Post by yihunt on Nov 1, 2009 8:03:34 GMT -4
Many factors combined to produce this autumn's heavy acorn crop
Should help wildlife through the coming winter
Sunday, November 01, 2009
By Ben Moyer
Jim Mendenhall/Post-GazetteWere it all to happen at once, the Earth might quake all the way to Pittsburgh's Point. Since early September, all across Western Pennsylvania's ridges, millions of acorns have been falling to the ground. Hunters and hikers say few autumns in memory rival the acorn production of 2009.
Roger Baker of Huntsville, Ala., saw evidence of this year's acorn crop during an early October week while hiking the Laurel Highlands Trail.
"I've never seen anything like it," Baker marveled. "There are so many acorns that they roll under your boots, making tricky footing."
Joanne Rebbeck, a research plant physiologist at the U. S. Forest Service Northern Research Station in Delaware, Ohio, says heavy acorn production occurs at roughly three to five-year intervals, and that she recalls similar abundance in 2001.
"I was involved with research on the Moshannon State Forest in Pennsylvania that year," Rebbeck said. "Northern red oak acorns were off the chart. Surveys documented more than 200,000 acorns per acre."
But Rebbeck cautions that acorn production in any given year results from a complex set of conditions.
"There are a lot of factors at work," Rebbeck said. "Late frost, humidity during flowering, drought, insects and the various species' responses to these conditions all influence production year-to-year. This summer Western Pennsylvania had abundant rain, which may have contributed, in part, to the region's successful acorn development."
Acorns are the seeds of oak trees, among which the white oak, chestnut oak, northern red oak and black oak are most common in this region. Scientists classify these into two broad sub-groups, white oaks and red oaks, each of which has evolved a different strategy for acorn development and seedling germination:
• White oaks are easily recognized by their round-lobed leaves. White oak acorns mature and fall in one growing season, and germinate immediately after falling.
• Red oak leaves have sharply pointed lobes along the leaf margin, and their acorns remain on the tree through two seasons and must lie dormant through winter before germination the following spring.
Hunters know that acorn abundance can influence the location and behavior of game such as deer, turkeys, squirrels and bears. But less obvious are the opportunities and challenges presented to wildlife by white and red oaks' different reproductive strategies.
Red oak acorns are higher in fat and protein than those of white oaks, but are less palatable because their high tannin content results in bitter taste. In response, animals seek out white oak acorns if both kinds of seeds are available, sacrificing higher nutrition for better taste, at least initially.
But as red oak acorns lay dormant, winter's rain and melting snow leaches away much of the tannin, rendering them more palatable in early spring when few other foods are available and when their densely concentrated nutrients are most needed.
"It is amazing how wildlife responds to a good acorn crop," Rebbeck said. "You can document differences in populations of mice and other small mammals, and researchers have shown that survival of white-tailed deer fawns improves the next year, due to better nutrition for the doe."
Human cultures around the world have used acorns as food for thousands of years. Native Americans living among the diverse oak forests of California soaked baskets of acorns in flowing water to leach away tannins, then ground the nuts into flour or a thickening agent for soups and stews. Acorn gelatin is still popular in Korean cuisine.
Because so many insects, birds and mammals seek out acorns, some scientists suspect that poor acorn production spaced between heavy fruiting may, itself, be a survival strategy for oak species.
Richard Ostfeld, an animal ecologist at the Institute for Ecosystem Studies in Millbrook, N.Y., suggests oaks evolved cyclic acorn production as a way of depressing the populations of seed-eating animals.
"The existence of one to several low mast [seed] production years, which may cause declines in consumer populations, may be as important to seed survival as the heavy mast year itself," Ostfeld wrote in an Institute research abstract.
Rebbeck observes that this year's acorn fall does not necessarily bode well for the future of oak forests in the region.
"Even if you have this huge acorn crop, there are still many other factors in play before an acorn grows into a viable seedling," Rebbeck said. "There may be no snow to protect the seedling, or there may be severe freezing, it may not get enough sunlight, or a seedling can be browsed by deer. In 2002 on the Moshannon, we saw poor seedling survival after a heavy acorn fall the previous year. Oaks and their environment are marvelously complex and we are only beginning to study them in an integrated way."
Should help wildlife through the coming winter
Sunday, November 01, 2009
By Ben Moyer
Jim Mendenhall/Post-GazetteWere it all to happen at once, the Earth might quake all the way to Pittsburgh's Point. Since early September, all across Western Pennsylvania's ridges, millions of acorns have been falling to the ground. Hunters and hikers say few autumns in memory rival the acorn production of 2009.
Roger Baker of Huntsville, Ala., saw evidence of this year's acorn crop during an early October week while hiking the Laurel Highlands Trail.
"I've never seen anything like it," Baker marveled. "There are so many acorns that they roll under your boots, making tricky footing."
Joanne Rebbeck, a research plant physiologist at the U. S. Forest Service Northern Research Station in Delaware, Ohio, says heavy acorn production occurs at roughly three to five-year intervals, and that she recalls similar abundance in 2001.
"I was involved with research on the Moshannon State Forest in Pennsylvania that year," Rebbeck said. "Northern red oak acorns were off the chart. Surveys documented more than 200,000 acorns per acre."
But Rebbeck cautions that acorn production in any given year results from a complex set of conditions.
"There are a lot of factors at work," Rebbeck said. "Late frost, humidity during flowering, drought, insects and the various species' responses to these conditions all influence production year-to-year. This summer Western Pennsylvania had abundant rain, which may have contributed, in part, to the region's successful acorn development."
Acorns are the seeds of oak trees, among which the white oak, chestnut oak, northern red oak and black oak are most common in this region. Scientists classify these into two broad sub-groups, white oaks and red oaks, each of which has evolved a different strategy for acorn development and seedling germination:
• White oaks are easily recognized by their round-lobed leaves. White oak acorns mature and fall in one growing season, and germinate immediately after falling.
• Red oak leaves have sharply pointed lobes along the leaf margin, and their acorns remain on the tree through two seasons and must lie dormant through winter before germination the following spring.
Hunters know that acorn abundance can influence the location and behavior of game such as deer, turkeys, squirrels and bears. But less obvious are the opportunities and challenges presented to wildlife by white and red oaks' different reproductive strategies.
Red oak acorns are higher in fat and protein than those of white oaks, but are less palatable because their high tannin content results in bitter taste. In response, animals seek out white oak acorns if both kinds of seeds are available, sacrificing higher nutrition for better taste, at least initially.
But as red oak acorns lay dormant, winter's rain and melting snow leaches away much of the tannin, rendering them more palatable in early spring when few other foods are available and when their densely concentrated nutrients are most needed.
"It is amazing how wildlife responds to a good acorn crop," Rebbeck said. "You can document differences in populations of mice and other small mammals, and researchers have shown that survival of white-tailed deer fawns improves the next year, due to better nutrition for the doe."
Human cultures around the world have used acorns as food for thousands of years. Native Americans living among the diverse oak forests of California soaked baskets of acorns in flowing water to leach away tannins, then ground the nuts into flour or a thickening agent for soups and stews. Acorn gelatin is still popular in Korean cuisine.
Because so many insects, birds and mammals seek out acorns, some scientists suspect that poor acorn production spaced between heavy fruiting may, itself, be a survival strategy for oak species.
Richard Ostfeld, an animal ecologist at the Institute for Ecosystem Studies in Millbrook, N.Y., suggests oaks evolved cyclic acorn production as a way of depressing the populations of seed-eating animals.
"The existence of one to several low mast [seed] production years, which may cause declines in consumer populations, may be as important to seed survival as the heavy mast year itself," Ostfeld wrote in an Institute research abstract.
Rebbeck observes that this year's acorn fall does not necessarily bode well for the future of oak forests in the region.
"Even if you have this huge acorn crop, there are still many other factors in play before an acorn grows into a viable seedling," Rebbeck said. "There may be no snow to protect the seedling, or there may be severe freezing, it may not get enough sunlight, or a seedling can be browsed by deer. In 2002 on the Moshannon, we saw poor seedling survival after a heavy acorn fall the previous year. Oaks and their environment are marvelously complex and we are only beginning to study them in an integrated way."