acid rain or parasites Forest fragmentation – occurring when forests are cut down in a manner that leaves relatively small, isolated patches of forest, resulting in high amounts of edges and subsequent loss in wildlife habitat and biodiversity Forest transition – shift from a period of net forest area loss (deforestation) to a period of net forest area gain (afforestation) for a given region or country High grading – type of selective logging that removes the highest timber quality trees, resulting in poor genetic stock for subsequent generations Illegal logging – the unlawful harvest, transportation, purchase or sale of timber, contributing to deforestation, corruption, and destabilization of international markets Forest resource assessment Forest inventory – systematic collection of data and forest information for assessment or analysis. An estimate of the value and possible uses of timber is an important part of the broader information required to sustain ecosystems. Timber metrics Diameter at breast height (DBH) – measurement of a tree's diameter standardized at 1.3 meters (about 4.5 feet) above the ground Basal area – defines the area of a given section of land that is occupied by the cross-section of tree trunks and stems at their base Tree taper – the degree to which a tree's stem or bole decreases in diameter as a function of height above ground Girard form class – an expression of tree taper calculated as the ratio of diameter inside the bark at 16 feet above ground to that outside the bark at DBH, primary expression of tree form used in the United States Quadratic mean diameter – diameter of the tree that coordinates to the stand's basal area Leaf Area Index – the ratio of total upper leaf surface of the forest canopy divided by the surface area of the land on which the vegetation grows Tools Biltmore stick – utilizes ocular trigonometry to quickly measure diameter and height Diameter tape – cloth or metal tape that is wrapped around the bole, scaled to diameter Caliper – two prongs connected to a measuring tape are placed around the most average part of the bole to determine diameter Relascope – multiple-use tool that is able to find tree height, basal area, and tree diameter anywhere along the bole Clinometer – common tool used to measure changes in elevation and tree height Cruising rod – similar to a caliper, calculates the number of pieces of lumber