川西亚高山次生林恢复过程中乔木层优势种变化及其影响因子

川西亚高山森林在20世纪下半叶遭受长时期连续砍伐,形成了采伐迹地上天然次生林恢复演替序列。该研究采用空间代替时间方法,以立地条件相似的暗针叶林作为对照,分析川西亚高山暗针叶林采伐迹地上次生林自然恢复过程中乔木层优势种组成及其影响因子。结果表明:(1)研究区亚高山天然次生林恢复演替过程中,不同演替阶段土壤各养分差异显著,其中土壤总氮、土壤总磷、土壤有效磷、土壤有效氮均在针阔混交林阶段最高,土壤pH值的变化在5.42～7.39范围波动,土壤有机碳随恢复的进行而增加,土壤C/N主要集中在15左右,只有针叶林达到18.62。(2)研究区次生林以16个乔木树种为主,针叶树种主要有粗枝云杉、岷江冷杉,阔叶树种主要有红桦、青榨槭等,且不同恢复阶段的群落乔木层优势种差异显著(R_(ANOSINM)=0.439,P0.001)。(3)多元回归树分析发现,次生林乔木层优势种组成主要受林龄、土壤有机碳和总氮的影响,其中在次生林恢复演替后期(80a后),乔木层组成可能主要由于种间竞争导致,在次生林恢复演替前、中期(80a前),环境选择可能是影响乔木层组成差异的主导因素。(4)反向选择筛选结果显示,土壤总氮、海拔高度、土壤有效磷和土壤有机碳是影响乔木层优势种差异的主要因子。

Changes of Dominant Species in Arbor Layer along Restoration Gradients of Sub alpine Secondary Forests in Western Sichuan, China

Sub alpine forests in Western Sichuan suffered from long term continuous deforestation in the second half of the 20th century, and a series of secondary forests on logging land have been formed by natural restoration, which provides the good natural experimental site for studying the forest vegetation succession and structure. In this study, by using the method of replacing space with time, we analyzed the changes of dominant species composition along vegetation restoration and their influencing factors in Miyaluo of western Sichuan. Our results showed that: (1) a significant difference in soil nutrient was found among different succession stages. The content of soil total nitrogen, soil total phosphorus, soil available phosphorus and soil available nitrogen were the highest in coniferous broadleaved mixed forest stage. Soil pH values among different restoration stages were 5.42-7.39. Soil organic carbon presented an exponential growth pattern along time. The mean soil C/N value was about 15 and only soil C/N in coniferous forest was 18.62. (2) We recorded 16 major arbor tree species in research area. The dominant species in coniferous forest were Picea asperata and Abies faxoniana. While Betula albo sinensis and Acer davidii were the dominant species in broad leaved forest. The analysis of community similarity showed that there was a significant difference in the composition of dominant species in arbor layer along the different recovery stages (R_ANOSINM = 0.439, P <0.001). (3) The analysis of the multivariate regression tree revealed that the variations of dominant species in arbor stratum were mainly influenced by forest age, soil organic carbon (SOC) and total nitrogen (TN). The interspecific competition is the dominant factor affecting the difference of community composition in arbor layer before the 80 years of succession. However, environmental selection affects the tree species composition after 80 years. (4) The analysis of sequential tests showed that the variations of dominant trees species were primarily affected by soil TN, altitude, available phosphorus (AP) and SOC. The results can provide scientific basis for the restoration of degraded forests and secondary forest ecosystem management in the alpine region of western Sichuan.