Twenty-five-year growth and mortality of planted ponderosa pine repeatedly thinned to different stand densities in northern California

Abstract

A 20 yr old ponderosa pine (Pinus ponderosa ponderosa) plantation on a productive site on the west slope of the Sierra Nevada in northern California was thinned four times over a 25 yr period. Stand densities tested were Stand Density Indexes (SDI) of 73, 128, 183, 238, and 293 (equivalent to 40, 70, 100, 130, and 160 ft2/ac of basal area), replicated three times in a randomized design. Growth was analyzed for each of five 5 yr periods. Periodic annual increments (PAI) of diameter, net basal area, and net total volume differed significantly among periods and, in the earlier periods, among stocking levels. Mortality from winter storms and bark beetles was largely confined to the higher stand densities and in periods 3 and 4 caused PAIs of net basal area and net total volume to decline below that of lower densities. The sensitivity of mortality to stand density suggests a thinning target of SDI 183 (about 100 ft2 lac of basal area) for similar stands - no higher than that recommended for eastside stands of much lower site productivity. This sensitivity coupled with rapid growth suggests that multiple thinnings will be necessary in similar stands to maintain healthy, vigorous trees.