Carbon sequestration of mature black locust stands on the Loess Plateau, China

Abstract

In Northwestern China, the carbon fixing capacity of black locust (Robinia pseudoacacia) has been questioned because of its slow growth following the return of unproductive farmland to forest. To explore the effects of stand age on the carbon sequestration potential of R. pseudoacacia in a semi-arid, ecologically fragile area, parameters related to carbon fixation were investigated in plots of three stand ages (5, 10, and 25 years). Each plot was divided into four subsystems: R. pseudoacacia, understory vegetation, litter, and soil, and the carbon stored capacity of each subsystem was estimated. The organic carbon density of R. pseudoacacia, understory vegetation, and litter ranged from 3.4-16.8% and increased gradually with increasing stand age. Soil organic carbon increased with increasing stand age and accounted for 83.2-96.6% of the total carbon stored. Soil CaCO 3 content also increased with increasing soil depth and stand age. Because total plant and soil carbon storage increased with increasing age of R. pseudoacacia stands, the 25-year-old R. pseudoacacia community had the highest carbon fixation capacity, which was substantial even in this arid region. 116Vol. 61, 2015, No. 3: 116-121 Plant Soil Environ.doi: 10.17221/931/2014-PSE Premature senescence in R. pseudoacacia resulting from severe soil moisture deficit is of particular concern, as this species is the most widely used for afforestation. In addition, there are few data on the relationship between carbon fixation and stand age or on the carbon fixation capacity of man-made forests in the Loess Plateau. In this study, R. pseudoacacia plots in stands of three ages (5, 10, and 25 years) were selected in the Zhifanggou valley and each plot was divided into four subsystems: R. pseudoacacia, understory vegetation, litter, and soil. Our aim was to compare carbon storage in the plots and to estimate the carbon fixation capacity of R. pseudoacacia forests that were established on retired farmland. We also examined how carbon sequestration in R. pseudoacacia forests on arid retired farmland varies with stand age. MATERIAL AND METHODSStudy site. The study was conducted in the Zhifanggou valley (36°43'34''N, 109°15'28''E) in the Ansai county, Shaanxi province, in the Loess Plateau hinterland, China. Mean annual temperature and precipitation are 9.4°C and 465.2 mm, respectively. R. pseudoacacia was planted as the major forest type on gently sloped retired farmland in 1984, 1999, and 2004.Biomass measurement. Plots with the same aspect and slope containing 5, 10, and 25-yearold R. pseudoacacia trees were selected for biomass investigation. Each plot contained a grid of R. pseudoacacia with 21 columns and 24 rows. The columns and rows were spaced 3 m apart; tree density was 0.145 individuals/m 2 . In each plot, three 10 m × 10 m quadrats were established, and the height and diameter at breast height (DBH) of each R. pseudoacacia tree was recorded and used to calculate average DBH and tree height. These averages were used to calculate R. pseudoacacia ...

Assessing Black Locust Biomass Accumulation in Restoration Plantations

“…In fact, our results correspond to the V th growth class, the first of the two poorest classes, of the Hungarian black locust yield and biomass tables [46]. Similarly low was the above ground biomass estimated by Wang et al [47] for 5 to 25 years old black locust restoration plantations on degraded agricultural lands at the Loess Plateau in China, which ranged from 4.1 to 27.5 t ha −1 Deadwood represented 6 to 10% of the standing biomass at the studied plantations. Under unfavorable conditions, black locust cannot withstand shade, resulting in high self-thinning [6]; thus, the amount of dead wood is expected to increase in the future, considering that the studied plantations have not been managed and thinned to date.…”

Carbon sequestration and soil nitrogen enrichment in Robinia pseudoacacia L. post-mining restoration plantations

“…This is resulted by the increase in above-ground biomass with age, previously indicated by Tziaferidis et al (2022) for the same sites. A similar positive age effect is reported for R.pseudoacacia restoration plantations of the same age range (5-25 years; Zhang et al, 2010;Wang et al, 2015), as well as for younger plantations (Böhm et al, 2011). Approximately 2.44 t ha −1 yr −1 C are stored annually in the above-ground biomass of the studied black locust plantations (Table 2), consistent to the findings in 14-years-old black locust (Quinkenstein et al, 2011).…”

“…Still, it is important to note that all abovementioned studies refer to young plantations (<25 years old) that have not been subjected to any forest management practices yet. Black locust reaches maturity at the age of 25-30 years, while growth and ABG production is levelling off after that age, as observed at other degraded sites (Wang et al, 2015;Guo et al, 2022) and at our study site (Manolopoulos et al, 2022). Based on these, we assumed an average age for stand maturity at 27.5 years and we estimated that the current total above-ground biomass of the plantations (28.5 t ha −1 ; Figure 2) at a mean age of 16 years, represents less than 40% of the total AGB at maturity, which is expected to reach at least 80.0 t ha −1 if the linear increase with time (Figure 4A) continues until that age.…”

“…Based on the DBH distribution of the black locust trees, five DBH classes were identified: 0-5, 5-10, 10-15, 15-20, and >20 cm. Given that the carbon content in tree wood is rather stable (Wang et al, 2015;Ma et al, 2019;Bārdule et al, 2021;Martin et al, 2021), five samples from stem disks at breast height (1.3 m) representative of the five DBH classes of the plantations were selected for elemental analysis to determine their carbon content.…”

Environmental Drivers of Gross Primary Production and Evapotranspiration at a Robinia pseudoacacia L. Restoration Plantation

“…The studied plantation grows on a flat area and is approximately 20 years old with a mean tree height of 13.5 m. Based on these traits, tree height has peaked [24] and the stand is close to reaching maturity and maximum growth [42][43][44]. The understorey vegetation consists of perennial grasses, dominated by Cynodon dactylon Pers., with a significant contribution to the phenology and fluxes for the period before leaf expansion and after leaf fall [9].…”