【作者】 王鹏；

【导师】 陈丽华；

【作者基本信息】 北京林业大学 ， 水土保持与荒漠化防治， 2012， 硕士

【摘要】 华北土石山区天然次生杨桦林群落是该地区最为常见的林分类型,其原生树种为华北落叶松林,在长期经受不同程度的人为干扰后被破坏严重,经过数十年的自然恢复,逐渐形成了以杨、桦为先锋树种的次生混交群落,成为该地区地带性植被自然恢复演替过程中典型的过渡群落。本研究以该地区不同混交程度的次生山杨、白桦纯林和杨桦混交林为研究对象,对其不同群落的优势种群的组成、生态位、生物多样性及空间分布格局进行分析,并对比了不同群落之间的近自然度和林分优势度,分析了该地区天然次生杨桦群落的发展趋势,并探讨了该地区的森林演替模式。主要研究结果分述如下：(1)研究区北沟林场天然次生林群落林分密度较大,植被种类较为丰富,乔木层共有11个树种,均以山杨和白桦为优势种,占据了绝对的比重,而伴生树种以华北落叶松、五角枫和云杉为主。4块公顷级标准样地分别为1个山杨群落,1个白桦群落,以及两个不同混交度的杨桦混交群落。其中林分密度最大的为样地A山杨群落,为853株/hm2,最小的为样地C2杨桦混交群落,为572株/hm2；胸径断面积以C1群落最大,为20.156m2/hm2,山杨群落次之,各树种胸径断面积以山杨、白桦和落叶松为主,三者胸径断面积占据群落绝对优势；各样地径级结构较为典型,优势树种的山杨和白桦种群基本上都呈单峰曲线,而各群落的伴生树种则均呈反J曲线；各群落林分垂直结构有所差别,除山杨群落呈单峰曲线外,其他3个群落均呈双峰曲线,分层明显。(2)研究区内各乔木和灌木种群生态位宽度分布较为均匀,乔木层中五角枫、华北落叶松、花楸和白桦的生态位宽度较大,而黑桦、硕桦和油松生态位宽度较小：灌木层中生态位宽度较大的为五角枫、毛榛和沙株,较小的为荚迷、大叶小檗和华北忍冬。从生态位重叠度来看,占据生态位优势的种群之间重叠度也明显较高,其中花楸、五角枫、蒙古栎和云杉为杨桦林乔木层主要伴生种,而灌木层则明显以毛榛和五角枫为优势种,沙株、锦带花为其主要伴生种。(3)天然次生杨桦林群落的a多样性三类指标中,草本层明显高于灌木层和乔木层,但灌木层与乔木层之间的差异性并不明显,在物种丰富度和多样性上灌木层略微高于乔木层,而其均匀度指数却略低于乔木层,表明灌木层多样性分化程度并不高,这主要是由于五角枫和毛榛的密度巨大,几乎占据了群落整个灌木层。而不同群落类型比较来看,杨桦混交林群落乔木层生物多样性明显大于山杨群落、白桦群落,而灌木层来看,白桦群落的生物多样性最高,其次是杨桦混交群落,山杨群落最低,而在草本层则是山杨群落最高,混交群落次之,白桦群落最低。(4)由点格局分析结果可以看出,天然次生林群落各主要种群均呈现不同程度的聚集分布,其各自的聚集程度均随尺度变化而呈现出各自不同的趋势。在种间关系方面,除了较小尺度外,作为优势种的山杨与白桦和落叶松种群在r<25m的各尺度范围内均呈显著负相关,竞争激烈；而白桦种群除了与山杨种群显著负相关外,在中尺度到大尺度范围内均与落叶松种群呈正相关,但在唯独在样地B白桦优势群落内,与落叶松在中尺度内呈显著负相关,而与蒙古栎相关性不明显。(5)分析不同天然次生群落的近自然度和优势度可以看出,各群落近自然度大小为：C2群落>B群落>C1群落>A群落,总体来看杨桦混交群落更接近自然稳定状态；而各群落优势度的大小顺序为：C2群落>C1群落>B群落>A群落,说明混交群落比山杨、白桦纯林具有较强的活力,更适宜生长。(6)综合以上数据,全面的分析天然次生杨桦林各群落类型的生态结构,我们可以看出,山杨种群结构较差,乔灌层生物多样性较低,种群更新慢,且大面积出现林木枯死现象,种群发展前景堪忧；白桦种群较山杨种群稍好,幼龄木较多,生活力较强,在一定时期内能够继续维持其优势度；而杨桦混交林则为最优,林分结构较好,优势度和近自然度都较高,稳定性也最好。作为次生演替的先锋种,华北土石山区天然杨桦次生林已进入演替中期,从幼苗更新情况来看,次顶极树种五角枫幼苗大量着生,将逐步演替成为该地区的主要优势树种和建群种,形成五角枫次顶极群落,并最终向油松、落叶松顶极群落发展。更多还原

【Abstract】 In this research, we conducted the natural Populus davidiana-Betula platyphylla secondary forest communities of North China in Rocky Mountain Area. As the native species, after the severely damage course by different levels of human disturbance and following decades of natural recovery, Larix principis-rupprechtii communities have been gradually replaced by Populus davidiana-Betula platyphylla secondary mixed communities which has been the typical transition communities of the zonal vegetation natural restoration and succession process in that region. The study chose Populus davidiana pure stand, Betula platyphylla pure stand, and their mixed stand with different mingling degree, analyzed the dominant populations structure, niche, biological diversity and spatial distribution patterns in different communities, moreover, compared their near natureness and stand dominance, analyzed the development trend of natural Populus davidiana-Betula platyphylla secondary forest in the region. The main findings are as follows;(1) The stand density of natural secondary forest communities was relatively large, and the species was abundant which total11tree species were included. In these communities, dominant species Populus davidiana and Betula platyphylla account the absolute weight, with the main associated tree species were Larix principis-rupprechtii, Acer truncatum and Picea asperata. Four hectare standard plots contained a Populus davidiana community (A plot), a Populus davidiana community (B plot), and two Populus davidiana-Betula platyphylla mixed communities with different mingling degree (C1, C2plot). Plot A had the largest stand density,853trees/hm2, and the smallest was plot C2with572trees per hectare; the basal area of plot C1was the largest, followed by plot A, the basal area of Populus davidiana, Betula platyphylla and Larix principis-rupprechtii occupied the absolute advantage; the diameter class structure were relatively typical, Populus davidiana and Betula platyphylla populations were basically presented single peak curve, the associate tree species in different communities were presented reverse J curves; the vertical stand structure were different in each communities, excluding the Populus davidiana community, the others were presented bimodal curve with obvious stratified.(2) In the study area, the arbor and shrub populations had even niche breadth distribution. Larix principis-rupprechtii, Acer truncatum, S. pohuashanensis, Bemla platyphylla were relatively larger in arbor layer, and Betula dahurica. Betula costata, Pinus tabulaeformis were smaller; larger niche breadth in shrub layer were Acer truncatum, Corylus mandshurica and Swida bretchneideri, and Viburnum dilatatum, Berber is amurensis, Lonicera tatarinowii were relatively smaller in niche breadth. The populations of dominance in niche also had higher overlap, in arbor layer, Sorbus pohuashanensis, Acer truncatum, Quereus mongolica and Picea asperata were the main association tree species in Populus davidiana-Betula platyphylla forest, and that Corylus mandshurica and Corylus mandshurica were the dominant species in shrub layer which Swida bretchneideri and Weigela hortenis appeared as the main association species.(3) compared the three type a diversity indicators of natural secondary Populus davidiana-Betula platyphylla forest, the herb layer was significantly higher than the shrub layer and arbor layer, but there was not obvious differences between the shrub layer and arbor layer. In species richness and diversity, shrub layer was slightly higher than the arbor layer while the evenness index was opposite slightly lower, indicating that the shrub layer diversity was not high in differentiation due to the huge density of Acer truncatum and Corylus mandshurica which occupied throughout the shrub layer of community. Comparing the different type of communities, the arbor layer biodiversity of mixed communities were significantly higher than Populus davidiana community and Betula platyphylla community, while in the shrub layer, Betula platyphylla community had the highest biodiversity, followed by mixed communities. Populus davidiana community was the lowest biodiversity in shrub layer but highest in herb layer, which followed by mixed communities and Betula platyphylla community.(4) According to the results of point pattern analysis, the main populations of each community in natural secondary forest were showing the aggregative distribution in different levels, which of the respective different trends with different scales. In the relationship between species, except smaller scale, the dominant Populus davidiana and Betula platyphylla populations showed a significant negative correlation with Larix principis-rupprechtii population in all scales among r<25m, intense competition; in addition to showing a significant negative correlation with Populus davidiana population, Betula platyphylla population was positively correlated with Larix principis-rupprechtii population. Only in B plot was Betula platyphylla population negatively correlated with Larix principis-rupprechtii population, and showed non-significant correlation with Quercus mongolica.(5) Analysis of the near natureness and stand dominance of different natural secondary forests provided an order of near natureness:C2plot> B plot> Cl plot> A plot, and an order of stand dominance:C2plot> Cl plot> B plot> A plot. According above it could be clear that the mixed Populus davidiana-Betula platyphylla community was more closer to natural steady state and more vigorous than respective pure stands for growth.(6) Based on the above data, analyzing the ecological structure comprehensively, it could be concluded:the structure of Populus davidiana population was relatively poor, the arbor and shrub layer were of low biodiversity, the population restorage was slow, and it emerged a large area dead wood phenomenon meantime, showing the pessimistic prospectation for the population; Betula platyphylla population was slightly better with its more young trees and relatively strong viability, which were able to maintain its dominance in a given period; compared to those, the mixed stand was the optimal with the relatively better stand structure, dominance and near natureness, as well as the stability of all other stands. As a pioneer species of secondary succession, natural secondary Populus davidiana-Betula platyphylla forest of North China in Rocky Mountain Area had entered a medium-term of succession, considering the seedling regeneration, the emerged of large number of secondary climax species Acer truncatum seedlings suggested it would gradually become the major dominant species and constructive species in that region, moreover, it would gradually form an Acer truncatum secondary climax community, and ultimately developed to Pinus tabulaeformis and Larix principis-rupprechtii climax community.更多还原