14. Allelopathy

Plants that supress other plants  - often using chemicals - is called allelopathy. It's a way of eliminating any competition. You certainly will have seen this process in action, even if you didn't know what was going on (EDIS 2018)

We have all seen a Laurel hedge in a garden Prunus laurocerasus, the evergreen hedge with 180 mm long thick glossy green leaves that often separates one terraced house front garden from the next, another plant that uses allelopathy is rhododendron Rhododendron sp, often seen in posh gardens or national trust parks. 

What you don't see, is much growing underneath laurel or rhododendron, because these plants produce a chemical in the leaves that works like a weed killer. The leaves drop off evergreen plants continuously unlike many other plants that shed leaves in one go (Autumn). Because they drop off all the time we don't notice it, but each time a laurel leaf falls to the ground it contains chemicals that leech into the soil and kills the competition, In Laurel I think it may be Antracyanin, but need to check this out?

So I was standing in a wood, on each side of me were several different Allelopathic plants, some evergreen trees, some deciduous trees and a fern. 

If I faced West it was all scots pine and bracken, if I faced East it was all Beech and birch trees.

 

Looking West, dense bracken Pteridium aquilinum beneath scots pine Pinus sylvestris, no other understory plants, although many fungi persist.

 Looking East Beech Fagus sylvatica and Birch Betula pendula , the greenery in the distance, two thirds up the photo, is where the wood becomes a wet habitat dominated by alder and poplar.

Beneath the beeches and birch in the foreground there is no understorey, just leaf litter.

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Looking North at the very distinctive dividing line between to different habitats

All of these plants beech, birch, scots pine and bracken, are allelopathic. one of the few plants that can grow under scots pines is bracken also an allelopath. But Bracken cannot grow under Beech. In late spring through summer this picture would even more distinctive, with the Bracken bright green on the left and the right side still bare, not even a blade of grass, apart from brown beech leaf mulch and fungal fruiting bodies.

And one of the few plants that can compete with Bracken and 'out alleopath' another alleopath, is Rhododendron, which will invade bracken areas and take over. Which is a problem because rhododendron should really be in the Himalayas, not in the UK, its an invasive species.

University of Florida, Edis (2018) Allelopathy: How Plants Suppress Other Plants. Available at: https://edis.ifas.ufl.edu/hs186 (Accessed on: 01/03/2020)