Quadrat device in ecology

    A quadrat, first used in the early 20th century, is a rigid frame, typically 0.5 or 1.0 meters square, used to measure the contents of a random sample of plant diversity within the surrounding area. Traditionally, a small stone thrown over the shoulder sets the south-west corner for placement of the quadrat in a SWNE orientation.  The numbers of plants of each species within the quadrat are then counted. Note that this quadrat is further divided into a 10 x 10 cm grid by wires, if a finer mesh is desired. Multiple quadrats may be used to re-sample a given area. Quadrat data may also be recorded as 'presence / absence' or '+ / -' counts, where the occurence or non-occurrence of a plant of interest is noted rather than the actual count.

    The composition of a quadrat can also be determined from a photograph of the quadrat, or with a camera with fixed height and field size, and species counts determined afterwards by eye or a computer. Vertical composition of a quadrat may also be determined by a laser scanner.