Urban agriculture is common in China, which is often promoted by government to ensure food supply for urban citizens while increasing farmers’ income. Given that vegetables are the main crop and cultivated year-round, urban farmland increases open greenery cover in a city. However, little attention has been given to ecological aspects of urban agriculture, e.g., its role in biodiversity conservation and ecosystem service/disservice. More importantly, there is considerable lack of knowledge of environmental characteristics associated with flora and fauna in urban agroecosystem. We examined how environmental characteristics within and between urban farmlands influence cabbage white butterfly and honey bee in southern China. We selected 34 farmlands in Guangzhou, one of the largest cities in China and established one site (50m-radius area; local scale) within a farmland. At each site, abundance data of cabbage white butterfly and honey bee were collected using line transect method and pan trap (three sample stations), respectively during December 2019 and January 2020. Crop and non-crop features were identified and on-screen digitized. We also surveyed crops within a 5m-radius area of sample station (fine scale) and created land cover map of 500m-radius area surrounding a center of site (landscape scale). Linear mixed models were used for data analysis.
Results/Conclusions
Abundance of cabbage white butterfly was positively influenced by crop diversity, i.e., Shannon-Wiener diversity of crop, but negatively by percent cover of farmlands and weeds at landscape scale. Cabbage white butterfly did not show a significant response to percent cover of cruciferous crops and weeds at local scale and mean farmland size (spatial arrangement of farmlands at landscape scale). Although abundance of honey bee was not related to crop or non-crop features at both local and landscape, there was a weak positive effect of crop diversity at fine scale, i.e., a 5m-radius area. These results indicate variations in environmental characteristics and spatial scales associated with cabbage white butterfly and honey bee at urban farmlands. They also suggest that cultivating too diverse crops at small urban farmlands can increase the risk of crop damage by pest insect such as cabbage white butterfly; however, creating small patch of diverse crop within a farmland where crop diversity is not high may increase pollination service by beneficial insect such as honey bee.