Speaking of science Environment

Of trees and men: 422 for every human on earth

The tropical and subtropical regions (such as India) have about 1.39 trillion trees. Photo: H.Vibhu  

How many trees are there on earth? The latest estimate by a group of 38 researches across the world, published two weeks ago in the journal Nature, gives the colossal number of 3.04 trillion (or 3,040 billion) trees all across the globe. That leads to about 422 trees per person (or “a tiny forest for every person on the plant”, as CNN News of September 4, 2015 mentioned). This is indeed a bounty that Mother Earth has given us.

How did the authors estimate this number? They used three major methods. One is based on images obtained through satellites, the second to measure tree densities using about 4,30,000 forest inventories across the entire globe, and thirdly using computational methods to calculate the number of trees per hectare. And how do they define a tree? A tree is a plant with woody stems larger than 10 cm diameter at breast height (DBH).

The tropical and subtropical regions (such as India) have about 1.39 trillion trees (close to 43 per cent of the trees of the world) 0.74 trillion in “boreal” forests in the sub-Arctic regions of Russia, Scandinavia and North America (25 per cent), and 0.61 trillion (or 22 per cent) in the temperate zones. Some regions such as the boreal up in the North, or the Amazon forests are far denser (more trees per area) than the tropics such as India. Interestingly (and expectedly), the population density of humans is higher in the tropics than elsewhere, indicative of how dependent we are on trees. We humans are essentially tree-dependent species. What is said of elephants in Tamil ( Yaanai Irundalum Aayiram Pon, Irandalum Aayiram Pon — an elephant is worth 1,000 sovereigns alive or even after death) is even more true of trees. This dependence has been appreciated since ancient times, and myths from various ancient civilizations hold them in great respect, and some have even deified them. Hindu mythology has it that as the world was born from the churning of the ocean of milk ( samudra manthan), the tree Kalpataru (the tree of life which gave us all plants, animals and us) and the cow Kamadenu (the holy cow who provides endlessly for all needs) emerged.

Evolutionary biology tells us about how plants and trees came about. The rough period for the evolution of land plants is anywhere between 500-650 million years ago, and they originated from the green algae present in shallow fresh waters, which could already harvest sunlight and use the atmospheric carbon dioxide (which comes out of wildfires and similar burning of organic matter) to generate energy for growth. The waste product they discharged in the environment is the gas oxygen. And as land plants grew in numbers, and spread across vast areas, the oxygen levels went up remarkably, thanks to photosynthesis. On the flip side, this global increase in oxygen over time led to oxidation or the burning of many life forms. Added to this toxicity was also the periodic environmental assaults (from meteors and comets) that wiped out many life forms and fossilized them, leaving charcoal and oil beneath the ground. This is the origin of what we now call fossil fuels.

Adaptation to the environment is the hallmark of evolution. Oxygen breathing animals (and we humans) were born, which use oxygen for ‘burning’ food and use the energy for metabolism and growth, and release carbon dioxide as waste.

There is a give and take between humans and plants. We take the waste product (oxygen) of the plants and trees, and emit carbon dioxide as waste, while the latter do the reverse. Equilibrium can be maintained as long as the input and output are balanced. What we have done, in our rush to ‘advance’ our living comfort, is to deeply upset this balance.

We burn more and more fossil fuel for energy, and at the same time, greedily chop off 15 billion trees (the gobblers of carbon dioxide) every year, to make more space for ourselves. Carbon dioxide is a greenhouse gas (one that absorbs sunlight and warms up the earth, but does allow the heat to escape into the sky). This warming has played havoc with the globe’s climate — a totally unsustainable situation. There is thus the urgent need to save the trees and look for alternate fuels (wind, solar, water and such).

dbala@lvpei.org


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Printable version | Jun 10, 2021 8:58:43 AM | https://www.thehindu.com/sci-tech/energy-and-environment/of-trees-and-men-422-for-every-human-on-earth/article7645526.ece

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