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The term 'forest' encompasses an enormous range of habitats, from elfin cloud-forests a few metres
tall to 50 metre-high stands of redwoods or eucalypts; and from single-species conifer plantations to
tropical moist forests of extraordinary complexity.
The major problem in mapping forests is in deciding at what point tree cover becomes dense enough to be
called a forest rather than, say, an open woodland. There is no straightforward answer. The UN Food and
Agriculture Organisation (FAO) classifies as forest any area with more than 10 per cent canopy cover.
But this very wide definition includes many areas which few would regard as forests. A more satisfactory
definition is one covering closed-canopy forest: any area with over 40 per cent crown cover. This works
well with broadleaf or mixed coniferous and broadleaf forests but less well with purely coniferous
forests, where canopy cover is often less than 40 per cent.
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