Self-thinning lines and allometric relation in Chinese fir(Cunninghamia lanceolata) stands

We calculated a self-thinning exponent of 1.05 for tree mass using the 3/2 power equation in 93 Cunninghamia lanceolata plots.According to Weller’s allometric model,the self-thinning exponent for tree mass was calculated as 1.28 from the allometric exponents h and d.The both self-thinning exponents were significantly lower than 3/2.The self-thinning exponent of organs was estimated to be 1.42 for stems,0.93 for branches,0.96 for leaves,1.35 for roots and 1.28 for shoots,respectively.The self-thinning exponent of stem mass was not significantly different from 3/2,whereas thinning exponents of trees,branches,leaves and roots were significantly lower than 3/2.The stand leaf mass and stand branch mass were constant regardless of the stand density.The scaling relations among branch,leaf,stem,root and shoot mass（MB,ML,MS,MR and MA,respectively） showed that MB and ML scaled as the3/4 power of MS,whereas MS or MA scaled isometrically with respect to MR.

Foliar C/N stoichiometry in urban forest trees on a global scale

Foliar C/N stoichiometry is an indicator of geochemical cycling in forest ecosystems,but the driving changes for its response to urbanization at the wide scale is not clear.In this study,data on tree-leaf C and N stoichiometry were collected in papers from across 105 tree species from 82 genera and 46 families.The foliar C/N of urban forest trees varied among different climate zones and tree taxonomic variation and tended to be higher in trees of urban forests near the equator and in eastern regions,mainly driven by lowered foliar N concentration.Neither the foliar C concentration nor foliar C/N for trees of urban forests was statistically higher than those of rural forests.For variation by taxonomic classification,C_4 species Amaranthus retroflexus and Chenopodium ambrosoides(Amaranthaceae) had lower foliar C/N than did other species and families.Myrsine guianensis(Primulaceae) and Myconia fallax(Asteraceae) had the highest foliar C/N.Therefore,urbanization has not caused a significant response in forest trees for foliar C/N.The change in foliar N concentration was globally the main force driving of the differences in foliar C/N for most tree species in urban forests.More work is needed on foliar C/N in trees at cities in polar regions and the Southern Hemisphere.

Variation of carbon and nitrogen stoichiometry along a chronosequence of natural temperate forest in northeastern China

Aims Carbon(C)and nitrogen(N)stoichiometry contributes to under-standing elemental compositions and coupled biogeochemical cycles in ecosystems.However,we know little about the temporal patterns of C:N stoichiometry during forest development.The goal of this study is to explore the temporal patterns of intraspecific and ecosystem components’variations in C:N stoichiometry and the scaling relationships between C and N at different successional stages.Methods Along forest development in a natural temperate forest,northeastern China,four age gradients were categorized into ca.10-,30-,70-and 200-year old,respectively,and three 20 m×20 m plots were set up for each age class.Leaves,branches,fine roots and fresh litter of seven dominant species as well as mineral soil at depth of 0-10 cm were sampled.A Universal CHN Elemental Analyzer was used to determine the C and N concentrations in all samples.Important Findings Intraspecific leaf C,N and C:N ratios remained stable along forest development regardless of tree species;while C,N concentrations and C:N ratios changed significantly either in branches or in fine roots,and they varied with tree species except Populus davidiana(P<0.05).For ecosystem components,we discovered that leaf C:N ratios remained stable when stand age was below ca.70 years and dominant tree species were light-demanding pioneers such as Betula platyphylla and Populus davidiana,while increased signifi-cantly at the age of ca.200 years with Pinus koraiensis as the dom-inant species.C:N ratios in branches and fresh litter did not changed significantly along forest development stages.C concentrations scaled isometrically with respect to N concentrations in mineral soil but not in other ecosystem components.Our results indicate that,leaf has a higher intraspecific C:N stoichiometric stability compared to branch and fine root,whereas for ecosystem components,shifts in species composition mainly affect C:N ratios in leaves rather than other components.This study also demonstrated that C and N remain coupled in mineral soils but not in plant organs or fresh litter during forest development.

Relationships among the Stem,Aboveground and Total Biomass across Chinese Forests

Forest biomass plays a key role in the global carbon cycle. In the present study, a general allometric model was derived to predict the relationships among the stem biomass Ms, aboveground biomass MA and total biomass MT, based on previously developed scaling relationships for leaf, stem and root standing biomass. The model predicted complex scaling exponents for MT and/or MA with respect to Ms. Because annual biomass accumulation in the stem, root and branch far exceeded the annual increase in standing leaf biomass, we can predict that MT ∝MA ∝ Ms as a simple result of the model. Although slight variations existed in different phyletic affiliations （i.e. conifers versus angiosperms）, empirical results using Model Type Ⅱ （reduced major axis） regression supported the model＇s predictions. The predictive formulas among stem, aboveground and total biomass were obtained using Model Type I （ordinary least squares） regression to estimate forest biomass. Given the low mean percentage prediction errors for aboveground （and total biomass） based on the stem biomass, the results provided a reasonable method to estimate the biomass of forests at the individual level, which was insensitive to the variation in local environmental conditions （e.g. precipitation, temperature, etc.）.