Distribution Of Adult Trees Research Articles

Climate change decouples dominant tree species in African savannas

To understand how two dominant African savanna trees will continue to respond to climate changes, we examined their regeneration niche and adult tree distributions. Specifically, we wanted to (1) determine if distributional patterns were shifting, (2) predict future distributions under different climate change scenarios and (3) evaluate the realism of predicted future distributions. We randomly placed 40 grids into 6 strata across a climate gradient in the kingdom of Eswatini. Within these grids, we sampled adult and seedling marula (Scelerocarya birrea) and knobthorn (Senegalia nigrecens) trees and used the data to model their abundance. Next, we quantified shifts in distributional patterns (e.g., expansion or contraction) by measuring the current and projected areas of overlap between seedling and adult trees. Finally, we predicted future distributions of abundance based on predicted climate conditions. We found knobthorn seedlings within a small portion of the adult distribution, suggesting it was unlikely to track climate changes. Alternatively, finding marula seedlings on and beyond one edge of the adult distribution, suggested its range would shift toward cooler climates. Predicted future distributions suggest suitable climate for both species would transition out of savannas and into grasslands. Future projections (2041–2070) appeared consistent with observed distributions of marula, but knobthorn predictions were unrealistic given the lack of evidence for regeneration outside of its current range. The idiosyncratic responses of these species to climate change are likely to decouple these keystone structures in the coming decades and are likely to have considerable cascading effects including the potential rearrangement of faunal communities.

Canopy gaps facilitate upslope shifts in montane conifers but not in temperate deciduous trees in the Northeastern United States

AbstractMany montane tree species are expected to migrate upslope as climate warms, but it is not clear if forest canopy gaps, which can facilitate tree seedling recruitment, serve as an important mechanism driving tree species range shifts. Patterns of tree seedling establishment can inform us about early stages of tree species migrations and are critical to examine in the context of global climate change.We contrasted elevational distributions of tree seedlings both within and outside of forest canopy gaps with the distributions of conspecific adults and saplings across the deciduous‐coniferous ecotone on ten mountains in four states of the Northeastern United States. We tested if seedling distributions of four dominant tree species (Abies balsamea,Picea rubens,Acer saccharumandFagus grandifolia) were shifted upslope of conspecific adult and sapling distributions. We also examined if this shift was facilitated by canopy gaps and what environmental drivers affected species distributions.There was limited seedling recruitment of dominant tree species at the temperate‐coniferous ecotone, which we attributed to (i) an observed downslope shift of seedling distributions of the low‐elevation deciduous species (Acer saccharum,Fagus grandifolia) and (ii) an upslope shift in seedling distributions of the high‐elevation conifers (Abies balsamea,Picea rubens). The upslope shift of conifer seedlings contrasts with our previous research at these sites which observed downslope shifts of sapling distributions inPicea rubens, suggesting that seedlings may be responding to more recent climate warming. Canopy gaps in high‐elevation conifer forests facilitated these upslope shifts by promoting conifer seedling recruitment. However, gaps at lower elevations did not play a significant role in seedling recruitment or the observed downslope shifts of the dominant deciduous species. Climate was the dominant predictor of adult tree distributions whereas both climate and soil were important predictors of seedling distributions.Synthesis.Our study illustrates that tree seedlings have the potential for monitoring the early stages of tree species migrations, and particularly so in canopy gaps in high‐elevation conifer forests. Further, we stress that species range shifts are sensitive to local scale heterogeneity in light availability (i.e. canopy gaps) and other non‐climatic factors.

Are small abandoned plantations a threat for protected areas in Andean forests? The potential invasion of non-native cultivated species

Abandoned farms with small fruit plantations of the non-native species Prunus cerasus and Malus domestica are common in protected areas of the temperate forests of southern South America (TFSA), in Patagonia. Our aims were to determine whether an invasion of P. cerasus and M. domestica might be starting in protected areas, and whether either native or alien animal species are involved in the dispersal process. We evaluated sapling and seed spread, adult tree distribution in three habitats, and seed dispersal vectors of P. cerasus and M. domestica in “Los Alerces” National Park (Argentina). We sampled mature trees, saplings and seeds of P. cerasus and M. domesticain in two plots located next to plantations. Adult trees and mammal faeces also were searched for on roads, hiking trails, deforested areas, plots and transects opened by us. We monitored fruiting trees with cameras and we caught birds to obtain faeces. Saplings of P. cerasus were abundant and their locations were not related to adult locations, but saplings of M. domestica were rare. Ninety-two percent of P. cerasus adult trees were found in successional forest, whereas 99% of M. domestica trees were in deforested areas. Faeces of native foxes contained high number of intact seeds of both plant species studied, but we did not find any in the bird faeces. Our results indicates that P. cerasus has been invading natural habitats in protected areas of TFSA, and that foxes can be the major dispersal vectors. Further, successional forest is the most invasible habitat.

Diverging distribution of seedlings and mature trees reflects recent climate change in British Columbia

The composition and health of forests across western North America have shown signs of change over the last half-century associated with altered climate conditions. Most models developed to predict responses to variation in climate assume that the ecological distribution of adult trees provides a sound basis for projecting potential shifts in a species’ range. Under a dynamic climate, however, recently established seedlings may more closely reflect changes in climate conditions. This study combined the simple, widely tested physiological model 3-PG with an empirical regeneration dataset, composed of 21,097 plots, to assess regional scale changes in tree species distributions across British Columbia, Canada. We geographically registered all plot locations to correspond with topographically-adjusted 1 km monthly climatic data for the period 2000–2009. By comparing the distribution of seedlings to that of mature trees present in an earlier period (1950–1975), we could assess where alterations in the environment have occurred, and the extent to which changes may make a species vulnerable to replacement in some places or likely to regenerate and migrate elsewhere. Decision tree models were developed to assess the relative importance of suboptimal temperatures, frost, soil water deficits and evaporative demand on the growth and distribution of four widely distributed species: Douglas-fir (Pseudotsuga menziesii), lodgepole pine (Pinus contorta), western larch (Larix occidentalis), and subalpine fir (Abies lasiocarpa). Tree responses varied by species, with areas suitable for lodgepole pine experiencing the largest relative increase in summer drought and areas dominated by western larch experiencing the least. Those areas modelled as suitable for species range expansions occurred 79% (SD = 16%) of the time in places where seedlings of a designated species were predicted in 2000–2009 using the regeneration dataset. We conclude that employing seedling surveys in concert with tree surveys provide valuable ecological insights when predicting species responses to climate shifts.

Structure of plant community in tropical deciduous forests of Kanyakumari Wildlife Sanctuary, India

Abstract. Kothandaraman S, Sundarapandian S.2017. Structure of plant community in tropical deciduous forests of Kanyakumari Wildlife Sanctuary, India. Biodiversitas 18: 391-400. Plantcommunity structure of two tropical deciduous forest sites (I and II which are in different locations with different terrain characteristics viz., elevation and slope pattern) in Kanyakumari Wildlife Sanctuary, Western Ghats were assessed using standard phytosociological methods. Ten plots of 20 m x 20 m each were laid for woody species enumeration and 40 quadrats of 1 m x 1 m (4 in each plot) for understorey vegetation (herbs and plant species that are < 1 m in height) in each site. Overall, 76 plant species were recorded from 41 families, of which 23 contribute to understory. Site I (62) was twice as speciose as site II (31). Greater diversity index of adult woody vegetation was observed in site I (2.30) than site II (2.01). The woody individuals (diameter at breast height, DBH ≥ 10 cm) were more abundant in site I (518 individuals ha-1) than site II (448 individuals ha-1). The basal area of adult trees in sites I and II are 34.7 m2 ha-1 and 30.8 m2 ha-1 respectively. Euphorbiaceae was the most speciose family in both the sites. Twenty-five families in site I and seventeen families in site II were represented by singletons. Diameter class-wise distribution of adult trees showed a typical ‘reverse J-shaped’ curve indicating good regeneration status. Concerning understory, site I (19 species) has a greater diversity than site II (six species). The observed differences in the vegetation patterns between the two deciduous forest sites are possibly due to variations in elevation, terrain features and edaphic characteristics.
 Keywords: Phytodiversity, species richness, tropical forests, Western Ghats

Elevational Distribution of Adult Trees and Seedlings in a Tropical Montane Transect, Southwest China

Montane habitats are characterized by high variation of environmental factors within small geographic ranges, which offers opportunities to explore how forest assemblages respond to changes in environmental conditions. Understanding the distributional transition of adult trees and seedlings will provide insight into the fate of forest biodiversity in response to future climate change. We investigated the elevational distribution of 156 species of adult trees and 152 species of seedlings in a tropical montane forest in Xishuangbanna, southwest China. Adult trees and seedlings were surveyed within 5 replicate plots established at each of 4 elevational bands (800, 1000, 1200, and 1400 m above sea level). We found that species richness of both adult trees and seedlings changed with elevation, showing a notable decline in diversity values from 1000 to 1200 m. Tree species composition also demonstrated distinct differences between 1000 and 1200 m, marking the division between tropical seasonal rain forest (800 ...

Spatial patterns of primary seed dispersal and adult tree distributions:Genipa americanadispersed byCebus capucinus

Abstract:The spatial distribution of adult trees is typically not expected to reflect the spatial patterns of primary seed dispersal, due to many factors influencing post-dispersal modification of the seed shadow, such as seed predation, secondary seed dispersal and density-dependent survival. Here, we test the hypothesis that spatial distributions of primary seed shadows and adult trees are concordant by analysing the spatial distributions of adultGenipa americanatrees and the seed shadow produced by its key primary disperser, the capuchin monkey (Cebus capucinus) in a tropical dry forest in Costa Rica. We mapped the dispersal ofG. americanaseeds by the capuchins during focal animal follows (mean = 463 min,n= 50) of all adults in one free-ranging group over two early wet seasons (May–July, 2005 and 2006). We mapped the locations of allG. americanatrees within a 60-ha plot that lay within the home range of the capuchin group. We conducted multiple spatial point pattern analyses comparing degrees of clustering of capuchin defecations andG. americanatrees. We found that adult tree distributions and primary dispersal patterns are similarly aggregated at multiple spatial scales, despite the modification of the primary dispersal patterns and long dispersal distances.

Environmental heterogeneity and dispersal processes influence post-logging seedling establishment in a Chiquitano dry tropical forest

Selective logging is becoming more and more influential in forest use in the tropics, especially as it provides local communities and regions with timber resources. Logging greatly alters abiotic and biotic factors which are fundamental in seedling establishment and spatial heterogeneity of tree recruitment. Niche and dispersal processes may affect post-logging seedling establishment, particularly in water-constrained tropical dry forests (TDF). To understand how selective logging affects tree recruitment and how forest exploitation can become a sustainable practice, a theoretical framework has been set up based on these processes. We assessed post-logging seedling establishment in a Bolivian Chiquitano TDF by: (i) characterizing logging microsites and the variability in abiotic (canopy openness, soil compaction and soil water content) and biotic (short and long-distance dispersal) factors among them, (ii) evaluating the roles played by those factors, here considered surrogates of niche and dispersal processes, on seedling establishment, and (iii) providing guidelines to ensure tree regeneration in similar logged TDFs. One year after logging, seedling establishment of five canopy tree species was assessed in four microsite types created by selective logging and in undisturbed TDF. Dispersal processes were described by interpolated kernel estimates of abundance of adult trees, i.e. potential seed sources. After logging, the abiotic environment was considerably altered, especially in the most disturbed logging microsites, leading to significant changes in canopy openness and soil compaction, the most important factors determining seedling establishment in four out of the five studied species. Dispersal processes also influenced regeneration in three tree species. Since the spatial distribution of adult trees influences post-logging regeneration, this should be considered to improve sustainability in logging operations across the tropics.

A neighborhood analysis of the consequences of Quercus suber decline for regeneration dynamics in Mediterranean forests.

In forests, the vulnerable seedling stage is largely influenced by the canopy, which modifies the surrounding environment. Consequently, any alteration in the characteristics of the canopy, such as those promoted by forest dieback, might impact regeneration dynamics. Our work analyzes the interaction between canopy neighbors and seedlings in Mediterranean forests affected by the decline of their dominant species (Quercus suber). Our objective was to understand how the impacts of neighbor trees and shrubs on recruitment could affect future dynamics of these declining forests. Seeds of the three dominant tree species (Quercus suber, Olea europaea and Quercus canariensis) were sown in six sites during two consecutive years. Using a spatially-explicit, neighborhood approach we developed models that explained the observed spatial variation in seedling emergence, survival, growth and photochemical efficiency as a function of the size, identity, health, abundance and distribution of adult trees and shrubs in the neighborhood. We found strong neighborhood effects for all the performance estimators, particularly seedling emergence and survival. Tree neighbors positively affected emergence, independently of species identity or health. Alternatively, seedling survival was much lower in neighborhoods dominated by defoliated and dead Q. suber trees than in neighborhoods dominated by healthy trees. For the two oak species, these negative effects were consistent over the three years of the experimental seedlings. These results indicate that ongoing changes in species’ relative abundance and canopy trees’ health might alter the successional trajectories of Mediterranean oak-forests through neighbor-specific impacts on seedlings. The recruitment failure of dominant late-successional oaks in the gaps opened after Q. suber death would indirectly favor the establishment of other coexisting woody species, such as drought-tolerant shrubs. This could lead current forests to shift into open systems with lower tree cover. Adult canopy decline would therefore represent an additional factor threatening the recruitment of Quercus forests worldwide.

Species coexistence in a mixed Mediterranean pine forest: Spatio-temporal variability in trade-offs between facilitation and competition

Studying species coexistence is key to understanding the way in which forests will respond to climate change. We studied the patterns of mixed stands including two main Mediterranean pine species: Pinus pinaster Ait. and Pinus pinea L. The spatial distribution of adult trees and saplings was studied via a point pattern approach. The effect of competition on growth of adult trees was investigated by comparing the performance of several competition indexes for each pine species through generalized linear models. Adult trees formed mixed clumps in which individuals of both species appeared together. Part of the tree growth variation was explained by tree size along with tree competition. However, the effect of conspecific vs heterospecific competition on tree growth differed and reflected species-specific neighbor-asymmetric competition. Facilitation was fundamental in the early stages for tree species development. The spatial distribution of saplings was strongly related to the spatial distribution of adult trees, also being asymmetrically clustered and neighbor-species-dependent. However, the required facilitation in early life-stage trees shifted to competition among trees in the adult stage. Species mixture may be desirable in terms of increasing and diversifying productivity, although the conditions currently present in the stand are likely to lead to future dominance of P. pinea over P. pinaster due not only to the greater competition tolerance of the former but also to a greater ability to successfully recruit in the plots, forming clusters that may be in turn be impenetrable to P. pinaster. Therefore, in order to maintain mixed stands, it would be necessary to enforce adequate silvicultural management strategies which avoid future stand dominance by P. pinea.

Seed dispersal and seedling recruitment of trees at different successional stages in a temperate forest in northeastern China

Aims Spatial distribution of adult trees in a forest community is deter mined by patterns of both seed dispersal and seedling recruitment. The objectives of our study were to understand the processes of seed dispersal and seedling recruitment of dominant tree species in a temperate forest of northeastern China and to identify the factors constraining seed dispersal and seedling establishment at different stages of forest succession. Methods During three summer and autumn sessions between 2006 and 2008, altogether 113 080 seeds from 22 different tree species were collected in three large field plots representing different for est types in the Changbai Mountain region of northeastern China. The spatial distribution of seed abundance was analyzed using a Syrjala test. Regeneration success of nine major tree species was assessed using variables defining ‘limitations’ in ‘seeds’ and ‘seedling establishment’. Important Findings We found that seed production fluctuated between years and varied greatly with forest types. Four tree species, Acer spp., Fraxinus mandshurica, Tilia amurensis and Betula spp., had the greatest seed production and the widest range of seed dispersal, whereas Quercus mongolica showed the most sustained seed production pattern. The spatial patterns of seed abundance differed significantly among for est types and years. The tree species investigated in this study differed in the degree of seed limitation, as well as in limitation of seedling establishment. There were both negative and positive cor relations between seed density and seedling density, depending on site and parental tree density. Seeds of 16 tree species were found in the Populus davidiana–Betula platyphylla forest (PBF) plot, 11 in the conifer and broad-leaved mixed forest (CBF) plot but only 8 in the broad-leaved-Korean pine mixed forest (BKF) plot. The number of seed-contributing species was not only greater in the secondary forests (CBF and PBF plots) than in the primary forest (BKF plot) but was also more variable during the 3 years of assessment. Results from the correlations between seed density and seedling occur

Sorbus aucuparia regeneration in a coarse‐grained spruce forest – a landscape scale

AbstractQuestionsWhat is the spatial range of regeneration of the fleshy‐fruited tree Sorbus aucuparia (rowan) in a coarse‐grained spruce stand on a large landscape scale? Does the spatial distribution and size of stands of different ages affect the probability of rowan regeneration? What are the consequences of the dynamics of dominant coniferous tree species for the dynamics of admixture rowan?LocationA sub‐alpine spruce forest in the Tatra Mountains, Poland.MethodsWe mapped all mature rowans in a 203‐ha area and counted the rowan seedlings and saplings on a grid of evenly distributed plots. In plots, the age and diameter of trees were measured. Patches of homogenous stands were distinguished and each rowan tree and each plot was assigned to one of four stand categories: dense small‐crowned stands, dense large‐crowned stands, sparse large‐crowned stands and sparse stands near the upper forest limit. Areas above the upper forest limit formed a separate fifth category.ResultsThe distribution of rowan trees was clumped. Most of them grew in dense spruce stands up to 135 yr old and near the upper forest limit. Substantially fewer rowan trees were in sparse spruce stands of nearly 200 yr old. Seedlings and saplings occurred at high density (mean 24.8 individuals 100 m−2) only up to 40 m from trees bearing fruits, and at much lower density at longer distances. In consequence of the clumped distribution of adult trees and the short range of seed dispersal, most of the old spruce stands were outside the range of abundant regeneration of rowan.ConclusionsThe presence of fine‐ vs coarse‐grained mosaics of coniferous stands of different ages can strongly influence population processes in a rowan population on a large landscape scale. Extensive disturbances resulting in large homogenous patches of coniferous stands, the long lifespan of a single generation of spruce and spatial limitation of rowan seed dispersal seem responsible for the small contribution this broad‐leaved species makes to sub‐alpine forests. A high share of rowan can be expected in forests with fine‐grained mosaics of stands, where small patches of young and old stands are inter‐mixed, assuring delivery of seeds to stands of each category.

Population structure of two low-density neotropical tree species under different management systems

This article analyses the density, spatial distribution, and diameter structure of two neotropical tree species, Dipteryx odorata (Aubl.) Willd. and Copaifera reticulata Ducke, in undisturbed forests, logged forests, and forests used for the extraction of Non-Timber Forest Products (NTFPs). Both species are commercially harvested for timber and non-timber products which can fetch high prices on national and international markets. In undisturbed forests, both species display a low tree density, a random adult tree distribution pattern and a flat diameter structure, or one biased towards larger trees. The random spatial distribution pattern did not vary in the three types of forests analysed, whereas individual density and diameter structure did. The NTFP extraction areas exhibited the highest population densities for both species. In the logged forests, there was a lower density of very large D. odorata trees, while the areas used for D. odorata seed extraction showed a drastic reduction in the frequency of young trees. The results of this study seem to suggest that oil extraction from C. reticulata does not have any effect on the regeneration of that species, whereas D. odorata seed collection could affect the viability of populations.

Fine‐scale Spatial Genetic Structure of Ten Dipterocarp Tree Species in a Bornean Rain Forest

AbstractFine‐scale spatial genetic structure is increasingly recognized as an important factor in the studies of tropical forest trees as it influences genetic diversity of local populations. The biologic mechanisms that generate fine‐scale spatial genetic structure are not fully understood. We studied fine‐scale spatial genetic structure in ten coexisting dipterocarp tree species in a Bornean rain forest using microsatellite markers. Six of the ten species showed statistically significant fine‐scale spatial genetic structure. Fine‐scale spatial genetic structure was stronger at smaller spatial scales (≤ 100 m) than at larger spatial scales (> 100 m) for each species. Multiple regression analysis suggested that seed dispersal distance was important at the smaller spatial scale. At the larger scale (> 100 m) and over the entire sample range (0–1000 m), pollinators and spatial distribution of adult trees were more important determinants of fine‐scale spatial genetic structure. Fine‐scale spatial genetic structure was stronger in species pollinated by less mobile small beetles than in species pollinated by the more mobile giant honeybee (Apis dorsata). It was also stronger in species where adult tree distributions were more clumped. The hypothesized mechanisms underlying the negative correlation between clump size and fine‐scale spatial genetic structure were a large overlap among seed shadows and genetic drift within clumped species.

Interactive effects of land use history and natural disturbance on seedling dynamics in a subtropical forest

Human-impacted forests are increasing in extent due to widespread regrowth of secondary forests on abandoned lands. The degree and speed of recovery from human disturbance in these forests will determine their value in terms of biodiversity conservation and ecosystem function. In areas subject to periodic, severe natural disturbances, such as hurricanes, it has been hypothesized that human and natural disturbance may interact to either erase or preserve land use legacies. To increase understanding of how interactions between human and natural disturbance influence forest regeneration and recovery, we monitored seedlings in a human- and hurricane-impacted forest in northeastern Puerto Rico over a approximately 10-yr period and compared seedling composition and dynamics in areas that had experienced high- and low-intensity human disturbance during the first half of the 20th century. We found that land use history significantly affected the composition and diversity of the seedling layer and altered patterns of canopy openness and seedling dynamics following hurricane disturbance. The area that had been subject to high-intensity land use supported a higher density, but lower diversity, of species. In both land use history categories, the seedling layer was dominated by the same two species, Prestoea acuminata var. montana and Guarea guidonia. However, seedlings of secondary-successional species tended to be more abundant in the high-intensity land use area, while late-successional species were more abundant in the low-intensity area, consistent with patterns of adult tree distributions. Seedlings of secondary-forest species showed greater increases in growth and survival following hurricane disturbance compared to late-successional species, providing support for the hypothesis that hurricanes help preserve the signature of land use history. However, the increased performance of secondary-forest species occurred predominantly in the low-intensity land use area, suggesting that hurricanes act to homogenize differences in species composition between areas with differing land use histories by increasing secondary-forest species regeneration in areas that experienced little direct human disturbance. Our results suggest that, through effects on seedling dynamics, hurricanes may extend the signature of land use history beyond the average recovery time of forests not subject to intense natural disturbance events.

Effects of seed dispersal, adult tree and seedling density on the spatial genetic structure of regeneration at fine temporal and spatial scales

Several demographic factors can produce family structured patches within natural plant populations, particularly limited seed and pollen dispersal and small effective density. In this paper, we used computer simulations to examine how seed dispersal, density, and spatial distribution of adult trees and seedlings can explain the spatial genetic structure (SGS) of natural regeneration after a single reproductive event in a small population. We then illustrated the results of our simulations using genetic (isozymes and chloroplast microsatellites) and demographic experimental data from an Abies alba (silver fir) intensive study plot located in the Southern French Alps (Mont Ventoux). Simulations showed that the structuring effect of limited dispersal on seedling SGS can largely be counterbalanced by high effective density or a clumped spatial distribution of adult trees. In addition, the clumping of natural regeneration far from adult trees, which is common in temperate forest communities where gap dynamics are predominant, further decreases SGS intensity. Contrary to our simulation results, low adult tree density, aggregated spatial distribution of seedlings, and limited seed dispersal did not generate a significant SGS in our A. alba experimental plot. Although some level of long distance pollen and seed flow could explain this lack of SGS, our experimental data confirm the role of spatial aggregation (both in adult trees and in seedlings far from adult trees) in reducing SGS in natural populations.

Genetic diversity in rosewood saplings (Aniba rosaeodora ducke, Lauraceae): an ecological approach

This article takes an ecological approach to the genetic diversity of Rosewood (Aniba rosaeodora Ducke) in a central Amazonian terra firme forest north of Manaus. Planted Rosewood setting, under partial shaded canopy, were assessed in terms of fruiting production, frugivory, and seed dispersal. Using RAPD molecular analysis procedures, the influence of the spatial distribution of adult trees on the genetic diversity (polymorphism) of saplings was assessed with genetic samples from 34 reproductive trees and 60 saplings. The density and distribution patterns the reproductive trees did not modify the sapling"s diversity (1.86%, AMOVA). Two types of adult tree dispersion were identified; i) clumped and ii) more widely dispersed. Polymorphism (77.5%) and gene flow were high between these. Although more sapling genetic variability in areas with a higher density of mature plants was not as high as expected, density did not affect the genetic diversity of samplings, indicating a high incidence of gene flow amongst trees. In planted Rosewood population (surrounded by low disturbed forest), fruiting trees experienced a high level of removal of seeds by toucans (Rhamphastidae), about of 50%. The high gene flow found among native trees suggested that toucans, promoting seed rain at short and long distances from maternal trees, actively contribute to the maintenance of genetic diversity within wild rosewood populations.

PARTITIONING THE FACTORS OF SPATIAL VARIATION IN REGENERATION DENSITY OF SHADE-TOLERANT TREE SPECIES

Understanding coexistence of highly shade-tolerant tree species is a longstanding challenge for forest ecologists. A conceptual model for the coexistence of sugar maple (Acer saccharum) and American beech (Fagus grandibfolia) has been proposed, based on a low-light survival/high-light growth trade-off, which interacts with soil fertility and small-scale spatiotemporal variation in the environment. In this study, we first tested whether the spatial distribution of seedlings and saplings can be predicted by the spatiotemporal variability of light availability and soil fertility, and second, the manner in which the process of environmental filtering changes with regeneration size. We evaluate the support for this hypothesis relative to the one for a neutral model, i.e., for seed rain density predicted from the distribution of adult trees. To do so, we performed intensive sampling over 86 quadrats (5 x 5 m) in a 0.24-ha plot in a mature maple-beech community in Quebec, Canada. Maple and beech abundance, soil characteristics, light availability, and growth history (used as a proxy for spatiotemporal variation in light availability) were finely measured to model variation in sapling composition across different size classes. Results indicate that the variables selected to model species distribution do effectively change with size, but not as predicted by the conceptual model. Our results show that variability in the environment is not sufficient to differentiate these species' distributions in space. Although species differ in their spatial distribution in the small size classes, they tend to correlate at the larger size class in which recruitment occurs. Overall, the results are not supportive of a model of coexistence based on small-scale variations in the environment. We propose that, at the scale of a local stand, the lack of fit of the model could result from the high similarity of species in the range of environmental conditions encountered, and we suggest that coexistence would be stable only at larger spatial scales at which variability in the environment is greater.

Dispersal Modes and Spatial Patterns of Tree Species in a Tropical Forest in Arunachal Pradesh, Northeast India

We characterized the dispersal modes and spatial patterns of 128 tree species in a tropical semi-evergreen forest of Arunachal Pradesh, northeastern India. A high percentage of species are animal-dispersed (78%), while about 22% (28) are dispersed abiotically (wind or gravity-dispersed). Of the animal-dispersed species, 54 species were primarily bird-dispersed, 25 were mammal-dispersed, and 21 were dispersed by both groups. We hypothesized that adult tree distribution patterns were related to dispersal mode and fruit size. We predicted that tree species with mechanisms for long-distance seed dispersal are likely to show more uniform or random spatial patterns than those with limited seed dispersal. Tree species with large fruits were also predicted to have greater levels of clumping than those that have small fruits. However, all tree species had a clumped distribution pattern. At the community level, we found no differences in spatial patterns based on dispersal mode for a subset of 50 tree species. Fruit size was, however, positively correlated with higher levels of spatial aggregation suggesting that tree species distributions are to an extent limited by dispersal. The importance of dispersal mode in determining adult tree distribution patterns at the community level may be obscured by interacting effects of other factors such as patchy habitat conditions and density-dependent mortality factors at different life-history stages that ultimately determine adult tree distributions.

Spatial distribution patterns of trees at different life stages in a warm temperate forest

We have investigated tree distributions in relation to topography between different tree life history stages, from the seed-dispersal stage to the adult stage in a warm temperate evergreen broadleaved forest on Yakushima Island, Japan, to clarify the critical stages in determining adult tree distributions. We conducted a census of all living trees > or =30 cm tall and collected seed falls over three years using 25 seed traps in a 50 m x 50 m quadrat. Four life stages were defined: stage 1, dispersed seed; stage 2, individuals taller than 30 cm and diameter at breast height (DBH) < 1 cm; stage 3, trunks 1 cm < or = DBH < 10 cm; stage 4, trunks with DBH > or = 10 cm. We classified 17 common tree species into three groups; group A was distributed mainly on the upper slope, group B on the lower slope, and group C on both. Most of group A and B trees at stages 2-4 showed an aggregated distribution along the topographical gradient. The densities at stage 1 showed weaker aggregations according to slope. Topography-specific tree distribution was probably determined at the regeneration stage, and later survival was less effective as a mechanism of vegetation differentiation.