辽河源不同龄组油松天然次生林生物量及空间分配特征

油松是中国暖温带区域主要的森林植被,精确计算油松天然林生物量及准确表征空间分布特征对其在固碳释氧、林木积累营养物质等方面的生态服务功能评估具有重要意义。目前,国内基本上没有进行油松天然次生林生物量及空间分配在一个年龄序列上的研究。研究的主要目的是准确估算河北省平泉县辽河源自然保护区4个龄组油松天然次生林林分各组分的生物量,并揭示生物量在空间的分配特征。在每种林分内,林下植被层(灌木和草本)和凋落物层生物量通过样地调查和全挖取样的方法计算。基于胸径(DBH)和树高(H)的异速生长方程则用于计算乔木层生物量。结果表明:(1)林分生物量大小排序为:成熟林(397.793 t/hm2)近熟林(242.188 t/hm2)中龄林(203.801 t/hm2)幼龄林(132.894 t/hm2);(2)乔木层生物量成熟林(373.128 t/hm2)近熟林(224.991 t/hm2)中龄林(187.750 t/hm2)幼龄林(119.169 t/hm2)。地上部分各组分生物量大小关系略有差异,幼龄林和近熟林为:干根枝叶干皮球果,而中龄林和成熟林则是干根枝干皮叶球果。干生物量对于各龄组乔木层生物量来说是最大的贡献者,所占比例表现为:中龄林(66.25%)近熟林(64.38%)成熟林(62.09%)幼龄林(38.41%),而贡献较小的球果则是成熟林(1.02%)幼龄林(0.88%)近熟林(0.72%)中龄林(0.53%)。根系总生物量在18.315 t/hm2(中龄林)—44.849 t/hm2(成熟林)之间,其组分生物量大小整体上表现为:根桩粗根大根细根小细根;(3)灌木层生物量成熟林(0.861 t/hm2)近熟林(0.790 t/hm2)中龄林(0.559 t/hm2)幼龄林(0.401 t/hm2),各组分生物量大小为根茎叶;(4)草本层生物量幼龄林(3.058 t/hm2)近熟林(2.017 t/hm2)中龄林(1.220 t/hm2)成熟林(1.181 t/hm2),地下部分生物量均大于地上部分;(5)凋落物层生物量成熟林(22.623 t/hm2)近熟林(14.390 t/hm2)中龄林(14.272 t/hm2)幼龄林(10.265 t/hm2),各层生物量大小为:未分解层半分解层全分解层。(6)在各层次生物量的比较中,4个龄组均表现为乔木层凋落物层草本层灌木层。其中,幼龄林乔木层生物量占89.67%、中龄林占92.13%、近熟林占92.90%,成熟林占93.80%。

Biomass and spatial distribution characteristics of Pinus tabulaeformis natural secondary forest at different age groups in the Liaoheyuan Nature Reserve, Hebei Province

P. tabulaeformis is one of the major forest vegetation species in the warm temperate zone of China. It is of great scientific value to accurately calculate the biomass of natural P. tabulaeformis forest and to characterize the spatial distribution for assessing forest ecological services in the aspects of fixing carbon and releasing oxygen, and nutrient accumulation. To date, the pattern of biomass and distribution across a chronosequence of P. tabulaeformis natural secondary forest is poorly documented. The objectives of this study were to examine the biomass and distribution of the main ecosystem components in an age sequence of four P. tabulaeformis natural secondary forest stands (young, middle-aged, immature, and mature) in the Liaoheyuan Nature Reserve of Pingquan County, Hebei Province. Within each stand, biomass of understory (including shrubs and herbs) and litter was determined from plot-level inventories and destructive sampling. The allometric equations using diameter at breast height (DBH) and height (H) have been developed to quantify (above- and belowground) tree biomass. The results are as follows. (1) The size of the stand biomass follows the order of mature (397.793 t/hm²) > immature (242.188 t/hm²) > middle-aged (203.801 t/hm²) > young (132.894 t/ hm²); (2) Biomass size of the tree layer ranks from high to low as mature (373.128 t/hm²) > immature (224.991 t/hm²) > middle-aged (187.750 t/hm²) > young (119.169 t/hm²). The order of biomass size of tree components is slightly different; young and immature forests follow the order of stem > root > branch > needle > bark > pine cone, while middle-aged and mature forests order as stem > root > branch > bark > needle > pine cone. The stem is the largest contributor to the total tree biomass, and the order of proportion is middle-aged (66.25%) > immature (64.38%) > mature (62.09%) > young (38.41%); pine cones contribute least, following the order of mature (1.02%) > young (0.88%) > immature (0.72%) > middle-aged (0.53%). The total root biomass of four stands ranged from 18.315 t/hm² for the middle-aged stand to 44.849 t/hm² for the mature stand, and the root component biomass ranks on the whole as root pile > coarse root > big root > fine root > small fine root; (3) The biomass of shrub layer orders as mature (0.861 t/hm²) > immature (0.790 t/hm²) > middle-aged (0.559 t/hm²) > young (0.401 t/hm²), and the order of organ biomass is root > stem > needle; (4) The biomass of the herb layer ranks as young (3.058 t/hm²) > immature (2.017 t/hm²) > middle-aged (1.220 t/hm²) > mature (1.181 t/hm²), and the biomass of underground portion is greater than that of the aerial parts; (5) Litter layer biomass follows the order of mature (22.623 t/hm²) > immature (14.390 t/hm²) > middle-aged (14.272 t/hm²) > young (10.265 t/hm²), and the decomposition layer > semi-decomposed layer > full decomposition layer. (6) The comparison of biomass of the four age groups at all levels shows the consequence of tree layer > litter layer > herb layer > shrub layer. Across this chronosequence, the tree layer biomass accounts for 89.67%, 92.13%, 92.90% and 93.80% of the total tree biomass for young, middle-aged, immature, and mature stands, respectively.