Trees Lose Ground as Climate Warms

Scientists expect the ranges of many North American trees to shrink over the next century if the climate gets as warm as models forecast. Out of 130 tree species studied, the area with suitable growing weather for 72 species will decline. All trees would no longer tolerate the temperature and precipitation conditions in at least 13 percent of their present range.

Southern trees will particularly undergo dramatic reductions in where they can survive. Climate changes could eliminate loblolly bay from 93 percent of its current range. Another tree of the southeastern United States, live oak, could lose 82 percent of its growing area. On the US west coast, suitable conditions will contract by 77 percent for California red fir and 65 percent for Lawson cedar. Much of the southern states will become too hot for most of the 130 species examined, except white fir.

There'll also be winners in a warmer climate. Gains of over 25 percent in area with appropriate weather would be seen for red alder, white fir, boxelder and narrowleaf cottonwood.

Researchers with the Canadian Forest Service forecast that by the year 2100 the range midpoint of all 130 species would have crept north by an average of 700 kilometres (435 miles). How far a species might extend varies. Sugar maple, black willow, American basswood and white alder could shift 1000 km northwards.

As trees move into new areas, some regions of North America will become richer in species. The biggest diversity gains would occur in Canada's maritime provinces, Quebec, Ontario, northern prairies and Alaska, with up to 60 new types of trees appearing in some areas.

Whether trees can actually migrate and then survive on new sites as the climate changes nevertheless remains to be seen. Other factors may hold sway. For instance, the fertility of Canada's northern soils is so poor it may curtail northward migration of some species.