Land-use mosaic effects on insect abundance, bat activity and macadamia production, South Africa

Abstract

Rapid increases in the global human population have led to agricultural intensification worldwide, highlighting the need for conserving the remaining fragmented natural areas and incorporating more sustainable farming techniques. South Africa is currently the largest producer of macadamia nuts in the world and macadamia plantings are increasing rapidly, resulting in the loss of natural vegetation. The study area, Hazyview in Mpumalanga, is an agricultural mosaic, with fragments of natural vegetation patches in between. These natural vegetation patches are key to retaining important ecosystem services for the agricultural industry such as pollination and pest-control. This study evaluated how a land-use mosaic, represented by an agricultural landscape with natural vegetation retained around the farms, is related with macadamia nut yield and quality, the activity of insectivorous bat species, and nocturnal insect abundance, with a specific focus on five different macadamia farms. The role and contribution of bats and insects in agro-ecosystems are becoming more apparent, and their importance as indicator species which can reflect environmental changes in plant and insect communities is of key value. With this information, I could gain a better understanding of the relationships between the surrounding biodiversity and the commercial macadamia nut production industry, as well as the potential impact that agriculture-induced landscape fragmentation has on the biodiversity in the region. Firstly, on-farm characteristics (e.g. tree age, density, height) for five farms were used, aswell as their yield and quality measures and land-use types surrounding each farm to determine potential relationships between macadamia nut yield and/or quality and proximity to surrounding natural vegetation. Farm characteristics such as the height and density of the macadamia trees planted had a significant association with yield and quality of the nuts which both decreased with increasing tree height and density. Additionally, a characteristic of land-use type (in this case, extent of waterbodies such as rivers/ dams and wetlands surrounding the farms) was found to have an association with yield. The surrounding natural areas likely act as a reservoir for both insects and their predators, which could be beneficial for the neighbouring agricultural lands by improving pollination, yield and nut quality through biological pest-control. Secondly, the Hazyview landscape composition was assessed, using National land-cover data and buffer zones around each of the five farms. Within a 5 km radius, land-cover composition varied across the five farms, reaching high proportions of natural vegetation (64.83 %), agriculture and forestry plantations (55.78 %), settlements (10.78 %) and water bodies (1.78 %) in some areas. This indicates the extent of the remaining natural vegetation surrounding each farm. Bat echolocation calls (bat activity) and insect collection (insect abundance) were conducted on two study farms. Sample points were located at different edge sites (land-use types), natural vegetation, river and road edges, to determine whether bats (activity) show preferences for foraging over macadamia orchards bordering natural vegetation and if insect abundance follows the same trend. Corresponding with other studies, land-use type, specifically natural vegetation bordering the farms, was significantly associated with increased bat activity and insect abundance within this agricultural landscape, with natural vegetation edges being preferred and road edges being least favoured by both. Bats from all three foraging guilds (clutter, clutter-edge and aerial) were recorded during the study, which indicates that the Hazyview farming region still appears to support a high bat species richness. In conclusion, this study highlights the importance of natural vegetation within an agricultural land-use mosaic and the benefits it can bring, both to the farmer and the surrounding biodiversity. Although ecosystem services were not directly measured, it can be deduced from the association of higher yield and better crop quality with surrounding natural vegetation, where the presence of bat and insects was found to be higher. Given the future increase in agricultural land expansion, information must be made publicly available, to allow farmers to consider all beneficial ecosystem services that the surrounding natural vegetation has to offer, namely pollination and pest-control. Farm management practices, which are aligned with consideration for ecosystem services have the potential to improve ecosystem functioning and service provision across agricultural landscapes.