Forest Dimensions and Production in the Great Smoky Mountains

Abstract

Samples based on stand measurements and borings of trees, and clippings of undergrowth, were taken from 24 forests and forest heaths in the Great Smoky Mountains. Samples were taken also from heath balds and grassy balds and a California coastal redwood forest. Available information on ratios and regressions of forest tree and shrub dimensions were used to estimate stand biomass and net annual production above ground. Mature climax forests of mesic environments below 1,400 m are characterized by: wood basal areas of 50—64 m 2/ha and basal area increments of 0.3—0.6 m 2/ha/yr, stem wood volumes (parabolic estimate) of 750—900 m 3/ha and estimated wood volume increments of 530—590 cm 3/m 2/yr, aboveground biomasses of 500—610 t/ha and aboveground net annual productions of 1,000—1,200 g/m 2, and biomass accumulation ratios of 40—50. These and other stand dimensions decrease along the moisture gradient to xeric sites and decrease toward higher elevations. Above—ground net annual productions of forest heaths of xeric slopes and forests of highest elevations are 420—650 g/m 2. Evergreen spruce—fir forests are more productive than deciduous forests above 1,400 m. Among mesic high—elevation beech and fir forests, production is higher on south slopes than on north slopes. Production and biomass of steady—state forests were estimated from multiple correlations using elevation and weighted—average index of site moisture as independent variables. Apart from some high—elevation stands, production is not significantly correlated with evergreen vs. deciduous foliage or with direction of exposure affecting incident sunlight. When unstable stands are excluded, production and biomass are strongly correlated with each other and with mean tree height and other stand dimensions. A wide range of temperate—zone climax forests of relatively favorable environments have net annual productions above and below ground of 1,200—1,500 g/m 2. Productions of stable closed heath balds are lower, 700—1,200 g/m 2, but productions of heath balds and less productive forests overlap broadly. Production of unstable forests, both successional stands and those opened by removal of large trees, exceeds that of steady—state forests of similar environments. Canopy coverage and light penetration are not strongly correlated with forest production. Light penetration to the herb stratum ranges from 1.4—7.0% of incident sunlight in more open forests and forest heaths to 0.3—0.9% in cove forests. Foliage live/dry ratios decrease along the moisture gradient from mesic to xeric stands–from about 5.0 to 2.8 in shrub clippings, 7.6 to 2.8 in herb clippings. Undergrowth production and biomass are trivial compared with the tree stratum in many forests. Shrub production is generally higher in xeric environments and is 20—145% of tree production in forest heaths. Herb production is higher at the extremes of the moisture gradient (exceeding 3% of total aboveground production in mesic and in open xeric stands) than in intermediate stands (below 1%). Apart from such differences, her and thallophyte biomass and production increase with elevation to maximum values in fir forests of the highest summits.