秦岭北坡不同生境栓皮栎种子雨和土壤种子库动态

为了阐明栓皮栎种子雨和种子库动态,以秦岭北坡林下、林窗、林缘3种生境栓皮栎天然林为对象,采用离地和地面收集种子的方法,连续定位观测了栓皮栎种子雨、种子库的数量、质量动态,以及幼苗发育过程.结果表明:栓皮栎种子雨从8月中旬开始,9月中旬到10月上旬达到高峰期,11月上旬结束;3种生境种子雨降落历程、发生时间和组成不同;林下种子雨强度最大,为(39.55±5.56)粒·m-2,林窗种子雨降落时间最早,持续时间最长,种子活力最高,而林缘成熟种子占其种子雨的比例最大,达58.7％.从种子雨降落结束到翌年8月,土壤种子库总储量均以林下最大,林缘最小;各生境的土壤种子库中成熟、未成熟、被啃食种子数量和种子活力均随时间变化呈递减趋势,而霉烂种子数量则相反.各生境的土壤种子库中的种子均主要集中在枯落物层,其次为0～2 cm土层,2～5 cm土层中只有极少量种子存在.3种生境中栓皮栎幼苗的密度差异显著,林窗幼苗最多,林缘次之,林下最少.说明林窗更适合栓皮栎种子的萌发和幼苗生长.在栓皮栎林的经营中,通过适当间伐、增加林窗数量,可以促进栓皮栎林的天然更新.     

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%)。     

文峪河上游华北落叶松林的种子雨、种子库与幼苗更新

华北落叶松林下更新不良,为探究其制约因素,开展了山西省文峪河上游5个华北落叶松林分的种子雨、土壤种子库和幼苗更新的研究。结果表明:(1)华北落叶松种子主要集中于9—10月散落。2011年为华北落叶松种子丰年:种子产量高,种子雨密度达(961.93±377.40)粒/m2;种子质量高,完整种子占(89.31±16.13)%。2012年为种子平年,种子产量低,种子雨密度为(252.73±115.12)粒/m2。华北落叶松种子雨主要源于毗邻树木,华北落叶松纯林和落叶松云杉林的种子雨密度显著高于其他3个针阔混交林。(2)土壤种子库主要由上年种子雨组成,2012年4月的土壤种子库密度为(695.18±297.23)粒/m2,完整种子占(59.73±9.56)%。种子自然萌发前,约(78.98±24.76)粒/m2具发芽力,基本可满足更新需要。但种子活力保持期少于2 a,只能形成短期持久土壤种子库。(3)华北落叶松更新不良,种子年后仍难以实现幼苗建成,当年生幼苗的出现频度平均为1.6%,且林下难以存活。幼苗发生与种子储量关联性不强,种源条件不是制约华北落叶松更新的主要因素。     

黄土高原子午岭油松林的种子雨和土壤种子库动态

对黄土高原区子午岭不同林龄(18a、29a、40a、54a)油松(Pinus tabulaeformis carr.)人工林及天然林(约75a)的种子雨和土壤种子库进行了研究.结果表明,该区油松种子雨一般从每年9月初开始,一直到11月底结束,种子雨降落历程与林龄大小有关,种子雨发生时间和降落高峰期有所不同.不同林龄的油松种子雨强度不同,种子雨总量大小顺序为:40a人工林((489 9±8.64)粒· m-2)＞29a人工林((346.8±7.45)粒· m-2)＞54a人工林((327.1±8.13)粒· m-2)＞天然林((146.9±5.25)粒· m-2)＞18a人工林((78.1±2.72)粒· m-2).种子雨总量随林龄的增加而增加,约40a时达到高峰,种子雨活力也以40a时最高.不同林龄油松林土壤种子库存在显著差异,其中18a人工林种子库最小,40a人工林种子库最大.从种子雨降落到次年4月,5种林分土壤种子库总量下降了42.34%～53.59%,空粒种子增加了26.72%～48.69%;从4月到8月份种子腐烂率由10.28%～13 62%增加到57.25%～63.28%.动物的搬运、取食和种子腐烂死亡是种子库损耗的主要因素.土壤种子库中的油松种子主要集中在枯枝落叶层,其次为0～2cm层,2～10cm层种子最少.到8月中旬,土壤中98.26%的油松种子都已丧失活性.不同林分下油松幼苗的密度差异较大,40a人工林下幼苗最多,其余依次为29a人工林、54a人工林和天然林,18a人工林下的实生苗极少,幼苗死亡率极高.在一定龄级范围内,人工林结实能力和更新潜力随林龄增加而增加,40a时更新潜力最大.虽然有大量种子下落,但由于种子大量损耗和幼苗死亡,通过环境筛作用而最终可以成熟的个体数量十分有限.     

海南霸王岭陆均松种子雨和土壤种子库特征

为了解陆均松(Dacrydium pierrei)的自然更新能力,对海南霸王岭陆均松进行为期3年的种子雨、种子库及幼苗幼树观测,并分析其与环境因子的关系。结果表明,陆均松种子雨和种子库有效种子数量太少并存在季节性差异;其结实存在大小年现象;种子雨的扩散密度随着距母树距离的增加而逐渐减少;土壤种子库种子数量在枯枝落叶层所占比例最大,但有活力种子数量极少。幼苗幼树适宜生存的海拔范围为800~1 400 m,经度、纬度、坡度与幼苗幼树分布有明显相关性。因此,选择适宜季节采摘种子,提高种源数量和质量,清除林下枯枝落叶,增加种子萌发能力等以减少陆均松更新的限制条件的人工抚育措施应适当考虑。     

林窗对格氏栲天然林更新层物种多样性和稳定性的影响

采用物种多样性指数和改进的M.Godron稳定性法研究林窗干扰对格氏栲(Castanopsis kawakamii)自然保护区天然林更新层物种多样性和稳定性的影响.结果表明:林窗干扰改善了微环境,表现在林窗和林下乔灌层树种重要值和多样性存在差异.林窗乔木层中丰富度指数R、优势度指数D、Shannon-Wiener指数H、均优多指数Z均高于林下,均匀度指数Js和群落优势度指数C低于林下;灌木层中R、D、H、Js、Z指数均高于林下,群落优势度指数C低于林下,林窗物种多样性更为丰富,生态优势种不明显,群落向复杂化和均匀化方向发展.林窗与林下乔木层Jaccard相似性系数Cj、Sorenson相似性系数CS、Bray-Curtis指数CN相对较低,Morista-Horn指数CmH较高,林窗对树种更新具有促进作用;灌木层相似性系数Cj、Cs、CN、CmH均较高,物种组成基本一致.根据M.Godron稳定性原理拟合出稳定性模型,林窗和林下乔木层分别为对数模型与二次函数模型,林窗和林下灌木层最佳拟合模型均为对数模型.林窗乔木层植物处于稳定状态,林下乔木层植物不稳定;林窗和林下灌木层植物均处于稳定状态.林窗和林下乔木层树种中以桂北木姜子(Litsea subcoriacea)重要值最高,说明其在森林更新中占有重要地位,可能对格氏栲种群更新产生较大影响.林下乔木层中格氏栲重要值较低,格氏栲更新存在困难,而林窗干扰促进了格氏栲的向上生长和重要值的提升,可有效实现格氏栲种群的更新和恢复.     

山西文峪河上游河岸林的土壤种子库与树种更新特征

以山西文峪河上游13种典型的河岸林为研究对象,通过土壤种子库和树种更新研究,分析群落种子库与林下更新随演替进展的变化趋势,以及该区河岸树种的繁殖对策。结果表明：13种群落的土壤种子库密度间于1290±103～3950±154粒/m2,63.5%的种子留存于0～5 cm的层次;种子库包含49种植物,以多年生草本为主,存在耐干扰种和湿地植物的种子;处于相同或相邻演替阶段的群落,种子库相似性较高;随演替进展,种子库密度、丰度、Shannon-Wiener指数及种子库与地上植被的相似性均呈降低趋势;处于演替后期的青杄Picea wilsonii林存在丰富的＂青杄幼苗库＂;先锋种白桦Betula platyphylla的种子存在于演替各阶段的群落中,储量丰富,其更新主要依赖于风媒种子,并存在少量萌蘖;青杄、白杄P.meyeri、华北落叶松Larix principis-rupprechtii、油松Pi-nus tabulaeformis和辽东栎Quercus liaotongensis的种子库损耗严重,没有或仅存少量种子,其中云杉和油松的更新幼苗幼树多,属持久幼苗库更新;华北落叶松幼苗幼树少,且仅出现于林缘或林窗等开阔地,属植被空隙中季节性更新;辽东栎主要依赖丰富的幼苗库进行更新,同时存在一定的萌蘖;青杨Populus cathayana以大量风媒种子更新结合营养扩展。     

毛红椿天然林种子雨、种子库与天然更新

2008-2011年,调查江西九连山国家级自然保护区毛红椿天然林的种子雨、种子库及林下幼苗数量.结果表明:在毛红椿天然林,种子雨散布时间为10月下旬至12月下旬.2010年不同样地的种子雨强度为虾公塘气象观测站(320.3±23.5粒·m-2)＞虾公塘保护站(284.7±24.2粒·m-2)＞大丘田保护站(251.6±24.7粒·m-2),分别以222.0、34.3和22.6粒·m-2完好种子供土壤萌发更新;毛红椿种子储量取决于结实量、鸟类取食和种子活力等因素,鸟类取食是其种子储量大幅下降的首要因素;由于种子不耐储藏以及大量腐烂,种子有效贮藏期不足1个月.12月天然林种子库平均萌发数≤2株·m-2,次年1月土壤种子库种子量最少,为6.7～11.8粒·m-2,平均仅萌发0.4～0.6株·m-2,与林下实生幼苗分布极少相吻合.毛红椿种子雨储备、种子库种子活力保存及幼苗建成等因素影响其天然更新.     

福建闽清福建青冈天然林种子雨和种子库

对福建闽清黄楮林自然保护区的福建青冈(Cyclobalanopsis chungii)天然林的种子雨和土壤种子库进行了观测和分析.结果表明,福建青冈种子雨持续2个月,其高峰期在11月下旬～12月上旬,总量为12.44个m~(-2),在种子散布过程中完好种子、虫蛀种子、败育种子、霉烂种子和萌发种子的比例差异明显,其中虫蛀种子是萌发种子的19.44倍.土壤种子库中虫蛀种子占53.79%,与种子雨相比,完好种子和萌发种子数量分别减少2.15个m~(-2)和0.20个m~(-2).土壤种子库种子存活率仅13.51%,动物捕食率达45.90%,说明动物的捕食和搬运是福建青冈种子缺失的原因之一.福建青冈天然林土壤种子库有69种植物种子,但种子数量较少,且分布不均匀,种子库中78.42%种子分布在2～5 cm土层中.福建青冈天然林中实生幼苗少与福建青冈种子本身特性及其生长环境密切相关,福建青冈种子发育成熟后因动物侵扰、虫蛀、霉烂和败育等情况发生,难以在土壤中长期保存,以致福建青冈林分天然更新严重受阻.     

林窗对格氏栲天然林更新层物种生态位的影响

采用改进更新生态位宽度和更新生态位重叠模型分析林窗干扰对福建三明市格氏栲天然林更新层物种生态位的影响。结果表明:林窗中格氏栲更新生态宽度值大于林下,林窗在促进格氏栲更新过程中具有重要作用。林窗和林下更新生态位宽度最大的为桂北木姜子,其与格氏栲更新生态位重叠值也较大。林窗中的格氏栲与其它物种更新生态位重叠值低于0.6,林窗微生境的异质性导致格氏栲与其它树种间对资源的利用存在明显的共享趋势,促进了物种间共存。林下的格氏栲与木荷、木荚红豆和短尾越桔的更新生态位重叠值均高于0.6,格氏栲与这些物种相互争夺资源与空间,种间竞争较强。格氏栲天然林未来树种组成中,主要由桂北木姜子、木荷、矩圆叶鼠刺与格氏栲等组成的混交群落,整个群落正向物种组成多样化的方向演变。     

种子散布位置对格氏栲幼苗根系形态及生长特征的影响

种子从母株掉落于地面萌发后,其根系在不同散布位置(凋落物上层、土壤表层和凋落物下层)的生长形态影响幼苗定居及建成,而目前对其根系形态及生长特征的了解并不充分,限制了对幼苗根系在不同散布下适应策略的理解。为此,以格氏栲(Castanopsis kawakamii)为研究对象,通过模拟种子在凋落物中位置,设置凋落物上层(种子下层铺垫2 cm和4 cm凋落物,U2和U4处理)、土壤表层与凋落物下层(种子上层覆盖0、2、4、6 cm和8 cm凋落物,CK、D2、D4、D6和D8处理)等3种散布,探讨不同散布位置对格氏栲幼苗根系9个生长指标的影响。结果表明：(1)种子散布位置对幼苗根干物质质量具有显著影响,D2处理达最大值。(2)D2处理的幼苗根长、根表面积、根尖数、分枝数和比根长高于其它处理;根系平均直径在D6处理达最大值。(3)相关分析表明根长、根表面积、根尖数、分枝数和比根长与根系平均直径呈显著负相关关系。(4)对根系9个生长指标提取主成分后聚类为4个类群,D2与D4处理各划分一类;U2与U4处理划分一类,其余三个处理划分一类。综上所述,凋落物浅层覆盖(D2处理)适宜格氏栲根系生长;凋落物...     

Seed rain and soil seed bank of Picea asperata Mast. in subalpine coniferous forest of western Sichuan,China

Abstract

Dragon spruce (Picea asperata Mast.) is widely planted on clear-cuts from natural subalpine coniferous forests in western Sichuan. To assess the natural regeneration potential of this species in spruce plantations of different ages, field studies on the seed rain, seed bank, and seedling recruitment were conducted in 20-year, 30-year, and 60-year plantations, and in a retained natural forest ca. 150 years old for comparison. Moreover, a series of temperature and light regimes were also designed in March 2003 to test germination/dormancy responses of the P. asperata seeds to different conditions. In the plantations considered, both the densities of seed rain and soil seed bank increased with increasing stand age, whereas they were both low beneath the natural forest partially due to low adult density of P. asperata adult trees. P. asperata has a transient seed bank, and ca. 60% of seeds were found in the litter layer. Seed decay and seed predation were the two most important factors affecting soil seed bank dynamics, which caused a number of seed losses from the soil. Only a small fraction germinated and produced seedlings, and the indices of the losses from the seed bank via germination in the 30-year plantation, 60-year plantation and natural forest were 4.75, 5.10, and 2.80%, respectively. High seedling mortality was observed after seedling emergence, and most of the germinated seedlings died out within one growing season. The P. asperata seeds showed a high percent germination and no significant differences under most light and temperature regimes except for full sunlight or temperature below 5°C. In conclusion, despite a substantial number of seed produced, the high depletion of soil seed, the low seedling output, and high seedling mortality may obscure the natural regeneration potential of this tree species.     

Soil seed bank composition along a forest chronosequence in seasonally moist tropical forest,Panama

Abstract. We used a forest chronosequence at the Barro Colorado Nature Monument (BCNM) to examine changes in the abundance and species composition of seeds in the soil during forest succession. At each of eight sites varying from 20 yr to 100 yr since abandonment, and at two old-growth (> 500 yr) forest stands, we established two 160-m transects and sampled the surface 0–3 cm of soil in cores collected at each 5 m interval. Seed densities were estimated from the number of seedlings germinated from the soil over a six-week period. Contrary to expectation, neither the density of the soil seed bank, nor species richness or diversity were directly related to age since abandonment, but the density of the soil seed bank was correlated with the abundance of seed-bank-forming species in the standing vegetation. In marked contrast to published studies, herbaceous taxa were rare even in the youngest stands, and the common tree species, which accounted for most seeds in the soil, were present in all stands. The pioneer tree Miconia argentea (Melastomataceae) was the single most common species in the seed bank, accounting for 62% of seeds and present in 92% of soil samples. Rapid recovery of the vegetation of young regrowth stands on BCNM, when compared to sites elsewhere may be partly due to allochthonous seed rain from nearby mature forest stands and the lack of seed inputs of weeds and grasses from agricultural and pasture lands which may inhibit forest succession.     

Regeneration by seeds in alpine meadow and heath vegetation in sub‐arctic Finland

Abstract. This paper compares the regeneration by seeds of heath and meadow and studies relationships between the floristic composition of phases in the regeneration pathway. Seed densities in the seed rain and seed bank as well as the densities of emerged seedlings in gaps and in closed vegetation were greater in the meadow than in the heath. In the heath, environmental constraints hindered seedling emergence almost completely so seeds accumulated in the seed bank. In the meadow, the decrease in the seed bank was due to high seedling emergence. Within both plant communities, seedling emergence in gaps and in closed vegetation was comparable. In the meadow, the seed rain and seedling emergence in gaps, as well as the seed bank and seedling emergence in gaps were positively correlated. Differences in seed and adult plant sizes were reasons for the low correlation between the standing vegetation and the other phases. In DCA ordination the first axis separated the phase of seedling emergence in closed vegetation and seed bank. The second axis separated the standing vegetation from the other phases. The structure of the seed rain was more heterogeneous than that of other phases. In the heath, the standing vegetation and the seed rain were positively correlated. The ordination of these phases reflected the patchiness of standing vegetation and the ability of the diaspores of Betula nana to disperse over long distances.     

Effects of microhabitat on palm seed predation in two forest fragments in southeast Brazil

The establishment of plants depends crucially on where seeds are deposited in the environment. Some authors suggest that in forest understory seed predation is lower than in gaps, and higher than at the forest edge. However, most studies have been carried out in large forest patches and very little is known about the effects of microhabitat conditions on seed predation in forest fragments. We evaluated the effects of three microhabitats (gaps, forest edge, and understory) on seed predation of two palm species (Euterpe edulis and Syagrus romanzoffiana) in two semi-deciduous forest fragments (230 and 2100 ha) in southeast Brazil. Our objective was to test two hypotheses: (1) Low rodent abundance in small fragments as a result of meso-predator action levels leads to lower seed predation in small fragments. (2) Most mammal species in small fragments are generalists with respect to diet and habitat, so that seed predation is similar in different microhabitats (gaps, forest edge and understory) in the small fragment, but not in the larger one. The study community of small fragments is usually composed of generalist species (in diet and habitat aspects), so we expected the same rate of seed predation among microhabitats (gaps, forest edge and understory) in the tested smaller fragment. The experiment was carried out in the dry season (for E. edulis) and in the wet season (for S. romanzoffiana) in 1999. We conclude that post-dispersal seed predation in forest fragments can be directly connected with mammal communities, reflecting their historical and ecological aspects.     

Ficus seed shadows in a Bornean rain forest

Due to their copious seed production and numerous dispersers, rain forest fig trees have been assumed to produce extensive and dense seed shadows. To test this idea, patterns of seed dispersal of two species of large hemiepiphytic fig tree were measured in a Bornean rain forest. The sample included four Ficus stupenda and three F. subtecta trees with crop sizes ranging from 2,000 to 40,000 figs (400,000 to 13,000,000 seeds). Seed rain out to a distance of 60 m from each study tree was quantified using arrays of seed traps deployed in the understory. These trees showed a strongly leptokurtic pattern of dispersal, as expected, but all individuals had measurable seed rain at 60 m, ranging from 0.2 to 5.0 seeds/m². A regression of In-transformed seed rain density against distance gave a significant fit to all seven trees' dispersal patterns, indicating that the data could be fitted to the negative exponential distribution most commonly fitted to seed shadows. However, for six of seven trees, an improved fit was obtained for regressions in which distance was also In-transformed. This transformation corresponds to an inverse power distribution, indicating that for vertebrate-dispersed Ficus seeds, the tail of the seed rain distribution does not drop off as rapidly as in the exponential distribution typically associated with wind dispersed seed shadows. Over 50% of the seed crop was estimated to fall below each fig tree's crown. Up to 22% of the seed crop was dispersed beyond the crown edge, but within 60 m of the tree. Estimates of the maximum numbers of seeds which could have been transported beyond 60 m were 45% for the two largest crops of figs, but were under 24% for the trees with smaller crops. Seed traps positioned where they had an upper canopy layer above them were associated with higher probabilities of being hit by seeds, suggesting that vertebrate dispersal agents are likely to perch or travel through forest layers at the same level as the fig crown and could concentrate seeds in such areas to some degree. The probability of a safe site at 60 m from the fig tree being hit by seeds is calculated to be on the order of 0.01 per fruiting episode. Fig trees do not appear to saturate safe sites with seeds despite their large seed crops. If we in addition consider the rarity of quality establishment sites and post-dispersal factors reducing successful seedling establishment, hemiepiphytic fig trees appear to face severe obstacles to seedling recruitment.     

Seed predation patterns favor the regeneration of dominant species in forest gaps compared with the understory in an oak-pine mixed forest

Recent studies have demonstrated the higher likelihood of regeneration in forest gaps compared with the understory for the dominant species in pine-oak mixed forest. Here, we tested whether rodent seed predation or dispersal was beneficial for gap regeneration. We tracked the seed predation and dispersal of Quercus aliena var. acuteserrata and Pinus armandii using coded plastic tags in the forest understory close to gaps. Our results demonstrated that the proportions of initial buried seeds of both species were significantly more abundant in the forest understory compared with gaps. After seed caching, however, significantly lower proportions of the seeds of both species survived in the forest understory compared with gaps during the 30-day observation period. The final survival proportions of the seeds cached in the forest understory were lower than those cached in the gaps the next spring, which indicated that small rodents rarely retrieved scatter-hoarded seeds from forest gaps. Our findings suggest that rodent seed predation patterns contribute to the regeneration of the dominant species in gaps compared with the understory in a pine-oak mixed forest. In the study area, reforestation usually involves planting seedlings but direct sowing in forest gaps may be an alternative means of accelerating forest recovery and successional processes.