Distribution Of Saplings Research Articles

Contrasting spatial distribution of pioneer versus non‐pioneer saplings in a Taiwanese forest: A multiple scale approach

AbstractDispersal limitation and environmental filtering were recognized as the main dispersal‐based and niche‐based processes responsible for community assembly. These interactions usually leave more spatial signatures in sapling communities and create detectable spatial patterns in different functional types of species. We investigated saplings of pioneer and non‐pioneer species, which facilitated an understanding of species co‐existence and biodiversity recovery. Based upon mapped tree data in the subtropical evergreen broad‐leaved forest dynamics plot in Taiwan, we endeavored to: (1) determine the different spatial scales contributing to distribution patterns of pioneer and non‐pioneer saplings; (2) understand how dispersal limitation affects distribution of pioneer and non‐pioneer saplings; and (3) evaluate the degree to which the different environmental factors explain variation in species composition in pioneer and non‐pioneer saplings. We used the principal coordinates of neighbor matrices (PCNM) method, and variation partitioning to disentangle the contributions of these processes. Fine‐scale spatial patterns were more important for pioneer than for non‐pioneer saplings. Dispersal limitation was the main process influencing the spatial distribution of the non‐pioneer saplings. Environmental filtering was also an important process regulating the spatial distribution of saplings for both functional types, especially for pioneer saplings. Disturbance effects contributed to fine‐scale spatial variation in pioneer saplings, whereas topographic and soil effects contributed to broad and medium scale spatial variation in non‐pioneer saplings. It was evident that different spatial patterns of saplings of different functional types served to facilitate tree regeneration and maintain species co‐existence in this subtropical broad‐leaved forest.

Trees species’ dispersal mode and habitat heterogeneity shape negative density dependence in a temperate forest

Conspecific negative density dependence (CNDD) is a potentially important mechanism in maintaining species diversity. While previous evidence showed habitat heterogeneity and species’ dispersal modes affect the strength of CNDD at early life stages of trees (e.g., seedlings), it remains unclear how they affect the strength of CNDD at later life stages. We examined the degree of spatial aggregation between saplings and trees for species dispersed by wind and gravity in four topographic habitats within a 25-ha temperate forest dynamic plot in the Qinling Mountains of central China. We used the replicated spatial point pattern (RSPP) analysis and bivariate pair-correlation function (PCF) to detect the spatial distribution of saplings around trees at two scales, 15 and 50 ​m, respectively. Although the signal was not apparent across the whole study region (or 25-ha), it is distinct on isolated areas with specific characteristics, suggesting that these characteristics could be important factors in CNDD. Further, we found that the gravity-dispersed tree species experienced CNDD across habitats, while for wind-dispersed species CNDD was found in gully, terrace and low-ridge habitats. Our study suggests that neglecting the habitat heterogeneity and dispersal mode can distort the signal of CNDD and community assembly in temperate forests.

Endangered Dracaena ombet Population in the Red Sea Hills, Sudan, Recovers After Abrupt Change

The endangered and endemic Nubian dragon blood tree, Dracaena ombet, has been feared extirpated from core distribution areas in the Red Sea Hills, Sudan, after reported mass death events in the 20th century. Populations of dragon tree species are generally reported to be in decline, with a noticeable lack of recruitment and possible poor resilience. Rare recruitment events are, however, normal for species with remnant population dynamics, and when eventually occurring, such events can restore seemingly degraded populations. In response to recently reported observations of dracaena saplings in a historically core distribution area of the Red Sea Hills, we assess the status of this long-lived arboreal species. We describe a current realized niche, investigate a potential range shift by comparing the spatial distribution of saplings and older individuals, and assess population recovery based on pre-disturbance system identity derived from qualitative, historical observations. We document a beginning recovery of the dracaena population in the study area. Around half of the mapped population are individuals in the sapling stage, and they are in good health. Its current realized niche is described by higher altitudes, steeper slopes, more concave landscape forms and east-facing aspects compared to areas where dracaena individuals are absent. However, for the new generation of dracaena saplings we find signs of a leaning range shift where saplings are shifted towards higher altitudes near the mist-influenced escarpment. A full collapse and eventual extirpation of the endangered Dracaena ombet population may at best be averted, or at least delayed in the study area. Our resilience analysis indicates that a full recovery will be a slow process due to the inherent natural climate variability of arid lands, only allowing sporadic regeneration. Considering this species’ information legacy, saplings seem to be well equipped to survive such variability, but perhaps within a restricted safe operating space. Conservation measures should therefore be taken to secure the survival of the new generation along with broader spatial scale studies to confirm whether our findings reflect a regional phenomenon.

Contrasting interactions of remnant spruce trees with indigenous broadleaves in a partially converted stand from a former plantation

Although important for both restoration and conservation provisions, little is known of the multispecific tree interactions involved in secondary spruce-broadleaf stands undergoing natural conversion from conifer monospecific plantations. We aimed to identify signals of such interactions in a partially converted, 60-year-old stand located in the Eastern Carpathians (northern Romania) and composed of sycamore, ash, maple, and wych elm (hereinafter, SAE), beech and remnant spruce trees.The position and size of all standing tree species individuals at least 1.50 m tall were measured within a 1.5 ha plot. Bivariate spatial pattern analysis, hierarchical Strauss models, and generalised linear squares regression were used for estimating tree neighbourhood interaction and interference.At fine scales, the beech sapling distribution was closely described through opposite models of attraction or inhibition with respect to spruce and SAE trees, respectively. The repulsion detected within the 3 m neighbourhood between SAE and spruce trees translated also in a significant inhibition process. This was in accordance with the negative effect of the nearest spruce on SAE tree growth. The significant segregation and spatial dissociation between beech and SAE trees was very likely related to the negative effect of neighbouring beech veterans on SAE tree diameter. Negative effects on spruce tree growth were only detected through interference with the nearest beech tree.In the given context of site conditions and stand development stage, the observed spatial interdependence and interference patterns were probably determined, to a large extent, by the intense interspecific competition for below-ground resources and light. The remnant spruce trees can act as both growth promoter and inhibitor in relation to the neighbouring beech and SAE trees, respectively. The spruce trees slow down the natural conversion to a mixed SAE stand by contributing to beech dominance, but that will eventually lead through negative feedback to the gradual exclusion of spruce.

Plant functional traits explain species abundance patterns and strategies shifts among saplings and adult trees in Araucaria forests

AbstractSpecies‐rich communities are composed of several locally rare and a few abundant species. A trait‐based approach can derive general explanations for such species abundance distribution. However, for tree species in forests, the intraspecific variation of traits associated with the ontogeny and understory/canopy conditions must be considered. Here, we quantified intraspecific variation of leaf traits across saplings and adults in trees and tested if leaf and/or regenerative traits mediate the species abundance distribution of saplings and adults, and if saplings abundance also determines the abundance of adults in tree communities of Araucaria forests in Southern Brazil. We found intraspecific variation for specific leaf area (SLA) and leaf dry matter content (LDMC), but not for leaf area (LA). Adults have higher LDMC and lower SLA than saplings, suggesting a shift in investment strategies. Species abundant in saplings were associated with larger LA, whereas abundant species in the adults had lower SLA and LA and a larger number of seeds per fruit. The abundance of saplings also contributed to explaining the abundance of species as adults. Saplings experience low light availability in the understory, larger leaves are essential to maximising light capture. On the other hand, adult trees face high irradiation, windy and frost exposure conditions; species with lower SLA reach higher abundance. Regenerative traits were only relevant for the model of adults. Species abundance distribution in forests is related to functional traits, but the relationship is distinct for saplings and adults as leaf traits vary according to the ontogenetic stage and/or the environmental conditions imposed to individuals. In addition, we suggest the assembly of trees in the upper forest stratum is not only mediated by abiotic and biotic filters that favour some leaf and regenerative attributes, but also by lasting effects of variables that filtered out individuals in former development stages.

Density and diameter distributions of saplings in naturally regenerated and planted coniferous stands in Québec after various approaches of commercial thinning

A model describing species composition, density and diameter distribution of saplings was developed from operational inventory data. It could be used as an input into growth models calibrated exclusively with merchantable trees to correct some recruitment bias. Important differences in distributions were found between plantations and naturally regenerated stands. Longer-term monitoring would be required to observe the effects of thinning treatments on saplings. Saplings play important ecological and structural roles in forest stands. They also constitute the pool of candidate trees that are responsible for recruitment of merchantable sized trees. However, sapling information is often absent from regular inventory measurements (e.g. where no saplings are measured) even though they could be used as inputs in predicting recruitment in merchantable trees. The objectives were to develop models describing density and diameter distribution of saplings from operational inventories, e.g. having only merchantable tree inventory, and to evaluate how stand type (naturally regenerated stands and plantations) and various thinning treatments influence these distributions. Using data from both white spruce (Picea glauca [Moench] Voss) plantations and naturally regenerated balsam fir (Abies balsamea (L.) Mill.) stands having been commercially thinned, a zero-inflated poisson regression was used to model the stand density and a gamma regression to predict the two parameters of the Weibull used to characterize the diameter distribution. Despite the fact that the operational inventory data is often limited (e.g. species, dbh, height), the accuracy of the models was good and unbiased. It could be integrated into growth models to complete missing sapling distributions and help to correct some recruitment bias. Important differences in species composition, density and diameter distribution were found between plantations and naturally regenerated stands, but only a moderate response in diameter distribution was observed with thinning treatments. These models will enable managers to estimate saplings in intermediate aged softwood forests of eastern Quebec using harvesting inventories or National Forest Inventory. Characterization of differences between plantations and naturally regenerated stands will be useful for integrating intensive plantation silviculture with ecosystem-based management. Longer-term follow-up would be needed to better evaluate the effects of thinning treatments.

Leaf functional trait variation in a humid temperate forest, and relationships with juvenile tree light requirements.

The species-rich arborescent assemblages of humid tropical forests encompass much of the known range of the leaf economics spectrum, often including >20-fold variation in leaf lifespan. This suite of traits underpins a life-history continuum from fast-growing pioneers to slow-growing shade-tolerant species. Less is known about the range of leaf traits in humid temperate forests, and there are conflicting reports about relationships of these traits with the light requirements of temperate evergreen angiosperms. Here I quantify the range of leaf functional traits in a New Zealand temperate evergreen forest, and relationships of these traits with light requirements of juvenile trees and shrubs. Foliage turnover of saplings of 19 evergreen angiosperms growing beneath gaps (12–29% canopy openness) and in understories (1.2–2.9%) was measured over 12 months. Dry mass per area (LMA), dry matter content, thickness, density and nitrogen content (N) of leaves were also measured. Species minimum light requirements were indexed as the 10th percentile of the distribution of saplings in relation to canopy openness. Interspecific variation of leaf lifespan was ∼6-fold in gaps (0.6 to 3.8 yrs), and ∼11-fold in the understorey (0.7 to 7.7 yrs). Six small tree and shrub species are effectively leaf-exchangers, with leaf lifespans of c.1 year in gaps—albeit usually longer in the shade. Interspecific variation in other leaf traits was 2.5 to 4-fold. Lifespans and LMA of both sun and shade leaves were negatively correlated with species light requirements i.e., positively correlated with shade tolerance. However, light environment (gap vs shade) explained about the same amount of variation in LMA as species’ identity did. Species light requirements were not significantly correlated with leaf N, dry matter content, density or thickness—except for a marginally significant correlation with dry matter content of shade leaves. Species light requirements were thus less consistently related to leaf structural traits than appears to be the case in humid tropical forests. Whereas the wide interspecific variation in leaf economic traits of tropical rainforest species outweighs plastic response to light availability, temperate evergreen woody angiosperms appear to occupy a narrower range of the leaf economic spectrum. Standardization of the light environments in which LMA is measured is vital in comparative studies of humid temperate forest evergreens, because of countergradient responses of this trait to light, and because of the relative magnitudes of plastic and interspecific variation in LMA in these forests.

Upward expansion of distribution ranges of tree species: Contrasting results from two national parks in Western Carpathians

We analysed the distribution of trees along the elevation gradient in two national parks located in the Western Carpathians (49°30′–49°37′ N; 19°28′–20°15′ E), dominated by natural forest stands to answer two questions: do immature trees occur at higher elevations compared to mature ones? Has the upper limit of the distribution of the seedlings increased during the period under study, and were the changes proportional to the increase in the mean annual temperature in that period? Data used in our study had been collected in permanent sample plots, distributed regularly over the entire forest area in two national parks. The measurements were taken twice, separated by at least 12 years. We analysed the upper distribution range of the most abundant tree species following tree ontogenic stages for two measurement times. The analysed tree species showed contrasting patterns of the distributions of saplings related to the distributions of mature individuals. In one of the national parks, two species (Silver fir and European beech) showed a significant upward expansion. As three measurements were taken in this park, we found that the expansion has increased over time. In the second national park, located only 45 km to the west from the first one, we found no upward expansion in the distribution of both European beech and Silver fir, while Sycamore maple showed a slight downward trend. We conclude that the dynamics of the tree distributions along the elevation gradient in the mountain areas do not follow a uniform path; the indirect effects of changes in environmental conditions may produce different patterns, reflecting the complex nature of the interactions shaping the distributions of the trees.

Modeling sapling distribution over time using a functional predictor in a generalized additive model

The effect of adult trees on sapling density distribution during the regeneration fellings is determined in a Pinus sylvestris L. Mediterranean forest using generalized additive models. Spatial pattern of adult trees determines the number of new individuals after regeneration fellings, which modify the light and air temperature under tree canopy. We proposed a novel spatiotemporal model with a functional predictor in a generalized additive model framework to describe nonlinear relationships between the size of the adult trees and the number of saplings of P. sylvestris and to determine if the spatial pattern of the number of saplings remained constant or changed in time. In 2001, two plots (0.5 ha) were set up in two phases of regeneration fellings under the group shelterwood method. We mapped the trees and saplings and measured their diameter and height. The inventories were repeated in 2006, 2010, and 2014. We found a negative association between the diameter of adult trees and number of saplings up to 7–8 m. Beyond these distances, the diameter of adult trees was not associated with the number of saplings. Our results indicate that the spatial pattern of the number of saplings remained quite constant in time. The generalized additive models are a flexible tool to determine the distance range of inhibition of saplings by adult trees.

Life stage, not climate change, explains observed tree range shifts.

Ongoing climate change is expected to shift tree species distribution and therefore affect forest biodiversity and ecosystem services. To assess and project tree distributional shifts, researchers may compare the distribution of juvenile and adult trees under the assumption that differences between tree life stages reflect distributional shifts triggered by climate change. However, the distribution of tree life stages could differ within the lifespan of trees, therefore, we hypothesize that currently observed distributional differences could represent shifts over ontogeny as opposed to climatically driven changes. Here, we test this hypothesis with data from 1435 plots resurveyed after more than three decades across the Western Carpathians. We compared seedling, sapling and adult distribution of 12 tree species along elevation, temperature and precipitation gradients. We analyzed (i) temporal shifts between the surveys and (ii) distributional differences between tree life stages within both surveys. Despite climate warming, tree species distribution of any life stage did not shift directionally upward along elevation between the surveys. Temporal elevational shifts were species specific and an order of magnitude lower than differences among tree life stages within the surveys. Our results show that the observed range shifts among tree life stages are more consistent with ontogenetic differences in the species' environmental requirements than with responses to recent climate change. The distribution of seedlings substantially differed from saplings and adults, while the distribution of saplings did not differ from adults, indicating a critical transition between seedling and sapling tree life stages. Future research has to take ontogenetic differences among life stages into account as we found that distributional differences recently observed worldwide may not reflect climate change but rather the different environmental requirements of tree life stages.

Spatiotemporal strategies that facilitate recruitment in a habitat specialist tree species.

Our understanding of processes underlying plant recruitment emerges from species and habitats that are widely distributed at regional and global scales. However, the applicability of dispersal-recruitment models and the role of dispersal limitation versus microsite limitation have not been examined for specialized habitats. In patchy, freshwater Myristica swamp forests (Western Ghats, India), we examine the roles of primary seed dispersal, secondary seed removal and microsite suitability for the establishment of a swamp specialist tree, Myristica fatua We estimated primary seed shadows, performed secondary removal experiments and enumerated recruits in swamp sites. Steady-state fruiting was observed with the extended production (>7 months) of small numbers of fruits. Frugivores dropped most of the large and heavy seeds under parent crowns, while a few seeds were transported over short distances by hornbills. Seed placement experiments indicated that removal, germination and establishment were similar within swamp microsites, while seeds failed to survive in matrix habitats surrounding the swamp. Crabs, which were major secondary removers of M. fatua, did not alter the initial seed dispersal patterns substantially, which led to the retention of seeds within the swamp. Distribution of saplings and adults from previous seasons also suggest that dispersal-recruitment dynamics in the swamp specialist M. fatua did not strictly follow predictions of Janzen-Connell model while abiotic effects were significant. Large seeds, steady-state fruiting and small crop sizes may be significant selective forces facilitating escape from density and distance-dependent effects in space and time in specialist plant species such as M. fatua.

The role of frugivorous birds and bats in the colonization of cloud forest plant species in burned areas in western Mexico

The extension of montane cloud forests in western Mexico is threatened by several disturbances that limit their extension. In this study we aim to assess the contribution of birds and bats in the dispersal and colonization of cloud–forest plants in contiguous surface–burned pine forests. We sampled seed rain and sapling establishment over one year in two surface–burned sites, which differed in the size of their closest cloud forest patch. A total of 17 plant species were found, most of which were late–successional trees, shrubs and climbers. Distance influenced the seed rain of only one dispersed taxon (Solanum sp.) and had no effect on the sapling distribution of this or other plants. In turn, marked differences were found between sites, with more seeds dispersed and higher sapling density in the site that was next to the larger cloud forest patch. The role of long–distance dispersers and the existence of seed banks before fire could explain the little importance of distance from seed source on seed dispersal and sapling distribution. Nevertheless, dispersal by birds and bats before or after fire facilitates the regeneration and conservation of cloud forests in disturbed areas formerly occupied by other habitats.

Recruitment patterns and potential mechanisms of community assembly in an Andean cloud forest

AbstractQuestionWhat are the conditions necessary for the establishment and development of seedlings and an early stage sapling community in an old‐growth cloud forest? Cloud forests are one of the most threatened ecosystems in the world; however, recruitment patterns in these forests remain largely unknown.LocationCloud Forest, Northern Peruvian Andes.MethodsWe constructed a sapling community model through the unconstrained technique of non‐metric multidimensional scaling. We related the distribution of saplings of each species to the distance from conspecific adult (potential parent) trees through a point pattern analysis. We also used zero‐inflated Poisson models to investigate the relationship between sapling distributions and environmental conditions and forest structure.ResultsWe found that recruitment in woody plant species tends to be widely spread throughout the forest. The distribution of some sapling species was either positively or negatively related to the position of adult conspecific trees. Several species tended to occur within particular microhabitat conditions, with some differentiation between canopy and understorey species.ConclusionsCloud forest species recruitment may require the cover provided by the forest canopy. Under closed canopy conditions, both dispersal assembly and niche assembly mechanisms appear to simultaneously influence sapling distribution. The different strategies of various species may result in a trade‐off between the importance of microhabitat conditions and distance mechanisms, with one prevailing over the other, depending on species and forest structure conditions.

Disentangling the effects of shrubs and herbivores on tree regeneration in a dry Chaco forest (Argentina).

Successful persistence of dry forests depends on tree regeneration, which depends on a balance of complex biotic interactions. In particular, the relative importance and interactive effects of shrubs and herbivores on tree regeneration are unclear. In a manipulative study, we investigated if thornless shrubs have a direct net effect, an indirect positive effect mediated by livestock, and/or an indirect negative effect mediated by small vertebrates on tree regeneration of two key species of Chaco forest (Argentina). In a spatial association study, we also explored the existence of net positive interactions from thorny and thornless shrubs. The number of Schinopsis lorentzii seedlings was highest under artificial shade with native herbivores and livestock excluded. Even excluding livestock, no seedlings were found with natural conditions (native herbivores present with natural shade or direct sunlight) at the end of the experiment. Surprisingly, seedling recruitment was not enhanced under thornless shrubs, because there was a complementary positive effect of shade and interference. Moreover, thornless shrubs had neither positive nor negative effects on regeneration of S. lorentzii. Regeneration of Aspidosperma quebracho-blanco was minimal in all treatments. In agreement with the experiment, spatial distributions of saplings of both tree species were independent of thornless shrubs, but positively associated with thorny shrubs. Our results suggest that in general thornless shrubs may have a negligible effect and thorny shrubs a net positive effect on tree regeneration in dry forests. These findings provide a conceptual framework for testing the impact of biotic interactions on seedling recruitment in other dry forests.

Heterogeneity in soil water and light environments and dispersal limitation: what facilitates tree species coexistence in a temperate forest?

In the present study, we analysed the habitat association of tree species in an old-growth temperate forest across all life stages to test theories on the coexistence of tree species in forest communities. An inventory for trees was implemented at a 6-ha plot in Ogawa Forest Reserve for adults, juveniles, saplings and seedlings. Volumetric soil water content (SMC) and light levels were measured in 10-m grids. Relationships between the actual number of stems and environmental variables were determined for 35 major tree species, and the spatial correlations within and among species were analysed. The light level had no statistically significant effect on distribution of saplings and seedlings of any species. In contrast, most species had specific optimal values along the SMC gradient. The optimal values were almost identical in earlier life stages, but were more variable in later life stages among species. However, no effective niche partitioning among the species was apparent even at the adult stage. Furthermore, results of spatial analyses suggest that dispersal limitation was not sufficient to mitigate competition between species. This might result from well-scattered seed distribution via wind and bird dispersal, as well as conspecific density-dependent mortality of seeds and seedlings. Thus, both niche partitioning and dispersal limitation appeared less important for facilitating coexistence of species within this forest than expected in tropical forests. The tree species assembly in this temperate forest might be controlled through a neutral process at the spatial scale tested in this study.

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.

Estructura de una población del árbol Peltogyne purpurea (Cesalpinaceae) en un bosque intervenido de la Península de Osa, Costa Rica

The regeneration of the rain forest tree Peltogyne purpururea Pittier after selective logging was studied in Mogos, Osa Peninsula, Costa Rica. The distribution of all adult trees of P. purpurea according to diameter at breath height (dbh) categories revealed that the distribution of the adult trees followed a bell-shaped curve. The largest number of individuals was found in the 70 to 80 cm dbh category. We did not find any significant differences in the distribution of saplings around seed-producing trees. There were similar numbers of saplings in the four transects established around each reproductive tree following the four cardinal directions. Overall, the majority of the saplings were found in the first meters around each seed-producing tree. There was another peak in the number of saplings at the distance where the crown of the tree ended. Logging can negatively affect the regeneration of P. purpurea.

Is the Seed Dispersal Related to Spatial Pattern of Individuals in Populations? The Case of Dalbergia cearensis

The spatial distribution of plant species reveals how members of a population are horizontally organized in the environment. Individuals at different development stages can be influenced differently by abiotic and biotic factors because they are temporally separated. This may cause changes in spatial patterns in ontogenetic stages. The objectives of this study were to verify the pattern of spatial distribution of saplings and adults in Dalbergia cearensis Ducke and relate it to the pattern of seed dispersal. In two areas of 4.0 ha each, located in a Private Natural Heritage Reserve (RPPN) “N&atildeo Me Deixes”, there were counted all saplings and adults. This data were applied to the spatial analysis by distance indices, using the software Sadie Shell, version 8.0. The aggregation index (Ia) of adults was significant for both areas and showed aggregated distribution. D. cearensis saplings showed an aggregated distribution in the area I and area II. The dispersion distance was proportional for both areas, and the highest proportion of seeds was 10 - 20 m away from the center of the aggregation. Spatial analysis by distance indices showed an aggregated spatial distribution pattern for saplings and adults of D. cearensis.

Sprouting extends the regeneration niche in temperate rain forests: The case of the long-lived tree Eucryphia cordifolia

Sprouting is a widespread trait of geographical, ecological and taxonomical scales that allows resource exploitation, space colonization, vegetative reproduction and post-disturbance persistence. It is considered that persistence is the most frequent functional role of sprouting in woody plants. Here we propose that niche differentiation between sprouts and saplings extends the regeneration niche to suboptimal conditions for sexual recruitment. To test this hypothesis, we sampled root suckers (sprouts) and saplings of the long-lived tree species Eucryphia cordifolia Cav. in an even-aged coastal temperate rain forest. Canopy openness was measured over each recruit as a proxy of regeneration niche. Sapling survival was checked after two years. The entire forest canopy openness range was used as an estimation of niche availability. Light and microclimatic conditions were recorded for different canopy openness. Sprouts and saplings occupied a narrow range of the canopy openness near to the closest extreme of the gradient (4.8–14.1%). The distribution of saplings was explained by the lower survival of small saplings under more open canopies, as a consequence of the interactive effect of higher evaporative demand and radiation load in more opened canopies. Although the niches of sexual and vegetative recruits slightly overlapped (31% of the interquartile range on average), sprouts inhabit the more opened sites. Therefore, sprouts extend the regeneration niche to suboptimal conditions for sapling establishment. Our results contribute toward explaining the high colonization ability of E. cordifolia in this kind of forest, whose composition is strongly driven by gap dynamics.

Spatial variation of local stand structure in an Abies forest, 45 years after a large disturbance by the Isewan typhoon

Heterogeneity of forest stand structure often results from repeated small disturbances, but structural variation also arises in a stand that has regenerated after a single large stand-replacing disturbance. We explored the structural variation within a subalpine Abies forest in Japan that regenerated after a large typhoon in 1959. In 2004, four 50 × 50 m plots were established at two sites in the regenerated forest. To characterize local stand structure within each plot, we determined the stem density, stand basal area, mean diameter at breast height (DBH), and coefficient of variation (CV) of DBH in 10 × 10 m subplots. We analyzed the spatial distribution pattern of the trees in each subplot using the L(t) function and categorized the distributions as clumped or non-clumped. The analysis revealed marked variation among subplots in the stand's structural characteristics. Although the spatial distribution patterns of the trees in all plots were clumped, 11 of 50 subplots at one site and 39 of 50 subplots at the other site were non-clumped. Subplots with a clumped distribution pattern generally had a smaller basal area, smaller mean DBH, and greater CV of DBH than subplots with the same density but a non-clumped pattern. These results illustrated the spatial heterogeneity of forest structure that can arise in Abies forest that has experienced a large disturbance, probably because of the different densities and distribution of saplings surviving the disturbance and the different forest growth dynamics that result.