Monday, November 29, 2010

The Truth About Trees

When one thinks of trees and the benefit they have for us as humans, the obvious comes to mind: Trees help reduce the effects of global warming by reducing carbon dioxide concentration in the atmosphere. The photosynthetic process provides the trees with nutrients, and humans with the primary element required to sustain life - oxygen. Trees are often referred to as the “lungs of the world.”
All of the above is mainstream knowledge. It is the basic information we learn as children in grade school. But what if I told you it’s only the tip of the iceberg? Trees are more than just the “lungs of the world”.  Their role on this earth is pervasive, yet so often taken for granted.
So, what is a tree? 

A tree is a cooperative, a protector, a moderator, a creator, and a teacher.
The tree as a cooperative
A tree stands tall with its stem and crown.  This is visible to you as you admire it.  The common mental representation of a tree is made of up of just those ‘above ground’ parts.
 The parts of the tree that we often do not think about are the humus and detritus collected at the soil surface boundary, and the root and root associates under our feet. These are equally, if not more, essential to the existence of the tree than the more visibly pronounced parts.  In essence, a tree is perpetually standing in its own decomposition. Much of the tree, as it sheds its weight many times over to earth and air, eventually becomes grass, fungus, insect life, birds and mammals. It is the cooperation of these many ‘by-products’ that make a tree so rich – they exist because of the tree, belong with it and function as part of it. Birds nest, squirrels burrow and eat fungus, and insects prune and assist in decomposing the surplus leaves and activate essential soil bacteria. Animals are messengers to the tree and trees act as a garden for animals. This is a pure example of life depending on life. It is a total being that involves minerals, plants, animals, debris (detritus) and life.  All of these elements make up the ‘tree cooperative’.

The tree as a protector
Trees protect us from many elements.  Forest edges are the strongest collection of trees and should never be cut down. Trees adapt to withstand high winds by spreading their root mats to rely on their weight or anchoring their roots deep in rock crevices. They create special wood cells to bear the tension and compression from wind. With the wind come many particles of dust, ice, sand and other small particles. Within a few hundred meters, a forest of trees can remove fine dusts and industrial aerosols.  Therefore, trees protect us from wind that could be damaging to our habitats and small air particles that could be damaging to our lungs.  

The tree as a moderator
Trees moderate temperature due to two distinct processes – evaporation and condensation. Evaporation causes local heat loss during the day which cools the air in hot weather. Condensation causes local heat gain which warms the air at night.  Additionally, leaves have twice the specific heat (the heat capacity per unit mass of a body) than soil, meaning plants can be up at 15 degrees warmer than their surrounding environment. In certain climates, trees even act as dehumidifiers by directly absorbing moisture in the air. If dry hot air enters a forest, it is shaded, cooled, and humidified. If cold humid air enters the forest, it is warmed, dehumidified and slow released through the leaves of the trees.  As humans, we can strategically place trees and plants to moderate temperature. Reddish and white coloured leaves reflect light (up to 85%). This reflection can be used to cool down areas in warm summer months. Dark green leaves only reflect about 2% of light; the rest is absorbed and radiated as heat. This absorption and radiation of heat can be used to provide heat during cold winter months. The trees moderate extreme temperatures and humidity so it is tolerable enough to accommodate life.

Not only do trees moderate temperature, they moderate and conserve incoming energy. Every tree or plant species intercepts raindrops, decreasing the impact of the raindrops to prevent erosion. The leaves catch the rain, some of which is absorbed through them as required,  and the remainder is left to return to the air through evaporation. Any rain that falls through the canopy (throughfall) has, on its way down, collected plant cells and nutrients and is much richer than regular rainwater. This throughfall is then directed in patters to peripheral roots, and serve all the needs of growth in that forest.  Therefore trees use, collect, enrich and properly direct water so it can be optimized in the forest system naturally with no human intervention.

The tree as a creator
Trees play a key role in the creation of soil by producing root pressure and humic acid to breakdown the rock underground. Trees also contribute to the creation of the atmosphere through gaseous exchange (the production of oxygen) and the establishment and maintenance of the water -vapour cycle.
Furthermore, trees create precipitation through compression, condensation, evapo-transpiration and melting:
Wind blowing at a forest edge will be compressed. This compression causes more water vapour which, in turn, cools the ascending air. This phenomenon, referred to as an “Ekman Spiral”, can produce rainfall in the right conditions.  Therefore, lines of trees impact the air moving over them which can affect the climate and rainfall in the local area. This upward spiral of humid air coming up from the forest carries insects, pollen, and bacteria. These organic particles create the nuclei for rain. Materials given up by vegetation may be a critical factor for rainfall inland from forests.
Along coastline, warmer land surface causes cool in-land air flow. When this air is humid, it can fall on leaves as condensation (droplets of water). In this situation, condensation precipitation can be higher than rainfall precipitation. Examples can be found as rain forest along the coasts of Hawaii, Washington and Oregon as well as the redwood forests of California. A large tree can increase the available surface for condensation due to the large surface area given by leaves. Bigger trees intercept more moist air, thus creating more condensation. Fog also increases the precipitation through condensation over that of clear air.
Forests create clouds. Clouds are made through evaporation off the leaves by day and water transpiration as part of life process. Trees can return up to 75% of their water to air – which can be enough to form new rain clouds. The 25% water that is not returned to the air from trees is sent down into the soil and eventually reaches the streams and rivers.  Forested areas return ten times as much moisture as bare ground and twice as much as grasslands. It is highly likely that the deforestation of an area is directly related to downwind drought. It is important to note that the forest is continually recycling water to air and rain whilst producing 50% of its own rain.
Trees also slow the melting of snow and prevent the snow sublimation directly to air. The benefits of trees are not limited to coast line, but can be seen on any high slope. Even a small belt of trees entraps large quantities of drifting snow, and the release of this snowmelt is a more gradual process.

The tree as a teacher
Trees indicate local wind direction and intensity and from these indicators we can place windbreaks to reduce heat loss in homes, avoid damage from catastrophic winds and to steer the winds to well-placed wind turbines. They are biologically equipped to protect us from strong winds that could be damaging to our habitats. Trees also teach us about nature – through observing the ‘tree cooperative’, we can identify key behaviours and patterns of animals, bacteria and fungi, insects, water, sun and shade. 

In conclusion, trees are NOT just here to convert carbon dioxide to oxygen for us to breathe. Their purpose reaches much farther and cannot be ignored. Trees fight drought, prevent soil erosion, stabilize earth, shade us from sun, are key in the conservation of water, provide us with heat, control the effects of wind, provide shelter for animals and encourage biodiversity and nutrients for soil.  So, the next time you see a beautiful tree, don’t just thank it for being beautiful; thank it for being on of the most valuable things on this planet.

Written by: Julia Mitchell (Southern Alberta Permaculture)


  1. My only reservation about your otherwise excellent article on trees is your failure to mention the problems caused by tree species grown outside of their natural range. For example: California's Pinus radiata (Monterey Pine) invades natural areas here in Australia and has caused ecosystem collapse. Likewise, the Australian Melaleuca quinquenrvia (Broad-leaf Paperbark) has devastated huge swathes of the Florida Everglades. See also Tim Low's 'Feral Future: The Untold Story of Australia's Exotic Invaders' and the Weeds page of my firm's website

  2. great article! i love trees even more now, thanks. i will share this so that people know more about the many functions of a natural wonder. gordon, i think that goes to say for a lot of things...but i do not think that the point of the article was to say ..."hey, let's put a palm tree in edmonton because it is a creator, a moderator, a protector and a teacher..." but it is rather to show, "hey...maybe we shouldnt be trying to cut down all the trees and the forests and green spaces."

    the african palm tree shouldnt be grown in latin america, just because it is a cash crop---yes. but the issue is more than is cutting down natural forests and tree-ed areas to make ways for cash crops.

  3. Great article! Trees also store large amounts of water and can actually move fluids downward and replenish soil through their taproots. Pretty crazy!!!! Most people think of them as water and nutrient hogs. Not so! They also possess electrical current. I don't know if anyone has figured out the significance of this within ecosystems yet. Very interesting...