Abatement – Reduction in hazard, either by treatment of tree of removal of target.
Adventitious Root – Root tissue that develops from newly organized meristems, sometimes associated with fill and/or stem decay.
Adventitious Shoot – Vegetative tissue that develops from newly organized meristems rather than latent buds; frequently associated with pruning wounds.
Allelopathy – The inhibition of growth of one plant by another, usually through chemical compounds released into the soil environment.
ANSI A300 – The American National Standards Institute standard for pruning trees and shrubs (corresponding secretariat: National Arborist Association, Manchester, New Hampshire).
Antagonism – Situation in which the activity of a combination of pesticides or other chemicals is less than the expected effect of each applied separately.
Apical Control – Relative superiority of the central leader to lateral branches; excurrent trees have strong apical control, as the central leader is superior in size to all other branches.
Air Spade – Common term used to refer to a method of removing soil from around tree roots by the use of air pressure to minimize root damage. Generally requires a compressor with the minimum capacity of 150 cubic feet per minute (cfm). Requires pre-wetting of the soil for best results.
Amendment (Soil) – Any substance other than fertilizers, such as lime, sulfur, gypsum and sawdust, used to alter the chemical or physical properties of a soil, generally to make it more productive.
Anthracnose – A fungal disease causing dead areas on leaves, buds, stems, or fruit; commonly caused by Cryptocline, Disula, Clomerella, and Gnomonia sp.
Angiosperm – Flowering plants having seeds enclosed in an ovary.
Arboriculture – The science and art of caring for trees, shrubs, and other woody plants in landscape settings.