Acorn: Nut-like fruit of an oak with a scaly or warty cap.

Alternate Leaves: Leaves arranged on alternating sides of the twig.

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.

Angiosperm: Flowering plants having seeds enclosed in an ovary.

Annual Rings: A layer of wood including spring-wood and summer-wood grown in a single season; best seen in the cross-section of the trunk.

Biomass: The total mass, at a given time, of living organisms. Can be used to quantify weight for parts of a tree (e.g. roots, leaves, truck) all the way up to an entire forest community.

Bleeding: Flow of sap from wounds and/or other injuries.

Broadleaf: Trees having broad, flat-bladed leaves rather than needles; also a common name for hardwoods.

Cambium: Layer of tissue one to several cells thick found between the bark and the wood; divides to form new wood and bark.

Canopy: The part of the crown composed of leaves and small twigs.

Capsule: Dry fruit that splits open, usually along several lines, to reveal many seeds inside.

Cavity: An open and exposed area of wood, where the bark is missing and internal wood has been decayed and dissolved.

Chlorotic: Foliage that has yellowed due to disease or mineral deficiency.

Compaction: The compression of soil, causing a reduction of pore space and an increase in the density of the soil. Tree roots cannot grow in compacted soil.

Common Name: Familiar name for a tree; can be very misleading because common names vary according to local custom, and there may be many common names for one species.

Compound Leaves: Leaves with more than one leaflet attached to a stalk.

Conifer: Plant that bears seeds in a cone. Also called a gymnosperm.

Critical root zone: Portion of the root system that is the minimum necessary to maintain vitality or stability of the tree. Encroachment or damage to the critical root zone will put the tree at risk.

Crown: The portion of the tree that bears foliage.

Cultivar: A cultivated variety of a plant. A named plant selection from which identical or near-identical plants can be produced, usually by vegetative reproduction or cloning.

Decay: Progressive deterioration of organic tissues, usually caused by fungal or bacterial organisms, resulting in loss of cell structure, strength, and function. In tree this results in the loss of structural strength. Commonly referred to as rot.

Deciduous: Perennial plant that loses all its leaves at one time during the year.

Deep Root Fertilize: The insertion, (by means of high pressure hydraulic action), of a dilute liquid fertilizer. This is injected directly into the root zone, and is primarily used for trees on soils with poor nutrient status or obvious deficiencies.

Defoliation: Loss of leaves.

Diameter Breast Height (DBH): Diameter at Breast Height (measured at 4 1/2 feet above soil grade).

Dormant: Seasonal quiescent state in which the plant suspends growth. Usually occurs during winter months.

Dripline: The width of the crown, as measured by the lateral extent of the foliage.

Drupe: Fleshy fruit with a single stone or pit.

Evapotranspiration (ET): Water loss from the soil resulting from water uptake by roots and water evaporation from the leaves and into the air.

Evergreen: Plant that retains its leaves for more than one growing season. Does not just apply to conifers.

Fibrous Root System: System composed of profusely branched roots with many lateral rootlets, and often with no main taproot development.

Field Capacity (FC): The percentage of water remaining in a soil 2 or 3days after having been saturated and after free drainage has practically ceased.

Foliage: The live leaves or needles of the tree; the plant part primarily responsible for photosynthesis.

Gall: A localized swelling of branch or stem generally caused by fungi, bacteria, insects or a physiological disorder.

Genus: A group of species that are similar; the plural of genus is genera.

Growth Increment: The incremental growth added as new wood each growing season over existing wood. This is seen as growth rings in cross-sections of wood.

Hardwood: Trees that lose their leaves in autumn; also refers to the wood produced by these trees. Hardwoods are the predominant type of tree in the deciduous forest.

Heart Rot: Decay present in the heartwood (center) of a tree.

Heartwood: Darker-colored wood toward the center of a stem that has become physiologically inactive. It no longer functions for the transport of water and nutrients, but may be a site for storage.

Horticulture: Cultivation of fruits, vegetables and ornamental plants.

Inflorescence: The flowering portion of a plant.

Landscape: Areas of land that are distinguished by differences in landforms, vegetation, land use, and aesthetic characteristics.

Lateral: A branch or twig growing from a parent branch or stem in a horizontal direction from the parent stem.

Leader: A dominant upright stem, usually the main trunk.

Limb: Same as branch, but usually larger and more prominent.

Node: The point on a stem at which leaves and buds are attached.

Nut: Hard, dry fruit with an outer husk that sometimes does not split open readily.

Nutrients: The substances, such as mineral elements and compounds, including water and air that a plant synthesizes into the complex compounds of tissue.

Opposite Leaves: Leaves arranged directly across from each other on the twig.

Palmately Compound: Compound leaves in which several leaflets radiate from the end of a stalk; like the fingers around the palm of a hand.

Petiole: A slender stalk that supports a simple leaf.

Phloem: Inner bark of a tree that carries food and sugars from the leaves to other parts of the tree.

Photosynthesis: The transformation, in the presence of chlorophyll and light, of carbon dioxide (from air) and water (primarily from soil) into a simple carbohydrate and oxygen.

Pollard: A drastic means of pruning mature trees, involves removal of all green growth, leaving a "hat rack" impression. Not recommended for maturing and mature trees. It can be a useful way of controlling certain species of trees if the process is started when the tree is young (less than 5 years), and then done annually.

Root System: The portion of the tree containing the root organs, including buttress roots, transport roots, and fine absorbing roots; all underground parts of the tree.

Root Zone: The area and volume of soil around the tree in which roots are normally found. May extend to three or more times the branch spread of the tree, or several times the height of the tree.

Root Ball: Refers to the root system of a container or balled-in-burlap nursery sack.

Root Hairs: A hair-like tubular outgrowth, from near the tip of a rootlet, performing the work of absorption.

Saturation: In soil moisture, the condition in which both macro- and micropores are filled with water.

Scale-like leaves: Small, short, fish-scale-like leaves which cover the entire twig; found on juniper and Red Cedar.

Scientific Names: Latin-based names used worldwide to standardize names of trees and other plants and animals.

Serrate: With teeth.

Senescence: The process of aging, decline and death.

Shrub: Low-growing woody plant with many stems rather than one trunk.

Simple Leaves: Leaves with one blade attached to a petiole, or stalk.

Sinker Roots: Roots that grow vertically from horizontal roots, adding stability to the tree and increasing the volume of deeper soil exploited by the roots.

Softwood: Cone-bearing trees with needles or scale-like leaves; also refers to the wood produced by these trees. Softwoods are the predominant tree type in coniferous forests.

Species: A group of plants that resemble each other closely and that interbreed freely. Starch-A chain of sugars linked together that stores energy for later use by the plant.

Stem: A woody structure bearing foliage and buds that gives rise to other stems.

Stomata: Minute opening in the leaves through which gas exchange, including water vapor and carbon dioxide, occurs.

Symbiotic: The relationship of two dissimilar organisms living together to the mutual benefit of each other.

Thin Crown: A preferred method of pruning by removing interior growth and selectively thinning out branch tips. Overall size of the tree remains the same and retains its natural form.

Topping: Pruning technique to reduce height by heading of large branches. Generally considered poor practice.

Tree Root Protection Zone: The tree protection zone designates an area surrounding a tree or grouping of trees that is to be fenced off from all access until designated by a certified arborist. The RPZ is commonly defined as one (1) foot radial distance for every one (1) inch in tree diameter (DBH).

Xylem: The wood of a tree, made up of strong fibers, tracheids and vessels.