The Changing Sounds of Mt. Kilimanjaro: Relationship between tree structural attributes and soundscape-based biodiversity indices supporting ecosystem functions

Addressing biodiversity loss in human-altered tropical landscapes is a critical conservation priority, yet the role of tree structural properties and their interaction with landscape features in shaping animal communities within agroforestry systems remains poorly understood. We conducted one of the first ecoacoustic assessment of the Kihamba agroforestry system by deploying autonomous recorders across 30 farm plots along an elevational gradient and across seasons, capturing one-minute recordings every five minutes. Biodiversity inference was based on soundscape indices (ACI, ADI, BI, H, NDSI), complemented by measurements of tree structural properties, farm plot characteristics, and landscape variables. Acoustic indices exhibited distinct diel, seasonal, and elevational patterns, with soundscapes shaped by farm plot and landscape features. The complexity of sounds (ACI) decreased with tree species diversity and proportion of native trees (nativeness). Sounds variability (ADI) increased with increased surrounding forest and fallow gap cover but decreased with tree diversity and nativeness. Acoustic energy (BI) slightly increased in larger homegardens but reduced as fallow gaps and tree diversity increased. Higher tree structural diversity, surrounding forest, and fallow gaps increased the randomness of sounds (H). Conversely, human-related sounds (NDSI) had a positive association only with tree structural diversity. Significant variation in indices remained unexplained, reflecting index-specific sensitivities, taxon or activity-specific responses, and other environmental/temporal factors. Acoustic indices revealed distinct ecological and anthropogenic patterns in the Kihamba landscape, underscoring the value of a multi-index approach. Integrating acoustic monitoring into agroforestry management prioritising tree structural diversity and landscape connectivity can help maintain soundscape integrity and associated biodiversity.