Litter fall transfers of dry matter and nutrients in ponderosa pine stands

Abstract

A 34-month study was conducted in an Arizona ponderosa pine (Pinusponderosa Laws.) forest to determine the effect of stand type and silvicultural treatment on rates and components of dry matter and nutrient (C, N, P, S, Ca, Mg, K, and Na) transfers via litter fall. Forest stand conditions (treatments) studied were dense saplings and small poles, large poles, thinned large poles, and clear-cut strips through thinned large poles. Total annual litter fall (<10% coarse woody litter fall) varied from 2795 kg•ha−1 for large-pole stands to 460 kg•ha−1 for clear-cut strips. Peak seasonal needle fall occurred in September–October, whereas the rate of non-needle litter fall was uniform across seasons but irregular in composition. Nutrient concentrations of litter fall differed significantly among treatments, but nutrient transfer was primarily a function of litter fall mass. Thus, dry matter and nutrient transfer patterns were similar. The mean nutrient concentrations of needle fall were as follows: C, 49.9%; N, 0.55%; P, 0.064%; S, 0.055%; Ca, 3133 ppm; Mg, 1349 ppm; K, 1487 ppm; and Na, 90 ppm. Needle fall had high concentrations of N, P, Mg, and K and low concentrations of Ca and Na compared with other (non-needle) fine litter fall, which was relatively high in Ca and Na and low in N. The ranking by treatments for dry matter and nutrient mass transfer was sapling and small poles = large poles > thinned large poles > clear-cut strips. The low concentration of nutrients in fine litter fall, especially N, compared with that of other cold temperate coniferous forests, suggests high N use efficiency for these stands.