Effects of microenvironmental heterogeneity on the seed-to-seedling process and tree coexistence in a riparian forest

In a temperate riparian forest, the effects of substrate types, canopy gaps and conspecific seedfall density were investigated on the seed-to-seedling process for the five dominant species (Aesculus turbinata, Fagus crenata, Acer mono, Pterocarya rhoifolia and Cercidiphyllum japonicum). Densities of seedfall and subsequent seedling recruits were measured in the stand over a period of 6 years. A model assuming that local density of seedling recruits is proportional to seedfall density in the preceding year significantly explained a spatial variation in seedling recruits for all species. Several environmental factors were then added. Substrate composition had a positive effect on P. rhoifolia and C. japonicum. P. rhoifolia was favored by gravel substrate, which also explained the adult distribution of this species in this forest. C. japonicum appeared to be facilitated by a mineral-soil substrate. However, the distributions of this substrate and adults of C. japonicum did not follow each other closely. A. mono was negatively affected by gaps, and F. crenata was negatively affected by conspecific seedfall density. In contrast, A. turbinata was not significantly affected by any of the environmental factors tested. The microenvironmental heterogeneity in this forest explained species coexistence to a limited extent in the context of seed-to-seedling processes. Performances at later stages of the life-cycle and/or catastrophic disturbances (e.g. landslides) might have a stronger influence on species coexistence in this forest.     

Growth Ecology of Carapa nicaraguensis Aublet. (Meliaceae): Implications for Natural Forest Management1

The probability of achieving a sustainable tropical logging operation is increased if the growth of surviving trees is maximized after logging. This research examined the growth ecology of seedlings and trees of the Neotropical timber species, Carapa nicaraguensis (Meliaceae). Shadehouse experiments, field plantings, and growth rate analyses tested the hypothesis that Carapa seedlings and trees experience higher growth rates in high light levels (recently formed logging gaps or logged forest plots) than in low light levels (old logging gaps or undisturbed forest plots). Consistently poor seedling growth rates under low light conditions suggest that seedlings establishing in newly formed gaps will be more successful than those establishing in building-phase gaps. Thus, the first year after logging is a critical time for gap recolonization by Carapa, and seed casting into gaps after logging is recommended. Growth of Carapa trees was significantly faster in logged forest than in undisturbed forest, and was positively associated with light availability. The results provide evidence that harvest models can be both diameter- and illumination-based. Crown illumination was not significantly higher in logged forest than in undisturbed forest, indicating that the illumination scale for this study was not sensitive enough to detect increases in light availability brought about by selective logging. Potential silvicul-tural methods (particularly poison-girdling) that maintain adequate forest light levels in Carapa swamps without significantly altering long-term tree diversity or allowing invasion of secondary species should be explored.     

吉林蛟河不同演替阶段针阔混交林木本植物幼苗空间分布与年际动态

幼苗的空间分布对群落更新具有重要意义。于2011年夏季在蛟河地区3个不同演替阶段针阔混交林样地内共设置了451个种子雨-幼苗观测样站,并于2012—2014年对幼苗样方内胸径1 cm的木本植物幼苗进行了连续3a的调查。对木本植物幼苗的数量分布以及水曲柳(Fraxinus mandshurica)、五角枫(Acer mono)、杉松(Abies holophylla)和东北枫(Acer mandshuricum)4个主要树种幼苗与大树的空间关系及其年际变化进行了分析,并用Syrjala检验分析了样站尺度上幼苗密度、丰富度空间分布在年际间的差异。结果显示:(1)木本植物幼苗的数量分布在不同群落和年际之间都表现出明显的差异,样站尺度上3个样地内的幼苗密度存在着较大的空间变异性,而幼苗丰富度的空间异质性较低。表明幼苗分布的空间异质性对幼苗密度有着重要影响。(2)样站尺度上幼苗数量和物种数的空间分布在不同年份之间是存在差异的。在一定程度上证实了种子产量、扩散方式和群落组成对幼苗空间分布的影响。(3))从死亡幼苗与大树空间关系来看,4个主要树种的死亡幼苗与成树表现出相似的分布格局,这既表明成体植株的空间分布特征也能够影响幼苗的空间分布格局,也从侧面说明了负密度制约效应对幼苗空间分布的影响。     

Demography of the long‐lived conifer Agathis ovata in maquis and rainforest,New Caledonia

Abstract. The endemic New Caledonian conifer Agathis ovata occurs as an emergent tree in fire‐prone shrublands (maquis), and fire‐sensitive rainforest. Growth, survivorship and recruitment over 5 yr were compared for populations from forest and maquis on ultramafic substrates in New Caledonia to investigate whether demographic behaviour varied in response to the strongly contrasting forest and shrubland environments. Growth of seedlings and of small (30–100 cm height) and large (100 cm height; 5 cm DBH) saplings was slow, but varied significantly among stages, site types and years. The greatest difference in growth rates was among stages, seedlings growing 0.34 cm.yr^?1, small saplings 1.06 cm.yr^?1 and large saplings 2.13 cm.yr^?1. Tree DBH increased by only 0.05 cm.yr^?1 and, based on these rates, individuals with DBH of 30 cm are estimated to be more than 700 yr old. Few trees (3.5%) produced cones in any year and seedling recruitment was low, but some recruitment was recorded each year in both maquis and forest. Rates of recruitment per parent were highest in forest (1.28.yr^?1, cf 0.78.yr^?1), but the higher density of trees in maquis meant that overall recruitment was greater there (92 ha^?1.yr^?1, cf 56 ha^?1.yr^?1). Seedling mortality ranged from 0.9 to 2.9% among years with no significant difference between maquis and forest. No sapling mortality was recorded, but annual tree mortality ranged from 0 to 1.4%. Evidence from a recently burned site indicated that while trees may survive fire, seedlings and saplings do not. Post‐fire seedling recruitment per ha from surviving trees was four times lower than in unburned sites, but growth rates were four times higher. Similar demographic attributes, including high survivorship, low growth rate and low rates of recruitment over a long reproductive life, characterize Agathis ovata populations in both maquis and rainforest in New Caledonia and are indicative of a broad tolerance of light environments that is unusual among tree species. These demographic attributes help to explain the long‐term persistence of the species in these strongly contrasting habitats.     

SEEDLING ESTABLISHMENT IN FORESTS AFFECTED BY TEPHRA FROM MOUNT ST. HELENS

Seedling density on permanent plots at five sites was monitored for the first four summers following the deposition of 4.5 to 15 cm of tephra from the 1980 eruption of Mount St. Helens. Because the old-growth forests at the sites were not destroyed by the volcanic eruption, the plots were under a normal tree canopy. Almost no seedlings established in 1980. By 1983 tree seedling density exceeded 35 m^−-2 at all sites. Tsuga heterophylla seedlings were most common, with Abies amabilis seedlings next in abundance. A dense layer of small trees may develop on the tephra and long-term forest dynamics could be affected. There was no successful invasion by species not already present in the stands. Seedlings of some forest herbs, especially Tiarella trifoliata, were common, but many other common forest species produced none. It is still problematical if or when these species will return to areas of the forest from which they were extirpated.     

Demography of the seedling bank of Manilkara zapota (L.) Royen,in a subtropical rain forest of Mexico

Selection of individuals in tropical trees, occurs mainly in the seedling phase, which in part explains the low densities of most species. The main objective of this work was to gain an insight into those factors that influence growth and survival of Manilkara zapota seedlings, one of the most abundant species in the lowland forests of Mexico and Central America. Eight 10-m² rectangular plots (5m×2m) were established, in which all < 35-cm-high M. zapota seedlings were marked, measured and enumerated at bimonthly intervals. In each census seedling height, number of leaves, length of largest leaf, type of damage and seedling death were registered. Seedling survival during 2 yr was high, reaching 82% including newly emerged seedlings. A maximum likelihood regression analysis showed that both number of leaves and length of largest leaf had a direct influence on seedling survival; however, neither type of damage nor seedling density and height had significant effect. Seedling height growth averaged 2.8 cm in the 2 yr of study. The combined effect of high seedling survival, reduced growth, and impact of physical damage mainly due to falling branches and leaves reveals the occurrence of a persistent seedling bank. Such a bank would contribute to recruitment of individuals in the juvenile and eventually in the adult stages. This seedling bank could explain the high density of individuals of M. zapota in the tropical forests of Mexico.     

Testing for Janzen–Connell Effects in a West African Montane Forest

The Janzen–Connell hypothesis proposes that density dependent seed and seedling mortality, combined with increasing seed and seedling survival away from the parent tree, together promote regular spacing of species and thus α diversity. This hypothesis has rarely been tested in tropical Africa, and rarely in montane forests anywhere. We tested this hypothesis using a combination of field experiments and observations in the most floristically diverse dry submontane forest in Nigeria. We investigated distance effects on seedling herbivory, seedling survival and seedling height growth. We found a significant decrease in herbivory with distance from conspecific adult trees for all three species of experimentally planted seedlings (Entandrophragma angolense, Deinbollia pinnata and Sterculia setigera), and also for naturally occurring seedlings of Pouteria altissima but not of Newtonia buchananii or Isolona pleurocarpa. The relative density of large seedlings/saplings of P. altissima, N. buchananii and I. pleurocarpa increased significantly at greater distance from conspecific adult trees; however, we found no significant distance effect on survival or height growth over 3 mo for all three experimentally planted species. Taken together, our results are some of the first to show that Janzen–Connell effects occur on the African continent and in particular montane tropical forest and suggest that such effects may be pantropical.     

Seedling bank dynamics of Fagus grandifolia var. mexicana before and after a mast year in a Mexican cloud forest

Abstract. Fagus grandifolia var. mexicana seedling dynamics were studied in a relict forest inside the crater of a volcano where it is the only canopy tree species. The objectives of the study were (1) to determine changes in seedling density before and after a mast year, as well as to monitor seedling recruitment, mortality and growth rate in relation to the micro‐environment, and (2) to discuss the impact of masting on seedling dynamics of the population. Before masting, seedling density was 8.8 seedlings m^–2, afterwards seedling density peaked at 51.5 seedlings m^–2, then decreased by 50% in 3 months and by 85% after 8 months, down to levels of before the mast year (9.9 seedlings m^–2) after 16 months. Seedlings in the forest floor before the mast‐seeding event showed a low relative growth rate – 0.14 mm mm^–1 mo^–1 against 1.27 mm mm^–1 mo^–1 for seedlings that emerged immediately after masting. Seed germination was high (83%) and rapid (L₅₀= 7 days) following masting. Seedling growth was positively correlated with soil water content but not with temperatures and relative humidity. Data suggested that seed production in mast years is important in maintaining the seedling bank, and thus the viability of relict Fagus populations.     

Different responses to shade of evergreen and deciduous oak seedlings and the effect of acorn size

An evergreen oak species, Cyclobalanopsis multinervis, and a deciduous oak species, Quercus aliena var. acuteserrata were grown from acorns under two light levels (full sunlight and shade at about 18 % of full sunlight, simulating the light intensities in forest clearings and gaps, respectively) for one growing season. Three hypotheses were tested: (i) the deciduous species grows faster than the evergreen species in forest gaps and clearings; (ii) the deciduous species responds more strongly in terms of growth and morphology to variation in light climate than the evergreen species; and (iii) seedling size is positively correlated to acorn size. The results showed: (i) at both light levels, the deciduous seedlings gained significantly more growth in biomass and height than the evergreen seedlings; (ii) both species produced significantly more biomass in full sunlight than in shade, without showing any significant difference in height between treatments. Increase in light intensity improved the growth of the deciduous seedlings more strongly; (iii) at a similar age, the deciduous seedlings showed a greater response in leaf morphology and biomass allocation to variation in light levels, but when compared at a similar size, biomass allocation patterns did not differ significantly between species; (iv) bigger acorns tended to produce larger seedlings, larger leaf sizes and more leaf area, between and within species. These differences demonstrate that the deciduous species is gap-dependent and has the advantage over the evergreen species in forest gaps and clearings.     

Impact of invasion of Acer platanoides on canopy structure and understory seedling growth in a hardwood forest in North America

Invasion by exotic plant species is known to affect native communities and ecosystems, but the mechanisms of the impacts are much less understood. In a field study, we examined the effects of a tree invader, Acer platanoides (Norway maple, NM), on canopy structure and seedling growth in the understory of a North American deciduous forest. The experimental site contains a monospecific patch of A. platanoides and a mixed patch of A. platanoides with its native congener, A. rubrum (red maple, RM). In the study, we examined canopy characteristics of three types of trees in the forests, i.e., RM trees in the mixed forest, NM trees in the mixed forest, and NM trees in its monospecific patch. Height growth and biomass production of RM and NM seedlings under intact canopies and newly created gaps of the three types of trees were followed for two growing seasons. We found that removal of half of the canopy from focal trees increased canopy openness and light transmission to the forest floor, but to a greater extent under NM trees than under RM trees. Seedlings of these two Acer species varied greatly in biomass production under canopies of the same type of trees and in their responses to canopy opening. For example, seedlings of the exotic NM grown under the native RM trees in the mixed forests increased biomass production by 102.4% compared to NM seedlings grown under conspecific trees. The native RM seedlings grown under NM trees, however, reduced biomass production by 23.5% compared to those grown under conspecific trees. It was also observed that RM was much more responsive in biomass production to canopy opening than NM. For instance, total seedling biomass increased by 632.2% in RM, but by only 134.6% in NM in response to the newly created gaps. In addition, we found that NM seedlings allocated a greater portion of biomass below-ground as canopy openness increased, whereas the same trend was not observed in RM seedlings. Our results thus demonstrated that invasion of NM significantly altered canopy structure and community dynamics in the hardwood forest. Because the exotic NM seedlings are able to grow well under the native RM trees, but not vice versa, NM will likely expand its distribution in the forests and make it an ever increasingly serious tree invader in its non-native habitats, including North America.     

Structure and dynamics of a tropical dry forest in Ghana

Forest under low rainfall (averaging 745 mm yr^-1) on the Shai Hills in S.E. Ghana has redeveloped following cessation of farming in the 1890s. Forest stature is low, with a canopy at about 11 m, principally of three species, Diospyros abyssinica, D. mespiliformis and Millettia thonningii. Drypetes parvifolia and Vepris heterophylla are common understorey trees. Twelve species of woody liane were recorded. Species of thicket vegetation in the area were also present at low density. Most species are evergreen.Tree mortality averaged 2.3% yr^-1 and exceeded recruitment (1.5% yr^-1). Differences between species in mortality and recruitment were pronounced: canopy species showed a small decline in density; understorey species increased markedly and the thicket species declined. Seed production was very variable, but seedling establishment was very poor for all species. Seedling mortality was high (11% yr^-1) especially for small seedlings. These population trends probably represent the latter stages of succession of forest regrowth after farming about 100 years ago.Compared with tropical rain forest, Shai Hills forest has similar relative tree diameter growth (1–3.5% yr^-1), mortality and recruitment rates, and small-litter fall (5.52 t ha^-1 yr^-1).Shai Hills forest differs from rain forest by its short stature, relatively few (evergreen) tree species, poor regeneration from seed, high soil nutrient status and low rainfall. Similar forests have been reported in east Africa and in parts of New Guinea.Abbreviations dbh diameter at breast height (1.3 m) - gbh girth at breast height died May 1984     

Testing for enemy‐mediated density‐dependence in the mortality of seedlings: field experiments with five Neotropical tree species

The coexistence of plant species in species‐rich tropical forests can be promoted by specialised enemies acting in a negatively density‐dependent manner. While survival of tropical tree seedlings is often negatively density‐dependent, the causes have rarely been identified. We tested whether insects and plant pathogens cause density‐dependent seedling recruitment and survival in five forest tree species in Belize, Central America. We manipulated densities of seeds or newly germinated seedlings in small (1 m² or 0.25 m²) plots close to fruiting conspecific trees. Using a factorial design, we excluded enemies from subsets of the plots with fungicides and insecticides. Seed germination (for two species) and early seedling survival (for all species) were monitored at approximately weekly intervals for up to eight weeks, during the period when plants are likely to be most susceptible to natural enemies. In Terminalia amazonia, seed germination was negatively density‐dependent and the proportion of seeds germinating increased when insects were excluded. However, the magnitude of the insecticide effect was independent of density. The only significant density effect for survival of young seedlings was in Acacia polyphylla; counter to expectation, seedling survival was higher at high densities. In a few cases pesticide application had a significant effect on seedling survival, but in only one case (Terminalia amazonia) was a significant pesticide × density interaction detected. Our results caution against generalising from studies conducted on a single species at a single time and place and illustrate the challenges of experimentally testing for enemy‐mediated negative density‐dependence. Experimental outcomes are likely to depend on the spatial scale at which the principal enemies disperse and respond to plant density, and the timescales over which they act. Gathering information on these variables will improve our understanding of the natural histories of tropical forest species and help inform the design of future experiments.     

Spatial pattern of seedlings 1 year after fire in a Mediterranean pine forest

Summary The spatial distribution of seedlings of the dominant perennial plant species (Pinus halepensis, Cistus salviifolius, Rhus coriaria) and may annual species was studied after a wild fire in an eastern Mediterranean pine forest. The spatial distribution of all seedlings is affected by the location of the old burned pine trees. Seedling density of Pinus and Cistus is higher at a distance from the burned pine canopy and lower near the burned pine trunk. It is also higher beneath small burned pine trees than under big ones. Rhus seedling density is higher under big burned pine trees and also near the burned trunks. Seedlings of Pinus, Cistus and Rhus growing under the burned canopy of big pine trees tend to be taller than seedlings under small ones or outside the burned canopy. Most annual species germinate and establish themselves outside the burned canopies, and only a few annual species are found beneath them. It is suggested that variation in the heat of the fire, in the amount of ash between burned pine trees of different sizes, and in the distance from the burned canopy are responsible for the observed pattern of seedling distribution. The possible ecological significance of the spatial pattern of seedlings distribution and their differential growth rate are discussed.     

Density Effects of a Dominant Understory Herb,Isoglossa woodii (Acanthaceae), on Tree Seedlings of a Subtropical Coastal Dune Forest

Suppression of tree seedlings by the understory is an important ecological filter with implications for tree diversity and dynamics. In a greenhouse competition experiment, we used seedlings of four canopy species from coastal dune forest (Diospyros natalensis, Euclea racemosa, Sideroxylon inerme and Apodytes dimidiata) to examine the relative competitive effects of the dominant understory herb Isoglossa woodii on seedling performance. We manipulated I. woodii density, light and nutrient levels and measured growth responses. Total seedling biomass decreased with density of I. woodii. The magnitude of biomass suppression with competitor density was similar among tree species. Consequently there was no discernable hierarchy of competitive ranking among tree species. The relative growth rate of seedlings decreased at higher densities of I. woodii and increased at higher nutrient levels but was unaffected by variation in light conditions. Aboveground biomass decreased at higher densities of I. woodii and at higher light levels but increased at higher nutrient levels. Size asymmetric competition for light and nutrients may be the major driver of aboveground interactions between tree seedling and I. woodii. While tree species showed no hierarchy of competitive ability their seedlings exhibited equivalent responses to competition from an understory dominant, permitting species coexistence and the maintenance of species diversity.     

Vegetation structure and dynamics of Pinus gerardiana forests in Balouchistan,Pakistan

Abstract. 44 forest stands, including 42 stands with Pinus gerardiana Wall, ex Lamb dominant and two stands with broad-leaved trees, were sampled in the Suleiman Range in Balouchistan. Density oi Pinus gerardiana trees ranged from 24 to 930 trees / ha with a mean of 266 individuals / ha; the average basal area was 25.5 m² ha^-1. Adequate recruitment of Pinus seedlings was observed; higher seedling density is recorded from east-facing slopes, while tree density was higher on west-facing slopes. The average growth rate was estimated as 0.08 cm / yr radial growth. However, trees on high elevations and cooler slopes grow faster. Soil variables showed no correlation with density, basal area or importance values. It is suggested that the present degraded stage of the forests in the study area is of anthropogenic origin.     

Habitat fragmentation changes the adaptive value of seed mass for the establishment of a tropical canopy tree

To cope with the limiting light conditions in the rain forest understory, many tropical tree species have evolved large seeds that provide the emerging seedlings with nutritional reserves. Habitat fragmentation might change the adaptive value of seed size by modifying the biotic and physical conditions of the forest understory. We experimentally assessed the potential of fragmentation to alter how seed mass affects seedling survival, vigor, and attack by natural enemies of the tropical tree Nectandra ambigens. Seeds from different mother trees (families) were individually weighed and sown in experimental sites established in continuous forest and in forest fragments. Seedling survival, vigor, and damage by herbivores and pathogens were recorded periodically. While seedlings derived from larger seeds had higher survival rates in both habitats, seedling survival and vigor were significantly greater in forest fragments, and the seedlings also suffered fewer attacks by natural enemies. We found genetic variance for seed mass among families with a heritability value (h²) of 0.66, and we found evidence for selection on seed size. Average seed size differed between dead and living seedlings in three sites. In one fragment, seed size was selectively neutral in relation to survival. Overall, selection for seed size promoted survival and thus appears to affect the distribution of this trait. The maintenance of genetic variance could be related to the stochastic nature of the formation of light gaps. Our results highlight the importance of evaluating the adaptive value of traits susceptible to environmental changes for conservation purposes.     

Seedling and Sapling Dynamics of Treefall Pits in Puerto Rico1

Seedling and sapling dynamics in a Puerto Rican rain forest were compared between forest understory and soil pits created by the uprooting of 27 trees during Hurricane Hugo. Soil N and P, organic matter, and soil moisture were lower and bulk densities were higher in the disturbed mineral soils of the pits than in undisturbed forest soils ten months after the hurricane. No differences in N and P levels were found in pit or forest soils under two trees with N–fixing symbionts (Inga laurina and Ormosia krugii) compared to soils under a tree species without N–fixing sym–bionts (Casearia arborea), but other soil variables (Al, Fe, K) did vary by tree species. Forest plots had greater species richness of seedlings (<10 cm tall) and saplings (10–100 cm tall) than plots in the soil pits (and greater sapling densities), but seedling densities were similar between plot types. Species richness and seedling densities did not vary among plots associated with the three tree species, but some saplings were more abundant under trees of the same species. Pit size did not affect species richness or seedling and sapling densities. Recruitment of young Cecropia schreberiana trees (>5 m tall) 45 months after the hurricane was entirely from the soil pits, with no tree recruitment from forest plots. Larger soil pits had more tree recruitment than smaller pits. Defoliation of the forest by the hurricane created a large but temporary increase in light availability. Recruitment of C. schreberiana to the canopy occurred in gaps created by the treefall pits that had lower soil nutrients but provided a longer–term increase in light availability. Treefall pits also significantly altered the recruitment and mortality of many understory species in the Puerto Rican rain forest but did not alter species richness.     

Role of nurse plants in Araucaria Forest expansion over grassland in south Brazil

Abstract Araucaria Forest expansion over grassland takes place under wet climate conditions and low disturbance and it is hypothesized that isolated trees established on grassland facilitate the establishment of forest woody species beneath their canopies. Forest with Araucaria angustifolia is a particular type of Brazilian Atlantic Forest and the main forest type on the highland plateau in south Brazil, often forming mosaics with natural Campos grassland. The objectives of this paper were to evaluate the role of isolated shrubs and trees as colonization sites for seedlings of Araucaria Forest woody species on grassland, to determine which species function as preferential nurse plants in the process and the importance of vertebrate diaspore dispersal on the structure of seedling communities beneath nurse plants. The study was conducted in São Francisco de Paula, Rio Grande do Sul State, where we sampled isolated shrubs and trees in natural grassland near Araucaria Forest edges. Seedlings were counted and identified, and seedling diaspore dispersal syndromes, size and colour were registered. We detected 11 woody species with a potential role in nucleating grassland colonization by forest species. Beneath the canopies of nurse plants more forest species seedlings were found compared with open field grassland and the seedlings had diaspores mostly dispersed by vertebrates. Also, more seedlings were found under the canopy of A. angustifolia than beneath other nurse plant species. We conclude that A. angustifolia trees established on grassland act as nurse plants, by attracting disperser birds that promote colonization of the site by other forest species seedlings, and that under low level of grassland disturbance, conservation of frugivorous vertebrate assemblages may increase forest expansion over natural grassland and also facilitate the regeneration of degraded forest areas.     

Seedling establishment of Acacia tortilis and Hyphaene compressa in the Turkwel riverine forest, Kenya

This study reports on the spatial and temporal patterns of seedling establishment in the Turkwel riverine forest, Kenya. Seedlings of the dominant tree species Acacia tortilis and Hyphaene compressa were mapped and monitored to assess the underlying causes of seedling recruitment and mortality. The broad‐scale distribution of A. tortilis was not correlated with any environmental variables, while H. compressa seedlings were confined to flood‐exposed sites in the arid downstream section of the floodplain. One year of monitoring showed that seedling recruitment of A. tortilis was evoked by prolonged rainfall, while seedling mortality was caused by desiccation, browsing and trampling. In contrast, seedling recruitment and mortality of H. compressa was largely unaffected by rainfall and livestock, probably due to the high moisture requirements of seeds and the tolerance of seedlings to disturbance. There were no effects of soils, light, or seedling density on the establishment of A. tortilis and H. compressa seedlings. This study demonstrates the importance of parallel mapping and monitoring of riverine seedlings in order to understand patterns and processes of forest regeneration in arid and semi‐arid floodplains.     

A comparison of sites suitable for the seedling establishment of two co-occurring species, Swintonia glauca and Stemonurus scorpioides, in a tropical peat swamp forest

Spatial and temporal ground-surface dynamics are major factors that affect regeneration and species coexistence in tropical peat swamp forests. We studied the seedling survivorship and morphological features of two tree species that play important roles in maintaining the ground-surface dynamics of a peat swamp forest in Sumatra. Large Swintonia glauca trees form mounds, whereas large Stemonurus scorpioides trees occupy non-mounds. We monitored the demography of naturally dispersed Swintonia and Stemonurus seedlings that germinated in 2000. Survivorship of Swintonia seedlings was high under conditions of late germination, high-light environment, and elevated ground surface, and was negatively affected by distance to the nearest conspecific adult. Survivorship of Stemonurus was high under conditions of early germination and high conspecific seedling density, and was also negatively affected by distance to the nearest conspecific adult. The allometric features of Stemonurus seedlings indicated characteristics of stress tolerance, that is, low growth rate and thick, porous roots. Stemonurus, which has large wingless seeds, regenerated in non-mounds around the parental trees, while winged Swintonia seeds dispersed farther from the parent and established in patchily distributed gaps and mounds. Thus, Swintonia seedlings can survive on non-mound sites within gaps and possibly create mounds, while Stemonurus seedlings tend to maintain non-mounds around the parental trees.