Comparison of three seed trap types in a chalk grassland: toward a standardised protocol

In a chalk grassland in north-western France, vegetation and seed rain were studied along two transects. We compared the efficiency of three types of seed traps (funnel traps, sticky traps, pots exposed in the field) to estimate the annual seed rain and to reveal various processes involved in plant community regeneration. Data were analysed to compare seed density, species richness and composition across seed traps and vegetation. Geostatistical analyses (semivariograms. were used to detect possible autocorrelation and to examine patterns of spatial variation in seed rain and vegetation. The results show that (1) funnel traps are most efficient (56 species, 8079 seeds.m^–2). (2) Each type of seed traps brings different information about the processes involved in seed dispersal and seedling establishment. Sticky traps help to understand import and export of seeds in a community through anemochory. Funnel traps may provide a measure of the auto-regeneration capacity of the vegetation through its local seed production. Pot traps integrate various processes involved between seed dispersal and seedling emergence. (3.) The exposition to environmental conditions generates marked spatial patterns in species richness measured in pots and in vegetation, selecting species able to survive. Pot traps indicate that numerous species producing seeds in standing vegetation are unable to establish in the field through seedling recruitment. Our study emphasizes the need of using different types of seed traps and spatial sampling configurations to assess the regenerative potential of standing vegetation and the various mechanisms involved in seed dispersal. A standardised protocol for seed rain sampling was finally developed.     

Dispersal and microsite limitation in Australian old fields

The recovery of native communities after cultivation may be constrained by (a) the failure of species to reach a site or (b) their failure to survive once there. Although seed addition is a common method to test for seed versus microsite limitation, most studies do not follow populations beyond seedling establishment, nor do they measure seed dispersal. We examined dispersal across native grassland/old field boundaries and investigated the relative importance of seed and microsite limitation across multiple life-history stages and generations. Seed trapping showed little movement of native seeds into old fields and that most species had extremely localized dispersal. Consequently, there was no pattern of seed density with distance from boundaries, and similarity between the seed rain and standing vegetation was moderate to high. Seed addition showed that two annual species were able to establish in all, and flower in most, subplots in the first year, and that seedling establishment increased with sowing density, consistent with seed limitation. However, the relative importance of microsite limitation increased over the lifespans of the species. Density dependence reduced the number of flowering plants, resulting in a large decline in seedling density in the following generation. This decline continued so that the initial positive effect of sowing density on seedling numbers disappeared by the fourth generation and hence the persistence of populations is uncertain. Thus, by monitoring seed dispersal and following experimental populations beyond seedling establishment, we showed that dispersal limits species distributions, but microsite plays an important role in limiting population growth and persistence.     

Inter-annual variability of seed rain and seedling establishment of two woody Mediterranean species under field-induced drought and warming

We aimed to assess the impact of warmer and drier climate change conditions on the seed rain and seedling establishment of Globularia alypum L. and Erica multiflora L., two dominant species in Western coastal Mediterranean shrublands. We performed a non-intrusive field experiment in which we increased the night-time temperatures and excluded spring and autumn rainfall. We monitored the seed rain over 5 years and the seedling recruitment over 9 years on these experimental plots. Seed rain of E. multiflora was enhanced by warming treatment in relation to control, and higher annual rainfall, while seed rain of G. alypum was increased by drought treatment in relation to control, dry years and higher minimum annual temperature. Annual rainfall enhanced the seedling emergence of both species, which also positively correlated with annual mean temperatures. Drought treatment significantly decreased seedling emergence for both species, which was higher in open areas than below vegetation cover. The seedling survival of both species diminished at closer distances to competing neighbours, and in G. alypum seedling survival was higher with lower annual mean temperatures and higher annual rainfall, but also in drought treatment, which have experienced vegetation cover decline. The study confirms that the increasing aridity in Mediterranean ecosystems would constrain the early stages of development in typical co-occurring shrubs. However, there are contrasting responses to climatic conditions between species recruitment, which might favour changes in vegetation through modification of species relative abundance.     

I. Introduction

Background: Past research and ecological theory supports the hypothesis that alpine plants should be predominantly clonal, long-lived and reproduce by seed infrequently.

Aims: To challenge the entrenched view that alpine seedling establishment is uncommon and perhaps unsuccessful in maintaining alpine plant populations.

Methods: We looked for patterns in seedling establishment across a stress gradient of alpine sites and tested the notion that natural seedling recruitment would be reduced at higher altitudes due to a combination of stressful environmental conditions such as frosts, wind and extended snow cover.

Results: Seedlings were common at all study sites and there was a partial trend in mean seedling density with altitude. Seedling emergence was best predicted by a combination of altitude, plant litter and soil wilting point. Many seedlings survived to become established plants (37–61%) but there was no significant relationship between establishment and altitude. There was low similarity between the seedling flora and the standing vegetation, suggesting that patterns in seedling establishment are unlikely to be driving the patterns in the standing vegetation assemblage.

Conclusions: Although Australian alpine species predominantly reproduce vegetatively, this study shows that many plants depend on recruitment from seed in order to become established.     

Linking seed dispersal,germination and seedling recruitment in the invasive species <Emphasis Type="Italic">Berberis darwinii</Emphasis> (Darwin’s barberry)

Seedling recruitment is a multi-phased process involving seed production, dispersal, germination, seedling establishment and subsequent survival. Understanding the factors that determine success at each stage of this process is of particular interest to scientists and managers seeking to understand how invasive species spread and persist, and identify critical stages for management. To understand the factors and processes influencing recruitment of the invasive species Berberis darwinii Hook. (Darwin’s barberry), temporal and spatial patterns of seed dispersal, germination and seedling establishment were examined. Seed dispersal from a large source population was measured over two fruiting seasons, and subsequent patterns of seedling emergence and survival within each cohort were measured. Seed longevity was tested under both natural and artificial conditions. Seeds were widely dispersed by birds, up to 450 m from the source population. Dispersal was essential to seedling establishment, as few seedlings survived beneath the parent canopy. Seeds were relatively short-lived in the soil under both field and glasshouse conditions, with few surviving for more than 1 year. Patterns of newly emerged seedlings largely reflected patterns of seed rain, but seedling survival was significantly affected by distance from source population, seedling density and light environment. These results suggest that recruitment of B. darwinii is dependent on dispersal of seeds to favourable microsites. Management priorities should include the removal of fruiting plants, and seedling control in highlight areas.     

Seedling emergence responds to both seed source and recruitment site climates: a climate change experiment combining transplant and gradient approaches

Seedling recruitment allows genetic recombination and production of dispersal units. Both the climate experienced by the source populations (seed source effect) and the weather experienced by the seeds during germination and seedling emergence (recruitment site effects) are important for seedling recruitment. Separating these effects in the field is essential to assess potential climate change impacts on plant population. We combine experimental seed transplant and gradient analyses to separate the effects of seed source and recruitment site temperature and precipitation for the seedling emergence of two alpine/lowland species pairs (Viola biflora/Viola palustris, Veronica alpina/Veronica officinalis). Combining these approaches allows us to compare local responses versus responses along environmental gradients, but also tests for local adaptation and/or pre-conditioning effects (adaptive seedling emergence responses). Veronica officinalis emergence increased with increasing seed source temperature in both the experimental and the gradient approaches, and showed adaptive seedling emergence. Viola biflora, Viola palustris and Veronica alpina emergence decreased with recruitment site temperature in both approaches. Both Violas emergences increased with recruitment site precipitation, in both approaches for the alpine violet, and in the gradient approach for lowland one. Emergence was primarily affected by the environment of the recruitment site, whereas seed source climate and adaptive seedling emergence impacted recruitment in only one of our species. The responses to recruitment site temperatures were negative, whereas the response to seed source temperature was positive. Ignoring the distinctions between these different mechanisms can lead to erroneous conclusions regarding potential climate change impacts on plant recruitment.     

Rodent seed predation and seedling recruitment in mesic grassland

Seedling recruitment of two grasses (Arrhenatherum elatius and Festuca rubra) and two herbs (Centaurea nigra and Rumex acetosa) was measured in areas with and without rodents to which seeds of each species were sown at three seed densities (1000, 10,000 and 50,000 seeds m⁻²) in two seasons (spring and autumn 1995). Seed removal was measured for 10-day periods and the fate of seedlings was followed for 15 months after sowing. The proportion of seed removed ranged from 6 to 85% and increased with increasing seed density for each species. Rodents had no effect on seedling emergence or survival in the spring sowing. In the autumn sowing, rodents reduced seedling emergence of all four species sown at 1000 and 10,000 seeds m⁻² but had no impact at 50,000 seeds m⁻², presumably because of microsite limitation. We suggest the difference between spring and autumn arose because emergence was seed limited in autumn but microsite limited in spring; microsite availability was higher in autumn because a summer drought killed plants, reduced plant biomass and opened up the sward. Fifteen months after the autumn sowing, fewer A. elatius and C. nigra seedlings survived on plots exposed to rodents. This result reflected not only the reduced seedling emergence but also increased seedling mortality (seedling herbivory) in sites exposed to rodents. In contrast, F. rubra and R.acteosa showed density-dependent seedling survival which compensated for initial differences in seedling emergence, so that no effect of rodents remained after 15 months. The results suggest that rodent seed predation and seedling herbivory exert strong effects on seedling recruitment of A.elatius and C. nigra when recruitment conditions are favourable (conditions that lead to high microsite availability) and may contribute to both species being maintained at low densities in the grassland. The results also demonstrate that highly significant impacts of rodent seed predation at the seedling emergence stage can disappear by the time of plant maturation. Received: 2 March 1998 / Accepted: 28 September 1998     

Plants as reef fish: fitting the functional form of seedling recruitment

The life histories of many species depend first on dispersal to local sites and then on establishment. After dispersal, density-independent and density-dependent mortalities modify propagule supply, determining the number of individuals that establish. Because multiple factors influence recruitment, the dichotomy of propagule versus establishment limitation is best viewed as a continuum along which the strength of propagule or establishment limitation changes with propagule input. To evaluate the relative importance of seed and establishment limitation for plants, we (1) describe the shape of the recruitment function and (2) use limitation and elasticity analyses to quantify the sensitivity of recruitment to perturbations in seed limitation and density-independent and density-dependent mortality. Using 36 seed augmentation studies for 18 species, we tested four recruitment functions against one another. Although the linear model (accounting for seed limitation and density-independent mortality) fitted the largest number of studies, the nonlinear Beverton-Holt model (accounting for density-dependent mortality) performed better at high densities of seed augmentation. For the 18 species, seed limitation constrained population size more than other sources of limitation at ambient conditions. Seedling density reached saturation with increasing seed density in many studies, but at such high densities that seedling density was primarily limited by seed availability rather than microsite availability or density dependence.     

Variation in exotic and native seed arrival and recruitment of bird dispersed species in subtropical forest restoration and regrowth

Invasive bird-dispersed plants often share the same suite of dispersers as co-occurring native species, resulting in a complex management issue. Integrated management strategies could incorporate manipulation of dispersal or establishment processes. To improve our understanding of these processes, we quantified seed rain, recruit and seed bank density, and species richness for bird-dispersed invasive and native species in three early successional subtropical habitats in eastern Australia: tree regrowth, shrub regrowth and native restoration plantings. We investigated the effects of environmental factors (leaf area index (LAI), distance to edge, herbaceous ground cover and distance to nearest neighbour) on seed rain, seed bank and recruit abundance. Propagule availability was not always a good predictor of recruitment. For instance, although native tree seed rain density was similar, and species richness was higher, in native plantings, compared with tree regrowth, recruit density and species richness were lower. Native plantings also received lower densities of invasive tree seed rain than did tree regrowth habitats, but supported a similar density of invasive tree recruits. Invasive shrub seed rain was recorded in highest densities in shrub regrowth sites, but recruit density was similar between habitats. We discuss the role of microsite characteristics in influencing post-dispersal processes and recruit composition, and suggest ways of manipulating these processes as part of an integrated management strategy for bird-dispersed weeds in natural areas.     

Seed Dispersal and Seedling Emergence in a Created and a Natural Salt Marsh on the Gulf of Mexico Coast in Southwest Louisiana, U.S.A.

Early regeneration dynamics related to seed dispersal and seedling emergence can contribute to differences in species composition among a created and a natural salt marsh. The objectives of this study were to determine (1) whether aquatic and aerial seed dispersal differed in low and high elevations within a created marsh and a natural marsh and (2) whether seedling emergence was influenced by marsh, the presence of openings in the vegetation, and seed availability along the northern Gulf of Mexico coast. Aerial seed traps captured a greater quantity of seeds than aquatic traps. Several factors influenced aquatic and aerial seed dispersal in a created and a natural salt marsh, including distance from the marsh edge, cover of existing vegetation, and water depth. The natural marsh had a high seed density of Spartina alterniflora and Distichlis spicata , the low-elevation created marsh had a high seed density of S. alterniflora , and the high-elevation created marsh had a high seed density of Aster subulatus and Iva frutescens . The presence of adult plants and water depth above the marsh surface influenced seed density. In the natural marsh, openings in vegetation increased seedling emergence for all species, whereas in the low-elevation created marsh, S. alterniflora had higher seedling density under a canopy of vegetation. According to the early regeneration dynamics, the future vegetation in areas of the low-elevation created marsh may become similar to that in the natural marsh. In the high-elevation created marsh, vegetation may be upland fringe habitat dominated by high-elevation marsh shrubs and annual herbaceous species.     

Habitat degradation,topography and rainfall variability interact to determine seed distribution and recruitment in a sand dune grassland

Question: Understanding the mechanisms underlying how habitat degradation, topography and rainfall variability interactively affect seed distribution and seedling recruitment is crucial for explaining plant community patterns and dynamics. Interactions between these major factors were studied together in a semiarid sand dune grassland. Location: Eastern Inner Mongolia, China. Methods: The study system used four sites of fixed, semifixed, semishifting and shifting sand dune grasslands, representing a gradient of habitat degradation. We investigated the density of germinable seeds deposited in the top 5 cm of soil and in situ seedling emergence (number of seedlings emerging early in the growing season) and establishment (number of plants recruited at the end of the growing season) at three topographic positions (dune top, windward and leeward sides) within each site over 2 years that differed in rainfall. Habitat characteristics (i.e. vegetation cover, plant species composition and diversity, soil moisture and nutrient availability and soil erodibility) of the four sites were also measured. Results: Habitat degradation (i.e. decreased vegetation cover and enhanced wind erosion rate) significantly reduced the size of the germinable soil seed bank. On average, germinable seed number from the high‐vegetation cover fixed dune was 36‐fold larger than the low‐vegetation cover shifting dune, and eight‐ and two‐fold larger, respectively, than the semishifting and semifixed dunes with intermediate vegetation cover. We observed within‐habitat variability in seed distribution, but among‐topographic position variation differed among habitats. Seedling recruitment showed large between‐year, and among‐ and within‐habitat variability, but these variations varied significantly depending on the response variables evaluated (i.e. initial seedling density, final plant density, emergence rate and recruitment rate). Path analysis revealed complex density‐dependent positive and negative, direct and indirect effects of germinable seed density and initial seedling density on recruitment, but the relative importance of these density‐dependent effects varied depending on habitat type and rainfall availability. Conclusion: Our results suggest that habitat degradation, microtopography and rainfall availability interact in shaping sand dune seed bank and plant community recruitment patterns and dynamics. Their effects were mainly mediated through changes in both the biotic and abiotic environment during the process of habitat deterioration.     

The Interplay among Acorn Abundance and Rodent Behavior Drives the Spatial Pattern of Seedling Recruitment in Mature Mediterranean Oak Forests

The patterns of seedling recruitment in animal-dispersed plants result from the interactions among environmental and behavioral variables. However, we know little on the contribution and combined effect of both kinds of variables. We designed a field study to assess the interplay between environment (vegetation structure, seed abundance, rodent abundance) and behavior (seed dispersal and predation by rodents, and rooting by wild boars), and their contribution to the spatial patterns of seedling recruitment in a Mediterranean mixed-oak forest. In a spatially explicit design, we monitored intensively all environmental and behavioral variables in fixed points at a small spatial scale from autumn to spring, as well as seedling emergence and survival. Our results revealed that the spatial patterns of seedling emergence were strongly related to acorn availability on the ground, but not by a facilitationeffect of vegetation cover. Rodents changed seed shadows generated by mother trees by dispersing most seeds from shrubby to open areas, but the spatial patterns of acorn dispersal/predation had no direct effect on recruitment. By contrast, rodents had a strong impact on recruitment as pilferers of cached seeds. Rooting by wild boars also reduced recruitment by reducing seed abundance, but also by changing rodent’s behavior towards higher consumption of acorns in situ. Hence, seed abundance and the foraging behavior of scatter-hoarding rodents and wild boars are driving the spatial patterns of seedling recruitment in this mature oak forest, rather than vegetation features. The contribution of vegetation to seedling recruitment (e.g. facilitation by shrubs) may be context dependent, having a little role in closed forests, or being overridden by directed seed dispersal from shrubby to open areas. We warn about the need of using broad approaches that consider the combined action of environment and behavior to improve our knowledge on the dynamics of natural regeneration in forests.     

Interaction between large herbivore activities,vegetation structure,and flooding affects tree seedling emergence

Tree establishment in grazed vegetation mosaics involves a series of early bottlenecks, including seed dispersal, germination, seedling emergence, survival and growth. In a field experiment, we studied seedling emergence of two species with contrasting recruitment strategies, Fraxinus excelsior and Quercus robur, in five structurally different vegetations: grazed and ungrazed grassland, ruderal pioneer vegetation, soft rush tussocks, tall sedge mats and bramble scrub. In a simulation experiment, we studied the interaction effects of pre-emergence flooding (3 weeks of inundation), trampling and grazing (simulated by clipping) of grassland vegetation on the emergence and early growth of both tree species in grass swards. Seedling emergence was enhanced in low swards and sparse vegetation types. Despite different recruitment strategies, the interaction of flooding and trampling of swards enhanced seedling emergence of both species. Grazing of soft rush and tall sedges enhanced emergence of F. excelsior. Clipping grass swards increased early growth of emerging Q. robur. Our results support the hypothesis that natural disturbances of soil and vegetation create microsites for seedling emergence and reduce above-ground competition. In grazed systems however, these results suggest a discordant relationship between successful seedling emergence and subsequent seedling growth/survival during the establishment process in structurally different vegetations.     

Spatial concordance at a regional scale in the regeneration process of a circum-Mediterranean relict (Buxus balearica): connecting seed dispersal to seedling establishment

Both microhabitat and temporal scales have significant effects on the regeneration process of plant species. However, the consistency of those patterns at large scales is largely unknown, despite of being essential from both an ecological and a conservation viewpoint. In this study, we examined the spatio‐temporal variation in the process of regeneration through seeds of the relict Mediterranean shrub Buxus balearica. By means of observations and experiments, we quantified the losses at different recruitment phases (seed rain, seed predation, seedling emergence and establishment) both at a small spatial scale (distance and microhabitat effects) and at a temporal scale (four years), and compared them at a regional scale (10 different localities). We additionally studied transition probabilities between phases in two populations and measured the size structure of 18 localities encompassing all the distributional range of the species. The results show that seed shadow follows a leptokurtic pattern which is consistently maintained until the seedling phase (i.e. there is spatial concordance). Despite post‐dispersal factors are spatially uncoupled, they do not remove the gradient established in the seed shadow. Although the importance of different seed predators varied between regions, post‐dispersal seed predation (ca 80%), together with seedling emergence (usually lower than 10%, some years even nil), and seedling mortality during the first summer (ca 70%) were – consistently in all populations – the most critical bottlenecks in the regeneration of the species. Moreover, an absence of seed bank prevents the buffering of dramatic losses during such phases. Watering of sown seeds increased seedling emergence and survival, and number of leaves per seedling, and survival was consistently higher under vegetation coverage. These results suggest that hydric stress notably contributes to limit the regeneration of this once widespread species evolved under a subtropical climate, which nowadays appears in old‐structured populations throughout its distributional area.     

Spatial and temporal variability in propagule limitation of California native grasses

Community composition and diversity arise from limitations in propagule supply (i.e. propagule or seed limitation) and propagule establishment after arriving at a site (i.e. establishment or microsite limitation). Recent meta‐analyses suggest that the degree of propagule limitation depends on local abiotic and biotic conditions, which in turn are likely to vary spatially and temporally. Nevertheless, seed addition studies testing propagule limitation are rarely replicated in multiple locations and years and often lack experimental manipulations of critical determinants of propagule limitation, such as the density and species richness of the propagule pool and disturbance and resource supply of recipient site. The invasion of California (USA) grasslands by exotic annual species from the Mediterranean region is unique in its scope (over 9 million ha) and persistence (more than 150 years). This invasion provides an exciting context in which to test the role of spatial and temporal variability in mediating propagule limitation and ultimately the potential for restoration. Here I present the results of native‐grass, seed‐addition trials conducted along a 500 km gradient in California in three consecutive years spanning a wide range of environmental conditions and initial conditions (e.g. rainfall, seeding density and disturbance). While native grasses were able to establish at many locations, per capita seed survival was low suggesting that the fate of these species is governed by interplay between propagule and establishment limitation. Establishment primarily varied spatially, with the most successful establishment occurring at fertile locations with low resident species richness. While recruitment was highly variable among years initially, there was no difference among seedling trials after three years.     

子午岭三种生境下辽东栎幼苗定居限制

辽东栎(Quercus wutaishanica)是子午岭地区的乡土乔木树种,也是该地区气候顶极群落的建群种,其幼苗的补充更新影响着森林群落的结构及物种组成。在3种典型生境(辽东栎林、人工油松林、灌草丛)中,设置3因素(种子、干扰、遮荫)两水平的野外播种实验(随机区组设计),记录辽东栎幼苗出苗量,并监测幼苗同生群在3种生境中3a间的生长状况,以确定种子及微生境在辽东栎幼苗补充过程中的限制作用。播种实验样方大小30cm×30cm,共计216个样方。结果显示,在辽东栎林及油松林内,增加种子和干扰强度(去除枯落物),能引起出苗量和幼苗补充量的显著增加,且2种处理方式间存在交互作用,表明在郁闭林冠下,辽东栎幼苗的补充受到了种子和微生境的双重限制,枯落物是导致微生境限制的主要因素之一。在灌草丛生境,各种处理方式均不能增加幼苗的补充量,表明辽东栎无法在开阔生境(强光照、干旱)中完成实生幼苗的补充更新。3种生境中的幼苗同生群生存分析表明,辽东栎幼苗在森林群落中存活率显著高于灌草丛群落。根据幼苗生长指标判断,在3种生境中,人工油松林是辽东栎幼苗定居的最佳场所。与实验预期相反,灌木对辽东栎幼苗的补充无显著影响。     

Land crabs as key drivers in tropical coastal forest recruitment

Plant populations are regulated by a diverse assortment of abiotic and biotic factors that influence seed dispersal and viability, and seedling establishment and growth at the microsite. Rarely does one animal guild exert as significant an influence on different plant assemblages as land crabs. We review three tropical coastal ecosystems–mangroves, island maritime forests, and mainland coastal terrestrial forests–where land crabs directly influence forest composition by limiting tree establishment and recruitment. Land crabs differentially prey on seeds, propagules and seedlings along nutrient, chemical and physical environmental gradients. In all of these ecosystems, but especially mangroves, abiotic gradients are well studied, strong and influence plant species distributions. However, we suggest that crab predation has primacy over many of these environmental factors by acting as the first limiting factor of tropical tree recruitment to drive the potential structural and compositional organisation of coastal forests. We show that the influence of crabs varies relative to tidal gradient, shoreline distance, canopy position, time, season, tree species and fruiting periodicity. Crabs also facilitate forest growth and development through such activities as excavation of burrows, creation of soil mounds, aeration of soils, removal of leaf litter into burrows and creation of carbon-rich soil microhabitats. For all three systems, land crabs influence the distribution, density and size-class structure of tree populations. Indeed, crabs are among the major drivers of tree recruitment in tropical coastal forest ecosystems, and their conservation should be included in management plans of these forests.     

Seedling dynamics at elevation limits: Complex interactions beyond seed and microsite limitations

? Premise of the study: Limited availability of seeds and microsites are important constraints for seedling emergence and survival. However, little is known about population-level feedbacks between seed and microsite limitation and how these relationships vary in contrasting conditions. Focusing on Armeria caespitosa, a high-mountain endemic, we asked whether seedling establishment was simultaneously limited by seed and microsite availability, whether the balance between seed and microsite limitations varied with contrasting environments, and whether seed and microsite limitations interacted with each other. ? Methods: We studied seedling emergence and survival at the edges of the elevation range of A. caespitosa in central Spain over 4 years. We used mixed linear models and structural equation modeling. ? Key results: Our results showed that A. caespitosa recruits similar numbers of new seedlings per plot in contrasting environments. Seedling emergence and survival in A. caespitosa were both limited by seed and microsite availability. Habitat suitability (the surrogate of microsite limitation) varied between populations and indirectly affected fertility (the surrogate of seed limitation). ? Conclusions: Seedling emergence and survival are both seed and microsite limited, there are interactions between seed and microsite limitations, and both factors, which control seedling establishment, and their interconnections, vary among local populations.     

Early reduction of post-fire recruitment of Pinus nigra by post-dispersal seed predation in different time-since-fire habitats

This study analyses the effects of post-dispersal predation of Pinus nigra seeds on the initial recruitment of this species in areas burned by large wildfires, where P. nigra shows very low regeneration. In three different habitats obtained in a gradient of time since fire in Catalonia (NE Spain), we have evaluated the effects of seed predators (ants, rodents and birds) on post-dispersal seed removal and early seedling establishment of P. nigra by using selective exclosures limiting their access to seeds. Ants were the most efficient seed predator group, followed by rodents and birds. The contribution of each group to overall predation showed large seasonal variations. The first seeds dispersed in winter were mainly predated by rodents, which also registered their highest abundance in this season of the year. In spring, at the end of the natural dissemination period of P. nigra seeds, ants became the major predators, this fact coinciding with their increased abundance. Birds showed the lowest predation values. In the seedling establishment experiment, only in the exclusion treatment of the three predator groups was there initial establishment in all habitats, especially in the recently burned area, where there was seedling establishment in all exclusion treatments. The post-dispersal seed predation by different animal groups and low seedling emergence in the different habitats obtained in this study, together with the low seed availability of P. nigra seeds in burned areas, do not predict a favourable outlook for the natural post-fire recolonization of this species, which might even affect its overall distribution area in the region.     

Seedling emergence patterns and dormancy/germination physiology of <Emphasis Type="Italic">Primula modesta</Emphasis> in a subalpine region

On the basis of the germination/dormancy responses of seeds to temperature and light, and local seed rain, we attempted to interpret the seedling emergence patterns of Primula modesta Bisset et Moore (Primulaceae) in two different types of habitats in a subalpine zone of Mt. Asama: an oligotrophic flat moor and a grassland with relatively dense herbaceous vegetation cover. The seasonal pattern of seedling emergence was well explained by the dormancy/germination physiology revealed in laboratory germination tests. The seeds were demonstrated to have a strict light requirement even after experiencing moist chilling, which might facilitate the incorporation of the seeds into the soil seed bank. Despite sufficient seed production, the seedlings emerging were far less at the grassy site than the moor site, but the number of seedlings was significantly dependent on the seed rain within previous season and on the litter cover of the microsite in both sites. Therefore, the spatiotemporal patterns of seedling emergence in the habitats could be well explained by the spatiotemporal patterns of seed rain and safe-sites for germination.