Synergies of camera traps and environmental DNA for wildlife surveys in tropical forests

Abstract

Considering the importance of addressing the current biodiversity crisis, effective wildlife monitoring is increasingly essential, particularly in logging concessions where the combined impacts of logging and hunting pose severe threats to wildlife. Traditional monitoring methods can be labor-intensive and costly, necessitating the exploration of more efficient alternatives. To address these challenges, we compared three alternative wildlife monitoring techniques—camera traps (CT), leaf swab environmental DNA (eDNA), and water eDNA—across four contrasting forest areas within an FSC-certified logging concession in northern Congo, each with different logging histories and hunting pressures. Our objectives were to (1) compare the accuracy of these methods in assessing species richness, occupancy, and relative abundance; (2) measure the effectiveness of each method in terms of species richness accuracy and precision, as well as associated costs, to propose an optimal wildlife survey method; and (3) discuss the influence of logging and hunting on species diversity. Camera traps proved highly effective for medium-to-large mammals, while leaf swab eDNA was valuable for detecting a broader range of species including bats, smaller species, and arboreal species. Water eDNA, while capturing key species with relatively less sampling effort, showed limited cost-effectiveness due to higher expenses than leaf swabs. Although leaf swab eDNA was the most cost-efficient, it required more extensive sampling to match the diversity detected by camera traps. This study highlights the strengths and complementary roles of different monitoring methods. The choice of method should align with specific conservation goals: eDNA could be used to identify areas of high conservation value, while camera traps are better suited for repeatedly monitoring medium to large mammal populations. Our findings indicate that hunting pressure was more influenced by accessibility and proximity to human settlements than logging history. The comparable species richness across forest grids suggests that well-managed, certified forests can be critical refuges for diverse wildlife. The results highlight the conservation potential of certified forests, emphasizing the importance of integrated and sustainable management practices to support diverse wildlife populations.