Basal cover or basal area is determined by considering the cross-sectional area of plants near the ground, usually taken at a height of 2.5 cm for herbaceous plants and 140 cm for trees. Although basal cover is generally regarded as a more stable measure of cover than canopy cover, particularly for perennial grasses, it can still be sensitive to factors including stage of growth, seasonal conditions, and the history of utilization by herbivores.
References and Further Reading
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Daubenmire, R. 1968. Plant communities: A textbook on plant synecology. Harper Row, New York, NY. pp 47-49.
Gibbens, R.P., and R.F. Beck. 1988. Changes in grass basal area and forb densities over a 64-year period on grassland types of the Jornada Experimental Range. Journal of Range Management 41:186-92. (pdf)
Lister, P.B., and F.X. Shumaker. 1937. The influence of rainfall upon tuft area and height growth of three semidesert range grasses in southern Arizona. Journal Agricultural Research 54:109-121.