Spatial structure of genetic variation within populations of forest trees

The spatial pattern and structure of genetic variation are important aspects of the population genetics of forest stands. Combined with limits to seed and pollen dispersal, spatial structure affects the level of inbreeding and the action of natural selection. The genetic constitution of stand regeneration, following different forestry practices, is also influenced by spatial structure. For example, natural regeneration with seed trees involves sampling seed trees from a stand that may be genetically nonhomogeneous. This paper reviews theoretical and empirical results on spatial patterns of genetic variation, produced under limited gene flow and selection, in terms of recently developed spatial statistics (e.g., spatial autocorrelation). Genetic correlations in samples from spatially structured populations are also described, as well as how spatial samples can be used to characterize the structure of genetic variation, and how inferences can be made about (spatially distributed) components of fitness and yield.     

Gene flow among wild and cultivated common walnut (Juglans regia) trees in the Qinling Mountains revealed by microsatellite markers

Patterns of gene flow and gene introgres sion can be used to assess the risk of genetic pollution of wild forest trees from widespread cultivated trees.A comprehensive understanding of the genetic relationships and levels of gene flow among wild and cultivated common walnut(Juglans regia) has become an urgent issue.Using twelve microsatellite markers,we investigated the genetic diversity and gene flow between cultivated and wild trees of J.regia in the Qinling Mountains,China.A high level of genetic variation was detected in both cultivated and wild trees.The mean number of alleles per locus was 17.5.Observed heterozygosity(H_O)and expected heterozygosity(H_E) were 0.777 and 0.800,respectively.Pollination of mother trees was not by nearest neighbors,and a paternity of 60.7% of offspring evaluated could not be assigned to a local,sampled tree.Pollen flow from cultivated trees to wild trees was infrequent(5.4%),and selfing rates ranged from zero to 25.0%.Male parents were located from 0 to 1005 m from their female partners,with an average pollination distance of 285.1 m.These results are discussed in light of the cultivated species' diversity,outlining the frequent spontaneous genetic contributions from the wild to the cultivated compartment.In addition,the pollen flow parameters provide useful information about the dynamics of pollen movement within J.regia populations.     

Contemporary pollen flow and mating patterns of a subtropical canopy tree Eurycorymbus cavaleriei in a fragmented agricultural landscape

China's subtropical forests have experienced severe deforestation and most native forests have been fragmented into an archipelago-like landscape. The genetic effect of habitat fragmentation depends largely on the level of gene flow within and among population fragments. In the present study, Eurycorymbus cavaleriei, a canopy tree found throughout subtropical China, was selected as a representative insect-pollinated plant species to assess genetic consequence of forest fragmentation. Contemporary pollen dispersal and mating patterns were estimated in two physically isolated stands of E. cavaleriei within fragmented forests using six highly polymorphic microsatellite loci. We found high genetic diversity (H_E = 0.670–0.754) in both adults and offspring in the fragmented agricultural landscape, suggesting that habitat fragmentation did not necessarily erode genetic diversity of E. cavaleriei. Although substantial pollen travelled less than 100 m, paternity analysis revealed that a large amount of long-distance pollination events occurred, with the average pollen dispersal distance being 1107 m and 325 m for the two stands, respectively. Extensive pollen immigration (39.3–42.6%) indicated that there was effective genetic connectivity among E. cavaleriei stands in the fragmented forests. twogener analysis revealed that the exponential power model was the best-fitting dispersal curve with a fat-tailed (b < 1) dispersal feature. The results from a multilocus mating system analysis suggested that a small amount of biparental inbreeding and some correlated mating events occurred in the fragmented forests, which were similar to our parallel findings in the continuous forests of E. cavaleriei. Estimates of pollen pool structure (Φ_FT = 0.128–0.174) indicated large genetic differences between pollen clouds accepted by maternal trees. The number of effective pollen donors (N_ep) in E. cavaleriei, estimated using both mltr (N_ep = 4.2–5.3) and twogener (N_ep = 2.9–3.9) models, was equivalent to the number of effective pollen donors detected in continuous forests of E. cavaleriei. The pollen dispersal and mating patterns detected here indicated that habitat fragmentation did not have a negative impact on pollen movement in E. cavaleriei, possibly due to its generalist pollination system and the resilient foraging behavior of its pollinators in response to changes in landscape structure. The long distances of pollen-mediated gene flow between patches highlight the conservation value of remnant forest fragments in maintaining genetic connectivity at the landscape scale in subtropical China.     

High levels of pollen dispersal detected through paternity analysis from a continuous Symphonia globulifera population in the Brazilian Amazon

In this study, six highly polymorphic microsatellite loci and a categorical paternity analysis approach were used to investigate the contemporary pollen gene flow in the neotropical tree species Symphonia globulifera. Data for this study were taken from a 500 ha experimental plot in a dense terra firme forest in the Eastern Brazilian Amazon and included the mapping and genotyping of 161 reproductive trees, representing more than 90% of all adult trees, and the collection of 748 open-pollinated seeds from 56 seed-trees over two field seasons (2002 and 2003). High levels of pollen immigration from outside of the study plot were detected in both sampled seed-years (≥49%) suggesting long distance pollen gene flow. Low levels of self-fertilization were also detected (≤2%). The analysis showed long distance pollen dispersal occurred within the study area in both 2002 (δ = 907 ± 652 m SD) and 2003 (δ = 963 ± 542 m SD). Patterns of pollen dispersal distance within the plot were also found to be shorter than the distances between potential male parents and seed-trees. This result indicates that the distance between trees does not explain the identified pollen dispersal pattern. Our results support the hypothesis that animal pollinated species occurring in low-density populations can disperse pollen in long distances, despite the very dense nature of the forest.     

Genetic variation and gene flow among Prunus cerasoides D. Don populations in northern Thailand: analysis of a rehabilitated site and adjacent intact forest

This study describes the level of genetic variation and gene flow within and among populations of Prunus cerasoides in rehabilitated sites and adjacent intact forest. The seven microsatellite loci employed detected a total of 75 alleles (n = 401). Polymorphic information content (PIC) varied from 0.34 to 0.83. Between the adult populations there was moderate genetic differentiation with an F _ST value of 0.0575, which suggests that the restoration plots had a similar genetic composition to that of the natural population. The gene flow assessment provides some interesting insights into the genetic diversity of P. cerasoides. In the 16 naturally occurring trees over 83% of the genotyped seed were fathered by unidentified trees whereas in restoration plot A only about 32% of the pollen came from an unidentified father. This proportion was even less in Plot C where 25% of the pollen parents were unidentified. The naturally occurring trees within Doi Suthep were surrounded by planted trees, which were contributing to the paternity of the seed crop. This result demonstrates that ‘‘fill in’’ planting should consist of locally sourced material if it is considered important to conserve the genetic integrity of the local populations.     

Roles of seed and pollen dispersal in natural regeneration of Castanopsis fargesii (Fagaceae): Implications for forest management

Natural regeneration is an important process to reverse the loss of forests. Understanding the process of natural regeneration is crucial for achieving sustainable forest management. In this study, we examined the effects of seed and pollen dispersal in naturally regenerated populations of Castanopsis fargesii. Genetic variation in six populations along two successional series (three successional stages in each series: early, pre-climax, and climax) was assayed using RAPD (random amplified polymorphic DNA) markers. High genetic variability was observed as measured with Shannon's information index. A majority of genetic variation was distributed within populations (Φ_st = 0.1271) and significant isolation by distance existed among populations. A contrasting pattern of genetic variation along these two series was observed, representing different scenarios of natural regeneration processes. The ratio of the number of migrants between the mature populations to the number of migrants from the mature to immature populations was estimated as 1.146 ± 0.099 to 1.981 ± 0.164, implying that comparable seed and pollen dispersal might exist at a fine spatial scale (∼2 km²). The results suggest the critical role of seed dispersal in shaping genetic composition and diversity in the second-growth forests. Barriers to seed dispersal from a variety of genetic sources could result in low genetic diversity in naturally regenerated populations. Management that facilitates the connectivity of newly regenerated stands with mature forests could be effective for natural regeneration given the predominant role of short-distance dispersal of seeds in this species.     

Fine-scale analysis reveals a potential influence of forest management on the spatial genetic structure of Eremanthus erythropappus

Forest management may have significant effects on forest connectivity and natural population sizes.Harvesting old-growth single trees may also change natural patterns of genetic variation and spatial genetic structure.This study evaluated the impacts of forest management using a silvicultural system of seed trees on the genetic diversity and spatial genetic structure of Eremanthus erythropappus(DC.)MacLeish.A complete survey of 275 trees on four plots was undertaken out to compare the genetic variation of a managed stand with an unmanaged stand.We genotyped all adult and juvenile individuals 60 months after the management and compared the genetic diversity and the spatial genetic structure parameters.Genetic diversity was considered high because of an efficient gene flow between stands.There were no genetic differences between stands and no evidence of inbreeding.Genetic clustering identified a single population(K=1),indicating no genetic differentiation between managed and unmanaged stands.Adult and juvenile individuals of the unmanaged stand were more geographically structured than individuals from the managed one.There was a tendency of coancestry among juveniles at the first class of distance of the managed stand,suggesting a drift of genetic structure possibly caused by management.Understanding early responses to management on genetic diversity and stand structure is a first step to ensuring the effectiveness of conservation practices of tree species.The sustainability of forest management of E.erythropappus on genetic diversity,and more accurately,on spatial genetic structure needs evaluation over time to promote effective conservation of the population size and genetic variability.     

Spatial genetic structure in populations of the green oak leaf roller, Tortrix viridana L. (Lepidoptera, Tortricidae)

The green oak leaf roller (Tortrix viridana L.) is a major pest on oaks. The green oak leaf roller is one reason within a disease complex for the oak decline, and it leads to defoliation of oaks in spring. In Germany, Quercus robur L. is mainly affected. The partitioning of genetic variation within and among populations of forest pests is linked to their capacities for migration. And the capacity for migration is the basis for dispersal of the pest species to different host trees and host populations and, therefore, for further outbreak events. Thus, the within population spatial genetic structure (SGS) of T. viridana was investigated based on nuclear (AFLP) markers to analyse the dispersal capacity of this insect pest species at a very small spatial scale. A total of 401 individuals of the green oak leaf roller from four stands in North Rhine-Westphalia (Western Germany) were examined. In three of four populations, the AFLP markers revealed clearly SGS up to 40 m, which can be explained by the mating behaviour within this species.     

Isozyme variation in tropical trees: patterns of genetic organization

Tropical forests have long been of interest to biologists because of their high species diversity and their complicated patterns of community organization. The traditional notion of the rain forest as an ancient, unvarying archive of species has been challenged by a host of recent ecological studies which have demonstrated that tropical trees are diverse in their reproductive biology and dynamic in their population structure.Data from 97 isozyme studies on the genetics of tropical woody species demonstrate that cultivated taxa maintain higher percentages of polymorphic loci and higher mean heterozygosities than native tropical species. Levels of within-population variation in tropical taxa are as high or higher than in plants in general, previously reviewed by Hamrick and Godt (1989). Levels of genetic variation differ significantly among species with different geographic ranges, life forms, and taxonomic affinities. Levels of population differentiation, measured by Gs, values, are significantly different only between species with different seed dispersal modes. Outcrossing rates in 16 tropical tree species showed a preponderance of highly outcrossed breeding systems. Genetic evidence suggests that gene flow among local populations is high, but geographically separated populations show moderate levels of genetic differentiation.Ecological and historical processes provide the mechanisms influencing the genetic architecture of plant species. Where appropriate, data on isozyme variation in tropical trees are related to breeding systems, seed dispersal mechanisms, demography, and patterns of environmental heterogeneity. Profitable avenues for future research are suggested.     

Short distance pollen movement in a wind-pollinated tree, Quercus lobata (Fagaceae)

Short distance pollen dispersal shapes the local genetic structure of plant populations and determines the opportunity for genetic drift and local selection. In this paper we focus on short distance dispersal (SDD) of pollen in a low-density stand of a savannah oak, Quercus lobata Née. Specifically, we are interested in the proportional contributions of pollen donors, the pollen dispersal kernel that describes local matings, the extent to which wind influences mating success, and the extent to which pollen sources vary within the large canopy of these trees. Using maximum likelihood paternity analysis, we assigned sires for 474 outcrossed progeny of five seed trees, representing 120 of 160 potential mating pairs within a 250 m radius of each focal tree (ca. 20 ha plots). We first established that the effective number of pollen donors for progeny with sires within the plot was about 10 individuals, with average weighted pollination distances of 114.1 m. We estimated 18.5% pollen immigration into the 20 ha plots. We next established that the SDD portion of the dispersal kernel is best described by the exponential power, inverse power, and Weibull functions, all that capture high local dispersal with steep decay. Two of these models suggest that long distance dispersal is abundant, represented by a fat tail, while the Weibull indicates depauperate long distance dispersal, represented by a thin tail. The addition of a directional component corresponding to the predominant wind axis had no meaningful impact on these models. Finally, we established that different parts of an individual tree canopy of Q. lobata sample from the same homogeneous pollen pool showing no bias towards pollen sources near that part of the canopy. Overall findings suggest low-density Q. lobata populations show steep decay of SDD. Policies and ordinances governing the amount of allowable tree removal of savannah oak populations should recommend the preservation of local clusters of adults, as well as some connectivity among clusters.     

Gene flow pattern and mating system in a small population of Quercus semiserrata Roxb. (Fagaceae)

Pollen flow from external sources is important for the conservation of tree species in fragmented forests or small populations, because it can be sufficient to prevent differentiation among them, and appears to be able to prevent the loss of their genetic diversity through genetic drift. In this study, we examined the genetic heterogeneity of pollen pools accepted by each Quercus semiserrata seed parent at the Khun Wang Royal Agriculture Research Center, Thailand, both within and among two mast fruiting years (2005 and 2007), using paternity analysis and analysis of molecular variance (AMOVA). The mating systems of the trees were also examined using the multilocus mating system model (MLTR), after determining the genotypes at eight microsatellite loci of 26 seed-trees and 435 seeds from 8 seed-trees in the 2 mast fruiting years. The average distance of effective pollen flow within the plot was estimated to be 52.4 m, and 95% of effective pollen was dispersed within 200 m, indicating that effective pollen flow is highly localized and that most effective pollen is contributed by near-neighbor trees. The proportion of effective pollen that immigrated from external sources was estimated to be 26.2%. The AMOVA analysis based on the pollen haplotypes showed that the pollen pools, both total and for each reproductive year, significantly genetically differed among the seed parents. Using a mixed mating model, the estimate of biparental inbreeding for the total population (t_m − t_s) was 0.013, indicating that a low proportion of mating occurred among close relatives. The effective number of pollen donors (N_ep) was estimated to be 9.987 using the TwoGener model, or 10.989 using the mixed mating model. The effective number of pollen donors of seeds was higher in the mast fruiting year 2005 than in the other examined year, 2007. Consequently the allelic richness and genetic diversity of seeds produced in 2005 were higher than those produced in 2007. Overall, the results show that high outcrossing rates, high levels of gene flow from other populations and heterogeneity in the pollen received by an individual may enhance the ability of populations to maintain effective population sizes. Therefore, these processes may be sufficient to prevent loss of genetic diversity through genetic drift of Q. semiserrata at this study site.     

Genetic diversity of Pinus densiflora pollen flowing over fragmented populations during a mating season

We attempted to evaluate the genetic diversity of long-distance transported pollen flowing over fragmented Pinus densiflora populations during a mating season. A P.?densiflora clonal seed orchard, which was located in a rural area where many fragmented populations exist, was selected for pollen capture. Immigrant pollen captured by three clones having different flowering times was regarded as the pollen flowing over fragmented populations during a mating season. The genetic diversity (H _e) values of the immigrant pollen captured by the three clones were high (H _e?>?0.894). The correlation of paternity (r _p) values of the seeds having immigrant parent generated from the three clones were calculated to be negative. From these parameters, the pollen cloud is considered to have maintained high genetic diversity during the mating season. The genetic composition of the pollen cloud showed slight variation. The pollen captured by different trees (i.e., clonal ramets of the three clones) was significantly different based on analysis of molecular variance. Especially, the pollen pools captured by trees planted in the western side of the orchard were significantly different from the gene pool of the surrounding populations. Factors affecting this differentiation could be that the donors of the pollen transported to the orchard vary with time, as well as nonuniform dispersal of the pollen. From these results, the pollen flowing over fragmented P.?densiflora populations is considered to have high genetic diversity, compensating to some extent for fragmentation.     

Effects of selective logging on the mating system and pollen dispersal of Hymenaea courbaril L. (Leguminosae) in the Eastern Brazilian Amazon as revealed by microsatellite analysis

Using nine microsatellite loci, we studied the effects of selective logging on genetic diversity, mating system and pollen dispersal in a population of the tree species Hymenaea courbaril, located in a 546 ha plot in the Tapajós National Forest, Pará State, Brazil. We analyzed 250 offspring (nursery reared seedlings) collected after a logging episode from 14 open-pollinated seed trees. These were compared to 367 seedlings from 20 open-pollinated seed trees previously collected from the pre-logging primary forest. The genetic diversity was significantly lower in the post-logging seed cohort. In contrast to the pre-logging population, significant levels of selfing were detected in the post-logging population (t_m = 0.962, P < 0.05). However, correlated matings were reduced and the effective number of pollen donors almost doubled after harvesting (3.8 against 7.2). Logging also reduced pollen immigration into the plot (from 55% to 38%) and we found no significant correlation between the size of the pollen donors and the number of seeds fathered. Inside the plot, pollen dispersal distance was shorter before logging than after (827 and 952 m, respectively) and the reproductive pollination neighbor area (A_ep) was larger (average of 178 ha). The individual and average variance effective population size within families (ranged from 1.80 to 3.21, average of 2.47) was lower than expected in panmictic populations (N_e = 4). The results indicate that while logging greatly reduced the levels of genetic diversity after logging, it also increased genetic recombination within the population and constrained crossing among related individuals. The results show that low-density tropical tree species such as H. courbaril, when harvested in moderate levels may be resilient to a reduction in the reproductive population and may maintain similar levels of outcrossing and pollen dispersal after logging.     

Maternally and paternally inherited molecular markers elucidate population patterns and inferred dispersal processes on a small scale within a subalpine stand of Norway spruce (Picea abies [L.] Karst.)

The within-population spatial structure of genetic diversity is shaped by demographic processes, including historical accidents such as forest perturbations. Information drawn from the analysis of the spatial distribution of genetic diversity is therefore inherently linked to demographic-historical processes that ultimately determine the fate of populations.All adult trees and saplings in a 1.4-ha plot within a mixed Norway spruce (Picea abies [L.] Karst) stand were characterised by means of chloroplast (paternally inherited) markers, and a large sub-sample of these were genotyped at mitochondrial (maternally inherited) molecular markers. These data were used to analyse the spatial distribution of genetic variation and to compare the patterns corresponding to the two marker types. The plot presented non-homogeneous local stem density in the younger cohorts, and the indirect effect of this source of variation on the spatial genetic structure was investigated. Results suggest that (i) spatially limited seed dispersal induced patchiness in genotype distribution, while pollen flow had a homogenising effect; (ii) deviations from random spatial structure were stronger in the demographically most stable portions of the stand, while they were weaker where sudden bursts of regeneration occurred; (iii) spatially overlapping adult and sapling cohorts displayed the same spatial genetic structure (stronger on stable areas, weaker in portions of the stand undergoing events of intense regeneration), which was substantiated by the influence of local demographic processes. Regeneration dynamics as modulated by demography thus influences the distribution of genetic diversity within the stand both in the younger life stages and in the adult population.     

Genetic diversity in young and mature cohorts of cultivated and wild populations of Picea asperata Mast (Pinaceae), a spruce endemic in western China

Dragon spruce (Mast) is a conifer endemic to western China and a popular species for reforestation programs of this region. We used inter simple sequence repeats (ISSRs) molecular markers to conduct a population genetic study of nine geographically close stands from three types of dragon spruce forests: (1) intact, (2) plantation, and (3) natural regenerated following clearcut. Our main objective was to investigate the genetic structure of these populations and our expectation was that gene flow was an important evolutionary force among them. We were unable to sample a large number of individuals in each cohort. However, when young and mature cohorts from a particular stand were interpreted as a single unit, then sample size increased significantly. The highest levels of genetic diversity were found in mature cohorts of the intact forests, the lowest in young cohorts of these stands. Contrary to our expectations, low levels of gene flow existed between mature and young cohorts of different forest types; and most gene flow occurred between cohorts belonging to the same stand. There were major differences in the genetic structure of the three types of stands. Our results have conservation implications as the majority of wild populations of dragon spruce are small and fragmented. Low gene flow among populations will lead to high levels of genetic drift and a decline of genetic diversity within populations.     

Factors influencing male mating success in bur oak,Quercus macrocarpa

Pollen donors of acorns and saplings in a stand of bur oak were identified by paternity exclusion using microsatellite genotype analysis. Here we examine the influence of several factors likely to affect reproductive success of males with wind-dispersed pollen, including distance of pollen donor from maternal tree, genetic relatedness of pollen donor to maternal tree, direction of pollen donor relative to maternal tree, and size of pollen donor (crown volume and trunk diameter). Surprisingly, none of these factors were strongly correlated with fertilization success, although weak but significant correlations with crown volume and distance were found. The slight influence of distance is actually overestimated here, because our analysis necessarily excluded a large proportion of pollinations that were effected by trees outside the stand. The pollen donors outside the stand were not identified, but were more than 150 meters away. Pollination patterns in this stand of bur oak are quite complicated. Seed parents were fertilized by multiple pollen donors within the stand from all directions and as far as 200 m away. These results caution against the use of models of pollination that are based on simple distance or directional parameters because they will not adequately predict gene flow or male reproductive success. Our results further emphasize the importance of genetically identifying successful pollen donors rather than relying on patterns of physical movement of pollen.     

Intrapopulation variation in flowering phenology and fecundity of silver birch, implications for adaptability to changing climate

Earlier modeling has suggested that long distance gene flow is of importance in increasing the adaptability of tree populations in a changing climate. In times of warming temperatures, early flowering phenotypes may be favored, because early flowering may be connected to early onset of growth. Long term direct measurements of flowering, pollen cloud and intrapopulation fecundity variations are needed to test this hypothesis. Having one of the furthest transported types of pollen grains, birch may have good potential for long distance gene flow. Our daily observations over eight years, of 30 silver birches (Betula pendula Roth), showed that the onset and duration of flowering phenology was determined by the accumulation of spring temperature sums, but the window for potential long distance gene flow was narrow. The interannual phenology variations were large, the order of timing of female and male catkins in various trees of this monoecious species tended to differ, and the timing of generative and vegetative spring phenologies were not correlated at tree level. Early flowering trees tended to have a higher variation in germinability than later flowering trees. No other connection between timing of phenology of flowering and seed quantity or quality was found. Although stochastic climatic conditions produce interannually variable phenological windows, probability for long distance gene flow from areas differing in timing of spring temperature accumulations may be low in silver birch. Intertree variations in fecundity were high, and the majority of seeds and pollen were produced by only a few trees. Moreover, the amount of seeds produced was positively related to seed germinability, thus large phenotypic fecundity variations may decrease interannual genetic variations in seed sets.     

Pollen dispersal,mating patterns and pollen contamination in an insect-pollinated seed orchard of <Emphasis Type="Italic">Schima superba</Emphasis> Gardn. et Champ.

Pollen flow and mating patterns are the most important factors influencing the genetic structure of insect-pollinated forest trees and are essential parts of genetic management in seed orchards. We investigated pollen flow, the mating system and the level of pollen contamination in a clonal seed orchard of Schima superba Gardn. et Champ. In total, 328 open-pollination progenies coming from 11 mother trees were identified using 13 polymorphic microsatellite loci. A total of 203 full-sib families were identified and were nested among the 11 studied seed donors. The male reproductive success rate from 0.49 to 7.77% for most male parents, with an average of 2.44%. More than 80% of the crosses were found within a distance of 60 m, and the most frequent pollination distance between female parent and male parents was approximately 20 m. Mating system analysis showed that the outcrossing level was very high (t _m  = 1.000, outcrossing rate = 98.5%) in the seed orchard and that there was an average of 2.3 effective pollen donors (N _ep ) per female parent. In addition, the mating success of individual males within neighborhoods was moderately influenced by their fecundity and the direction of their location relative to mother trees. The pollen contamination from outside the seed orchard was high (7.01%). Our findings are valuable for the assessment of seed orchards, and it may be worthwhile to use pollen management strategies to decrease pollen contamination and increase the genetic quality of the seeds produced.     

How meso-scale pollen dispersal and its gene flow shape gene conservation decisions

Pine pollen dispersal has been well-studied over a century due to its ubiquity, robust shape and unusual longevity; this knowledge can be brought to bear on forest population genetics applications and gene conservation programs for pines and other high-latitude wind-pollinated species. Dispersal models are shifting towards meso-scale transport processes so I assert here that this shift in transport scale is important to population genetics assumptions inherent to gene conservation decision-making. Support comes from the following: (1) aerodynamic properties for pollen is more akin to spores than seeds. (2) Gradient-free dispersal is typical of pollen transported at meso-scale distances. (3) Importance of vertically uplifted pollen on meso-scale transport has been overlooked and its interaction with atmospheric processes is not yet understood. (4) A fraction of pine pollen retains its capacity for germination and seed fertilization after meso-scale transport. These findings raise the question of whether forest fragmentation aligns with genetics theory of small populations; this question shapes ex situ and in situ collections. The shift to meso-scale transport of pine pollen can re-shape forest gene conservation decision-making about ex situ and in situ collection strategies.     

Genetic succession and spatial genetic structure in a natural old growth Cryptomeria japonica forest revealed by nuclear and chloroplast microsatellite markers

Spatial genetic structure and diversity of Cryptomeria japonica trees in old growth forest but selectively logged in approximately 300 years ago were analyzed using seven nuclear microsatellite markers and one chloroplast microsatellite marker. The individuals were sampled from a 4-ha natural forest plot (200 m × 200 m), which are consisted of three size classes including newly regenerated individuals such as regenerated individuals (REG class; stem diameter at breast height (DBH), 5–110 cm), remaining individuals (REM class; DBH ≥ 110 cm), and old stumps. Genetic diversity was similar between the three groups. These results suggest that genes from the old growth forest may have been passed on to the next generation (i.e., the current forest). DNA extraction and analysis from old stumps was partly successful and we could compare the genetic diversity between old stumps and living trees using four microsatellite loci. Patterns of spatial genetic structure detected by analyses of the nuclear and chloroplast markers differed substantially; all nuclear markers showed significant positive autocorrelation (P < 0.05) over short distances, but the chloroplast marker showed no significant autocorrelation over any distance. We concluded that Moran's I spatial autocorrelation pattern for the chloroplast microsatellite may have been influenced by the extensive pollen flow characteristic of this species, because chloroplast DNA of C. japonica is paternally inherited through pollen and is a wind-pollinated species that produces abundant pollen every few years. In contrast, Moran's I spatial autocorrelation pattern for nuclear microsatellites may reflect limited seed dispersal in gaps where the forest has regenerated and low levels of seed shadow overlap due to past logging. The average seed dispersal distance was 86.0 m at the study site and about 34.0% of the seeds were from the outside of the site, which revealed by parentage analysis. The individuals remaining after logging, and the extensive pollen flow from outside our study plot, may play important roles in maintaining the forests on this island. Gaps created by the selective logging activities appear to have been important for the regeneration of this species in the past but in the present time, natural disturbances such as typhoon and landslide are also important for gap creation.