Why We Need Trees.
There is so much to say about how important trees are to soil health (and soil building), to wind and rain patterns, and to flood and erosion control that there is no way I will cover it all.
A single tree has a lot going on just on a day-to-day basis. They provide us with so many free services its just mind-boggling.
I will try to cover some, leaving many more things untouched, for sure!
Temperature regulation
The denser the foliage the more shade is cast. Trees along pavements, roads and in car parks reduce ambient air temperatures, by casting shade, and rehumidify the air by transpiration. This prevents the ground from warming up, especially cement or bitumen, reducing ground temperature by a good few degrees. Shade is a readily recognized element, though too few folk will grow shade rather than nail it up as shadecloth.
For this reason alone urban trees are vital. Ground being shaded doesnt heat up, so doesnt stay hot as happens in cemented cities, the heat lag allowing no relief on hot summer nights.
Garden/forest canopy
As UV rises it is becoming clear that we need shelter from the mighty sun. Avenues of trees and selected trees in gardens can protect us and our low-growing plant layers (eg shrubs, creepers ) from intense UV.
Moisture capturing/evaporation.
At night the leaf area may be catching large amounts of condensation, especially near the coast. This moisture can keep the plants alive and can even supply enough moisture for rainforests on humid coasts . Certain types of foliage are better at this job than others.
This capturing of moisture is termed interception. It applies to the amount of water caught by the leaves, stems, bark, animals, spiders webs etc that catch any moisture within the tree or shrub which can then be released slowly to the soil or the air through evaporation.
A single tree can catch a lot of water when it rains, which is why trees are good to get under in a rain shower. The leaf area index or leaf surface of a large tree can be 16 hectares - which can catch a lot of condensation.
This strategy can also be copied to collect water in deserts using upright ceramic walls, which trap condensation and collect it in gutters . Even stones, broken roof tiles and plastic tree-bags can collect enough dew from the damp night air to keep a young plant alive.
Part of the result of this moisture catching is that when evaporation occurs the next day clouds can be reformed from the amount of water being transpired and evaporated (evapotranspiration). Cloud forming needs some water to exist already in the soil to happen.
Soil protection and creation.
Slowing rainfall hitting the ground is also part of the interception process. When there is heavy rain, the raindrops can damage bare soil surfaces.
Trees slow down the rain by stopping its impact on the ground- intercepting it and redirecting it along branches to the base of the plant or out along the drip-line to its outer root area. The rain that passes through the canopy of leaves is termed throughfall, and is nutrient rich, from airborne dust particles, and insect and bird wastes.
Large buttress roots hold trees down by weight to prevent blowing over while others have deep clinging roots reaching down into crevasses and cracks in rock. In this and other ways trees create soil by burrowing down, breaking up rocks, allowing water into holes left by dead roots left underground; mining for their own mineral needs. Deciduous trees provide some of the best humic material for compost heaps and allow northern winter sun to warm our homes and gardens.
Soil water.
Ground with trees or gardens on it is also able to allow water back down into the ground to recharge the water table. Paving and roads stop most water soaking back into the earth so “bore water” isn’t being replenished. Tree roots allow water to slowly soak down. Large amounts of water can exist in the soil, reducing the need of irrigation if enough is stored in the ground.
'Water For Every Farm' - by PA Yeomans describes the author's groundbreaking work in collecting as much water in the ground as possible by special contouring and deep chisel ploughing to allow maximum water penetration where previously there was run-off and erosion.
Windbreaks can be planted to mimic some effects of forests. In very windy areas, such as near the coast and on slopes, trees can be seen to be wind-blown away from the prevailing conditions.
Multi-layered rows of tough species can reduce wind impact on establishing gardens.
In a true forest wind is slowed by trees, and one kilometre into the forest the air will be still. Dust settles out and the air is clean.
Urban forestry.
Some councils in Europe have actually planted timber trees within urban areas that will be sold as fine timber, the money going to community projects.
Tree products.
There are many trees with edible products, many easy to grow for home fruit and nut supplies. Not all of these edible crops are well known. There are many hardy and less commercialised types of fruit available that may not transport well, so are best grown in your own backyard, where the only fuel needed is yourself.
We mustn't of course forget the thousands of other products such as spices, tool handles, posts, furniture, medicine and timber and more, which trees can provide.
But I won't go into that now........
Vicki B