Managing Invasive Plants in Natural Areas: Moving beyond Weed Control

Exotic invasive plants present one of the greatest challenges to natural resource management. These weeds can alter entire communities and ecosystems, substantially degrading important ecosystem services such as forage for wild and domestic herbivores, water and soil quality, recreational values, and wildlife habitat. Traditionally, weed management in natural areas has focused on removing the target weed under the assumption that its impacts would dissipate and the system would recover following control or suppression of the invader. This approach arose presumably because most weed management tools originated in agricultural systems where removal of the weed commonly translates to increased crop yields. However, accumulating studies in natural areas indicate that simply suppressing the target weed does not ensure mitigation of its impacts. This is due primarily to the complexity of natural systems and the limitations of available management tools. To improve weed management in natural systems, we need to better understand three important factors that greatly complicate natural areas weed management: invader impacts, management side effects, and secondary invasion. Weed invasion is complex. Weeds not only impact native plants, they affect higher trophic levels, alter community interactions, and sometimes disrupt ecological processes structuring the system. Therefore, mitigating weed impacts first requires determining what the impacts are and which ones may be amenable to mitigation given current tools. Additionally, weed management tools are imprecise. As a result, management tools inevitably incur side effects on native species and system processes due to their limited selectivity and the often complex response of system components to management action. Minimizing deleterious side effects requires understanding how and why they occur. Finally, even when weed control is successful, suppression of the target weed commonly results in secondary invasion by other exotic invasive plants, thereby undermining mitigation objectives. Thus, successful natural areas weed management requires that we understand much more than just weed suppression. First, a basic understanding of the No part of this digital document may be reproduced, stored in a retrieval system or transmitted in any form or by any means. The publisher has taken reasonable care in the preparation of this digital document, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained herein. This digital document is sold with the clear understanding that the publisher is not engaged in rendering legal, medical or any other professional services. Dean Pearson and Yvette Ortega 2 system under consideration and the impacts of the target weed on system components and processes is required to determine to what extent mitigation may be feasible. Additionally, a working knowledge of how management tools interact with the target weed, nontarget species, and system processes is necessary to maximize intended outcomes and minimize side effects of management actions. Finally, further knowledge of the ecological conditions and processes underlying successive weed invasions is needed to develop strategies for reducing the risk of secondary invasion following target invader suppression. Here, we explore these issues by examining research and management of spotted knapweed (Centaurea maculosa) in Western North America.