GLOSSARY Biodiversity    The variety, distribution and abundance of different plants, animal and microorganisms, the ecological functions and processes they perform, and the genetic diversity they contain at local, regional or landscape levels. Branch a secondary division of a tree Canopy  Typically the uppermost continuous layer of branches and foliage in a stand of trees or shrubs, but can also refer to muddle and lower layers in stands with multiple stories. Chlorosis    A pronounced yellowing of normally green tissue.  It is often a symptom of mineral deficiencies, disease, feeding by sucking insects or root or stem girdling.  A plant suffering from chlorosis is said to be chlorotic. Crown   The upper part of a tree or other woody plant that carries the main system of branches and the foliage. CTLA  the Council of Tree and Landscape Appraisers.  The authority within the International Society of Arboriculture has developed a method of tree valuation based solely on the replacement cost per centimeter of cross-sectional area at 1.4 meters above ground.  This value is based on the current value of trees available for transplanting.  The basic price is then adjusted for the species, tree condition and tree location. Dbh    Diameter at Breast Height.  This refers to the diameter measurement of the main stem(s) taken at 1.4 meters above ground.  If a tree has multiple stems, dbh is measured for each stem and recorded as an average diameter. Dieback     The progressive dying from the tips downward or inward of shoots, twigs, tops, branches, or roots.  It may or may not lead  to death. Drip line  (Figure 1)The drip line refers to the area beneath the spread of the crown at its widest distance.  This is considered the minimum area which should remain as permeable surface (for aeration and water percolation), and beneath which the root system is undisturbed by trenching and construction.  In reality, the root system spreads radially out past the drip line by one or two times the height of the tree. Figure 1: Drip line   Epicormic shoots     A shoot that develops from a dormant bud, often in response to some stress endured by the tree.  There are two types of shoots: 1. watersprouts, which develop on older wood above ground, and 2. suckers, develop from roots below the ground. Exotic species    A species accidentally or purposefully introduced into an area where it did not formerly grow as part of the natural compliment of vegetation. Flush cut     A pruning technique where both branch and stem tissue are removed by cutting off a branch exactly flush with the stem.  It is considered poor pruning practice. GIS   Geographic Information Systems.  The use of a computer system to overlay large volumes of spatial data of different kinds.  The data are referenced to a set of geographical coordinates and encoded in computer format so that they can be sorted, selectively retrieved, statistically and spatially analysed. Habitat     The specific environmental conditions required for different organisms to thrive. Hard surface     Refers to the impermeable ground surface beneath the drip line.   This includes surfaces that are paved, graveled, bricked, severely compacted, or any surface which does not allow for percolation of rain water and soil aeration. Hazard Tree     In arboriculture, a hazard tree is any tree or part of a tree that if it were to fall, might hit a target, usually people or property.  Hazard-tree assessment of the standing tree for signs of structural weakness caused by growth habit, disease or decay, and assessment of whether or not a target exists in the potential fall zone.  If no target exists, the tree is automatically not a hazard tree. Heritage tree     A designation for a tree considered desirable based on the tree's age, historical significance, aesthetic value, size or horticultural value.  These trees are objects of preservation. Inspection cycle     The interval in a management schedule in which a tree inventory is carried out. Leaf      An appendage attached to the stem of plants by a petiole. The leaf surface is the principle area of photosynthesis. There are numerous types and shapes of leaf. (Parts of a leaf here?) Native species     Usually, a species known to have existed on a site prior to the influence of humans.  More generally, any species not introduced by planting. Pollarding     A technique that encourages rapid growth of sprouts from a tree.   In amenity trees, the technique is used to shape or form the crown.  Once the main scaffold structure has been established, the watersprout growth is pruned back annually to a head or knob of latent buds at the end of each branch. Ram's Horn     A failed attempt by the tree to close a crack.  Increasing pressure by growing bark at the fissure site forces the bark to turn inward on itself, forming the characteristic shape of a ram's horn.    (Figure 2) Figure 2: Ram's Horn Root      the part of the tree below ground, serving the purpose of anchorage and water and nutrient uptake for the tree. There are different types of roots belonging to a tree. Some are for the purpose of feeding and others are for the purpose of stabilization. Stem    The principal axis of a plant from which bids and shoots develop giving the plant its characteristic form. With woody species, the term applies to all ages and thickness', unlike the terms trunk and bole, which refer to tree stems of substantial thickness. Sunscald    Localized injury to bark and   cambium often resulting in wounds or a blanching of leaves.  It is caused by a sudden increase in exposure of the plant to intense sunshine and high temperatures. Tree     a woody plant characterized by one main trunk, bearing a more or less distinct and elevated crown of branches. Typically, trees are larger than shrubs. Urban Forestry      A specialized form of forest management concerned with the cultivation and management of trees in the entire area influenced and/or utilized by the urban population. It includes trees on streets in parks, on private property many benefits, including climate amelioration, engineering, architectural and aesthetic uses.