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%)。     

北京东灵山区两种生境条件下辽东栎幼苗补充与建立的比较

 北京东灵山区的人工油松（Pinus tabulaeformis）林中常常混生有萌生的辽东栎（Quercus wutaishanica）种群。局部地带辽东栎与油松形成混交林,在山脊及山坡上部一些特殊生境辽东栎甚至取代油松林成为优势种。为了探讨北京东灵山区辽东栎林的天然更新机制及辽东栎幼苗在人工油松林中的天然更新,在油松人工林的林下和林缘两种生境条件下将辽东栎种子播种于2 cm深的土中,对辽东栎幼苗的补充和建立进行了对照试验。结果显示,在辽东栎结实丰年,两种生境条件下播种后辽东栎种子丢失差异并不显著,而辽东栎幼苗补充和建立方面的差异极显著。由于森林动物特别是啮齿类动物的活动对辽东栎幼苗建立的影响具有二重性：消耗种子与促进萌发,本试验特别关注辽东栎幼苗子叶丢失现象及其丢失后果。由于辽东栎种子萌根较早,在幼苗出土前其粗大的主根长达10～20 cm,并已初步形成根系,表明已有相当比例的营养物质从子叶转移到根部。因此当幼苗出土后如果仅仅只是子叶的丢失对辽东栎幼苗的成活和生长均无明显的影响。通过研究发现辽东栎幼苗期子叶丢失有3种形式：1）仅丢失子叶,幼苗其它部位未受伤害,多发生在林缘生境中,占发芽坚果的29.69%;2）整个幼苗连根被拖出地面,多发生在林下生境,占62.43%;3）在子叶与根颈的连接处主干被咬断,林缘为50.88%,显著高于林下的8.41%。但只有后两种形式才导致幼苗死亡。导致这些现象的原因是由于林缘土壤腐殖质含量低,比较干燥,土质较坚实,以及幼苗出土前坚果主根生长得较长等缘故,当幼苗遭受动物捕食时不会轻易地被拖出地面,拖走的往往仅仅是子叶。至生长季节结束,林缘样方辽东栎幼苗的成活率接近20%,茎干平均高度7.94 cm,芽数11.24·株-1,叶片平均干重为81.14 mg·株-1,且几乎全部由丢失子叶的幼苗所构成;而林下样方辽东栎幼苗的成活率不足2%,茎干平均高度4.74 cm,芽数7.52·株-1,叶片平均干重仅为42.27 mg·株-1,以未丢失子叶的幼苗为主。试验结果表明,林缘及类似林缘的环境条件更有利于辽东栎的实生更新。     

西双版纳热带森林树种幼苗的组成、空间分布和旱季存活

林下树种幼苗是森林生态系统的一个重要组成部分, 在森林的自然更新过程中发挥着重要作用。于2007年10月底在西双版纳20 hm²热带森林动态监测样地内设置了450个幼苗样方(1 m²), 对样方内的树种幼苗(胸径＜1 cm)进行了调查, 并观测了当年的实生苗(H≤30 cm)在2007~2008年旱季期间的存活变化。结果表明, 该区森林林下树种幼苗的组成比较丰富, 但个体数在物种间的分布极为不均匀。除4.17%的幼苗个体未鉴定外, 调查到的已知树种幼苗共计6 367株, 隶属于49科116属161种, 并且Simpson、Shannon-Wiener和Pielou指数分别达到了0.69、2.29和0.45。个体数少于5株的幼苗贡献了50.31%的物种数; 在1 m²的样方尺度上, 幼苗密度和种丰富度两者的平均值分别为(14.15±0.72)株·m^-2和(3.73±0.10)种·m^-2(Means±SE, n=450); 优势幼苗为望天树(Parashorea chinensis)、短刺锥(Castanopsis echidnocarpa)和假海桐(Pittosporopsis kerrii)等, 它们的空间分布格局与地形、海拔和母树分布三者之间存在着密切的相关性; 旱季期间, 幼苗的死亡比例较大(26.49%), 主要集中在优势幼苗。幼苗在干旱胁迫环境下的死亡格局表现出了明显的种间差异: 香花木姜子(Litsea panamanja)和望天树两优势幼苗的死亡率分别为62.65%和35.87%, 而假海桐和蚁花(Mezzettiopsis creaghii)等7种优势幼苗的死亡率较低(＜ 9%), 除望天树等13种优势幼苗外, 其余692株幼苗(共129种)仅死亡了10.40%, 而且有91种幼苗均没有发生死亡。幼苗间的存活差异有待于从种子大小、幼苗的形态和生理特性及其所在空间位置的生境特征等多方面开展深入的研究。     

光照强度对乐昌含笑幼苗生长及光合特性的影响

为探析乐昌含笑(Michelia chapensis)在不同光照强度下生长及光合能力的适应机制,以乐昌含笑2年生幼苗为试材,经100%(CK)、70%(T1)、50%(T2)、30%(T3)、10%(T4)全光照5个不同遮荫处理1年(3年生),进而对其生长及光合指标进行测定。结果表明,在70%全光照和100%全光照下,乐昌含笑幼苗存活率与株高、地径生长显著高于其他处理。净光合速率在70%光照强度处理时达最高值(8.553μmol·m^-2·s^-1);随着遮荫胁迫的加重,净光合速率逐渐下降,在50%全光照下净光合速率下降主要由气孔限制导致,30%全光照和10%全光照下由非气孔限制导致。与其他遮荫处理相比,100%全光照和70%全光照下乐昌含笑叶片具有更高的最大净光合速率(8.166和8.735μmol·m^-2·s^-1)、光饱和点(1215.956和1145.328μmol·m^-2·s^-1)和光补偿点(16.280和13.572μmol·m^-2     

陕北黄土高原辽东栎林分布区北部边界形成的光合作用机制

为阐明辽东栎林分布区边界形成的原因,沿秦岭到陕北黄土高原的水热梯度,选取秦岭北坡(鸡窝子)和陕北黄土高原森林区南部(陈家山)、中部(槐树庄)及北部(下寺湾)4个辽东栎林样地,测定了辽东栎叶片的气体交换与叶绿素荧光参数、气孔密度和气孔大小.结果表明: 随着水热梯度由南到北呈现出由凉湿到偏温干的变化,辽东栎叶片最大净光合速率(P_{n max})和光饱和点(L_sp)分别由13.34 μmol CO₂·m^-2·s^-1、1489.9 μmol·m^-2·s^-1显著减少到6.99 μmol CO₂·m^-2·s^-1、1055.6 μmol·m^-2·s^-1,暗呼吸速率(R_d)、光补偿点(L_cp)分别由0.313 μmol CO₂·m^-2·s^-1、7.49 μmol·m^-2·s^-1显著增加到1.080 μmol CO₂·m^-2·s^-1、31.96 μmol·m^-2·s^-1;初始荧光(F_o)与非光化学猝灭系数(NPQ)呈增加趋势,而PSⅡ实际光化学量子产量(Φ_PSⅡ)、表观电子传递速率(ETR)、光化学猝灭系数(q_P)等均显著降低.辽东栎的光合能力沿此梯度逐渐减弱,除黄土高原的陈家山外,其他3个样地辽东栎叶片的气孔密度和气孔大小无显著差异.陕北森林区北部辽东栎叶片的光化学活性和电子传递速率等降低,导致光合速率下降可能是其分布区边界形成的重要影响因素之一.     

北京东灵山3种温带森林土壤呼吸及其20年的变化

土壤呼吸是陆地生态系统最主要的碳释放过程。为了探讨温带森林土壤呼吸在长时间尺度的变化, 利用北京东灵山地区的白桦(Betula platyphylla)林、辽东栎(Quercus wutaishanica)林和油松(Pinus tabuliformis)林3种温带森林永久样地, 于2012-2015年对其土壤呼吸进行测定, 并与1994-1995年的测定结果进行了比较。结果显示: 2012-2015年, 白桦林的平均年土壤呼吸量为(574 ± 21) g C·m^-2·a^-1, 显著高于辽东栎林(455 ± 31) g C·m^-2·a^-1和油松林(414 ± 35) g C·m^-2·a^-1, 比20年前(1994-1995年)的估测值分别增加了85%、17%和73%。这些结果表明, 近20年来这3种生态系统的碳周转速率明显加快。     

三江源地区人工草地的生态系统CO2净交换、总初级生产力及其影响因子

为了揭示三江源区垂穗披碱草(Elymus nutans)人工草地生态系统(100°26′-100°41′ E, 34°17′-34°25′ N, 海拔3 980 m)的净生态系统CO₂交换(NEE), 该研究利用2006年涡度相关系统观测的数据分析了该人工草地的NEE, 总初级生产力(GPP)、生态系统呼吸(R_eco)以及R_eco/GPP的变化特征及其影响因子。CO₂日最大吸收值为6.56 g CO₂·m^-2·d^-1, 最大排放值为4.87 g CO₂·m^-2·d^-1。GPP年总量为1 761 g CO₂·m^-2, 其中约90%以上被生态系统呼吸所消耗, CO₂的年吸收量为111 g CO₂·m^-2。5月的R_eco/GPP略高于生长季的其他月份, 为90%; 6月R_eco/GPP比值最低, 为79%。生态系统的呼吸商(Q₁₀)为4.81, 显著高于其他生态系统。该研究表明: 生长季的NEE主要受光量子通量密度(PPFD)、温度和饱和水汽压差(VPD)的影响, 生态系统呼吸则主要受土壤温度的控制。     

吉林蛟河针阔混交林乔木幼苗组成与月际动态

以吉林省蛟河42 hm²针阔混交林动态监测样地为平台, 在样地内选取224个1 m × 1 m幼苗监测小样方, 基于2013年6至8月每月中旬的幼苗监测数据, 对乔木幼苗物种组成、数量特征、月际动态及幼苗与同种大树之间的关系进行分析。结果表明: (1)该群落共调查到乔木树种幼苗16种。物种组成在6月和7月间变化不大, 但与8月差异较大。物种组成在各样方间表现出极大的差异性, 不同种幼苗出现的样方数为1-159。(2) 6月至8月, 幼苗个体从1722株减少到1214株, 降幅达29.5%。不同种幼苗在个体数量上变异较大, 个体数超过100的幼苗有色木槭(Acer mono)、水曲柳(Fraxinus mandschurica)、紫椴(Tilia amurensis)和东北槭(Acer mandshuricum), 四者个体数之和占所有物种个体总数的84.26%; 不同种幼苗密度变异性较大, 只有色木槭、水曲柳、紫椴和东北槭密度大于1株·m^-2, 其他种幼苗密度均较低。(3)新生幼苗更新、死亡格局表现出明显的种间差异与月际间差异, 7月新生幼苗总体死亡率(48.9%)显著高于8月(28.3%); 整个调查季(6-8月), 新生幼苗总体死亡率(40.56%)明显高于多年生幼苗(7.34%)。就幼苗更新情况而言, 该研究群落一年中更新主要集中在6月。(4)色木槭、紫椴、杉松(Abies holophylla)幼苗的密度与同种成年个体的胸高断面积之和之间存在显著的正相关关系(p = 0.006、0.013、0.037), 表明三者幼苗密度随周围母树多度的增加而增加, 其他物种幼苗密度与同种个体数目或同种胸高断面积之和未表现出显著的相关关系。     

模拟氮沉降对南亚热带两种乔木幼苗生物量及其分配的影响

探讨了南亚热带季风常绿阔叶林两种优势树种荷木(Schima superba)和黄果厚壳桂(Cryptocarya concinna)幼苗的生物量及其分配对氮沉降增加的响应。实验分为对照(CK)、T₅、T₁₀、T₁₅和T₃₀ 5个处理,每个处理设置3次重复。所施氮肥为NH₄NO₃,以溶液方式喷施,5个处理浓度分别为0、0.12、0.24、0.36、0.72 mol N·L^-1。每月喷施2次,5个样方1年喷施的总氮量分别相当于氮沉降率0、5、10、15、30 g N·m^-2·a^-1。经过11个月的施氮处理,两种幼苗对氮沉降的响应存在差异,其中黄果厚壳桂幼苗的基径、株高、全株生物量和相对生长速率除最高处理T₃₀外,均高于对照,但荷木幼苗的基径、全株生物量和相对生长速率除T₁₀外,均小于对照。氮处理也对生物量的分配产生了明显的影响,两种幼苗的叶重比以T₃₀最低,表明高氮处理不利于幼苗叶片的生长;枝重比均以T₃₀最高,反映了高氮处理的幼苗生物量分配到枝干的比例最高;根重比和根冠比均以对照样方幼苗的最高,表明氮处理抑制根的生长,分配到根部分的生物量下降。总的来看,经过11个月的处理,除最高处理T₃₀外,氮处理仍对黄果厚壳桂幼苗的生长有促进作用,而对荷木幼苗的生长则趋向于一定程度的抑制效应,表明黄果厚壳桂幼苗更能耐受高氮条件。     

不同栽植密度对斑叶稠李苗木培育质量的影响

以斑叶稠李（Padus maackii）1年生苗木为研究对象,通过4种不同栽植密度（60、80、100、120 株·m^-2）试验,测定其苗木形态、生物量、光合速率及养分含量,旨在探明不同密度对斑叶稠李苗木生长及养分含量的影响,为其高质量苗木培育提供理论依据。结果表明：（1）栽植密度显著影响苗木生物量,各密度下苗木根、茎、叶生物量由大到小顺序均为80 株·m^-2 > 60 株·m^-2 > 100 株·m^-2 > 120 株·m^-2;60和80 株·m^-2密度下斑叶稠李苗木质量指数显著高于100和120 株·m^-2密度处理。（2）栽植密度显著影响苗木侧根数,在80 株·m^-2的密度下达到最大;（3）80 株·m^-2密度较其它密度显著提高了苗木氮、磷、钾养分含量。（4）叶生物量、根生物量和侧根数与苗木各质量指标间Pearson相关性系数均达到了显著水平（P<0.1）,而光合速率和主根长与苗木各质量指标均不相关（P>0.1）。综合以上结果,斑叶稠李1年生苗木最适栽植密度为80 株·m^-2,且密度处理主要影响斑叶稠李苗木叶生物量、侧根数及根生物量指标,进而影响苗木质量。     

Differential seed and seedling predation by crabs: impacts on tropical coastal forest composition

Recently, the importance of seed predation by crabs on mangrove species distributions and densities has been established by several studies. In a tropical coastal terrestrial forest in Costa Rica, we investigated the relative importance of predation by land crabs, Gecarcinus quadratus, and hermit crabs, Coenobita compressus, on measured forest composition through a series of seed removal and seedling establishment experiments. We also used natural light-gaps and adjacent non-gap sites to test how canopy cover affects crab predation (seed removal) and seedling establishment. We found fewer tree species (S=18) and lower densities (seedlings, saplings, and adults) in the coastal zone within 100 m of coastline, than in the inland zone (S=59). Land crab densities were higher in the coastal zone (3.03±1.44 crabs m^–2) than in the inland zone (0.76±0.78 crabs m^–2), and hermit crabs were not present in the inland zone. Seed removal and seedling mortality also were higher in the coastal zone than in the inland zone, and in the open controls than in the crab exclosures. Mortality of seeds and seedlings was two to six times higher in the controls than exclosures for four of the five experiments. Crabs preferred seeds and younger seedlings over older seedlings but showed no species preferences in the seed (Anacardium excelsum, Enterolobium cyclocarpum, and Terminalia oblonga) and seedling (Pachira quinata and E. cyclocarpum) stages. We conclude that the observed differences in tree densities were caused by differential crab predation pressure along the coastal gradient, while the differences in species composition were due to predator escape (satiation) by seed quantity. Canopy cover did not affect seed removal rates, but did affect seedling survival with higher mortality in the non-gap versus gap environments. In summary, crab predation of seeds and seedlings, and secondarily canopy cover, are important factors affecting tree establishment in terrestrial coastal forests.     

Rodent seed predation and seedling recruitment in mesic grassland

Seedling recruitment of two grasses (Arrhenatherum elatius and Festuca rubra) and two herbs (Centaurea nigra and Rumex acetosa) was measured in areas with and without rodents to which seeds of each species were sown at three seed densities (1000, 10,000 and 50,000 seeds m⁻²) in two seasons (spring and autumn 1995). Seed removal was measured for 10-day periods and the fate of seedlings was followed for 15 months after sowing. The proportion of seed removed ranged from 6 to 85% and increased with increasing seed density for each species. Rodents had no effect on seedling emergence or survival in the spring sowing. In the autumn sowing, rodents reduced seedling emergence of all four species sown at 1000 and 10,000 seeds m⁻² but had no impact at 50,000 seeds m⁻², presumably because of microsite limitation. We suggest the difference between spring and autumn arose because emergence was seed limited in autumn but microsite limited in spring; microsite availability was higher in autumn because a summer drought killed plants, reduced plant biomass and opened up the sward. Fifteen months after the autumn sowing, fewer A. elatius and C. nigra seedlings survived on plots exposed to rodents. This result reflected not only the reduced seedling emergence but also increased seedling mortality (seedling herbivory) in sites exposed to rodents. In contrast, F. rubra and R.acteosa showed density-dependent seedling survival which compensated for initial differences in seedling emergence, so that no effect of rodents remained after 15 months. The results suggest that rodent seed predation and seedling herbivory exert strong effects on seedling recruitment of A.elatius and C. nigra when recruitment conditions are favourable (conditions that lead to high microsite availability) and may contribute to both species being maintained at low densities in the grassland. The results also demonstrate that highly significant impacts of rodent seed predation at the seedling emergence stage can disappear by the time of plant maturation. Received: 2 March 1998 / Accepted: 28 September 1998     

Intraspecific and phylogenetic density-dependent seedling recruitment in a subtropical evergreen forest

Recent evidence suggests that plant performance can be influenced by the phylogenetic diversity of neighboring plants. However, no study to date has examined the effect of such phylogenetic density dependence on the transition from seed to seedling. Using 6 years of data on seedling recruitment and seed rain of 13 species from 130 stations (one 0.5 m² seed trap and three adjacent 1 m² seedling plots) in a subtropical evergreen forest, we asked: (1) Does negative density dependence act across seed to seedling stages? (2) Is there evidence for phylogenetic density dependence during the seed to seedling transition? (3) Does the strength of density dependence vary among years? Generalized linear mixed-effects models were used to model seed to seedling transition as a function of conspecific seed and seedling densities, heterospecific seed and seedling densities, and mean phylogenetic distance of heterospecific seeds and seedling. Conspecific seed density had a significant negative effect on seedling transition rates for 12 of 13 focal species. In contrast, conspecific seedling density had a positive effect for 7 species, suggesting species-specific habitat preferences. Few species were significantly affected by the density or phylogenetic relatedness of heterospecific seeds and seedlings. Only conspecific seed density effects varied among years for most focal species. Overall, our results reveal that conspecific seed and seedling densities play a more important role than the density or relatedness of heterospecific seeds and seedlings during the seed to seedling stage, suggesting that species-specific seed predators, along with habitat preferences, may contribute to diversity maintenance in this forest.     

黄土高原马栏林区辽东栎更新特性研究

研究了黄土高原马栏林区主要植被类型中的辽东栎幼苗的数量特征,更新层幼苗、幼树的实生和萌生特性及其辽东栎在垂直结构上的数量分布。结果表明:(1)辽东栎幼苗在黄土高原马栏林区分布广泛且数量充足。不同的植被类型中辽东栎种群表现出不同的大小级结构,在油松—辽东栎混交林、油松林和辽东栎林中辽东栎种群的幼苗、幼树和成树均占一定的比例,而在油松—白桦混交林、白桦林、山杨林和山杨—白桦混交林中辽东栎种群则以幼苗和幼树为主。表明辽东栎种群在该地区植被的发展过程中将产生重要的作用。(2)辽东栎在这一地区是由实生和萌生的个体混合组成的。在各种植被类型中实生植株的密度都高于萌生植株,辽东栎种群的更新在该地区可能主要是通过实生植株来完成的,即辽东栎实生植株在更新过程中起重要的作用。但萌生植株作为辽东栎顺利通过瓶颈的一种手段,作为辽东栎种群繁衍和稳定的一种途径,在辽东栎种群的更新中也起着一定的作用。     

樟树(Cinnamomum camphora)幼苗细根形态对氮磷添加和幼苗密度的响应

全球氮沉降对森林生态系统结构和功能的影响已成为现代生态学研究热点之一,我国华南地区氮沉降的增长引起了土壤酸化和磷限制加剧等一系列生态问题。密度制约着植物个体对环境资源的吸收利用,是自然界中十分重要的选择压力之一。因此研究樟树(Cinnamomum camphora)幼苗的细根形态对氮磷添加和密度的响应,有利于了解亚热带树木根系对氮沉降和磷添加与林分密度的响应过程和机制,并为全球变化背景下樟树林生态系统的管理提供依据。本研究以1年生樟树幼苗为试验材料,选择氯化铵(NH_4Cl)作为氮肥以模拟大气氮沉降,并且以二水合磷酸二氢钠(NaH_2PO_4·2H_2O)模拟磷添加,氮磷处理设置4个水平,即对照、施N、施P和施N+P;种植密度设置10、20、40和80株/m~2 4个水平。测定各处理樟树幼苗细根的根长、表面积、体积和根尖数,分析氮磷添加、密度和两者交互作用对樟树幼苗细根的影响。研究结果表明,与对照处理相比,N、P和N+P处理促进了幼苗细根长度、表面积、体积以及根尖数的增加。低密度条件下的N添加对幼苗根系形态的促进效果强于P添加。N+P处理对10、20、40株/m~2幼苗根系形态的促进效果最佳,而各处理对80株/m~2幼苗根系形态的促进效果均无显著性差异。随着种植密度的增大,幼苗细根长度、表面积、体积和根尖数均减少。樟树幼苗的细根长度、表面积、体积和根尖数在各密度间和不同氮磷添加处理间均有显著性差异,密度和氮磷处理间的交互作用对根系形态各指标均无显著影响。     

Sawgrass Seedling Responses to Transplanting and Nutrient Additions

Understanding Cladium jamaicense (sawgrass) seedling establishment is an important component of an Everglades restoration program because the degree of sawgrass recovery and concurrent Typha domingensis (cattail) decline will be used to evaluate restoration success. To understand sawgrass recovery at locations with increased soil nutrients, we tested the effects of transplanting sawgrass seedlings to pots at different densities and investigated how nutrient additions affect seedling growth. Survivorship of seedlings transplanted into moist commercial potting soil at three densities ranged from 61% to 95%. After 6 months, maximum survivorship (90%) occurred at medium densities (2–4 seedlings per pot 16 cm in diameter). Nutrient additions, totaling 6.5 N g/m², 9.8 P g/m², 6.5 g/m², were applied approximately 4 months after seedlings were transplanted. The biomass of the plants receiving nutrient additions (pulsed) was significantly higher (by over 30%) than plants with no nutrient addition (control). Photosynthetic rates for nutrient-enriched plants (measured 6-weeks after the nutrient additions) were significantly greater (by 32–45%) than for control plants. Instantaneous leaf water use efficiency increased significantly (by more than 20%) in pulsed plants. The results suggest that preventing root damage is crucial for the success of trans planted sawgrass seedlings and that nutrient additions enhanced seedling growth.     

Recovery of aSasa tsuboiana population after mass flowering and death

The recovery process of aSasa tsuboiana population after a mass flowering and death in 1977 was investigated by 15 years of observation in the Hira Mountains, Kinki district, western Japan. Seed production was high (6600–13 800 seeds m⁻² inSasa plots and 3900 seeds m⁻² in a forest plot) but emergent seedling density was low (14–21 seedlings m⁻²), probably because of seed predation byMicrotus montebelli occurring between seed shedding and the next spring. The seedling density had decreased further by the next year and theS. tsuboiana population recovered from only a limited number of seedlings. In spite of such a low initial density, theS. tsuboiana population was able to regenerate successfully and attained the previous full stand height in 7–16 years.Miscantbus sinensis invaded and delayed the recovery ofS. tsuboiana in one plot, butS. tsuboiana became dominant as it caught up with the height ofM. sinensis. Seedling growth patterns, such as frequent tillering, the onset of rhizome extension in the early stage of seedling growth and frequent culm production from rhizomes, played important roles in the successful regeneration ofS. tsuboiana.     

Seedling bank dynamics of Fagus grandifolia var. mexicana before and after a mast year in a Mexican cloud forest

Abstract. Fagus grandifolia var. mexicana seedling dynamics were studied in a relict forest inside the crater of a volcano where it is the only canopy tree species. The objectives of the study were (1) to determine changes in seedling density before and after a mast year, as well as to monitor seedling recruitment, mortality and growth rate in relation to the micro‐environment, and (2) to discuss the impact of masting on seedling dynamics of the population. Before masting, seedling density was 8.8 seedlings m^–2, afterwards seedling density peaked at 51.5 seedlings m^–2, then decreased by 50% in 3 months and by 85% after 8 months, down to levels of before the mast year (9.9 seedlings m^–2) after 16 months. Seedlings in the forest floor before the mast‐seeding event showed a low relative growth rate – 0.14 mm mm^–1 mo^–1 against 1.27 mm mm^–1 mo^–1 for seedlings that emerged immediately after masting. Seed germination was high (83%) and rapid (L₅₀= 7 days) following masting. Seedling growth was positively correlated with soil water content but not with temperatures and relative humidity. Data suggested that seed production in mast years is important in maintaining the seedling bank, and thus the viability of relict Fagus populations.     

Recruitment and survival of Argyrodendron actinophyllum seedlings in an Australian rainforest

The capacity of seedlings to survive for extended periods beneath intact forest increases the likelihood of regeneration of many species of canopy trees in rainforests. I studied the demographics of Argyrodendron actinophyllum (F.M.Bail.) H.L.Edlin seedlings in a subtropical rainforest in northern New South Wales. A mast seeding of A. actinophyllum was observed and subsequent survival of seedlings monitored over a four year period. Densities of seedlings that emerged correlated with seedfall, while seedfall depended on the size and distance to the surrounding trees. Mortality of seedlings showed density-dependence at higher seedling densities (above about 100 seedlings m^?2), apparently in response to browsing pressure that varied with the density of seedlings. Seedlings that were protected from vertebrates by exclosure cages had lower mortality rates than unprotected seedlings and showed no density response. Glasshouse experiments showed seedling growth was reduced by defoliation, light intensity and initial seed weight, and that seedlings could not persist at light intensities below about 1% ambient, which occur in darker patches on the forest floor. Possible mechanisms whereby the observed spatial and temporal patterns of seedling recruitment could reduce the likelihood of the species becoming more common relative to other tree species in the forest are discussed.     

Aristida beyrichiana (Wiregrass) Establishment and Recruitment: Implications for Restoration

Restoration of the longleaf pine ecosystems of the southeastern United States has focused interest on the regeneration and establishment of Aristida sp. (wiregrass) as a means to reestablish ecological function and structure of the ecosystem. This study examined dispersal distance from planted adults and canopy cover and density effects on establishment and reproduction. In 1994 wiregrass plugs were planted in two densities (500 seedlings/100 m² and 49 seedlings/100 m²) and three canopy‐thinning treatments (25 m² basal area/ha, 16 m² basal area/ha, and 8 m² basal area/ha) were implemented in a 20‐year‐old longleaf plantation in southwestern Georgia. Due to the intense site preparation and the density of pines planted, virtually no understory vegetation was present. The site was burned in June 1995, which promoted seed production of the planted wiregrass. Results indicate that the 8 m² basal area/ha treatment results in larger plants that in turn produce a greater number of seedling recruits. No seedling recruitment occurred in control plots. Dispersal distances of up to 594 cm were recorded. Natural seedling recruitment occurred at low‐density transplanting (5 plants/10 m²), denoting that high‐density planting similar to natural density (5 plants/m²) is not required for successful establishment or reproduction. However, overstory thinning in dense pine plantations is required for reproduction and increases the survival of individual plants due to changes in the environmental conditions at the forest floor.