Book Description

Although the effects of invasive plant species on native biodiversity are well-documented, the extent of their impact on ecosystem services is poorly understood. Moreover, current knowledge on impacts of plant invasions on ecosystem services is skewed towards terrestrial systems and material services, whereas wetland systems and non-material services are largely ignored. This study provides a comprehensive view of environmental, economic, and socio-cultural impacts of ten invasive plant species, deemed as noxious weeds in the Mid-Atlantic region of the United States, on ecosystem services. Plant impacts (i.e., change in ecosystem properties, socio-economic effects, and/or human values) were observed to be spatio-temporally contingent and highly contextual, i.e., impacts were positive in certain settings while negative in others. Results suggest that plant invasions are not synonymous with negative impacts to ecosystem service provisioning exclusively but, rather, there are a multitude of interconnected factors that can magnify, diminish, or species impacts by co-occurring disturbance and/or landscape context. An invasive plant classification coding system is recommended to strengthen the explanatory power of the language used to describe those plants that demonstrate a high level of impact in a specific landcover type, reinforcing the idea that plant invasions are context-dependent, which was a critical finding in this study. Additionally, a weight of evidence (WOE) scoring system was devised to determine ecosystem vulnerability to species-specific plant invasions using the magnitude and direction of species effects. Species impacts were also classified by their connection to regulating (e.g., natural hazards, pollination, climate regulation), material (e.g., food, fuel, natural medicines), and non-material services (e.g., recreation, ethical values, existence values), and species impacts on these ecosystem service (ES) types were evaluated spatio-temporally. There was a relatively disproportional concern over species impacts in forests and wetlands, prompted by research focusing on the biodiversity loss. Many plant species had beneficial impacts on services that may override their negative associations in different regional contexts over time. Notably, plant species with minimal documented impact and/or positive impact on ecological processes or function were listed as noxious weeds at the state-level. These results can be attributed to the fact that some species are excluded from noxious weed lists for political purposes while other species of high impact merely go unrecognized due to a lack of data verifying their impacts. These findings suggest that there is a high rate of misclassification by overestimating invasion risk, which may undermine both control and educational efforts. Within the context of ES and plant functionality, non-native and invasive plant species are a critical part of plant functional assessments but are often excluded because of their general characterization as a detriment to the environment, economy, and society. Using a trait-based approach, plant functional groups were devised to capture the level of ecosystem functionality in different wetland types for six ecosystem services. This approach was used to create plant functional scores for individual species by ecosystem service type. A modifier-based approach was also employed to identify what environmental stimuli may potentially lead to ecosystem service uplift for the newly derived plant functional groups using machine learning methodologies. Species were not equal in their contribution to ecosystem processes, and a few key species, some of which are invasive plant species, accounted for the majority of ecosystem functioning. These findings suggest that plant identity is essential for understanding community assembly and ecosystem service dynamics in association with invasive plant species. As such, invasive plant species were classified into 'weak' and 'strong' types. There also appears to be no universal measure of invasiveness (i.e., traits reflecting the ability of a species to spread across multiple scales) and the degree of invasiveness (i.e., weak vs. strong invasive species) observed depends on the plant functional composition and ecosystem service type examined; there are traits promoting plant invasions under many different circumstances. Decision support tools and structured decision-making, such as the Integrating the Management of Plants Around Collaborating Conservation Targets (IMPACCT) framework for assessment of species impacts on ecosystem services, can help decision-makers explore broad scenarios of risk and develop actions that account for uncertainty, optimize trade-offs, and enhance functional capacity in different environmental systems. Taking on a socio-ecological perspective, the IMPACCT framework brings attention to the socio-economic context of species impacts using early and inclusive public engagement and open, responsive communication strategies for a more collective action take on invasive plant management. In many regards, the challenges and response to plant invasions are also social constructs. Species impacts reflect the ecological, economic, and socio-cultural value people ascribe to species. Future work should explore how and why the public and private sector perceive invasive plants as an issue and what types of information, support, and resources would be beneficial for current as well as future invasive plant management. Through the use of a comprehensive literature review and trait-based and modifier-based approaches, I developed (1) WOE scoring system, (2) a preliminary invasive plant classification coding system, (3) an IMPACCT framework alongside a WOE invasion diagram, (4) six sets of ecosystem service-based plant functional groups, and (5) a wide-ranging plant list of functional scores for different ecosystem services found in wetland systems in the Mid-Atlantic region of the United States. Overall, plant identity was found to be critical for understanding community assembly and ecosystem service dynamics. And though there was evidence of a high rate of misclassification by overestimating invasion risk, likely due to spatio-temporal variability in species impacts, management tools such as the WOE scoring system and IMPACCT framework can be applied to advance understandings of invasive plant impacts and to better guide invasive plant management.