森林凋落物对林地微生境的影响

评述了凋落物改变林地微生境的效应.凋落物减弱了林地地表及表层土壤(2mm厚)中的光照,改变了光谱特性,降低了PPFD和Pfr,缩小了日温差,提高了土壤湿度和肥力,增加了毒素和土壤动物的活动等,但凋落物改变生境的效应强度与凋落物组成、厚度、分解状态和周围生境(如植被、气候、地形和地貌等特性)等有关.在自然森林生态系统中,凋落物对林地微生境的效应因凋落物、植被、气候、地形和地貌的多样化变得更为复杂,而凋落物对植被天然更新的影响也因其对生境改变效应的复杂性而具有多样性和综合性.最后,对凋落物改变生境效应的复杂性和有关研究进行了展望.     

古尔班通古特沙漠植被与环境的关系

对古尔班通古特沙漠进行了纵向及横向的路线调查,植被测度和土壤理化性质分析。对比发现该沙漠地貌形态纵、横向上的显著差异,使沙漠植被分布格局存在着异质性,即植物群落的物种多样性、优势度及盖度在纵、横向上明显不同。CCA排序结果显示,土壤的有机质含量、全盐含量、分选系数、含水量和pH值等微生境使植被沿其变化梯度以不甚耐盐碱的短命、类短命草本和小半灌木、半灌木为主的群落逐渐向耐盐碱的灌木、小乔木类群落转变。地形和土壤质地可使横向上相当数量的植物种产生空间分化,而这种分化在纵向上不明显。沙漠植被物种在各生境梯度作用下形成3类组合,其在横向上对应3个地段,但在纵向上没有清晰的对应空间(除南北边缘区外),原因是多数植物的生境处于沙漠纵向微生境梯度的中间序位。     

内蒙古草原凋落物分解对生物多样性变化的响应

生物多样性与生态系统功能紧密相关。凋落物分解作为生态系统重要功能之一, 对植物群落的物种组成和多样性具有反馈作用。本研究在内蒙古草原通过功能群去除产生不同的多样性梯度, 应用分解网袋法, 研究了草原生态系统的生物多样性变化对凋落物分解过程的影响。实验分为相互补充的三个部分, (1)分解微生境实验: 研究了由于功能群多样性改变引起的分解微生境变化对凋落物分解的影响; (2)凋落物组成实验: 研究了4个功能群的优势物种羊草(Leymus chinensis)、大针茅(Stipa grandis)、细叶葱(Allium tenuissimum)、刺穗藜(Chenopodium aristatum)的单种及不同组合的混合凋落物在相同的分解微生境下物种间的相互作用对凋落物分解过程的影响; (3)综合分解微生境和凋落物组成两种影响因素, 将收集的凋落物的单种及其混合物放回原样方进行分解。结果表明, 功能群多样性高的样方中, 其微生境有利于凋落物的分解; 混合凋落物的分解具有非加和性效应。混合凋落物的分解速率与其初始碳含量呈负相关, 与其初始氮、磷含量呈正相关; 当混合凋落物在功能群多样性不同的微生境中分解时, 重量降解速率与微生境中的功能群多样性没有显著的相关关系, 氮流失与功能群多样性呈正相关。我们的研究表明, 群落中凋落物组成和凋落物的功能群多样性相比, 前者是影响凋落物分解的决定性因素; 与地上存活植株所参与的生物学过程相比, 凋落物分解受生物多样性的影响较小; 在生物多样性更高的区域, 氮的循环加速, 有利于提高群落的生产力。     

鄂西南亚高山湿地泥炭藓的生长与分解

泥炭藓(Sphagnum)是湿地土壤碳的重要来源,在土壤碳累积过程中发挥着关键作用,但有关亚热带湿地泥炭藓生长与分解的研究鲜有报道。该研究选择鄂西南亚高山泥炭藓湿地为研究区域,原位开展不同微生境泥炭藓的生长及其凋落物的分解实验,室内测试凋落物的化学成分,探讨亚热带亚高山湿地泥炭藓的生长与分解规律。结果表明:泥炭藓在自然状态生长12个月后,丘上和丘间两种微生境下泥炭藓的平均高度增长量分别为2.9和2.7cm,对应的净生产量分别为270.94和370.88g·m~(–2),生长时间与微生境对泥炭藓的高度增长量及净生产量均有显著影响,且两者之间存在交互作用,但是两种微生境下泥炭藓的生长变化过程不同;两种微生境下泥炭藓的平均生长速率(2017年7–10月)为0.33 mm·d~(–1),其生长速率高于寒温带地区。另外,分解时间对泥炭藓的分解量有显著影响,其残留率随时间增加表现为先减少后增加的趋势。12个月后,丘间、丘上和水坑3种微生境下最终残留率分别为100.67%、90.54%和85.63%。凋落物中碳含量、碳氮比和多酚含量相比初始值均有所下降,氮含量则为增加。同时,微生境对凋落物分解的影响取决于分解时间。分解3个月时,微生境之间凋落物的分解量差异显著,其他时间段差异不明显。     

鄂西南亚高山湿地泥炭藓的生长与分解

泥炭藓(Sphagnum)是湿地土壤碳的重要来源, 在土壤碳累积过程中发挥着关键作用, 但有关亚热带湿地泥炭藓生长与分解的研究鲜有报道。该研究选择鄂西南亚高山泥炭藓湿地为研究区域, 原位开展不同微生境泥炭藓的生长及其凋落物的分解实验, 室内测试凋落物的化学成分, 探讨亚热带亚高山湿地泥炭藓的生长与分解规律。结果表明: 泥炭藓在自然状态生长12个月后, 丘上和丘间两种微生境下泥炭藓的平均高度增长量分别为2.9和2.7 cm, 对应的净生产量分别为270.94和370.88 g·m ^-2, 生长时间与微生境对泥炭藓的高度增长量及净生产量均有显著影响, 且两者之间存在交互作用, 但是两种微生境下泥炭藓的生长变化过程不同; 两种微生境下泥炭藓的平均生长速率(2017年7-10月)为0.33 mm·d ^-1, 其生长速率高于寒温带地区。另外, 分解时间对泥炭藓的分解量有显著影响, 其残留率随时间增加表现为先减少后增加的趋势。12个月后, 丘间、丘上和水坑3种微生境下最终残留率分别为100.67%、90.54%和85.63%。凋落物中碳含量、碳氮比和多酚含量相比初始值均有所下降, 氮含量则为增加。同时, 微生境对凋落物分解的影响取决于分解时间。分解3个月时, 微生境之间凋落物的分解量差异显著, 其他时间段差异不明显。     

黄顶菊凋落物分解对节肢动物群落结构的影响

选择黄顶菊(Flaveria bidentis)入侵的林地、农田、荒地、沟渠等4种生境作为调查样地, 比较黄顶菊与本地植物凋落物的分解速率及凋落物分解对节肢动物群落结构的影响。于2014年10月凋落物高峰期在各样地内分别搜集黄顶菊与本地植物的凋落物, 每种凋落物称取20 g装入尼龙网分解袋中, 放入各生境。2015年的每个月将不同生境不同处理凋落袋各取回10袋, 用Tullgren法分离节肢动物。 4种生境共捕获17,466头, 隶属8纲18目, 4种生境的优势类群皆为蜱螨目和啮目。其中, 林地、农田、荒地、沟渠4种生境处理组中节肢动物数量分别为1,698头, 1,838头, 2,631头, 3,413头, 分别比对照组高18%, 53%, 22%, 11%。多数月份黄顶菊凋落物中的节肢动物丰富度及多样性指数高于同生境对照组, 并且在黄顶菊生长盛期差异显著; 黄顶菊凋落物的分解速率高于对照植物分解速率, 且各月份凋落物分解速率动态与节肢动物数量变化动态呈显著相关。黄顶菊凋落物对节肢动物的影响与人为干扰程度有关, 这种影响在人为干扰较小的荒地与沟渠生境中更为明显。综上所述, 黄顶菊凋落物的分解改变了节肢动物群落结构, 并引起节肢动物多样性的升高。     

不同林龄马尾松人工林年凋落量与养分归还动态

利用空间代替时间的方法,对不同发育阶段马尾松人工林年凋落量与养分归还量动态进行了研究。结果表明:1)马尾松人工林凋落物量具有明显的季节变化,受树种本身生物学特性和气候影响,气候对凋落量的影响效应具有滞后性;2)马尾松各凋落物组分的养分浓度具有明显的季节变化,季节差异可达1倍以上;3)随着林龄增长,通过凋落物归还到林地的K量呈下降趋势,其他养分量则呈"V"字型,51年生时有较高的养分利用效率。凋落物对马尾松人工林林地养分维持具有重要作用,凋落物尤其凋落针叶的输出切断了人工林生物地球化学循环过程中凋落物养分归这个关键环节,会加剧土壤贫瘠化进程,导致林地生产力降低,因此在经营马尾松人工林过程中要尽量降低凋落物输出量,以维持林地的长期生产力。     

微地形改造的生态环境效应研究进展

干旱缺水和生境不良使世界上许多地区的植被恢复和生态改善面临困难。为了提高植被成活率、遏制土壤侵蚀和土地退化态势,国内外许多重点地区都开展了多种微地形改造与下垫面整地措施,使得地表生境和植被状况得到一定改善。但微地形改造对生态环境影响的基础研究仍严重滞后于实践的客观需求,许多关键效应和科学机理不明。本文系统梳理和总结了国内外学者在不同生态系统类型区和自然地理单元上开展的相关研究。认为微地形改造对土壤属性和微生境、降雨入渗和水蚀过程、植被恢复的效果及其生态服务功能发挥等多个方面都有重要影响,并综述了相关研究进展。同时指出当前微地形改造研究中存在的突出问题。包括科学分类标准有待系统化、实地量化技术相对滞后、微地形改造的水文效应有待强化、影响植被恢复的机理不明等若干重要局限。建议应进一步加强微地形改造的分类体系研发、发展微地形改造方式的定量刻画技术;设立野外定位站,跟踪监测其长期效应,并加强不同微地形改造措施的生态环境效应对比,为科学筛选和优化下垫面改造技术、服务区域生态改善和应对气候变化提供科学依据。     

基于结构方程的云冷杉阔叶混交林土壤有机碳影响因子

植被、凋落物、地形以及土壤属性都是土壤有机碳(SOC)变化的驱动因素,而多个驱动因素如何同时作用于SOC的研究较少。本文以云冷杉阔叶混交林为对象,通过样地调查、采样以及实验测定获得200组数据,包括不同土层土壤、植被以及不同分解层凋落物的数据,并通过遥感技术获得了地形数据。采用相关分析以及结构方程模型量化这些因子对SOC的影响。基于相关分析结果构建了5个潜变量,包含植被、地形、凋落物归还特征、土壤属性以及SOC含量和土壤有机碳密度(SOCD),选取了15个观测变量进行建模。结构方程模型的各项检验系数基本通过,且多元平方系数值为0.94,表明方程构建合理且效果较好,模型的收敛效度达标。4个预测潜变量对SOC含量和SOCD均有显著正效应,总效应从大到小表现为土壤属性(0.938)>地形(0.383)>植被(0.131)>凋落物归还特征(0.099),可解释部分效应贡献占比分别为60.5%、24.7%、8.4%和6.4%,其中高程、20～40 cm土壤全磷、20～40 cm土壤全氮、0～20 cm土壤全氮、20～40 cm土壤含水率为效应贡献前五位,对SOC含量和SOCD有...     

森林生态系统凋落物多样性对分解过程和土壤微生物特性影响研究进展

凋落物的分解过程是森林生态系统养分循环的关键环节, 也是林分内植被层可利用养分的重要来源。一般来说, 在自然生态系统中, 地上植被的种类越丰富, 其凋落物的多样性也越高, 多样化的凋落物在混合分解过程中存在的相互作用关系也更为复杂, 对其自身的分解过程、分解生境以及分解者群体也会产生重要影响。文章以凋落物的多样性为着眼点, 综述了凋落物的多样性对其分解过程以及对分解过程中最重要的分解者-土壤微生物特性所产生的影响, 重点阐述了凋落物多样性对分解过程中土壤微生物的生物量、群落结构、多样性以及分解活性的影响, 并对其可能的原因和潜在的机理进行了分析。综述结果表明, 较高的凋落物多样性总体上能够加速凋落物的分解, 提高分解过程中土壤微生物的生物量、多样性及分解活性。在此基础上, 对今后凋落物多样性在分解过程中的效应研究进行了展望, 为人工林可持续经营的混交林营造以及林下植被的科学管理提供理论依据。     

六盘山区辽东栎的实生苗更新及其影响因子

研究了六盘山区辽东栎(Quercus liaotungensis)灌丛的种子产量、土壤种子库组成、湿沙和风干贮藏对种子寿命的影响以及动物取食子叶对种子萌发和幼苗建立的影响。结果表明, 辽东栎灌丛种子的完好率为27.51%, 被动物取食或搬运种子的比例(41.51%)显著高于其他类型种子(p < 0.01); 辽东栎次生林土壤种子库中萌发和虫蛀种子分别占35.16%和38.29%, 完好种子仅占13.65%, 捕食动物主要通过贮藏或搬运而影响土壤种子库中的种子密度。湿沙贮藏60天的辽东栎种子自动萌发率高达96.67%, 短期贮藏可加快种子的萌发进程, 提高萌发率和萌发指数, 但随着贮藏时间的延长, 种子萌发进程延迟, 萌发率、萌发指数和活力指数均不同程度地降低。排除动物取食处理的幼苗在林窗和林下生境的存活率分别为80%和83%, 而不排除动物取食幼苗在2种生境中分别仅有25%和31%能够存活, 表明子叶在幼苗建立中具有重要作用。林窗中幼苗子叶的动物取食率(85.00%)高于林下(71.00%), 子叶留存的幼苗在林窗中的存活率(6.00%)低于林下(15.50%), 而子叶被取食幼苗的存活率在两种环境中基本相等(分别为18.50%和18.00%)。     

西双版纳季节雨林更新的研究

 根据定位试验研究和组成森林树种的生态习性,对季节雨林的更新进行了研究。结果表明雨林种子年产量高。残落物中、下层至表土2—4cm处是种子,特别优势种种子的贮存库。一年中,种子萌发,幼苗生长是雨季>雾季>干季,死亡则是干季>雨季>雾季。1—2龄苗易死,多龄苗不易死,雨季腐烂,干季干旱缺水致死,雾季叶锈病是致死的主因。年复一年的种子萌发、幼苗生长、抑制、死亡、残存、补充是该雨林更新的特征。如果除去残落物层或羽蕨层,保羽蕨层翻土,除蕨层、残落物层翻土可促进种子萌发,幼苗生长,减少死亡,由此可反映出蕨层,残落物层,表土层是影响森林更新的主要生态因子。借助乔木死亡形成林窗而繁衍的种和无须林窗繁衍的种,其幼苗经干旱后残存,可发育成顶极种及先锋种的更新苗和小树,其中顶极种更新苗在更新中起主要作用,是本雨林与典型雨林共有的特点。根据优势顶极种的更新苗和小树罕见,而常见顶极种的更新苗和小树相对地多来看,当优势顶极种消亡后,整个森林或森林片段将被那些相对多度小的常见顶极种替换,从而形成循环镶嵌更新。     

The regeneration of pioneer tree species under browsing pressure of Sika deer in an evergreen oak forest

The effects of Sika deer (Cervus nippon) browsing on the regeneration of pioneer species were studied in relation to canopy gaps in a warm temperate evergreen oak forest in Kasugayama, Nara City. Four study sites, three in canopy gaps and one under a closed canopy, were selected and each divided into fenced and unfenced plots. Under the closed canopy, seedlings of all the pioneer species died irrespective of browsing pressure. However, in the canopy gap sites, seedlings of the pioneer species could establish and grow well. The seedling survival ratio in the fenced plots in the canopy gaps was >60% 1 year after germination. However, in the unfenced plots, only <20% of the seedlings survived 1 year, with all dying within 3 years after germination. Thus, the regeneration of pioneer trees in this forest was strongly inhibited by deer browsing. Successful regeneration of a pioneer,Zanthoxylum ailanthoides, occurred for several years even after two major wind disturbances during the past 90 years. This may be due to less browsing pressure from the deer.     

Seed dispersal, seedling establishment and gap partitioning among tropical pioneer trees

1 We examined the abundance and distribution patterns of pioneer seeds in the soil seed bank, and of pioneer seedlings in 53 recently formed gaps, in a 50‐ha forest dynamics plot on Barro Colorado Island (BCI), Panama. The aim was to assess the importance of dispersal limitation (failure of seeds to arrive at all sites suitable for their germination) and establishment limitation (failure of seeds having reached a site to germinate successfully and establish as seedlings) in determining patterns of gap occupancy.
2 The abundance of seeds in the soil seed bank was strongly negatively correlated with seed size, but was not correlated with the abundance of reproductive‐sized adult trees in the plot. In contrast, the abundance of pioneer seedlings > 10 cm height in natural gaps was strongly correlated with adult abundance, but was not correlated with seed size.
3 Seedlings were non‐randomly distributed among gaps, but seedling abundance was not directly related to gap size, and there was no evidence of partitioning of the light environment of gaps by small seedlings. Large differences in growth and mortality rates among species were observed after 1 year, and this may result in the gap size partitioning previously found in saplings of the same species.
4 Seedlings of most species, particularly those with large seeds, were relatively more abundant than expected in gaps close to their conspecific adults. Proximity to reproductives, and by inference dispersal limitation, therefore exerts some effect on seedling distribution. None the less, large differences between seed and seedling abundances for some species, and low seedling occupancy rates in some gaps close to adult conspecifics, suggest that seedling emergence probabilities and species‐specific establishment requirements may also be important determinants of local abundance.     

Tree Regeneration in Church Forests of Ethiopia: Effects of Microsites and Management

Tree regeneration is severely hampered in the fragmented afromontane forests of northern Ethiopia. We explored how trees regenerate in remnant forests along the gradient from open field, forest edge to closed sites and canopy gaps inside the forest. We investigated the effects of seed sowing, litter removal, and weeding on the regeneration success along this gradient. Regeneration success was investigated for four indigenous tree species, and measured in terms of seedling establishment, growth, and survival. Species performed differently according to site conditions. Within the forest, local canopy openings facilitated seed germination ( Ekebergia ), seedling growth (all species except Olea ), or survival ( Ekebergia and Olea ), suggesting that all species benefited from local high light conditions in the forest. Outside the forest, germination (all species) and growth rates ( Juniperus and Olea ) were lower in the open field, most probably due to water stress in the dry season. Outer edge conditions favored growth for three of the four species. Natural seed germination was, however, zero at any site for Juniperus and Olea and low for Ekebergia and Prunus in the open field. Soil scarification influenced germination positively, while weeding did not have a positive effect. These results suggest that simple measures may improve seedling establishment, and that, for some species, forest edges are particularly useful for growth and survival after succesful establishment. Together with erecting fences, needed to protect seedlings against grazing, seed sowing, planting seedling, and soil scarification may contribute to maintain and restore church forests in the fragmented landscapes of northern Ethiopia.     

On the adaptive value of large seeds for tropical moist forest trees: A review and synthesis

In moist temperate and tropical environments species that typically become established in closed, shaded habitats tend to have larger seeds than those that regenerate in open, secondary habitats. Despite this common pattern and the frequency with which benefits of small seed size for early successional species (large number, enhanced dispersal potential) have been discussed, little attention has focused on the advantages of large seeds for species that regenerate in closed, late successional associations. It is generally considered that large seeds enhance seedling survivorship at low light intensities. However, light intensity is only one of several factors that differ between shaded and sunlit habitats. This review examines microclimatic and biotic differences between shaded subcanopy habitats in mature tropical forests and those in sunlit, light gap habitats in which the early stages of tropical forest succession occur. Each factor is examined as a possible selective agent responsible for maintaining seed size differences between two guilds of tropical rainforest trees; the pioneer species that have small seeds and typically become established in large, sunlit gaps in the forest canopy and the persistent, relatively shade-tolerant species that have larger seeds and produce seedlings that survive for variable periods of time in the shade beneath the forest canopy. Three microclimatic factors that differ in subcanopy and gap habitats are examined; temperature, moisture, and light intensity. It is unlikely that temperature has been an important selective agent in maintaining the differences in seed sizes observed between the pioneer and persistent tree guilds. However, greater desiccation stress in light gaps might prevent successful regeneration of larger seeds in this habitat and thus might impose the smaller mean seed sizes of pioneer species. Reduced light intensities in subcanopy habitats also could favor larger seeds in the persistent guild because large seed reserves might 1) enhance the abilities of seeds to persist until suitable light (or moisture) conditions arise by providing for metabolic requirements of seeds during quiescent periods, 2) provide secondary compounds for defense of persistent seedlings against pathogens and predators during periods of low energy availability, 3) provide energy for construction of large amounts of photosynthetic tissue needed to maintain a positive net energy balance when light conditions are just above the leaf light compensation point of the plant, 4) provide energy for growth into higher light intensity strata, and 5) provide nutrients for replacement of lost or damaged tissues in persistent seedlings. Differences between soils in light gaps and subcanopy habitats are considered briefly. It is concluded that too little is known for predictions to be made regarding the probable effects of soil differences on the sizes of seeds able to survive in each habitat. Finally, differences between the two habitats in four biotic factors (competition, predation, pathogens, and mycorrhizal availability) are considered. Of these, greater competition for nutrients in the subcanopy habitat, and competition among co-germinating seedlings for light could have been important in favoring large seeds in the guild of persistent species. Pathogens are known to be more effective in shaded habitats, but data on seedling resistance to pathogens do not provide support for a role of seed size in enhancing resistance. Although differences in predation intensity and in mycorrhizal abundance in the two habitats have not been evaluated in the field, potential roles of these two factors in maintaining the seed size differential between these two guilds of forest trees are discussed. Despite the existence of numerous potential benefits of large seed reserves, seed sizes often must reflect compromises between conflicting selective pressures. Environmental conditions (e.g., moisture availability) can impose upper limits on seed size. Enhanced dispersal potential and greater total propagule numbers from maternal energy reserves are benefits of small seed size that can counterbalance selection for large seed reserves. The interactions between selective forces in molding seed sizes are discussed in a final section.     

Seed germination of a tropical rain forest pioneer tree (Heliocarpus donnell-smithii) in response to diurnal fluctuation of temperature

The tropical rain forest pioneer tree Heliocarpus donnell-smithii Rose establishes itself only in light gaps of the forest canopy. A series of experiments with fluctuating temperatures have shown that the germination is increased if the temperature rises above 31°C during a few hours each day. The laboratory experiments were complemented with determinations of the seed viability in the soil each month during one year, and with determinations of germination under the natural diurnal fluctuation of temperature in a forest gap. Germination increases under fluctuating temperatures, and the seeds can remain dormant when buried in the soil during several months. The diurnal heating of the soil of light gaps as contrasted with the almost constant temperature under undisturbed canopies may be a precise environmental indicator of appropriate conditions for germination and establishment of the pioneer heliophytes of the rain forest.     

The effects of shrub patch sizes on the colonization of pioneer plants on the volcano Mount Koma,northern Japan

Vegetation recovery on Mount Koma, Hokkaido, Japan, has been slow after the catastrophic eruption in 1929, due to undeveloped soil and limited plant colonization. Nowadays, the seedling establishment is supported mostly by a nurse plant, Salix reinii forming shrub patches, facilitates the plant colonization. Although the effects of shrub patches should differ with patch sizes, the size effects have not been examined well. To examine the size effects, seed-sowing experiments were conducted on two common pioneer herbaceous species, Miscanthus sinensis and Polygonum sachalinense, in the field. The seed germination and seedling survival were monitored by the seeds sown into S. reinii patches (0.97 m²–4.12 m² in area) for 4 months during snow-free periods. Microenvironments altered by the patches were measured. Lab-experiments were performed to characterize the seed germination and seedling growth.Larger patches decreased light intensity and temperature more and increased litter and water content. The large patches promoted the seed germination of the two species. Interspecific interactions, examined by a seed mixture experiment, showed that the interaction increased the seed germination on M. sinensis and decreased that on P. sachalinense. On the lab-experiments at three temperatures (15, 20 and 25 °C), M. sinensis seeds germinated more at higher temperatures and obtained higher seedlings biomass. P. sachalinense germinated the seeds more at 20 °C and grew faster at lower temperatures. The total biomass of the two species was reduced by shade that intercepted 50% of light intensity. The seed germination and seedling growth of these two species became higher on litter with 2 cm in depth than on no litter. Soil water supported seed germination when the seeds of these two species were mixed while the water reduced the growth of P. sachalinense seedlings. Therefore, the dry soils were suitable for their growths. In all the treatments, P. sachalinense seedlings showed higher mortalities than M. sinensis.In conclusion, the large patches facilitated more to the colonization of pioneer plants via seed germination and growth. Large patches acted as a nursery supporting the natural regeneration in the disturbed area by improving litter accumulation, maintaining soil water, reducing strong light and/or protecting from heat.     

Tree seed germination and seedling establishment in treefall gaps and understorey in a subtropical forest of northeast India

Abstract Seed germination, and survival and growth of seedlings of four dominant tree species, Quercus dealbata, Quercus griffithii, Quercus glauca and Schima khasiana were studied in the treefall gaps and forest understorey of an undisturbed mature-phase humid subtropical broadleaved forest in northeast India. Three important microenvironmental factors namely photosynthetically active radiation (PAR), soil moisture and litter depth, were also measured in the forest understorey and gaps and correlated with seedling mortality. Seed germination of S. khasiana was significantly higher in the treefall gaps than in the understorey; among the tree species studied, it had the highest germination. Quercus seedlings were abundant in the understorey and small gaps, while S. khasiana seedlings were more numerous in the large gaps. The survivorship curves for the seedling populations revealed that the three Quercus species survived better in the understorey, while S. khasiana did so in the gaps. PAR and soil moisture were positively correlated with tree seedling mortality, which occurred mainly during the winter months. The Quercus seedlings grew better in the forest understorey and small gaps and S. khasiana seedlings in the large gaps. The differential performance of the tree seedlings to the conditions prevailing in the understorey and gaps of two sizes indicates that different species were adapted to different light environments depending upon their optimum requirements. This could be an effective mechanism for promoting species coexistence in the forest community.     

广东南澳岛不同森林群落的林窗环境对3种移植树苗生长的影响

 先锋种和非先锋种可能对林窗产生不同的反应。在广东南澳岛4个不同的森林群落样地里移植了大叶相思（Acacia auriculaeformis A. Cunn.）、尾叶桉（Eucalyptus urophylla S. T. Blake）和荷木（Schima superba Gardn. et Champ）3种树苗,其中大叶相思和尾叶桉是先锋种,而荷木是非先锋种,测定了林窗和非林窗生境中的透光率和幼苗生长高度。结果表明,林窗的透光率大于非林窗的;各群落的透光率有季节性的变化,变化幅度各不同。3种幼苗在林窗内比