A Summary of Forest Ecosystem Benefits
Part I: Ecosystem Benefits
Providing and Protecting Habitat for Valued and Endangered Species Trees and forests provide homes for wildlife; rivers and streams kept cold and silt-free by surrounding trees retain supportive habitats for salmon and many other fish species. Entire ecosystems are sustained in the unique canopy environment of old growth forests. The many levels of a forest ecosystem, with varying light and moisture, allow multitudes of habitats to co-exist in a small area, and promote biodiversity.
Offsetting Air Pollution Trees help clean the air. They trap dust and filter pollutants, including particulate matter, out of the air.
Supplying and Purifying Fresh Water Forests collect and filter rainwater, and from it generate and store groundwater. The porous soil created by decomposing leaves, bark, and tree trunks acts as a huge sponge, absorbing water and purifying it as it seeps into the ground, surfacing later in springs or drilled wells. The natural aquifer of pure groundwater created by the New Jersey Pine Barrens contains 30 times more water than all the reservoirs serving New York City. More water is present under the forests of the planet than under all of the earth's fresh water lakes.
Producing and Improving Soil The byproducts of trees, decomposed leaves, branches, and tree trunks, become soil. They also provide a motherlode of nutrients that enrich our soil. Trees also help water seep in to the ground where their roots have permeated it, making soil more moist and fertile. Trees "load up" rainwater with nutrients accumulating on tree leaves and needles, as well as bird droppings, etc., on and under trees, before passing it into the sub-soil layers.
Cycling and Retaining Minerals and Nutrients Through growth, transpiration, and death, trees tie up minerals and nutrients from air, water, soil.
Reducing Erosion, Flood Waters, and Mudslides
Trees reduce erosion by cutting the speed with which wind and water rush across the landscape. This stabilizing effect helps keep soil in place. Soil washed into streams and rivers makes them shallower, and forces rising flood waters more quickly out of normal channels.
Removing trees by clearcutting can subject the terrain and residents below to increased, sometimes lethal, mudsliding.
Conserving energy. In very localized ecosystems, strategically placed deciduous trees help cool buildings in summer by providing shade. They also can ease the chill of winter by allowing sunlight to shine directly on them. As few as three large shade trees strategically located around a home can cut the energy bill for air conditioning in half.
Moderating Harsh Weather Extremes Trees work as natural barriers to wind, snow, rain, and intense sun in local areas. Forests also help prevent droughts by maintaining steady stream flows into drier seasons.

Part II: Global Benefits

Preserving and Enhancing Global Biodiversity Many species survive primarily in forests, which in the aggregate provide habitat for perhaps half the forms of life on the planet. A tree stump will serve for many decades as the home of a vast array of wildlife from bears and bobcats to woodpeckers and insects which eventually chew it into an ideal mulch for young saplings. A single fallen dead tree in an ancient forest may shelter as many as 1,500 invertebrates, many of them containing still undiscovered medicinal properties.
As habitat for biodiversity, forest ecosystems serve as a critical medium for evolution. Without them, much of life on the plant would be unable to adapt and evolve to new forms.
The biodiversity found in forest ecosystems serves as the planet's gene pool for many species, providing a source of plant strains that can resist pests and produce higher yields when cultivated.
Serving as the Reverse Lungs of the Planet Producing Breathable Air
Trees generate vast amounts of the oxygen we breathe. An average tree in a rural forest releases about 13 pounds of oxygen a year, enough to meet the breathing needs of a family of four. When we breathe, our lungs take in oxygen and release carbon dioxide. Trees and other plants do just the opposite: through photosynthesis they take in carbon and release oxygen.
Maintaining the Carbon Balance
An average tree absorbs and ties up to 26 pounds of carbon dioxide a year, the amount emitted by a car traveling 11,300 miles. Forests, as the plant forms with the largest biomass, take in and store enough carbon in their wood fiber and leaf canopy that carbon levels in the atmosphere, even far from forests, show a measurable decline during the growing season. Keeping the earth's carbon levels in balance is critical; carbon build-up in the atmosphere is a major contributor to global warming (see below).
Reducing Global Warming and Moderating Extremes of Weather and Climate Change Associated with Global Warming
The burning of gasoline and other fossil fuels has added more carbon dioxide to the atmosphere than trees and the oceans can absorb. That is the principal cause of global warming. The more trees there are, the more carbon dioxide is absorbed, and the less global warming we have. With global warming comes a host of problems: including submersion of populated areas from rising sea levels, extremes of weather, climate change (areas now providing agricultural wealth will migrate toward the poles, with attendant disruptions), and an increase in certain diseases.
Because tree cover offsets global warming, it mitigates these effects. For example, severe precipitation events, now occurring with greater frequency (so-called "100-year" events now occur ever more often in some places) can be moderated by increasing or slowing the rate of decrease of the globe's tree cover.
Serving as an Orchestrator of Ecosystems Driving the Hydrological Cycle
Trees help drive the hydrological cycle, which carries water from sea to air to land and back to the sea again. Without this cycle vegetation would not exist. Trees absorb vast amounts of water through their roots and leaves. They then "sweat" moisture back into the atmosphere, producing clouds which produce rain. Trees also "seed" existing clouds with drop-producing compounds.
Generating Micro-climates
The operation of this cycle in forests, especially ones with larger and more mature trees, can in itself create and maintain micro-climates that generate added rainfall and support rich and diverse forms of life not present in unforested ecosystems. The capacity of tree cover to create a livable climate even in barren places is well-captured in the classic Jean Giono fable "The Man Who Planted Trees."
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art III: Non-Environmental Benefits
Trees provide many non-environmental benefits. Among them are the following. Food Source We consume vast quantities of fruit, nuts and other foods from trees.
Energy Source Wood remains a fuel source for heat and cooking in much of the world. While the percent of overall wood use devoted to fuel is declining as modernization progresses, this use still accounts for nearly half of all wood consumed worldwide.
Economic Values Because of availability and low cost, we make heavy use of wood and wood products ranging from lumber, paper, and chemicals to pencils and garden mulch. We leave to others the task of spelling out the economic benefits of forests and trees, which in our society have become formidable. See for example, materials available from the American Forest and Paper Association (www.afandpa.org).
Health-Related Values Medicine.
Trees are a direct source of cures for a range of ailments. Healing.
Studies show that people in hospital rooms affording a view of trees recover more quickly than those in rooms without a tree view. Stress Reduction.
Close-by trees have been shown to reduce employee stress.
Cultural Values Cultures defined by closeness to and use of forests are at the heart of innumerable communities world-wide.
Spiritual and Other Intangible Values Many relate to forests, trees, and wood almost mystically. The "woods" are an infinite source of spiritual renewal and tranquil restoration. Forests with large trees bring out deeper thoughts and wonderment that for some are the stuff of religious experience. The majesty of a towering tree lifts us. The beauty of trees is a positive force that pervades our existence. Working with wood brings a sense of satisfaction to artisans, craftsmen, furniture makers, and builders. A handsomely crafted piece of furniture can bring joy and pride for generations. The glow of hot embers in a fireplace brings warmth and a sense of peace. We leave a just description of these aspects to writers and poets who speak far more eloquently here than we can.

Part IV. The Downside of Trees
In the interest of completeness, we must also note that trees can have a downside. In settled areas, they require maintenance. They eventually die and need to be disposed of (though in a forest, even in death, they are alive with abundant creatures, and eventually return to the soil). They can cause harm. They fall on people, sometimes fatally. They fall on houses and across roads and power lines. They can burn in the wrong places or at the wrong times. Their leaves can be a nuisance, such as when they clog drains. Some trees or their fruits are poisonous. They can cause shade where it isn't wanted, such as over a vegetable garden, and they can grow up to block a view.