昌邑海洋保护区柽柳灌丛枝干生物量估算方法

Modeling stem and branch biomass of Tamarix spp.in the marine protected area in Changyi,China

柽柳属植物(Tamarix spp.)是我国沙漠干旱地区和滨海盐渍化地区的重要树种,具有较高的生态价值。在滨海地区,柽柳是一种典型灌木,分枝多、可塑性高,以往对柽柳生物量模型的研究,多以直立枝基径和长度作为自变量,此方法虽有较高精度,但工作繁琐。因此,研究以昌邑海洋生态保护区的柽柳林为对象,分别以株高冠幅组合、冠幅为自变量,以一元线性、幂函数、二次多项式等形式建立柽柳枝干鲜重的回归方程,并进行验证比较,目的是建立准确高效且适合滨海地区的柽柳生物量估测方法。结果表明:(1)对滨海地区柽柳林,冠幅和株高是较好的测树因子,以此建立回归方程,简便易行、准确可靠,应用前景较好;(2)综合方程的准确性和稳定性,无论以冠幅株高组合,还是单以冠幅作为自变量,均确定幂函数形式的回归方程为最优,经验证与实测值的偏差分别为-2.22%和2.92%;(3)基于冠幅的方程虽预测精度稍差,但由于冠幅面积可从高分辨遥感影像上直接提取,因而有极好应用前景;(4)R2~是评价模型优劣的重要标准,但仅以此为标准并不严谨,还需结合其他验证方法;(5)测区柽柳的株高、冠幅、鲜重的均值分别为(215.2±41.4)cm,(2.49±2.21)m^2,(4.15±5.80)kg,建议通过人工管理的方式提高林分质量。

Tamarix spp. are woody plants that are widely distributed throughout the world, and they have ecological importance in the arid and salinized areas of China. However, methods for modeling the biomass of Tamarix spp. and other multi-stemmed shrubs are inadequate. Diameter measurements （such as diameter at breast height） are frequently used and have proved to correlate well with biomass ; however, such methods are difficult to apply for Tamarix because of its irregular growth patterns and multiple stems. Modeling shrub biomass has received more attention in recent years, and several studies have indicated that for shrubs shaped like cylinders or cones, the crown area was significantly correlated with shrub biomass. Considering the constraints of diameter measurements for Tamarix spp., we modeled Tamarix spp. biomass using crown width and height in Changyi Marine Protected Area （Shandong Province, China; 37°06′15″N, 119°22′00″E）. The area containing Tamarix spp. （ T. chinensis and T. austromongolica ） was approximately 20.7 km^2. In February 2014, nine sample plots （ 30 m × 30 m） were selected, and three embedded plots （ 5 m × 5 m） were placed randomly in each plot. Prior to harvesting, the height （H）, basal diameter （BD）, and crown area （C） of 247 Tamarix individuals in the embedded plots were measured. Fresh weights （FW） were collected after harvesting. At the time of sampling, the trees had no foliage, and thus the FW included only stems and branches. One hundred and eighty-nine individuals were selected randomly to establish the regression equations, while the remaining 58 individuals were used for testing the accuracy of these equations. CH （the product of C×H） and C were chosen as independent variables, and the regression equations were established in the form of linear, power-law, and quadratic polynomials.The equations based on CH were FW = 0.856 × （CH） - 0.879 （R^2= 0.884, F = 1428.5）, FW = 0.403 × （CH） 1.226 （n2= 0.900, F = 1396.1）, and FW = 0.010 × （CH） 2 ＋ 0.562 ×（C/T） ＋ 0.114（R^2= 0.903, F = 875.7）, whereas the equations based on C were FW = 2.462 × C - 1.893 （R^2= 0.825, F = 881.8）, FW= 0.900 × C^1.440 （R^2= 0.861, F = 966.3）, andFW= 0.144 × C2 ＋ 1.007 × C ＋ 0.127 （R^2= 0.864, F = 600.7）. Although quadratic polynomial equations had higher R^2 values, the power-law functions performed best in the test, as they had deviations of -2.22% （CH） and 2.92% （C）. Furthermore, because the power-law function is the most widely used allometric equation, we recommend establishing regression equations using power-law functions in this area. As tree crown properties can be reconstructed using high-resolution satellite data, allometric equations that use C as the only independent variable may provide a more cost-efficient way of monitoring, reporting, and verifying the carbon stocks of Tamarix spp. The mean values of H, BD, C, and FW in the study area were （215.2 ± 41.4）cm, （4.2 ± 1.9） cm, （ 2.49 ± 2.21 ） m^2, and （ 4.15 ± 5.80） kg （ mean ± SD） , respectively ; therefore, artificial management should be enhanced to improve the stand quality.