It's autumn and many trees are putting on a beautiful show of colour for us, so I wanted to take the opportunity to celebrate all the other things that trees do for us - just in case you still need to be convinced that planting trees is a good idea! I offer a few good reasons here (can you think of any more?). Remember that most of the trees we’re enjoying today were planted for us by our ancestors. Now it's our turn.
1. Trees make oxygen. Okay, I’m starting with the obvious ones, but without the miracle of photosynthesis we would not be here at all. It’s important to remember though that trees and plants need us just as much, to replenish atmospheric carbon dioxide.
2. Trees sequester carbon. I’m sure we all appreciate the importance of that right now, but throughout the history of Life on Earth, the ability of photosynthesisers to take carbon out of the air and reduce greenhouse gases has kept the global temperature ‘just right’, despite our sun increasing in temperature by around 25%.
3. Trees shade us from the hot sun. Yes, I know it rarely gets that hot in Britain, but there are still days when we seek out shade and trees provide it well. Grazing animals, when they have access to trees, always seek out their shelter too.
4. Trees shelter us from the rain. They shelter everything else beneath their canopy too, including, and especially, the soil. In woodlands their leaf fall provides a carpet that slows water before it hits the soil itself, allowing it to percolate in rather than run off.
5. Trees slow water run-off. Where we do find run off (from fields or hard surfaces), trees can slow it and again allow it to percolate down into the soil. The root buttresses of trees act like mini dams that catch water –and the slower the run off, the less chance there is of flooding occurring downstream.
6. Trees stabilise slopes, retaining soil. The root systems of trees act like a net, holding the soil together and reducing the risk of erosion, even on fairly steep slopes.
7. Trees shelter us from the wind. They are an excellent windbreak, each tree slowing the wind a little, creating relative calmness in their lee. Less wind means less evaporation losses from other plants or bodies of water. A more sheltered spot will also permit more pollinators to fly. One of the greatest limiting factors on the growth and pollination of most trees is wind.
8. Trees de-compact soil. Oh yes…! When the wind is blowing on the canopy, the root systems are flexing in the ground and countering the slow compaction of soil through gravity pulling water and soil particles downwards. Of course a healthy soil full of life also does this work, though not quite so dramatically. This effect was noticed at Kew Gardens in London after the great storm of 1987. The canopies of some trees, that were heavily blown about but not blown over, grew in size by 30% the following season. That was when they realised that all the people visiting the trees were trampling the root plates , so Kew instigated a programme of de-compaction of the soil around many of their mature trees, with great success in canopy regeneration.
9. Trees clean the soil. They absorb and transform many pollutants that find their way into the ground, making conditions safer for many other lifeforms.
10. Trees pump water and minerals from deep underground. They partner with mycorrhizal fungi who have the ability to extract minerals from rocks and make them biologically available. A lot of these minerals and nutrients are later released by deciduous trees each autumn, through leaf fall and fine root turnover (the dropping of annual roots).
11. Trees make clouds and, ultimately, rain. This one is especially important, though it needs a lot of trees for it to be significant. Many of the clouds we see in Britain were evaporated off the sea – we are on a small island after all. Despite this, there’s still a strong drop off in rainfall between the west and the east of the country. A band of high land that runs north-south causes most clouds to drop their rain on the side of the prevailing winds – the west, leaving the east relatively dry. Imagine if we were talking about a continent thousands of miles across. So how does rain cross large continental bodies? With the help of forests. If trees can re-evaporate much of the rain then the wind can continue to take it further inland where it can fall again. If there are trees there too, then clouds can form again and so on. Forests can ensure the rain keeps on going, but we’ve cut many of them down.
12. Trees clean the air. The moisture that trees transpire dampens dust particles, making them heavier and helping to bring them down to earth. Dust blowing against moist leaves also gets stuck and the next rain can wash them down to ground level. This is one reason why trees are especially important in towns and cities.
13. Trees trap air beneath their canopy, stabilising the temperature. The shelter they provide slows the movement of air and the warmth it holds. Cold air falling from above at night is deflected out to the sides of the canopies of trees, keeping woodlands relatively warm when it’s cold as well as relatively cool when it’s hot.
14. Trees provide important habitats. To how many other species is very much dependent on the tree. Oaks are well known for being great for wildlife –many of the species that depend on them actually eat the tree as it dies (and that can take 100 years or more). Willow is a great wildlife tree too.
15. Trees provide us with food and fodder. All grazing animals will eat tree branches given the chance. We humans might of course prefer the fruits and nuts of certain species, but there are some good edible leaves for us too, Lime (Tilia species) in particular.
16. Trees reduce noise pollution. They scatter traffic and other noise, breaking up the pressure waves as they pass through their canopies.
17. We co-evolved with trees. Life would be very strange without them.
18. Green is our most calming colour. Enough said.