灵山湾国家森林公园刺槐林下垂序商陆种子雨时空动态

垂序商陆(Phytolacca americana)的入侵给山东省沿海防护林的生物多样性及乔木更新造成了严重的危害, 为揭示其繁殖特性和扩散机制, 在灵山湾国家森林公园刺槐(Robinia pseudoacacia)林下由林缘至林内60 m设置5个梯度, 采用机械布点法对垂序商陆的结实量、种子雨分布和扩散格局进行了调查。结果表明: 1)垂序商陆的结实量与种子雨量由林缘至林内逐渐减小, 分别为2 273-1 846和1 382-621粒·m^-2, 不同空间种子雨密度占结实密度的60.80%-33.64%, 平均为49.52%, 人为搂割及动物取食是种子雨量损失的主要原因; 2)种子雨始于9月中旬, 林缘种子雨的发生早于林内, 种子雨的平均强度由林缘至林内逐渐减小, 在10月下旬和12月中旬各有一次种子雨高峰, 最大强度分别为32-4和59-5粒·m^-2·d^-1; 3)种子雨由林缘至林内散布范围逐渐减小, 同时随距母株距离的增加而减小, 其中最大散布距离与加权平均距离分别为210-180 cm和94.32-63.03 cm, 整体加权平均距离为81.00 cm。表明垂序商陆种子雨具有明显的时空异质性, 对预测其扩散潜力及群落结构组成趋势有重要的意义。     

沙质海岸防护林入侵植物垂序商陆的防治

垂序商陆的入侵给我国沿海防护林造成了严重危害.本研究在入侵程度相对一致的刺槐林下设置样地,采用物理(刈割、切根)、化学(喷洒无公害除草剂)方法进行控制试验,并以林下紫穗槐发育良好、未进行处理的地段作为对照,探索控制垂序商陆生长的有效方法.结果表明:刈割能快速降低垂序商陆各项生长指标,但次年即恢复至对照水平.1/3切根仅减少了当年地上部分生长量,第3年又恢复至处理前水平,而2/3切根和完全切根处理一次即可有效地清除垂序商陆.精喹禾灵和百草枯仅能杀死其地上部分,次年即恢复至处理前水平,而45g·L-1草甘膦处理的垂序商陆死亡率达到100％,第3年新萌发垂序商陆生长与结实量已明显恢复.紫穗槐发育良好地段的垂序商陆各生长指标始终处于较低的平衡状态.采用紫穗槐替代法是长期控制垂序商陆的有效防治方法.     

东灵山林区不同森林植被水源涵养功能评价

森林植被发挥着涵养水源的作用,主要表现在以下几个方面:对降水的截留与再分配;调节河川径流,调节林内小气候,减小林内地表蒸发,改善土壤结构,减少地表侵蚀等. 通过对几种林分各层拦蓄降水和保土功能指标定性评价的基础上,用综合评定法对不同林分水源涵养和保土功能进行综合评价,选择出综合功能最好的林分,以期为北京山区的生态环境建设、植被恢复与保护提供一定的依据。在测定东灵山4种森林植被林冠层、枯枝落叶层和土壤层蓄水和土壤保持功能指标的基础上,采用综合评定法对4种森林植被水源涵养和土壤保持功能进行了评价。结果表明:各植被类型的林冠层截留各不相同,在雨季(6-9 月份) 辽东栎林的截留率最大,华北落叶松的最小;枯落物最大持水深以辽东栎林的最大,油松的最小;土壤水文特性各异,0-80 cm 土层平均容重以落叶阔叶林的最小,华北落叶松的最大;稳渗速率以落叶阔叶林的最大,油松的最小,初渗速率以辽东栎林的最大,油松的最小。不同林分水源涵养和土壤保持综合能力由大到小顺序为落叶阔叶混交林、辽东栎林、华北落叶松林、油松林。常绿阔叶灌丛水源涵养和土壤保持综合能力评价值(0.1039) 比其它植被类型少3个数量级,说明其水源涵养和土壤保持功能明显优于其它植被类型。由此可见,树种组成丰富、林下灌草盖度高、枯落物储量多的落叶阔叶混交林水源涵养和土壤保持能力最强,优于单一的阔叶林,而油松林最差。     

不同植被恢复模式下煤矸石山复垦土壤性质及煤矸石风化物的变化特征

为了探讨植被恢复模式对煤矸石山复垦土壤和矸石风化物的影响,对煤矸石山6种主要植被类型(刺槐林、刺槐-柠条混交林、榆树-紫穗槐混交林、侧柏-刺槐混交林、荆条林、紫花苜蓿草丛)下土壤和煤矸石风化物的理化性状及重金属进行了比较研究。结果表明:(1)煤矸石山上种植植被可使土壤容重、土壤持水量和孔隙度明显改善。乔木模式更明显。矸石山植被恢复后,可明显增加土壤养分含量。不同植被模式下,土壤养分增加存在显著差异。侧柏-刺槐和榆树-紫穗槐混交模式效果较好。(2)植被对煤矸石风化物容重和机械组成改善作用依次为针阔混交林>乔灌林>乔木纯林>灌木林>草本。植被促进有机质与全氮积累依次为:侧柏-刺槐>刺槐>刺槐-柠条>榆树-紫穗槐>荆条>紫花苜蓿。荆条林下煤矸石风化物全P含量最大。荆条林与侧柏-刺槐混交林利于速效P积累。对速效K积累有利的是荆条林与榆树-紫穗槐混交林。(3)植被种植可以减少煤矸石风化物中重金属含量。榆树-紫穗槐混交模式对减低超标重金属Cd的效果好,其次是针阔混交林(侧柏-刺槐)。对于超标重金属As而言,侧柏-刺槐模式优于其它植被模式,基本达到重金属As不超标。     

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.     

辽西半干旱区几种人工林生态系统涵养水源功能研究

从森林生态系统树冠截留降雨、枯落物持水及土壤蓄水3个层次对辽西半干旱区5种人工林生态系统的涵养水源功能进行了定量研究．结果表明,各人工林生态系统树冠对降雨的平均截留率为14．58％～37．19％,依次为沙棘林>油松沙棘混交林>杨树沙棘混交林>油松纯林>杨树纯林;枯落物层厚度为1．6～4．1cm,枯落物贮量为1890．4～6425．2kg·hm^-2,枯落物层厚度和贮量均为沙棘林>油松沙棘混交林>杨树沙棘混交林>油松纯林>杨树纯林,枯落物最大持水量取决于枯落物贮量及其最大持水率,枯落物最大持水量为5957．7～19332．9kg·hm^-2,依次为沙棘林>油松沙棘混交林>杨树沙棘混交林>油松纯林>杨树纯林;各人工林生态系统0～40cm土壤层非毛管蓄水量为23．70～37．85mm,依次为沙棘林>杨树沙棘混交林>油松沙棘混交林>杨树纯林>油松纯林．在5种人工林生态系统中,沙棘林的涵养水源功能最好,混交林较油松和杨树纯林有更好的涵养水源功能．     

黄土丘陵区刺槐与油松人工林生态系统生态化学计量特征

为阐明不同人工林生态系统间生态化学计量特征的差异,采用野外采样与室内分析相结合的方式分析了陕北黄土丘陵区落叶阔叶树种刺槐和常绿针叶树种油松人工林乔木、灌草、枯落物和土壤(土层深度0—100cm)C、N、P化学计量特征。结果表明:1)刺槐乔木各器官(叶、枝、干、皮、根)C含量显著低于油松,但N和P含量显著高于油松。因此,油松的C∶N和C∶P显著大于刺槐,而N∶P小于刺槐。2)刺槐林下枯落物N和P含量显著高于油松,但C含量显著小于油松。此外,油松林下枯落物C∶N(70.21)大于刺槐林下枯落物C∶N(19.71),说明油松林下枯落物分解较慢,有利于养分的存储。3)刺槐和油松人工林土壤C、N含量均随土壤深度增加而减少,P含量则基本保持不变。刺槐人工林土壤中C含量低于油松,N、P含量在两者之间无显著差异。4)刺槐人工林内乔灌草叶、枯落物与土壤C、N、P及其计量比的相关性多集中在10—20、20—30cm土层,而油松林中各组分与土壤营养元素的相关性相对较小,其中20—30cm土层中无显著相关性,说明相比刺槐人工林而言,油松人工林内土壤层N、P供应量对植物叶片N、P含量影响不显著。本研究为深入了解黄土丘陵区生态系统养分耦合循环机制奠定了基础,同时也为黄土丘陵区的植被恢复工作提供了一定的指导意义。     

茂兰喀斯特森林林隙种子雨、种子库空间变异

以贵州茂兰国家级自然保护区喀斯特森林为研究对象,研究了林隙植被的种子雨、种子库的数量特征及动态变化规律。结果表明:观察期林隙种子雨量达117.4±32.6粒/m2,其中未成熟种子56.3±10.3粒/m2,成熟被害种子15.7±4.7粒/m2,成熟有效种子45.4±8.2粒/m2,林隙更新的种子来源比较丰富。林隙中种子雨的丰富度具有时空异质性特征,将对林隙植物的更新格局产生深刻影响。枯落物层中的种子密度、物种数及Shannon-wiener多样性指数从林隙中心至非林隙林地递减,而土层中的种子变化则相反。林隙中心、近中心、林隙边缘的种子密度分别为2415±639粒/m2、2218±421粒/m2和1815±311粒/m2,林隙植物有很好的更新潜力。林隙与非林隙中枯落物层种子的相似性系数最大,5~10cm土层的次之,0~5cm土层的相似性系数最小。林隙与非林隙中均表现为枯落物层的种子库与现存植被的相似性较大,并随土层的加深而减小。研究结果表明茂兰喀斯特森林林隙植被的更新主要来源于土壤种子库,土壤种子库对林隙填充与发育的贡献较大。     

青羊湖林场不同林分物种多样性与水源涵养能力的研究

通过群落调查和林下土壤及枯落物特性的分析,研究了青羊湖林场南酸枣（Choerospondias axillaris）林、未抚育马尾松（Pinus massoniana）林、抚育马尾松林、马尾松-南酸枣混交林4种林分的物种多样性及水源涵养能力。结果表明：（1）4种林分共有维管束植物135种,隶属58科97属,其中南酸枣林物种相对较丰富(88种),混交林次之(76种),抚育马尾松林较少(64种),未抚育马尾松林则相对最少(55种);（2）林分类型对物种多样性有重要影响,南酸枣林和混交林草本物种多样性较两种针叶林高,而灌木物种多样性则较低;（3）DCA排序结果显示,南酸枣林和混交林物种相似性程度较高,两种马尾松林与南酸枣林、混交林差异明显;（4）林分类型对水源涵养能力有重要影响,相比两种马尾松林,南酸枣林和混交林的林下枯落物蓄积量分别降低10.1%和15.2%,最大持水量降低34.1%和44.7%,而且0～10 cm土壤容重降低14.7%和7.4%,10～20 cm土壤容重降低14.1%和4.0%,20～30 cm土壤容重降低8.7%和4.9%,但总储水量增加15.8%和4.5%,即南酸枣林和混交林具有较高的水源涵养能力。研究认为,生态抚育增加了马尾松林的水源涵养能力。     

间伐对日本黑松海岸林更新的影响

为弄清间伐对海岸林内环境因子 ,进而对海岸林天然更新的影响 ,在黑松海岸林内进行了 4种不同强度的块状间伐试验 .林分间伐后 ,对更新状况和环境因子进行了连续观测 .结果表明 ,间伐可以改善林内光环境、提高土壤的含水量、加强空气流动、促进枯枝落叶的分解等 .4 0年生的黑松海岸林 5 0 %间伐处理后 (密度为 15 0 0株·hm-2 ,林冠开阔度 >30 % )不会对海岸林本身造成风害 ,也不会对防护功能产生较大影响 ,但却能为黑松海岸林天然更新提供良好的生态环境 .试验结果证实了间伐产生的林隙内日本黑松的更新规律 ,提出间伐可作为同龄黑松海岸林向复层、异龄海岸林演化的主要经营措施 .     

Mechanisms of plant regeneration during succession after shifting cultivation in eastern Amazonia

The role of seed bank, seed rain, and regeneration from seedlings and sprouts after swidden agriculture was compared in 5-, 10- and 20-year-old secondary forest and in a primary forest in Bragantina, Pará, Brazil. The seed bank (0–5 cm soil depth) was largest in the 5-year-old forest (1190 ± 284 seeds m⁻²) and decreased nearly ten-fold with age to 137 ± 19 seeds m⁻² in the primary forest. The highest seed rain was in the 5-year-old forest (883 ± 230 seeds m⁻² year⁻¹) and the least in the primary forest (220 ± 80 seeds m⁻² year⁻¹). Large plants (≥5 cm dbh) had more individuals and species that regenerated from sprouts than from seeds and the most abundant tree species in the secondary forest stands of all ages appear to be maintained by sprouting. The smaller individuals (≥1 m tall, <5 cm dbh) in the 5-year-old forest were mainly from sprouts, but those in the older secondary forests originated mainly from seeds. These results show that at the beginning of succession, although many species can be introduced to swidden fallow from seed bank and seed rain, it is the sprout that is the main source of recruits of primary forest species in secondary forests in Bragantina.     

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。     

Relationships among the seed rain,seed bank and vegetation of a Hawaiian forest

Abstract. Hawaiian ecosystems are prone to invasion by alien plant species. I compared the seed rain, seed bank, and vegetation of a native Hawaiian forest to examine the potential role that seed ecology plays in allowing alien species to invade native forest. Absolute cover of seed plants in the forest was 126 %, annual seed rain was 5 713 seeds m^-2 yr^-1, and the mean density of seedlings emerging from the seed bank averaged across four seasons was 1 020/m². The endemic tree Metrosideros polymorpha was the most abundant species in the vegetation, seed rain and winter seed bank. Overall, native seed plants comprised 95 % of the relative cover in the vegetation and 99 % of the seeds in the seed rain, but alien species comprised 67 % of the seeds in the seed bank. Alien species tended to form persistent seed banks while native species formed transient or pseudo-persistent seed banks. Dominance of the seed bank by alien species with persistent seed banks suggests that aliens are favorably placed to increase in abundance in the vegetation if the forest is disturbed.     

天山中部天山云杉林土壤种子库年际变化

通过定点采样,采用萌发法对天山中部天山云杉(Picea schrenkiana Fisch.et Mey.)近熟林(101-120a)和成熟林(121-160a) 2004-2011年(8a)土壤种子库物种组成、种子密度的年际变化和不同间隔年限土壤种子库物种组成的相似性进行了分析.结果表明:(1)土壤种子库中共萌发鉴定出种子植物87种,隶属29科70属,其中乔木种子植物2种,灌木种子植物2种,草本种子植物83种,土壤种子库中草本植物种子密度远远大于木本植物种子密度;8个采样年份土壤种子库恒有种仅有6种;(2)土壤种子库种子密度及其中天山云杉种子密度存在巨大的年际变动,且不具有同步性;土壤种子库种子密度最大(2009年)值为(953.75±66.12)粒/m2,最小(2008年)值为(186.50±20.37)粒/m2,其中天山云杉种子密度最高(2006年)达到(584.50±53.58)粒/m2,最低(2005年)仅有(0.25±0.26)粒/m2;(3)天山云杉林土壤种子库年际间物种组成的相似性不高,Czekanowski相似系数均值仅为0.344,并随间隔年限的增加呈现减小—增大—减小的变化趋势.天山云杉林土壤种子库物种组成和种子密度稳定性差,年际间相差悬殊,物种组成的相似性不高,种子库中天山云杉种子密度主要受其种子库采样前一年天山云杉结实丰歉的影响,属间断型.土壤种子库年际变化特征可为天山森林的更新恢复和可持续经营提供科学依据.     

Seed rain and seed bank of Chinese yew (Taxus chinensis var. mairei) population in Tianmu Mountain☆

Seed rain and seed bank of a Chinese yew (Taxus chinensis var. mairei) population in Tianmu Mountain were researched in 2008 and 2009. The seed rain lasted from 16th–23th of October to 5th–14th of December, and the heaviest seed falling period was from 2nd to18th of November. The intensity of seed rain showed a great inter-annual variation, with a good harvest in 2008. The fallen seeds were composed of 49.9% proportion of immature seed, 33.8% proportion of chewed seed and 16.3% proportion of mature seed. The analysis on the soil seed bank under mother forest showed that the number of intact seeds was 122.75 ± 108.08 grain/m² in October, 279.25 ± 210.73 grain/m² in December 2008, and 166.5 ± 165.34 grain/m² in October, 322.5 ± 275.73 grain/m² in December 2009. The increased number of seed was 156.5 ± 222.723 grain/m² in 2008 and 156 ± 275grain/m² in 2009, which showed a significant variation. Large number of intact seeds added into soil seed bank after seed rain each year. The number of intact seeds in soil seed bank decreased 112.75 ± 47.74 grain/m² from December 2008 to October 2009. Large number of intact seeds lost from seed rot and seed predation by animals. The number of seeds in soil bank under bamboo forest was much lower than that of mother tree forest, and the increased number of seeds was 0.63 ± 1.60 grain/m² in 2008 and 2.88 ± 1.86 grain/m² in 2009. The number of seedling was 0.73 ± 1.10 trees/m² in mother tree forest and 0.09 ± 0.35 trees/m² in bamboo forest. Seedling survival ratio was 0.37% in mother tree forest and 10.23% in bamboo forest. The micro-habitat in bamboo forest was fit for seed germination. Birds transported seeds to bamboo forest, and had an important effect on the regeneration of Chinese yew.     

Early postfire seed dispersal, seedling establishment and seedling mortality of Pinus coulteri (D. Don) in central coastal California, USA

Seedling recruitment in many highly serotinous populations of Pinus coulteri on California's central coast depends almost entirely on periodic, stand-replacing fire. Compared to serotinous pines of the Mediterranean Basin, little detailed information is available on the postfire demography of California closed-cone pines, including P. coulteri. In September 1996 a wildfire burned the 760-ha American Canyon Research Natural Area (RNA). Using aerial photography, we mapped burn severity of P. coulteri-chaparral woodlands and forests within the RNA. From May to September of 1997, we also quantified seedling establishment and mortality in relation to biophysical site characteristics including fire severity. Seventy-six percent of P. coulteri forests and woodlands experienced high-severity burns, 9% moderate-severity burns, and 15% low-severity or unburned. Of the 53 plots used for seedling counts, 70% were high-severity, 26% moderate-severity, and 4% low-severity. Seedling densities 13 months postfire were low (0.21 m^–2), but seedling mortality also was low (8.4%). Aerial seed bank size increased from north-facing to south-facing slopes and from high-severity to low-severity burns. Seedling recruitment was unrelated to burn severity and increased with the size of the canopy seed bank (cone density). Many seedlings established from rodent seed caches; 23% of the seedlings established in clumps from seeds cached by Dipodomys agilis, Chaetodipus californicus and Peromyscus maniculatus. Pinus coulteri seeds have low potential for dispersal by wind, but secondary dispersal by rodents moves seeds away from source trees and into neighboring chaparral. We discuss the potential importance of rodent seed caching to postfire demography of California and Mediterranean serotinous pines.     

The role of the soil seed bank in vegetation recovery on an oceanic island severely damaged by introduced goats

Question: Are the seed banks of an isolated subtropical oceanic island capable of naturally regenerating vegetation either with species of the historical forest community or with the existing grassland community after severe damage to the vegetation by goats? Location: Nakoudojima Island, Bonin Archipelago (Ogasawara Shoto), Japan. Methods: Soil samples were collected at 0–5 cm and 5–10 cm depths from seven plots in forests, grasslands, artificially matted areas and bare land. Soil seed banks were assessed using the seedling emergence method followed by the hand‐sorting of ungerminated seeds. We determined the size and composition of the seed banks in upper soil layers of plots and compared the seed banks to the standing vegetation. Results: A total of 12 220 seedlings belonging to 42 species from 20 families germinated. Total mean seed density (0–5 cm depth) was low in all plots within forest, grassland, and heavily degraded vegetation types (34.7 ± 8.6 to 693.5 ± 123.6, 58.6 ± 7.8 to 107.1 ± 10.0, and 1.1 ± 0.5 to 7.2 ± 2.3 seeds/m², respectively). Forbs and graminoids dominated the seed banks of grassland and forest plots including Cyperus brevifolius, Gnaphalium pensylvanicum, Oxalis corniculata and Solanum nigrum, and these alien species comprised 90% of the density of the seed bank. There was little correlation between seed banks and standing vegetation of the island (Sørensen similarity coefficient values 0.26 to 0.45). Conclusions: If natural regeneration occurs from the seed bank of the island, future vegetation will not move toward the original forest community, because the seed bank is dominated by non‐native herbaceous grassland species. Though isolated, a few forest remnants with low species richness could be an important source for the natural re‐establishment of forest on the island; however, seed availability may be limited by either poor dispersal or pollination so that woody species will probably recover very slowly on this goat‐impacted island.     

Depth distribution and composition of seed banks under different tree layers in a managed temperate forest ecosystem

In the present work we examined the composition and distribution across three soil layers of the buried soil seed bank under three different overstory types (Fagus sylvatica, Quercus robur, Pinus sylvestris) and in logging areas in a 4383-ha forest in central Belgium. The objectives were: (1) to investigate whether species composition and species richness of soil seed banks are affected by different forest stands; (2) to examine how abundant are habitat-specific forest species in seed banks under different planted tree layers. The study was carried out in stands which are replicated, managed in the same way (even-aged high forest), and growing on the same soil type with the same land-use history. In the investigated area, the seed bank did show significant differences under oak, beech, pine and in logging areas, respectively in terms of size, composition and depth occurrence. All species and layers taken together, the seed bank size ranked as follows: oakwood > beechwood > logging area > pinewood. The same pattern was found for forest species. Seed numbers of Betula pendula, Calluna vulgaris, Dryopteris dilatata and Rubus fruticosus were significantly higher under the beech canopy. Carex remota, Impatiens parviflora and Lotus sp. showed a significantly denser seed bank in logging areas, while Digitalis purpurea seeds were significantly more abundant in soils under the oak canopy. The fact that the seed bank of an originally homogeneous forest varies under different planted stands highlights that a long period of canopy conversion can affect the composition and depth of buried seeds.     

格氏栲天然林林窗和林下种子散布及幼苗更新研究

以格氏栲(Castanopsis kawakamii)天然林为研究对象,探讨了林窗和林下格氏栲种子雨、种子库的分布特征及幼苗更新状况。结果表明:林窗种子雨总量和完好种子密度高于林下,未成熟种子比例低于林下;林窗和林下种子雨高峰期掉落数量分别占种子雨总量的77.13%和74.5%;林窗种子库储量低于林下,种子库中以全食或捡拾种子比例最高,其中种子库储量垂直分布表现为枯落物层(约占2/3)>腐殖质层(0～5 cm)(约占1/3)>心土层(5～10 cm)(小于1%),以格氏栲种子占绝对优势;格氏栲从种子到幼苗的转化率低,林窗中格氏栲完好种子密度与幼苗密度均高于林下。林窗微生境提高了种子散布过程中格氏栲成熟种子的密度和比例,有利于促进格氏栲的幼苗更新,表明林窗在格氏栲种群恢复过程中扮演着重要角色。     

Tree seed rain and seed removal,but not the seed bank,impede forest recovery in bracken (Pteridium aquilinum (L.) Kuhn)‐dominated clearings in the African highlands

Considerable areas dominated by bracken Pteridium aquilinum (L.) Kuhn occur worldwide and are associated with arrested forest recovery. How forest recovery is impeded in these areas remains poorly understood, especially in the African highlands. The component processes that can lead to recruitment limitation—including low seed arrival, availability and persistence—are important determinants of plant communities and offer a potential explanation for bracken persistence. We investigated key processes that can contribute to recruitment limitation in bracken‐dominated clearings in the Bwindi Impenetrable National Park, Uganda. We examined if differences in seed rain (dispersal limitation), soil seed bank, or seed removal (seed viability and persistence) can, individually or in combination, explain the differences in tree regeneration found between bracken‐dominated areas and the neighboring forest. These processes were assessed along ten 50‐m transects crossing the forest–bracken boundary. When compared to the neighboring forest, bracken clearings had fewer seedlings (bracken 11,557 ± 5482 vs. forest 34,515 ± 6066 seedlings/ha), lower seed rain (949 ± 582 vs. 1605 ± 335 tree seeds m^?2 year^?1), comparable but sparse soil seed bank (304 ± 236 vs. 264 ± 99 viable tree seeds/m²), higher seed removal (70.1% ± 2.4% vs. 40.6% ± 2.4% over a 3‐day interval), and markedly higher rodent densities (25.7 ± 5.4 vs. 5.0 ± 1.6 rodents per 100 trapping sessions). Camera traps revealed that rodents were the dominant animals visiting the seeds in our seed removal study. Synthesis: Recruitment limitation contributes to both the slow recovery of forest in bracken‐dominated areas, and to the composition of the tree species that occur. Low seed arrival and low persistence of unburied seeds can both explain the reduced density of seedlings found in bracken versus neighboring forest. Seed removal, likely due to rodents, in particular appears sufficient to constrain forest recovery and impacts some species more severely than others.