The role of tropical forest fragment vegetation in maintaining arthropod diversity and spillover to adjacent sugarcane fields

The degradation of forests in tropical agricultural landscapes has reduced biodiversity and may negatively affect ecosystem services. However, the role of forest fragments in the provision of ecosystem services for agroecosystems, such as biological control, is still not well understood. This study analyses the relationship between tree diversity and arthropod communities in forest fragments and adjacent sugarcane fields around Jaboticabal (São Paulo, Brazil) to evaluate the benefits of preserving Atlantic Forest fragments. We tested the hypotheses: (1) arthropod diversity and the abundance of key functional groups in forest fragments are favoured by tree diversity, (2) diversity and abundance of these functional groups in sugarcane fields depend on adjacent forests and (3) the insect community composition of forest fragments and sugarcane fields is similar due to spillover effects. Arthropods were sampled in 10 forest fragments over 2 years (2020 and 2022) using traps (Malaise, yellow pan) and direct tree sampling. We identified arthropods to morphospecies (2020) and family level (2022) and associated families to functional groups. We found that the quality of forest fragments, particularly tree species richness, was positively related to forest arthropod richness and frequency (occupied samples) of functional groups involved in ecosystem services such as predators, but also of phytophagous insects. There was also a strong positive correlation between insect family richness and functional groups of forest fragments and adjacent sugarcane fields, indicating potential spillover and spatial connectivity between habitats. Although insect community composition was significantly different between forest fragments and sugarcane fields, NMDS ordination revealed partial overlap of family communities, suggesting many shared taxa in both habitats. This study highlights the importance of diverse forest fragments in preserving insect biodiversity and related ecosystem services in tropical agricultural landscapes and advocates for the conservation and restoration of these habitats. However, the benefits in terms of crop damage reduction and yields remain to be confirmed.