Fire,canopy cover and seedling dynamics in Mediterranean shrubland of northeastern Spain

Abstract. Seedling establishment and survival of the main woody species of early-successional shrubland in northeastern Spain were studied from 1992 to 1995 with emphasis on the importance of vegetation cover (existence of open areas and the situation beneath the plant canopy) and microhabitat (occurrence of stones, litter and bare soil). In the absence of fire, vegetation cover (measured at a scale of 30cm × 30 cm) was not correlated with seedling emergence of most species, nor with growth and survival of seedlings up to one year old. Seedlings older than one year showed a similar pattern: their density was not significantly different in both kinds of habitats. The emergence of seedlings was mainly associated with the presence of mature plants – which can provide seeds – and with the absence of unsuitable microhabitats (large stones, deep litter and bare soil). In April 1994 a wildfire burned the study area. This enabled a study of the pattern of post-fire establishment. After the wildfire, seedling emergence of several species increased and most species produced seedlings with higher survival and growth rates than in the period before the fire. Pre-fire cover, however, did not show significant effects on post-fire seedling dynamics in most cases.     

The role of the soil seed and seedling bank in the regeneration of diverse plant communities in the subtropical Ailao Mountains,Southwest China

We compared species composition and diversity of the soil seed and seedling banks in three secondary vegetation types (shrubland, Populus bonatii forest, Lithocarpus regrowth forest) and a primary old-growth forest in the subtropical Ailao Mountains of southwestern China to clarify the importance of seed and seedling banks for forest dynamics. The average species richness was the highest in soil samples from the shrubland (26.80 ± 1.98), and the lowest from the primary forest (9.93 ± 0.50). The density of germinable tree seeds increased from the secondary vegetation to the primary forest, and the density of shrub, forb, and graminoid seeds decreased significantly. The most abundant seedlings recorded in soil samples were light-demanding species in the shrubland and Populus bonatii forest. For ground flora, the number of shrub seedlings strongly decreased with the increase in stand age, and shade-tolerant tree seedlings tended to increase. The species similarity between the seed bank and the aboveground vegetation in all sites was low (Sørensen’s index = 0.11–0.33), however, the shrubland had higher similarity compared with the other three plant communities. In the primary forest, light-demanding woody species dominated in soil seed banks, while shade-tolerant species dominated in the overstory and the forest floor. In the primary forest, seedlings of dominant tree species were rare in the understory, and no seeds of the dominant species were found in the soil. Results indicated that the early stages of vegetation recovery should take into account the possibility of recovering soil seed bank processes. However, colonization and establishment of tree seedlings will be difficult once a primary forest is destroyed.     

东灵山地区辽东栎幼苗的建立和空间分布

研究树木实生苗的建立对森林生态系统的保育和恢复具有重要意义,在北京东灵山地区调查了辽东栎(Quercus liaotungensis)实生和萌生幼苗在几种典型的植被类型中的空间分布以及辽东栎一年生实生幼苗在1个林窗梯度上的建立。选择几种典型的植被类型,研究辽东栎实生幼苗和萌生幼苗在森林中的空间分布。结果显示,在不同植被类型中辽东栎实生和萌生幼苗的密度存在空间差异,实生苗密度随幼苗年龄增大逐渐降低,种群的更新主要依靠萌生苗完成。在1个落叶阔叶林中选择1个林窗,在不同梯度(即林窗中间、林窗和树冠连接处,以及树冠下)上,播种辽东栎坚果,第二年秋季调查实生幼苗的2个生长指标和出苗率。结果显示,林窗对一年生实生幼苗的生长高度有影响。幼苗高度在林窗中比在树冠下大;林窗对辽东栎幼苗最长叶片长度和幼苗的出苗率没有影响。说明辽东栎实生幼苗的良好生长需要阳光比较充足的生境条件。本项研究结果建议,对辽东栎种群的更新,应该适当择伐一些较大个体,使森林形成一些林窗或林中空地,以利于辽东栎实生幼苗的建立,这样才能使辽东栎种群通过实生苗进行更好的自然更新。     

Sugar maple (Acer saccharum Marsh.) establishment in boreal forest: results of a transplantation experiment

Aim To evaluate whether seedlings of sugar maple (Acer saccharum Marsh.) can establish beyond the species northern range limit in adjacent boreal forest. Location The hardwood–boreal forest transition zone on the north‐east shore of Lake Superior, Ontario, Canada. Methods Seed fall of sugar maple was monitored for 5 years in a stand of this species at its northern range limit, and seed from this stand was transplanted to five micro‐habitat types in an adjacent boreal forest. The establishment and survival of sugar maple seedlings there, and in the seed‐source stand, was monitored for the following 7–11 years. Soil‐surface light levels were measured in both forest types. Results Most seed fell in the final year of monitoring, when c. 250 seeds m^?2 were recorded. First‐year seedling establishment rates in the maple stand, deriving from this mast seed year, was approximately double that deriving from seed transplanted to the boreal forest sites; this is tentatively attributed to seed predator satiation in the maple stand. However, subsequent seedling survivorship in the boreal forest was greater than that in the maple stand, resulting in comparable seedling densities by the end of 6 years. This difference is tentatively attributed to better illumination in the boreal forest sites, and canopy‐opening disturbances appear to be especially facilitative of seedling survival. Main conclusions There is no fundamental impediment to sugar maple seedlings establishing in boreal forest communities if climate warming occurs and seed is available. If management intervention is needed to accelerate seed availability in a rapidly warming boreal forest, then diffuse seed application to disturbed boreal forest sites during mast years of local boreal tree species is recommended as the most effective way of avoiding seed predation and increasing seedling survival.     

Succession and Micro-elevation Effects on Seedling Establishment of Calophyllum brasiliense Camb. (Clusiaceae) in an Amazonian River Meander Forest1

I investigated the effects of successional stage and micro‐elevation on seedling establishment of Calophyllum brasiliense (Clusiaceae), a common canopy tree of seasonally flooded lowland forest along the Manú River meander zone in southeastern Peru. To compare seedling establishment between microhabitat types, I planted C. brasiliense seeds in a fully crossed experimental design of three successional stages (early, mid, and mature) and two micro‐elevations (levees and backwaters). Seedling establishment success in this study was affected by both successional stage and micro‐elevation, but micro‐elevation was most important in mid‐successional habitats. In general, seedlings in early succession experienced better conditions than in mature forest; light levels were higher, herbivory lower, and seedling growth higher. In mid‐successional forest, micro‐elevation determined habitat quality; backwaters had higher light levels, lower herbivory, and higher seedling growth and survival than levees. Mid‐successional backwaters were similar in quality to early successional forest for seedling establishment, while levees in that same successional stage were the poorest microhabitats for establishment. Although mid‐successional backwaters are similar to early succession for seedling establishment, in the long run, seedlings that establish in mid‐succession have a lower chance of reaching reproductive size before their habitat ages to mature forest than members of their cohort that established in early succession. I hypothesize that successful recruitment for C. brasiliense in the Manú River meander system requires dispersal to early successional habitat.     

Establishment of

We compared establishment of Douglas fir (Pseudotsuga menziesii) and Corsican pine (Pinus nigra) seedlings in kanuka (Kunzea ericoides) and manuka (Leptospermum scoparium) shrubland to test the hypothesis that Douglas fir, because of its greater shade tolerance, is better able to establish in woody communities than pine species. Seed of the conifer species was sown under a range of canopy covers at six sites, the cover being low-statured vegetation in openings between stands, stand edges, and moderate and dense canopies. After three growing seasons, survival of Corsican pine seedlings was greatest in the open and declined progressively as canopy cover increased. This contrasted with Douglas fir, where survival was greatest at the canopy edge. Survival of Douglas fir seedlings significantly exceeded that of Corscican pine seedlings under dense canopy positions. Seedling numbers of both species declined significantly with increasing leaf area index of manuka, but not kanuka stands, where seedling numbers were lower. Leaf area index of manuka stands accounted for substantially greater variation in number and survival of Corsican pine than Douglas fir seedlings. It is concluded that Douglas fir is better able to establish in shaded environments in woody communities than Corsican pine; however, further monitoring is required to confirm the long-term survival of both species under the moderate and dense canopy positions in this trial.     

Scatter Hoarding of Seeds Confers Survival Advantages and Disadvantages to Large-Seeded Tropical Plants at Different Life Stages

Scatter hoarding of seeds by animals contributes significantly to forest-level processes, including plant recruitment and forest community composition. However, the potential positive and negative effects of caching on seed survival, germination success, and seedling survival have rarely been assessed through experimental studies. Here, I tested the hypothesis that seed burial mimicking caches made by scatter hoarding Central American agoutis (Dasyprocta punctate) enhances seed survival, germination, and growth by protecting seeds from seed predators and providing favorable microhabitats for germination. In a series of experiments, I used simulated agouti seed caches to assess how hoarding affects seed predation by ground-dwelling invertebrates and vertebrates for four plant species. I tracked germination and seedling growth of intact and beetle-infested seeds and, using exclosures, monitored the effects of mammals on seedling survival through time. All experiments were conducted over three years in a lowland wet forest in Costa Rica. The majority of hoarded palm seeds escaped predation by both invertebrates and vertebrates while exposed seeds suffered high levels of infestation and removal. Hoarding had no effect on infestation rates of D. panamensis, but burial negatively affected germination success by preventing endocarp dehiscence. Non-infested palm seeds had higher germination success and produced larger seedlings than infested seeds. Seedlings of A. alatum and I. deltoidea suffered high mortality by seed-eating mammals. Hoarding protected most seeds from predators and enhanced germination success (except for D. panamensis) and seedling growth, although mammals killed many seedlings of two plant species; all seedling deaths were due to seed removal from the plant base. Using experimental caches, this study shows that scatter hoarding is beneficial to most seeds and may positively affect plant propagation in tropical forests, although tradeoffs in seed survival do exist.     

Fruit removal,pyrene dispersal,post-dispersal predation and seedling establishment of a bird-dispersed tree

The recruitment of a dioecious bird-dispersed tree, the hollyIlex aquifolium (Aquifoliaceae), was studied consideringthe stages of fruit removal by birds, seed rain, post-dispersal seed predation,seed germination and seedling survival. The main objective was to test theeffect of different microhabitats within a beech forest on recruitment stages.Migrant thrushes were the main dispersers of this tree whose fruit crops wereentirely removed during two study years. Seed rain was greatest beneath hollytrees regardless of their sex and lowest in the open sites. Post-dispersal seedpredation was examined by two experiments and did not differ betweenmicrohabitats despite its quantitative importance (about 70%). Seedlingemergence, which probably corresponded to seeds from several cohorts, wasgreater beneath trees than in open sites and the density of second-yr to 5cm seedlings depended on the presence-absence of ungulateherbivores and litter. While the former had a detrimental effect, the latterhada beneficial effect on seedling abundance. Seedling survival showed nosignificant variations between microhabitats but depended on seedling densityinsome microhabitats (holly, beech). Finally, the initial seed arrival seemed todetermine microhabitat suitability for holly seedling establishment. However,under heavy browsing the density of seedlings may be strongly reduced leadingtomicrohabitat homogeneity for holly seedling establishment.     

贮藏种子的啮齿动物对油茶种子沉积形式的影响

种子沉积的质量常常涉及种子扩散作用者(如鸟类和小型啮齿动物)对生境和微生境的选择以及种子沉积的形式(如种子埋藏).然而,很少的研究涉及到种子在离开母树后被这些动物沉积在何处.在四川省都江堰一个实验林场的2个林分(次生林和原生林)内,通过追踪用带编号的金属薄片标记的油茶(Camellia oleifera Abel.)种子的命运,研究了贮藏种子的啮齿动物对种子沉积的影响.研究发现:在2个林分内,80%以上的种子被很好地埋藏在0～60 mm深的土壤中,而小部分种子则被放置在地表(但有少量落叶遮盖).小型啮齿动物喜好在灌丛下或灌丛边缘贮藏和取食种子,可能是在这样的微生境下它们在觅食时将遭遇较小的捕食风险.研究还发现,贮藏点的微生境分布随贮藏点等级而逐渐变化:在两个林分内较高等级的贮藏点(如次贮藏点和三级贮藏点)比初级贮藏点有更多的种子被贮藏在灌丛下或灌丛边缘.这表明,啮齿动物对油茶种子的埋藏可能更有益于种子的存活、萌发以及幼苗的建成.啮齿动物将散落在母树下或其附近的油茶种子扩散到不同的微生境,这可能有利于他们遭遇到更多的适宜环境而萌发,实现幼苗补充.     

Rodent‐mediated plant seed dispersal: What happens to the seeds after entering the gaps with different sizes?

In general, it is accepted that gap formation significantly affects the placement of scatter‐hoarded seeds by small rodents, but the effects of different forest gap sizes on the seed‐eating and scatter‐hoarding behaviors of small rodents remain unclear. Thus, we examined the effects of a closed‐canopy forest, forest edge, and gaps with different sizes on the spatial dispersal of Quercus variabilis acorns and cache placement by small rodents using coded plastic tags in the Taihang Mountains, China. The seeds were removed rapidly, and there were significant differences in the seed‐eating and caching strategies between the stand types. We found that Q. variabilis acorns were usually eaten after being removed from the closed‐canopy forest and forest edges. By contrast, the Q. variabilis acorns in the forest gap stands were more likely to be scatter‐hoarded. The dispersal distances of Q. variabilis acorns were significantly longer in the forest gap plots compared with the closed canopy and forest edge plots. However, the proportion of scatter‐hoarded seeds did not increase significantly as the gap size increased. In small‐scale oak reforestation projects or research, creating small gaps to promote rodent‐mediated seed dispersal may effectively accelerate forest recovery and successional processes.     

Ecosystem Services from Keystone Species: Diversionary Seeding and Seed‐Caching Desert Rodents Can Enhance Indian Ricegrass Seedling Establishment

Seeds of Indian ricegrass (Achnatherum hymenoides), a native bunchgrass common to sandy soils on arid western rangelands, are naturally dispersed by seed‐caching rodent species, particularly Dipodomys spp. (kangaroo rats). These animals cache large quantities of seeds when mature seeds are available on or beneath plants and recover most of their caches for consumption during the remainder of the year. Unrecovered seeds in caches account for the vast majority of Indian ricegrass seedling recruitment. We applied three different densities of white millet (Panicum miliaceum) seeds as “diversionary foods” to plots at three Great Basin study sites in an attempt to reduce rodents' over‐winter cache recovery so that more Indian ricegrass seeds would remain in soil seedbanks and potentially establish new seedlings. One year after diversionary seed application, a moderate level of Indian ricegrass seedling recruitment occurred at two of our study sites in western Nevada, although there was no recruitment at the third site in eastern California. At both Nevada sites, the number of Indian ricegrass seedlings sampled along transects was significantly greater on all plots treated with diversionary seeds than on non‐seeded control plots. However, the density of diversionary seeds applied to plots had a marginally non‐significant effect on seedling recruitment, and it was not correlated with recruitment patterns among plots. Results suggest that application of a diversionary seed type that is preferred by seed‐caching rodents provides a promising passive restoration strategy for target plant species that are dispersed by these rodents.     

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.     

Forest processes in the presence of wild ginger (

Wild ginger (Hedychium gardnerianum) is a tall rhizomatous herb that invades forests and shrubland fragments in northern New Zealand. In order to determine the impacts of this invasive weed on forest processes, comparisons of conifer-broadleaved forest patches with different densities of ginger were made at Opononi and Whangarei in Northland. Soil properties, vegetation structure, floristics, and seed rain were recorded. Annual litter fall biomass and chemical composition were measured. There were no significant differences between soils under forest with sparse (< 5% cover) and dense (> 50% cover) ginger. A sparse subcanopy layer and fewer saplings were common factors in ginger plots. Forest canopy litter fall (c. 6.8 t ha-1 yr-1) and total N (45.1-56.2 kg ha-1 yr-1) were similar in plots with sparse or dense ginger. Species richness of adult trees and seed fall richness varied little. In contrast, seedling density and richness were lower in dense ginger stands and seedling composition was dominated by species with large (> 200 mg) seeds, i.e. Corynocarpus laevigatus, Dysoxylum spectabile and Rhopalostylis sapida. These seedlings may produce a different forest canopy from that currently found in areas where ginger is sparse.     

Limitations to seedling establishment in a mesic Hawaiian forest

While invasive species may be visible indicators of plant community degradation, they may not constitute the only, or even the primary, limitation to stand regeneration. We used seed-augmentation and grass-removal experiments under different canopy conditions to assess the relative importance of dispersal limitation, resource availability, and competition on seedling establishment in the understory shrubs Sophora chrysophilla, Dodonea viscosa, and Pipturus albidus in a montane mesic forest in Hawaii. The study location was an Acacia koa-Metrosideros polymorpha forest at 1000–1500 m elevation on the leeward side of Hawaii Island; it is a closed-canopy forest historically subject to logging and grazing by cattle and sheep and currently dominated by the exotic grass, Ehrharta stipoides, in the herb layer. Seedling establishment after 1 and 2 years was strongly dispersal limited in Sophora and Dodonea, but not in Acacia, a non-augmented species in which abundant seedlings established, nor in Pipterus, in which only one seedling established in 2 years. Grass cover reduced seedling establishment in Acacia, Sophora, and Dodonea and, for the latter two species, seedling establishment was substantially greater in the warmer, more moist forest at the lowest elevation. Light, moisture, and resin-captured N and P were more strongly affected by elevation and canopy composition than by grass cover, but in most cases seedling establishment was not positively correlated with resource availability. Limitations to the establishment of woody seedlings in this forest-grassland mixture vary among species; however, both dispersal limitation and competition from a shade-tolerant grass are important deterrents to regeneration in these forests.     

Limiting mechanisms in the regeneration of the Chilean matorral – Experiments on seedling establishment in burned and cleared mesic sites

The Chilean matorral is characterized by multispecific shrub clumps in dry areas but has a continuous canopy in wetter sites. It has been hypothesized that this difference is due to easier recolonization of open patches by shrub seedlings under more mesic conditions. Within the mesic range of the matorral we designed a field experiment to compare shrub seedling emergence, growth, and survival under the closed canopy of a secondary forest versus three types of open patches: burned, cleared of shrubs but with a herbaceous layer present, and clear without a herbaceous layer. After the first summer, survival of Quillaja saponaria seedlings was 75% in the burned site, 30% in the cleared patch without herbaceous vegetation, and 15% with herbaceous vegetation present, whereas there was 0% survival under the secondary forest canopy. After eight years, the percentages had dropped to: 22%, 12% and 3%, respectively. These results contrast strongly with the seedling establishment patterns in drier areas of the matorral where early seedling survival is higher under the shade of large shrubs. In the experimental mesic sites, seedlings did best on the burned site, not only in terms of survival, but also in terms of growth. After one year, seedling mean height was 10.2 cm in the burned site, whereas 3.8 cm and 5.3 cm in the cleared patches without and with herbaceous respectively. After eight years, mean height differences between treatments had increased further: 147.7 cm in the burned site, 40.3 cm in the cleared patch without herbaceous cover and 13 cm in the cleared patch with herbs. Our results indicate that the facilitative effect of nurse shrubs on seedling establishment found in dry ranges of the matorral is less important in more mesic sites. This difference may explain the continuous shrub cover in relatively mesic areas as opposed to the characteristic patchy structure of the matorral in its drier range.     

啮齿动物对不同林木种子的搬运和取食微生境选择机制

不同植物种子依靠不同的方式实现扩散,啮齿动物对林木种子搬运后在取食点微生境和贮藏方式的选择存在偏好,研究其贮藏行为与微生境的关系是探究幼苗建成的关键。在秦岭中段火地塘林区,采用标签标记法,以锐齿槲栎、华山松和油松种子为材料,探究了小型啮齿动物对松栎混交林建群种种子扩散过程的影响。结果表明:1)油松种子原地取食率显著高于锐齿槲栎和华山松种子,且啮齿动物更倾向于搬运后取食(60%)和埋藏(4.33%)华山松种子,搬运后取食距离也为华山松最大(2.49 m);锐齿槲栎小种子被搬运后埋藏的距离最大(4.92 m)。2)除华山松种子外,其他类型种子被搬运后单个取食的比例均在85%以上;油松种子不存在埋藏点,而其他类型种子90%以上均以单个形式被埋藏。3)大部分种子被啮齿动物搬运后选择在裸地丢弃;锐齿槲栎大种子(87.5%)、小种子(78.57%)和华山松种子(53.33%)较大比例被啮齿动物埋藏在灌丛下方,埋藏在裸地的种子较少。4)大部分种子在灌丛下方被取食,仅华山松种子被啮齿动物搬运到洞穴取食;除油松种子被大量原地取食外,其他类型种子被搬运到取食点的种子比例基本呈现由微生境植被复杂到简单(灌丛—草丛—灌丛边缘—裸地)而逐渐减小的趋势。种子的营养价值及取食和搬运过程中啮齿动物付出的成本是影响种子命运的关键性因子,且啮齿动物对种子埋藏和取食地点的微生境存在较明显的选择性。     

Consequences of disperser behaviour for seedling establishment of a mistletoe species

The dispersal process in plants links adults and their offspring. For frugivore‐dispersed plants, animal behaviour can have a strong effect on plant fitness. Many mistletoes are totally dependent on animals that deposit seeds on suitable hosts and particular branch diameters. We characterised the seed dispersal and seedling establishment of the mistletoe Tristerix corymbosus, which at our study site, is exclusively dispersed by the marsupial Dromiciops gliroides. Mistletoes’ fruits have a viscous pulp that remains in the seed even after dispersal. This substance adheres the seed to the host branch. We estimated host branch availability in the forest and seed deposition (faeces) by the marsupial in the study area. Specifically, the branch suitability factors we assessed were host identity, branch status (alive or dead), branch diameter, height, and canopy cover. Lodged faeces were individually marked and the number of seed deposited within these droppings was counted, and we recorded the number of seedlings with true leaves that had established after 1 year to estimate the probability of seedling establishment. Branch diameter and canopy cover had a significant positive effect on seed deposition probability. Seedling establishment probability decreased with the number of seeds deposited per faeces and with canopy cover. In general, the marsupial deposited mistletoe seeds in microsites that increase the chance of seedling establishment. Thus, the movement behaviour of the marsupial has a positive effect on the regeneration process of this mistletoe species.     

Impacts of secondary seed dispersal and herbivory on seedling survival in Aesculus turbinata

Abstract. Aesculus turbinata is a tree species with large seeds (6.2 g mean dry weight). We studied the demography of its seeds and seedlings in a temperate deciduous forest in northern Japan to elucidate the ecological significance of large seeds with special reference to herbivory and secondary dispersal. Both seed and seedling stages suffered greatly from herbivores. Seedling herbivory was important judged from experiments with shoot clipping and hypogeal cotyledon removal. However, some seedlings survived through re-sprouting after herbivory. Survival rate and percentage resprouting seedlings were lower than those with remaining cotyledons, though seedling size was not affected. This suggests that stored resources in hypogeal cotyledons are working as a kind of ‘risk hedge’ against severe aboveground shoot clipping experienced by A. turbinata. The spatial distribution of seedlings was expanded via seed scatter-hoarding by rodents. Seedling survival rate was higher within canopy gaps than under closed canopy, indicating that canopy gaps are safe sites for establishment, and was negatively correlated with seedling density. Therefore, secondary seed dispersal in this species seems to be effective in ‘finding’ safe sites and in ‘escaping’ density-dependent mortality. The large seeds and seedlings of A. turbinata are attractive to herbivores, but the high resistance of seedlings to herbivory due to large reserves and the effective secondary dispersal appear to mitigate these disadvantages.     

Variation in stand structure,light and seedling abundance across a tropical moist forest chronosequence,Panama

Abstract. We asked whether forest structure and understory light environments across a tropical moist forest chronosequence followed predictions of a 4‐phase model of secondary succession (establishment, thinning, transition and steady‐state) and whether seedling density and diversity were functions of light availability as predicted by this model. Using aerial photographs, we identified eight second‐growth stands (two each aged ca. 20, 40, 70, and 100 yr) and two old‐growth stands within Barro Colorado Nature Monument, Panama. Trees and seedlings were sampled in nested, contiguous quadrats in 2 160‐m transects in each stand. Light was measured as percent transmittance of diffuse photosynthetically active radiation (TPAR) at each seedling quadrat and by estimation of percent total incident radiation during the growing season from hemispherical canopy photographs. Basal area, tree density, and canopy height followed predictions of the 4‐phase model. Percent total radiation, but not TPAR, declined with stand age as did seedling density. While seedlings were more likely to occur in quadrats at higher light levels, much variation in seedling density was not related to light availability. Seedling patch sizes were small irrespective of light patches, estimated as semivariance ranges. Seedling species richness was a function of seedling density; estimates of species diversity unbiased by density did not vary systematically as a function of stand age. Proximate seed sources, efficient dispersal mechanisms, and appropriate establishment conditions can promote establishment of species‐rich communities early in successions of heterogeneous tropical moist forest.     

Regeneration of a Coastal Pine (Pinus thunbergii Parl.) Forest 11 Years after Thinning,Niigata, Japan

To examine the effects of thinning intensity on wind vulnerability and regeneration in a coastal pine (Pinus thunbergii) forest, thinning with intensities of 20%, 30% and 50% was conducted in December 1997; there was an unthinned treatment as the control (total 8 stands). We re-measured the permanent sites to assess the regeneration characteristics 11 years after thinning. In the 50% thinned stand, seedlings aged from 2 to 10 years exhibited the highest pine seedling density and growth. The age composition ranged from 1–3 years with densities of 9.9 and 5.1 seedlings m⁻² in 30% and 20% thinned stands; only 1-year-old seedlings with a density of 6.1 seedlings m⁻² in the unthinned stand. Similar trends were found for the regeneration of broadleaved species such as Robinia pseudoacacia and Prunus serrulata. We speculate that the canopy openness and moss coverage contributed to the regeneration success in the 50% thinned stand, while the higher litter depth and lack of soil moisture induced the regeneration failure in the unthinned stand. The stands thinned at 20% or 30% were less favourable for pine regeneration than the stands thinned at 50%. Therefore, thinning with less than 30% canopy openness (20% and 30% thinned stands) should be avoided, and thinning at higher than 30% canopy openness (50% thinned stand, approximately 1500 stems ha⁻¹ at ages 40–50 years) is suggested for increasing regeneration in the coastal pine forest. The implications of thinning-based silviculture in the coastal pine forest management are also discussed. The ongoing development of the broadleaved seedlings calls for further observations.