Climate Change Gives Invasive Trees An Even Greater Advantage

Invasive trees have demonstrated their adaptive mettle, so it shouldn’t come as a shock that they are likely to outperform natives as climate change alters growing conditions. But a U.S. Forest Service analysis shows the invaders hold a dramatic advantage.

“A lot of our least vulnerable species are invasive species,” said Leslie Brandt, a climate change specialist for the United States Forest Service.

Brandt was the lead author of the Chicago Wilderness Region Urban Forest Vulnerability Assessment, published last year by the USFS. One of many regional assessments conducted by USFS, it found that native trees are more vulnerable to the changes in temperature, precipitation, growing season, and other effects of accumulating greenhouse gases.

“European buckthorn is one of the most common trees in the Chicago region, and not surprisingly it’s not very vulnerable,” Brandt said Thursday in an appearance at the Morton Arboretum near Chicago. “It has a lot of capacity to adapt and disperse to new areas and so it’s going to continue to thrive in the future. Whereas some of our native trees, especially those that are more common north of this area, might experience some additional stresses.”

Brandt singled out Wisconsin’s pine forests as particularly at risk. The Assessment predicts significant decreases in white pine, red pine, shortleaf pine and white spruce. After modeling two climate scenarios, it also anticipates trouble for deciduous species including the bigtooth aspen, black ash, black cherry, northern pin oak, paper birch, quaking aspen, and scarlet oak.

Some natives are expected to do better and even increase habitat, including hickories and oaks, dogwoods and redbuds.But the resilient natives are in the minority. The Assessment found that 88 percent of invasive tree species are expected to prove resilient in the changing climate, ranked with low vulnerability, compared to 20 percent of natives.

Almost half of natives have less than moderate vulnerability, but among invasives that number is 95 percent.

As its climate begins to resemble the climate of East Texas, the Midwest may not lose its canopy of hickories and oaks, Brandt said, but the canopy will likely consist of different hickories, different oaks:

Oaks and hickories are native to Illinois, they’re native to both northern and southern Illinois and a lot of them go into places south of here and west of here as well. Some of the more northern oak species and northern hickory species might become a little more stressed, but there are a lot of alternatives that are found in central and southern parts of the state that might be a potential replacement, and so overall what the general consensus is among a lot of forest ecologists is that the oak hickory forest in the central hardwoods region which is more south of here will continue to thrive and it’s just the exact species composition that might shift slightly.”

Brandt appeared on a panel at the Morton Arboretum’s event, “The Future Of Trees: Hope In A Changing Climate,” which also explored the best way property owners, municipalities and foresters can prepare for the changing climate.

Read Part Two: How To Plant Trees In A Changing Climate

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