A group or growth of tall plants or trees: a stand of pine. (American Her.)
A young tree, usually reserved when other trees are cut; also, a tree growing or standing upon its own root, in distinction from one produced from a scion set in a stock, either of the same or another kind of tree. (Webster)

Deve existir um termo da área, mas se não houver eu usaria "árvores maduras".

Boa sorte

me parece ser isto

Pelo contexto, parece-me uma tradução adequada.
Boa sorte.

Questões ambientais
... são cultivadas em fileiras ou grupos naturais; as árvores« mãe » geram constantemente
as mudas que substituem as árvores maduras que foram cortadas. ...
www.christmastree.net/env_por.htm - 14k - Em cache - Páginas Semelhantes


http://www.fs.fed.us/r6/siuslaw/5rivers/glossary.htm

Mature conifer stand--A mappable stand of trees for which the annual net rate of growth has peaked. Stands are generally older than 80-100 years and younger than 180-200 years. Stand age, diameter of dominant trees, and stand structure at maturity vary by forest cover types and local site conditions. Mature stands generally contain trees with smaller average diameter, less age-class variation, and less structural complexity than do old-growth stands of the same forest type.

Boa sorte!