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Chen W.,Beijing Forestry University | Jia X.,Beijing Forestry University | Zha T.,Beijing Forestry University | Zha T.,Chinese Institute of Green Carbon | And 8 more authors.
European Journal of Soil Biology | Year: 2013

We investigated how soil temperature (Ts) and water content (VWC) affect soil respiration (Rs) in a mixed urban forest. Continuous half-hourly measurements of soil surface efflux were made during the period March-December 2011 in a mixed forest in Beijing Olympic Forest Park, China. Daily mean Rs varied from 0.28 to 3.62 μmol CO2 m-2 s-1. Over this period of record, Rs increased exponentially with rising temperature; a Q10 model with 5-cm soil temperature as the independent variable explained 76% of the variation in half-hourly Rs. The temperature sensitivity of respiration (Q10) varied seasonally, being greater in fall than in spring, suggesting seasonal hysteresis in the Rs-Ts relationship. During the summer months (June-August 2011), when Ts was high and had relatively little day-to-day variation, Rs was hyperbolically related to VWC, increasing with increasing VWC up to a VWC threshold of 0.17 m3 m-3, but decreasing with increasing VWC above the threshold. A bivariate Q10-hyperbolical model, which incorporated both Ts and VWC effects, improved the performance of Rs simulation in summer, but not annually. These results indicated that Rs was dominantly controlled by soil temperature over the annual cycle. However, VWC served as the dominant control in summer. The annual total of Rs estimated from the Q10 model was 475 g C m-2. We recommend the use of the Q10 model for predicting annual soil respiration due to its good performance and physiological basis. © 2012 Elsevier Masson SAS.

Cao J.,Beijing Forestry University | Cao J.,Chinese Academy of Forestry | Wang X.,Beijing Forestry Carbon Administration | Wang X.,Chinese Institute of Green Carbon | And 4 more authors.
Ecological Research | Year: 2012

The pattern of carbon (C) allocation across different stages of stand development of Chinese pine (Pinus tabulaeformis) forests is poorly documented. In order to understand the effects of stand age on the C pool of the Chinese pine forest ecosystem, we have examined the above- and belowground C pools in three differently aged stands of Chinese pine in the northern mountains of Beijing, China, by plot-level inventories and destructive sampling. Our results suggest that tree branch and foliage biomass should be estimated by age-specific equations. Reasonably accurate estimates of tree stem, tree root, aboveground, and total tree biomass in a Chinese pine forest at different development stages were obtained using age-independent allometric equations from tree diameter only. The ratio of belowground to aboveground tree biomass was relatively constant with stand aging, remaining around 21 %. The contribution of aboveground tree biomass C increased from 21 % of the total ecosystem C in a 25-year-old stand to 44 % in a 65-year-old stand, subsequently falling to 41 % in a 105-year-old stand, while the contribution of mineral soil C decreased from 64 % of the total ecosystem C in 25-year-old stand to 38 % in a 65-year-old stand, subsequently increasing to 41 % in a 105-year-old stand. The C stock of the total ecosystem and its aboveground tree, tree root, forest floor, and mineral soil components continuously increased with stand ageing, whereas the C stock of the understory showed a declining trend and contributed little to the total site C pool. © 2012 The Ecological Society of Japan.

Shi Z.,Chinese Academy of Forestry | Shi Z.,Chinese Institute of Green Carbon | Gao J.,Nanjing Institute of Environmental Sciences | Yang X.,Chinese Academy of Forestry | And 5 more authors.
Journal of Food, Agriculture and Environment | Year: 2012

Tree radial growth is sensitive to climate change. A tree-ring width chronology of Mongolian pine (Pinus sylvestris var. mongolica) in Hulunbuir, Inner Mongolia, China, was developed in this paper. There was consistent variance in the ring-width of different samples and they were suitable for studying dendroclimatology. The relationships between ring width and climatic factors were evaluated using correlation and response function analyses. Radial growth of Mongolian pine in sandy lands was negatively related to the average monthly temperature and monthly maximum temperature, with significant negative correlations in April and the growing season (June-September) (p<0.05). Tree-ring width significantly positively correlated with monthly precipitation during May-August, and with the Palmer Drought Severity Index (PDSI) from the previous October to the current September, most obviously during May. The response function analysis showed that the chronology was significantly correlated with the average temperature during June-July, the amount of precipitation during May-July and the previous October, and is positively related to the PDSI during May-July. The growth of Mongolian pine in Hulunbuir Sand Land is limited by both temperature and precipitation, but the influence of temperature on tree-ring growth is less than that of precipitation. The relationship between radial growth and climate factors can be described as precipitation sensitive. We also found that a 50% increase in annual precipitation would lead to a 45.9% increase in radial growth, and an increase of 1.0°C in June-July mean temperature would lead to a 13.21% decrease in tree radial growth.

Chen W.J.,Beijing Forestry University | Li C.Y.,Beijing Forestry University | He G.M.,Beijing Forestry Carbon Administration | He G.M.,Chinese Institute of Green Carbon | And 5 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2013

The area of urban forests and green-land is expanding dramatically across China in order to face rapid urbanization. Urban green-land ecosystems with plantations as their main vegetation type, have the great potential to sequestrate atmospheric carbon. Continuous measurements of CO2 flux were made using eddy covariance technique from December 2011 to November 2012 in a mixed forest in Beijing Olympic Forest Park to quantify the seasonal dynamics of net ecosystem CO2 exchange (NEE) and its responses to environmental factors. Gross ecosystem productivity (GEP), ecosystem respiration (Re), and net ecosystem productivity (NEP = -NEE) showed strong seasonal pattern, with CO2 uptake dominating during the growing season from April to November, and a respiratory release of CO2 dominating during the non-growing season. The carbon flux was influenced by photosynthetically active radiation (PAR), water vapor pressure deficit (VPD) and air temperature (Ta). In growing season, daytime net ecosystem carbon exchange (NEEday) increased with increasing PAR. The ecosystem quantum yield (α) and maximum photosynthesis (Amax) showed an apparent seasonal pattern, both peaking in July. VPD also affected NEE through its direct effect on photosynthesis. NEE increased with the increasing PAR up to a threshold of 1200 μmol·m-2·s-1, then decreased with increasing PAR above this threshold. GEP, Re and NEP were all influenced by Ta, but responded differently. Re increased exponentially with air temperature (Ta), with the temperature sensitivity (Q10) being 2.5. GEP also increased with Ta. This differential response of GEP and Re determined the relationship between NEP and Ta. NEP decreased with increasing Ta when Ta < 10.0 °C, but increased when Ta > 10.0 °C. NEEday increased with PAR. The ecosystem quantum yield (α) and maximum photosynthesis (Amax) showed an apparent seasonal pattern, both peaking in July with the value of 0.083 μmol CO2 /μmol PAR and 29.46 μmol·m-2·s-1, respectively, and reaching a minimum in November with the value of 0.017 μmol CO2/μmol PAR and 4.16 μmol·m-2·s-1. The predicted annual totals of GEP, Re and NEP were 1192, 1028 and 164 g C/m2, respectively. The present results could contribute to the carbon budget of urban ecosystems, and help make carbon-oriented management strategies for sustainable urban development under global climate change.

Shi Z.,Chinese Academy of Forestry | Shi Z.,Chinese Institute of Green Carbon | Xu D.,Chinese Academy of Forestry | Yang X.,Chinese Academy of Forestry | And 4 more authors.
Journal of Food, Agriculture and Environment | Year: 2012

Eucalyptus plantations were established rapidly over large areas of the world raising concerns over water resources and potentially negative ecohydrological effects. In this paper the impacts of Eucalyptus plantations on ecohydrology were summarized. In general, transpiration rates ranged from 0.5 to 6.0 mm per day and were affected by leaf area index (LAI), soil water, stand age, and species conversion. Catchment water yield increased after deforestation due to clearcutting, thinning, or fire, and declined after afforestation or reforestation. Water yield of catchments declined for the first 20-30 years after planting or regeneration of Eucalyptus as trees matured and closed canopies; water yield returned slowly to normal levels as stem density and LAI of Eucalyptus forests declined. Eucalyptus plantations may extract water from shallow groundwater sources in arid and semiarid areas, and in some tropical wet areas during drought years or seasons.

Chen J.,Beijing Forestry University | Liu J.,Beijing Forestry University | Yang X.,Chinese Academy of Forestry | Wang Y.,Chinese Academy of Forestry | And 2 more authors.
Journal of Food, Agriculture and Environment | Year: 2011

The western Ordos Plateau, China, is characterized by shrub species richness. Serious desertification in the western Ordos is threatening some shrub species with high conservation value. We used spatial indices and spatial point pattern analysis methods to investigate several aspects of three western Ordos desert shrub communities. We examined the general spatial patterns of the whole community and of each pair of individual shrub species, and we investigated the interactions of each pair of individual shrub species and of each pair of physiological groups. In the three communities studied, general aggregated patterns were found for the whole community and for each shrub species. These patterns can be explained by the patchy desert environment and by low seed production and dispersal. In this harsh desert environment, the positive interaction between gravel-tolerant and salt-tolerant shrub species in the three communities results in a relatively stable community with a positive successional process. Sand-tolerant shrub species, encroaching on this region from the peripheral desert, are in competition with gravel-tolerant or salt-tolerant shrub species. The formation and development of Nitraria tangutorum sand mounds poses a major threat to gravel-tolerant and salt-tolerant shrub species and to the communities they form. This study offers insights into the aggregated patterns of individual species, into the interactions among pairs of shrub species and among pairs of physiological groups, and into the degradation of endangered ecosystems. This degradation is associated with the loss of key shrub species in the three desert shrub ecosystems. These insights will be useful for implementing protective strategies for endangered shrub species in this region.

Li C.,Beijing Forestry University | Zha T.,Beijing Forestry University | Zha T.,Chinese Institute of Green Carbon | Liu J.,Beijing Forestry University | Jia X.,Beijing Forestry University
Forestry Chronicle | Year: 2013

Information about carbon (C) and nitrogen (N) pools is lacking for lacebark pine forests. Ecosystem C (93.38-240.34 Mg C ha-1) and N (6.60-8.63 Mg N ha"1) increased with stand age. This pattern applied to all tree components and litter. However, changes in C and N stocks during stand development showed the reverse U-shaped pattern for the understory and for mineral soil. Mineral soil was the dominant N pool for all stands (79%-96%) and the largest C pool in younger stands (53%-71%). Trees were the largest C pool in older stands (55%-62%). The contribution of trees to ecosystem C and N pools increased with stand age but that of mineral soil decreased with stand age. These findings contribute to the development and evaluation of forest C and N storage models and to forest management for enhancing C. sequestration.

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