Modeling in-situ pine root decomposition using data from a 60-year chronosequence

Abstract

Because the root system of a mature pine tree typically accounts for 20–30% of the total tree biomass, decomposition of large lateral roots and taproots following forest harvest and re-establishment potentially impact nutrient supply and carbon sequestration in pine systems over several decades. If the relationship between stump diameter and decomposition of taproot and lateral root material, i.e., wood and bark, can be quantified, a better understanding of rates and patterns of sequestration and nutrient release can also be developed. This study estimated decomposition rates from in-situ root systems using a chronosequence approach. Nine stands of 55- to 70-year-old loblolly pine (Pinus taeda L.) that had been clear-cut 0, 5, 10, 20, 25, 35, 45, 55, and 60 years ago were identified on well-drained Piedmont soils. Taproot and lateral root systems were excavated, measured, and weighed. Although more than 50% of the total root mass decomposed during the first 10 years after harvest, field excavations recovered portions of large lateral roots (>5 cm diameter) and taproots that persisted for more than 35 and 60 years, respectively. Results indicate that decomposition of total root biomass, and its component parts, from mature, clear-cut loblolly pine stands, can be modeled with good precision as a function of groundline stump diameter and years since harvest.

Soil carbon, after 3 years, under short-rotation woody crops grown under varying nutrient and water availability

“…Root decomposition rates will vary by factors such as genotype, soil texture and drainage but will probably be in the same magnitude as observed by Ludovici et al [22]. Even so, buried root systems (i.e., coarse and tap roots) are a larger source of C and may persist much longer than C inputs from masticated forest slash or fine roots.…”

“…The larger belowground biomass realized in these managed systems may persist long after the stand is harvested. Ludovici et al [22] demonstrated that loblolly pine stumps remaining after a harvest can persist for several decades in a silty loam soil.…”

“…South Carolina ranged from 40 to 170 g C m À2 year À1 , and most soil C at each site was associated with the silt-clay soil fraction [20]. Additionally, at the end of a rotation the roots left after harvest can also have a strong impact on soil C contents [21][22][23].…”

Soil carbon and nitrogen content and stabilization in mid-rotation, intensively managed sweetgum and loblolly pine stands

“…Residual root systems (coarse and tap roots) can persist in the soil (Ludovici et al, 2002) and their decomposition can impact C and nutrient release over several decades (Jenny, 1980;Vogt et al, 1991;Chen et al, 2001). Considering that tree roots in an unmanaged, mature stand may account for 20-30% of a tree's total biomass (Van Lear et al, 2000); this represents a considerable soil organic matter pool.…”

Accounting Carbon Storage in Decaying Root Systems of Harvested Forests

“…Following harvest or natural tree mortality, root systems become a ''source'' of carbon as they decay in a negative exponential Carbon content of root systems is estimated at the time of harvest, representing the maximum amount of C in decomposing roots pattern over decades, releasing CO 2 to the atmosphere. However, coarse roots persist after harvest (Johnsen et al 2001;Ludovici et al 2002), providing a longer term C storage mechanism than that provided by fine roots. Therefore, it is important to quantify coarse-root C in both live trees and dead, decaying root systems.…”