Comparative taxonomic structure of the floras of two Mediterranean-climate regions: Iberia and California

Two major events were invoked to understand recent biodiversity patterns in Mediterranean floras: northern hemisphere glaciations and historical human impacts. These two events were considered in this work, where we investigated general patterns in plant species richness and rarity attributes in two different Mediterranean regions: California and Iberia. Our goal was to assess whether comparisons of this sort provided evidence of different extinctions rates, making an effort to decouple anthropogenic from ice age‐related effects in both regions. We employed a taxonomically revised database for eight Mediterranean floras containing information on species richness for 298 families and rarity attributes for 11,834 taxa. We used summary statistics (Gini coefficient) and randomly generated models to test for general patterns of the distribution of diversity within and among taxonomic groups. We then used this general pattern among Mediterranean floras to provide a context in which to evaluate our two focal areas. Results indicated that floras of California and Iberia share the closest taxonomic structure among Mediterranean regions. Differences emerged in rarity attributes and the taxonomic identities of rarity rich groups. These findings were interpreted in the light of Pleistocene changes. In addition, a closer focus on rarity attributes allowed us to pinpoint some segments of these floras where anthropogenic activities may drive variation from general patterns, specifically for rare species in ecologically sensitive habitats.     

Why are ferns regularly over‐represented on state and provincial rare plant lists?

Several recent studies have suggested that rare species are not randomly distributed throughout plant taxa. This would appear to apply to North American ferns, which are frequently over-represented on local lists of rare plant species. However, such lists often paint a skewed portrait of the true situation because of our tendency to recognize the rarity of well-known and charismatic species while ignoring that of lesser-known or less-appreciated species. In order to verify if this over-representation of ferns is a real and consistent trend throughout local floras in North America, we used data from what we consider to be the most complete and objective available database: NatureServe Explorer ( http://www.natureserve.org/explorer/ ). We compiled data on total vascular plant species, total fern species, as well as rare vascular plant species and rare fern species for each North American subnational (Canadian province or US state) flora. Rare species were defined as those belonging to one of NatureServe's 'at risk' categories. The null hypothesis that the contribution of rare ferns to total rare species did not differ from their contribution to the total vascular flora was assessed using χ². Out of 64 subnational floras, we obtained significantly higher values than expected in 28 cases, and significantly lower in only one case. Similar trends hold true for individual fern families. These tendencies could be related to several factors of anthropogenic, biological, climatological, evolutionary, and geographical origin. However, we believe that the main reason is related to scale, namely the geopolitical units at which rarity is often studied. Our results illustrate one of the problems of a parochial approach to conservation, where the perceived rarity of an entire taxon is exaggerated because of the scale at which rarity is addressed.     

Are rare primate taxa specialists or simply less studied?

Aim Rare species are reported to be specialized. However, rare taxa are usually less studied than are common taxa. If so, the reported specialization might be just a result of paucity of records. We here test for this sampling artefact in primates, a taxon in which rarity has been explained by specialization. Location Tropical Africa, Madagascar, Asia, Americas. Methods We define rare and common species as those with geographical range sizes in the lower and upper quartiles, respectively, for primates in each realm. We conducted two independent searches of published literature to determine if there were significantly fewer studies on a common measure of specialization, diet, for rare vs. common species. We then tested for sampling artefact in reported diet breadth by comparing the number of references needed to obtain it for both rare and common species. Results We found, in both literature searches, significantly fewer studies on diet for rare primates – a mode of zero references for rare species, and one for common. By contrast, no significant difference existed for number of references needed to attain the full reported diet breadth: a median of one reference for both specialized, rare and generalized, common species. Main conclusions Rare species are indeed studied less. Nevertheless, the finding that rare primates are specialists is not necessarily mere sampling artefact.     

DIOECISM AND ITS CORRELATES IN THE CAPE FLORA OF SOUTH AFRICA

Floral sexuality is characterized for the flora of the Cape region of South Africa. Among angiosperms (N = 8,497), monostylous hermaphroditism constitutes the largest proportion of species with 77.7%, followed by gynomonoecism (7.1%), dioecism (6.6%), andromonoecism (4.0%), monoecism (2.6%), heterostylous hermaphroditism (1.9%), polygamomonoecism (0.01%) and polygamodioecism (0.01%). The incidence of dioecism is significantly higher (P < 0.001) at the species level for two smaller floras within the Cape flora that consist mostly of species-rich fynbos vegetation (Cape of Good Hope Nature Reserve: 11.6% [N = 1,349], Cape Hangklip: 9.7% [N = 1,046]). The relatively high incidence of dioecism in all three floras compared to other temperate floras is due to the large number of Restionaceae species. Excluding these rush-like plants, dioecism at the species level is only 3.0% for the Cape flora, 4.2% for the Cape Hangklip flora and 3.6% for the Cape of Good Hope flora. At the generic level there are no significant differences in the incidence of dioecism between the three floras. Among dioecious species and genera in the Cape flora, there is a higher than expected incidence of wind pollination, fleshy fruits and nonwoodiness when each variable is analyzed independently. The association between nonwoodiness and dioecy has not been reported for other floras and is due to the large proportion of nonwoody wind-pollinated Restionaceae. If this family is excluded from the analysis, dioecy becomes associated with biotic pollination, fleshy fruits, and woodiness. Interactions among the variables themselves as well as with dioecism indicate the need for a joint analysis of the variables. At the genus level, analyses reveal the following: 1) There is a higher than expected incidence of wind pollination among dioecious plants with dry fruits. If the Restionaceae are excluded from the analysis, wind pollination is more common than expected only for woody plants with dry fruits. 2) Dioecious plants that are biotically pollinated have a significantly higher incidence of fleshy fruits than expected. 3) Dioecious plants with dry fruits that are biotically pollinated have a higher than expected incidence of woodiness. If the Restionaceae are excluded from the analysis, woodiness is more common than expected among both nonwind and wind-pollinated dioecious genera.     

Allozyme variation in Atlantic salmon from the British Isles: associations with geography and the environment

Data on geographical variation in allele frequencies at enzyme coding loci in Atlantic salmon from the British Isles were collated from published and unpublished sources. Statistically significant differences in allele frequencies were found among samples both within and among river systems, suggesting that the Atlantic salmon in the British Isles is not a panmictic population and that even within major river systems it cannot be treated as a single genetic stock for fisheries management purposes. Although there was some evidence of regional differences in the frequency of some rare alleles, most single‐locus variation did not show strong geographic patterns, with the exception of the AAT‐4 * locus at which allele frequencies had a significant latitudinal cline. There was some evidence for the existence of genetically‐distinct celtic and boreal races of Atlantic salmon in the British Isles as previously has been suggested. Multiple regression analyses revealed associations between genetic variation and local environmental conditions ( i.e . between variation at MEP‐2 * and both temperature and local river gradient), providing additional evidence for adaptive population divergence in the species.     

Common species have lower taxonomic diversity Evidence from the urban floras of Brussels and Rome

The species pool hypothesis claims that the large‐scale regional species pool is the chief parameter in determining small‐scale species richness through filtering of species that can persist within a community on the basis of their tolerance of the abiotic environment. Accordingly, different environmental conditions give rise to different species assemblages. From a taxonomic perspective, under the assumption of trait conservatism, co‐occurring species that experience similar environmental conditions are likely to be more taxonomically similar than ecologically distant species. The next step consists in understanding how commonness and rarity of individual species produce the observed taxonomic diversity. In this paper, the importance of environmental filtering in regulating the taxonomic structure of rare and common plant species in the urban floras of Brussels (Belgium) and Rome (Italy) is tested. First, we computed the taxonomic diversity of the rare and common species of Brussels and Rome based on the branching topology of the Linnaean taxonomic trees. Next, using a randomization procedure, we determined whether the taxonomic diversity of the rare species was significantly higher than the diversity of the common species. Results show that, for both urban floras, common species that shape the community matrix and experience similar environmental conditions have a taxonomic diversity that is significantly lower than that of the rare species that represent a relatively incidental set of species of more ‘disperse’ origin. Finally, from a conservation/management perspective our results imply that, given their high taxonomic heterogeneity, the protection of rare species is a central issue for preserving high levels of diversity in urban areas.     

Patterns and correlates of plant diversity differ between common and rare species in a neotropical dry forest

Determining which factors affect species richness is important for conservation theory and practice. However, richness of common and rare species may be affected by different factors. We use an extensive inventory of woody plants from a tropical dry forest landscape in Yucatan, Mexico to assess the unique effects of environmental variables, spatial dependence of sampling sites, forest stand age and the combined effect of all groups of variables on species richness of woody plants with different levels of rarity (common, intermediate, rare, very rare)—according to their abundance, habitat specificity and spatial distribution range in the landscape. Analyzing separately common species and those with different levels of rarity uncovered contrasting patterns and correlates of species richness that were not apparent when focusing on all woody plants. In particular, richness of common and intermediate species was influenced mainly by environmental factors, whereas richness of very rare species was affected mostly by the unique effect of spatial dependence of sampling sites, suggesting a main role of environmental filtering and dispersal limitation, respectively. However, common and very rare species also responded inversely to some landscape metrics, revealing contrasting environmental preferences of these groups of species. These contrasting results suggest different underlying mechanisms and the need for very different conservation strategies. Therefore, basic and applied research on tropical forest biodiversity should consider separately species with different levels of rarity, focusing on which factors control variation in each level, and paying special attention to very rare species, generally the most specious and vulnerable to local extinction.     

Incidence of dioecy in relation to growth form,pollination and dispersal

Summary Recent theories predict the evolution of dioecy among higher plants, in association with certain pollination and fruit dispersal traits. However, reported associations of dioecy with pollination, dispersal and growth form traits have not distinguished the effects of each trait separately, controlling for the others. Because these traits are associated among themselves, existing analyses may involve spurious or indirect correlations. This paper reports the incidence of dioecy in a subarctic and an arctic flora, and analyzes the occurrence of dioecy among vascular plants classified jointly by growth form, floral (pollination) syndrome, and fruit (dispersal) syndrome. Dioecism is no more frequent in the arctic flora as a whole, but its incidence increases northward among woody plants. This increase is associated with an increase in the proportion of woody species having small, inconspicuous flowers, and not with the syndrome of fleshy or animal dispersed fruits. Within the floras of Alaska, California, and the Northeastern US, dioecy is markedly more frequent among woody plants and among plants having small, inconspicuous flowers, and that is the only strong statistical association of dioecy for the species of these floras. When genera and families are analyzed similarly, dioecy is also associated significantly with dispersal syndrome. Thus, among angiosperms, evidence currently does not support either an uniquely strong or exclusive association of dioecy with dispersal traits, as it does for gymnosperms (Givnish 1980). It is extremely desirable to analyze the occurrence of dioecy among taxa classified jointly by all relevant ecological traits, rather than analyzing marginal distributions.     

Contribution of rarity and commonness to patterns of species richness in biogeographic transitions regions: Woody plants of Uruguay

There is a growing body of evidence suggesting that widespread (i.e. common) rather than geographically restricted species (i.e. rare) shape the overall distribution patterns of species richness. This is a non‐intuitive fact, given that local and regional assemblages are normally composed by numerous rare species and few common ones. We evaluated here the primacy of common species in a biogeographic transition zone, where rarity has frequently a higher incidence. We analysed the geographical variability of trees and shrubs in Uruguay, located in a transitional zone between prairie and forest biomes, to assess the relative contribution of rare and common species to the generation of richness patterns. The distribution of 301 species of the native woody assemblage of Uruguay was mapped over the national grid system (302 quadrants of approximately 22 × 30 km), using published data and herbarium records. The overall assemblage was segregated into four subassemblages in function of species distribution (quartiles). Species richness in the four quartiles was positively correlated with overall richness, but common species (quartile 3) showed the highest level of correlation. Then, we ranked species from the most widespread to the most restricted (common‐to‐rare) and from the most restricted to the most widespread (rare‐to‐common). Along each stage of the sequences we obtained a series of species richness patterns for increasing numbers of species. Correlating the species richness pattern for each subassemblage of both sequences with that of the full assemblage, we also found higher correlations in the common‐to‐rare sequence. We conclude the Uruguayan woody plants assemblage has a very large number of rare species as expected for a transitional biogeographical zone, but it was the common species that contributed most to the overall pattern of species richness. We propose the low contribution of rare species is explained by the most interspecific variability in ecological determinants within the assemblage of rare species. Therefore the spatial covariance among rare species is low, and so is the relationship with overall species richness.     

Patterns of commonness and rarity in central European birds: reliability of the core-satellite hypothesis within a large scale

The frequency distribution of species’ area of occupancy is often bimodal, most species being either very rare or very common in terms of number of occupied sites. This pattern has been attributed to the nonlinearity associated with metapopulation dynamics of the species, but there are also other explanations comprising sampling artifact and frequency distribution of suitable habitats. We tested whether the bimodal frequency distribution of occupied squares in central European birds could be derived solely from the frequency distribution of species population sizes (i.e. the sampling artifact hypothesis) or from the spatial distribution of their preferred habitats. Both models predict high proportion of very common species, i.e. the right side of frequency distribution. Bimodality itself is well predicted by models based on random placement of individuals according to their abundances but neither model predicts the observed prevalence of rare species. Even the combined models that assume random placement of individuals within the squares with suitable habitat do not predict such a high proportion of rare species. The observed distribution is more aggregated, rare species occupying a smaller portion of suitable habitat than predicted on the basis of their abundance. The pattern is consistent with metapopulation processes involving local population extinctions. The involvement of these processes is supported by two further observations. First, species rarity is associated with significant population trend and/or location on the edge of their ranges within central Europe, both situations presumably associated with metapopulation processes. Second, suitable habitats seem to be either saturated or almost unoccupied, which is consistent with the predictions of the metapopulation model based on nonlinear dynamics of extinction and colonization. Although the habitat suitability is an important determinant of species distribution, the rarity of many species of birds within this scale of observation seems to be affected by other factors, including local population extinctions associated with fragmentation of species’ habitats.     

Why Some Plant Species Are Rare

Biodiversity, including plant species diversity, is threatened worldwide as a result of anthropogenic pressures such as an increase of pollutants and climate change. Rare species in particular are on the verge of becoming extinct. It is still unclear as to why some plant species are rare and others are not. Are they rare due to: intrinsic reasons, dispersal capacity, the effects of management or abiotic circumstances? Habitat preference of rare plant species may play an important role in determining why some species are rare. Based on an extensive data set of soil parameters we investigated if rarity is due to a narrow habitat preference for abiotic soil parameters. For 23 different abiotic soil parameters, of which the most influential were groundwater-table, soil-pH and nutrient-contents, we estimated species responses for common and rare species. Based on the responses per species we calculated the range of occurrence, the range between the 5 and 95 percentile of the response curve giving the habitat preference. Subsequently, we calculated the average response range for common and rare species. In addition, we designed a new graphic in order to provide a better means for presentation of the results. The habitat preferences of rare species for abiotic soil conditions are significantly narrower than for common species. Twenty of the twenty-three abiotic parameters showed on average significantly narrower habitat preferences for rare species than for common species; none of the abiotic parameters showed on average a narrower habitat preference for common species. The results have major implications for the conservation of rare plant species; accordingly management and nature development should be focussed on the maintenance and creation of a broad range of environmental conditions, so that the requirements of rare species are met. The conservation of (abiotic) gradients within ecosystems is particularly important for preserving rare species.     

The role of frugivory in plant diversity maintenance – a simulation approach

Frugivores may play a key role in plant species coexistence by equalizing the species’ representation in the seed rain. Rare species may benefit from enhanced dispersal if frugivores prefer locally scarce fruits, or if rare plants are found in neighborhoods of high fruit density. Using a simulation model of frugivorous birds foraging on landscapes we tested if increased diversity in the seed rain could emerge from rare‐biased fruit selection, from the spatial configuration of plants, or both. In the absence of rare‐biased fruit selection, frugivores were not able to increase the diversity of the seed rain in any of our simulated landscapes. In contrast, when frugivores were attracted to locally scarce fruits, we found increased diversity in the seed rain whenever frugivore mobility across the landscape was high and plant species were well‐mixed in the fruiting neighborhoods. Irrespectively of the behavioral mechanism involved, landscape fragmentation lead to losses in diversity and species richness of simulated communities. In all simulations, density‐dependent mortality of dispersed seeds increased diversity in the community of seedlings. However, landscape homogenization at the scale of frugivores movements decreased the magnitude of this diversification effect. In summary, our study shows that frugivory has the potential to increase diversity in the seed rain when frugivores display rare‐biased fruit choices, provided that rare and common plants form heterogeneous neighborhoods. They also show that fragmentation is a major threat for diversity maintenance in the early‐regenerating community. Finally, they show that rarity confers advantages during regeneration only if it occurs at the scale of frugivores’ foraging decisions.     

Distribution trends of rare vascular plant species in Estonia

On the basis of quantitative analysis of the vascular plant distribution maps for Estonia, we specified the list of rare species which occur in less than 5% of grid quadrangles, and studied the possible correlations between their rarity and habitat preference, distribution, and sensitivity to human impact. Rare species occur statistically more often among species that are at the limit of their geographical range. The proportion of rare species was significantly higher among arctomontane and disjunct circumpolar taxa. Among apophytes, there were less rare taxa than would be expected according to the common native flora, but among hemerophobes, there were significantly more rare species than would be expected. The number of rare species was in strong positive correlation with the species richness of the region. Besides the western part of Estonia, where the greatest number of rare species occur, some small areas rich in rare species also lie in East and North Estonia.     

Phylogenetic and phenotypic originality and abundance in a cerrado plant community

The originality of a species is how much that species contributes to the rarity of traits in a community. Here we tested the relation between abundance and both phylogenetic and phenotypic originality. We measured nine traits associated with defence against herbivory, as well as phylogenetic information and abundance for woody plant species in a woodland cerrado in southeastern Brazil. About 90% of the species accounted for about 50% of the phylogenetic and phenotypic originality: most woody species had low originality. Abundance was related to tougher leaves, lower specific leaf area and lower originality based on nutritional quality. Our results suggest that herbivory may reduce the abundance of species with low resistance to herbivory and with different nutritional quality. Nevertheless, abundance was not related to either phylogenetic or phenotypic originality, so extinction of rare species may not endanger overall community function as long as more abundant species are retained. We argue that this is a consequence of the low complementarity of a large number of woody species.     

Effects of contemporary environment and Quaternary climate change on drylands plant diversity differ between growth forms

Previous studies on large‐scale patterns in plant richness and underlying mechanisms have mostly focused on forests and mountains, while drylands covering most of the world's grasslands and deserts are more poorly investigated for lack of data. Here, we aim to 1) evaluate the plant richness patterns in Inner Asian drylands; 2) compare the relative importance of contemporary environment, historical climate, vegetation changes, and mid‐domain effect (MDE); and 3) explore whether the dominant drivers of species richness differ across growth forms (woody vs herbaceous) and range sizes (common vs rare). Distribution data and growth forms of 13 248 seed plants were compiled from literature and species range sizes were estimated. Generalized linear models and hierarchical partitioning were used to evaluate the relative contribution of different factors. We found that habitat heterogeneity strongly affected both woody and herbaceous species. Precipitation, climate change since the mid‐Holocene and climate seasonality dominated herbaceous richness patterns, while climate change since the Last Glacial Maximum dominated woody richness patterns. Rare species richness was strongly correlated with precipitation, habitat heterogeneity and historical climatic changes, while common species richness was strongly correlated with MDE (woody) or climate seasonality (herbaceous). Temperature had little effects on the species richness patterns of all groups. This study represents the first evaluation of the large‐scale patterns of plant species richness in the Inner Asian drylands. Our results suggest that increasing water deficit due to anthropogenic activities combined with future global warming may increase the extinction risk of many grassland species. Rare species (both herbaceous and woody) may face severe challenges in the future due to increased habitat destruction caused by urbanization and resource exploitation. Overall, our findings indicate that the hypotheses on species richness patterns based on woody plants alone can be insufficient to explain the richness patterns of herbaceous species.     

Commonness,rarity, and oligarchies of woody plants in the tropical dry forests of Mexico

We assessed woody plant communities in two widely separated forests in the tropical dry forest (TDF) biome of Mexico for evidence of similar patterns of species commonness and rarity. We used belt transects laid out along contour lines (i.e., constant elevation) and stratified across elevation gradients at sites in Jalisco and Oaxaca to sample woody plant species diversity, abundance, relative frequency and basal area. We assembled a combined species list and compared species found in both sites (shared) to species found in only one site, assessing whether the most and least common species at a site tended to be shared or unshared. Of the 8242 individuals sampled, 370 species or morpho‐species were identified, with 222 species recorded at the Jalisco site and 270 at the Oaxaca site—122 (33%) species were shared across sites. Abundance, frequency and basal area of shared species were greater on average than for unshared species, and were positively correlated across sites. A subset of 68 shared species (18%) accounted for over half of all individuals encountered at the two sites. Species in the most common quartile were more likely to be shared than expected by chance, while species in the least common quartile were less likely. A genus‐level analysis found similar patterns. Our findings suggest that the TDF of Pacific coast Mexico shows evidence of widespread dominance by a small subset of species. These findings have potentially important implications for predicting species composition, understanding the role of oligarchic species in ecological processes, and conserving rare species.     

Patterns of rare woody species richness: the influence of environment, landscape attributes and spatial structure across different spatial scales

The aim of this study was to evaluate the relative contributions of the environment, landscape patterns, and spatial structure to explaining the variation in richness of rare woody species at three levels of rarity (low, medium, and high) and at different grain sizes and spatial extents. We used herbarium records of 195 rare woody species to quantify species richness—overall and for three levels of rarity—of the Yucatan Peninsula, Mexico. We assessed relationships between rare species richness and different sets of explanatory variables (environmental, landscape patterns, and spatial structure of sampling units) using linear regression and variation partitioning analyses at three grain sizes (625, 400, and 225 km²). We also conducted a principle coordinates of neighbor matrices analysis to allow interpretation of the results in terms of different spatial extents. The percentage of variation in rare species richness explained by the models was highest for the largest grain size and spatial extent. At the larger extents, rare species richness was explained mainly by the environment, whereas landscape patterns played a more prominent role at the local extent. Landscape patterns also contributed more to explaining species richness at low to medium levels of rarity, whereas the richness of extremely rare species was better explained by spatial structure. We conclude that the relative contribution of the factors explaining the variation of rare species richness depends on both grain and extent, as well as on the level of rarity. These results underscore the importance of considering the different components of scale (grain and extent) as well as different levels of species rarity in order to better understand the patterns of distribution of rare species richness and to be able to frame appropriate conservation strategies.     

Wider spectrum of fruit traits in invasive than native floras may increase the vulnerability of oceanic islands to plant invasions

Plant–animal mutualisms such as seed dispersal can play an important role in enabling some species to become invasive. For example, an introduced species could become invasive because birds prefer its fruits to those of native plants. To investigate this possibility, we compared various measures of fruit quality of 22 of the most common native and invasive woody species on the oceanic island Mahé (Seychelles, Indian Ocean). Individual measures of food quality tended to vary much more amongst invasive species than amongst native species; thus, whereas for particular traits the fruits of some invasive species had higher values than any native species, others had relatively low values. However, invasive species consistently produced fruits with a lower water content, resulting in a higher relative yield (i.e. dry pulp weight to total wet fruit weight ratio), and a higher energy content. The fruits of the most abundant invasive tree Cinnamomum verum (Lauraceae) were of particularly high nutritional quality, with individual berries containing 3.5 times more protein and 55 times more lipid than the median values of the native species. We suggest that our results may reflect a general tendency for island plants to produce fruits of low energy content, perhaps reflecting reduced competition for dispersal agents on isolated islands. In addition, we argue that inconsistent results on the relevance of fruit quality for plant invasions reported in the literature may be resolved by comparing the widths of trait spectra for native and alien floras rather than average values. Gaps in the native fruit trait spectrum may provide opportunities for particular invasive species, and weaken the resistance of regional floras to invasions. Such empty niche opportunities may occur for several reasons, including generally broader trait spectra in globally assembled alien than regional native floras (especially on oceanic islands), or the loss of native species due to human activities. More generally, a focus on trait variation rather than average trends may help to advance generalisation in invasion biology.     

Patterns of plant sexual systems in subtropical evergreen broad-leaved forests in Ailao Mountains,SW China

Aims Sexual systems influence many components of the ecology and evolution of plant populations and have rarely been documented in subtropical evergreen broad-leaved forests (SEBLF). Here we report frequency distribution and ecological correlates of plant sexual systems in SEBLF at Ailao Mountains, and compare our results with that of tropical and cool temperate forests.Methods We examine the sexual systems of 703 species of woody angiosperms belonging to 103 families and 296 genera based on a comprehensive survey of SEBLF at Ailao Mountains Natural Reserve. Information of plant sexual systems and ecological traits were mainly based on published literatures and specimens as well as our field observations. The associations between plant sexual system and ecological traits were assessed with chi-square tests.Important findings Among these species, 60.2% were hermaphroditic, 15.8% were monoecious and 24.0% were dioecious. The percentage of dioecious sexual system among tree species (22.2%) in SEBLF was comparable to those of tropical tree floras, but much higher than those of temperate forests at North America. The percentage of monoecious sexual system among tree species (30.1%) in SEBLF was higher than that of tropical tree floras, but much lower than those of temperate forests at North America. Monoecy was significantly associated with the tree growth form and was relatively common in temperate genera. Dioecy was significantly associated with fleshy fruits and monoecy was significantly associated with dry fruit type in SEBLF. The high percentage of diclinous sexual systems (monoecy and dioecy) in SEBLF may be associated with the origin of the flora and the prevalence of relatively small inconspicuous flowers of the forests in the Oriental Region.