Modeling Historical Patterns of Tree Utilization in the Pacific Northwest: Carbon Sequestration Implications

We have developed a model, HARVEST, that predicts the mass of woody detritus left after timber harvest in Pacific Northwest forests from 1910 to the present. Inputs to the model include the species, diameter at breast height, and age distribution of trees: the minimum tree size to be harvested; the minimum top diameter; and stump height and slope steepness. Model output includes the absolute amount and the proportion of bole biomass removed as well as that left as stumps, tops, breakage, and decay. The model also predicts the biomass of nonmerchantable parts such as branches, coarse roots, and fine roots left after harvest. Model predictions were significantly correlated to residue levels reported in the literature over this period. Both model output and historical data indicate that the total amount of aboveground woody residue left after logging has decreased at least 25% over the last century. This means that release of carbon to the atmosphere from woody residue has decreased by a similar amount.