Xiaoqin Cheng

Variation in biomass and carbon storage by stand age in pine (Pinus tabulaeformis) planted ecosystem in Mt. Taiyue, Shanxi, China

Forest ecosystems play dominant roles in global carbon budget because of the large quantities stored in live biomass, detritus, and soil organic matter. Researchers in various countries have investigated regional and continental scale patterns of carbon (C) stocks in forest ecosystems; however, the relationship between stand age in different components (vegetation, forest floor detritus, and mineral soil) and C storage and sequestration remains poorly understood. In this paper, we assessed an age sequence of 18-, 20-, 25-, 38-, and 42-year-old Pinus tabulaeformis planted by analyzing the vertical distribution of different components biomass with similar site conditions on Mt. Taiyue, Shanxi, China. The results showed that biomass of P. tabulaeformis planted stands was ranged from 88.59 Mg ha−1 for the 25-year-old stand to 231.05 Mg ha−1 for the 42-year-old stand and the major biomass was in the stems. Biomass of the ground vegetation varied from 0.51 to 1.35 Mg C ha−1 between the five stands. The forest floor biomass increased with increasing stand age. The mean C concentration of total tree was 49.94%, which was higher than C concentrations of ground vegetation and forest floor. Different organs of trees C concentration were between 54.14% and 47.74%. C concentrations stored in the mineral soil for each stand experienced decline with increasing soil depth, but were age-independent. Total C storage of five planted forests ranged from 122.15 to 229.85 Mg C ha−1, of which 51.44–68.38% of C storage was in the soil and 28.46–45.21% in vegetation. The study provided not only with an estimation biomass of P. tabulaeformis planted forest in Mt. Taiyue, Shanxi, China, but also with accurately estimating forest C storage at ecosystem scale.

Point pattern analysis of different life stages of Quercus liaotungensis in Lingkong Mountain, Shanxi Province, China

Quercus liaotungensis natural secondary forest is an important vegetation formation and has a large distribution area in Lingkong Mountain Nature Reserve, Shanxi Province, China. The spatial patterns of trees at different life stages give important clues about the underlying processes driving regeneration and succession of the forest. In this paper, the trees of a population were mapped, characterized and the spatial distribution patterns and spatial associations of Q. liaotungensis among different life stages (juveniles – J, premature – P, mature – M, overmature – O) were analyzed using O-ring univariate O(r) and bivariate O(subscript 12)(r) statistics. We found that: (1) Q. liaotungensis was a discontinuously regenerating population. (2) The distribution patterns of Q. liaotungensis varied at different life stages. Q. liaotungensis (J) and Q. liaotungensis (M) showed significant aggregations at scale 0–19 m and 0–23 m, respectively. Q. liaotungensis (P) exhibited significant aggregations at the majority of scales, whereas Q. liaotungensis (O) showed a random distribution pattern at most scales. (3) Intraspecific spatial association varied with tree size and scales. Negative or independent association was a dominant pattern for Q. liaotungensis at different life stages, whereas positive associations were found at small scales for only three pairs: Q. liaotungensis (J)–Q. liaotungensis (P), Q. liaotungensis (J)–Q. liaotungensis (M), and Q. liaotungensis (P)–Q. liaotungensis (M).

Response of soil organic carbon and nitrogen to nitrogen deposition in a Larix principis-rupprechtii plantation

Plant growth and ecosystem production are limited by nitrogen (N), however, the mechanisms of N limitation in terrestrial carbon (C) sequestration in soil remains unclear. To examine these mechanisms N was deposited at rates of 0, 50, 100, and 150 kg N ha−1 yr−1 for two years in a subalpine Larix principis-rupprechtii plantation. Soil C and N components were measured three times encompassing the entire growing season (spring, summer, and autumn) in the second year of the experiment. Results showed that N-deposition affected soil organic carbon (SOC) in the upper soil layer (0–10 cm) especially in the summer season. Dissolved organic carbon (DOC) played the key role in C loss under the high-N treatment (p < 0.01) with higher N-deposition significantly increasing both DOC and DOC/SOC in summer (p < 0.01). In the summer season when there was sufficient precipitation and higher temperatures, the average DOC across all treatments was higher than spring and autumn. The active C components contributed to SOC sequestration in low and medium N- treatment and DOC, DON dynamics in summer were responsible for the C and N pool loss under the high N-treatment.

Dynamics of nitrogen and active nitrogen components across seasons under varying stand densities in a Larix principis-rupprechtii (Pinaceae) plantation

Changes in the concentration of soil nitrogen (N) or its components may directly affect ecosystem functioning in forestry. Thinning of forest stands, a widely used forestry management practice, may transform soil nutrients directly by altering the soil environment, or indirectly by changing above- or belowground plant biomass. The study objectives were to determine how tree stem density affects the soil N pool and what mechanisms drive any potential changes. In this study, N and its active components were measured in the soil of a Larix principis-rupprechtii plantation across two full growing seasons, in 12 (25 × 25 m) plots: (low thinning, removal of 15% of the trees, three plot repetitions), moderate thinning (MT) (35% removal) and heavy thinning (HT) (50% removal) and no thinning control. Environmental indices, like the light condition, soil respiration, soil temperatures, and prescription, were measured in the plots also. Results indicated that soil total nitrogen (STN) was affected by tree stem density adjustments in the short-term; STN generally increased with decreasing tree stem density, reaching its highest concentration in the MT treatment before decreasing in HT. This pattern was echoed by the DON/STN ratio dissolved organic nitrogen (DON) under MT. A lower DON/STN was measured across the seasons. Microbial biomass nitrogen (MBN) and the SOC/STN (soil organic carbon (SOC)) ratio and density treatments influenced MBN concentration and inhibited SOC/STN. MT tended to accumulate more STN, produce lower DON/STN and had a generally higher microbial activity, which may be partly ascribed to the higher MBN value, MBN/STN ratio and lower DON/STN. The water conditions (soil moisture), light and soil temperatures could partly be responsible for the N pool dynamic in the different density treatments.

Effect of intraspecific competition on biomass partitioning of Larix principis-rupprechtii

ABSTRACT It is acknowledged that trees biomass allocation in response to environmental conditions. However, it remains poorly understood what strategies of plant biomass allocation with inter- and intraspecific interactions of tree species in forest stands. Such information is important for revealing strategies of plant biomass allocation with plant competition. To address this problem, a study was conducted in Larix principis-rupprechtii plantations to evaluate the impact of plant competition on plant biomass allocation in Shanxi Province, China. We measured a competition index (CI), stem, branch, foliage, and root biomass as well as element content (Carbon (C), Nitrogen (N), Phosphorus (P), Potassium (K)). Stem-foliage ratio (S/F), aboveground–belowground biomass ratio (T/R), average annual increment of biomass (AAB), height (AAH), and DBH (AAD) were calculated. The study found that the competition intensity of neighboring trees was closely related to the partitioning of biomass. Our results demonstrated that competition pressure of neighboring trees was a crucial factor to drive and regulate the distribution of biomass. Predicting biomass allocation–competition relationships could represent a supportive method for improving management of Larix principis-rupprechtii plantations in Mountain Taiyue areas.