It is not surprising but indeed sad that we, humans, are partially responsible for contributing to a process through which the Earth’s forests have become substantially shorter and younger on average than they were a century ago.
A new study, published in the journal Science, has determined that Earth’s forests are transforming in response to a combination of human actions and natural processes such as wildfires, causing them to lose their oldest trees and grow shorter. Needless to say that this catastrophic trend is set to continue as the climate grows ever hotter on account of mostly human actions. There are worrying consequences for the ability of forests to store carbon and mitigate the climate emergency and for the endangered wildlife that depends on rich, ancient forests.
The analysis of more than 150 previous studies found the death rate of trees has increased, doubling in North America and significantly increasing in the Amazon, for example. The impact of forest destruction had cut the area of old growth forest by a third since 1900, the researchers said. The forests that cover a little under a third of our planet’s landmasses are home to an astounding variety of life, and comprise a vital part of Earth’s global ecosystem. This is partially due to their ability to remove carbon dioxide from the atmosphere, and capture it in a solid state as biomass.
It may be recalled that increasingly, human-induced climate change, wood harvesting, and a range of naturally occurring processes are placing forests around the world under stress. Rising temperatures caused by global heating also cuts growth and increases tree deaths by limiting photosynthesis. Furthermore, high temperatures, drought, high storm winds and pests and disease affect older trees more and are all on the rise.
Tom Pugh, a scientist at the University of Birmingham, UK, said: “Our study reviews mounting evidence that climate change is accelerating tree mortality, increasingly pushing the world’s forests towards being both younger and shorter. They have been getting smaller and younger over the last century, primarily because of the effects of human land use change, and disturbances like wildfires and insect outbreaks and droughts. These are things that are increasing in frequency and severity.” There were exceptions, Pugh said, such as forests in high latitudes: “But in a world that’s generally hotter, more of the world will be covered by forests that are generally shorter.”
The research, including analysis of satellite data on land-use change, estimated that human felling of trees had cut total forest area by 12% since 1900. The proportion of old growth forest, more than 140 years old, fell from 89% to 66% in that time. Lack of data meant the researchers were not able to make a precise estimate of how much shorter the forests had become. Rising levels of carbon dioxide in the atmosphere could increase tree growth but the researchers said this appeared to happen only in younger forests with abundant nutrients and water. However, most forests have limited nutrients and water, which drastically reduces the carbon dioxide benefits to trees. Pugh said the vast majority of forests in the UK and Europe were examples of unnaturally short and young woodlands.
Sadly, the continuing transformation of our planet’s forests will likely come hand in hand with a loss of biodiversity. The ideas in the new report do not change what the world needs to do: stabilise the climate by quickly and protect the forests.
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