黄河上游退耕地人工林的碳储量研究

黄河上游地区10～27 a的退耕地人工林，其植物体、枯落物层和土壤层的碳密度平均为111.3、5.1和164.9 t/hm2，分别占同一地区天然次生林的28.6%、13.8%和61.0%.植物体、枯落物层和土壤层3个层次所占总碳密度的比例，对于退耕地人工林来说为39.6∶1.8∶58.6，而天然林为57.4∶2.7∶39.9.退耕地人工林的植物体和枯落物层碳密度均随林龄的增加而呈幂函数增长趋势.这2部分在总碳密度中所占比例随林龄而逐步提高.退耕地人工林目前的总碳密度平均为281.2 t/hm2，相当于同一地区天然次生林总碳密度677.4 t/hm2的41.5%,但年均碳密度却高达15.2t/(hm2·a)，较天然次生林的13.6 t/(hm2·a)提高了11.7%；与全国20世纪90年代中期(1994—1998年)人工林的年均碳密度1.95 t/（hm2·a）相比，提高了6.8倍.黄河上游退耕地人工林较天然次生林及荒山人工林具有更强的生长及碳储量优势.总之，科学有序的退耕还林工作，对于形成碳汇、减轻温室效应具有非常重要的意义. 

Carbon storage of artificial forests in rehabilitated lands in the upper reaches of the Yellow River.

For the last 10 to 27 years, artificial forests had been located in rehabilitated lands in the upper reaches of the Yellow River. The objective of present study was to compare the carbon densities of various layers under artificial and natural forests. Following are the results of the comparison. Under artificial plantations, the vegetation layer (including roots) has a mean carbon density of 111.3 t/hm2, the litter layer has a density of 5.1 t/hm2and soil layer contains 164.9 t/hm2.These values account for 28.6%, 13.8% and 61.0% of their respective counterparts in the natural secondary forests under the same site conditions of the area. The ratios of carbon density among vegetation, litter and soil layers are 39.6∶1.8∶58.6 for artificial forests and 57.4∶2.7∶39.9 for natural forests. As well, the carbon densities of the vegetation and litter layers are increasing exponentially with forest age. Also, their total carbon density ratios are increasing gradually. Although the mean total carbon density of the present artificial forests in the rehabilitated lands is 281.2 t/hm2 in the experimental area, it accounts for only 41.5% of the carbon density of the natural secondary forests (677.4 t/hm2). In the artificial forests, the annual increase in total carbon density is as high as 15.2t/(hm2\5a), which is 11.7% more than that of the natural forests and 6.8 times higher than the corresponding value (1.95t/(hm2\5a)) of artificial forests in the entire country as measured for the years 1994 to 1998 This indicates better growth and carbon storage capacity of artificial forests in the rehabilitated lands compared with that of the barren hills and the secondary forests. It can be concluded that the scientific pursuit and continuing conversion project from cropland to forest and grass land is very important in the formation of carbon sinks and reduction of the greenhouse effect.