A forest as an entity is a complex integrated, self-regulated system, very different from stands of trees grown for economic value, which are usually even-aged monocultures of fast-growing non-endemic species. In most current afforestation schemes, forests are collection of trees of varying timber value or social utility. This narrow perception has allowed application of monoculture, including aged plantations, to meet with most global forestry needs.
It is not a valid assumption that any collection of trees is a forest. When a natural forest is examined, an ecosystem of tremendous complexity is always revealed, demanding special management if its complexity (the greatest amount of genetic and ecological information) is to be conserved. Complexity in a forest is synonymous with biodiversity. There is a growing body of knowledge that demonstrates a link between the loss in biodiversity and the loss of forest cover. Indigenous forest management may be more sophisticated in terms of biodiversity conservation than modern designs. The synthesis of Mayanmarese (Burmese) tradition and forestry science in 1806 produced the taungya method of establishing teak (Tecona grandis) plantations, which was so successful that it has proliferated to most of the tropical world and became the precursor of modern agroforestry.
Multinational companies have realized that they may run out of raw wood if they do not plant more trees, so they are producing eucalyptus and other fast-growing trees. These are extravagant users of water and nutrients, competing with crops and degrading good land, and producing little social benefit for the neighbouring people. During the period 1968 to 1980, 32 forestry projects were financed through the world. Of these, 21 used pines (Pinus spp) or eucalyptus (Eucalyptus spp) as the main species. The total number of species chosen for internationally-funded projects worldwide was about 35.
It was reported in 1997 that public money running into millions of pounds was wasted replanting trees in Great Britain after the great storm of 1987 and the places where nature was left alone had the most prolific regrowth. The woodlands have seen a burst of regeneration where the canopy was opened and light let in. Saplings and shrubs grew up to 20 feet in ten years and there was a noticeable increase in insects, birds and flowering plants such as violets and primroses. Natural disturbance added variety to a woodland. More damage was done by well-intentioned cleaning up than by the storm itself. Many of the trees planted that autumn were planted hurriedly, badly, and they died. Clearing up with bulldozers and tractors had compacted the seedbed and many places had ended up "something like a car park". "Politicians feel they need to be doing something. They need to feel they are spending money and the most obvious way to do it was to clean up the damage. It would not be politically possible to just do nothing at all.".
Forestry is defined as the "art and science of growing forests". Current ecological and social problems suggest that the quality of both art and science has been rather lacking. The human-created forest estate around the world provides a living statement of the poor criteria applied. The present stock of man-made forests comprises an uncomfortable short list of species. Although these forests provide timber and wind or erosion control, they do not provide social or environmental stability and biodiversity conservation.