西南地区天然林资源近60年动态分析

天然林资源是衡量区域生态环境状况的重要指标之一。分析天然林资源动态对提高其管理水平和促进区域可持续发展具有重要意义。通过对西南地区1949年以来天然林资源数据的挖掘和比较分析,结果表明:天然林发展可以1981年为界分为前后两个阶段,前阶段天然林面积和蓄积因木材消耗分别降低了26%和33%,后阶段在生态建设工程推动下两者分别增加了58%和42%,达到2008年的25.87×106hm2和31.84×108m3,恢复到了1949年的资源总量水平;但天然林整体质量提高缓慢,平均每hm2蓄积123 m3尚处历史低位;天然林年龄结构也不均衡,幼、中龄林的面积占天然林的58%,蓄积仅占30%,成、过熟林面积占28%,蓄积却占55%;目前天然林中公益林和商品林的面积比约7∶3,蓄积量比约8∶2;商品材采伐量在天然林保护(简称天保)工程实施初期锐减了80%,但在2008年又回升到了天保工程前,且总体增长趋势未变。经过10 a天保和退耕还林工程后,目前西南地区天然林总面积增长放缓,但单位面积的蓄积还很低,故建议天然林发展策略从增加天然林面积转向保持面积和提高整体质量。保持面积的关键是划定天然林面积红线和严格控制天然林采伐,提高整体质量的重点是调整商品林年龄结构,适当提高薪炭林和特用林面积比重,加强退化天然林的生态恢复和重建。

Resource Dynamics of Natural Forests in Southwest China in Recent 60 Years

The natural forests (NFs) play a more important role than planted forests in ecological services. The NFs resource is one of the important indicators for characterizing local ecological environment status. Dynamics analysis of NFs resources is beneficial to the improvement of management efficiency and promotion of local sustainable development. We analyzed the NFs data extracted from forests inventory reports published by government since 1949. The results showed that the development of NFs could be divided into two phases over the past 60 years: wood consumption and ecological restoration. In the first 30 years, the NFs area and volume declined by 26% and 33% respectively because of timber harvest, whereas they continually recovered under ecological environment construction in the latter 30 years. The NFs area reached the top point of 25.87 million hm² in 2008 and its stands volume of 3.2 billion m³ was close to the figure of 1949, especially with the remarkable promotion of Natural Forest Protection Program (NFPP) since 1999. But the quality of overall NFs improved slowly and 123 m³ per hm² was still at the low level in 2008. And the age structure of NFs was unbalanced. Forests volume of young and middle NFs was not increased rapidly with its area, its area accounted for 58%, but its volume only 30%. At present the ratio of commercial forests area to ecological ones was almost 7 ∶3 resulted from the increase of shelter forests and decrease of timber forests since the 1980s. The amount of commercial timber harvested dropped sharply after the implementation of NFPP, but it resumed gradually since 2001 and reached the peak of 9.46 million m³ in 2008. The increasing trend of commercial timber logging amount was not changed over the past 60 years. Based on these dynamic analysis results, considering the future development strategies of NFs in Southwest China, we suggest establishing red line to control the NFs areas, adjusting age structure of commercial forests, shifting NFs area expansion to improve forests quality, strictly controlling the logging of NFs and strengthening ecological restoration of degraded NFs.