The death rate of the world’s largest and oldest trees has been rising significantly in recent years, according to new research. These big old trees often form the basis of many ecosystems and contribute significantly to their health and the health of the other species that live in them.

A new report, just released by three of the world’s leading ecologists, is warning that the “alarming” and rapid increase in the death rates of trees 100-300 years old will have very negative effects on the health of ecosystems around the world. The deaths aren’t confined to any particular areas either, they are spread out amongst the forests, savannahs, woodlands, farming regions, and cities of the world.

“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 Washington University, 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.”

The researchers say that the change first came to their attention while investigating Swedish forestry records that extend back to the early 1860s. This was then confirmed using a previously done 30-year study of Mountain Ash forests in Australia. The known causes are very varied too, no specific cause is responsible. Large and old trees were dying in large quantities in forest fires, but also in very large numbers due to drought, high temperatures, logging, agricultural spread, disease, and other causes. In places at 10 times the average death rate, even without forest fires.

After seeing all this,the researchers then looked around the world, and found similar trends. Throughout “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.

These changes are of course nothing new. Massive old-growth forests once covered the majority of the globe; most of Europe, and large amounts of Australia, and the Near East, was once forest. But the death rates seem to be increasing now exponentially. The causes appear to be much the same as they have always been: the clearing of land for agricultural use, environmental changes caused by farming, man-made changes in fire regimes, logging, the loss of apex predators, timber gathering, insect ‘plagues’ and rapid climatic changes. In short, deforestation, and the soil erosion, desertification, and loss of biodiversity that go with it.

“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 draw a comparison between this current loss of the world’s big trees, and the massive decline of the the world’s largest mammals that has already taken place. In the last 15,000 years ago or so, an incredible number of megafauna animals have gone extinct, all that really remains are dwindling numbers of animals like elephants, lions, rhinos, whales, and tigers.

“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.

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.

Source: Australian Research Council Centre of Excellence for Environmental Decision (ARC CEED)

Image Credits: Bill Laurence; Te Matua, Jomon, Opal Creek, Baobob, via Wikimedia Commons