Q:

Plausibility Check: Territorial Trees?

Background
In case you haven't heard: there are places in the Amazonian Jungle called Devil's Gardens. The gardens are large swaths of land composed of almost entirely one single tree the Duroia hirsuta. This tree's roots have the ability to secrete growth inhibitors along side it's symbiotic relationship between this tree and the lemon ant, this tree is able to negate competition by killing them. There are other trees that create clonal colonies in which the colony grows new trunks from a root system underground.
Question
So I am wondering: is it feasible that a tree could evolve to use its roots to search our other trees and grow a new clone through the trunk of its competitor? Which should split the competing tree in half and kill it all at the same time reproducing.

A:

Something similar to what you depict is done by the Ficus watkinsiana, better know as strangler fig.
Its well deserved name comes from its growth cycle: when a bird eats one of its figs, it can drop one of the seeds, through its excrement, on a tree. When this happen the seed grows around the tree trunk, reaching the ground and enveloping the host tree until it dies for lack of light and air.
The fig strategy allows for a better position of the young plant with respect to light gathering (sprouting higher than the ground) and also ensure a suitable support while the plant grows.
In your case the young plants should start from the ground level (thus with less light), and should compete with an adult plant. Moreover, being a clone, could not randomly pick advantageous genetic traits.
I am not saying it is impossible, there are trees propagating via roots, I just think this might be possible but less effective.

Of course, using the strangler fig mechanism, preventing other trees from growing is a bad idea, as then one will lack growth substrates.

A:

In regards to the splitting aspect of your question, I believe that a mistletoe hybrid would be best.
Mistletoe seeds, deposited by birds and other animals, burrow into the trunks of nearby trees, and split the bark as they grow, sapping nutrients from the original tree as they go.

As it stands, even naturally occurring mistletoe has the potential to kill many native trees, though generally it is not in the mistletoe's best interest, as it gets a majority of its nutrients from its living host tree. If the hybrid were to be able to establish a more effective root system that spread down to the ground or perhaps take over the host's own root system, then it could completely displace any plant that it takes over.
With birds being the main way in which it spreads, the mistletoe hybrid could spread very quickly through an area, since most mistletoe-eating birds nest in non-mistletoe plants, effectively planting the seeds in exactly the places where they are needed the most.

