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Glossary - A

Acidification
Acidication of surface waters occurs where there are large inputs of acidic pollutants and where catchments have susceptible acid soils and underlying rock.
Afforestation
Establishment of plantations on treeless land.
Alternate
Terms used of leaves or buds of broad-leaved trees that arise first on one side of a twig, then on the other.
Amenity value
Environmental or landscape benefit of trees rather than their commercial value as a timber crop.
Ancient woodland
Woodland which has been in continuous existence since 1600 (1750 in Scotland).
Annual ring
The sleeve of wood put on each growing season over the previous year's wood and under the bark on both stern and branches. Consists of spring wood and summer wood, the latter usually darker and thereby showing up as a ring in cross section.
Arboretum
A collection of specimen trees.
Arboriculture
Management of individual trees or groups of trees primarily for their amenity value.
Assortment (Stand)
The breakdown of a stand of timber into different products. Estimated using stand assortment tables, and based on the average dbh of the stand and the minimum top diameter required for the products being considered.