They defy the natural laws of physics, secretly communicate via an elaborate fungi network, and receive preferential treatment from their mothers. Bob Taylor, STRI’s head of ecology and environment, discusses the wonder of trees.
My relationship with trees
I used to think trees were very boring. But, that was because I found them hard to identify and I was of the opinion that they didn’t do very much. How wrong I was! Trees are amazing in so many ways. Admittedly, they can be hard to identify especially in the winter. Though with a little practice tree ID it does get much easier, perhaps that’s a BTME workshop session in waiting? Hmm..
Trees are also static, except that they actually move, or should I say distribute via their offspring. It is the seeds that enable their distribution far and wide through the countryside. Okay, some spread vegetatively by suckering, Blackthorn and other Prunus species being typical of this.
Get past first impressions and we can start to wonder:
- How do trees feed themselves when they have been in the same spot for more than 100 years?
- How do they reach such heights which through normal gravitational processes defy the laws of physics?
- How do trees communicate with each other?
Trees don’t go anywhere, so to feed, they must derive all they need from the sky or from their immediate surroundings. For grass and indeed any form of crop growing we fertilise to avoid nutrient depletion. Trees sit in the same place year on year with no opportunity to actively seek nutrients, this is where fungi come in to their own.
Let’s talk fungi
Fungi and trees have co-evolved over millennia. They have established relationships, the kind of relationship we call mycorrhizal. A mycorrhizal relationship is really a sort of parasitism but one that proves beneficial to both partners. There are different forms of mycorrhizae.
Greenkeepers will know of vesicular arbuscular and endo-mycorrhizae, but a third type is referred to as ectomycorrhiza. It is the type of relationship that has evolved to help larger fungi such as the mushrooms we see each autumn in the woods and the trees themselves.
There are other fungi whose role it is to decompose falling leaves and woody debris making the nutrients released available to the mycorrhizal fungi, which in turn pass them back to the trees. These fungi are not totally altruistic, they pass the nutrients back to the trees in turn for sugars that have been collected and produced by the trees.
Ectomycorrhizal fungi produce what is termed a “Hartig net” around the feeding roots, the hyphae of the fungus penetrate into the cortex of the root and pinch the sugars they need. See it’s a parasite but oddly and to ensure the host (the tree lives) the fungus being able to spread its mycelial net far and wide captures nutrients and passes them on to the tree.
Just think if that same fungus could also join with the next tree, and the next, then its total area within the leaf litter will be considerable. That is exactly what happens. Some species of fungi may only connect with similar trees but others will connect with different species of tree.
As well as feeding the trees, the fungus is creating a communication network allowing trees to communicate with each other. Trees pass on messages through the fungi notifying neighbours when disease is near this allows trees to build resistance. Wow, how cool is that!
Perhaps even more special is the fact that within any woodland there are mother trees. These act like hubs in the internet. Feeding trees with radioactive carbon tracers we now know that mother trees pass on nutrients selectively to their own offspring. This gives them a competitive advantage over others that are also fungal connected to the same roots.
Now if you weren’t impressed with all of the above you must be now. Trees can preferentially feed their young.
A final consideration is that trees, as they age, become hollow. This is not an accident or a problem for the tree, it actually helps the tree in many ways.
Firstly, the centre of the tree is where all of the stuff it doesn’t want is stored – after all they cant take their waste to the bin!
Secondary metabolites, tannins etc. are all stored here. Fungi evolving with trees have developed a role where they enter the tree and gradually decompose the soft centre.
Water may enter pushing those nutrients downwards to the roots, exactly where they are needed. The only problem with this superb relationship is when man thinks he knows best decides to chop the tree down thinking it is diseased. Another advantage of the tree becoming hollow is that it will have more flex than a solid tree and therefore withstand wind throw better – another evolutionary advantage.
Trees are not boring. Without man trees would dominate much of this planet. Perhaps we should give them a little more respect, possibly even credit them with a degree of intelligence!