Kim Stoddart and Sally Morganuncover one of the unexpected threats of climate change on the plot
Climate change brings other threats to our gardens. It’s not just extremes of climate that we have to cope with, it’s also the arrival of new pests and diseases, plus competition from invasive plants. As the world warms up, pest and disease organisms can expand their range and travel further afield than they would do otherwise. With these widening territories, pests can become highly competitive and invasive once they set out establishing themselves in a new area.
In addition, warming temperatures, and especially milder winters, enable some pests to overwinter, emerge, and breed more rapidly than they have previously, resulting in greater numbers overall. For example, in the northeastern United States, Mexican bean beetles, Colorado potato beetles, and others might have produced just one generation of offspring in the past. Now, two generations per season is sometimes the case. With potentially greater pest numbers, pests arriving earlier in the growing season, and new emerging threats, this can make it more challenging for the gardener to keep pest numbers and their impact in check over a longer period of time.
Over the last few decades, globalization has led to more international trade in plant materials, including wood, foods, ornamental plants, and more. This has resulted in insects being unwittingly introduced to areas outside of their normal range. In the past, these insects may not have been able to get a foothold, but our changing climate means that sometimes they now can. Diseases too can be spread around the world via infected timber or ornamental plants.
Invasive insects are a threat to natural ecosystems and agriculture, with concerns around food security and potential economic losses through crop failures. It’s a worry to gardeners also. Certainly Henrik Sjöman is anxious. He is a researcher from Sweden and the scientific curator for Gothenburg Botanical Garden. He says that more than half of the trees growing in northern European cities are of just two or three species, so if they prove vulnerable to attack by pests and diseases, the urban landscape will be changed, and not for the good. He quotes one example: Helsinki in Finland, where almost half the trees in urban streets and parks are linden trees. And other cities around the world are not much better, with just a few species making up the bulk of the urban trees.
How species are on the m
