The idea of talking trees has captured the human imagination for ages and has been depicted in folklores across the world, even as far as being featured in the Marvel Universe, LoTR trilogy, and The Wizard of Oz. But these were all make-believe tales, right? Well, yes and no. Of course, trees do not literally “talk” to us humans, but it turns out, in the right environment, trees are, in a very effective way, sending messages to each other, trading resources, and in some cases, even waging war on one another!
There is no doubt in the fact that a natural forest is an extremely complex ecosystem, having reached, or is in the process of reaching a state of climax vegetation through the process of ecological succession of species, spanning hundreds of years in the making. And it is in these natural forests that you can find the oldest social networking system available, roughly 400 million years old. Nicknamed as the Wood Wide Web, this networking is happening all under our feet through a vast network of tree roots and fungal mycelia. This symbiotic, reciprocal relationship is termed as Mycorrhiza where the fungus basically absorbs water and nutrients from the soil, brings them back to the tree, and trades them for photosynthetic carbon.
But anyone with an elementary knowledge of botany might say that both Ectomycorrhizal and Endomycorrhizal connections, such as VAM, have been well-documented and studied for years. What is so new in that? And how do trees communicate via them?
Well, the fun part starts with a study done in the UK, where they injected radioactive carbon isotopes in seedlings and colonized them with mycorrhizal fungi, which then showed to transmit those carbon isotopes from one seedling to another.
Further studies in Douglas Fir forests using DNA microsatellites have shown that these mycorrhizal networks act as pathways for transmitting nutrients and water, such as supplying sugars to the seedlings in the understory to boost their growth. The biggest, oldest dominant trees, called “Hub trees”, also known as "Mother trees" are highly connected, sometimes each tree going as far as having around 50 hyphal connections. When one seedling is under nutrient or water stress and showing poor growth, the other plants, most prominently the Hub trees, send more carbon and other essential nutrients to it. This increases the survival rate and growth of the seedlings, and their overall health.
A mapping of the mycorrhizal network in a Douglas fir forest
It has also been noticed that when a particular tree is infested with a disease, it sends warning signals to its neighbors using mycorrhiza, and the neighboring trees respond by increasing the production of their defense enzymes, thus making them more disease resistant.
Mother trees can recognize which seedlings in the neighborhood are related, sending more carbon and nutrients to kin seedlings than to the strangers. When injured or dying, they dump even more resources into the network, as a means to pass their energy to the next generation.
Sometimes, certain allelopathic tree species, such as Black walnuts also make clever use of this network to release toxins in the soil to compete with the neighboring trees of different species that take up their space.
A black walnut tree. As you can see, there is no vegetation in the floor
All this information is very contradictory to what I had learned in Forestry school. The currently used silvicultural systems for timber harvest in the tropics, such as the Irregular Shelterwood systems and Selection systems aim at removing these oldest dominant trees from the stand, citing the logic that the removal of these individuals will help the seedlings attain more light and nutrients for a viable regeneration. However, this new information sheds light on the fact that we are probably doing more harm than good to the natural forest.
We could learn a lot about the sustainable use of forest resources from the indigenous tribal communities, who are probably the most dependent on them. Most of the South Asian indigenous tribes believe in something called “The Spirit of the Forest” and have their respective “Sacred groves” where harvesting and any act of disrespecting the forest entities are not allowed.
A sacred grove in Kerala, India
So, what is the solution to all this? With large scale deforestation and the ever-increasing pressure on natural forests for timber due to the increasing population, the gene pool in the natural forests is under threat. Every day, we are losing valuable genetic resources that could have helped us fight climate change.
If you ask me, I can think of only a few solutions. One is incorporating more woody elements in the farmer’s field and grasslands using suitable Agroforestry techniques. And the other is, of course, the establishment of plantation forests in degraded areas unsuitable for cultivation, to meet the timber demands. Using species of bamboos and rattan can also be a viable replacement for wood, as these species have much lower rotation periods.
Alley cropping is a method of incorporating both woody and non-woody components in the field
As very complex systems, old-growth forests have an enormous capacity to heal by themselves. With methods such as retention of specific hub trees, and artificial regeneration of diverse species and genotypes, this mycorrhizal network can be recovered fast. We need good, local foresters who have a clear idea about the local conditions and will help to protect our old-growth forests, which are the repositories of genetic resources, so that they can withstand the stress of climate change that is inevitably coming down the road.
Dedicated to my dear 5'2".