帽儿山温带落叶阔叶林通量塔风浪区生物量空间格局

采用网格法在帽儿山温带落叶阔叶林通量塔风浪区(1500 m×400 m)内设置直径为20 m的圆形样地106个,运用地统计学方法和回归分析法研究了乔木生物量空间格局及其驱动因子。结果表明,风浪区总生物量平均值为153.63 Mg/hm~2,变异系数为37.89%;根冠比平均0.25(变化范围0.18—0.36)。总生物量、地上生物量和地下生物量的空间自相关显著,半方差模型的结构比分别为0.50、0.61和0.50,空间异质性尺度分别为276 m、198 m和375 m。硬阔叶林与杂木林的生物量组分和根冠比差异均不显著,但以胸高断面积(BA)为协变量,生物量组分差异显著。硬阔叶林和杂木林生物量组分与BA均呈极显著的线性正相关关系,BA可以解释总生物量和地上生物量空间变异的85%以上,表明局域尺度上BA可作为森林乔木生物量的预测因子。两种林型的生物量与优势高呈对数线性关系,但相关程度较低(R~20.41)。杂木林的各生物量组分与坡度显著正相关,但硬阔叶林的关系不显著。帽儿山落叶阔叶林乔木生物量受BA、优势高、林型、坡度和坡向共同驱动而存在空间变异,因此在整合通量塔与地面碳汇测量时需要考虑空间异质性。

Spatial patterns of biomass in the temperate broadleaved deciduous forest within the fetch of the Maoershan flux tower

To cross-validate the accuracy of carbon flux estimates of the eddy covariance with that of the stand inventory method in temperate forests, we investigated the spatial variations in forest biomass and their driving factors within the fetch (1500 m×400 m) of the Maoershan flux tower using a geostatistics approach and regression methods.One hundred and six circular plots with diameters of 20 m were established by a 100 m×50 m grid using a total station. All of the trees with diameter at breast height (DBH) greater than 2 cm were measured in each plot. The biomass and its components were calculated based on the DBH data and the site-species-specific biomass equations developed previously. The ranges of the total, above-, and below-ground biomasses were 22.68-304.89, 17.99-245.96, and 4.69-69.25 Mg/hm², respectively, with corresponding means of 155.64, 124.17, and 31.47 Mg/hm². The root:shoot ratio (RSR) ranged between 0.18 and 0.36, with a mean of 0.25. For the total biomass, the contribution of specific species was ranked in the following order:Ulmus japonica (22.80%) > Fraxinus mandshurica (15.70%) > Betula platyphylla (15.52%) > Betula costata (7.23%) > Juglans mandshurica (6.21%) > Acer mono (6.20%), with the remaining 26.34% contributed by other species (each<5%). The coefficients of variation for the total, above-, and below-ground biomasses were 37.89%, 37.75%, 41.27%, respectively. The structural ratios of the semivariance functions for total, above-and below-ground biomasses were 0.50, 0.61, and 0.50, respectively, whereas the corresponding ranges were 276, 198, and 375 m. These data indicated a moderately significant spatial autocorrelation for the biomasses, whereas that for the RSR was week. The geostatistical mean of the total biomass density within the fetch of the flux tower (153.63 Mg/hm²) was close to the simple mean of the 106 plots, indicating the effective spatial representation of these plots. The biomass and RSR between the hardwood and mixed deciduous stands did not differ significantly (P>0.1). However, when the basal area (BA) was used as the covariate, the difference in biomass between the two forests was highly significant (P<0.001). The total and above-ground biomasses were more closely correlated with the BA (R² > 85%) than with dominant tree height (R²<41%) for both forest types. The biomass and its components were positively correlated with the slope of the terrain for the mixed deciduous (P<0.001), but was not the hardwood stand. Stepwise regressions for all data of the 106 plots indicated that BA and the dominant tree height were the first and second contributors to the variations in the total and above-ground biomasses, whereas BA and aspect were the most important in the below-ground biomass and RSR. In conclusion, the spatial patterns of biomass and its components were significant within the fetch of the Maoershan flux tower, highlighting the importance of considering spatial variation in the estimation of carbon fluxes using the eddy covariance and biometric methods. The spatial variations were significantly associated with stand basal area, dominant tree height, slope, and aspect, indicating the predictability of the variations.