Risk: The Game of Invasive Plants

Controlling the Invasions

Invasive species have become a common buzzword in agricultural, horticultural, and scientific circles within the last few decades, in the wake of increasingly rapid and uncontrollably spreading plant species degrading and invading ecosystems around the world. The rate and breadth of the impacts from invasive plants has led to significant research into controlling and predicting invasive species around the world. Whether motivated by threatened economic livelihoods, undermined aesthetic values, or declining environmental quality, there has been considerable literature and research performed in the attempt to limit invasive species.

Many different tactics and perspectives on how controlling invasives might be done most efficiently have been put forward. The recent study “A Geographic Assessment of the Risk of Naturalization of Non-native Woody Plants in Iowa” published by Widrlechner and Iles (2002) has taken a different approach in predicting relative ‘invasiveness’ of plants, using geographic comparison and analysis to denote greater likelihood of invasive qualities and behaviors in plants. Many factors have been suggested as the supposed linchpin to securing or inhibiting invasive qualities in plants. Other approaches to quantifying and limiting invasiveness in plants have included comparative growth rates in plants, where relative growth rate (RGR), the comparative speed at which plants grow, and associated variables are examined in association with known and suspected invasive plants. Grotkopp et al. (2010) used this approach in their assessment of woody native and nonnative plant species, finding that RGR values for known invasive species were indeed significantly higher than that of native woody species. Another dominant line of thinking has identified life histories of plant species as the key feature enabling invasive qualities and behaviors. Reichard and Hamilton (1997) investigated the role that various life history qualities and facts, ranging different physical mechanics and seasonality factors, can have on plant invasiveness. Taking into account biological and life-history qualities led the authors to approximately 80% predictive accuracy in identifying invasive plants from a selected pool, illustrating the valid role these assessments can play in determining invasive qualities.

Look to the Land

Widrlechner and Iles use geographic clues and trends to explore potentially predictive connections between analogous climates and greater invasiveness by nonnative plants in the Midwest. Motivated by the absence of detailed invasive criteria, the authors set up their research to establish geographic risk assessment as an effective tool in predicting relative invasiveness in plants. Their study focused specifically on naturalized and naturalizing woody invasive species in Iowa, specifically investigating patterns of naturalization and geographic origin of these nonnative woody plants. The authors compiled data comparing the geographic origins of a species with its relative success in naturalizing to Iowa, creating a map highlighting regions that contribute greater proportions of successfully naturalizing woody species. Species sourced from northeastern China and southeastern Europe were especially adept in naturalizing to Iowa’s environment, leading the authors to caution against importation of nonnative woody species from these regions. Their high naturalization success points towards potential in those plants to evolve invasive behaviors when introduced to the Iowa environment.

 Widrlechner and Iles’ take a novel approach to invasive species management by tackling the problem from a preventative stance, predicting and fending off invasions before they occur instead of looking to limiting invasive damage once an invasion has taken root. However, their techniques in creating predictive criteria are undermined by a weak data set. The correlations between geographic origins and invasive potential can illustrate coarse trends in invasive behaviors, but lack sufficient detail and quantified analysis to decidedly contribute to invasive risk analysis. The broad categorization of relative risk, as outlined by Widrlechner and Iles, based on proportional correlations of geographic and climatic similarity seems to counteract the goals they set for themselves in pursuing this project; that is, identifying specific criteria for predicting invasiveness in plants. The sample sizes used by the authors is not particularly exhaustive either, with a selection of only 100 nonnative species covering the global spectrum of origin.

Predicting and Preventing

Despite its flaws, the concept suggested by Widrlechner and Iles is sound and would stand to reduce accidental introduction of aggressive invasive species through the horticultural industry, which has its legacy in creating invasive species problems. Using the concept of analyzing geographic origin and climatic similarities when profiling nonnative plant species has significant potential as a resource for horticulturalists and other parties to remain informed of risks in nonnative plant introduction. A database combining different predictive factors of plants to create a more comprehensive predictive criteria for nonnative plants, woody and otherwise, would benefit the horticulture field as well as other related parties and individuals. The more preventative measures and awareness of risks that can be installed on both global and local scales, the more effective our defenses against invading species will be. 

                Figure 1: Suggested map combining different factors to create cohesive and comprehensive                 predictive criteria for invasive potential in nonnative plants.