|Denslow, Julie - USDA, FOREST SERVICE|
|D Antonio, Carla|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 24, 2004
Publication Date: N/A
Interpretive Summary: Biological control projects for weeds are typically initiated when a weed is causing economic damage. The goals of controlling the weed are therefore to halt or slow the economic damage that it is causing. Most weed control projects nonetheless rank control as 'successful' if the biological agent has established and cause some sort of reduction in the host plant. This alone may not be equivalent to the reversal of measured or perceived impacts. Responses of the entire plant and animal community to control and indirect responses of communities and ecosystems to control are rarely monitored or reported. Yet they are important towards understanding both how to achieve better control and how to reverse the economic costs incurred by the original infestations. In this article, we review several 'successful' case studies of biological weed control to highlight what community and ecosystem variables are typically measured or ignored during biological control. Our intention is to highlight the need for more thorough, thoughtful and varied monitored of the responses of biological assemblages and ecosystem processes to the control of target weeds.
Technical Abstract: Development of biological control agents for weeds has been motivated by the need to reduce the abundance and distribution of a pest plant where chemical and mechanical control were not cost effective. Primary objectives have been direct reduction in abundance of the target and, secondarily, the increase of desirable species. Recently wildland weeds have become a focus of biological control projects. Here, desired outcomes include both reduction of the target and indirect effects of increased diversity and abundance of native species and restoration of ecosystem services. However, goals and benefits of biocontrol programs are not always well articulated and direct and indirect impacts are not easily predicted. We evaluated the extent to which several successful biological control projects for weeds of rangelands and waterways measured indirect impacts on invaded ecosystems. We also examined biocontrol of a wildland pest tree for which the principal objective is restoration of ecosystem services. We found few quantitative assessments of the impacts of pest plant reduction on community composition or ecosystem processes. All examples documented variation in the impacts of agent(s) across the invasive range of the target plant as well as variation in impacts on the invaded ecosystem. However, without appropriate quantitative information, we cannot evaluate site characteristics that may influence vegetation responses. Most successful weed management programs integrated the use of biocontrol agents with other weed management strategies, especially modifications of disturbance and competing vegetation. Discussion and evaluation of responses of nontarget species would improve our understanding of the context-specificity of outcomes.