World's Big Trees Are Dying:
Alarming Increase in Death Rates Among Trees 100-300 Years Old
The largest living organisms on the planet, the big, old trees that harbour and sustain countless birds and other wildlife, are dying.
"It's a worldwide problem and appears to be happening in most types of forest," says lead author Professor David Lindenmayer of the ARC Centre of Excellence for Environmental Decisions (CEED) and Australian National University.
"Large old trees are critical in many natural and human-dominated environments. Studies of ecosystems around the world suggest populations of these trees are declining rapidly," he and colleagues Professor Bill Laurance of James Cook University, Australia, and Professor Jerry Franklin of the University of Washington, USA, say in their Science report.
"Research is urgently needed to identify the causes of rapid losses of large old trees and strategies for improved management. Without… policy changes, large old trees will diminish or disappear in many ecosystems, leading to losses of their associated biota and ecosystem functions."
Prof. Lindenmayer says they were first tipped off to the loss of big old trees while examining Swedish forestry records going back to the 1860s. Then a 30-year study of Mountain Ash (Eucalyptus regnans) forest in Australia confirmed not only that big old trees were dying en masse in forest fires, but also perishing at ten times the normal rate in non-fire years -- apparently due to drought, high temperatures, logging and other causes.
Looking round the world, the scientists found similar trends at all latitudes, in California's Yosemite National Park, on the African savannahs, in the rainforests of Brazil, the temperate forests of Europe and the boreal forests of the far north. Losses of large trees were also pronounced in agricultural landscapes and even cities, where people make efforts to preserve them.
"It is a very, very disturbing trend. We are talking about the loss of the biggest living organisms on the planet, of the largest flowering plants on the planet, of organisms that play a key role in regulating and enriching our world," says Professor Bill Laurance of James Cook University.
"Large old trees play critical ecological roles. They provide nesting or sheltering cavities for up to 30% of all birds and animals in some ecosystems. They store huge amounts of carbon. They recycle soil nutrients, create rich patches for other life to thrive in, and influence the flow of water within landscapes and the local climate.
"Big trees supply abundant food for numerous animals in the form of fruits, flowers, foliage and nectar. Their hollows offer nests and shelter for birds and animals like Australia's endangered Leadbeater's Possum (Gymnobelideus leadbeateri) -- and their loss could mean extinction for such creatures.
"In agricultural landscapes, large old trees can be focal points for vegetation restoration; they help connect the landscape by acting as stepping stones for many animals that disperse seeds and pollen," he says.
The alarming decline in old trees in so many types of forest appears to be driven by a combination of forces, including land clearing, agricultural practices, man-made changes in fire regimes, logging and timber gathering, insect attack and rapid climatic changes, says Prof. Jerry Franklin.
"For example, populations of large old pines in the dry forests of western North America declined dramatically over the last century because of selective logging, uncharacteristically severe wildfires, and other causes," he adds.
The researchers liken the global loss of big trees to the tragedy that has already befallen the world's largest mammals, such as elephants, rhinos, tigers and whales, cautioning that almost nowhere do conservation programs have the time-frames lasting centuries, which are needed to assure the survival of old trees.
"Just as large-bodied animals such as elephants, tigers and cetaceans have declined drastically in many parts of the world, a growing body of evidence suggests that large old trees could be equally imperilled," they warn.
They call for an urgent world-wide investigation to assess the extent of big tree loss, and to identify areas where big trees have a better chance of survival.
Their paper "Rapid Worldwide Declines of Large Old Trees, by David B. Lindenmayer, William F. Laurance and Jerry F. Franklin appears in today's issue of the journal Science.
CEED is the Australian Research Council Centre of Excellence for Environmental Decisions. CEED's research tackles key gaps in environmental decision making, monitoring and adaptive management.
Handful of Heavyweight Trees Per Acre Are Forest Champs
Big trees three or more feet in diameter accounted for nearly half the biomass measured at a Yosemite National Park site, yet represented only one percent of the trees growing there.
This means just a few towering white fir, sugar pine and incense cedars per acre at the Yosemite site are disproportionately responsible for photosynthesis, converting carbon dioxide into plant tissue and sequestering that carbon in the forest, sometimes for centuries, according to James Lutz, a University of Washington research scientist in environmental and forest sciences. He's lead author of a paper on the largest quantitative study yet of the importance of big trees in temperate forests being published online May 2 on PLoS ONE.
"In a forest composed of younger trees that are generally the same age, if you lose one percent of the trees, you lose one percent of the biomass," he said. "In a forest with large trees like the one we studied, if you lose one percent of the trees, you could lose half the biomass."
In 2009, scientists including Lutz reported that the density of large-diameter trees declined nearly 25 percent between the 1930s and 1990s in Yosemite National Park, even though the area was never logged. Scientists including co-author Andrew Larson of the University of Montana, also have found notable numbers of large trees dying in similar areas across the West.
Because of this, scientists have been keen to study a plot large enough to detect forest ecosystem changes involving large trees, including the effects of climate variability and change, possible culprits in the declines, Lutz said.
The new 63-acre study site in the western part of Yosemite National Park is one of the largest, fully-mapped plots in the world and the largest old-growth plot in North America. The tally of what's there, including the counting and tagging of 34,500 live trees, was done by citizen scientists, mainly undergraduate college students, led by Lutz, Larson, Mark Swanson of Washington State University and James Freund of the UW.
Included was all above-ground biomass such as live trees, snags, downed woody debris, litter and what's called duff, the decaying plant matter on the ground under trees. Even when big trees die, they continue to dominate biomass in different ways. For example, 12 percent of standing snags were the remains of large-diameter trees, but still accounted for 60 percent of the total biomass of snags.
Live and dead biomass totaled 280 tons per acre (652 metric tons per hectare), a figure unmatched by any other forest in the Smithsonian Center for Tropical Forest Science network, a global network of 42 tropical and temperate forest plots including the one in Yosemite.
Trees in the western U.S. with trunks more than three feet across are typically at least 200 years old. Many forests that were heavily harvested in the 19th and 20th centuries, or those that are used as commercial forest lands today, don't generally have large-diameter trees, snags or large wood on the ground.
One implication of the research is that land managers may want to pay more attention to existing big trees, the co-authors said. Last year in the Yosemite National Park, for example, managers planning to set fires to clear out overgrown brush and densely packed small trees first used data from the study plot to figure out how many large trees to protect.
"Before the fires were started, crews raked around some of the large trees so debris wouldn't just sit and burn at the base of the tree and kill the cambium, the tissue under the bark that sustains trees," Lutz said.
In some younger forests that lack big trees, citizens and land managers might want to consider fostering the growth of a few big-trunked trees, Lutz said.
Another finding from the new work is that forest models based either on scaling theory or competition theory, which are useful for younger, more uniform forests, fail to capture how and where large trees occur in forests.
"These trees started growing in the Little Ice Age," Lutz said. "Current models can't fully capture the hundreds of years of dynamic processes that have shaped them during their lifetimes."
Old, Large, Living Trees Must Be Left Standing to Protect Nesting Animals, Study Shows
Old trees must be protected to save the homes of more than 1,000 different bird and mammal species who nest, says a study from the University of British Columbia. Most animals can't carve out their own tree holes and rely on holes already formed. The study found that outside of North America, most animals nest in tree holes formed by damage and decay, a process that can take several centuries.
The study, published in the journal Frontiers in Ecology and the Environment, examined the holes birds and mammals were using for nesting around the world. The research team, led by Kathy Martin, a professor in the Faculty of Forestry at UBC, wanted to find out how the holes were created and which species were using them.
In forests, tree holes are created either quickly by woodpeckers or more slowly as trees age and begin to decay. Birds like owls, songbirds and parrots, and mammals like flying squirrels and opossums, make homes in the holes of trees because they offer safe environments for sleeping, reproduction and raising young. Insects, snakes and amphibians will also make use of tree cavities.
Martin and her research team found that on most continents -- South America, Europe, Asia and Australia -- more than 75 per cent of the holes used by birds and mammals were created by damage and decay.
"When wildlife depends on decay-formed cavities, they are relying on large living trees," says Martin, also a senior research scientist with Environment Canada. "Most trees have to be more than 100 years old before decay cavities begin to form and often several centuries old before large cavities or many cavities develop in one tree."
In North America, the team found very different results -- woodpeckers make up to 99 per cent of the cavities used by birds and mammals.
Worldwide, tree holes are in short supply and many efforts to protect the animals living in these holes have been focused on protecting woodpeckers because it was presumed that they make most of the holes.
"Most forest policies help protect younger trees but promote the harvest of older, larger, living trees -- the very trees needed by cavity-nesting animals," says Martin.
The researchers monitored 2,805 tree holes in Canada, Poland and Argentina between 1995 and 2010. They identified how the holes were formed and every year checked to see if they were still usable.
"Some of the tree cavities in Canada were used 17 times in 13 years by up to five different species," says Martin. "One tree cavity can sustain a lot of wildlife over its lifetime."
Martin and her research team found that although woodpeckers live in Argentina and Poland and make good quality holes, holes formed from decay were used more extensively outside of North America because they last much longer.
In Argentina, woodpecker holes would last only about two years, while those made by decay could be used as homes for 25 years. In Poland, the differences were less dramatic: the woodpecker-formed holes survived for six years and decay-formed holes for 13 years. In Canada, where animals nest in woodpecker holes, all holes last the same length of time, about 14 years after they are created.
"The value of these large living trees needs to be recognized and we need to ensure that a supply of these trees is retained especially in tropical forest systems where decay-formed tree holes last for many years and support a lot of wildlife."
From Science Daily @ http://www.sciencedaily.com/releases/2012/12/121206162519.htmand and http://www.sciencedaily.com/releases/2012/05/120502184416.htm and http://www.sciencedaily.com/releases/2011/06/110616121908.htm
For more information about old growth trees and forests see http://nexusilluminati.blogspot.com/search/label/forests
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