Big trees aged 100-300 years old are dying at what scientists say is an alarmingly fast rate and at all latitudes in Africa’s savannahs, in Brazil’s rainforests, in Yosemite Park in California and in both the temperate and northern forests of Europe, and in agricultural and urban areas.
Noting that these towering trees are the largest organisms on the earth, Professor Bill Laurance of James Cook University describes their key role in “regulating and enriching” our planet:
“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.”
Big trees also act as “stepping stones” for other animals who distribute seeds and pollen. They and smaller, though certainly no less important, trees, face an ever more precarious for these five reasons.
According to a report in Science, Mountain Ash (Eucalyptus regnans) forests in Australia are dying “en masse” due to forest fires. Elsewhere, scientists from Columbia University’s Earth Institute have found that the depopulation of rural areas in the Peruvian Amazon (some communities have lost 60 percent of their population as people move to cities) is contributing to bigger fires burning unchecked. There are simply fewer people in rural areas to monitor and control fires and more fields are left fallow and taken over by small trees and grasses; experts in Spain have also said that repopulation is necessary to avoid major fires.
2. Invasive Species
Cheatgrass was accidentally introduced by settlers in the 1800s in the Great Basin, a 600,000-square kilometer area that includes large parts of Nevada and also parts of California, Oregon, Utah, Colorado and Idaho. Scientists have found that, in the past decade, cheatgrass fueled 39 of the largest 50 fires in the Great Basin. Cheatgrass spreads rapidly and fills in the ground between other plants, including junipers and pinyons and shrubs.
That is, native plants are not only losing ground to invasive species, but going up in flames due to them.
Massive droughts occurred in the Amazon between 2005 and 2010, events that had been predicted to happen only once in a century. The Columbia University team found that these droughts were connected to fluctuations over the faraway Atlantic Ocean.
Drought has also been mentioned as a cause of the rising death rate of the majestic baobabs in Tanzania.
4. Logging and Overuse of Trees for Commerce
Deforestation caused by logging — of humid old rainforests in the Amazon, for example — led to fires that burned 800,000 acres (a conservative estimate) in 2005. Plenty of damage can be done to trees without cutting them down: in Ethiopia, frankincense is harvested by wounding the bark of the tree Boswellia papyrifera with a chisel-like device and collecting the resin. This procedure is repeated 8-12 times a year but high demand has led to excessive tapping of trees. More wounds on trees mean that more insects can attack them and some populations are dyring out.
Ethiopia is the main exporter of frankincense, trading some 4,000 tons a year, and villagers are at risk of seeing their livelihood destroyed.
5. Climate Change
Climate change affects trees not only through drought. Scientists studying Bishop pine trees on Santa Cruz Island off the coast of Santa Barbara have found that droplets from the fog that rolls in is crucial to keeping the trees alive. In the changing global climate, clouds are also affected; they are “one of the largest uncertainties,” says Mariah S. Carbone, a post-doctoral fellow with UC Santa Barbara’s National Center for Ecological Analysis and Synthesis (NCEAS).
Carbone and the study’s lead author, Oregon State University professor Christopher J. Still, have found that fog and low-stratus clouds play a crucial role in the coastal ecosystem, keeping temperatures cooler and increasing the amount of moisture in the soil. As the seas warm, fog and low-stratus clouds could decline, with effects on the pine tree population in California.
Conservationists are advocating for changes in policy to better protect, and preserve, trees. As the scientists studying the rapid rise in the death rate of big trees say, “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.”
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