Jill Johnstone is one of many researchers working in the area of climate change. A graduate student at the University of Alaska at Fairbanks, she is looking at the long-term effects of climate change on vegetation in the boreal forest. But she says that even setting up a study on this subject is no easy task.

"Right now I'm exploring the questions more than the answers," she says. "There are lots of interactions that we need to understand."

Johnstone wants to look at how a changing climate could affect the stability of ecosystems. While that might sound straightforward enough on the surface, the groundwork she is doing says a lot about the complexity of the matter at hand.

She says that some experiments have been done on short-term changes in ecosystems. For example, it's known that more carbon dioxide in the atmosphere leads to more plant growth in the short-term. But in the long term, an increase in carbon dioxide could change the balance between the amounts of carbon and nitrogen in plants.

Plants containing more carbon could decompose more slowly, slowing the rate at which nutrients are released back into the soil. This change could lead to less plant growth in the long term.

Johnstone says that this change between short and long term effects shows the need to really understand all of the factors affecting an ecosystem. She is particularly interested in how fires will affect the boreal forest and has prepared a flow chart showing some of the possibilities. The series of loops and arrows indicate the complexity of the topic.

The general consensus right now is that summers in the Yukon will be warmer and drier in the next century, and these conditions usually mean an increase in forest fires. Right now spruce trees dominate the boreal forest, but in a warmer world, it is not known whether conifers will still prevail.

If more deciduous trees start to come back after forest fires, they could actually help to cool the local climate as they have high evapotranspiration rates and return moisture to the air. Trees such as aspen and birch could help to dampen the affects of increased atmospheric temperatures.

Spruce and pine trees contain lots of resin, so they burn more easily than deciduous ones. They can also burn up all of the organic soil on the forest floor, including the underground roots that allow deciduous trees to resprout after a fire.

Conifer forests may also be warmer than deciduous ones as less water evaporates from needles than from leaves. If conifers regenerate after a fire they could help to make the local climate even warmer, and increase the frequency of fires.

The intensity of fires could also affect the types of trees in future forests. Conifers are more likely to return after blazing infernos that consume all of the organic soil, while low intensity fires would favour deciduous trees.

The sequence of plants that grow back after a disturbance can affect the long-term health of an ecosystem as well. She gives an example from Glacier Bay in Alaska, where glaciers have retreated a substantial amount over the last century.

Alder can fix nitrogen in the soil, improving it for whatever species invade later on. The Glacier Bay study found that in areas without alder there were fewer nutrients so the forest there might be more susceptible to diseases and insect outbreaks in the future.

Johnstone thinks that in a warmer world we should expect to see changes, and more instability. She makes the point that resource managers should keep all of this uncertainty in mind when making decisions. She uses the concept of maximum sustainable yield in forestry as an example. "Maximum sustainable yield is based on the concept of a stable environment. If we are headed towards ecological instability, these ideas might not apply."

Johnstone's work shows the difficulties facing all researchers in the area of climate change. No one knows exactly how the climate will change, so trying to see into the future is decidedly challenging. "Prediction is very difficult," says Johnstone. "We are just starting to understand how tough some of these issues are."

Johnstone plans to start fieldwork next summer, looking at what plants grown back in different types of burn areas. She hopes that by comparing plant succession in relatively moist spruce forests in Alaska with drier pine forests in southcentral Yukon, she will get some idea of how future climate changes could affect the boreal forest.

Jill Johnstone can be contacted at Ftjfj@uaf.edu.