What comes to your mind when you hear the term ‘monodominance’? I thought of a monoculture plantation that has the same kind of trees packed closely together in a space – a space planted with a single tree species, maintained and harvested by humans. Such vegetation might be a sour sight for true-blue dendrophiles, since dominance is an antithesis to diversity. But what if I tell you that monodominant tree stands are not just an artificial human creation designed for exploitation, but they occur naturally too?

Enroute a trek to Kurinjal Peak while staying at Bhagawathi Nature Camp in Karnataka’s Western Ghats, I came across a whole forest patch of Poeciloneuron indicum trees, commonly known as the Indian Milled-Leaf tree. The most striking feature of the tree is its buttress roots: these roots are shallow and visible above the ground. Older trees’ buttress roots look like they are supported by swirling planks at the base, while younger trees’ buttress roots look like the appendages of an octopus. This patch is an instance of naturally occurring monodominance.

Older P. indicum trees have swirling roots at the base.

Younger trees’ roots look like the appendages of an octopus.

The criteria for a forest patch or area to be labelled ‘monodominant’ is that greater than 60% of the canopy trees must be occupied by a single tree species. But how does a species outcompete and occupy most of the area? There are multiple explanations for the phenomenon. Imagine a rainforest so tightly packed with trees that they do not allow sunlight to enter through their canopies. For a seedling to establish here, it has to tolerate the shade and grow to the height of the canopy to even see the light of day. And as expected, many monodominant species are shade tolerant when they are young, resulting in a cluster of the same tree settling in a patch that we observe today.

The canopy of a monodominant forest.

In addition to shade being a factor, there is sometimes hardly any gap for another tree to establish itself – such forests are indicators of the patch remaining undisturbed for aeons. In such a scenario, what would happen if a couple of trees grew old and came crashing down, opening up the canopy and letting in a flood of sunlight? Would this invite other species of trees to establish and create a more diverse forest? Not necessarily. The leaves shed by trees are slow to decompose on the ground, causing insufficient nutrients cycling, which other tree species depend on for their survival. Additionally, the high depth of leaf litter also does not allow small-seeded trees to germinate easily. And as expected, tree species that are monodominant usually have large seeds to overcome this problem too; in other words, these trees seem to be creating an environment conducive only to their own kind.

A relatively old tree with large roots and its neighbouring younger counterparts.

One perceived weakness large-seeded tree species have is that their seeds don’t disperse to long distances and fall very close to their parents, probably because they are large and heavy, and cannot be carried by the wind. But even that might be an explanation for how they slowly take over an area – a tree disperses seeds near itself and these seeds establish themselves around the parent tree and then radially expand their range in concentric circles.

Many trees of the same species, established near each other.

Which brings me back to the Indian Milled-Leaf tree (P. indicum) – enamoured with their buttress roots during the trek, I forgot to look up and see if the trees were flowering or fruiting. Thankfully, the internet satisfied my curiosity later – the tree has an inflorescence of yellowish-white flowers, and its fruit is a capsule that holds one large brown seed (see photos and detailed description here). As literature suggests, these large seeds can probably germinate even if they are buried underneath thick leaf litter. The buttress roosts of the tree, besides supporting it from falling during a storm or the heavy rains that the Western Ghats receive, serve the function of storing nutrients probably in response to the slow decomposition of the leaf litter that makes the environment nutrient-depleted. All these traits fit perfectly with the explanation of how the tree species carved a niche for itself in an undisturbed part of a forest.

An Indian Milled-Leaf tree forest.

Dominance of a tree species is not exclusive to P. indicum forest patches. Trees like Shorea robusta, commonly known as Sal, occupy much of Central, Eastern, and Northern Indian landscapes so much, that the forests are referred to as Sal forests. Similarly, the higher altitudes of the Himalayas are dominated by Pinus roxburghii, and these forests are referred to as pine forests. It is also important to note that while these trees do occupy most of the canopy in a forest, other plant species do co-exist with them. In fact, Sal forests provide unique climatic conditions that support certain kinds of plant species growing underneath them.

A Sal forest in Central India.

So the next time you are on a trek or doing field-work, you could maybe look away from flashy birds like the Malabar Trogon or butterflies like the Southern Birdwing, and see whether the forest you are walking in is dominated by a type of tree. If it is, try to deduce what traits might be responsible for the species’ success, like an ecological detective.


For more information on monodominant forests, check out these scientific publications. 

  1. Peh, K. S. H., Lewis, S. L., & Lloyd, J. (2011). Mechanisms of monodominance in diverse tropical tree‐dominated systems. Journal of Ecology, 99(4), 891-898.
  2. Anbarashan, M., & Parthasarathy, N. (2013). Tree diversity of tropical dry evergreen forests dominated by single or mixed species on the Coromandel coast of India. Tropical ecology, 54(2), 179-190.
  3. Rahman, M. M., Rahman, M. M., Guogang, Z., & Islam, K. S. (2010). A review of the present threats to tropical moist deciduous Sal (Shorea robusta) forest ecosystem of central Bangladesh. Tropical Conservation Science, 3(1), 90-102.

I would like to thank Pritha Dey, Seshadri K S, Kavitha Devadas, and the JLR Explore team for reading the draft article and providing valuable comments.