Size–mass allometry and biomass allocation of two larch species growing on the continuous permafrost region in Siberia

Abstract

We examined size–mass allometry and biomass allocation of two larch species ( Larix gmelinii (Rupr.) Rupr. and Larix cajanderi Mayer) that grow on the continuous permafrost regions in Siberia. Sample tree data (total n = 27) gathered from four mature stands (>100 years old) were employed for analysis. First, to determine good size predictor of biomass, site-specific allometric relationships (log-linear equation form) were derived between dry mass of four components (stem, branch, needle and coarse root; ≥5 mm in diameter) and seven size variables; stem diameters (breast height, 30 cm height and crown base), sapwood areas (breast height and 30 cm height), and two combined-variables (tree height × diameter). For all components, site-specific allometric equations based on breast-height diameter ( D) always gave high correlations as those using other size variables. However, between-stand comparisons of the D-base site-specific allometry indicated that size dependency (i.e., regression slope) differed for stem mass. Besides, needle and coarse root mass for a given size (i.e., regression intercept) differed significantly among the four stands. These facts implied that D-base regression model was reliable for biomass estimation by site-specific allometry, but was not suitable for developing general (i.e., site-common) allometry. Second, to examine carbon allocation pattern, we estimated each stand biomass by applying corresponding site-specific D-base allometry. Stand total biomass ranged from 8.6 to 33.1 Mg ha −1, and aboveground-total/coarse root biomass ratio (i.e., T/ R) ranged from 1.5 to 2.6. The variation was mainly due to trade-offs between stem and root biomass. Average T/ R was about 2.3 that was calculated for some reported L. gmelinii and L. cajanderi stands ( n = 16), including our four stands. This average T/ R was extremely small in comparison to that (5.1) of Scots pine ( Pinus sylvestris L.) stands on the non- or discontinuous permafrost regions in Siberia. This finding strongly suggested that the two Larix species invested annual carbon gains largely into root growth. We discussed its ecological implications in relation to stand structure and permafrost soil-N conditions in the larch taiga ecosystem.