Under higher CO2 levels, plants often grow faster and larger. Research has shown that under the same conditions, invasive plants are able to more effectively utilize the increased CO2 when compared to native plants, and are therefore able to outcompete native species.

Warmer temperatures and drought result in more stressed trees and more abundant pests. As cities and natural habitats become hotter and drier, insects that take advantage of stressed trees may become more abundant.

The melting of the Arctic sea ice opens new direct routes for both aquatic and terrestrial invasive species to become introduced- from both commercial shipping and new tourism pressures.

Warm weather arriving sooner each spring is a direct effect of climate change. Research is showing that invasive species take advantage of the earlier spring warmup by sprouting and leafing out long before the native species do. This gives them an edge in which they can monopolize the soil space, nutrients, and sunlight to outcompete native species and create monocultures.

This is occurring in both terrestrial and aquatic environments. Eurasian watermilfoil (Myriophyllum spicatum) , Curly pondweed (Potamogeton crispus L.), and Leafy spurge (Euphorbia esula L.) are examples of plants that can sprout before native species. They can take advantage of warmer water or soil temperatures, and longer growing seasons, which allows them to further displace native species.

As the climate is warming and historic temperature-based limits on species habitats are opening up, species are shifting their ranges. Species are moving further north into spaces where they were not able to survive before. Terrestrial plants and forest pest species are both making the move north. Pests are no longer limited by historically stable and cold winter temperatures and can survive in previously uninhabitable locations.

Asian clams and water hyacinth are aquatic invasive species that are considered intolerant to cold temperatures, however their current range extends much farther north than was previously thought possible.

Not only is climate change exacerbating the spread and impact of invasive species, invasive species are directly contributing to climate change. We are losing millions of trees to invasive pests, which directly reduces the ability of our forests to store carbon. In landscapes consistently damaged or stressed by invasives, even if the trees can survive, ecosystem health is reduced and carbon sequestration decreases.

Extreme events cause native species mortality and allow invasive species opportunities to take over. Studies have shown that the woodland ground layer following disturbance from Hurricane Katrina was overwhelmingly noxious weeds. The damaged tree canopy opened opportunities for invasive species to establish. The native species are unable to compete after being damaged and stressed by the hurricane.

For example, a 2013 study in the United States showed that invasive cheatgrass alters regional fire regimes, leading to more frequent and more extensive fires.⁶ If future climate conditions involve both warmer temperatures and higher water availability, a novel cycle of grass fires could lead to the loss of woody shrubland species.

Some non-native species are present but are not considered invasive because they do not cause significant harm. Often, this is because their population growth is limited by some naturally occuring balance within their introduced range. These “sleeping” species may take advantage of an opportunity due to the warming climate to “wake up” and become invasive. Often climate-based conditions were the limiting factor and if the climate shifts to become more suitable, the species will proliferate. For example, the mountain pine beetle  (MPB) (Dendroctonus ponderosae) is native to Western Canada, but has rapidly spread beyond its historical range in recent years. Warming winters have enabled spread into areas where the cold previously killed up to 98% of populations. MPB is now acting ‘invasive’ and threatens pine trees across Canada.

Non-native viruses, bacteria, fungi, and other pathogens that harm wildlife and people may also be considered invasive species. One example is the loss of bats from the invasive fungus causing white nose syndrome, which is a deadly infection exacerbated by sudden changes in cave temperatures, and is made more severe through the effects of climate change.

Neonative nuisance species are native species that have established themselves beyond their historical range and begun to damage or disturb their newly entered ecosystem. Black locust is a native tree in parts of central and eastern United States, but it has been expanding this range northward. In some of its newly established ranges, such as Wisconsin and Massachusetts, it now fits the profile of a neonative nuisance species and has been declared an invasive species. Black locust has been planted in BC as an ornamental plant and is still sold in nurseries despite being listed provincially as an invasive plant. Within the CKISS region, black locust is concentrated in Kaslo, Nelson, Castlegar and Trail. This tree illustrates how a species native to one part of the continent may become a serious problem elsewhere.

Climate change can also result in the reduced efficacy of control methods for the management of invasive species. Herbicides and pesticides are less effective for some species because of genetic resistance, but also because some invasive plants will absorb less of an applied treatment if they are drought-stressed.

Biocontrol agents are very specifically matched to their invasive species targets. Researchers suspect that biological control agents for invasive species may become less effective due to climate change, as there are several mechanisms by which this could occur. Climate change induced changes in ranges, growth, seasonality, and reproductive rates of either the biocontrol agent or target may cause ecological misalignments and decoupling the biological control organism from its target.

• Columbia Basin Climate Source
• CKISS EcoGarden Project- make a difference in your own backyard
• An Overview of Climate Change in Southeast British Columbia:  Climate History, Climate Projections and the Scope of the Problem. Presented by Dr. Mel Reasoner.
• Preliminary Strategic Climate Risk Assessment for BC
• NAISMA Climate Change and Invasive Species Video. Presented by Carrie Brown-Lima, NY Invasive Species Research Institute.
• Regional Invasive Species & Climate Change Management Challenges
• Northwest Regional Invasive Species and Climate Change Network