LB 23-193 - Effects of shade-grown cacao agroforestry management on acoustic indices.

Acoustic indices are becoming an increasingly popular monitoring tools to assess and track biodiversity, in part, because they offer several logistical advantages over traditional biodiversity surveys. Despite those advantages, the efficacy of acoustic indices to accurately describe biodiversity is inconsistent because they can vary widely over temporal and spatial scales. As a result, it is recommended that acoustic indices should be ground truthed in the system they will be employed before they can be relied on as indicators of biodiversity. The goal of this study was to provide an initial assessment of whether acoustic indices differed among shade-grown cacao plots of differing age and whether those indices differed significantly from reference sites of intact tropical forest. In southern Belize, we deployed automated acoustic recorders in four shade-grown cacao plots of varying age (0.25-14 years) and five reference sites during the wet and dry seasons. We tested the effects of season, time, and cacao plot on six commonly employed acoustic indices. As has been reported in other studies, we found a clear diel pattern for all six acoustic indices (p < 0.001). The Bioacoustic Index (BI), Acoustic Evenness Index (AEI), Acoustic Complexity index (ACI), and the Normalized Difference Soundscape Index (NDSI) all declined during the day, while the reverse pattern was observed for the Acoustic Diversity Index (ADI) and Mid-Frequency Cover (MFC) where values declined a night. For five indices, the effect of time was influenced by season (p < 0.001) with diel changes becoming more pronounced during the wet season for some indices (BI, MFC) while others (NDSI, AEI) showed the reverse trend. The age of the cacao plots significantly influenced all the acoustic indices (p < 0.001) except for the ACI (p=0.122). In cases where the effect of plot age was significant, the older cacao plot most closely resembled the control site suggesting that the soundscapes of older shade-grown cacao plots are most similar to undisturbed tropical forest. In conclusion, the age of a shade-grown cacao plot influenced the soundscape and was significantly different from undisturbed tropical forest habitat, but that effect is influenced by diel and seasonal patterns and is also not consistent among all acoustic indices. Future studies should compare these indices with traditional measures of diversity to better elucidate these patterns.