Biomass Partitioning Of Lacebark Pine And It’s Tree-ring Growth In Relation To Climatic Factors

Forests play an important role in carbon (C) exchange between the atmosphere and the terrestrial biosphere, and store more C per unit area than any other terrestrial ecosystem. Therefore afforestation/reforestation may act as an effective measure to mitigate elevated atmospheric CO2concentrations. Information on tree biomass is essential in the sustainable ecosystem management and estimation of C pools. There is therefore a continuing need for accurate information on forest biomass, the capacity of forests to sequester C and the relationship between forest growth and climate factor. Accurate data on biomass accumulation and partitioning are crucial for many ecological applications, from forest management to global carbon accounting. We investigated in an age-sequence of secondary lacebark pine (Pinus bungeana Tucc. et Endl.) forests (16-,35-,50-, and68-year-old) in western China, to understand the pattern of biomass partitioning, C and N pools during stand development, to develop allometric equations, to build climate factor-treering-biomass model and to predict the biomass, C and N pools under global warming scenarios. The main results showed that:(1) With stand ageing, biomass in all tree components of lacebark pine increased. The mean biomass of each of tree component increased steadily as the stand aged. The average tree growth rate increased with stand age, being1.91,4.72,6.16and9.75kg tree-1year-1for the16-,35-,50-, and68-year-old stand, respectively. The ratio of below-to aboveground biomass (～0.28) was, independent of stand age. The pattern of biomass distribution for different components of the tree was in the order of stem wood> branch> root> foliage> stem bark> fine root.(2) Power equation is the best model for predicting the biomass of lacebark pine components. Compared to DBH-H allometric equations, the DBH-only equations performed slightly better and are much more efficient to apply.(3) Total tree biomass demonstrated a rapid increase from the young stand to the mature stand, from47.96t ha-1for the16-year-old stand to299.23t ha-1for the68-year-old stand. The forest ecosystem biomass increased from54.13t ha-1in the16-year-old stand to313.73t ha-1in the 68-year-old stand. The understory biomass increased in earlier stages of stand development and then declined in later stages.(4) C concentrations of individual tree components varied conservatively from49to52%over stand age but N concentrations differed significantly among components and remained constant across stand ages, ranging from0.21to1.55%, suggesting a constant C concentration of49.62%for C and0.43%for N conversion in modeling.(5) Mineral soil organic C and N amounts decreased with increasing soil depth in all stands. Soil C and N concentrations in the younger stands tended to be lower than that in the older stands. Approximately60%of mineral C and N were stored within the upper20cm soil layer.(6) Ecosystem C (93.38～240.34Mg C ha-1) and N (6.60～8.63Mg N ha-1) of lacebark pine increased with stand age. However, the changes in C and N stocks during stand development showed the reverse U-shaped pattern for understory and the U-shaped pattern for mineral soil. Mineral soil was the dominant N pool for all stands (79-96%) and was 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, but that of mineral soil decreased, with stand age.(7) The relationship between radial growth of lacebark pine and climate factors was analyzed and the following model was built: RWI=0.277-0.029×TmaxC3+0.058×TmeanP9, where RWI is the index of tree-ring, TmaxC3the mean temperature in current March and TmeanP9the mean temperature in previous September. Assuming a future temperature increase of1.4,2.7and4.0°C the radial growth of lacebark pine was predicted to increase by4.5%,8.6%and12.7%, respectively. The biomass of lacebark pine would increase by11.9%～32.2%,6.1%～25.4%,11.8%～32.2%and5.9%～25.2%for the16-,35-,50-, and68-year-old stand, respectively.