Climate Change Favours Invasive Plant Species

Invasion biology looks at how plants overtake new ecosystems

Prof. Andrew MacDougall

Prof. Andrew MacDougall

Invaders. Climate change. Plants on the march. They might all sound like elements of a low-budget thriller. But they’re serious business for Guelph ecologist Andrew MacDougall. In a new paper written with international colleagues, he urges conservationists and resource managers to look to invasive plants for clues about how plants and their ecosystems might respond to projected climate change.

Published in the journal Oikos, the paper discusses how invasion biology might provide insights into climate change ecology.

For ecologists concerned about plant species threatened with extinction by climate change, the paper suggests two principles, says MacDougall, Department of Integrative Biology.

First, consider helping those plants to colonize new areas – but proceed with caution. Second, don’t lose sight of broader ecosystem impacts in focusing on single plant species.

Before deciding to intervene, says the paper, ecologists need to be clear about ecological processes and social values involved in changing ecosystems. And look to invasion biology – an older field – for ideas, says MacDougall.

In warmer conditions, invasive thistles grow taller, helping to disperse seeds. Light, winged seeds allow pines to spread far and quickly. Producing lots of seeds has helped acacia to invade grasslands in South Africa’s Western Cape region.

Many ecologists studying the effects of climate change have been reminded of how invasive species spread in different ecosystems, he says. A species of southern beech tree native to New Zealand, for instance, has naturally found its way above the climatic tree line in one mountain range. That scenario looks much like expansion of an invasive pine on a mountain grassland elsewhere in the country.

“Trees go up because it’s warmer or down where it’s wetter,” he says. “If that happens on an altitude gradient, then it’s likely with latitude as well. Trees could go north with warmth or south for water.”

For another example closer to home, look at crested wheatgrass. The plant was introduced to the North American prairies from Eurasia to reseed abandoned cropland destroyed by the dust-bowl droughts of the 1930s. It has been blamed for loss of biodiversity in native grasslands.

Conditions on the prairies are changing, says MacDougall, an expert in prairie ecology and restoration. In recent years, warmer springs and wetter summers allow wheatgrass to grow and germinate earlier than native species. Grow those species under drier and cooler conditions – as researchers have tried – and you halt the invasion.

“It’s almost like a perfect storm. It’s actually a climate story that looks like an invasive species story.”

He says looking at biological invasions around the world can help us learn about ecological consequences as species move under changing environmental conditions. Invasion biology might also help us avoid repeating the mistakes of assisted migration, from gypsy moths in North America to cane toads in Australia.

When European foresters tried to grow their pines in New Zealand, the trees failed. Eventually, someone realized that the trees needed root fungi to thrive. Importing soil allowed the trees to grow – but now they threaten the native grasslands, including the iconic vistas captured in the Lord of the Rings trilogy filmed in that country, says MacDougall.

The paper discusses how plant species will respond to climate change and how their movement will affect ecosystems, and how humans should manage species and ecosystems under climate change.

The authors hail from Canada and the United States, France, Switzerland, Germany, Australia, New Zealand and South Africa. The lead author is ecologist Paul Caplat, formerly a U of G researcher. While writing the paper, he worked with the Commonwealth Scientific and Industrial Research Organization, Australia’s national science agency.

Managers might have to help move species threatened by climate change, says MacDougall. But few studies have compared deliberate relocations, such as biological control, and relocations for climate change adaptation.

And it’s a bigger issue than single species alone. Earlier invasion ecologists often looked at individual species. Instead, he says, we need to look at the broader ecosystem.

The paper’s authors hope to spark discussions among researchers and encourage managers to think about applying invasion ecology to impacts of climate change.

“Invasion ecology only has a fraction of the answers that we need in order to better live with and manage our changing world,” they write. “However, we believe that collaborations or inspirations between these two fields will lead to better outcomes for ecosystems threatened by all forms of global change.”

MacDougall says humans’ role in climate change is unclear. But he says carbon dioxide – a greenhouse gas – is rising in the atmosphere, and various climatic events, such as excessive rainfall and flooding in Europe this spring suggest changes are occurring. “There are enough warning signs, I think.”

He says climate change may also favour weedy plants rather than so-called charismatic species in various parts of the world. That raises not just scientific but cultural and even ethical concerns for ecologists and resource managers. “We may have to live with new plant communities.”

MacDougall belongs to the Nutrient Network, a group of ecologists studying grasslands at about 70 sites in 12 countries. His fieldwork takes him to the Rare Charitable Research Reserve in Cambridge, Ont., and to oak savannah grasslands on Vancouver Island.