Production ecology of Thuja occidentalis

Equations to predict branch and tree leaf area, foliar mass, and stemwood volume were developed from 25 destructively sampled northern white-cedar (Thuja occidentalis L.) trees, a species whose production ecology has not been studied. Resulting models were applied to a large sample of 296 cored trees from 60 sites stratified across a soil gradient throughout northern Maine. Nonlinear regression analysis was used to assess alternative forms of the relationship between volume increment (VINC) and projected leaf area (PLA); analysis of covariance was used compare stemwood growth efficiency (GE) among soil-site classes, light exposure classes, and the presence of decay. Stem volume was estimated with Honer's equation (T. G. Honer. 1967. Forest Management Research and Services Institute) with refitted parameters. PLA was best predicted with Maguire and Bennett's nonlinear model (D. A. Maguire and W. S. Bennett. 1996. Can. J. For. Res. 26: 1991-2005) using sapwood area or crown length and the ratio of tree height to diameter at breast height. A sigmoid model form captured the relationship between VINC and PLA more precisely and with less bias than the simple power function; this implies that the relationship between GE and PLA reaches a peak rather than decreases monotonically. At PLAs > 50 m(2), GE gradually declined with increasing crown size and was significantly influenced by site and light exposure. With PLA, site, and light held constant, decayed trees had a significantly lower (by 11%) GE than sound stems, a finding not previously reported for other tree species.