What future for plant invasions?May 7th, 2012 at 8:33
When it comes to invasives, three key words are prevention, prevention, and prevention. We know that an efficient and strategic way to combat invasive species is to keep them from establishment in the first place, such as through quarantines, screening mechanisms, or black lists. A useful question for such prevention policies is, “Which are the probable future invaders, where and how should we target our efforts?” Well, particular traits (high resource allocation to reproduction, wide environmental tolerance) and a “bad reputation” (invasiveness elsewhere) can be useful predictors. Now, a recent article in Frontiers in Ecology and the Environment demonstrates a new and interesting way of predicting future invasives. They analyze trends in the global trade and climate change to identify emerging scenarios of foreign plant introduction and establishment, e.g., where are plants coming from, where are they being planted, and what are their characteristics.
The authors focus on plant introductions to the USA via the horticulture trade- legal sale of ornamental species. Among these species, climate change is likely to reduce need for cold-hardy plants and increase the need for drought-tolerant plants. Simultaneously, several regions of the world are rapidly increasing their involvement in global trade, primarily the Middle East, the tropics, and Eastern Europe. Putting these two facts together, one sees that “global change will influence not just the success of introduced plants but the introduction process itself.” As most new plant introductions occur soon after trade partnerships are formed, these regions are expected to contribute a “wave” of new introductions.
This may be especially relevant for the relatively dry, low population density Central-Western USA, where introduced species currently make up 10 to 15% of the flora, compared to 25 to 30% for many mesic, Eastern states. Human populations are now expanding in the West, which will likely increase propogule pressure of non-natives. Gardeners are also planting more drought-tolerant species (called xeriscaping), due to increased recognition of water scarcity. The authors point out that there is much potential for native species to play a role in xeriscaping, but a survey of nursery catalogs shows an uncertain future: despite a trend for greater use of native species, more than half of currently offered drought-tolerant species are non-native.
The authors also look at temperature trends, specifically at a northward shift in hardiness zones, a way of predicting where plants can survive, based on low winter temperatures. Strong northward shifts are expected for warmest zones 8 and 9. The authors predict two main consequences for these areas: native species will show decreased fitness in these areas while newly introduced, pre-adapted non-natives can show increased performance. This imbalance in competitive ability makes invasions more likely here.
Tne main conclusion is that emerging trade partners have climatic conditions just suited to trends in changing temperature and water conditions in the USA, so policy should focus on these regions and types of species. One policy is weed risk assessments, a pre-emptive examination of an imported species’ ability to invade, to create “white lists” of allowed species. Unfortunately, information on biology, ecology and invasive potential of species new to the horticulture trade will likely be low. The authors caution that low information does not mean low invasion probability. The authors propose increasing communication between invasive species biologists and the buyers and sellers of plants, especially to identify and encourage native alternatives for gardening. In the other direction, nurseries can share information with biologists about the results of field trials of new plants. Collaboration among industry, local gardening clubs, government and scientists, could effectively prevent many new invasions.
Effective prevention might spell the end of our invasivore diets, but I think we would agree that would be for the best!