兴安落叶松天然林碳储量及其碳库分配特征

兴安落叶松天然林作为大兴安岭林区的主要植被类型,在森林生态系统碳循环中具有重要的作用。在大兴安岭林区选择不同林龄的兴安落叶松天然林,调查其乔木、灌草、枯落物和土壤,并结合已建立的单木异速生长方程分别计算其碳储量,以期为明确该地区碳库动态及其碳库分配特征提供参考。结果表明,兴安落叶松天然林总碳储量随林龄的增加逐渐增大,由幼龄林到过熟林分别为140.46、186.63、208.64、308.62和341.03 Mg C/hm2,整体表现为碳汇,这主要与乔木碳储量随林龄的增加逐渐增大有关;乔木碳库的变化范围为45.44—212.67 Mg C/hm2,且其占总碳储量的比例也随林龄的增加逐渐增大,由幼龄林的32.60%到过熟林的62.36%;灌草碳储量占总碳储量的比例较小,仅为0.48%—0.93%;枯落物碳库在过熟林中较多,为26.11Mg C/hm2,这与过熟林较少的人为干扰有关;土壤碳储量以幼龄林最小,成熟林最高,分别为78.06和131.93 Mg C/hm2,但这与我国其他地区天然林相比均较低,这与该地区较浅的土壤发生层有关;土壤碳储量随林龄的变化并不明显,但其占总碳储量的比例却随林龄的增加逐渐减小,由幼龄林的56.01%减小到过熟林的29.35%。

Carbon storage and its distribution pattern in the natural Larix gmelinii forests on Daxing'an mountains

The natural Larix gmelinii forests are the major forest type in the Daxing''an Mountain region of Northeast China. As such they play an important role in forest ecosystem carbon storage and the carbon cycle. Quantifying carbon storage dynamics and distribution patterns of these forests with forest age is of scientific importance in gaining a better understanding of forest ecosystem carbon cycles. This study selected age classes of natural Larix gmelinii forests in Daxing''an mountains, including young, mid-aged, premature, mature and over-mature forests, to assess tree, understory, forest floor and soil carbon pools. Tree carbon was estimated through allometric equations that were established for tree species in the Daxing''an mountains. Both understory and forest floor carbon pools were calculated through dry weights multiplied by their carbon contents; and soil carbon pool was obtained via soil organic carbon content multiplied by bulk density and soil profile depth, both of which were obtained from soil profiles. Results showed that total carbon storage of the natural Larix gmelinii forests increased with forest age, which was attributed mainly to increased tree carbon storage. Carbon storage levels of 140.46, 186.63, 208.64, 308.62 and 341.03 MgC/hm² were found in young, mid-aged, premature, mature and over-mature forests, respectively; with mature and over-mature forests displaying significantly higher levels than those in young and mid-aged forests. Tree carbon storage ranged from 45.44 MgC/hm² in young forests to 212.67 MgC/hm² in over-mature forests. At the same time, the contribution of tree carbon pools to total carbon pools also increased from 32.60% in young forests to 62.36% in over-mature forests. Moreover, both understory carbon pools and forest floor carbon pools displayed increasing patterns with forest ages, rising from 1.29 and 14.58 MgC/hm², respectively, in young forests to 2.15 and 26.11 MgC/hm², respectively, in over-mature forests. This was attributed primarily to the much higher carbon storage levels in over-mature forests, which have historically been disturbed only slightly by human activities in this region. The contribution of understory carbon pool to total carbon pool accounted for only 0.48%-0.93%; while the contribution of forest floor carbon pool to total carbon pool ranged from 7.08%-10.46%, suggesting that forest floor carbon pools also play an important role in carbon sequestration in the Daxing''an mountains. Soil carbon storage ranged from 78.06-131.93 MgC/hm², with highest storage levels in mature forests, and lowest levels in young forests. However, soil carbon storage did not exhibit a rising trend with increasing forest age. Conversely, the contributions of soil carbon pools to total carbon pools decreased significantly with forest age, from a high of 56.01% in young forests to a low of 29.35% in over-mature forests. In addition, both soil organic carbon content and carbon storage level decreased significantly as depth of soil profile increased, with the organic carbon contents of 4.10%-7.41% and carbon storage of 36.40-78.26 MgC/hm² in the top-soil (0-10cm) decreasing to 1.29%-1.59% and 8.96-19.76 MgC/hm², respectively, in the bottom (20-40cm) soil layer. In general, all of those are of scientific importance to estimating and predicting carbon sequestration in forest ecosystems and their overall contributions to the carbon cycle.