Down-regulation of photosynthesis and its relationship with changes in leaf N allocation and N availability after long-term exposure to elevated CO2 concentration.

Down-regulation of photosynthesis under elevated CO2 (eCO2) concentrations could be attributed to the depletion of nitrogen (N) availability after long-term exposure to eCO2 (progressive nitrogen limitation, PNL) or leaf N dilutions due to excessive accumulation of nonstructural carbohydrates. To determine the mechanism underlying this down-regulation, we investigated N availability, photosynthetic characteristics, and N allocation in leaves of Pinus densiflora (shade-intolerant species, evergreen tree), Fraxinus rhynchophylla (intermediate shade-tolerant species, deciduous tree), and Sorbus alnifolia (shade-tolerant species, deciduous tree). The three species were grown under three different CO2 concentrations in open-top chambers, i.e., ambient 400 ppm (aCO2); ambient × 1.4, 560 ppm (eCO21.4); and ambient × 1.8, 720 ppm (eCO21.8), for 11 years. Unlike previous studies that addressed PNL, after 11 years of eCO2 exposure, N availability remained higher under eCO21.8, and chlorophyll and photosynthetic N use efficiency increased under eCO2. In the case of nonstructural carbohydrates, starch and soluble sugar showed significant increases under eCO2. The maximum carboxylation rate, leaf N per mass (Nmass), and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) were low under eCO21.8. The ratio of RuBP regeneration to the carboxylation rate as well as that of chlorophyll N to Rubisco N increased with CO2 concentrations. Based on the reduction in Nmass (not in Narea) that was diluted by increase in nonstructural carbohydrate, down-regulation of photosynthesis was found to be caused by the dilution rather than PNL. The greatest increases in chlorophyll under eCO2 were observed in S. alnifolia, which was the most shade-tolerant species. This study could help provide more detailed, mechanistically based processes to explain the down-regulation of photosynthesis by considering two hypotheses together and showed N allocation seems to be flexible against changes in CO2 concentration.

Physiological and transcriptomic analyses characterized high temperature stress response mechanisms in Sorbus pohuashanensis.

Sorbus pohuashanensis (Hance) Hedl. is a Chinese native alpine tree species, but the problem of introducing S. pohuashanensis to low altitude areas has not been solved. In this study, we aimed to explore the molecular regulatory network of S. pohuashanensis in response to high-temperature stress using RNA-Sequencing technology and physiological and biochemical determination. Based on transcriptomic data, we obtained 1221 genes (752 up-regulated and 469 down-regulated) that were differentially expressed during 8 h 43℃ treatment and candidate genes were related to calcium signaling pathway, plant hormone signal transduction, heat shock factors, chaperones, ubiquitin mediated proteolysis, cell wall modification, ROS scavenging enzymes, detoxification and energy metabolism. The analysis of high temperature response at the physiological level and biochemical level were performed. The chlorophyll fluorescence parameters of leaf cells decreased, the content of osmotic regulators increased, and the activity of ROS scavenging enzymes decreased. The molecular regulatory network of S. pohuashanensis in response to high-temperature stress was preliminarily revealed in this study, which provides fundamental information improving introducing methods and discovering heat-tolerant genes involved in high-temperature stress in this species and provides a reference for other plants of the genus Sorbus.

The nature and way of root adaptation of juvenile woody plants Sorbus and Pyrus to drought.

The functional root traits of Pyrus pyraster (L.) Burgsd. and Sorbus domestica L. during early growth stages were evaluated. The aim of the study was to identify the functional traits of root systems that determine the adaptability of these woody species to drought conditions. The experiment was carried out under the controlled environment of a growth chamber. The root systems were analyzed using WinRhizo software. Several functional root traits were identified, including specific root length, root surface area, root length, root volume, root-to-shoot mass ratio (R:S), fine root (ϕ ˂ 2 mm) volume, coarse root (ϕ > 2 mm) volume, and fine-to-coarse root volume ratio (F/C). In drought, P. pyraster maintained the absorptive root surface unchanged, when increased the volume of the fine root fraction. The different strategy of adaptation to drought has been confirmed for S. domestica, which accumulated more dry mass in the root system in comparison to aboveground organs (significant increase of R:S ratio). The functional root traits analyzed here were species-dependent. The key functional traits that indicate the responses of studied tree taxa to drought conditions include root thickening, F/C, and R:S. Increased values of these parameters indicate the investment of the plant towards root extension. A higher proportion of fine roots increases the absorbing surface of the root system, thereby promoting water uptake from the soil.

Environmental Veto Synchronizes Mast Seeding in Four Contrasting Tree Species.

Synchronized and variable reproduction by perennial plants, called mast seeding, is a major reproductive strategy of trees. The need to accumulate sufficient resources after depletion following fruiting (resource budget), the efficiency of mass flowering for outcross pollination (pollen coupling), or the external factors preventing reproduction (environmental veto) could all synchronize masting. We used seed production data for four species (Quercus ilex, Quercus humilis, Sorbus aucuparia, and Pinus albicaulis) to parametrize resource budget models of masting. Based on species life-history characteristics, we hypothesized that pollen coupling should synchronize reproduction in S. aucuparia and P. albicaulis, while in Q. ilex and Q. humilis, environmental veto should be a major factor. Pollen coupling was stronger in S. aucuparia and P. albicaulis than in oaks, while veto was more frequent in the latter. Yet in all species, costs of reproduction were too small to impose a replenishment period. A synchronous environmental veto, in the presence of environmental stochasticity, was sufficient to produce observed variability and synchrony in reproduction. In the past, vetoes like frost events that prevent reproduction have been perceived as negative for plants. In fact, they could be selectively favored as a way to create mast seeding.

Breeding system and spatial isolation from congeners strongly constrain seed set in an insect-pollinated apomictic tree: Sorbus subcuneata (Rosaceae).

In plants, apomixis results in the production of clonal offspring via seed and can provide reproductive assurance for isolated individuals. However, many apomicts require pollination to develop functional endosperm for successful seed set (pseudogamy) and therefore risk pollination-limitation, particularly in self-incompatible species that require heterospecific pollen. We used microsatellite paternity analysis and hand pollinations to investigate pollen-limitation in Sorbus subcuneata, a threatened endemic tree that co-occurs with its congener, S. admonitor. We confirmed that S. subcuneata is an obligate pseudogamous apomict, but open-pollinated flowers rarely produced seed (flower-to-seed conversion < 1%) even though they rapidly accumulated pollen on their stigmas. Manual heterospecific pollination by S. admonitor resulted in a high flower-to-seed conversion rate (65%), however, we estimate that the ratio of self: heterospecific pollination in open-pollinated flowers was at least 22:1. Despite the efficacy of heterospecific pollination, the contribution of S. admonitor trees to paternity in seed from open-pollinated flowers of S. subcuneata decreased rapidly with the spatial separation between paternal and maternal trees. Conservation efforts aimed at maintaining species with this breeding system must therefore manage the congeners in tandem which will also maintain the potential for rare heterospecific fertilisation that typically cause rapid diversification in these lineages.

When sexual meets apomict: genome size, ploidy level and reproductive mode variation of Sorbus aria s.l. and S. austriaca (Rosaceae) in Bosnia and Herzegovina.

BACKGROUND AND AIMS: Allopolyploidy and intraspecific heteroploid crosses are associated, in certain groups, with changes in the mating system. The genus Sorbus represents an appropriate model to study the relationships between ploidy and reproductive mode variations. Diploid S. aria and tetraploid apomictic S. austriaca were screened for ploidy and mating system variations within pure and sympatric populations in order to gain insights into their putative causalities. METHODS: Flow cytometry was used to assess genome size and ploidy level among 380 S. aria s.l. and S. austriaca individuals from Bosnia and Herzegovina, with 303 single-seed flow cytometric seed screenings being performed to identify their mating system. Pollen viability and seed set were also determined. KEY RESULTS: Flow cytometry confirmed the presence of di-, tri- and tetraploid cytotype mixtures in mixed-ploidy populations of S. aria and S. austriaca. No ploidy variation was detected in single-species populations. Diploid S. aria mother plants always produced sexually originated seeds, whereas tetraploid S. austriaca as well as triploid S. aria were obligate apomicts. Tetraploid S. aria preserved sexuality in a low portion of plants. A tendency towards a balanced 2m : 1p parental genome contribution to the endosperm was shared by diploids and tetraploids, regardless of their sexual or asexual origin. In contrast, most triploids apparently tolerated endosperm imbalance. CONCLUSIONS: Coexistence of apomictic tetraploids and sexual diploids drives the production of novel polyploid cytotypes with predominantly apomictic reproductive modes. The data suggest that processes governing cytotype diversity and mating system variation in Sorbus from Bosnia and Herzegovina are probably parallel to those in other diversity hotspots of this genus. The results represent a solid contribution to knowledge of the reproduction of Sorbus and will inform future investigations of the molecular and genetic mechanisms involved in triggering and regulating cytotype diversity and alteration of reproductive modes.

Tree species composition affects the abundance of rowan (Sorbus aucuparia L.) in urban forests in Finland.

Recent studies have shown a considerable increase in the abundance of rowan (Sorbus aucuparia) saplings in urban forests in Finland, yet the reasons for this increase are not well understood. Here we investigated whether canopy cover or tree species composition, i.e., the basal areas of different tree species in Norway spruce dominated urban forests, affects the abundances of rowan seedlings, saplings and trees. Altogether 24 urban forest patches were investigated. We sampled the number of rowan and other saplings, and calculated the basal areas of trees. We showed that rowan abundance was affected by tree species composition. The basal area of rowan trees (≥ 5 cm in diameter at breast height, dbh) decreased with increasing basal area of Norway spruce, while the cover of rowan seedlings increased with an increase in Norway spruce basal area. However, a decrease in the abundance of birch (Betula pendula) and an increase in the broad-leaved tree group (Acer platanoides, Alnus glutinosa, Alnus incana, Amelanchier spicata, Prunus padus, Quercus robur, Rhamnus frangula and Salix caprea) coincided with a decreasing number of rowans. Furthermore, rowan saplings were scarce in the vicinity of mature rowan trees. Although it seems that tree species composition has an effect on rowan, the relationship between rowan saplings and mature trees is complex, and therefore we conclude that regulating tree species composition is not an easy way to keep rowan thickets under control in urban forests in Finland.

Stem CO2 efflux in six co-occurring tree species: underlying factors and ecological implications.

Stem respiration plays a role in species coexistence and forest dynamics. Here we examined the intra- and inter-specific variability of stem CO2 efflux (E) in dominant and suppressed trees of six deciduous species in a mixed forest stand: Fagus sylvatica L., Quercus petraea [Matt.] Liebl, Quercus pyrenaica Willd., Prunus avium L., Sorbus aucuparia L. and Crataegus monogyna Jacq. We conducted measurements in late autumn. Within species, dominants had higher E per unit stem surface area (Es ) mainly because sapwood depth was higher than in suppressed trees. Across species, however, differences in Es corresponded with differences in the proportion of living parenchyma in sapwood and concentration of non-structural carbohydrates (NSC). Across species, Es was strongly and NSC marginally positively related with an index of drought tolerance, suggesting that slow growth of drought-tolerant trees is related to higher NSC concentration and Es . We conclude that, during the leafless period, E is indicative of maintenance respiration and is related with some ecological characteristics of the species, such as drought resistance; that sapwood depth is the main factor explaining variability in Es within species; and that the proportion of NSC in the sapwood is the main factor behind variability in Es among species.

Seasonal patterns of leaf photosynthetic and secondary xylem vascular traits in current-year stems of three Sorbus species with contrasting growth habits.

Seasonal effects of environmental variables on photosynthetic activity and secondary xylem formation provide data to demonstrate how environmental factors together with leaf ageing during the season control tree growth. In this study, we assessed physiological responses in photosynthetic behaviour to seasonal climate changes, and also identified seasonal differences in vascular traits within differentiating secondary xylem tissue from three diploid species of the taxonomically complex genus Sorbus. From sampling day 150, a clear physiological segregation of S. chamaemespilus from S. torminalis and S. aria was evident. The shrubby species S. chamaemespilus could be distinguished by a higher photosynthetic capacity between days 150 and 206. This was reflected in its associations with net CO2 assimilation rate (PN), maximum photochemical efficiency of PSII (F(v)/F(m)), variable-to-initial fluorescence ratio (F(v)/F(0)), potential electron acceptor capacity ('area') in multivariate space, and also its associations with log-transformed vessel area and log-transformed relative conductivity between days 239 and 268. The maximum segregation and differentiation among the examined Sorbus species was on sampling day 206. The largest differences between S. torminalis and S. aria were found on day 115, when the latter species clearly showed closer associations with high values of vessel density and transpiration (E). Sampling day clusters were arranged along an arch-like gradient that reflected the positioning of the entire growing season in multivariate space. This arch-like pattern was most apparent in the case of S. chamaemespilus, but was also observed in S. torminalis and S. aria.

Patterns of evolution at the gametophytic self-incompatibility Sorbus aucuparia (Pyrinae) S pollen genes support the non-self recognition by multiple factors model.

S-RNase-based gametophytic self-incompatibility evolved once before the split of the Asteridae and Rosidae. In Prunus (tribe Amygdaloideae of Rosaceae), the self-incompatibility S-pollen is a single F-box gene that presents the expected evolutionary signatures. In Malus and Pyrus (subtribe Pyrinae of Rosaceae), however, clusters of F-box genes (called SFBBs) have been described that are expressed in pollen only and are linked to the S-RNase gene. Although polymorphic, SFBB genes present levels of diversity lower than those of the S-RNase gene. They have been suggested as putative S-pollen genes, in a system of non-self recognition by multiple factors. Subsets of allelic products of the different SFBB genes interact with non-self S-RNases, marking them for degradation, and allowing compatible pollinations. This study performed a detailed characterization of SFBB genes in Sorbus aucuparia (Pyrinae) to address three predictions of the non-self recognition by multiple factors model. As predicted, the number of SFBB genes was large to account for the many S-RNase specificities. Secondly, like the S-RNase gene, the SFBB genes were old. Thirdly, amino acids under positive selection-those that could be involved in specificity determination-were identified when intra-haplotype SFBB genes were analysed using codon models. Overall, the findings reported here support the non-self recognition by multiple factors model.

Surface tension phenomena in the xylem sap of three diffuse porous temperate tree species.

In plant physiology models involving bubble nucleation, expansion or elimination, it is typically assumed that the surface tension of xylem sap is equal to that of pure water, though this has never been tested. In this study we collected xylem sap from branches of the tree species Populus tremuloides, Betula papyrifera and Sorbus aucuparia over 3 months. We measured the instantaneous surface tension and followed changes over a period of 0.5-5 h using the pendant drop technique. In all three species the instantaneous surface tension was equal to or within a few percent of that of pure water. Further, in B. papyrifera and S. aucuparia the change over time following drop establishment, although significant, was very small. In P. tremuloides, however, there was a steep decline in surface tension over time that leveled off towards values 21-27% lower than that of pure water. This indicated the presence of surfactants. The values were lower for thinner distal branch segments than for proximal ones closer to the trunk. In some species it appears valid to assume that the surface tension of xylem sap is equal to that of water. However, in branch segments of P. tremuloides close to the terminal bud and hence potentially in other species as well, it may be necessary to take into account the presence of surfactants that reduce the surface tension over time.

[Sorbus pohuashanensis seed dispersal and germination and their relationships with population natural regeneration].

Sorbus pohuashanensis is an important non-timber tree species in Northeast China, but poor in natural regeneration via seed dispersal. In this paper, a field observation was made on the seed dispersal of S. pohuashanensis, its seedling emergence, and soil seed bank, aimed to study the factors affecting the natural regeneration of this tree species. There were 96.1% of naturally dispersed S. pohuashanensis seeds distributed within the range of 2 m around the stock tree, and 97.0% of the seeds in soil seed bank distributed in litter layer and 0-2 cm surface soil. The seed quantity in soil seed bank differed greatly with seasons, being the maximum [(257.7 +/- 69.2) seeds per square meter] in early November in the year of seed dispersal, and the minimum [only (2.9 +/- 2.9) seeds per square meter] in next July. Temperature was not the limiting factor affecting the seedling emergence of S. pohuashanensis [at 0 degrees C-5 degrees C, the seedling emergence percentage could reach (67.5 +/- 6.6)%], but strongly affected the seedling emergence rate. The most proper soil moisture content for the seedling emergence was 50% , under which, the seedling emergence percentage could reach (74.7 +/- 4.2)%. When the soil moisture content was up to 60%, the seedling mortality was the lowest (32.6% +/- 0.6%). All the results suggested that the seed dispersal pattern of S. pohuashanensis and the spatiotemporal dynamics of soil seed bank could affect the seedling emergence of the tree species, and further, affect the population natural regeneration of S. pohuashanensis via seed dispersal.

Frequent long-distance gene flow in a rare temperate forest tree (Sorbus domestica) at the landscape scale.

Precise empirical data on current gene flow by pollen, both with respect to distance and abundance, is crucial to understand whether habitat fragments are functionally connected. Based on a large-scale inventory ( approximately 100 km(2)) in which all individuals of a naturally scattered forest tree (Sorbus domestica) were mapped, we inferred current gene flow by pollen using genetic paternity analysis. We detected an extensive network of effective pollen transfer. Although short pollen flow distances were most abundant, 10% of the assigned pollen donors were more than 2 km away from their female mating partners, and 1.8% were even at a distance of 12-16 km. This latter pollen flow shows that current long-distance gene flow over a fragmented landscape clearly occurs. Pollen dispersal was well described by a fat-tailed inverse curve. Using parentage analysis of established trees, maternally inherited chloroplast markers and diameter at breast height measurements as an indicator of individual tree age, we were able to infer regular seed dispersal distances over several hundred metres up to more than 10 km. We conclude that in temperate, insect-pollinated and animal-dispersed tree species such as S. domestica, fragmented subpopulations are functionally connected by gene flow through both pollen and seed.

Pollen flow in the wildservice tree, Sorbus torminalis (L.) Crantz. IV. Whole interindividual variance of male fecundity estimated jointly with the dispersal kernel.

Interindividual variance of male reproductive success (MRS) contributes to genetic drift, which in turn interacts with selection and migration to determine the short-term response of populations to rapid changes in their environment. Individual relative MRS can be estimated through paternity analysis and can be further dissected into fecundity and spatial components. Existing methods to achieve this decomposition either rely on the strong assumption of a random distribution of pollen donors (TwoGener) or estimate only the part of the variance of male fecundity that is explained by few covariates. We developed here a method to estimate jointly the whole variance of male fecundity and the pollen dispersal curve from the genotypic information of sampled seeds and their putative fathers and geographical information of all individuals in the study area. We modelled the relative individual fecundities as a log-normally distributed random effect. We used a Bayesian approach, well suited to the hierarchical nature of the model, to estimate these fecundities. When applied to Sorbus torminalis, the estimated variance of male fecundity corresponded to an effective density of trees 13 times lower than the observed density (d(obs)/d(ep ) approximately 13). This value is between the value (approximately 2) estimated with a classical mating model including three covariates (neighbourhood density, diameter, flowering intensity) that affect fecundity and the value (approximately 30) estimated with TwoGener. The estimated dispersal kernel was close to previous results. This approach allows fine monitoring of ongoing genetic drift in natural populations, and quantitative dissection of the processes contributing to drift, including human actions.

Comparing direct vs. indirect estimates of gene flow within a population of a scattered tree species.

The comparison between historical estimates of gene flow, using variance in allelic frequencies, and contemporary estimates of gene flow, using parentage assignment, is expected to provide insights into ecological and evolutionary processes at work within and among populations. Genetic variation at six microsatellite loci was used to quantify genetic structure in the insect-pollinated, animal-dispersed, low-density tree Sorbus torminalis L. Crantz, and to derive historical estimates of gene flow. The neighbourhood size and root-mean-squared dispersal distance inferred from seedling genotypes (N(b) = 70 individuals, sigma(e) = 417 m) were similar to those inferred from adult genotypes (N(b) = 114 individuals, sigma(e) = 472 m). We also used parentage analyses and a neighbourhood model approach after an evaluation of the statistical properties of this method on simulated data. From our data, we estimated even contributions of seed- and pollen-mediated dispersal to the genetic composition of established seedlings, with both fat-tailed pollen and seed dispersal kernels, and slightly higher mean distance of pollen dispersal (248 m) as compared to seed dispersal (135 m). The resulting contemporary estimate of gene dispersal distance (sigma(c) = 211 m) was approximately twofold smaller than the historical estimates. Besides different assumptions and statistical nuances of both approaches, this discrepancy is likely to reflect a recent restriction in the scale of gene flow which requires manager's attention in a context of increasing forest fragmentation.

Aphids do not attend to leaf colour as visual signal, but to the handicap of reproductive investment.

The evolution of visual warning signals is well known in animals but has received scant attention in plants. The coevolutionary hypothesis is the most influential hypothesis on warning signals in plants proposing that red and yellow leaf colours in autumn signal defensive strength to herbivores. So far, evidence in support of the hypothesis, which assumes a coevolutionary origin of autumnal leaf colours, is correlative and open to alternative explanations. We therefore tested the coevolutionary hypothesis experimentally by colouring the leaves either red or green of same-aged mountain ash (Sorbus aucuparia) individuals. We monitored the response of winged aphids to leaf colour using insect glue on branches with natural and artificial leaf colours in each individual. In contrast to the prediction of the coevolutionary hypothesis, aphid numbers did not differ between the individuals with artificial green or artificial red leaves. Likewise, at the within-plant level, aphids did not colonize branches with natural green leaves preferentially. However, we suggest that plants emitted warning signals because aphids colonized the hosts non-randomly. We found a strong positive correlation between aphid numbers and fruit production, suggesting an allocation trade-off between investment in plant defence and reproduction. Our study demonstrates that aphids use warning signals or cues in host selection, probably volatiles, but that they did not use leaf colour.

Pollen flow in the wildservice tree, Sorbus torminalis (L.) Crantz. II. Pollen dispersal and heterogeneity in mating success inferred from parent-offspring analysis.

Knowing the extent of gene movements from parents to offspring is essential to understand the potential of a species to adapt rapidly to a changing environment, and to design appropriate conservation strategies. In this study, we develop a nonlinear statistical model to jointly estimate the pollen dispersal kernel and the heterogeneity in fecundity among phenotypically or environmentally defined groups of males. This model uses genotype data from a sample of fruiting plants, a sample of seeds harvested on each of these plants, and all males within a circumscribed area. We apply this model to a scattered, entomophilous woody species, Sorbus torminalis (L.) Crantz, within a natural population covering more than 470 ha. We estimate a high heterogeneity in male fecundity among ecological groups, both due to phenotype (size of the trees and flowering intensity) and landscape factors (stand density within the neighbourhood). We also show that fat-tailed kernels are the most appropriate to depict the important abilities of long-distance pollen dispersal for this species. Finally, our results reveal that the spatial position of a male with respect to females affects as much its mating success as ecological determinants of male fecundity. Our study thus stresses the interest to account for the dispersal kernel when estimating heterogeneity in male fecundity, and reciprocally.

Impacts of gene flow and logging history on the local genetic structure of a scattered tree species, Sorbus torminalis L. Crantz.

Sorbus torminalis L. Crantz is a colonizing tree species usually found at low density in managed European forests. Using six microsatellite markers, we investigated spatial and temporal patterns of genetic structure within a 472-ha population of 185 individuals to infer processes shaping the distribution of genetic diversity. Only eight young stems were found to be the result of vegetative reproduction. Despite high levels of gene flow (standard deviation of gene dispersal = 360 m), marked patterns of isolation by distance were detected, associated with an aggregated distribution of individuals in approximately 100-m patches. This spatial structure of both genes and individuals is likely to result from patterns of seedling recruitment combined with low tree density. Our results suggest that landscape factors and logging cycles markedly shape the distribution of favourable sites for seedling establishment, which are then colonized by sibling cohorts as a result of joint seed transportation by frugivores. These combined genetic and demographic processes result in similar genetic structure both within and among logging units. However, conversion to high forest may enhance genetic structuring.

Genetic effects of chronic habitat fragmentation on tree species: the case of Sorbus aucuparia in a deforested Scottish landscape.

Sustainable forest restoration and management practices require a thorough understanding of the influence that habitat fragmentation has on the processes shaping genetic variation and its distribution in tree populations. We quantified genetic variation at isozyme markers and chloroplast DNA (cpDNA), analysed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in severely fragmented populations of Sorbus aucuparia (Rosaceae) in a single catchment (Moffat) in southern Scotland. Remnants maintain surprisingly high levels of gene diversity (HE) for isozymes (HE = 0.195) and cpDNA markers (HE = 0.490). Estimates are very similar to those from non-fragmented populations in continental Europe, even though the latter were sampled over a much larger spatial scale. Overall, no genetic bottleneck or departures from random mating were detected in the Moffat fragments. However, genetic differentiation among remnants was detected for both types of marker (isozymes Theta n = 0.043, cpDNA Theta c = 0.131; G-test, P-value < 0.001). In this self-incompatible, insect-pollinated, bird-dispersed tree species, the estimated ratio of pollen flow to seed flow between fragments is close to 1 (r = 1.36). Reduced pollen-mediated gene flow is a likely consequence of habitat fragmentation, but effective seed dispersal by birds is probably helping to maintain high levels of genetic diversity within remnants and reduce genetic differentiation between them.