Wind-pollinated Tree Species Research Articles

Genetic differentiation across a steep and narrow environmental gradient: Quantitative genetic and genomic insights into Lake Superior populations of Quercus rubra.

Adaptive differentiation of traits and underlying loci can occur at a small geographical scale if natural selection is stronger than countervailing gene flow and drift. We investigated this hypothesis using coupled quantitative genetic and genomic approaches for a wind-pollinated tree species, Quercus rubra, along the steep, narrow gradient of the Lake Superior coast that encompasses four USDA Hardiness Zones within 100 km. For the quantitative genetic component of this study, we examined phenotypic differentiation among eight populations in a common garden, measuring seed mass, germination, height, stem diameter, leaf number, specific leaf area and survival. For the genomic component, we quantified genetic differentiation for 26 populations from the same region using RAD-seq. Because hybridisation with Quercus ellipsoidalis occurs in other parts of the species' range, we included two populations of this congener for comparison. In the common garden study, we found a strong signal of population differentiation that was significantly associated with at least one climate factor for nine of 10 measured traits. In contrast, we found no evidence of genomic differentiation among populations based on FST or any other measures. However, both distance-based and genotype-environment association analyses identified loci showing the signature of selection, with one locus in common across five analyses. This locus was associated with the minimum temperature of the coldest month, a factor that defines the climate zones and was also significant in the common garden analyses. In addition, we documented introgression from Q. ellipsoidalis into Q. rubra, with rates of introgression correlated with the climate gradient. In sum, this study reveals signatures of selection at the quantitative trait and genomic level consistent with climate adaptation, a pattern that is more often documented at a much broader geographical scale, especially in long-lived wind-pollinated species.

Effective population size of adult and offspring cohorts as a genetic monitoring tool in two stand-forming and wind-pollinated tree species: Fagus sylvatica L. and Picea abies (L.) Karst.

AbstractGenetic diversity is considered to be a prerequisite for adaptation and adaptability as it is a key element of biological diversity. However, the monitoring of genetic diversity has tended to be ignored in biodiversity monitoring. We report a comprehensive genetic monitoring effort in two dominant forest tree species, which was started with a baseline survey in 12 European beech populations and 10 Norway spruce populations in Germany. The standardized experimental design is based on collecting samples of at least 250 adult trees, and 400 natural regeneration and 400 seed samples and their genotyping with 15–16 high-resolution SSR markers. In addition to commonly used mean values across the markers to quantify genetic diversity, we placed special emphasis on various marker-based, pedigree-based and demographic models for estimating the contemporary effective population size Ne of the different generations. In both beech and spruce, no variation in genetic diversity with mean values across markers was detectable between the studied stands and between age cohorts. We detected that stable allelic diversity in progeny generations is ensured by sufficient gene flow from surrounding forests. However, estimates of effective population size show marked differentiation among populations and among age cohorts. Natural regeneration samples appear to converge on the parent generation, while seed samples show a clear bottleneck effect. The Ne parameter can be used to derive conclusions for sustainable natural regeneration management in forest stands and for seed stand approvals including adequate seed collections for appropriate artificial regenerations.The sibship frequency-based method for Ne estimates is presented as much more robust than the widely used LD estimates, which often fail for samples with too weak relatedness. Despite the distinct kinship structure in our monitoring plots, the contemporary effective population size proves to be an essential parameter for assessing the integrity of the reproductive system.

Contrasting effects of natural shrubland and plantation forests on bee assemblages at neighboring apple orchards in Beijing, China

Wild bees provide important pollination services for crops and wild plants. While land use intensification has resulted in steep declines of wild bee diversity across agricultural landscapes, the creation of semi-natural habitats has been proposed as a counter-measure. However, the relative value of semi-natural and natural habitats in promoting wild bees has rarely been studied, especially for China that harbors the world's largest plantation forest area, characterized by intensively managed, mono-dominant stands of wind-pollinated tree species. We sampled wild bees in apple orchards to assess how their assemblages were influenced by semi-natural habitats in the surrounding landscape and the local flowering ground-cover. Bee abundance declined with increasing isolation from natural shrubland. In contrast, wild bee diversity and abundance were negatively linked to plantation forests. For the abundance of large bees, this effect was partly ameliorated by local flowering ground-cover. Maintaining or restoring wild bee assemblages in agricultural landscapes therefore requires careful evaluations of restoration measures such as forest planting. Availability of local flower resources and nearby natural shrubland appeared particularly important to enhance wild bees and their potential services in apple orchards.

Testing individual inter-annual variations in flower production by means of retrospective analysis of meristem allocation in two tree species

High inter-annual variations in flower and seed production have been frequently reported for wind-pollinated tree species. Such variations have been generally studied from a population perspective. The present study focuses on the meristematic cost of flower production in main branches of Nothofagus obliqua and N. nervosa through a retrospective analysis of flower production over 4–5 consecutive years. In both species, the percentage of flowering nodes in one year varied between 0 and 55 %. In N. obliqua, total flower production was bimodally distributed: years of high and low production were more common than years of intermediate production. Bimodality was not significant either for total flower production in N. nervosa or for each flower type separately in both species. Flower production affected branching negatively, which meant a meristematic cost. Periodicity in flower production was uneven among co-specific trees; more than two consecutive years of high flower production were rare in all trees. Inter-annual variations in the production of staminate and pistillate flowers were synchronized. In N. nervosa, the production of pistillate flowers tended to be more variable among years than the production of staminate flowers. The applied technique helps in the assessment of individual variations of flower production and contributes to understanding factors promoting seed-production variations in tree species at population scale.

Unusually limited pollen dispersal and connectivity of Pedunculate oak (Quercus robur) refugial populations at the species' southern range margin.

Low-latitudinal range margins of temperate and boreal plant species typically consist of scattered populations that persist locally in microrefugia. It remains poorly understood how their refugial habitats affect patterns of gene flow and connectivity, key components for their long-term viability and evolution. We examine landscape-scale patterns of historical and contemporary gene flow in refugial populations of the widespread European forest tree Pedunculate oak (Quercus robur) at the species' southwestern range margin. We sampled all adult trees (n=135) growing in a 20km long valley and genotyped 724 acorns from 72 mother trees at 17 microsatellite loci. The ten oak stands that we identified were highly differentiated and formed four distinct genetic clusters, despite sporadic historical dispersal being detectable. By far most contemporary pollination occurred within stands, either between local mates (85.6%) or through selfing (6.8%). Pollen exchange between stands (2.6%) was remarkably rare given their relative proximity and was complemented by long-distance pollen immigration (4.4%) and hybridization with the locally abundant Quercus pyrenaica (0.6%). The frequency of between-stand mating events decreased with increasing size and spatial isolation of stands. Overall, our results reveal outstandingly little long-distance gene flow for a wind-pollinated tree species. We argue that the distinct landscape characteristics of oaks' refugial habitats, with a combination of a rugged topography, dense vegetation and humid microclimate, are likely to increase plant survival but to hamper effective long-distance pollen dispersal. Moreover, local mating might be favoured by high tree compatibility resulting from genetic purging in these long-term relict populations.

Substructuring of Scots pine in Europe based on polymorphism at chloroplast microsatellite loci

Scots pine (Pinus sylvestris L.) is a forest forming tree species of great ecological and economic importance in the Northern Hemisphere. Assessment of genetic relationships between populations is needed for a better understanding of demographic and evolutionary processes of the species. We analyzed genetic variation and population structure of 24 native populations of Scots pine across its broad European distribution using a set of 13 polymorphic chloroplast simple-sequence repeats loci (cpSSRs). The number of alleles per locus ranged from 3 to 11 providing a set of 458 different haplotypes (haplotype diversity, He=0.982). Genetic differentiation in most between-population comparisons was low (FST ranged from 0.00 to 0.08, RST ranged from 0.00 to 0.19) as expected for highly outcrossing and wind pollinated tree species. However, Bayesian clustering analysis revealed at least three distinct genetic clusters corresponding to geographical origin of the analyzed populations. Our results indicate genetic substructuring across the distribution range of Scots pine, and also point to the existence of populations of most likely different history that maintain their genetic identity.

Genetic differentiation in spite of high gene flow in the dominant rainforest tree of southeastern Australia, Nothofagus cunninghamii.

Nothofagus cunninghamii is a long-lived, wind-pollinated tree species that dominates the cool temperate rainforests of southeastern Australia. The species' distribution is more or less continuous in western Tasmania but is fragmented elsewhere. However, it is unknown whether this fragmentation has affected the species' genetic architecture. Thus, we examined N. cunninghamii using 12 nuclear microsatellites and 633 individuals from 18 populations spanning the species' natural range. Typical of wind-pollinated trees, there was low range-wide genetic structure (FST=0.04) consistent with significant gene flow across most of the species' range. However, gene flow was not high enough to overcome the effects of drift across some disjunctions. Victorian populations (separated from Tasmania by the 240 km wide Bass Strait) formed a genetic group distinct from Tasmanian populations, had lower diversity (mean allelic richness (Ar)=5.4 in Victoria versus 6.9 in Tasmania) and were significantly more differentiated from one another than those in Tasmania (FST=0.045 in Victoria versus 0.012 in Tasmania). Evidence for bottlenecking was found in small populations that were at least 20 km from other populations. Interestingly, we found little divergence in microsatellite markers between the extremes of genetically based morphological and physiological altitudinal clines suggesting adaptive differentiation is strongly driven by selection because it is likely to be occurring in the presence of gene flow. Even though the cool temperate rainforests of Australia are highly relictual, the species is relatively robust to population fragmentation due to high levels of genetic diversity and gene flow, especially in Tasmania.

Distance-dependent but genetically random mating in a Japanese beech (Fagus crenata) population

In plant populations, limited seed dispersal may generate the aggregation of related individuals, which is referred to as spatial genetic structure (SGS). If short-distance pollination frequently occurs in populations with SGS, it may lead to frequent mating between related individuals (biparental inbreeding). In this study, we examined patterns of pollen dispersal and inbreeding under such conditions in a population of the wind-pollinated tree species Fagus crenata Blume using microsatellite analyses of adult trees and dispersed seeds. The population showed weak but significant SGS and the pollen dispersal in the population involved a combination of distance-dependent (largely short-range) dispersion at the local scale and long-distance transport. Although SGS and distance-dependent pollination co-occurred, individual inbreeding coefficients for both adults and seeds were almost zero, suggesting that mating generating sound seeds was genetically random with little or no inbreeding, probably because of the weak SGS, long-distance pollen dispersal, and postpollination mechanisms including self-incompatibility and inbreeding depression. The production of sound seeds through genetically random mating may be important for maintaining F. crenata populations because the resulting seedlings may be less affected by inbreeding depression than those resulting from the mating of related individuals.

Tree density and population size affect pollen flow and mating patterns in small fragmented forest stands of pedunculate oak (Quercus robur L.)

In many parts of the world, once large and continuous forests have been replaced by a mosaic of isolated forest fragments embedded in an agricultural or urban landscape matrix. At the same time, stand characteristics such as tree population size and tree density have been strongly modified as a result of anthropogenic activities. Because increased geographical isolation can impede gene flow among forest fragments, and because decreased population size and tree density may reduce the number of local mating partners, this can be expected to lower the opportunity to trees for outcrossing, and to result in increased inbreeding, negatively impacting the viability of fragmented tree populations. In this study, we examined eight isolated stands of the wind-pollinated tree species Q. robur that strongly differed in population size, tree density and spatial isolation. In the centre of each Q. robur stand, adult leaves and seeds were collected in a circular plot, in which we evaluated the diversity and differentiation of the local pollen pool, and examined mating patterns. Most forest stands showed high proportions of out-of-plot pollen flow (range: 0.24–0.77), which were positively correlated with the number and density of adult trees within the forest stands. Despite high outcrossing rates (>0.998), seeds within seed families were stronger related than what could be expected under panmixia, which could be attributed to small but significant levels of correlated paternity (0.018–0.107) and biparental inbreeding (0.025–0.118) within the study plots. Next to increased coancestry coefficients, deviations from random mating also resulted in significant pollen pool differentiation (0.008–0.059) among seed parents. We also found that stand population size and tree density were significantly correlated to the relatedness of the seedlings and the degree of pollen differentiation within the study plots. These results suggest that, in small and isolated low density forest stands, reduced mate availability may decrease local pollen pool diversity, increasing the likelihood of consanguineous mating and pollen pool differentiation in the next generations. We conclude that preserving high levels of pollen flow within and between forest fragments may be more important in wind-pollinated tree species than what was previously thought.

Habitat differences influence genetic impacts of human land use on the American beech (Fagus grandifolia).

Natural reforestation after regional forest clearance is a globally common land-use sequence. The genetic recovery of tree populations in these recolonized forests may depend on the biogeographic setting of the landscape, for instance whether they are in the core or in the marginal part of the species' range. Using data from 501 individuals genotyped across 7 microsatellites, we investigated whether regional differences in habitat quality affected the recovery of genetic variation in a wind-pollinated tree species, American beech (Fagus grandifolia) in Massachusetts. We compared populations in forests that were recolonized following agricultural abandonment to those in remnant forests that have only been logged in both central inland and marginal coastal regions. Across all populations in our entire study region, recolonized forests showed limited reduction of genetic diversity as only observed heterozygosity was significantly reduced in these forests (H(O) = 0.520 and 0.590, respectively). Within inland region, this pattern was observed, whereas in the coast, recolonized populations exhibited no reduction in all genetic diversity estimates. However, genetic differentiation among recolonized populations in marginal coastal habitat increased (F(st) logged = 0.072; F(st) secondary = 0.249), with populations showing strong genetic structure, in contrast to inland region. These results indicate that the magnitude of recovery of genetic variation in recolonized populations can vary at different habitats.

Genetic structure and diversity ofPolylepis australis(Rosaceae) tree populations from central Argentina: Implications for forest conservation

AbstractWorldwide, large areas of forest are being transformed to other land cover types and the resulting fragmented populations may suffer from restricted gene flow leading to genetic pauperization and increased inbreeding. To assess the genetic constitution of fragmentedPolylepis australismountain forests of central Argentina, analyses of the structure and diversity of ISSR markers were carried out for 90 trees distributed throughout five river basins with differing degrees of fragmentation. Overall, average polymorphism (P) ranged between 87.2 and 94.9% (95% criterion) while marker diversity index (M) varied between 0.35 and 0.39; values which are comparable with other wind-pollinated tree species. Analysis of molecular variance (AMOVA) revealed that most genetic variation occurred within river basins (97.8%), with only a little occurring between river basins (2.2%; ΦST= 0.02). In addition, Mantel’s test indicated thatP. australisdoes not follow the usual pattern of isolation by distance; instead the UPGMA method showed that trees from the two most degraded river basins formed a group while trees from the three better preserved basins formed another. As such, either effective pollen flow has maintained high levels of genetic diversity, or present day genetic variability is a remnant of a recently fragmented ancestral panmictic population. We conclude that, at present, genetic degradation inP. australispopulations of central Argentina is not as important as ecological degradation – such as soil loss, intensive browsing by livestock or increased frequencies of wildfires, and that genetic variability is still fully available for forest restoration.

Efficient Long-Distance Gene Flow into an Isolated Relict Oak Stand

Geographically isolated and small populations outside a species' central distribution range are likely to be of major importance to a species' ability to quickly adjust its distribution range to global change dynamics. Gene flow from the outside plays a pivotal role in the fate of these marginal populations. It has been proposed that spatial fragmentation and perceived geographic isolation do not necessarily reflect a loss of genetic connectivity in tree species. However, the spatial limits of long-distance gene flow, as well as its magnitude and impact, are still generally unknown. In the present study, we analyzed long-distance pollen-mediated gene flow into an isolated relict stand consisting of 7 individuals of Quercus robur L. based on a total sample of 177 trees and 9 microsatellite loci. We show that pollen-mediated gene flow across more than 80 km in this wind-pollinated tree species contributed at least 35% of all successful pollinations in the investigated isolated and small oak stand at the eastern limit of the species' distribution. The observed pollen immigration shaped the genetic diversity of acorn progenies in the stand and might explain the comparably high genetic diversity in the persisting adult population.

Wind pollination over mesoscale distances: an investigation with Scots pine

There is a gap between the order of magnitude of maximum documented distances of airborne tree pollen transport (up to 10(2)-10(3) km) and effective wind pollination (up to 10(1) km), which may partly derive from greater difficulties in detecting the latter. This study aims to assess wind pollination over scales closer to the maximum observed physical pollen transport distances. The origin of effective pollen immigrants into a strongly isolated Iberian Pinus sylvestris remnant was investigated using paternally inherited microsatellite markers and maximum-likelihood estimation combined with Monte Carlo assessment of parameter uncertainty. The results revealed significant effective pollen flow (up to 4.4%) from a large population located 100 km away, suggesting that the well-known mesoscale airborne transport of viable pine pollen can result in successful pollination over larger scales than previously reported for wind-pollinated tree species. This study supports the view that the gap between documented potential and effective wind pollen dispersal scales might not accurately reflect biological reality. Expanding the expected range of effective wind pollination has an impact on the assessment of a wide range of ecological and evolutionary processes, including reproductive assurance on fragmentation or colonization, metapopulation connectivity and interactions with local adaptation in heterogeneous habitats.

Genetic diversity and differentiation of Fagus orientalis Lipsky in Hyrcanian forests revealed by nuclear and chloroplast microsatellite markers

Oriental beech (Fagus orientalis Lipsky) is a widespread monoecious and wind-pollinated tree species. It is one of the major components of the Hyrcanian forests of Iran and it is of both ecological and economical importance. Twelve beech stands were surveyed at 9 chloroplast (cp) and 6 nuclear (n) polymorphic microsatellite loci (simple sequence repeats, SSR) to provide information on distribution of genetic diversity within and among populations and on gene conservation and silvicultural management of this species. High levels of genetic differentiation were detected for the chloroplast genome (FST = 0.80 and RST = 0.95), in sharp contrast to the nuclear genome (FST = 0.06, RST = 0.05). The analysis of molecular variance (AMOVA) showed that 48% of the total cpSSR variation was attributable to differences among regions and 30% to differences among populations within regions, suggesting multiple origins of beech populations in Hyrcanian forests. Nuclear SSRs confirmed the presence of significant differentiation among populations and among geographic regions, even if, as expected, this was less pronounced than that found with cpSSRs (based on AMOVA, differences among regions and among populations within regions each contribute 5% to total nSSR variance). A highly significant correlation between genetic (nSSRs) and geographic distances (R2 = 0.522) was estimated, thus showing an isolation by distance effect. The application of spatial analysis of molecular variance (SAMOVA) using both marker data allowed identification of genetically homogeneous groups of populations. Possible applications of these results for the certification of provenances and/or seed lots and for designing conservation programs are presented and discussed.

Molecular biodiversity and population structure in common ash (Fraxinus excelsior L.) in Britain: implications for conservation

Current forestry policy promotes the use of local seed for new plantings, on the assumption that local material may be better adapted to local conditions. However, landscape-scale genetic studies which are necessary to underpin conservation and breeding strategies are often lacking. We investigated molecular diversity in common ash (Fraxinus excelsior L.) sampled from 42 British and six French sites with microsatellites. Chloroplast haplotype H04 was the most common and widespread in Britain, although rare and localized individuals with H02 and H09 were also detected. In addition, three new chloroplast haplotypes were identified, and these were rare and highly localized. In terms of nuclear microsatellite markers, allelic richness differed between sites and decreased in an east to west direction. Differentiation between sites was often very low (mean F(ST) 0.025), indicating few differences between the majority of sites. There was a clear excess of homozygotes (mean H(O) 0.669, mean H(E) 0.818) and a relatively high F(IS) (mean 0.182), suggests a consistent level of inbreeding or a widespread Wahlund effect in many F. excelsior sites. Gene pool ancestry analysis suggested that the majority of British F. excelsior belongs to a single meta-population which covers mainland western and central Europe. Three northern and western sites diverged markedly from the dominant population, and may represent remnants of two late potential Ice Age refugia in northern Britain. The data provide new information which will aid development of appropriate conservation policies for ash and other wind pollinated tree species.

Local adaptation at the range peripheries of Sitka spruce

High-dispersal rates in heterogeneous environments and historical rapid range expansion can hamper local adaptation; however, we often see clinal variation in high-dispersal tree species. To understand the mechanisms of the species' distribution, we investigated local adaptation and adaptive plasticity in a range-wide context in Sitka spruce, a wind-pollinated tree species that has recently expanded its range after glaciations. Phenotypic traits were observed using growth chamber experiments that mimicked temperature and photoperiodic regimes from the limits of the species realized niche. Bud phenology exhibited parallel reaction norms among populations; however, putatively adaptive plasticity and strong divergent selection were seen in bud burst and bud set timing respectively. Natural selection appears to have favoured genotypes that maximize growth rate during available frost-free periods in each environment. We conclude that Sitka spruce has developed local adaptation and adaptive plasticity throughout its range in response to current climatic conditions despite generally high pollen flow and recent range expansion.

The role of pollen in the changing environmental conditions of Scots pine

Rapid climate warming poses a challenge to forest trees adapted to cooler conditions. However, a genetic safety net may exist for wind pollinated tree species in the form of long distance gene flow mediated by pollen containing alleles that are (pre)adapted to a warmer climate. In order to examine long distance gene flow in Scots pine (Pinus sylvestris L.), we monitored flowering phenology in central, northern, and northernmost Finland and measured the amount and viability of airborne pollen over four years. Viable airborne pollen grains were detected during female flowering periods and prior to local pollen shedding in all study sites. Depending on the year and study site, female flowers were exposed only to pollen originating elsewhere for between one and four days. Foreign airborne pollen represented 2.3% of all viable grains detected and varied between years and study sites. Artificial pollination trials were conducted to evaluate the effect of pollen origin on seed siring success. Pollen genotypes originating from southern Finland sired 76% and 48% of seeds in competition experiments where pollen from both populations was introduced simultaneously into the female strobilus. Furthermore, we investigated the importance of pollen arrival order by introducing pollen of northern and southern genotypes in to the strobilus at two-hourly intervals. Northern genotypes sired 76% of the analysed seeds when injected first but when southern genotypes were supplied first, both pollen types enjoyed equal success. The first pollen grain in the pollen chamber did not always fertilize the ovum. Instead there is likely a more subtle and complex form of competition between genotypes and their pollen grains. To examine chemically-mediated pollen interactions we conducted an in vitro germination experiment where different genotypes were in chemical but not physical contact. Both positive and negative interactions were found. We found highly negative effects in the germinability of northern pollen grains when in contact with southern pollen, and an increase in the germinability of southern pollen when in contact with northern pollen. There was no variation in the size of dry pollen grains between sources, but after hydration and germination, northern pollen grains were larger than southern pollen. Genotypes with high hydration rates had low germinability and slow pollen tube growth rates. This suggests that early germination and growth of the pollen tube is more dependent on pollen storage materials and less dependent on water intake. Pollen source affected the outcome of competition experiments and therefore is an important factor in long distance gene flow. However, genotype also plays a role and must be taken into account.

High population differentiation and unusual haplotype structure in a shade‐intolerant pioneer tree species, Zanthoxylum ailanthoides (Rutaceae) revealed by analysis of DNA polymorphism at four nuclear loci

Differences in demographic history, life-history traits, and breeding systems affect nucleotide variation patterns. It is expected that shade-intolerant pioneer tree species have different patterns of genetic polymorphism and population structure than climax species. We studied patterns of nucleotide polymorphism at four putative starch pathway loci (agpSA, agpSB, agpL, and GBSSI) in Zanthoxylum ailanthoides, a shade-intolerant pioneer tree species that occupies forest gaps in warm-temperate forests of East Asia. Genetic diversity was lower within each population than among populations, and differentiation among populations was high across the loci (F(ST) = 0.32-0.64), as expected from the insect-pollinated breeding system and the metapopulation structure of this pioneer species. Numbers of haplotypes were smaller than those expected from the observed numbers of segregating sites. Single haplotypes accounted for more than 47% of all the sampled genes at the respective loci. These variation patterns were incompatible with neutral predictions for populations of a finite island model. Complex population dynamics, such as bottleneck and/or admixture, in the history of this pioneer tree species might have resulted in the observed patterns of genetic variation and population structure, which are different from those of climax wind-pollinated tree species, such as conifers. In contrast to the other loci investigated in this study, agpL showed nearly no variation in Z. ailanthoides (one singleton only), but there was some extent of variation in a closely related species, Zanthoxylum schinifolium. This suggests possibly a recent selective sweep at or near the locus in Z. ailanthoides.

Restricted gene flow in fragmented populations of a wind-pollinated tree

Fragmentation of natural populations can have negative effects at the genetic level, thus threatening their evolutionary potential. Many of the negative genetic impacts of population fragmentation can be ameliorated by gene flow and it has been suggested that in wind-pollinated tree species, high or even increased levels of gene flow are a feature of fragmented populations, although several studies have disputed this. We have used a combination of nuclear microsatellites and allele-specific PCR (AS-PCR) analysis of chloroplast single nucleotide polymorphisms (SNPs) to examine the levels and patterns of genetic diversity and population differentiation in fragmented populations of juniper (Juniperus communis) in Ireland and inform conservation programs for the species. Significant population differentiation was found for both chloroplast and nuclear markers, indicating restricted gene flow, particularly over larger geographic scales. For conservation purposes, the existence of genetically distinct clusters and geographically localised chloroplast haplotypes suggests that the concept of provenance should be taken into account when formulating augmentation or reintroduction strategies. Furthermore, the potential lack of seed dispersal and seedling establishment means that ex-situ approaches to seed and seedling management may have to be considered.

Fragment size, pollination efficiency and reproductive success in natural populations of wind-pollinated Polylepis australis (Rosaceae) trees

It is well known that habitat fragmentation is likely to negatively affect the reproductive success of a species. Despite this fact, studies on the effects of fragmentation on reproductive success in combination with effects on natural pollination of wind-pollinated tree species are very rare. In this study, we analyzed the relationships between fragment size, components of pollination efficiency, reproductive success and progeny vigour of the highly fragmented populations of the wind-pollinated treeline species Polylepis australis (Rosaceae) in Argentina. We conducted our study in the high mountains of Córdoba, comparing pollination efficiency and reproduction between four fragment sizes. Most of our results indicate that P. australis is currently insensitive to fragmentation. However, our study revealed also a linear increase in leaf area and biomass of 40-day-old seedlings with increasing fragment size. Inbreeding problems through fragmentation as well as decreased habitat quality in small fragments are discussed as possible causes for the impaired progeny vigour.