Tree bark suffers the first injury inflicted by a human axe as it attempts to harm its species in the name of development
In our previous article, we delved into the fascinating phenomenon of leaf orientation and the intriguing features of branches and trees while responding to their microenvironment. Now let us cast a spotlight on the often overlooked yet incredibly vital component of trees - the bark. Amidst the rustling leaves and towering trees, it stands quiet, not as spectacular as the vibrant flowers of spring or as commanding as the sprawling branches reaching for the sky. Tree bark, however, unveils itself to the keen observer as a masterpiece of nature's ingenuity, serving as a crucial player in the intricate dance of the forest ecosystem. It goes far beyond its appearance, performing a myriad of functions vital for the survival and growth of its arboreal host as well as that of humans.At the forefront of its responsibilities, bark acts as a robust shield against the constant threat of aphids, fungi, and bacteria.
These relentless organisms are always on the prowl, seeking to plunder the tree's bountiful treasures of sugar, cellulose, lignin, water, and an array of valuable minerals. A detailed examination shows that the tree's protective bark is, in fact, a fortress wall, akin to a securely locked door, staunchly guarding the tree's cherished reserves against would-be invaders. Interestingly, many trees have evolved unique adaptations within their bark, for example, acacia trees have unique stipular spines to deter browsers, honey locust trees employ long thorns on their bark to save themselves from herbivores, whitebark pine trees have bark rich in resin and chemicals that keep insects and fungal pathogens at bay, and semal or silk cotton tree has tough thorns to protect it from damage against potential predators. The battle for survival in the forest takes on a fascinating strategic dimension, where each tree's bark is a testament to its evolutionary prowess.
The protective prowess of tree bark extends beyond defending against biological threats; it also serves as a resilient shield against various physical challenges like fire, ultraviolet rays, and harsh weather conditions. Beyond its protective role, it also regulates temperature, preventing the tree from overheating in summer and freezing in winter. Remarkably, some bark can even photosynthesize, providing nourishment to the trees when leaves are absent. Some species of eucalyptus trees possess thick, fire-resistant bark; the cork oak tree features a unique bark structure that offers protection against ultraviolet rays; the peeling bark of paperback maple tree not only provides insulation against extreme temperatures but also regulates the tree's temperature, preventing overheating in summer and providing warmth in winter; and the Pacific madrone exhibits bark capable of photosynthesis.When one zooms out to encompass the broader ecological tapestry, the role of tree bark as a water reservoir also emerges as a pivotal element in the symphony of the forest ecosystem. This vital function is exemplified by various tree species like the thick, fibrous bark of redwood trees serving as an effective water reservoir; paper birch tree’s bark aiding in maintaining soil moisture, and transformation of stored water within the bark into vapour providing a natural defence mechanism for the living tissues.Trees, as vibrant living entities, necessitate a unique breathing mechanism facilitated by specialized structures known as lenticels. These microscopic pores, derived from stomata, play a crucial role in the exchange of gases between the tree and the atmosphere. The Banyan tree showcases distinctive lenticels on its greyish-brown bark, appearing like white dot-like formations, Someeucalyptus species boast a reddish-brown bark adorned with dark line-like lenticels, Further, the jamun tree's smooth, dark bark is complemented by light spot-like lenticels, and the sal tree, with its rough, scaly bark, features yellow dot-like lenticels. One can easily appreciate that bark not only contributes to the tree's individuality but also adds to the rich biodiversity of the surrounding environment.
Coming closer, the colour, texture, and smell of the bark convey valuable details about the tree's health, age, and species. Additionally, chemical signals, such as pheromones, emitted by the bark, play a role in attracting or repelling other organisms, contributing to the overall biodiversity of the forest. The richness of diversity within tree bark extends beyond the realm of lenticels to encompass a spectrum of characteristics. One can study, for instance, the eucalyptus tree adorned with its distinctive smooth, white, peeling bark. This unique feature unfolds as the tree's wood surpasses the bark's capacity, prompting it to gracefully shed.
The result is not only an individualized appearance but also a survival strategy: the peeling bark aids in reflecting sunlight, keeping the tree cool, and minimizing water loss—an invaluable adaptation in arid climates.The Dalbergia, Arjun, and peepal trees stand out for their resilience. Cloaked in thick, rough bark that becomes more fissured with age, these trees weave a tale of endurance. The fissures in their bark serve dual purposes, acting as havens for diverse organisms like insects and fungi, thus fostering the tree's ecosystem and promoting biodiversity. Beyond this, the fissures increase the tree's surface area, potentially enhancing its capacity to gather essential resources like moisture and nutrients.
The robust, rough, and fissured bark additionally acts as a formidable shield, safeguarding the tree against a myriad of environmental stresses.The appearance of a tree's bark undergoes a discernible transformation influenced by its age. In its youth, a tree boasts thin, smooth, and light-coloured bark. However, as the years advance, the bark evolves, becoming thicker, rougher, darker, and acquiring ridges. This metamorphosis results from the accumulation of dead cells and secondary metabolites, forming a protective layer that shields the tree from environmental stresses.
This ageing process is prominently observed in trees like the ash, celebrated for its bark characterized by deep ridges and furrows. For specific species, observing the status of bark can reveal its growth rate too. Trees with a faster growth pace tend to exhibit thicker bark, often enriched with more cork—a testament to their robust and vigorous expansion in the natural tapestry. The intricate interplay between age, growth rate, and bark characteristics unveils the dynamic journey of a tree, narrating the story of its resilience and adaptability over time.The tree's bark, akin to a living canvas, bears the indelible imprints of its surroundings. Environmental factors such as temperature, moisture, sunlight, and fire exert profound influences on the bark, notably shaping its colour through effects on pigment production and determining its texture.
Barks yield useful items like tannin, medicines like aspirin from willow bark, spices and flavourings, herbal remedies, natural fibres, essential oils, mulch and compost etc.While observing barks, one must not miss some of the most interesting evidence of the existence of wildlife in the forest areas.
One must look for the trees whose barks are conspicuously abraded due to deer rubbing their antlers still in velvet, scratch marks by tigers often made to mark their territory and for cleaning and sharpening their claws, the nail marks left by sloth bears that climb trees in search of honey, and during summers, you may find trees with their bark stripped and eaten by bison and sambars.Every tree has a unique story to tell through its bark—a story of life, lessons, charity, and beauty.
Bark, the protector of the channel of the flow of energy between the root and the shoot, the connection between the hidden and the visible, the link between earth and the sky, and the provider of a great variety of services to all living beings, is a silent but indispensable participant in the intricate dance of nature. It stands as a testament to nature's ingenious strategies and adaptations for ensuring the survival and thriving of trees. The same bark, unfortunately, is the first to suffer an axeman’s assault on trees in the name of development!
(The writers are former principal chief conservator of forests, UP and Maharashtra; views are personal)
