A
- aboveground biomass
- acid rain
- afforestation
- agricultural productivity
- agricultural runoff
- agricultural training
- agricultural watershed
- agrivoltaics
- agroecology
- agroecosystems
- agroforestry
- air pollutants
- air pollution
- air purification
- air quality
- air quality assessment
- air sampling
- algae
- algal blooms
- alternative crops
- alternative fuels
- alternative pollinators
- ammonia
- ancient ecology
- anthropocentrism
- apiaries
- applied ecology
- aquaculture
- aquaponics
- aquatic ecosystems
- aquatic environments
- aquatic habitats
- aquifer protection
- aquifers
- arable land
- arboriculture
- artificial lakes
- artificial ponds
- artificial reefs
- atmospheric rivers
- avalanches