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Above- and below-stump biomass and nutrient content were estimated for a mature loblolly pine (Pinustaeda L.) plantation on an eroded site in the upper Piedmont of South Carolina. Pine above-stump biomass was 144.9 t•ha−1; below-stump biomass was 36.0 t•ha−1, 20% of total pine biomass. Total pine biomass was partitioned as 17% crown, 63% stem, and 20% roots. About 55% of below-stump biomass was in taproots and 45% in lateral roots. Dominant and codominant trees had a greater proportion of below-stump biomass in lateral roots, indicating that larger trees absorb a disproportionate quantity of the site's moisture and nutrients. Lateral roots contained 66 to 75% of below-stump nutrients. Fine roots (<0.6 cm diameter) accounted for 11% of below-stump biomass, but contained 24 to 30% of below-stump nutrients. Nutrient content (kg•ha−1) of above-stump biomass ranked as follows: N 164.7, Ca 154.2, K 78.0, and P 14.0. Nitrogen was also the most abundant nutrient in below-stump biomass (60.2 kg•ha−1), followed by Ca (48.9 kg•ha−1), K (41.2 kg•ha−1), Mg (11.1 kg•ha−1), and P (7.5 kg•ha−1). Below-stump biomass contained 27, 35, 35, and 24% of total pine N, P, K, and Ca, respectively. Fine roots and foliage, only 4% of total stand biomass, had about one-fourth of the stand's N and P.

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A technique was developed for estimating below-stump biomass of mature loblolly pine (Pinustaeda L.). The technique required complete excavation of only three trees and partial excavation (taproot only) of 12 others. A regression methodology for roots > 0.6 cm diameter and traditional soil-core sampling for roots < 0.6 cm diameter formed the main elements of the technique. Strong relationships were found (1) between biomass of three diameter classes of lateral roots and their proximal end diameter and (2) between diameter at breast height and estimated below-stump biomass for roots > 0.6 cm diameter. This technique should be useful for estimating root biomass of plantations of loblolly pine and may be effective for large trees of other species.