Introduction to Trees and their Energy Transactions in Permaculture

Permaculture Designers Manual




Section 6.1 –

Introduction to Trees and their Energy Transactions in Permaculture

On the dry Island of HIERRO in the Canary Islands, there is a legend of the rain tree: a giant “Til” tree (Ocotea foetens), “… the leaves of which condensed the mountain mists and caused water to drip into two large cisterns which were placed beneath.

The tree was destroyed in a storm in 1612 A.D. but the site is known and the remnants of the cistern preserved … (This one tree) distilled sufficient water from the sea mists to meet the needs of all the inhabitants.” (David Bramwell)


For me, trees have always been the most penetrating teachers. I revere them when they live in tribes and families. In forests and groves … They struggle with all the forces of their lives for one thing only: to fulfill themselves according to their own laws, to build up their own forms, to represent themselves. Nothing is holier; nothing is more exemplary than a beautiful strong tree.

(Herman Hesse, “Trees”, Natural Resources Journal, Spring 1980)


I am astonished to find whole books on the functioning of trees which make no mention of their splendid mechanical and aerodynamic performance. (Vogel, Life in Moving Fluids, 1981)

A point which is often overlooked is the effect of trees in increasing the total precipitation considerably beyond that recorded by rain gauges.

A large proportion of the time which collects on the twigs of trees in frosts afterwards reaches the ground as water and in climates such as those of the British Isles, the total amount of water deposited on the twigs from fogs and drifting clouds is considerable and most of it reaches the streams or underground storage or at least replaces losses from subsequent rainfall.

Of more importance, however, to hydraulic engineers is the effect of woodlands in modifying the runoff.

The rush or water from bare hillsides is exchanged for the slower delivery from the matted carpet of the woodland, losses by evaporation may be much diminished and the melting of snow usefully retarded. In catchments from which flood waters are largely lost, woodlands may increase the available runoff by extending the period of surface flow.

The maximum floods of rivers are reduced and the lowest summer flow increased.

Woodlands are usually much more effective than minor vegetation, such as gorse and heather, in preventing the soil from being carried from the land into an open reservoir.

To protect a reservoir from silting, it may be unnecessary to plant large areas, the slit being arrested by suitable planting of narrow belts of woodland or by the protection of natural growth along the margins or the streams.

Some engineers consider that in the case of small reservoirs the shelter afforded by a belt of trees along the margins is of value in reducing the amount of scour of the banks caused by wave action.

Afforestation over considerable areas in large river basins would, in many cases, reduce the amount or silting in navigable rivers and estuaries.

A matter which does not receive sufficient attention in connection with hydraulic engineering is the effect of judicious planting or woodland conservation over small areas.

A narrow belt or woodland along the foot of a slope will arrest the soil brought down by rains from the hillside. The encouragement of dense vegetation along the bottom or a narrow valley may check the rate of flood discharge to a useful extent.

The planting of suitable trees along ridges and for a little way down the slope facing the rain bearing and damp winds, will produce the maximum of certain desired effects. In proportion to the area occupied.

Suitable tree and bush growths in swampy areas and around their margins will increase their effect in checking flood discharge and may prevent these areas from contributing large quantities of silt to the streams during very heavy rains.

Areas of soft, cultivable soil liable to denudation may similarly be protected. Generally, a country which is, in the ordinary English sense of the words, “well timbered” is, from the point of view of the hydraulic engineer, a favorable country: and in the development of new lands the future effects of a proposed agricultural policy should be considered from this point of view and in consultation with hydraulic engineers.

(R.A. Ryves, Engineering Handbook, 1936)



This Chapter deals with the complex interactions between trees and the incoming energies of radiation, precipitation and the winds or gaseous envelope of earth.

The energy transactions between trees and their physical environment defy precise measurement as they vary from hour to hour and according to the composition and age of forests, but we can study the broad effects.

What I hope to show is the immense value of trees to the biosphere. We must deplore the rapacity of those who, for an ephemeral profit in dollars, would cut trees for newsprint, packaging and other temporary uses.

When we cut forests, we must pay for the end cost in drought, water loss, nutrient loss, and salted soils.

Such costs are not charged by uncaring or corrupted governments and deforestation has therefore impoverished whole nations.

The process continues with acid rain as a more modem problem, not charged against the cost of electricity or motor vehicles, but with the inevitable account building up so that no nation can pay, in the end, for rehabilitation.

The “capitalist“, “communist“, and “developing” worlds will all be equally brought down by forest loss.

Those barren political or religious ideologies which fail to care for forests carry their own destruction as lethal seeds within their fabric.

We should not be deceived by the propaganda that promises “for every tree cut down, a tree planted“.

The exchange of a 50g seedling for a forest giant of 100 tones is like the offer of a mouse for an elephant. No new reforestation can replace an old forest in energy value, and even this lip service is omitted in the “cut-and-run” forestry practiced in Brazil and the tropics of Oceania.

The planting of trees can assuredly increase local precipitation, and can help reverse the effects of dry land soil salting.

There is evidence everywhere, in literature and in the field that the great body of the forest is in very active energy transaction with the whole environment.

To even begin to understand, we must deal with themes within themes, and try to follow a single rainstorm or airstream through its interaction with the forest.

A young forest or tree doesn’t behave like the same entity in age; it may be more or less frost-hardy, wind fast, salt tolerant, drought resistant or shade tolerant at different ages and seasons.

But, let us at least try to see just how the forest works, by taking one theme at a time. While this segmented approach leads to further understanding, we must keep in mind that everything is connected, and any one factor affects all other parts of the system.

I can never see the forest as an assembly of plant and animal species, but rather as a single body with differing cells, organs, and functions.

Can the orchid exist without the tree that supports it, or the wasp that fertilizes it?

Can the forest extend its borders and occupy grasslands without the pigeon that carries its berries away to germinate elsewhere?

Trees are, for the earth, the ultimate translators and moderators of incoming energy.

At the crown of the forest, and within its canopy, the vast energies of sunlight, wind, and precipitation are being modified for life and growth.

Trees not only build but conserve the soils, shielding them from the impact of raindrops and the desiccation of wind and sun.

If we could only understand what a tree does for us, how beneficial it is to life on earth, we would (as many tribes have done) revere all trees as brothers and sisters.

In this Chapter, I hope to show that the little we do know has this ultimate meaning:

Without trees, we cannot inhabit the earth.

Without trees we rapidly create deserts and drought and the evidence for this is before our eyes.

Without trees, the atmosphere will alter its composition, and life support systems will fail.

(Figure 6.1)

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