Posted on 08/06/2006 2:06:52 PM PDT by blam
Northern Refuge: White spruce survived last ice age in Alaska
Sid Perkins
Genetic analysis of white spruce trees at sites across North America suggest that that species endured the harsh climate of Alaska throughout the last ice age, a notion that scientists have debated for decades.
ICE AGE SURVIVORS. White spruce trees, common in high-latitude North American forests today, endured in Alaska during the last ice age, a new genetic analysis suggests. Inset shows Alaskan and other sites (red dots) sampled in that study. iStockphoto; (inset) Anderson, et al.
Picea glauca, the white spruce, is one of the most common trees in Alaska's forests today, says Lynn L. Anderson, a plant geneticist at the University of Illinois at Urbana–Champaign. However, scientists haven't unearthed Alaskan fossils of that species dating from the most recent ice age, which lasted from 25,000 to 12,000 years ago. During that time, most of Alaska was either a treeless tundra or covered in ice. The lack of white spruce fossils led some researchers to speculate that the species was wiped out in Alaska during the ice age and that trees from elsewhere recolonized the region once the climate warmed.
Other scientists had noted that Alaskan lake sediments from the last ice age contain trace amounts of white spruce pollen, a hint that small numbers of spruce survived. However, the grains might have blown in from distant forests.
To weigh in on the debate, Anderson and her colleagues looked at three stretches of DNA from chloroplasts, the cellular structures that produce energy in plants. The team analyzed 326 samples taken from white spruce trees at a dozen sites in Alaska and a dozen sites elsewhere in North America.
Overall, the team identified 17 combinations of genetic variations in the samples that they analyzed. While five of these combinations, called haplotypes, were in trees at all sites, seven showed up only in the Alaskan samples and five appeared only in non-Alaskan trees.
The haplotype differences suggest that today's Alaskan spruce forests arose from trees that survived locally during the ice age, says Anderson. At the rate that genetic mutation occurs in chloroplasts, it probably wouldn't have produced seven new haplotypes in just 12,000 years, the scenario required if the species had been wiped out in the region during the last ice age.
Moreover, if today's Alaskan white spruce trees were descended solely from those in distant forests, the genetic variations found in their chloroplasts would be a subset of the genetic diversity found in trees elsewhere. That's not the case, Anderson and her colleagues report in an upcoming Proceedings of the National Academy of Sciences.
Researchers who had suspected that small stands of white spruce survived in Alaska during the last ice age didn't have compelling proof, says Herbert E. Wright Jr., a paleoecologist at the University of Minnesota in Minneapolis. "These findings should be convincing enough to settle the debate," he adds.
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GGG Ping.
Here in Southern Wisconsin, on the border with Illinois, the land was covered in ice, except for a small section of the state just above the Illinois border and just east of the Mississippi. I believe they called it the "driftless" area. But it all melted! Can anyone tell us what caused all that ice to melt 20,000 years ago, before the age of autos and the burning of fossil fuels?
Dinopharts
George W. Bush of course.
Alaska is large enough that it is in several different climatic zones. The areas of glaciation are to the south for the most part, where the mountains meet the moist ocean air. The interior is much drier and was not glaciated during the recent ice age. The interior would, except there are no mammoths or sabertooth tigers now, have been very similar then and now. There might be white spruce in the interior, but most spruce are black spruce that on shallow permafrost grow very slowly and don't get large at all. Summer plants such as fireweed grow very quickly, mature overnight and go to seed immediately, as might be appropriate for a region that has a short, cool growing season at best.
Some believe it was a comet impact.
Coastal Alaska during the Wisconsinian maximum was not as cold as Ohio. There were plenty of refugia.
It didn't melt 20,000 years ago. The glacial maximum wasn't until about 13,000 years ago. It took about 7,000 years from that time for all the glacial ice to melt.
Blam--Please ping me tomorrow or Tuesday to post my review RE: the Markewich & Markewich paper on Pleistocene dunes in the Carolinas & Georgia.
It might be noted that the leaves are changing with some vigor as of today. They started a couple weeks ago in the willow, but it is also beginning in other deciduous species and certainly in leafy plants.
Be glad to if I can remember.
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That is somewhat true today too. The winters along the southern coast of Alaska do not get anywhere near as cold as it did when I lived in the midwest.
That species was the "glacial" version of ponderosa pine. It finally died out as the climate got too warm, and deciduous trees took over the canopy. I believe american black pine is now extinct.
L
Most interesting about the american black pine going extinct. Somehow I never thought of trees going extinct, in contrast to "living" creatures like the passenger pigeon.
Good observation. Plants are just like animals in that respect. Not such distant relatives, either. Something like 50% of the DNA is the same.
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