Seedling Distribution Patterns Research Articles

Distribution of sexually reproductive eelgrass (Zostera marina) seeds in microhabitats of eelgrass beds in intertidal zones

Eelgrass (Zostera marina) seedling establishment based on the sexually reproductive seed bank depends on habitat factors, and there are different microhabitats in eelgrass beds. Seedling abundance varies with microhabitat. Why is the distribution pattern of seedlings so? Is there an edge effect of eelgrass patches on seedling distribution? To clarify the distribution and variation patterns of ungerminated seeds, germinated seeds and seedlings in microhabitats, field investigations were conducted from December 2020 to April 2021. The density of the total seed bank varied with microhabitat except in March. In April, the density of germinated seed banks in the highland, low-lying area edge and low-lying area was 0.00 ± 0.00, 0.33 ± .33 and 7.44 ± 0.96 seeds.cm−3, respectively, and the density in the low-lying area was higher than that in the other microhabitats. The order of density of the seedling bank was highland < low-lying area edge < low-lying area in April. The relative proportion of germinated seeds in the low-lying area was higher than that in the highland from March to April, during which the increase rate in the seedling bank of the highland was lower than that of other microhabitats. The distribution pattern of eelgrass seeds varies with microhabitat. The change characteristics of germinated seeds or seedling banks are related to microhabitats. There are edge effects of eelgrass patches on the distribution of germinated seeds and seedlings. All these factors contribute to the formation of seedling distribution. Sowing eelgrass seeds in the edge area of a continuously distributed eelgrass bed can promote the seedling establishment rate.

Spatial associations between tree regeneration and soil nutrient in secondary Picea forest in Guandi Mountains, Shanxi, China.

According to the technical specifications of CTFS (Center for Tropical Forest Science), 190 sampling points of 4-hm2 plot (GDS plot) in Guandi Mountains of Shanxi Province, China were investigated to examine the spatial distribution pattern of seedlings and 14 soil indicators, including pH value and nutrient indicators. We analyzed the spatial associations between tree regeneration and soil nutrients, explored the mechanism of tree regeneration pattern of secon-dary Picea forest. The results showed that more seedlings survived in the patches with low contents of available N, available K, available Cu, available Fe, available Mn, available Ni and available Zn. Besides available K, the negative correlation between the other six soil nutrient factors and the number of regeneration seedlings of the Ⅱ (2.5 cm<GD≤4 cm) and Ⅲ (4 cm<GD≤5 cm) diameter classes with relatively large ground diameter (GD) was higher than that in the Ⅰ diameter class (0 cm<GD≤2.5 cm), indicating that soil nutrients had a greater influence on the distribution of regeneration seedlings in larger diameter class, and that the survival of regeneration seedlings was more dependent on soil condition. The soil of GDS was slightly acidic (5.5<pH<6.8). The increase of soil pH was accompanied by the decrease of available Al content, which was conducive to the regeneration and survival of trees. The total explanation of nine soil factors (including soil available N, available K, available Cu, available Fe, available Mn, available Ni, available Zn, available Al and pH value) on the regeneration and distribution of tree species in GDS plots was 19.7%.

Differences in seedling distribution patterns between wind-dispersed Liquidambar formosana and rodent-dispersed Quercus acutissima

Differences in seedling distribution patterns between wind-dispersed Liquidambar formosana and rodent-dispersed Quercus acutissima

Spatial analysis to identify invasion colonization strategies and management priorities in riparian ecosystems

Abstract Exotic species have different strategies to invade a new area. Invasive species limited by establishment have a wide dispersion range and high seedling mortality rate. Riparian forests are harsh environments for the establishment of plants. In this sense, we tested the hypothesis that the invasive process of G. triacanthos is limited by establishment in a riparian forest of the Uruguay River and that it begins in the fluvial bank at the transition zone between forest and grassland and moves towards the shore border. We expected that: (1) the distribution pattern of adults of G. triacanthos would be decoupled from the distribution pattern of seedlings and saplings (pre-reproductive stages); (2) the population would have a cluster distribution pattern related to the occurrence of punctual events that favoured the development to adult stages; and (3) the abundance of seedlings, saplings and adults would be higher in the transition zone (between forest and grassland) than in the shore border of the fluvial bank. The spatial pattern of G. triacanthos along the Uruguay River was analyzed using spatial point pattern analysis: autocorrelation indexes, hot spots and wavelet analysis. The effect of the fluvial bank position on the abundance of G. triacanthos was evaluated using non-metric multidimensional scaling (NMDS). This methodology allowed us to detect a primary invasion area, an invasion focus and the dispersal area. This pattern corresponded to an infiltration invasion pattern limited by establishment. It did not seem to be affected by position in the fluvial bank. This information could be relevant to establish correct decision-making in the control of an invasive process and provide an applicable methodology for any other invasion process, especially in riparian ecosystems.

动物在大别山五针松种群天然更新中的作用

PDF HTML阅读 XML下载 导出引用 引用提醒 动物在大别山五针松种群天然更新中的作用 DOI: 10.5846/stxb201710281933 作者: 作者单位: 南京林业大学南方现代林业协同创新中心,南京林业大学南方现代林业协同创新中心,南京林业大学南方现代林业协同创新中心 作者简介: 通讯作者: 中图分类号: 基金项目: 江苏省研究生创新工程（CXZZ12_0548） Role of animals in the natural population regeneration of Pinus dabeshanensis Author: Affiliation: Co-Innovation Center for Sustainable Forestry in Southern China,College of Biology and the Environment,Nanjing Forestry University,Co-Innovation Center for Sustainable Forestry in Southern China,College of Biology and the Environment,Nanjing Forestry University,Co-Innovation Center for Sustainable Forestry in Southern China,College of Biology and the Environment,Nanjing Forestry University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:大别山五针松（Pinus dabeshanensis）为我国特有树种，其天然植株较少且分布范围狭窄，种群更新困难，已被列为国家二级重点保护野生植物。分别于2015年和2016年的10-12月，在目前已知最大天然种群所在地安徽岳西县河图镇大王沟，研究了大别山五针松球果与种子特征、种子雨与土壤种子库、动物对种子的取食和搬运，幼苗分布格局及其与鼠穴分布的关系，以期探明动物在其天然更新中的作用，分析其天然更新不力的原因。结果显示：大别山五针松种子败育率较高，阳坡个体球果发育情况好于阴坡；种子成熟期间没有明显的种子雨，土壤种子库也未调查到完整种子。共记录到母树与球果的访问动物6目11科16种，其中7种动物确定取食种子；地面种子摆放实验显示超过95%以上的种子被啮齿动物捕食或搬运至他处取食或贮藏，不同的摆放处理对啮齿动物的捕食、搬运没有显著影响；小林姬鼠（Apodemus sylvaticus）盗食现象严重，埋藏实验中人工贮点当夜被发现的概率在90%左右，岩松鼠（Sciurotamias davidianus）和小林姬鼠是其种子主要捕食者。研究地的大别山五针松种群于2015年和2016年分别新增一年生幼苗5株和7株，这表明大别山五针松在当地存在天然更新。幼苗多单独生长在母树周围，点格局分析显示在0-0.6 m的尺度范围内呈随机分布；在 > 0.6 m尺度呈聚集分布。大别山五针松幼苗在小林姬鼠巢穴周边分布，其更新格局受到小林姬鼠贮点位置分布情况影响，小林姬鼠极有很可能为大别山五针松的传播者，啮齿动物对大别山五针松种子的捕食与搬运影响了大别山五针松的天然种群更新。 Abstract:Pinus dabeshanensis is listed as a national second-class protected wild plant species. Because of its rarity and narrow distribution, regeneration of its population is difficult. To determine the role of animals in natural population regeneration of P. dabeshanensis and causes of difficulties with natural regeneration of a P. dabeshanensis population, we studied P. dabeshanensis cone and seed traits, seed rain and soil seed banks, seed predation and removal by animals, spatial distribution patterns of seedlings and their relationships with the distribution of rat nests in the Ta-pieh Mountains, Yuexi County, Anhui Province during the period from November to December in the years 2015 and 2016. The results showed that P. dabeshanensis possessed a high rate of seed abortion, and cones grown on a sunny slope were better developed than those grown on a shady slope. We did not find seed rain or soil seed banks during seed maturation. Sixteen species of animals, belonging to 11 families and 6 orders, visited trees and cones. Seven species were identified as seed predators. A ground seed placement experiment showed that more than 95% of the seeds were preyed upon or removed to other places to be preyed upon or stored. The fates of P. dabeshanensis seeds among different placement locations were not significantly different. Apodemus sylvaticus was a good pilferer in our experiment; the seed discovery and storage rate was about 90% on the first night. Two species of rodents, Sciurotamias davidianus and A. sylvaticus, were the main seed predators. At the study site, we found 5 established seedlings in 2015 and 7 established seedlings in 2016. This indicated that there is a natural regeneration in the local area. The seedings mostly established around the seed tree independently, in a random distribution within 0-0.6 m and a clumped distribution at distances over 0.6 m. The natural regeneration pattern of P. dabeshanensis seedlings was affected by the location of A. sylvaticus nests, and the seedings established for the most part near the nests of A. sylvaticus. In summary, A. sylvaticus may be a seed disperser, and P. dabeshanensis seed predation and removal by rodents could affect P. dabeshanensis natural population regeneration. 参考文献 相似文献 引证文献

Linking Seedling Spatial Patterns To Seed Dispersal Processes In An Intermittent Stream

Abstract To better understand the colonization of bare riparian sites, I examined seedling distribution patterns and seed dispersal processes of 11 common riparian species. The study site was two in-channel sedimentation basins on an intermittent stream flowing into the Tijuana River Valley, southern California. The 11 species relied on one of two vectors to disperse seeds into the basins, either water or wind. Seven species dispersed to the basins via winter stream flows and, of these, three grew mainly at the basin periphery and four grew mainly in the bed. Seed buoyancy tests and tests of dispersal using seed mimics showed that, for these species, the main process producing seedling distributions was that of sorting of the seeds by the stream flows based on seed buoyancy. Most past work on seed dispersal in riparian habitats has been conducted in perennial systems where non-buoyant seeds usually remain in deep water and never germinate, and this has led to the notion that non-buoyant seeds are not effe...

甘肃省民勤连古城自然保护区沙木蓼种群的结构与动态

PDF HTML阅读 XML下载 导出引用 引用提醒 甘肃省民勤连古城自然保护区沙木蓼种群的结构与动态 DOI: 10.5846/stxb201409281913 作者: 作者单位: 甘肃省荒漠化与风沙灾害防治国家重点实验室,甘肃民勤荒漠草地生态系统国家野外科学观测研究站,甘肃省荒漠化与风沙灾害防治国家重点实验室,甘肃省连古城国家级自然保护区管理局,甘肃省荒漠化与风沙灾害防治国家重点实验室,甘肃省荒漠化与风沙灾害防治国家重点实验室,甘肃省荒漠化与风沙灾害防治国家重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 甘肃省创新群体资助项目（145RJIA335）；甘肃省创新团队资助项目（1207TTCA002） Structure and dynamics of Atraphaxis bracteata populations in Minqin Liangucheng Nature Reserve, Gansu Author: Affiliation: State Key Laboratory of Desertification and Aeolian Sand Disaster Combating,Wuwei,Gansu,Gansu Minqin National Field Observation and Research Station on Ecosystem of Desertification Rangeland,Minqin,Gansu,State Key Laboratory of Desertification and Aeolian Sand Disaster Combating,Wuwei,Gansu,,,State Key Laboratory of Desertification and Aeolian Sand Disaster Combating,Wuwei,Gansu,State Key Laboratory of Desertification and Aeolian Sand Disaster Combating,Wuwei,Gansu Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:根据甘肃省民勤连古城自然保护区沙木蓼种群的生境和植被差异，分别选择低山剥蚀残丘覆沙地（生境Ⅰ）和山前倾斜洪积扇沙地，有小型风积沙丘（生境Ⅱ）和无风积沙丘（生境Ⅲ）3种生境类型样地，对其种群的发育状况、年龄结构、静态生命曲线与分布格局进行了研究，揭示沙木蓼种群动态规律并评价其在构建荒漠植被方面的价值，为科学合理地管护和持续利用沙木蓼种质资源提供科学依据。研究结果表明，1）沙木蓼苗龄级、幼龄级、成熟龄级和老龄级种群密度大小顺序为生境Ⅲ > 生境Ⅰ > 生境Ⅱ，而3种生境中同龄级种群在株高、冠幅、新梢生长量方面差异不显著；2）苗龄级种群在3种生境下都占据了较大的优势地位，对沙木蓼种群的更新具有积极作用。生境Ⅰ和Ⅲ的幼龄级和成熟龄级的年龄结构为连续增长型，老龄级为独立的增长型，种群具有较大的发展空间。而生境Ⅱ的幼龄级和成熟龄级种群的年龄结构为连续的稳定型，老龄级种群为稳定型，种群结构比较稳定。3）种群lx，dx和qx曲线在苗龄级、幼龄级和成熟龄级阶段具有相同的变化趋势，其中苗龄级种群向幼龄级种群转变过程中均呈下降趋势，幼龄级和成熟级种群发育过程中基本保持平稳，但在老龄级种群阶段3种曲线变化趋势的差异性较大，其中生境Ⅰ和Ⅲ种群产生重叠，沙木蓼种群的死亡高峰主要发生在苗龄级和老龄级阶段，具有前期增长，中期稳定，后期衰退的一般规律。4）沙木蓼苗龄级、幼龄级和成熟级种群的分布格局均为聚集分布，而老龄级种群为随机分布。以上分析表明，3种生境下沙木蓼种群更新能力旺盛，种群结构趋于合理，生境差异（风沙流活动）只对土壤种子库、种子萌发和幼苗保存具有显著影响，对其它龄级种群发育没有显著影响，在荒漠植被演变中表现出较强的适应能力和优越性，因此沙木蓼在荒漠植被恢复和重建中具有重要的利用价值。 Abstract:The Minqin Liangucheng Nature Reserve has different types of habitats and vegetations of Atraphaxis bracteata populations. In this study, three types of habitats, i.e., the low denuded hills covered by gravel (habitat I), tilted alluvial fans with small aeolian sand dunes (habitat Ⅱ), and tilted alluvial fans without aeolian sand dunes (habitat Ⅲ), were selected to compare the development status, age structure, static life curve, and distribution pattern of A. bracteata populations at this reserve to reveal their succession dynamics, assess their ecological value, and provide the scientific knowledge for their rational management and sustainable usage. We found that (1) the population densities of young, mature, and old seedlings of A. bracteata were the highest at habitat I, followed by those at habitats Ⅱ and Ⅲ. However, there were no significant differences in the average height, average crown width, and new shoot growth among the same age groups at the three population habitats. (2) The seedlings of all ages dominated position at the three habitats and played a vital role on the propagation of A. bracteata. The age structures of young and mature populations at habitats I and Ⅲ showed continuous growth curves, but that of the old population showed a single growth curve, suggesting that A. bracteata populations at these habitats were developing. The age structures of young and mature populations at habitat Ⅱ showed continuous stable growth curves, but that of old population showed a single stable curve, indicating that A. bracteata populations at this habitat were stable. (3) The lx, dx, and qx curves of seedlings and young and mature populations at the three habitats showed similar change trends. These curves showed decreasing trends from seedling age stage to young age stage, and then stabilized in the young and mature age stages, whereas the curves of old age grade were significantly different, and the populations overlapped between habitats Ⅲ and I. This suggested that seedlings and older A. bracteata populations showed peak mortality, and there was a general pattern of growth at the earlier stage, which stabilized at the middle stage and then decreased at the later stage. (4) The distribution patterns of seedlings and young and mature populations were clump, whereas those for old populations were Poisson. The results indicated that the A. bracteata populations at the three habitats propagated vigorously and showed relatively optimal structure. The environmental difference among the three habitats only had significant impacts on soil seed bank, seed germination, and seedling preservation, but not on population development. These findings suggested that A. bracteata has strong adaptability and dominance in desert areas and can be restored and reconstructed. 参考文献 相似文献 引证文献

Conspecific negative density‐dependent mortality and the structure of temperate forests

Factors that control tree seedling dynamics are critical determinants of forest diversity. We examined the role of density‐dependent mortality and abiotic factors in the differential establishment and survival of tree seedlings at three, large, mapped forest plots in Indiana, Virginia, and Wisconsin, USA. We tested whether seedling densities and seedling survival are related to local biotic and abiotic factors with generalized linear mixed models. Spatial point pattern analyses were utilized to determine if the distribution patterns of seedlings and saplings are consistent with a pattern generated by negative density‐dependent mortality with respect to conspecific trees.Initial sampled seedling density for nearly a third of species showed a positive correlation with increasing conspecific basal area, indicating dispersal limitation, but few had any association with abiotic variables. By contrast, survival of seedlings over one year significantly declined with increasing conspecific basal area. Point pattern analyses indicated that nearly one‐third of tree species had significantly over‐dispersed point patterns of conspecific seedlings and saplings relative to adult densities; the majority of other species exhibited random spatial arrangements. Our results demonstrate that negative conspecific density‐dependent mortality of seedlings could generate the spatial patterns observed at later life stages. By differentially favoring seedlings of other species, this process may contribute to the maintenance of tree diversity in temperate forests, just as others have demonstrated for tropical forests.

The effect of habitat filtering on tree seedling distribution in a subtropical evergreen broadleaf forest in China

Niche theory hypothesized that habitat specialization would contribute to the high species diversity of tropical forests and adult tree patterns. However, the effect of habitat selection during early life stages on plant communities and the influence on seedling regeneration remains unresolved. We studied seedling distribution patterns in four habitat types of GTS 24 hm² forest dynamic plots. (1) The torus-translation test was used to detect the species-habitat associations. Out of 24 seedling species, 11 species were significantly associated with a certain habitat, with seven species showing positive associations. (2) Indicator species analysis was used to investigate the strength of seedling species habitat specialization. We found eight representative indicator species and eight pairs of species combinations of particular habitat types. (3) Compared with early studies based on trees with d.b.h.≥1 cm (non-seedling trees), we found habitat associations differed across plant-life stages. We conclude that habitat filtering influences the distribution and regeneration patterns at very early life stages, affecting the diversity of the whole community in this subtropical evergreen broadleaf forest in China.

Application of mathematical models in the spatial analysis of early tree seedling distribution patterns within a treefall gap at Gwangneung Experimental Forest, Korea

A spatial analysis was conducted on the characteristics of seedling recruitment and one-year mortality of two temperate deciduous tree species: Quercus serrata Thunb. ex Murray (QUSE) and Carpinus laxiflora (Siebold & Zucc.) Blume (CALA). A systematic grid of 64 seedling plots was established within a typhoon-induced treefall gap in a rare old-growth deciduous stand at Gwangneung Experimental Forest, South Korea. Inverse model, Ripley’s K function, and semivariogram tools were introduced to examine spatial relationships among seedling recruitment, one-year seedling mortality, and trees. Overall QUSE germinant density more than tripled that of CALA. Results suggest that dispersal patterns differ between the two species: for QUSE, 2Dt model yielded the best fit whereas the lognormal model was best fitted to CALA. Those differences may reflect different regeneration strategies between the two species. One-year mortality rates were similar for QUSE (76.15%) and CALA (72.25%). Mortality for both species exhibited substantial variance that was indicated as autocorrelation by the semivariogram, suggesting that mortality was not random for either species. Tree spatial patterns were also shown to be autocorrelated. Together, the observed spatial patterns in germination and first-year mortality indicate that the single treefall gap is among the factors that maintain the community structure associated with this forest type.

Effectiveness of Mistletoe Seed Dispersal by Tyrant Flycatchers in a Mixed Andean Landscape

AbstractThe dependence of mistletoes on few dispersers and the directed dispersal they provide is well known, yet no recent work has quantified either the effectiveness of these ‘legitimate’ dispersers, or the extent of redundancy among them. Here, I use the seed dispersal effectiveness (SDE) framework to analyze how birds (Mionectes striaticollis and Zimmerius bolivianus) contribute to mistletoe (Struthanthus acuminatus and Phthirusa retroflexa) infection in traditional mixed plantations within a humid montane forest in Bolivia. I calculated SDE for each bird–mistletoe pair and for the disperser assemblage, by estimating both the quantity and the quality of dispersal. The quantity of dispersal was measured as: (1) disperser abundance; (2) frequency of visits; and (3) number of seeds dispersed per visit, and the quality of dispersal was measured as: (1) germination percentage and speed of germination of seeds regurgitated by birds; and (2) the concordance of deposited seeds and seedling distribution patterns with adult mistletoe distribution at three scales (habitat, host, and microhabitat). Dispersers were not redundant: the more generalist species M. striaticollis dispersed more seeds, but provided lower quality seed dispersal, whereas the mistletoe specialist Z. bolivianus provided low‐quantity and high‐quality seed dispersal. Whereas S. acuminatus benefited more from the SDE of Z. bolivianus, P. retroflexa benefited from the complementary seed dispersal provided by both birds. These results demonstrate how sympatric mistletoes that share the same disperser assemblage may develop different relationships with specific vectors, and describe how the services provided by two different dispersers (one that provides high‐quality and one that provides high‐quantity dispersal) interact to shape spatial patterns of plants.

Influencing factors on early vegetation restoration in burned area of Pinus pumila – Larch forest

Pinus pumila (Dall.) Regel, a rare conifer and key species in high latitude and high altitude mountains, has an important role in soil and water conservation. This evergreen shrub grows 3–6m high in P. pumila – larch (Larix gmelini) open forest at altitudes of 800–1200m in the Greater Kingan Mountain Range (Daxing’an Mountain). Forest fires are major natural hazards to P. pumila – larch forest. The unique ecological role of this community gives important theoretical and practical significance to research on P. pumila – larch forest restoration after fires. Literature concerning factors influencing early vegetation restoration in burned areas in this habitat is sparse. We studied these factors, especially those related to P. pumila seedling establishment. The results showed fires in P. pumila – larch forest usually resulted in severe burns. Typically almost no P. pumila survived after fires. Nearly all ground fuels were consumed. Second growth after fires exhibited low species richness. The dominant tree/shrub seedlings found after fires were birch (Betula platyphylla) and larch, with small number of P. pumila. Other shrub seedlings found were Ledum palustre, Vaccinium vitis-idaea, Betula fruticosa, and Rubus arcticus. The main herb species found were Deyeuxia langsdorffii, and Chamaenerion angustifolium. Important factors influencing early vegetation restoration after fires included seed dispersal, fire size, and site condition. Seed dispersal in birch and larch is higher than in P. pumila; more seedlings of birch and larch were found in burned areas than seedlings of P. pumila. Most seeds germinated in the first year following a fire. The extent of the burned area influences seedling distribution patterns, especially in species with limited seed dispersal ability. Birch and larch seedlings were evenly distributed in the entire burned area, while seedlings of P. pumila were found only at the fire edge. No P. pumila seedlings were found more than 50m away from seed source trees. Site condition significantly influenced seed germination and growth in birch and larch; these seedlings only grew well in burned areas with good site conditions (shallow slopes, thick soils, etc.). They did not grow well in burned areas with poor site conditions (steep slopes, thin soils, etc.). However, P. pumila seedlings could grow well in burned areas with either good or poor site conditions. The strong vitality of P. pumila seedlings gives this species an enormous ecological advantage in soil conservation and environmental restoration and conservation. We conclude that the main factor influencing seedling establishment in P. pumila is its weak seed dispersal ability. Although the P. pumila seeds can germinate in all burned areas, natural regeneration rarely restores burned areas to the original P. pumila – larch forest. Planting seeds and/or seedlings may facilitate burned area restoration to P. pumila – larch forest. Because P. pumila seedlings grow very slowly, the restoration process may take decades.

Regeneration of Treeline Birch (Betula utilis D. Don) Forest in a Trans-Himalayan Dry Valley in Central Nepal

Abstract Distribution and community structure of treeline birch (Betula utilis D. Don) forest in a trans-Himalayan dry valley was studied in Manang (central Nepal) with the major focus on regeneration. Along 5 vertical transects, a total of 41 square quadrats (10 m x 10 m) were sampled to determine the importance value index (IVI) of tree species, distribution pattern of seedlings and saplings, and soil attributes. Regeneration was assessed by a density–diameter curve. Moisture plays an important role in spatial (horizontal) distribution of Betula utilis. Pure Betula forest forming the treeline was mature, with high basal area (2.3%), but mixed Betula forest at lower elevations was young. This might have developed after large-scale clear cutting of Abies spectabilis. If not severely disturbed, mixed Betula forest may be replaced by Abies spectabilis. In general, Betula utilis was regenerating, as evident from a reverse J-shaped density–diameter curve for both forests. However, the distribution of seedling...

Predation on propagules regulates regeneration in a high-density reforested mangrove plantation

Seedling recruitment underpins natural regeneration and contributes to the restocking of forest stands, which in the long term determines the structure and functioning of mangrove ecosys- tems. Propagule predation (among other factors) has been found to play an important role in deter- mining seedling distribution patterns in many mangrove stands. The role of propagule predation in influencing the observed regeneration in a Rhizophora mucronata reforested stand (9 yr old) with various spontaneously established mangrove species was investigated by looking at the effects of pruning, position (planted/vertical or prone/horizontal on the forest floor to simulate stranding) and species (Rhizophora mucronata, Ceriops tagal and Bruguiera gymnorrhiza) found to be sponta- neously growing in the plantation. Predation intensity was higher (p = 0.05) in the pruned part of the stand than in the unpruned part. Prone propagules were preyed on more (p = 0.05) than the planted category, while R. mucronata was the species least preyed on compared to C. tagal and B. gymnor- rhiza, suggesting that predation favors the recruitment of R. mucronata into this conspecific stand. Significant differences among prone and planted propagules suggest that predation is intense during the stranding phase, and this may play a critical role in limiting seedling establishment and subse- quent recruitment. Predation is suggested to be a regulator of competition in this high-density stand by eliminating or reducing potential competitors, alluding to a 'mutual relationship' between crab predators and mangrove trees.

THE ROLE OF ANTS IN SEED DISPERSAL OF GLOBBA LANCANGENSIS AND THE SPATIAL DISTRIBUTION OF ITS SEEDLINGS

Seed dispersal is a key process determining the spatial pattern of plant populations. Myrmecochory is a term referring to a plant_ant mutualism in which ants disperse plant seeds while using the nutritionally valuable elaiosomes as food. In this study, our goal was to understand how ants affect seed dispersal and seedling distribution patterns of a myrmecochorous plant, Globba lancangensis. G. lancangensis is a small perennial herb of Zingiberaceae mainly distributed in southwest Yunnan Province. It propagates primarily by seeds but also by a small number of bulbils. There are 31.2±2.13 (Mean±SE, n =32) seeds in each fruit. The seeds are 2-3 mm in length and bear a white_colored elaiosome. We conducted an observational study on the seed dispersal of G. lancangensis in October 2002 in its natural habitat in Xishuangbanna, Yunnan Province of China (21°59′ N, 100°16′ E; 1 180 m asl; annual mean temperature, 18.3 ℃; annual mean rainfall, 1 339 mm). A total of ten species of ants were identified that transported the seeds of G. lancangensis and their activities were recorded. The mean dispersal distance of seeds was (0.47±0.03) m ( n =216), ranging from 0.01 m to 3.35 m. Odontoponera transversa , Pheidole sp. and Pachycondyla luteipes were the most important seed dispersing ant species, occurring 61%, 50% and 28% of the time, respectively, with mean dispersal distances of (0.60±0.09) m, (0.20±0.01) m and (0.32±0.05) m, respectively. As a whole, ants promoted a decrease in the degree of aggregation of G. lancangensis seeds. Ants of Pheidole sp. collected a total of 43% of the seeds of G. lancangensis but consumed most of the seeds collected, suggesting that Pheidole sp. is a seed harvester ant O. transversa did not remove seeds with artificially removed elaiosomes and appeared to be the most sensitive ant species to seed elaiosomes. Overall, O. transversa made the most significant contribution to seed dispersal, as demonstrated by the highest visiting frequency (61%) and the greatest mean dispersal distance (0.60±0.09) m of all ants. These results imply that a tight mutualism exists between O. transversa and G. lancangensis. To understand whether ants influence the spatial pattern of seedlings, we compared the spatial distribution of seedlings of G. lancangensis in its natural habitat with that of two other species in the Globba genus, G. barthei and G. racemosa; the latter two species propagate mainly by bulbils which are dispersed by abiotic means. Nine 25 m×25 m plots, three plots for each species, were established and the location of every Globba seedling inside the plots was recorded. The mean distance to the nearest neighbor of G. lancangensis was significantly higher than both G. barthei ((36.8±1.45) cm vs. (29.8±2.70) cm, Mean±SE; t 73,33 = 2.11, p =0.037) and G. racemosa ((36.8±1.45) cm vs. (28.7±3.16) cm, t 73,31 =2.33, p = 0.022 ). We used Z _values to describe the degree of aggregation of the populations of the three species. The Z_value of G. lancangensis (-1.70±0.19, Mean±SE) was significantly larger than the Z_value of both G. barthei (-2.58±0.37, t 73,33 =2.36, p =0.020) and G. racemosa (-3.28±0.53, t 73,31 =3.54, p = 0.001), indicating that G. lancangensis was significantly less aggregated. These results suggest that ants make a significant contribution to dispersing G. lancangensis seedlings by increasing the distance to its nearest neighbor and decreasing the degree of aggregation in its natural habitat.

Role of dispersal in the recruitment limitation of neotropical pioneer species

Summary We examined the importance of seed dispersal in predicting the pioneer seedling composition in recent gaps in a forest plot on Barro Colorado Island (BCI), Panama. We characterize seed dispersal for 13 taxa from seed rain data collected over 13 years in 200 mesh traps, and for an additional species from germination from soil samples collected in one year. We describe seedling distribution patterns from a complete census of all seedlings of these 14 taxa present in 36 treefall gaps. A maximum likelihood model, incorporating both distance to adult trees and tree size, fitted observed seed rain to traps quite well for all taxa. The ability to predict seedling recruit number per gap varied greatly among taxa. For 8 of 14 taxa, regression models incorporating predicted seed rain were significantly better predictors of seedling recruitment than models in which recruitment probability was assumed constant in all sites. To see if variation in local dispersal patterns determined the community composition of gaps, we examined the relative abundances of these 14 pioneer taxa in the 36 gaps. We found that taxon abundances were significantly positively correlated with abundances predicted from seed dispersal models and seed–seedling regressions for 27 out of 36 gaps. Overall, we find evidence that limited seed dispersal is an important factor contributing, together with factors affecting post‐dispersal recruitment success, to seedling distribution patterns in gaps.

Ecological relationships between seedling emergence and litter cover in the earliest stage of plant succession on sandy soil

AbstractThe relationships between seedling emergence and litter cover were studied in the earliest successional stage of a plant community. During a period of 3 years, changes in vegetation cover and species composition were assessed on three permanent quadrats with virgin sandy soil substrates A successional pattern from summer annual grasses to winter annual herbacoeus plants to biennial and perennial plants was confirmed, and invasion and replacement of the component species were conspicuous. The spatial distributions of seedlings and litter were heterogeneous in winter, and some patches consisting of both seedlings and litter were observed. There was a strong positive correlation between distribution patterns of seedlings and litter; seedling density increased with increasing litter cover. The results suggest that the litter cover of the previous stage plays an imporrant role in promoting successional changes in the early stage of plant succession.

Safe Sites and the Regeneration of Clethra alnifolia L. (Clethraceae) in Wetland Forests of Central New Jersey

-Flowering phenology, seed set and dispersal, and seedling establishment patterns of Clethra alnifolia in three wetland forests are described. Flowering patterns were similar between years but differed among sites. Tagged shrubs had high rates of fruit set and most fruits persisted until seed dispersal. Seed fall and seedling distribution patterns suggested that seed are adequately dispersed from parent plants. Germination experiments showed high seed viability, but low numbers of seedlings at all sites suggested constraints on establishment. Significant differences were detected in seedling establishment success in different forest floor microsites. Availability of safe sites influenced the relative contributions of sexual and asexual reproduction to new recruitment. Environmental conditions in the wetland forest appeared unsuitable for successful seedling recruitment and Clethra appears to rely on vegetative reproduction to regenerate existing populations.

Light gaps and long-term seedling performance of a Neotropical canopy tree (Dipteryx panamensis, Leguminosae)

Tropical tree regeneration results from a complex interplay of biotic and abiotic factors: the actions of seed dispersers, seed predators, pathogens, and herbivores influence the distribution patterns of seedlings within an environment that is heterogeneous with respect to the light, water, and soil nutrients required for eventual growth to the canopy. In a study of the canopy tree Dipteryx panamensis (Pitt.) Rec. & Mell (Leguminosae) on Barro Colorado Island, Panama, De Steven & Putz (1984) found that seedling recruitment in most years was limited by mammalian predation on the large, 4-cm long seeds and that firstyear seedling growth and survival were strongly light-dependent. They hypothesized that Dipteryx regeneration required the establishment of a population of seedlings tolerant of understorey suppression while awaiting canopy gap formation and that high seed predation prevented such establishment on Barro Colorado Island. Continuation of observations for six years has now provided long-term data on differential seedling performance that suggests how canopy gap dynamics may influence Dipteryx regeneration. Methods. The tropical moist forest of Barro Colorado Island, Panama (90 09' N, 790 51' W) has been described extensively by Croat (1978). The area receives approximately 2600 mm of rainfall annually, with a distinct dry season during the 4-5 months from late December through April. Dipteryx panamensis is widely distributed on the island, but is more abundant in secondary forest areas that were extensively cleared about 100 years ago. De Steven & Putz (1984) provide a general description of its life history. Experimental microenvironments were selected to span a gradient in light availability. In the initial experimental design (described in De Steven & Putz 1984), seedlings germinated in three field sites in May 1981 were transplanted

MICRO‐SPATIAL HETEROGENEITY AND SEEDLING DEMOGRAPHY IN SPECIES‐RICH GRASSLAND

It is suggested that spatial niche‐separation between grassland species occurs in the regeneration phase and that the differential response of species to micro‐variations in leaf cover may allow coexistence at high density. A technique for measuring heterogeneity in leaf‐cover on a scale of 1‐cm2 units (micro‐cover) and the demography of seedling cohorts of Reseda lutea and Anthyllis vulneraria in relation to this heterogeneity is described. Densities of seedlings were significantly higher in micro‐sites of low micro‐cover for R. lutea and for one of the three cohorts of A. vulneraria studied. No relationship was found between mortality and density of seedlings or micro‐cover. The ultimate causes of these distribution patterns of seedlings and their consequences for the maintenance of species diversity in grassland are discussed.