Native cover crops enhance arthropod diversity in vineyards of the Cape Floristic Region

Abstract

Cover crops can enhance biodiversity in perennial agroecosystems, with native cover crops potentially having additional biodiversity benefits. We assessed the effect of native cover crops on vineyard arthropods in the Cape Floristic Region using pitfall traps and vacuum sampling. Generalized linear mixed models and Permanova analyses were used to compared the abundance, species richness and assemblage structure of soil surface-active (free living arthropods found on the soil surface) and plant-dwelling arthropods (arthropods found predominately on the vegetation). We also used model selection and BIO-ENV to determine environmental drivers of arthropod diversity among three treatments of vineyards with bare ground, exotic cover crops or native cover crops, and nearby fynbos remnants as reference sites. Vineyards with native cover crops had significantly higher overall plant-dwelling species richness (52.57 ± 3.03), compared to exotic cover crop (28.64 ± 2.66), bare ground vineyards (18.57 ± 2.98) and even the fynbos sites (21.29 ± 1.78). A similar trend was found for overall plant-dwelling arthropod abundance. In contrast, surface-active arthropod richness was not influenced by treatment, whereas surface-active abundance was higher in less densely vegetated sites. Generally, plant-dwelling arthropods responded strongly to vegetation-related variables, whereas surface-active arthropods were responsive to soil-related parameters. Assemblages in vineyards with native cover crops did not resemble those in the natural reference sites as expected, likely due to disturbance factors, and plant compositional and structural differences. However, both surface-active and plant-dwelling assemblages had a high proportion of unique species in the native cover crop than found in the other treatments. Our results show that native cover crops enhance foliar arthropod diversity over and above exotic cover crops and contributes to farm-scale compositional heterogeneity. It therefore has potential to reduce arthropod diversity loss within farmlands and to contribute to more resilient vineyard agroecosystems.