Don, Ed, Mike: Having lived at the edge of the prairie for 50 years, I am not convinced that trees near range edges are more sensitive to climate change (or to extreme events if the climate does not change) than trees in the interior of a range or the interior of the forest biome. For example, sugar maple, basswood and red oak forests in southern Minnesota have very little damage from the last five years of mid summer droughts, whereas many maple forests in northern Wisconsin and Upper Michigan, which are 200-400 miles from the prairie-forest border and edge of the range have massive dieback, even thought the droughts were worse at the edge of the prairie. I think this is because the forests at the edge of the prairie have undergone significant droughts periodically over time, and have adapted through natural selection to such extremes. In addition, they occur on sites with deep silty soils, whereas the maple forests of northern WI and MI occur across a range of soils from silt to loamy sand. Probably with global warming, the niche of maple forest will contract in northern WI and MI, so that it no longer grows on the sandier soils.
Another major point is that most species with large ranges have a large degree of ecotypic differentiation throughout the range. Often there is differentiation by latitude. There have been many common garden experiments published where trees from 20-60 location throughout the range were planted at each of the other locations. Performance of individual tree populations fall off when planted more than 1-2 degrees of latitude away from the seed source, for many species of trees. Any one population has a much narrower tolerance for climate than the range of the whole species. This is why forests will not be able to adapt to the degree of global warming predicted over the next century. Once the climate stops changing, forests will catch up with it several centuries later, as has been shown in the paleoecological literature to have happened many times in the past. The performance of individual trees (especially when planted as a shade tree) in other climates is not a good indication of their performance in a forest ecosystem context in a changing climate. Forest ecosystems have insect communities, detritivore communities, fungal communities and microbial communities that respond directly to climate and change rapidly with the climate, and they are the ones that really run the ecosystem, determining water and nutrient availability, and levels of stress on trees. For example, I have transplanted sugar maple trees from the Door Peninsula (Lake Michigan) in northern WI to the home where I grew up in southern WI, which has a mean summer temperature 8 degrees F warmer than the origin of the trees. They grew 4 feet per year after planting and are excellent shade trees 30 years later, but trees in the forest from which they came are undergoing dieback from a 2 degree increase in mean summer temperature (and there has been no logging or other disturbance). Lee DON BERTOLETTE wrote: > Ed- > I don't know if I fully grasped what you were saying, but I tend to > agree with you up to a point. > There are a few papers out on what I'd refer to as 'gradient analysis' > where any given sample of a population is related to its range, or > extent. It is generally assumed that as the populations sampled get > closer to the edge of the range, the more sensitive they will be to > external changes in such environmental gradients as local/regional > warming trends and local/regional moisture regimes. > That said, if the sub-populations do indeed have broader, more diverse > genetics, and survive, that would be great, and they would be a great > boon to silviculturists facing local/regional climate change. If they > don't, then it's back to Mike's approach...nothing lost. > -DOn > > ------------------------------------------------------------------------ > F > > --~--~---------~--~----~------------~-------~--~----~ Eastern Native Tree Society http://www.nativetreesociety.org You are subscribed to the Google Groups "ENTSTrees" group. To post to this group, send email to [email protected] To unsubscribe send email to [email protected] For more options, visit this group at http://groups.google.com/group/entstrees?hl=en -~----------~----~----~----~------~----~------~--~---
