Usually, when we refer to something as dead, the immediate thought that comes to our mind is that it has no more life in it. However, what is that one thing which is “alive” even when it is dead? A tree! That’s right. A dead tree is unique in that it serves as an active ecosystem that is conducive to the growth and development of many different lifeforms. In this blog article, I wish to highlight the usefulness and importance of dead trees in maintaining some important ecosystem functions.
Researches on tree mortality have revealed that the role of dead trees in a natural system has received less attention despite the fact that the value of a dead tree is no less than that of a living one. In scientific terms, a fallen dead tree and its branches are referred to as Coarse Woody Debris (CWD). CWD provides habitat for both autotrophs (organisms which make their own food through photosynthesis and chemical energy) and heterotrophs (organisms which rely on other organisms for food). While fallen dead logs are generally utilised by autotrophs and serve as an important space for the establishment of tree seedlings in a forest, standing dead trees are referred to as ‘snag’ in forest ecology, and are utilised by many animal species, particularly birds and invertebrates 1.
There are some significant roles that CWD performs in an ecosystem. Firstly, there are numerous species of autotrophs such as lichens, blue-green algae, diatoms, mosses, gymnosperms and several other species for which CWD is highly suitable habitat. The number of species and community structure that the habitat caters to is influenced by decomposition in CWD, which is actually mediated by the autotrophs themselves. Secondly, CWD serves as habitat and feeding site for a number of species of birds, bats, reptiles and mammals. Here, physical orientation, size and decay state of CWD matters significantly as it influences habitat utilization by species. While birds, bats and reptiles use snag, mammals prefer logs. In the Blue Mountains of Oregon and Washington, almost 57 per cent of breeding species of vertebrates are known to be utilising CWD. Thirdly, CWD, which was once considered as an obstacle to fish migration before 1970 is now seen as crucial in the formation and stabilisation of fish populations in river and stream ecosystems. However, in a flowing water system, due to continuous physical damage, the life of CWD gets shortened despite a slower biological processing rate as compared to the terrestrial habitat. And that is why the time frame in which CWD begins to play a significant role in maintaining a diverse ecosystem around it is almost the same in both habitats 1.
As can be seen in the preceding paragraph, through CWD, natural forest and river ecosystems provide valuable resources to several lifeforms, and if decayed trees and branches are removed, it can severely impact the number of species as well as the community structure of the ecosystem. The gradual and intentional removal of CBD from forest and river ecosystems through human interventions has carried on for years so much so that it has not only altered these habitats but has also caused the removal of CWD to go unnoticed 1.
Even in the urban, little attention has been given to the role of CWD in positively influencing the biodiversity in urban sprawls. There is a dearth of available deadwood trees and logs in urban green spaces as they are continuously removed largely due to their unaesthetic appeal, the possibility of injuring citizens and causing inconvenience to the movement of traffic. However, through proper management policies, these problems can be tackled. For instance, in urban and suburban areas where patches of forest are present, CWD should be allowed to exist. In other green spaces such as parks and recreational areas, CWD can be retained as long as they do not physically inconvenience citizens. Besides this, citizens should be made aware of the usefulness of deadwood trees to urban ecosystems through nature education and outreach programmes 2.
In recent times, when threats to biodiversity are increasing at a rapid pace across all continents and in almost every remaining ecosystem, maintenance of something as valuable as CWD should be considered seriously. The outcomes of ignoring this will be huge as CWD provides complexity to an ecosystem, and when this complexity is removed by humans, the composition, functions and pathways of the ecosystem are severely compromised.
1. Harmon, M.E., Franklin, J.F., Swanson, F.J., Sollins, P., Gregory, S.V., Lattin, J.D., Anderson, N.H., Cline, S.P., Aumen, N.G., Sedell, J.R., Lienkaemper, G.W., Cromack JR., K. & Cummins, K.W. (1986) Ecology of Coarse Woody Debris in Temperate Ecosystems. Advances in Ecological Research 15: 133-275.
2. Fröhlich, A. & Ciach, M. (2020) Dead wood resources vary across different types of urban green spaces and depend on property prices. Landscape and Urban Planning 197: 1-12.