habitat specificity, with termite mounds indicated as an important microhabitat feature. Our comparisons of animal activity budgets in different habitat types provide important reference information for other populations and contexts. In conclusion, this study provided empirical evidence of the high conservation value of this region that contributed to increasing the protected status of the Djéké Triangle.

Impact of industrial logging concession on deforestation and forest degradation in the DRC

The Congo Basin is home to the second largest tropical humid forest in the world and an important participant in climate change mitigation. While the Democratic Republic of Congo (DRC) boasts the largest proportion of Congo basin forests, it is also the main contributor to forest loss. Industrial logging concession is a forest management model that is likely to expand in the DRC in the coming years as the Government recently announced the probable end of the 2002 moratorium on logging concessions. It is thus crucial to understand whether this model can further the DRC’s deforestation reduction efforts. The literature suggests that the effect of titling forestland on avoided deforestation and forest degradation is generally limited, unless environmental restrictions are enforced. The DRC’s 2002 forest code introduced a new logging concession model that includes requirements to submit and implement Forest Management Plans (FMP) and increase benefit-sharing with communities. Our paper evaluates the impact of this new model of concession contracts signed in 2011 and 2014 on deforestation and forest degradation. We use remotely sensed data series to estimate difference-in-difference models. We ensured baseline parallel trends in deforestation and similarity in baseline characteristics between control and treated units. We find no evidence that deforestation and forest degradation is significantly different between logging concessions and control areas, even for concessions that had their FMP accepted. Our study highlights the need for evaluating the impact of FMPs once they are fully implemented, the importance to improve degradation outcome variables and to conduct complementary studies analyzing impact pathways.

Status of terrestrial mammals in the Yangambi Landscape, Democratic Republic of the Congo

AbstractIn this study we provide the first comprehensive camera-trap assessment of terrestrial mammals in the Yangambi landscape, comprising the Yangambi Biosphere Reserve and a logging concession in the Democratic Republic of the Congo. The terrestrial mammal community in this area exhibits lower occupancy and species richness compared to other conservation areas in the Congo Basin. The community is dominated by four species: Emin's pouched rat Cricetomys emini (1.3 kg), African brush-tailed porcupine Atherurus africanus (2.8 kg), blue duiker Philantomba monticola (5 kg) and bay duiker Cephalophus dorsalis (12 kg), which are known to be highly resilient. Large ungulates and medium-sized carnivores have particularly low abundances. Our study also confirmed the presence of four species categorized as threatened on the IUCN Red List: the chimpanzee Pan troglodytes, giant ground pangolin Smutsia gigantea, black-bellied pangolin Phataginus tetradactyla and white-bellied pangolin Phataginus tricuspis. Our findings highlight the need to consider wildlife conservation at the landscape level, including the logging concession, where species showed higher occupancy levels compared to the Biosphere Reserve, and highlighting the need for planning infrastructure construction and developing mitigation schemes, reducing forest degradation from logging and developing permanent cash crop agriculture. Landscape-level conservation will only be possible if a collaborative management model steered by local communities is developed with the participation of all constituencies.

Not all roads are barriers: Large mammals use logging roads in a timber concession of south-eastern Cameroon

In the literature, roads are often considered to be barriers for large vertebrates. In central Africa, the creation of roads and skid trails by logging operations leads to changes in the structure of forest landscapes that could influence wildlife movements. To assess the use of logging roads by six emblematic species of the central African forests, we conducted a camera trap (CT) survey on three types of tracks (secondary roads, skid trails, and elephant paths as control) in a logging concession of south-eastern Cameroon. The relative abundance indices (RAI) of each species derived from the CT data were used in a mixed linear model to test the effects of four factors (type of track; time: day vs. night; gregariousness: alone vs. group; and time after logging: less than one year vs. between one and two years). The results showed no preference for any type of track for gorillas (Gorilla gorilla) and chimpanzees (Pan troglodytes). In contrast, significantly higher RAI on secondary roads were observed for buffalos (Syncerus caffer), forest elephants (Loxodonta cyclotis), and bongos (Tragelaphus eurycerus). For the last two, the difference was only significant if they were detected in the most recently logged areas, at night (for elephants), or alone (for bongos). We could not test for leopard (Panthera pardus) as we captured only two events. Although none of the species appear to avoid roads and skid trails, nor do they perceive them as a barrier, further studies should be conducted to increase sampling efforts over time and space to consider seasonality, vegetation growth after logging, geographical variability, and other anthropogenic influence. However, these first results reveal the importance of closing roads after logging to limit encounters between wildlife and humans and highlight the relevance of characterizing roads (type of road, width, surfacing, and canopy structure over the road) when studying their impact on wildlife.

Mammal diversity and composition are not affected by certified timber extraction in Suriname

Increasing knowledge of species occurrence and assemblage composition is crucial to uncover the impacts of human activities on biodiversity. Here we investigate the effects of certified selective logging on assemblages of medium- and large-sized mammals in central Suriname. Using camera traps set in logged and unlogged parts of two logging concessions, we estimated mammal richness and assemblage composition within them and compared the results to other sites across Suriname obtained from a literature search. Then, using Bayesian multi-species occupancy models, we investigated if selective logging affects the richness, composition, and probabilities of habitat use and detection of mammals in the study sites. We recorded 27 mammal species in total, of which four are threatened globally. The study areas were amongst the richest concerning mammalian diversity throughout Suriname in response to the larger sampling effort employed. However, assemblage composition was overall similar to other sites previously sampled in the country, with variation in species richness mainly driven by sampling effort. Species richness and assemblage composition were similar concerning logged and unlogged parts of the concessions. At the species level, only a minor influence was observed in the probabilities of detection and habitat use of mammals. Most species presented positive responses to logging status, i.e., increasing their detection and habitat use probabilities in logged sites. Therefore, we conclude that selective logging to the extent practiced in the managed sites may fulfill the criteria of sustainability. Due to the continuous nature of Suriname's landscape, which allows for a constant flow of species from managed to unmanaged sites, it may act as a buffer to hamper the secondary and indirect impacts of selective logging.

Sparing old-growth maximises conservation outcomes within selectively logged Amazonian rainforest

Timber extraction threatens a vast area of tropical ecosystems, making it vital to design productive harvesting operations that limit biodiversity declines. Contrasting management options span a continuum from less-intensive, land-sharing logging applied over a larger area to land-sparing operations that combine intensive harvesting with the preservation of old-growth forest. Combining company-reported extraction rates with dung beetle surveys along an Amazonian logging gradient, we explore how individual species' abundances, geometric mean population sizes, functional diversity, and trait characteristics vary across simulated logging concessions and production targets. We substantially extend previous studies by evaluating 8000 mixed-harvesting scenarios and by assessing the profitability of contrasting practices. Simply maximising old-growth protection delivers the highest species' abundances and population sizes for species negatively affected by logging. Maximising old-growth also supports communities with a functional trait dissimilarity (FDis, RaoQ) and functional structure of nesting guilds, biomass, pronotum volume, front leg area, and front:back leg ratio traits that closely resembles old-growth forest. Functional evenness (FEve), richness (FRic), and divergence (FDiv) did not vary across logging strategies. Some 3 % of mixed approaches outperform extreme sparing (which maximises old-growth retention through intensive logging) but still involve substantial sparing, enabled by intensified logging elsewhere. However more-extensive business-as-usual harvesting is up to 90 % more profitable than extreme sparing, suggesting active policy mechanisms, standards, or regulations would be needed to make spatially-concentrated logging operations (which benefit biodiversity) more commercially attractive. Old-growth sparing appears key to limiting biodiversity declines within tropical timber concessions, but would require payments to compensate for reduced profits.

Six years of industrial logging in Ngoyla (East-Cameroon): what have been the outcomes for local populations?

The industrial exploitation of Cameroon's forests was, until the late 2000s, credited with little positive impacts on the communities living near logging concessions. In order to evaluate the outcomes of logging for local populations and to inform the sustainable management of Ngoyla-Mintom forest block, socio-economic data was collected from 2011 to 2018. Data from guided interviews, observations and questionnaires reveal that local populations have seen improvements in their living conditions, particularly in terms of formal employment, better housing and increased mobility. The main adverse effects observed were a reduction of some forest resources, an increase in certain diseases, and increased violations of the rights of Indigenous People. Despite identified favorable factors, the positive impacts from industrial logging in Ngoyla are below expectations.

Can wild forest foods contribute to food security and dietary diversity of rural populations adjoining forest concessions? Insights from Gabon, DR Congo and Cameroon

The potential of forest foods to address malnutrition, food insecurity and poor dietary intake is increasingly being recognized. However, most existing data presents average results of proximate analysis, overlooking the opportunities to document how forest foods contribute to nutrition, food security and dietary intake. In this study, food security was estimated using the HFIAS score while dietary intake was estimated using FFQ recalls among 720 households in and around six logging concessions in Cameroon, DR Congo and Gabon. There was a high diversity of forests foods consumed, with DR Congo (FFCS=16.2) registering the highest number. Cameroon had the highest number of food groups (HDDS=12.5) while Gabon had the highest number of food varieties (FVS=24.5). Despite a highly diverse pool of wild foods in the region, most households (82%) practicing farming on logged land suffered from food insecurity. A significant inverse correlation was observed between the HFIAS score and the FFCS (r 2 =–0.26, P=0.0002), revealing that forest foods can play a role in ensuring food security and nutrition among populations near forest concessions. The chi-square test revealed that age &gt;46 years, and access to income from business or salaries were associated with food security. Further work is required to document how wild forest foods can contribute to improved diets among these populations, including documenting the nutrient composition of more forest foods, integrating them into regional dietary guidelines and encouraging their domestication.

Habitat use of proboscis monkey (Nasalis larvatus) in production forests of West Kalimantan, Indonesia

Abstract. Wardatutthoyyibah, Pudyatmoko S, Imron MA, Subrata SA. 2023. Habitat use of proboscis monkey (Nasalis larvatus) in production forests of West Kalimantan, Indonesia. Biodiversitas 24: 1724-1734. Proboscis monkeys (Nasalis larvatus van Wurmb 1787) are endemic to Borneo and dependent on the presence ofwetlandforest as their habitat. Recent study shows that many potential habitats of this species are in non-protected areas including logging concessions. We investigate the use of logging concessions for the habitat of proboscis monkeys by determining habitat variables that influence the presence of proboscis monkeys in a selective logging system. We conducted research in seven logged-over areas/LOA during 2009-2015 and eight locations of unlogged forest as proboscis monkey habitat. We applied a logistic regression with the backward stepwise method for selecting environmental variables that influence the presence of proboscis monkeys. Our study showed that proboscis monkeys are no longer present in LOAs, which was indicated by the difference between the habitat characteristics of proboscis monkeys and LOAs. We found that if prosboscis monkeys are presentin an area, resource selection was influenced at site level for basal area of trees and poles explained the presence of proboscis monkeys. Reducing the number of trees logged and ensuring connectivity among trees in LOAs could help to reestablish habitat for proboscis monkeys.

'Glocalizing' land-use and forest governance in the tropics: examining research partnerships and international forest policies affecting Brazil, DRC and Indonesia.

Background: International and market forces are key drivers of deforestation and forest degradation, with transnational and market-based solutions in land-use and forest governance often missing economic, distributive, and environmental targets. Methods: This paper tackles both the framing and effectiveness of transnational initiatives affecting forest lands and peoples in the Global South, and the quality of relationships between institutions in the Global North and the Global South. Through more equitable research partnerships, this paper draws lessons from case studies in Indonesia (legality verification system in different forest property regimes), the Democratic Republic of the Congo (lifting of a moratorium on new logging concession), and Brazil (FSC in the Amazon region and the Amazon Fund). Results: International partnerships have privileged market-based instruments and commodity exchange between Global South and Global North countries, and the benefits of such mechanisms are unevenly distributed. Complementary and alternative policy instruments are discussed for each geography. Conclusions: Glocalizing land-use and forest governance implies in advancing equitable research partnerships between institutions in the Global South and Global North, and strengthening a community of practice for critical enquiry and engagement in partnerships for sustainable development. Land-use, climate and forest governance mechanisms must redress power dynamics, and partnership models, and commit to improving well-being and sustainable livelihood outcomes.

Changes in floristic diversity and stand damage of tropical forests caused by logging operations in North Kalimantan, Indonesia

Abstract. Matangaran JR, Anissa IN, Adlan Q, Mujahid M. 2022. Changes in floristic diversity and stand damage of tropical forests caused by logging operations in North Kalimantan, Indonesia. Biodiversitas 23: 6358-6365. Selective cutting of natural forests in Indonesia has been going on for decades. As a consequence, such activities cause disturbances in vegetation cover indicated by changes in diversity and evenness, forest stands damage and mortality of juvenile trees. This research aimed to determine changes in diversity and evenness of vegetation before and after harvesting at seedling, saplings, poles and tree levels, stand damage and forest opening, the number of natural regeneration, and the relationship between felling intensity and forest opening. The research was conducted in a logging concession applying Reduced Impact Logging (RIL) in North Kalimantan by restricting timber cutting to only commercial trees with a diameter of more than 50 cm. The result found 38 tree species in the research plot with average logging intensity of 6.5 trees per hectare. Before and after harvesting, it was found that there were slight changes in diversity and evenness indices at seedling, sapling, pole and tree levels. The percentage of stand damage was 17.8%, and the percentage of forest opening was 19.76 %, which was comparably lower than logging practices in other areas. Nonetheless, we found a strong positive relationship between felling intensity and forest opening. The findings of this study provide another evidence that it is necessary to implement reduced impact logging to reduce damage to forest ecosystems due to selective cutting in the tropical region. It is important to limit the number of trees logged per hectare in order to reduce logging damage and forest opening, minimize impacts on tree species diversity and facilitate natural regeneration.

Forest concessions and eco-certifications in the Peruvian Amazon: Deforestation impacts of logging rights and logging restrictions

Concessions that grant logging rights to firms support economic development based on forest resources. Eco-certifications put sustainability restrictions on the operations of those concessions. For spatially detailed data, including many pre-treatment years, we use new difference-in-differences estimators to estimate 2002–2018 impacts upon Peruvian Amazon forests from both logging concessions and their eco-certifications. We find that the concessions − which in theory could raise or reduce forest loss − did not raise loss, if anything reducing it slightly by warding off spikes in deforestation pressure. Eco-certifications could reduce or raise forest loss, yet we find no significant impacts.

Reliably mapping low-intensity forest disturbance using satellite radar data

In the last decades tropical forests have experienced increased fragmentation due to a global growing demand for agricultural and forest commodities. Satellite remote sensing offers a valuable tool for monitoring forest loss, thanks to the global coverage and the temporal consistency of the acquisitions. In tropical regions, C-band Synthetic Aperture Radar (SAR) data from the Sentinel-1 mission provides cloud-free and open imagery on a 6- or 12-day repeat cycle, offering the unique opportunity to monitor forest disturbances in a timely and continuous manner. Despite recent advances, mapping subtle forest losses, such as those due to small-scale and irregular selective logging, remains problematic. A Cumulative Sum (CuSum) approach has been recently proposed for forest monitoring applications, with preliminary studies showing promising results. Unfortunately, the lack of accurate in-situ measurements of tropical forest loss has prevented a full validation of this approach, especially in the case of low-intensity logging. In this study, we used high-quality field measurements from the tropical Forest Degradation Experiment (FODEX), combining unoccupied aerial vehicle (UAV) LiDAR, Terrestrial Laser Scanning (TLS), and field-inventoried data of forest structural change collected in two logging concessions in Gabon and Peru. The CuSum algorithm was applied to VV-polarized Sentinel-1 ground range detected (GRD) time series to monitor a range of canopy loss events, from individual tree extraction to forest clear cuts. We developed a single change metric using the maximum of the CuSum distribution, retrieving location, time, and magnitude of the disturbance events. A comparison of the CuSum algorithm with the LiDAR reference map resulted in a 78% success rate for the test site in Gabon and 65% success rate for the test site in Peru, for disturbances as small as 0.01 ha in size and for canopy height losses as fine as 10 m. A correlation between the change metric and above ground biomass (AGB) change was found with R2 = 0.95, and R2 = 0.83 for canopy height loss. From the regression model we directly estimated local AGB loss maps for the year 2020, at 1 ha scale and in percentages of AGB loss. Comparison with the Global Forest Watch (GFW) Tree Cover Loss (TCL) product showed a 61% overlap between the two maps when considering only deforested pixels, with 504 ha of deforestation detected by CuSum vs. 348 ha detected by GFW. Low intensity disturbances captured by the CuSum method were largely undetected by GFW and by the SAR-based Radar for Detecting Deforestation (RADD) Alert System. The results of this study confirm this approach as a simple and reproducible change detection method for monitoring and quantifying fine-scale to high intensity forest disturbances, even in the case of multi-storied and high biomass forests.

Riparian reserves protect butterfly communities in selectively logged tropical forest

AbstractSelective logging is the most widespread habitat disturbance in tropical forests. Primary forest set‐asides along riparian zones are mandated in many countries and a key question is whether these riparian reserves provide biodiversity conservation benefits.We characterise butterfly communities in fixed‐width riparian reserves of 30 m on each bank along narrow streams (&lt;10 m) paired with interior logged forest transects, and in primary forests within a selective logging concession in the south‐western Brazilian Amazon.We found that primary forest species richness was more similar to riparian reserves than to paired interior logged forest points, whereas abundance remained higher in both riparian reserves and interior logged points, likely due to the intrusion of canopy‐dwelling species in disturbed habitats, as previously reported in the literature. Butterfly assemblages within riparian reserves were more similar to unlogged primary forests than interior logged points, and canopy height in riparian reserves was associated with increased assemblage similarity to primary forest points.Changes in abundance relative to primary forest were of a larger magnitude in interior logged points than in riparian reserves within logged forests, highlighting the role of riparian reserves in maintaining primary forest‐like communities. We found no particular primary forest butterfly clades to be more sensitive to changes in abundance than other clades.Synthesis and applications. Mandatory conservation set‐asides around streams or rivers (riparian buffers) have an important role in protecting the abundance and composition of primary forest butterfly assemblages within selective logging concessions in tropical rainforests. This study highlights the need to assess the conservation value of protecting unlogged riparian forest strips in other taxa to inform policy.

Exploring spatio-temporal variation in soundscape saturation of an African tropical forest landscape

Monitoring biodiversity calls for efficient monitoring techniques. Soundscape analysis is a landscape-level approach to acoustic monitoring whereby acoustic indices are calculated as proxies for biodiversity based on all sounds occurring in a landscape, i.e. a soundscape. However, it is not fully understood what the influence is of environmental, anthropogenic and temporal heterogeneity on soundscapes and what soundscapes mean in terms of species diversity. Here, we use soundscape saturation, a proxy for acoustic diversity which calculates the degree of use of acoustic niches. We study how soundscape saturation responds to forest management and seasonality in the tropical forests of Gabon, while taking into account distance to rivers, human accessibility, signs of hunting, elevation and slope. To study the contribution of medium to large mammals to soundscape saturation, we relate soundscape saturation to the abundance of several animal guilds as estimated with camera trap data. Soundscape saturation was higher in a multi-use forest vs. logging concessions, in the rainy reason vs. the dry season, and in proximity of rivers and human access points. Elevation, slope, and hunting were less important covariates. We did not find strong evidence for a relationship between soundscape saturation and the abundance of several mammal guilds derived from camera traps. The lack of this relationship highlights the opportunity for a joint approach of eco-acoustics and camera trapping due to complementary species coverage. Our study provides the first soundscape saturation study in African tropical forests and the first to combine soundscape saturation with camera trap data. Soundscape saturation is considered a useful additional index for quantifying biodiversity across a range of land-use types. Future studies may aim to improve species inference and the site-specific interpretation of saturation levels by investigating species-specific contributions to, and spatiotemporal variation in, acoustic activity.

Variable detectability and El-Niño associations with riparian snakes in Sabah, Malaysian Borneo

AbstractAlthough snake populations are suffering numerous local declines, determining the scale of these declines is problematic due to the elusive nature of snakes. Determining the factors associated with species detection is therefore essential for quantifying disturbance effects on populations. From 2017 to 2019, we assessed the detectability associations of five river-associated snake species and all snake detections in general within two logging concessions in Sabah, Malaysian Borneo. Data collected from both stream transects and visual encounter surveys at 47 stream sites were incorporated into an occupancy-modelling framework to determine the climatological, temporal and survey distance associations with species detection probability. Detection probability of riparian snake species was significantly associated with humidity, month (2 spp. each), survey distance and total rainfall over 60 days (1 spp. each). Pooled snake species detectability was significantly positively associated with transect distance and the 2019 El-Niño year, whilst yearly pooled snake species detections in stream transects spiked during El-Niño (2017 = 2.05, 2018 = 2.47, 2019 = 4.5 snakes per km). This study provides new insights into the detectability of riparian rainforest snakes and suggests that future studies should account for short-term (climatological and temporal) and long-term (El-Niño) factors associated with detection probability when surveying and assessing snake populations.