Wildlife TV

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Quiet Battles: How do trees defend themselves from animal ‘attack’?

on April 20, 2013

There is a very quiet battle going on in the bush. An army of herbivores are eating their way through the body parts of plants, however, the plants are not giving up without a fight! Herbivorous mammals make up a huge proportion of the animal life in Africa and their diet consists of (although not 100% exclusively) on vegetable matter, or plants. Today I’ll outline a few of their tactics, there are some strategies that are obvious and others that are subtle and cunning.

Plants, like animals, have complex anatomies and are composed of different body parts with different functions. A plant’s leaves are used during photosynthesis; a chemical process whereby plants turn raw materials gained from the soil and the air into sugars, using sunlight for energy. As a result, plants’ leaves are very nutritious; they contain sugars and raw vitamins and minerals. Herbivorous animals ‘prey’ on the leaves of plants, feeding on them in large quantities; they are important to the animals, but they are of course important to the plants as well.
How can a plant physically keep an animal away from its leaves? Many plants created obstacles that make it physically difficult for feeding animals to reach the leaves. This might involve growing into shapes that make it hard to reach leaves, of growing defensive weaponry to repel threats.

 

Shapes

Several groups of trees in Africa grow into a typical umbrella shape. One reason for this shape is so that a tree might maximise the surface area of its leaves that it exposes to sunlight. But this shape also has a defensive purpose; by spreading its canopy out into a flattened disc, a tree is making it more difficult for animals to reach those leaves in the centre. A tall animal might be able to feed on the leaves on the edge of this disc, but it cannot reach into the centre and thus the leaves are spared.

Umbrella shape tree in South Africa

These trees are fanning out their canopies; partly for defence, partly for food production.

 

Thorns/Spikes

Many walks through the bush result in cuts and scratches, but not from lions and leopards, but rather from the seemingly innocuous bushes and trees. These plants equip themselves with spikes and thorns; weapons designed to cause pain to those animals that try to eat their leaves. Botanically speaking, when we talk about ‘thorns’ we are referring to those sharp structures that are formed by a plant modifying the growth of its stems into sharpened points and when we talk about spines, we refer to when plants modify leaves themselves into sharpened objects. Either way, when an animal dips its face into a tree or bush it has to be willing to put up with a considerable amount of pain in order to get its food. A plant lives in the hope that it will causes enough pain that an animal will avoid the plant all together.

Close-up spikes on an Acacia tree

Some impressive weaponry on an acacia.

 

Chemicals

But what is to stop animals from slowly eating their way through a plant’s leaves until nothing’s left? Plants have defences in their very tissues; chemicals that can prevent or reduce the amount that herbivores feed upon them. There some chemicals, called tannins, that protect plants in two ways; one way involves simply making leaves bitter and unpalatable, this means that animals will find the plant unpleasant tasting and they will avoid feeding upon it. Another way, perhaps even more cunning, is that the tannins decrease the efficiency of herbivores’ digestive systems, making it hard for animals to gain the required nutrients and so it is in their best interest to avoid eating plants with the bitter tastes because it will not do them good. There is also recent evidence that plants can communicate with each other chemically, to stimulate tannin production; we’ll talk more about that in a later post.

Adult Giraffe (Giraffa camelopardalis) feeding on leaves

A giraffe quietly feeds on leaves, while the plants flood their systems with toxic chemicals.

Plants may sit quietly, but they can look after themselves; they have to of course, it’s not like they can run away. In future posts, I hope to explore plant defences in more detail; there is plenty more to talk about. Hopefully I’ve got you interested in botany, even just a little; stay tuned for more!

Much love,

-Nick

 

If you liked this entry, make sure you check out our Botany category.
Previous Botany entries:
Botanical Intrigue
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4 responses to “Quiet Battles: How do trees defend themselves from animal ‘attack’?

  1. Jim Morrison says:

    Thank you for the info about plant defenses. I look forward to your posts.

  2. john says:

    really trees can defend…nice article

  3. I have just told been about this amazing tree protecting phoenomenon. Who would have thought it? That goes to show us that we are not the only species on this earth that is intelligent.

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