Net annual production of plant communities is traditionally determined by measuring or estimating dry matter accumulation at the end of the growing season. Published records list crop or forest yields, i.e. the bales of hay, tons of silage, bushels of grain or cords of wood harvested. The yield represents only a portion of the organic matter produced. Each year a tree forms leaves, twigs and bark which are not harvested, and each year an entire new corn plant-roots, stalks and leaves-must develop to produce the bushels of grain. Primary production is the entire amount of growth for the year. For many purposes, the accumulation of organic matter (on a dry weight basis) is an adequate measure of production; however, total dry matter production maybe misleading as a measure of the energy actually stored.
Kobriger, N. and F. Stearns. 1972. Productivity and energy storage. 5(2): 13-16.