Forests and Trees
Trees as Energy Transducers: Wind, Sun, and Rainfall
Wind
1. 40% of incoming wind is forced through the trees, friction causes heat inside the forest (no frost).
Outside trees have thicker trunks due to wind force; inner trunks are thinner.
2. Wind brings in dust and insects: at edge of forest there is fallout of these, so forest at wind edge receives more “fertilizer”. Rain run-off also more plentiful at windward edge (high pressure of wind keeps the moisture in).
3. 60% of wind is forced up over the trees, forms and falls as Ekman spirals. Rain is caused by
spirals if there is any moisture in the air. Trees can cause the moisture to drop because of the
upward, forced spiraling of the wind. The spirals change direction depending on the hemisphere
(to the left in Southern hemisphere).
Light
1. Light is absorbed, transmitted through, or reflected by the tree, depending on trunk color, leaf
shape and color, and canopy (and also depending on climate).
2. Light absorption is mainly on crown for photosynthesis. A high light absorption tree is a radiator
and is mainly found in low heat conditions (temperate climates).
3. Light reflection is also on the crown (in dense plantings) or all over the tree in the form of silver
leaves. A reflecting tree is a light “producer” and is usually in low light conditions. In trees where
bark is white, heat is reflected away from the trunk.
4. Transmitted light is red light, stimulates root growth.
Rain
1. Impact on crown causes some immediate evaporation (but in a dense planting, there is no impact
on the ground, and so prevents erosion under the trees).
2. Each leaf is wetted. No water falls through the crown until all leaves are wet- tree intercepts rain.
3. Throughfall: water begins to drip off the leaves towards the branches and trunk. Water now contains
nutrients (dust, insects, plant’s nutrients).
4. Canopy drip feeds the surface roots. Trunk drip feeds deeper ladder or tap root systems. Function
of tap roots is mainly mining. Minerals brought up to leaves and then washed off during rain to be used by the surface feeding roots.
5. Litter under tree impedes water absorption (3 inches of litter holds 1 inch of water). Roots are
then able to absorb what they need before water infiltrates the ground.
6. Infiltration: water coats all the soil crumbs (the tree roots can also soak the water up from the
soil crumbs).
7. When ground reaches field capacity or saturation, water then slowly percolates to groundwater
area.
Transpiration occurs when the process reverses from deep groundwater, goes back up through the
trees, and is released into the air as clouds. 60% of clouds inland (after the first rainfall of 100% moisture from the sea) is formed by trees.
The dust that rises off the trees is made from bits of leaves and pollen, two sorts of bacteria that live on
the leaves, and certain oils and waxes that exude off the leaves. At the center of every raindrop inland
(nucleus) is a dust particle off trees.
More water that comes to earth is condensation rather than rain. One tree can be as much as 20-40
acres of leaf area. Moisture is condensed at night because it is relatively cooler than the air or wind.
Trees put out negative ions (which attract positive ions, usually dust and pollution) so air around trees is
healthy. Need a lot of trees in cities to counteract the positive ions in the air which cause depression.
In forests ground water run-off is zero (100% vegetative cover). At 80% vegetative cover = 5% run-off; at 60% cover = 35% run-off; at 20% cover = 60% run-off. Severe soil loss occurs as vegetative cover is
removed.
Types of Forest: fuel, food, forage, natural, structural, conservation, shelter/animal barrier.
1. Fuel: Essentials are that least use should be made of solid fuels; barks and leaves should be
returned to the soil or the system will degrade.
• Liquid fuels: species yielding sugars for conversion to alcohol (toddy palm, carobs, fruit trees),
or directly to fuel (copaiba). These are permanent trees.
• Solid fuels: either as cones from nut pines, fallen wood, thinnings, or short term forest for soil
creation (acacia, laucana).
• Gas fuels: coppicing for conversion of biomass via composting for methane collection.
2. Food: Orchards- usually intercrop (fruits, nuts). Use of food trees to support vine crop.
3. Forage: Design forage trees into zones II, III, & IV for small livestock, sheep, cattle. Livestock
will eat leaves, fruits, nuts off many trees (some need to be fenced off or allowed to grow large
before livestock are put in). Trees include those that drop fruit (mulberry, coprosma, boxthorn, fig, etc.); nuts (oak, chestnut, etc.); pods (acacia, carob, honey locust); and green leaves (pampas grass, banna grass, tagasaste)
4. Shelterbelt and animal barrier
• Windbreak around house and farm site
• Select species that provide forage, shelter, and act as a barrier hedge (e.g. pampas grass,
coprosma)
• Shelter for animals and as protection for crop (can put 20% of ground into shelter without loss of
productivity)
Structural: range from bamboo to black walnut, and short to long term cycles. Use for:
• Round pole (poplar, locust)
• Milled timber (long term and old forests)
• Industrial (cellulose yields)
• Craft uses (rattan, bamboo)
Natural and Conservation: forests have an intrinsic worth: beauty, nesting sites for birds, creators
of oxygen, clean water supply, rain & moisture, soil. Prevent erosion, deflect winds, bring nutrients up from the ground.
Establishment of Forest
• Select species and use (timber forest, fuel, etc.) and design for placement (crown bearers and
flower bearers on outside of clump, stem and forest inside). Shrubs may last only 10 years, pioneers
may last only 20.
• Pioneer species can establish essential conditions for forest (nitrogen-fixation, nutrient build-up)
on poor soils.
• Important to establish trees in a clump (fed by several drip points if necessary) as these will support
one another. Individual plantings tend to get ignored, and are often droughted, wind-pruned,
and smothered by grass competition.
Forest Management: thinning, fire, coppice, standards, selection, nutrients
Establishment of Vegetation and Trees and Orchard Systems
• Food trees mixed in with non-food trees to confuse pests and encourage pest predators
• Nitrogen-fixing trees should also be included, e.g. leucaena, acacia
• Combine poultry and ground cover planting for manure resources
• Mulch species
Tree Planting Tips
• Site: find nuclei to start from which will end up being covered by vegetation
• Pest control around nucleus. 1) thorn fences (spiny jujube), living fence (boma) and 2) paint blood & bone or sheep grease & kerosene on stems
• Shelter: 1) plant near rock or tussock, dune to protect from wind & sun and 2) use a guardrail
to collect dust, manure, & fine vegetation
• Plant in old stockyards to start a nucleus of trees, a source of nutrients
• Sudanese technique; Lanzarote technique: dig hole in sand & line with mud. Mud holds water and provides moist microclimate, wind protection
• Polystyrene tubes (developed in W. Australia) 75mm lip protects from rabbits (don’t like to bite through plastic). Will nip off tops, but plant lives.
• Net and pan system on a slope gives trees water & prevents erosion and run-off
• Plastic sheet underground. Catches the water or prevents it draining away
[youtube=http://www.youtube.com/watch?v=PQyETUg2_I0&hl=en_US&fs=1&]