Allometry of tree biomass and carbon partitioning in ponderosa pine plantations grown under diverse conditions

Abstract

Forests not only provide forest products to meet people’s demands, but also sequester enough carbon to offset more than 11% of anthropogenic CO2 release in the United States. An accurate estimate of forest carbon sequestration over different forest and forest product combinations requires the species-specific and site-specific allometric biomass equations for trees and understory vegetation at particular forest developmental stages. Here, we constructed the above- and below-ground allometric equations by harvesting 108 20-year-old ponderosa pine (Pinus ponderosa) trees grown under four different silvicultural treatments (four combinations of with and without competing vegetation control (H) and fertilization (F): C = control with no vegetation control and no fertilization, H, F, and HF) at three diverse site conditions in northern California. We found that the logarithmic regressions provided superior estimations of biomass for total, aboveground, bole, coarse roots, branches, and foliage compared to simple or scaled power-law fits. Treatment effect in allometric equations was generally lacking but site effect was significant, suggesting site specific allometric relations exist. With the best allometric equations, we estimated the biomass and carbon for each plot among treatments and sites. In addition, understory woody plant biomass was also measured with fixed area subplots. Results show significantly more total carbon sequestration at the high-quality sites with 113.1–162.5 Mg ha−1 than the lower ones with 85.8–105.9 Mg ha−1 at the intermediate site and 29.3–70.4 Mg ha−1 at the poorest site, respectively. The range of carbon stocks indicates the treatment differences at each site, with the largest effect (240%) at the poorest site and similar at other two sites (~130%). If planted trees only were considered, a trend among sites exists with 93.4 – 149.3 Mg ha−1 at the richest site, 26.2–88.1 Mg ha−1 at the intermediate site, and 17.1–64.2 Mg ha−1 at the poorest site, respectively. Therefore, if we manage forests for carbon or forest products, intensive management practices will substantially enhance plantation productivity and stand development while site quality cannot be changed.