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Subject: Fine Overstory Issue by Bill Mollison on 
tree influence in plant, animal world
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::::::::::::::
Overstory #92 -  TREES AND THEIR ENERGY TRANSACTIONS
By Bill Mollison                       © Bill Mollison  1988, 2001

Contents:

: INTRODUCTION
: THE BIOMASS OF THE TREE
: WIND EFFECTS
: TEMPERATURE EFFECTS
: TREES AND PRECIPITATION
: SUMMARY
: REFERENCES
: ORIGINAL SOURCE
: ABOUT THE AUTHOR
: WEB LINKS
: RELATED EDITIONS OF THE OVERSTORY
: UPCOMING PERMACULTURE DESIGN COURSE BY BILL MOLLISON
: PUBLISHER NOTES


::::::::::::::
INTRODUCTION

This article 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.

The planting of trees can assuredly increase local precipitation, and can
help reverse the effects of dryland 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 fertilises 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 article, 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.


THE BIOMASS OF THE TREE
A tree is, broadly speaking, many biomass zones. These are the stem and
crown (the visible tree), the detritus and humus (the tree at the soil
surface boundary) and the roots and root associates (the underground tree).

Like all living things, a tree has shed its weight many times over to earth
and air, and has built much of the soil it stands in. Not only the crown,
but also the roots, die and shed their wastes to earth. The living tree
stands in a zone of decomposition, much of it transferred, reborn,
transported, or reincarnated into grasses, bacteria, fungus, insect life,
birds, and mammals.

Many of these tree-lives "belong with" the tree, and still function as part
of it. When a blue jay, currawong, or squirrel buries an acorn (and usually
recovers only 80% as a result of divine forgetfulness), it acts as the
agent of the oak. When the squirrel or wallaby digs up the columella of the
fungal tree root associates, guided to these by a garlic-like smell, they
swallow the spores, activate them enzymatically, and deposit them again to
invest the roots of another tree or sapling with its energy translator.

The root fungi intercede with water, soil, and atmosphere to manufacture
cell nutrients for the tree, while myriad insects carry out summer pruning,
decompose the surplus leaves, and activate essential soil bacteria for the
tree to use for nutrient flow. The rain of insect faeces may be crucial to
forest and prairie health.

What part of this assembly is the tree? Which is the body or entity of the
system, and which the part? An Australian Aborigine might give them all the
same "skin name," so that a certain shrub, the fire that germinates the
shrub, and the wallaby that feeds off it are all called waru, although each
part also has its name. The Hawaiians name each part of the taro plant
differently, from its child or shoot, to its nodes and "umbilicus."

It is a clever person indeed who can separate the total body of the tree
into mineral, plant, animal, detritus, and life! This separation is for
simple minds; the tree can be understood only as its total entity which,
like ours, reaches out into all things. Animals are the messengers of the
tree, and trees the gardens of animals. Life depends upon life. All forces,
all elements, all life forms are the biomass of the tree.


WIND EFFECTS
Apart from moisture, the wind may carry heavy loads of ice, dust, or sand.
Strand trees (palms, pines, and Casuarinas) have tough stems or thick bark
to withstand wind particle blast. Even tussock grasses slow the wind and
cause dust loads to settle out. In the edges of forests and behind beaches,
tree lines may accumulate a mound of driven particles just within their
canopy. The forest removes very fine dusts and industrial aerosols from the
airstream within a few hundred metres.

Forests provide a nutrient net for materials blown by wind, or gathered by
birds that forage from its edges. Migrating salmon in rivers die in the
headwaters after spawning, and many thousands of tons of fish remains are
deposited by birds and other predators in the forests surrounding these
rivers. In addition to these nutrient sources, trees actively mine the base
rock and soils for minerals.


TEMPERATURE EFFECTS
Evaporation causes heat loss locally and condensation causes heat gain
locally. Both effects may be used to heat or cool air or surfaces. The
USDA's Yearbook of Agriculture on Trees (1949) has this to say about the
evaporative effects of trees: "An ordinary elm, of medium size, will get
rid of 15,000 pounds of water on a clear dry hot day" and
"Evapotranspiration (in a 40 inch rainfall) is generally not less than 15
inches per year."

Thus, the evaporation by day off trees cools air in hot weather, while the
night condensation of atmospheric water warms the surrounding air. Moisture
will not condense unless it finds a surface to condense on. Leaves provide
this surface, as well as contact cooling. Leaf surfaces are likely to be
cooler than other objects at evening due to the evaporation from leaf
stomata by day. As air is also rising over trees, some vertical lift
cooling occurs, the two combining to condense moisture on the forest. We
find that leaves are 86% water, thus having twice the specific heat of
soil, remaining cooler than the soil by day and warmer at night. Plants
generally may be 15°C or so warmer than the surrounding air temperature.

Small open water storages or tree clumps upwind of a house have a pleasant
moderating effect. Air passing over open water is cooled in summer. It is
warmed and has moisture added even in winter. Only water captured by trees,
however, has a dehumidifying effect in hot and humid tropical areas, as
trees are capable of reducing humidity by direct absorption except in the
most extreme conditions.


TREES AND PRECIPITATION
Trees have helped to create both our soils and atmosphere. The first by
mechanical (root pressure) and chemical (humic acid) breakdown of rock,
adding life processes as humus and myriad decomposers. The second by
gaseous exchange, establishing and maintaining an oxygenated atmosphere and
an active water-vapour cycle essential to life.

The composition of the atmosphere is the result of reactive processes, and
forests may be doing about 80% of the work, with the rest due to oceanic or
aquatic exchange. Many cities, and most deforested areas such as Greece, no
longer produce the oxygen they use.

The basic effects of trees on water vapour and windstreams are:
* Compression of streamlines, and induced turbulence in air flows;
* Condensation phenomena, especially at night; Rehumidification by the
cycling of water to air;
* Snow and meltwater effects; and
* Provison of nucleii for rain.

We can deal with each of these in turn (realizing that  they also
interact).


Compression and Turbulence Effects
Windstreams flow across a forest. The streamlines that impinge on the
forest edge are partly deflected over the forest (almost 60% of the air)
and partly absorbed into the trees (about 40% of the air). Within 1000 m
(3,300 feet) the air entering the forest, with its tonnages of water and
dust, is brought to a standstill. The forest has swallowed these great
energies, and the result is an almost imperceptible warming of the air
within the forest, a generally increased humidity in the trees (averaging
15-18% higher than the ambient air), and air in which no dust is
detectable.

Under the forest canopy, negative ions produced by life processes cause
dust particles (++) to clump or adhere each to the other, and a fall-out of
dispersed dust results. At the forest edge, thick-stemmed and specially
wind-adapted trees buffer the front-line attack of the wind. If we cut a
windward forest edge, and remove these defences, windburn by salt, dust
abrasion, or just plain windforce may well kill or throw down the inner
forest of weaker stems and less resistant species. This is a commonly
observed phenomenon, which I have called "edge break." Conversely, we can
set up a forest by planting tough, resistant trees as windbreak, and so
protect subsequent downwind plantings. Forest edges are therefore to be
regarded as essential and permanent protection and should never be cut or
removed.


Condensation Phenomena
On the sea-facing coasts of islands and continents, the relatively warmer
land surface creates quiet inshore airflows towards evening, and in many
areas cooler water-laden air flows inland. Where this humid air flows over
the rapidly cooling surfaces of glass, metal, rocks, or the thin laminae of
leaves, condensation occurs, and droplets of water form. On leaves, this
may be greatly aided by the colonies of bacteria (Pseudomonas) which also
serve as nucleii for frost crystals to settle on leaves.

These saturated airstreams produce seaward-facing mosses and lichens on the
rocks of fresh basalt flows, but more importantly condense in trees to
create a copious soft condensation which, in such conditions, may far
exceed the precipitation caused by rainfall. Condensation drip can be as
high as 80-86% of total precipitation of the upland slopes of islands or
sea coasts, and eventually produces the dense rainforests of Tasmania,
Chile, Hawaii, Washington/Oregon, and Scandinavia. It produced the redwood
forests of California and the giant laurel forests of pre-conquest Canary
Islands (now an arid area due to almost complete deforestation by the
Spanish).

The effects of condensation of trees can be quickly destroyed. Felling of
the forests causes rivers to dry up, swamps to evaporate, shallow water to
dry out, and drought to grip the land. All this can occur in the lifetime
of a person.


Rehumidification of Airstreams
If it rains again, and again, the clouds that move inland carry water
mostly evaporated from forests, and less and less water evaporated from the
sea. Forests are cloud-makers both from water vapour evaporated from the
leaves by day, and water transpired as part of life processes. On high
islands, standing clouds cap the forested peaks, but disappear if the
forests are cut. The great bridging cloud that reached from the forests of
Maui to the island of Kohoolawe, remembered by the fathers of the present
Hawaiian settlers, has disappeared as cutting and cattle destroyed the
upper forests on Maui and so lifted the cloud cap from Kohoolawe, leaving
this lower island naked to the sun.

It is a wonder to me that we have any water available after we cut the
forests, or any soil. There are dozens of case histories in modern and
ancient times of such desiccation as we find on the Canary Islands
following deforestation, where rivers once ran and springs flowed. Design
strategies are obvious and urgent--save all forest that remains, and plant
trees for increased condensation on the hills that face the sea.


Effects on Snow and Meltwater
Although trees intercept some snow, the effect of shrubs and trees is to
entrap snow at the edges of clumps, and hold 75-95% of snowfall in shade.
Melting is delayed for 210 days compared with bare ground, so that release
of snowmelt is a more gradual process. Of the trapped snow within trees,
most is melted, while on open ground snow may sublime directly to air.
Thus, the beneficial effects of trees on high slopes is not confined to
humid coasts. On high cold uplands such as we find in the continental
interiors of the U.S.A. or Turkey near Mt. Ararat, the thin skeins of
winter snow either blow off the bald uplands, to disappear in warmer air,
or else they sublime directly to water vapour in the bright sun of winter.
In neither case does the snow melt to groundwater, but is gone without
productive effect, and no streams result on the lower slopes.
Provision of Nucleii for Rain

The upward spirals of humid air coming up from the forest carry insects,
pollen, and bacteria aloft. This is best seen as flights of gulls, swifts
and ibis spiralling up with the warm air and actively catching insects
lifted from the forest; their gastric pellets consist of insect remains. It
is these organic aerial particles (pollen, leaf dust, and bacteria mainly)
that create the nucleii for rain.


SUMMARY
All of these factors are clear enough for any person to understand. To
doubt the connection between forests and the water cycle is to doubt that
milk flows from the breast of the mother, which is just the analogy given
to water by tribal peoples. Trees were "the hair of the earth" which caught
the mists and made the rivers flow. Such metaphors are clear allegorical
guides to sensible conduct, and caused the Hawaiians (who had themselves
brought on earlier environmental catastrophes) to "tabu" forest cutting or
even to make tracks on high slopes, and to place mountain trees in a sacred
or protected category. Now that we begin to understand the reasons for
these beliefs, we could ourselves look on trees as our essential
companions, giving us all the needs of life, and deserving of our care and
respect.

It is our strategies on-site that make water a scarce or plentiful
resource. To start with, we must examine ways to increase local
precipitation. Unless there is absolutely no free water in the air and
earth about us (and there always is some), we can usually increase it
on-site.

Here are some basic strategies of water capture from air:
* We can cool the air by shade or by providing cold surfaces for it to flow
over, using trees and shrubs, or metals, including glass.
* We can cool air by forcing it to higher altitudes, by providing
windbreaks, or providing updraughts from heated or bare surfaces (large
concreted areas), or by mechanical means (big industrial fans).
* We can provide condensation nucleii for raindrops to form on, from
pollen, bacteria, and organic particles.
* We can compress air to make water more plentiful per unit volume of air,
by forcing streamlines to converge over trees and objects, or forcing
turbulent flow in airstreams (Ekman spirals).

If by any strategy we can cool air, and provide suitable condensation
surfaces or nucleii, we can increase precipitation locally. Trees,
especially crosswind belts of tall trees, meet all of these criteria in one
integrated system. They also store water for local climatic modification.
Thus we can clearly see trees as a strategy for creating more water for
local use.

In summary, we do not need to accept "rainfall" as having everything to do
with total local precipitation, especially if we live within 30-100 km of
coasts (as much of the world does), and we do not need to accept that total
precipitation cannot be changed (in either direction) by our action and
designs on site.


::::::::::::::
REFERENCES

Chang, Jenhu, Climate and Agriculture, Aldine Pub. Co., Chicago, 1968.

Daubenmire, Rexford F., Plants and Environment: a textbook of plant
autecology, Wiley & Sons, N. Y., 1974.

Geiger, Rudolf, The Climate Near the Ground, Harvard University Press,
1975.

Odum, Eugene, Fundamentals of Ecology, W. B. Saunders, London, 1974.

Plate, E. J., The Aerodynamics  of Shelterbelts, Agricultural Meteorology
8, 1970.

U. S. Department of Agriculture, Trees, USDA Yearbook of Agriculture, 1949.

Vogel, Stephen, Life in Moving Fluids, Willard Grant Press, Boston, 1981


::::::::::::::
ORIGINAL SOURCE

This edition of The Overstory is excerpted with the kind permission of the
author and publisher from:

Mollison, B. 1988.  PERMACULTURE: A Designer's Manual. Tagari Publications,
Tasmania, Australia. ©Bill Mollison

TAGARI PUBLICATIONS
Tagari Publications  - Permaculture Institute
31 Rulla Road
Sisters Creek Tasmania 7325
Australia    Ph: 61 (0)3 6445 0945 Fax: 61 (0)3 6445 0944
email: tagariadmin AT southcom.com.au


::::::::::::::
ABOUT THE AUTHOR

Bill Mollison, founder and director of the Permaculture Institute, Bill is
the most experienced Permaculture teacher and designer today. He has taught
and developed projects from the Arctic through Sub-tropics and Equatorial
regions of the planet. The Peoples of the Pacific, South East Asia, South
Africa and seven Amazonian language groups have been inspired by and acted
on his teachings, embracing Permaculture as a dynamic tool. He has also
given Courses in the drylands and developed projects with Native Americans,
Indigenous Australians, tribal women of the Deccan, Kalahari, San groups
and Pima people of the Sonora. In the USA, Europe and Scandinavia, Bill has
lectured and helped to develop ecological designs for urban and rural
properties, including many city-farms and CSA's (Community Supported
Agriculture). Bill Mollison's many roles include: scientist, naturalist and
University professor. Later he became a vigorous campaigner against
environmental exploitation which lead him to develop Permaculture as a
positive solution. Since then, Bill has devoted his energies towards
designing sustainable systems, writing books and articles on Permaculture,
and most importantly, teaching. Bill's publications include Introduction to
Permaculture, PERMACULTURE: A Designer's Manual, and The Permaculture Book
of Ferment and Human Nutrition.


::::::::::::::
WEB LINKS

Introduction to Permaculture: Concepts and Resources is an excellent
introduction with comprehensive resource links:
<http://www.attra.org/attra-pub/perma.html>

InterGarden - Permaculture Information - Discussion - Links has discussion
forums and extensive listing of permaculture-related links:
<http://sunsite.unc.edu/london/permaculture.html>

The Permaculture Activist site offers an array of information and resource
links: <http://www.permacultureactivist.net>


::::::::::::::
RELATED EDITIONS OF THE OVERSTORY

The Overstory #80--Forests and Water
<http://www.agroforester.com/overstory/overstory80.html>
The Overstory #69--Tree Basics
<http://www.agroforester.com/overstory/overstory69.html>
The Overstory #44--Integrated Systems Approach
<http://www.agroforester.com/overstory/overstory44.html>
The Overstory #18--Designing Resource Systems
<http://www.agroforester.com/overstory/overstory18.html>
The Overstory #7-- Agroforestry Systems
<http://www.agroforester.com/overstory/overstory7.html>


::::::::::::::
UPCOMING PERMACULTURE DESIGN COURSE BY BILL MOLLISON

BILL MOLLISON presents Permaculture Design Course -- 11th  to 25th
January, 2002

Bill Mollison, founding Director of the Permaculture Institute will present
this valuable course on his home turf, Tasmania. Those who wish to expand
their horizons and experience Bill in action are eagerly invited to bring
their questions and intellect to Tasmania and take this course. Bill
continues to research sustainable system design. He is preparing two books
devoted to this passion, and is in fine form for this course. Student
numbers are strictly limited.

For info and a Course Brochure contact:
Tagari Publications  - Permaculture Institute
31 Rulla Road
Sisters Creek Tasmania 7325
Australia     Ph: 61 (0)3 6445 0945 Fax: 61 (0)3 6445 0944
E-mail: tagariadmin AT southcom.com.au

::::::::::::::
PUBLISHER NOTES

Publisher: Permanent Agriculture Resources, P.O. Box 428, Holualoa, HI
96725 USA; Tel: 808-324-4427; Fax: 808-324-4129; E-mail:
<par AT agroforestry.net>; Web site: <http://www.agroforestry.net>

Editors: Craig R. Elevitch and Kim M. Wilkinson

Past editions of The Overstory: <http://www.overstory.org>