Forest Health Protection, Southern Region
Two types of surveys, general and intensive, are needed to determine the extent of forest damage from a storm.
General surveys are designed to determine geographical area affected by storms. These are very quickly and easily done from the air. Using aerial survey techniques, damaged areas may be sketched on preexisting maps or photographs, or damaged areas may be aerially photographed. A planimeter or other device is then used to determine acres affected.
Intensive surveys are designed to collect information on volumes of timber damaged and on conditions of surviving trees. Volumes of storm-damaged timber are difficult to estimate with aerial survey techniques because damaged trees are broken and twisted together. It is also difficult to determine tree condition from the air. Consequently, intensive surveys usually require ground-based plots for acceptable accuracy. The number and size of plots are determined by desired accuracy, and by time and personnel constraints.
Tornado damage surveys are unique because the storm tracks are usually long and narrow with few surviving trees. Volumes of tornado damaged timber may be estimated by taking systematic plots on a transect parallel to the storm track but just outside the damage area.
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