Wood is a renewable energy source in the sense that a tree cut for fuel will naturally be replaced by a young tree that springs up in its place. This is certainly true, but there are conditions attached. The use of wood as a fuel is not sustainable if the trees are harvested in a way that damages the site. For example, if a stand of mature hardwood trees were clear-cut the site could be damaged by erosion and the elimination of shade to such an extent that high value hardwoods would not re-grow there for many generations, if ever. Sustainable forest management usually means that the site is maintained with a variety of tree species of various ages and that harvesting practices select only those trees that can be removed without damaging the forest ecosystem. The best and most obvious examples of sustainable forest management are the wood lots in farm country that have yielded firewood and lumber for generations of farm families and today still look healthy and productive.
The use of wood fuel is also sustainable on the condition that it is converted to heat with reasonable efficiency. Wood that is burned in fireplaces at very low efficiency is wasted for just the brief pleasure of watching the flames. On the other hand, if wood is burned in a modern EPA certified stove or fireplace; its use can immediately reduce the consumption of one of the other heating fuels like oil, natural gas or propane. This type of displacement is important because it is one of the ways we can reduce the carbon dioxide emissions that are linked to the problem of global climate change.
For thousands of years, wood has been used as a building material and the fact is wood has huge environmental benefits over other building products. It is completely biodegradable, works as an effective insulator, and is 100 percent renewable.
Sawdust or wood dust is a by-product of cutting, grinding, drilling, sanding, or otherwise pulverizing wood with a saw or other tool; it is composed of fine particles of wood. It is also the byproduct of certain animals, birds and insects which live in wood, such as the woodpecker and carpenter ant. It can present a hazard in manufacturing industries, especially in terms of its flammability.
Airborne sawdust and sawdust accumulations present a number of health and safety hazards. Wood dust becomes a potential health problem when, for example, the wood particles, from processes such as sanding, become airborne and are inhaled. Wood dust is a known human carcinogen. Certain woods and their dust contain toxins that can produce severe allergic reactions.
Water-borne bacteria digest organic material in leachate, but use up much of the available oxygen. This high "biological oxygen demand" can suffocate fish and other organisms. There is an equally detrimental effect on beneficial bacteria, so it is not at all advisable to use sawdust within home aquariums, as was once done by hobbyists seeking to save some expense on activated charcoal.
sawdust may collect in piles and add harmful leachates into local water systems, creating an environmental hazard. This has placed small sawyers and environmental agencies in a deadlock.
Other scientists have a different view, saying the "dilution is the solution to pollution" argument is no longer accepted in environmental science. The decomposition of a tree in a forest is similar to the impact of sawdust, but the difference is of scale. Sawmills may be storing thousands of cubic metres of wood residues in one place, so the issue becomes one of concentration.
But of larger concern are substances such as lignins and fatty acids that protect trees from predators while they are alive, but can leach into water and poison wildlife. Those types of things remain in the tree and, as the tree decays, they slowly are broken down. But when sawyers are processing a large volume of wood and large concentrations of these materials permeate into the runoff, the toxicity they cause is harmful to a broad range of organisms.