兴安落叶松天然林碳储量及其碳库分配特征

Abstract

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 of140. 46,186.63,208. 64,308. 62 and 341. 03 Mg C / hm2 were found in young,mid-aged,premature,mature and overmature forests,respectively; with mature and over-mature forests displaying significantly higher levels than those in youngand mid-aged forests. Tree carbon storage ranged from 45.44 Mg C / hm2 in young forests to 212.67 Mg C / 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 Mg C / hm2,respectively,in young forests to 2.15 and 26.11 Mg C / 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 Mg C /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 Mg C / hm2 in the top-soil( 0—10cm) decreasing to 1.29% —1.59% and 8.96—19.76 Mg C / 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.