Bark-The Signature of Tree

TREES are enormous organisms far exceeding the height of human beings. But to identify a tree one needs flowers, fruits, leaves and twigs based on which a taxonomist may reach its correct identity. Beyond doubt, the flowers are reproductive parts and, therefore, show less variation in their structure within a species, no matter where it is growing on Earth. But the flowers are not there on the trees throughout the year, nor are these structures easily accessible on a tall tree in flowering. Flowers are meant for reproduction and therefore located on higher branches where pollinating agents (insects, birds, bats, or wind) can work upon them easily while having a safe distance from common herbivores and other land animals. Trees reach to reproductive phase in their life after many years of vegetative growth. When a tree enters to reproductive phase, thus now producing a flower, it has already exceeded the reach of a man with distinctly tall single bole-bearing inflorescence and leaf-laden branches. This further adds to the miseries of a plant taxonomist trying to collect flowers and leaves for identifying a tree. A tree may not be evergreen as in the case of the trees of seasonal climate and thus may be devoid of leaves for a long period in a year. Alas, neither flowers nor leaves are easily accessible organs as these are located far beyond the reach of walking herbivores or human beings.

Then how to identify a tree without flowers and leaves? Stand below the tree and hug it! No, it is not going to whisper its scientific name but you can feel the skin of tree which we call as ‘bark’. There are ridges and furrows, cracks or seams, smooth or lenticellate patches, scales, plates, vertical strips, numerous variations in exfoliation and colours, each unique to the bark of a species. Standing below a tree the closely observable part of tree is its trunk and bark and a tree can be identified by closely observing its bark. It is simply paradoxical in tree identification that we ignore easily observable characters of bark while try to look flowers and leaves located far beyond the access.

A variety of trees exists in nature and their identification can be done by knowing some specific taxonomic characteristics. In the absence of flowering or during the winter when the flowers and leaves may be lacking, the bark becomes easily visible and accessible character for the identification of large trees. Like the floral features, the bark of the tree shows much variation and has much diagnostic value. Along with its necessity for the survival of trees, the variations in its morphology serve as the tool for taxonomic identification. The bark is recognized by the appearance of the surface patterns which are different for different tree species. The morphology of bark changes with the types and species of trees. There are variations seen in surface patterns, texture, colour etc in different tree species. None of the two tree species can have the same surface patterns on bark. Even if there is similarity, there will be a unique identity differentiating one from the other very similar to discontinuous variations among closely related species. Surface patterns are as unique as fingerprints of a person. The diversity observed in bark character provides supplementary taxonomic evidence to identify trees and classify them into different types such as smooth bark, lenticellate bark, bark with scales and plates, bark peeling in curly strips, cracked bark, vertically striped bark, ridged and furrowed bark, rough and rugose bark. Bark textures are uniform for particular tree species and act as visual markers for broad tree identification. Several taxonomic doubts may be resolved by the study of bark as bark provides important and valuable taxonomic information. Being a new concept this should be initiated by considering some simply observable characters of broad categories. Bark morphology was studied to observe the surface patterns of trees in the Pantnagar region and this study presented a great range of variation in tree bark for identification of trees. Diversity in bark morphology paves the way for the identification of trees. The diversity seen in the patterns of bark is due to the differences in the development of the outer layer. Tree trunk experiences selective pressures leading to different types of bark morphology that provide an interesting and unique feature of identification. Databases may prove immensely helpful in the identification of trees, particularly in those cases where flowers, fruits or leaves are either absent or inaccessible. The bark images captured in this study may prove useful for future use and these images are made freely available in this database.