Estimated biomass carbon in thinned Cunninghamia lanceolate plantations at different stand-ages

Chinese fir(Cunninghamia lanceolate[Lamb.]Hook.)is a fast-growing species which is not only important as a timber-supplier,but also as an available sink for carbon(C)storage in biomass.Stand age and density are two critical factors that can determine tree C sequestration as interrelated drivers through natural self-thinning.C.lanceolate were planted using 1-year-old bare-root seedlings at the initial density of 1800 stems ha^(-1)in a 15-ha montane area of Hunan Province,China in 1987.The plantation was thinned twice 10 and 20 years after planting to leave trees of437.5±26.6,675.0±155.2 and 895.8±60.1 stems ha^(-1)as low,medium,and high densities,respectively.Tree height and diameter at breast height(DBH)were measured every2 years beginning from 23 years(2009)to 31 years(2018)after establishment,timber volume(TV)and biomass C were estimated accordingly.We did not find any interactive effect of age and density on any variables except for height.Both TV and biomass C increased with stand age or decreased in higher densities.The allometric heightDBH relationship can be fitted by an exponential risingto-maximum model with higher maximum value over time.The decline of biomass C along density fit with the inverse first-order polynomial model which indicated that at least1300-1500 stems ha^(-1)may be needed to maximize TV and biomass C for a longer term over 20 years.Therefore,to control the density to a reasonable level,over 1300 stems ha^(-1)in a rotation over 20 years old will be practical for tree biomass C in Chinese fir plantations.

Surface-deformation monitoring in the permafrost regions over the Tibetan Plateau,using Sentinel-1 data

Differential Interferometric Synthetic Aperture Radar(D-In SAR) has been widely used to measure surface deformation over the Tibetan Plateau. However, the accuracy and applicability of the D-In SAR method are not well estimated due to the lack of in-situ validation. In this paper, we mapped the seasonal and long-term displacement of Tanggula(TGL) and Liangdaohe(LDH) permafrost regions with a stack of Sentinel-1 acquisitions using the Small Baseline Subset In SAR(SBAS-In SAR) method. In the TGL region, with its dry soils and sparse vegetation, the In SAR-derived surface-deformation trend was consistent with ground-based leveling results; long-term changes of the active layer showed a settlement rate of around 1 to 3 mm/a due to the melting of ground ice, indicating a degrading permafrost in this area. Around half of the deformation was picked up on monitoring, in contrast with in-situ measurements in LDH, implying that the D-In SAR method remarkably underestimated the surface-deformation. This phenomenon may be induced by the large soil-water content, high vegetation coverage, or a combination of these two factors in this region. This study demonstrates that surface deformation could be mapped accurately for a specific region with Sentinel-1 C-band data, such as in the TGL region.Moreover, although the D-In SAR technology provides an efficient solution for broad surface-deformation monitoring in permafrost regions, it shows a poor performance in the region with high soil-water content and dense vegetation coverage.