Backfill: To return the soil to a planting area from which it was originally dug.

Bare-root seedling: A tree ready for transplanting that has had the soil removed from around its roots.

Biofuels: The product of biomass conversion; can be used directly to provide heat or electricity.

Biomass: In terms of energy production, biomass is wood and forest residues, crops and other plants, and animal manure.

Canopy: The cover of branches and foliage formed by tree crowns.

Canopy Cover: A measurement of how much of an area is covered by the leaves in the crown of its trees.

Carbon dioxide: (CO2) A colorless, odorless, non-combustible gas. Humans and all other living organisms give off carbon dioxide in respiration and decomposition. Trees and other plants absorb it and use it during photosynthesis. Also emitted as a by-product of burning fossil fuels.

Chlorofluorocarbons: (CFCs) Man-made compounds used as refrigerants and cleaning solvents, often long-lived in the atmosphere.

Coal: The most abundant fossil fuel, derived from prehistoric plant materials that were exposed to high temperatures and pressure.

Conifer: Cone-bearing, evergreen tree with needle-like, linear, or scale-like leaves. Found in temperate climate zones and is the most common tree in colder regions.

Conservation: The planning and management of resources so that we have continued access to these resources while maintaining their quality.

Crown: The branches and foliage of a tree.

Crown spread: The area covered by the branches and foliage of a tree.

Deciduous: Trees that shed their leaves regularly. they may be cold-deciduous and drop their leaves when the weather becomes cool (as in Autumn) or drought-deciduous, dropping their leaves when the water supply is low.

Deforestation: The removal of trees and often the plants associated with them.

Desertification: A process by which land becomes increasingly unproductive and barren.

Drain sump: A pipe that helps remove excess water from a planting hole.

Energy efficient: Using energy in the most productive, least wasteful ways.

Evaporative Cooling: The absorption of heat from the atmosphere during evapotranspiration.

Evapotranspiration: The loss of water through a plant's leaves, where it evaporates. One large tree can release up to 400 gallons of water into the atmosphere in one day!

Flow restrictor: A valve that reduces water flow from faucets.

Food chain: The plants and animals through which energy flows. Plants make up the base of the chain, by converting energy from the sun into food. Animals make up the next steps in the chain, by eating plants or other animals to get energy.

Fossil fuels: Includes coal, oil, and natural gas. Fossil fuels are derived from prehistoric plant and animal materials that were exposed to high temperatures and pressure.

Geothermal: Energy from the earth, derived as heat.

Global Warming: An overall rise in the temperature of the Earth's atmosphere; a projected result of the greenhouse effect.

Greenhouse Effect: The warming of the Earth's atmosphere caused by increasing levels of carbon dioxide and other gases in the air, which trap the sun's heat within the atmosphere.

Greenway: (Greenbelt) An area of green open space that surrounds and stretches into cities. It often contains trees and shrubs, and serves as a visual break between areas of urban buildup.

Heat Island: The phenomenon of higher temperatures in a city compared to the surrounding countryside, caused by the combination of paved surfaces, lack of shade, and heat retention of buildings.

Heartwood: (Sapwood, Xylem) The central part of the tree's stem (trunk), it provides support. No longer contains any live cells.

Hydrocarbons: Compounds made of carbon and hydrogen, used to describe many fossil fuels.

Hydropower: Energy derived from the flow of water.

Increment borer: A tool used to extract a core of wood from a tree. Using this technique, the age and condition of trees can be determined without destroying the tree. This tool should only be used by professionals because it can allow insects and disease to enter the tree, especially in urban areas.

Interdependence: Mutual dependence.

Landscaping: The art of placing trees, plants, and other features on a piece of land.

Leaf bud: A bud from which only leaves and stems develop.

Lobes: The division in leaves. For example, red maple leaves have five lobes.

Methane: (CH4) A fuel derived from the decomposition of plants; the main component of natural gas.

Microorganism: A living individual of microscopic size, such as a bacterium or protozoan.

Mulch: A protective covering, usually organic, placed around plants to keep in moisture and prevent the \ growth of weeds.

Natural gas: A mixture of gaseous hydrocarbons that occurs naturally in the earth.

Nitrogen oxides: (NOx) Compounds of nitrogen and oxygen; released during fossil fuel burning.

Non-renewable: A resource that is of a fixed quantity and can be used only once.

Ozone: (O3) A form of oxygen that is chemically unstable.

Phloem: (Inner bark) The layer of cells that transports nutrients from the crown to the roots.

Photosynthesis: The process by which plants convert sunlight, water and carbon dioxide into new plant tissue and oxygen.

Renewable: A resource that is of unlimited quantity and can be used indefinitely.

Riparian corridor: The area adjacent to a waterway such as a river, stream, or lake.

Root ball: The clump of soil containing the roots of a tree, often bound in burlap.

Roots: The underground part of the tree, they anchor the tree and absorb water and nutrients.

Rotary cultivator: A power-driven machine that uses rotating metal teeth to chop, separate and mix soil. A useful tool for large tree-plantings.

Sapling: A young tree that measures two to four inches in diameter.

Sapwood: (Xylem) The living wood of pale color next to the bark. it is formed from the cambium and conducts water and minerals from the roots to the leaves.

Seedling: A young tree shortly after it has sprouted from the seed.

Sequestration: The process of storing carbon within a plant. During photosynthesis, carbon dixoide from the atmosphere is broken down into oxygen, which is released back into the atmosphere, and carbon, which is stored (sequestered) in the tree's trunk, branches and roots.

Sidewalk pit: Small preserves of soil found in urban centers, usually within sidewalks. These pits are often the only place for trees in these areas, and constitute a sort of immovable "street planter."

Silviculture: The art and science of growing and harvesting forest products.

Solar energy: Energy from the sun.

Treelawn: The usually narrow area between the curb and the sidewalk.

Trunk: The main stem of a tree.

Urban forest: Created where people congregate and build communities. Since humans are the main inhabitants of the urban forest, they largely determine the tree species in this forest.

Urban heat island: The phenomenon of higher temperatures in a city compared to the surrounding countryside, caused by the combination of paved surfaces, lack of shade, and heat retention of the buildings and structures.

Utility company: A company that provides service to the public, usually electricity, gas, water, or telephone.

Well-aerated soil: soil that has been loosened enough so that at least fifty percent of its volume is air.

Well-developed soil: Soils sufficiently weathered to have readily identifiable layers, or "horizons." An organic layer is at the top; the mineral layer is close to the bottom.

Whip: A young tree. Often one that has developed a main stem but very few branches.

Wind power: Energy derived from the wind, usually from windmills.

Xylem: The layer of cells that transport water and nutrients to the leaves and branches from the roots.