TREES: MIRACLE OF SCIENCE AND ARTS

Trees have many benefits for the entire life of our planet. Trees tower majestically into the atmosphere where they absorb carbon and release oxygen, a process that permits the very life of aerobic organisms — like humans — to exist. Their roots penetrate deep into the soil where they recycle nutrients around the rhizosphere. Trees occupy only about a third of the terrestrial surface of the Earth — but they are responsible for approximately two-thirds of the planetary carbon capture through the process of photosynthesis. This is performed by tree leaves that grow along the stems and branches into the atmosphere.

And in this cycle of good, tree leaves are key organs for the energy of the Earth. Tree leaves aggregate into tree crowns and the tree crowns aggregate into forest canopies. These may form a single layer or several layers, depending on the number and kinds of trees that make up a forest. The over-story and sub-canopies form a complex ecosystem — each layer may have a myriad of dependent creatures, like insects, birds, mammals and other organisms, that add to the biodiversity of trees and forests.

The existence of canopies also explains how forests accumulate nitrogen from the atmosphere and survive without much fertilisation, while agricultural fields lose nitrogen and need to be fertilised for productivity. A number of leguminous and some non-leguminous trees fix nitrogen from the atmosphere using symbiotic microorganisms (rhizobia, Frankia), another striking fact of the natural world.

Also, forests ameliorate climate itself. During the 1930s, President Franklin D Roosevelt of the United States initiated a system of planting windbreaks to ameliorate the blowing away of top soil in the ‘dust bowl’ areas, from North Dakota to Texas. Tree crowns are the basis for this effect. In the winter, going into a forest seems warmer because of the reduction of wind. In the summer, forests are cooler because the tree crowns shield the forest floor from direct solar radiation. This effect is also seen in snowmelt — the snow melts first in open fields or meadows. This influences animals as well in these environments.

Trees have been around for about 400 million years — in contrast, humans have only existed for about 100 million years. Once conifers and other gymnosperms dominated Earth, but in the Cretaceous era, flowering plants arose and these are now the dominant flora of the planet. Many of the gymnosperm groups became extinct. Some tree species have become extinct quite recently. The American chestnut, for instance, once dominated the forests of northeastern United States, but an invasive fungus, called the chestnut blight, almost totally eliminated this stately and useful species.

Many of the redwoods have had their distributions greatly diminished because of climate change and pathogens like insects and diseases. These trees are liked most because they grow fast and live long. There are other long-lived species, like the bristlecone pine (Pinus longaeva), but they grow slowly and remain small in stature. In contrast, redwoods have great growth plasticity and change their leaf morphology and physiology with their height along the tree bole. They can also reiterate their architecture after mechanical damage.

Matter referenced:

Graeme P. Berlyn, EH Harriman Professor of Forest Management and Physiology of Trees, School of Forestry and Environmental Studies, Yale University; Times of India, Ahmedabad, Saturday, 18th April, 2020.

By: Dr. Bhawana Asnani.

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