Tree terms: a
- A weighting
- A0, A1…
- AA
- AA Tech. cert.
- AABC
- AAIS
- AARC
- abate
- abatement notice
- ABC
- ABC Certificate in arboriculture
- abiotic factors
- abscission
- absolute humidity
- absorbing roots
- accent planting
- access chamber
- access facilitation pruning
- access land
- Access to Neighbouring Lands Act 1992
- acid
- acid rain
- acidification of the oceans
- acoustic fence
- acre
- action hedge height
- active house
- active transport
- actus reus
- acute oak decline
- adaptive growth
- adopted road
- adoption
- advance regeneration
- adventitious roots
- adventitious shoot
- adverse possession
- adze
- aeration layer
- aeration well
- aerenchyma
- aerial inspection
- aerial part
- aerial root
- aerobic
- aerodynamics
- aerosol
- AFAG
- affidavit
- affordable housing
- afforest
- aftercare
- after-ripening
- agaric
- age class distribution
- age of maximum mean annual increment
- Agenda 21
- aggravated criminal damage
- aggravated damages
- aggravated trespass
- aggregate
- aggressive conservation
- agistment
- AGM
- agricultural land classification (ALC)
- Agriculture Act 1986
- agroforestry
- Aichi biodiversity targets
- AIE
- air entrained concrete
- air frost
- air pollution
- air pots
- air pruning
- air quality (energy usage)
- air quality (microclimate)
- air quality (overall effects of vegetation)
- air quality (removal of pollutants)
- air quality (tree management)
- air quality (volatile organic compounds)
- air spade
- ALARP
- albedo
- ALC
- alga
- algal bloom
- alien
- alien invasive species
- A-line
- alkaline
- alkylate
- allelopathy
- allopolyploid
- allotment
- alluvium
- ALMO
- alternative silvicultural systems
- altitude
- ambient
- ambrosia beetle
- amenity
- amenity arboriculture
- amenity valuation
- amenity woodland
- AMIUG
- ammonium sulphamate
- amphibian
- Amsterdam tree soil
- anaerobic
- anamorph
- Ancient Monuments and Archaeological Areas Act 1979
- ancient replanted woodland
- ancient semi-natural woodland
- ancient soil
- ancient tree
- Ancient Tree Forum
- ancient woodland
- ancient woodland (protection)
- ancient woodland buffer
- ancient woodland indicator species (AWI)
- ancient woodland inventory
- ancient yew
- andirons
- angiosperms
- angle of repose
- animals
- anion
- annual ring
- annular
- anoxia
- anthocyanins
- anthracnose
- anthropogenic
- anti-climb paint
- anti-compaction mat
- anti-heave
- anti-skid surface
- Anti-social Behaviour Act 2003
- Anti-social Behaviour, Crime and Policing Act 2014
- anti-transpirant
- AOD
- AONB
- aphids
- apical dominance
- apical meristem
- apomixis
- appeal
- appellant
- apple scab
- apron
- aquifer
- Arboradix
- arbor-archaeology
- arboreal
- arborescent
- arboretum
- Arboricultural Advisory and Information Service
- Arboricultural Association (AA)
- arboricultural consultant
- arboricultural impact assessment
- Arboricultural Information Exchange
- arboricultural information exchange
- arboricultural method statement
- arboricultural site appraisal
- arboriculture
- Arboriculture and Forestry Advisory Group
- arboriculturist
- arborist
- arbour
- arbtalk
- archaeophyte
- arched tree
- Architects accredited in building conservation
- arctic ice
- area (of trees)
- area of outstanding natural beauty
- area payment for nuts scheme
- aril
- arisings
- Armillaria spp.
- Arms Length Management Organization
- arris
- arris rail
- arthropod
- article 4 direction
- article 5 certificate
- artificial tree
- Arts & crafts movement
- Ascomycetes
- ash
- ash bud moth (Prays fraxinella)
- ash key gall (Aceria fraxinivorus)
- ash leaf curl (Psyllopsis spp.)
- ash midrib gall midge (Dasineura fraxini)
- Asian longhorn beetle
- aspect
- asphalt
- asphalt concrete
- assart
- asset of community value
- assisted migration
- Atinian elm
- Atlantic multidecadal oscillation
- Atlantic overturning circulation
- atmosphere
- attachment of earnings order
- attenuation
- attenuation cell
- attenuation pond
- Atterberg limits
- auger
- auger boring
- autograft
- autopolyploid
- autumn colour
- auxin
- available nutrients
- available water
- avenue
- average daylight factor
- Award of garden merit (AGM)
- awarding body
- Awarding Body Consortium
- AWI
- AWVP
- axe
- axial parenchyma
- axial, axis
- axil
- axillary bud
- axiom of uniform stress