Developing contemporary and historical live tree biomass estimates for old pine-hardwood stands of the Midsouth, USA

Calculating stand biomass potential is an increasingly important aspect of silviculture, particularly when attempting to restore forest ecosystems or determining additionality in sequestered carbon. However, the lumbering of the original forests of the Midsouth region of the United States of America, coupled with the accelerating conversion of unmanaged natural-origin stands to loblolly pine (Pinus taeda L.) plantations, make quantifying historic biomass difficult. If carefully done, it is possible to estimate presettlement biomass from past references and modern-day old pine-hardwood remnants. Pine sawtimber-only volume estimates from old reports indicated low biomass in the virgin pine-dominated forests of the Midsouth, from as little as 10–14 Mg/ha up to 72 Mg/ha. Given the incompleteness of these lumber yield-only data, a set of more detailed stand table-based historic descriptions were then coupled in this study with modern allometric equations to produce more complete estimates of biomass. These suggested that presettlement pine-hardwood stands of this region averaged ∼112 Mg/ha in total (above- and below-ground) live tree biomass (range = 54–171 Mg/ha; n = 6 stands). Contemporary old forests are considerably better stocked, with an estimated 224–318 Mg/ha (n = 6 stands). Individual loblolly pines from the historic period reached 183 cm in diameter and may have had as much as 32 Mg of biomass, though specimens <6 Mg were considerably more common. Large individual tree values but low stand levels imply disturbance (especially fire) regulated total tree biomass in historic forests of the Midsouth. These results further indicate that extensive restoration of modern unmanaged forests to past stand structures will likely decrease regional biomass.

► Little information on the biomass of historic pine-dominated old forests remains.
► Modern mature, unmanaged Midsouth pine forests have more biomass than virgin stands.
► The biggest historic pines have much more biomass than pines from today.
► Lower historic stand biomass with larger trees imply changes to disturbance regimes.
► Extensive restoration of historic conditions may reduce regional C storage.