Predicting small-diameter loblolly pine aboveground biomass in naturally regenerated stands
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There is growing interest in managing southern pine forests for both carbon sequestration and bioenergy. For instance, thinning otherwise unmerchantable trees in naturally regenerated pine-dominated forests should generate biomass without conflicting with more traditional forest products. However, we lack the tools to accurately quantify the biomass in these submerchantable size classes. To help remedy this, we destructively sampled 54 small-diameter loblolly pines (Pinus taeda L.) from stands on the Crossett Experimental Forest (CEF) in southeastern Arkansas. After harvesting, each tree was divided into stemwood, foliage and branch, and taproot components, then oven-dried and weighed. We then fit an exponential equation based on the National Biomass Estimator (NBE) to predict aboveground oven-dry biomass as a function of diameter at breast height (d.b.h.). The resulting model fit the sample data well (pseudo-R2 = 0.996). Comparing the CEF local biomass model with the pine submodel of the NBE suggested that the NBE would consistently underestimate small-diameter loblolly pine biomass on the CEF. While this difference appeared small, its cumulative effect could be appreciable. For example, in a young loblolly pine stand averaging 5 cm d.b.h. and 5,000 stems ha-1, the NBE would predict almost 9 percent less biomass than the new CEF biomass model—a difference of nearly 2 metric tons ha-1. Such locally derived equations offer silviculturists opportunities to better assess the potential of naturally regenerated pine stands to produce fiber and thus may be worth the investment of time and resources to develop.