Global change, global trade, and the next wave of plant invasions

A paper I co-authored with other members of an NCEAS working group has just been published in Frontiers in Ecology and the Environment.

Many plants imported to the US for horticultural purposes (landscaping, ornamental gardening etc…) in the past have become invasive. For example, Oriental Bittersweet was introduced to New England from China as an ornamental around 1860. Nowadays, the species is widespread in the US and, if left unchecked, shades out native trees, bushes and shrubs.

The horticultural trade is still prolific and as the global economic situation changes the US is trading with a wealth of new countries. Any of the species that the US is newly importing from these countries have the potential to become the next big invasive problem.

A garden in the Sonoran Desert planted predominantly with drought-tolerant species introduced from the Chihuahuan desert in Mexico

Another factor that needs to be considered is what kind of species US gardeners will want to import in the near future. As climate changes, the US is getting warmer. This means for example that gardeners in New England are starting to plant the kinds of species that previously could only be grown south of the Appalachians. The kinds of places that are being gardened are also changing. The massive influx of people into the southwest has led to a huge demand for garden plants that can survive the hot dry climates. This region has relatively few invasive species compared to the rest of the US, but as its human population grows this is likely to change.

So we wanted to know whether new trade relationships would promote the introduction of plants that are ideally adapted to become problematic invasives.

It turns out that emerging US trade partners  are clustered mainly across tropical regions, the Middle East, and
Eastern Europe – imports have risen by around 70% from these countries in the last 10 years.

We analysed invasive plants already in the US and found that species were likely to escape from gardens and grow wild in parts of the US that have the same kind of climate as the countries they come from. Armed with this information we realised that species imported from many of the emerging trade partners were likely to grow wild in the US because climate change is making US conditions more suitable for them, and these species are suited to the hot, dry conditions of the southwest where they are increasingly being planted.

The good news is that armed with this information we may be able to prevent invasives from arriving. Screening systems in place in Australia that aim to prevent imports of potentially invasive species have proved quite effective. These systems ask whether the climate in the export country is similar to climate in Australia. This kind of measure could be implemented in the US, but with the improvement that the similarity between the export country and future US climate conditions also be assessed. With new trade relationships emerging all over the world, we advise that screening systems used by any country be on the look out for species that have never before been exported outside their home region, as any of these untested species might turn out to be pests.

Bethany A Bradley, Dana M Blumenthal, Regan Early, Edwin D Grosholz, Joshua J Lawler, Luke P Miller, Cascade JB Sorte, Carla M D’Antonio, Jeffrey M Diez, Jeffrey S Dukes, Ines Ibanez, and Julian D Olden. 2011. Global change, global trade, and the next wave of plant invasions. Frontiers in Ecology and the Environment (e-View). Doi:http://dx.doi.org/10.1890/110145

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