Every change to growing conditions affects outcomes, favoring one species above another, which in turn is a change that affects future outcomes. We can only predict such outcomes in the most general way, and can't predict at all if we lack good knowledge.

The rising level of atmospheric carbon dioxide may be fueling more than climate change. It could also be making some trees grow like crazy. . .

The study, by scientists from the University of Wisconsin-Madison and the University of Minnesota at Morris (UMM) and published today (Dec. 4) in the journal Global Change Biology, shows that elevated levels of atmospheric carbon dioxide during the past 50 years have boosted aspen growth rates by an astonishing 50 percent. . .

What's more, according to the study's authors, the accelerated growth rates of aspen could have widespread unknown ecological consequences. Aspen is a dominant tree in mountainous and northern forested regions of North America, including 42 million acres of Canadian forest and up to 6.5 million acres in Wisconsin and Minnesota. Aspen and their poplar cousins are considered "foundation species," meaning they exert a strong influence on the plant and animal communities and dynamics of the forest ecosystems where they reside. . .

Previously, scientists have shown that plants and trees in growth chambers respond to levels of carbon dioxide well above levels in the atmosphere. The new study is the first to show that aspen in their native forest environments are already growing at accelerated rates due to rising ambient levels of carbon dioxide in the atmosphere.

"It's a change hiding right in front of us," says Cole, a biologist at UMM. "Aspens respond to all sorts of things we had to account for — water, genetics and other factors — but the strong response to carbon dioxide surprised all of us." . . .

while the researchers found that aspen grow much faster in response to elevated carbon dioxide, similar effects have not been observed in other trees species, notably oak and pine.

Findings from the new study, the authors note, could augur revisions of the estimates of how much carbon northern temperate northern forests can sequester.

"Forests will continue to be important to soak up anthropogenic carbon dioxide," says Waller. "But we can't conclude that aspen forests are going to soak up excess carbon dioxide. This is going to plateau."

"Aspens are already doing their best to mitigate our inputs," agrees Cole. "The existing trees are going to max out in a couple of decades."

There are other factors. Moisture levels are mentioned, but I suspect that other changes such as higher mineral nitrogen levels due to NOx emissions are a factor too, and that the variable responses of different species will accelerate as change continues.

Update: Another Data Point

One of the study's key findings is that while the combination of ambient carbon dioxide and nitrogen pollution reduces species richness by 16 percent, adding more CO2 to the mix reduces that change by half.

"From a biodiversity perspective, there was no evidence to support the worst-case scenario, in which impacts of rising CO2 and nitrogen deposition combine to suppress diversity by 30 percent, 40 percent or even 50 percent or more," Reich said. "Instead, their interaction ameliorated the diversity loss due to nitrogen enrichment that occurs under ambient CO2. Given the importance of biodiversity to the effective health and function of our ecosystems this is good news, or perhaps better labeled as "not quite as bad" news."

Their study was very limited, considering only a few species, and seems otherwise amateurish since so few relevant factors were measured and monitored, but it's not necessarily bad when a study raises more questions than it answers.