Urban landscape ecology and management for conservation biological control in lawns and gardens

Background/Question/Methods

How can urbanized landscapes be designed and managed in ways that restore and conserve beneficial biodiversity and ecosystem services? Investigations of this question have been completed, but precious few insights are available to answer it. Within urbanized landscapes, much of the green infrastructure is managed as lawns and gardens, an activity that engages 80% of Americans. Data about lawn and garden ecology are needed to guide their sustainable management and facilitate their use as foci for environmental education. Specifically, information about how to increase the ecosystem service of pest control by natural enemies (i.e., conservation biological control) can reduce the need for pesticides and foster education about urban biodiversity and food webs. To this end, this study has two objectives: 1) examine how ornamental annual flowers affect ground-dwelling arthropods; 2) review and synthesize diverse research that informs the development of landscaping guidelines to promote conservation biological control in lawns and gardens. Objective one was met with a 2011 field experiment in which ground arthropods were sampled on five dates using pitfall traps from three replicated 50cm X 50cm plots each of marigolds, petunias, coleus, wood mulch only and lawn. Objective two was met through a comprehensive literature review.        

Results/Conclusions

Experimental results showed that patches of annual flowers provided more favorable habitat for some arthropods (especially beetles, ants and entomobryomorpha collembolans) than lawns and wood mulch on some dates. Their activity/density levels were six to eight times higher, on average, from flower plots (particularly marigold and petunia) than lawns, especially in July when isopod populations also had significantly higher (40x) densities under flowers. These results indicate that patches of annual flowers may provide urban “refugia” for beneficial arthropods and help increase and conserve them and associated services like pest control. Some ground-dwelling arthropods may have found refuge from daytime heat in the humid shade under the denser canopies of the annual plants or may have been attracted to the flowers’ food resources. Are these conclusions supported by other studies? As revealed through the literature review, other research has found similar effects of urban landscape elements, including perennial flowers, on beneficial arthropods, including parasitoids. Further, some studies documented significant benefits from conservation biocontrol approaches for controlling lawn and garden pests. Several recent landscape-scale studies also bolster the conclusion that urban landscapes can successfully be designed and managed in ways that promote beneficial biodiversity and the ecosystem service of pest control.