2019 Conference Climate Change & Gardens 17. Richard Shaw

From 2019: Invasive plants, their “pests” and climate change – Dick Shaw

Invasive plants around the world have a huge impact on livelihoods, particularly in the developing world where a number of aid agencies actively encourage the planting of known invasives! Not all non-native organisms demonstrate invasive potential with the 10% rule providing a simple guide: 10% of established plants making it over the garden fence survive but only 10% of these have any invasive potential. Britain has more invasive plants that most other European countries but what makes an invader?

There are many different factors but a major one is that the species has been removed to an environment with no natural predator/pest and hence no control measure. Many plants, when seen in their native habitat, do not look invasive but with the controls removed, they are free to become bigger, bolder and more mobile. Travel, trade and tourism have created the invasive species problem more so than climate change, but a changing climate will begin to exert a greater impact in the future as more species survive winter wet/cold removing another control measure for ‘sleeper invasive’ plants such as Ailanthus altissima.

CABI UK are exploring a range of biocontrols for use in the UK. These can be inundative or classical biocontrols and largely exploit natural pests or diseases found in their natural habitat. Trials on Himalayan balsam and Japanese knotweed show the importance of obtaining the biocontrol from the area in which the plant was originally sourced to ensure pest-host

compatibility; it is also important (and an added layer of complication) to source the biocontrol from a climate that matches the UK as much as possible to ensure survival of the agent. With more funding in this area, cost-effective invasive controls will be more likely to be identified.