青藏高原东部采伐迹地早期人工重建序列梯度上植物多样性的变化

PLANT DIVERSITY ALONG A TIME SEQUENCE (1-30 YEARS) OF ARTIFICIAL FOREST REHABILITATION ON SUBALPINE CUT LAND IN THE EASTERN QINGHAI-TIBETAN PLATEAU

采伐是青藏高原东部亚高山森林过去经营管理中最常见的实践。采伐的一个重要后果就是林地生物多样性的衰退和损失。目前虽然对采伐环境退化与迹地人工林恢复重建开展过许多研究 ,但对采伐迹地以及人工重建过程中的生物多样性变化研究很少。人工重建时间序列上的植物组成变化还不清楚 ,也没有人去检测人工林早期发展阶段间多样性的差异。作者选择大渡河上游亚高山针叶林序列采伐迹地 ,调查了采伐后 8个人工造林时间序列梯度 (1年、2年、5年、7年、10年、15年、19年和 30年 )和相邻的原始林内的物种组成和丰富度 ,比较分析了序列梯度上的植物多样性的变化。结果表明 ,8个人工造林时间序列样地上共采集到种子植物 16 7种 ,其中大多数是喜光的草本植物和灌木。根据这些植物的重要值在该时间序列梯度上的变化 ,可基本分成具有不同适应性的 3个种组。重要值在林分郁闭前逐渐增加而后减少的植物种组成了侵入种组 ,包括 75种喜光植物 ;敏感种组包括 12种原来就存在于原始林下的耐荫植物种 ,它们的重要值在郁闭前逐渐减少而后增大 ,它们对采伐迹地环境退化敏感性强 ;忍耐种组有 2 2种 ,它们的重要值在时间序列上没有表现出明显的变化趋势 ,表明它们对环境的变化具有较强的适应性 ;另外 5

Clearcutting, a commonly used forest management practice in eastern Qinghai-Tibetan Plateau, is a major driving force for land use change resulted in the drastic degradation of subalpine forest ecosystems. One of the most serious consequences is causing decline and loss of the indigenous biological diversity. Many works have been done in checking the environmental degradation after clearcutting and promoting artificial forest restoration, but little focused on change and restoration of biological diversity. Shifts in plant species composition occurred on different time frame of artificial rehabilitation are unclear and none have attempted to examine differences throughout the early stages of artificial stand development. This study conducted in Jinchuan County in the upper reaches of Dadu River and examined plant diversity along a time sequence (1 a, 2 a, 5 a, 7 a, 10 a, 15 a, 19 a and 30 a after artificial forest rehabilitation) following clear-felling land and the nearby primary forest stand. Throughout the early stand development following clear-cuts and artificial rehabilitation, changes on alpha diversity were calculated as three stages, viz. the induction stage sustained 10 a after logging, high diversity stage in the second 20 a, and the consequent adjustment stage after 20 a of artificial restoration. Beta diversity change also implicated three environmental differentiation stages and separation by the second and seventh year respectively. A total of 167 species were found in eight restoring stands and the nearby primary forest, most of which were light-loving herbs or shrubs. According to the change of density along the time sequence, they could be divided into three species groups with different adaptation strategy. The invasive species group included 75 light-loving species, which increased their density before stand closed and afterwards decreased. The sensitive species group included 12 intolerant species existing in parent virgin stand, which decreased their importance before stand closed and gradually restored afterwards, which indicating that they are sensitive to forest environment degradation. The 22 tolerant species did not display changes in density along the time frame, hinting that they have strong adaptation ability to varied forest environment. No change was examined for another 58 species found in only one or two stand, being termed 'rare' species group. The change of alpha/beta index strongly explained community structure and tree coverage resulting in micro-environmental heterogeneity, which is a key determinant to change species composition of the stand. One important finding is that if there was no artificial restoration it would be difficult for restoring naturally indigenous species composition after subalpine coniferous forest was cut clearly. Artificial restoration is an important pathway not only for coniferous forest vegetation, also for plant diversity in subalpine ecosystem. The present results also suggested that the artificial reconstruction in methodology and management utilized extensively in the eastern Qinghai-Tibetan Plateau need to be improved in effort for restoration and conservation of indigenous tree diversity successfully.