Until the Maples come to Churchill

Forests on the Move

“Macbeth shall never vanquish'd be until
Great Birnam wood to high Dunsinane hill
Shall come against him.” MacBeth, William Shakespeare, Act IV, Scene 1

High school English, MacBeth – I loved MacBeth. MacBeth was safe because the forest would not “unfix his earthbound root” and march against him.

This week I read an interesting article on climate change and forests. It is also another opportunity for you to contribute to a research project. The article, The Potential Impacts of Climate Change on the Distribution of North American Trees, by Daniel McKenney and co-authors appeared in the journal Bioscience and it is available here. The study looks at 130 species of trees and how they might respond to climate change in the next 100 years.

As the readers of this blog know (and point out frequently) there is substantial natural variability of climate. One aspect of the global warming that will follow from the emission of carbon dioxide by burning of fossil fuels is that it will occur on times scales that are far faster than those normally associated with natural variability. We are excepting to see a temperature change in the next hundred years that would normally be spread out over thousands, if not tens of thousands of years. Therefore, one of the concerns that is raised is the ability of ecosystems to adapt to a warming planet --- and, of course, changing water and soil water.

Using the IPCC scenarios, one of the findings of the McKenney et al. paper is that trees will need to move on the order of 10 kilometers a year in order to keep up with the warming climate. Forestry research suggests that the natural ability of trees to move is 10 – 100 meters a year, far slower than that which will be required to keep up with warming at middle and high northern latitudes.

There are a couple of methods of this forest-impact research that are worth mentioning. The climate range in which a particular type of tree can live is determined mostly by temperature and precipitation. A species of tree has a certain range of temperature and precipitation variability that it is currently observed to occur in, and this defines an envelope of climate conditions suitable for the tree. Of course, the relationship to climate is much more complex than a simple relationship to temperature and precipitation. Soil types, nutrients, and the ability of the soil to hold and deliver moisture are important variables. There is also the potential that the seasonal availability of moisture is important, especially when thinking about the relationship to sunlight and the requirements for seed germination. This model is simple, but it is, at least, intuitively useful.

Also required in the research is some sort of model of how the trees will migrate. The authors made two assumptions, which bracket the range of possibility. In the first they assumed that the trees can keep up with the march of temperature and moisture. In the second they assumed, essentially, that the trees could not keep up. In this second case, therefore, the trees can only continue to grow where the geographic extent of climatic conditions in the future overlap the current climate conditions.

With this hierarchy of models and assumptions, the authors find that trees in North America and Canada will march northward between about 330 and 700 kilometers. Perhaps it is better to say that they will need to march northward. Perhaps Churchill, Manitoba, will become the maple syrup capital of the world.

Also with the hierarchy of models and assumptions one sees the need for more research and better models and more precise treatment of information. These researchers are working on a far more robust development of hardiness zones as well as calling for information about tree distributions in the U.S. and Canada. Here is a link for their project to collect information from the public. Here is an article about the research by first-author McKenney at scitizen.com. This figure is an example of the type of climatic range maps that you can help to generate.




Figure 1. Taken from The Canadian Forest Services Plant Hardiness Zone Research Effort. Distribution of Red Oaks. This is a sample, and on the web site they are requesting information about many types of trees in both the U.S. and Canada.

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Relevant Previous Blogs

Warm Snow (Talks about Younger Dryas and warming after the last ice age.)

Getting Ready for Spring a Few Days Early (Talks about conventional hardiness zones.)

Heat Flood and Fire (Mentions the pinyon pine die off in the U.S. Southwest and studies that attribute the die off to climate change.)