Modeling loblolly pine aboveground live biomass in a mature pine-hardwood stand: a cautionary tale
Carbon sequestration in forests is a growing area of interest for researchers and land managers. Calculating the quantity of carbon stored in forest biomass seems to be a straightforward task, but it is highly dependent on the function(s) used to construct the stand. For instance, there are a number of possible equations to predict aboveground live biomass for loblolly pine (Pinus taeda) growing in southeastern Arkansas. Depending on stem diameter at breast height (DBH), biomass varied considerably between four different prediction systems for loblolly pine. According to the tested models, individual tree oven-dry biomass for a 50 cm DBH loblolly pine ranged between 1,085 kg and 1,491 kg. Beyond this point, departures between these models became increasingly pronounced, with one even projecting an irrational decline to negative biomass for trees >138.7 cm DBH, while the others varied between 12,447 and 15,204 kg. Although some deviation is not surprising given the inherent differences in model form and three of the models were extrapolations across much of this diameter range, the difference between the extremes was unexpected. Such disparities significantly impact stand-level (cumulative) predictions of biomass in forests dominated by large-diameter individuals, as demonstrated for an existing stand (Hyatt’s Woods) in Drew County, Arkansas. Differences between these models caused loblolly pine aboveground live-tree biomass estimations in Hyatt’s Woods to vary by almost 34,000 kg/ha.