Organization of extensive biodiversity and ecosystem service production within community gardens of Los Angeles, CA

Background/Question/Methods

Community gardens can provide important ecosystem services to urban residents, including food production and recreational services. These user managed agricultural systems often include substantial biodiversity related to these services. How community garden biodiversity is structured and organized has been poorly researched and no clear mechanisms for diversity and species abundance have been established. We asked this important question: What regulates the diversity and abundance of garden plant species? We hypothesize that species area relationships, socioeconomics, and cultural factors interact to form plant biodiversity and abundance patterns. Fourteen gardens throughout the County of Los Angeles were visited in the summers of 2010 and 2011. We divided gardens both into immigrant (8) and non-immigrant (6) locations and Kitchen and Farm structures. Kitchen gardens had small plots maintained by individuals and families, while farms had large plots, crop sharing, and often sold produce for profit. All purposefully planted species and their relative abundance were recorded in each plot and were separated into edible, medicinal, and ornamental uses. Garden age, ethnicity, and socioeconomics were also recorded. 

Results/Conclusions

Over 400 plant species were recorded, and each garden contained between 43-190 species. Biodiversity in kitchen gardens was strongly correlated with plot size (r² =0.793; p<0.001), but not with garden size, while farms had no correlation. This result indicates that species area relationships only exist at the scale of an individual gardener. Multiple regression showed a significant positive relationship between plot biodiversity and neighborhood income (r²=0.390, p<0.01) which was still significant for ornamentals (r² =0.238, p<0.05). Further, the ornamental-income relationship was only present in non-immigrant gardens (r² =0.724; p<0.05). Though edible diversity varied little between gardens, immigrant kitchen gardens and farms had significantly higher edible cover than non-immigrants (ANOVA p<0.05). We interpret these culturally specific results through a hierarchy of needs framework. Lower income immigrant gardeners value ethnic edible species to augment food and cultural needs, while higher income non-immigrant gardeners are more likely to invest in luxury ornamentals with increasing financial security. These results link mechanisms of species-area relationships, culture, and income to urban plant biodiversity and lays groundwork for better quantification of ecosystem services in urban agriculture.