雪灾干扰后林冠开阔度对黄心树幼苗更新的影响

幼苗更新是森林更新的关键过程,而林窗对于植物幼苗更新、生长及最终存活具有重要影响。极端气候事件会使森林在短时间内形成大量林窗,从而显著影响林内幼苗更新和存活。本研究以2015年雪灾后云南省哀牢山中山湿性常绿阔叶林优势种黄心树(Machilus bombycina)幼苗为对象,对194个1 m×1 m样方中的幼苗生长和死亡动态进行为期4年的监测,利用线性混合模型(LMM)和广义线性混合模型(GLMM),分析林冠开阔度对幼苗高度相对生长率、叶片相对增长率、新增率和死亡率的影响,研究了雪灾干扰后的林冠开阔度对植物幼苗更新的影响。结果表明:(1)林冠开阔度随时间推移逐渐变小(20.07%～9.97%),且速度由快到慢;(2) 2015—2016年,已有幼苗高度相对生长率与林冠开阔度呈显著正相关(P0.05),其余年份两者间无显著相关性; 2016—2017年已有幼苗叶片相对增长率与林冠开阔度呈显著正相关(P0.05),其余年份两者间无显著相关性;(3)林冠开阔度与幼苗新增率和死亡率均无显著相关性。本研究表明,雪灾后造成的林冠开阔度增加有利于黄心树幼苗生长。     

林窗对热带雨林冠层树种绒毛番龙眼幼苗生长的影响

在林窗中央、林窗边缘和林冠下3种不同光照梯度的森林生境中,研究了西双版纳季节雨林冠层树种绒毛番龙眼幼苗的早期 (种子萌发后10周内) 生长和定居后 (实生苗生长3个月以上) 的生长特点.结果表明: 绒毛番龙眼幼苗在早期生长阶段,林窗中央的株高、基径、总干质量、单株叶面积和相对生长率最大,分别为24.45 cm、3.17 mm、0.79 g、122.45 cm²和14.78×10^-3 g·d^-1.林冠下根冠比 (0.87) 高于林窗中央 (0.20) ,可能是光照和水分共同作用的结果.林窗中央较强的光照有利于定居后幼苗的生长,株高、基径、总干质量、单株叶面积、相对生长率和净同化率均在林窗中央最大,实验结束时分别达到31.48 cm、3.80 mm、2.22 g、174.52 cm²、2.29×10^-3 g·d^-1和2.54×10^-5 g·cm^-2·d^-1.幼苗死亡可能与水分胁迫密切相关,由水分胁迫引起的幼苗死亡率在林冠下最高 (26.88%),但林冠下由脊椎动物捕食引起的幼苗死亡率较低(2.93%),从而使林冠下幼苗的最终存活率最高 (70.19%).光照是影响绒毛番龙眼幼苗形态学调节的重要因素, 林窗中央不同生长阶段幼苗的比叶面积最低,但相对生长率和净同化率最大.水分胁迫和光照在幼苗定居后仍是影响幼苗生物量分配的重要因素, 林窗边缘幼苗的根冠比最高 (0.33).     

林窗对川西亚高山岷江冷杉幼苗生物量及其分配格局的影响

采用样带法调查了川西亚高山原始岷江冷杉林林窗和林冠下岷江冷杉幼苗(H≤100 cm)的密度、高度、基径和各构件生物量,分析了各构件生物量间的相关性.结果表明：林窗与林冠下幼苗密度分别为12 903和2 017株·hm^-2;平均高度分别是26.6和24.3 cm,差异显著;平均基径分别为4.97和5.13 mm,差异不显著.林窗内各龄级幼苗的生物量与林冠下同龄级幼苗的生物量之间差异不显著.林窗对不同龄级幼苗各构件生物量积累的影响不同,林窗内幼苗枝干生物量比在12年达到最大(1.54),随后其比值维持在0.69左右;林冠下幼苗在15年后(含15年),枝条生物量大于主干生物量.生长在林窗和林冠环境的幼苗单株总生物量、叶生物量、茎生物量、地上生物量和根生物量与幼苗基径的平方(D²)和苗高(H)的乘积有显著的线性关系.林窗与林冠下幼苗各构件生物量之间有显著的正相关关系.     

常绿阔叶林林冠环境对栲幼苗建成的影响

植物幼苗建成阶段是决定种群自然更新的关键生活史阶段。研究林冠环境对常绿阔叶林优势种幼苗建成阶段的影响对该类森林的恢复和管理具有重要意义。2014–2016年,该研究在重庆市缙云山国家级自然保护区的常绿阔叶林的不同林冠环境(大林窗:150 m~2,中林窗:100–150 m~2,小林窗:50–100 m~2,对照:林下)下进行栲(Castanopsis fargesii)种子野外播种实验,并对栲幼苗命运和生长情况进行了3年的持续监测。结果表明:(1)栲幼苗出土时间从7月持续到12月,出苗时间较长,大林窗对幼苗出土具有延迟作用;(2)栲种子野外平均萌发率为(62.8±2.0)%,第3个生长季(2016年)末幼苗平均存活率为(65.1±2.2)%,枯萎是栲幼苗死亡的主要原因;(3)林冠环境对栲种子萌发率及第1个生长季(2014年)末的幼苗存活率无显著影响,对第2个(2015年)和第3个生长季末的幼苗存活率具有显著影响;(4)林冠环境在第1个生长季对幼苗生长无明显影响,但在第2个和第3个生长季具有显著影响,大、中林窗中幼苗总生物量、株高、基径、根长和叶片数显著高于林下,比叶面积显著低于林下;(5) 3个生长季内, 4类林冠条件下栲幼苗的叶质量比和茎质量比升高,根质量比和根冠比降低,并且从第2个生长季开始大林窗中栲幼苗的叶质量比显著高于林下,根质量比和根冠比显著低于林下。栲幼苗早期的存活和生长依赖种子储存的能量,受林冠条件影响较弱,后期则依赖光合作用,受林冠条件影响较强,从整个幼苗建成过程看,大、中林窗更有利于栲幼苗定居。     

哀牢山中山湿性常绿阔叶林林窗更新研究

对云南哀牢山中山湿性常绿阔叶林林窗更新状况的调查结果表明,林内优势树种在林窗阶段不占优势,其在林窗内的重要值显著低于成熟林分;林窗内外的乔木幼苗在组成上存在较大差异,林窗内的幼苗多样性(H=2．73,D=0．89)高于林冠下(H=2．25,D=0．82),二者的Jaccard相似系数只有0．6．许多树种的幼苗只出现在林窗内;林窗内的乔木幼苗密度(38636株·hm²)远远高于林冠下(17323株·hm²)．林窗内和林冠下的乔木幼苗(H≤50cm)均以高度为11～20cm幼苗的在数量上占优势,但林窗内高度超过20cm的幼苗比例明显高于林冠下;林窗大小对乔木幼苗更新有重要影响,不同树种的幼苗密度高峰出现在不同大小级别的林窗内．     

岷江冷杉林林窗小气候及其对不同龄级岷江冷杉幼苗生长的影响

对川西亚高山原始岷江冷杉(Abies faxoniana)林林窗内和林冠下小气候及岷江冷杉幼苗生长和生物量进行了两个生长季的连续观测。结果表明:6月林窗内与林冠下太阳辐射的日积累量没有显著性差异,而7~8月的日积累量则有显著性差异。整个生长季节,林窗内太阳辐射的平均积累量为8.10×MJ·m^-2,而林冠下太阳辐射的平均积累量为5.02×MJ·m^-2,两个位点太阳辐射积累量的显著差异主要来自7~8月日积累量的不同;林窗内5和15 cm层土壤的日平均温度比林冠下相应深度分别高2.1和2.7℃,差异显著。林窗内和林冠下3~8年岷江冷杉幼苗高增长率分别为1.2±0.3 cm·a^-1和1.1±0.3 cm·a^-1,差异不显著;9~20年岷江冷杉幼苗高增长率分别为6.2±2.4 cm·a^-1和3.0±0.9 cm·a^-1,差异显著。林窗内岷江冷杉幼苗根、主茎和总生物量与林冠下幼苗根、主茎和总生物量没有显著差异。不同年龄的岷江冷杉幼苗叶和侧枝生物量积累对林窗微环境的响应不同。     

常绿阔叶林林冠环境对栲幼苗建成的影响

植物幼苗建成阶段是决定种群自然更新的关键生活史阶段。研究林冠环境对常绿阔叶林优势种幼苗建成阶段的影响对该类森林的恢复和管理具有重要意义。2014-2016年, 该研究在重庆市缙云山国家级自然保护区的常绿阔叶林的不同林冠环境(大林窗: >150 m ², 中林窗: 100-150 m ², 小林窗: 50-100 m ², 对照: 林下)下进行栲(Castanopsis fargesii)种子野外播种实验, 并对栲幼苗命运和生长情况进行了3年的持续监测。结果表明: (1)栲幼苗出土时间从7月持续到12月, 出苗时间较长, 大林窗对幼苗出土具有延迟作用; (2)栲种子野外平均萌发率为(62.8 ± 2.0)%, 第3个生长季(2016年)末幼苗平均存活率为(65.1 ± 2.2)%, 枯萎是栲幼苗死亡的主要原因; (3)林冠环境对栲种子萌发率及第1个生长季(2014年)末的幼苗存活率无显著影响, 对第2个(2015年)和第3个生长季末的幼苗存活率具有显著影响; (4)林冠环境在第1个生长季对幼苗生长无明显影响, 但在第2个和第3个生长季具有显著影响, 大、中林窗中幼苗总生物量、株高、基径、根长和叶片数显著高于林下, 比叶面积显著低于林下; (5) 3个生长季内, 4类林冠条件下栲幼苗的叶质量比和茎质量比升高, 根质量比和根冠比降低, 并且从第2个生长季开始大林窗中栲幼苗的叶质量比显著高于林下, 根质量比和根冠比显著低于林下。栲幼苗早期的存活和生长依赖种子储存的能量, 受林冠条件影响较弱, 后期则依赖光合作用, 受林冠条件影响较强, 从整个幼苗建成过程看, 大、中林窗更有利于栲幼苗定居。     

不同生境栓皮栎天然更新幼苗植冠构型分析

栓皮栎存在于秦岭南坡的多种林分中,生活在不同生境中的个体往往形成不同的树冠形态和构型特征。为了说明不同生境条件下栓皮栎幼苗的植冠构型变化,采用典型抽样法,对秦岭南坡3种生境中(林冠下、林隙、林缘)的栓皮栎天然更新幼苗的侧枝、叶片特征及其空间分布进行了调查分析,结果表明:3种不同生境中栓皮栎幼苗植冠形态发生了明显的可塑性变化,(1)林冠下的幼苗明显为开阔型树冠,林隙和林缘处的幼苗树冠相对紧密;(2)幼苗的1级侧枝密度与分枝角度在3种生境下均差异显著(P0.05);从Ⅰ到Ⅳ层,林冠下幼苗的分枝角度在冠层内变化幅度不到5°,而林缘处幼苗的分枝角度变化高达40°;发生5个以上1级侧枝的概率以林冠下最大,为0.6;(3)从林缘、林隙到林冠下,幼苗的叶长、叶宽、单叶面积、叶面积指数逐渐降低,数量叶密度和比叶面积则逐渐增大,与其它两种生境相比,林冠下幼苗的叶片逐渐向树冠上层集中,且以更高序的侧枝为主要着生枝条;(4)林隙中栓皮栎幼苗的树高、地径明显优于林缘和林冠下,缩短了苗木进入主林层的时间,林隙对栓皮栎种群更新有利。在今后栓皮栎林的经营中,可以通过适当间伐来增加林隙数量,为森林更新和结构的优化的提供有利条件。     

小径竹对亚高山暗针叶林优势 树种林窗更新的影响

在亚高山岷江冷杉林中选取面积≤50m2,50~150m2,>150m2的林窗,每种类型内均包含3种小径竹盖度(≤20%、20%~50%、>50%),共调查林窗9个,并调查包含这3种小径竹盖度的三块林下对照样地,研究了该类森林林窗更新与小径竹生长的关系。结果表明:(1)无论林窗大小,林窗内的更新幼苗数量都比林下的多,林窗更新是岷江冷杉群落更新的主要途径;(2)所选林窗均为发育早期,林窗对更新树种的种类组成和数量的影响主要表现在幼苗上。糙皮桦幼树及幼苗数量随林窗面积的增加而急速增加,它的更新更需要较大的林窗;(3)不同小径竹盖度下幼苗的密度呈现显著性变化,小径竹的生长明显抑制了森林幼苗的更新及填充的进程;(4)华西箭竹的分散程度随林窗面积的增大而降低,而平均高度和基径则有增加的趋势。     

山地落叶阔叶林优势树种米心水青冈幼苗的定居

在郁闭的林冠下、模拟林窗和林间空旷地3种光照环境中,研究了施肥和未施肥的米心水青冈幼苗生存和生长发育过程．结果表明,幼苗在林下的发育受到光照不足的严重抑制,生长在林下的幼苗比生长在林窗和空旷地幼苗死亡快,死亡率高,幼苗在郁闭林下能够生存的时间不超过12周．施肥处理的幼苗比对照的幼苗死亡快,死亡率高．幼苗死亡很可能与土壤中的病原生物有关．虽然由林下光照强度增加到模拟林窗的光照强度后,幼苗发育有明显改善,但幼苗在模拟林窗环境和空旷地的生长没有显著差异．结果说明,米心水青冈新出土的幼苗在郁闭林冠下易受伤害,更新立苗阶段需要有比较好的光照条件,肥沃土壤可能也无助于改善郁闭林冠下幼苗的定居．     

八大公山常绿落叶阔叶混交林影响幼苗存活的主要因子分析

幼苗是植物生活史中最脆弱的阶段,对幼苗存活影响因子的分析有助于我们更清楚的了解森林群落的天然更新机制。利用广义线性混合模型（GLMM）对八大公山常绿落叶阔叶混交林中影响幼苗存活的主要生物与非生物因子进行了研究。结果表明：（1）在群落水平上,幼苗存活与生物因子中的同种幼苗密度呈显著负相关,与非生物因子中的冠层开阔度呈显著正相关;（2）从年龄上看,4年生以下龄级的幼苗存活更容易受到同种幼苗密度的影响,与同种幼苗密度呈显著负相关;4年生及其以上的幼苗存活则主要受非生物因子影响;（3）从生活型上看,相对于常绿物种,落叶物种的幼苗存活率更容易受到同种幼苗密度的影响,也与冠层开阔度呈正相关;（4）在物种水平上,生物因子与非生物因子对不同物种幼苗存活率的影响也不相同。其中,宜昌润楠（Machilus ichangensis Rehd.et Wils.）的存活率与冠层开阔度呈正相关;薄叶山矾（Symplocos anomala Brand）幼苗的存活率与同种幼苗密度、异种大树胸高断面积、林冠开阔度、坡向均呈显著负相关,而与异种幼苗密度和海拔呈显著正相关。本研究表明影响幼苗存活的因子是多样的,而且不是随机发生的。在不同水平上影响幼苗存活的因子不同。     

Natural regeneration of selected timber species in the Republic of Congo

Natural regeneration of timber species is critical to the sustainable management of tropical forests. To understand what determines regeneration success of timber species in the Congo Basin, we evaluated whether seedling recruitment rates differed between forest logged 30 years previously and unlogged forest and determined the environmental factors that influence seedling density, growth and survival. We monitored the fate of 2186 seedlings of seven timber species within 462, 25‐m² plots located along 21 transects. We characterized seedling plots by light availability, soil nutrient availability and pH, and abundance of mammalian herbivores and then used linear and generalized linear mixed models to evaluate the variables that influenced seedling density, growth and survival. Light availability and canopy openness were 18% and 81% higher in logged than unlogged forest, and concentration of soil nutrients varied between sites. Seedling density was 32% higher in unlogged than logged forest. Taking all species together, seedling survival was positively correlated with calcium and negatively with magnesium and available phosphorus. Rates of seedling growth increased with available light. Taken separately, seedlings of the selected timber species responded differently to abiotic and biotic factors, demonstrating species‐specific regeneration requirements.     

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.     

辽东山区次生林乔木幼苗组成及其年际动态

为了解辽东山区次生林乔木幼苗组成及其年际动态, 本文以4 ha动态监测样地为平台, 对样地内1,600个 5 m × 5 m样方进行监测。依据2014-2016年连续3年的调查, 对样地内乔木幼苗的组成、高度分布、新增和死亡年际动态、空间分布格局等进行分析。结果表明: (1)调查期间共记录到22种乔木幼苗, 3年间幼苗组成没有发生变化, 但各个样方间出现极大差异, 并且幼苗优势树种组成与样地内优势树种成分保持着一定的相似性。(2)幼苗数量在不同树种和年际间表现出较大的差异: 花曲柳(Fraxinus rhynchophylla)、色木槭(Acer mono)、胡桃楸(Juglans mandshurica)在3年间幼苗数量最多, 占幼苗总数的75.6%; 花曲柳和胡桃楸幼苗数量表现出较明显的年际波动, 其他树种波动较小, 不同树种的幼苗密度差异很大。(3)幼苗新增和死亡存在明显的种间和年际差异: 2014-2015年间幼苗的新增数量(3,888)明显高于2015-2016年间(1,710), 同时2014-2015年间幼苗死亡率(23.7%)也明显高于2015-2016年间(12.7%)。对2015-2016年间新增幼苗和已有幼苗的死亡情况进行比较可以发现, 新增幼苗总体死亡率(18.8%)明显高于已有幼苗(8.1%)。(4)对比幼苗和大树的空间分布可以发现, 样地内优势幼苗都表现出集群分布的特征。在空间分布上, 幼苗与母树保持一定的相似性。     

Ecology of Aglaia mackiana (Meliaceae) Seedlings in a New Guinea Rain Forest1

The large seeds of Aglaia mackiana (Meliaceae) germinate and produce vigorous seedlings under closed canopies or in large gaps. To assess seedling ecology after germination, we measured growth, herbivore damage, and survivorship of seedlings over one year. The sample included shaded seedlings from dispersed seeds, undispersed seeds under parent trees, and seedlings transplanted to gaps. We quantified the light environment using hemispherical canopy photographs taken above seedlings at the beginning and end of the one–year study. Seedlings transplanted to gaps grew faster and had more leaves, larger total leaf surface area, longer secondary roots, and greater root mass than shaded seedlings. Seedlings in gaps did not differ from shaded seedlings in survivorship or amount of herbivore– and pathogen–caused leaf damage. The canopy photographs taken one year apart suggest there is a rough equilibrium in closed canopies with slight changes occurring around an average light level. Sites with < 0.06 ISF (a unitless, relative measure of canopy openness or reflected sunlight) tended to remain the same with minor fluctuations toward brighter or darker. Sites with canopy openness > 0.06 ISF tended to close; few gaps grew larger. Seedlings under parenr trees and seedlings away from parent trees had similar amounts of leaf damage and virtually identical survivorship after 18 months, but seedlings under parent trees had slower growth rates and smaller total leaf surface areas. Dispersal did not strongly benefit seeds via escaping high levels of mortality or comperition around the parent.     

Early response of Abies balsamea seedlings to artificially created openings

Abstract. Small-scale canopy openings are being increasingly recognized for their importance in boreal forest stand development. Yet more work is necessary to understand their effects on seedling growth. This study investigated the effect of different degrees of canopy opening (all trees cut, conifers cut, conifers girdled and control quadrats) in different stand types on Abies balsamea seedling recruitment, growth and architecture. The lack of a treatment effect on seedling establishment suggests that gaps primarily affect advance regeneration. In the first year after treatment the seedlings in the cut blocks (both conifer cut and all trees cut) responded with an increase in height growth. Changes in the leader to lateral branch ratio were also significant. Continued architectural change in terms of number of branches produced did not occur until after two years had passed. Although not significantly different from the control, increases can be observed in all measurements for the girdled treatment. It is therefore concluded that the growth response of advance regeneration is more important following canopy opening than new seedling recruitment and that seedling performance is greatest where degree of opening is greatest.     

Differential survival among life stages contributes to co‐dominance of Abies mariesii and Abies veitchii in a sub‐alpine old‐growth forest

Questions: Are there interspecific differences in mortality and recruitment rates across life stages between two shade‐tolerant dominant trees in a sub‐alpine old‐growth forest? Do such differences in demography contribute to the coexistence and co‐dominance of the two species? Location: Sub‐alpine, old‐growth forest on Mt. Ontake, central Honshu, Japan. Methods: From 1980 to 2005, we recorded DBH and status (alive or dead) of all Abies mariesii and A. veitchii individuals (DBH ≥ 5 cm) in a 0.44‐ha plot. Based on this 25 year census, we quantified mortality and recruitment rates of the two species in three life stages (small tree, 5 cm ≤ DBH < 10 cm; subcanopy tree, 10 cm ≤ DBH < 20 cm; canopy tree, DBH ≥ 20 cm). Results: Significant interspecific differences in mortality and recruitment rates were observed in both the small tree and sub‐canopy tree stages. In this forest, saplings (< 5 cm DBH) are mostly buried by snow‐pack during winter. As a consequence, saplings of A. mariesii, which is snow and shade tolerant, show higher rates of recruitment into the small tree stage than do those of A. veitchii. Above the snow‐pack, trees must tolerate dry, cold temperatures. A. veitchii, which can more readily endure such climate conditions, showed lower mortality rate at the subcanopy stage and a higher recruitment rate into the canopy tree stage. This differential mortality and recruitment among life‐stages determines relative dominance of the two species in the canopy. Conclusion: Differential growth conditions along a vertical gradient in this old forest determine survival of the two species prior to reaching the canopy, and consequently allow co‐dominance at the canopy stage.     

Seedling recruitment ofChamaecyparis obtusa andSciadopitys verticillata in different microenvironments in an old-growthSciadopitys verticillata forest

Seedling recruitment ofChamecyparis obtusa andSciadopitys verticillata in different microenvironments in an old-growthS. verticillata forest was studied for five years. Exposed mineral soil beneath a gap, which was newly created by a typhoon, supported the best seedling emergence forC. obtusa. S. verticillata seemed to require no specific microenvironment for its seedling emergence. Mortality of seedlings was higher for both species beneath a closed canopy, where all new seedlings ofC. obtusa died within a year after their emergence. Beneath the gap, mortality of seedlings was generally lower for both species, regardless of the presence of litter on the ground. The occurrence of saplings was more frequent forC. obtusa beneath the gaps and forS. verticillata beneath a closed canopy. Difference of seedling recruitment behaviour could maintain the coexistence ofC. obtusa andS. verticillata in the canopy layer of this forest in a non-equilibrium state caused by occasional disturbance.     

Effect of canopy position on germination and seedling survival of epiphytic bromeliads in a Mexican humid montane forest

BACKGROUND AND AIMS: Seeds of epiphytes must land on branches with suitable substrates and microclimates to germinate and for the resulting seedlings to survive. It is important to understand the fate of seeds and seedlings in order to model populations, but this is often neglected when only established plants are included in analyses. METHODS: The seeds of five bromeliad species were exposed to different canopy positions in a Mexican montane forest, and germination and early seedling survival were recorded. Additionally, the survival of naturally dispersed seedlings was monitored in a census over 2.5 years. Survival analysis, a procedure rarely used in plant ecology, was used to study the influence of branch characteristics and light on germination and seedling survival in natural and experimental populations. KEY RESULTS: Experimental germination percentages ranged from 7.2 % in Tillandsia deppeana to 33.7 % in T. juncea, but the seeds of T. multicaulis largely failed to germinate. Twenty months after exposure between 3.5 and 9.4 % of the seedlings were still alive. There was no evidence that canopy position affected the probability of germination, but time to germination was shorter in less exposed canopy positions indicating that higher humidity accelerates germination. More experimental seedlings survived when canopy openness was high, whereas survival in census-seedlings was influenced by moss cover. While mortality decreased steadily with age in juveniles of the atmospheric Tillandsia, in the more mesomorphic Catopsis sessiliflora mortality increased dramatically in the dry season. CONCLUSIONS: Seedling mortality, rather than the failure to germinate, accounts for the differential distribution of epiphytes within the canopy studied. With few safe sites to germinate and high seedling mortality, changes of local climate may affect epiphyte populations primarily through their seedling stage.