Central Iberia Research Articles

Shrub diversity in Mediterranean shrublands: Rescuer or victim of productivity?

AbstractAimsUnravelling the most prevalent causal direction between diversity and function in naturally recovered plant assemblages can greatly improve our understanding of the functional significance of diversity and its applications under the ongoing environmental changes. In this study, we apply a structural equation model framework to unravel the most plausible causal direction in the diversity–productivity relationship in subseral Mediterranean shrub‐dominated communities.MethodsTotal shrub cover (as a proxy of productivity when controlled by the time since land use cessation or the last wildfire), the number of species, and the number of functional types based on the dominant life forms (phanerophytes vs. chamaephytes), and the dominant foliar syndromes (deciduous vs. evergreen, needled vs. broad‐leaved), were sampled in 195 circular plots distributed along an elevation gradient ranging from 400 to 1400 m a.s.l. in the Central Iberian Peninsula. We first explored the distribution of functional types along the elevation gradient using a non‐metric multidimensional scaling (NMDS). Secondly, a structural equation model (SEM) framework using mixed‐effects models was defined to unveil the prevalent causal direction between diversity (species and functional types) and productivity at the landscape scale.ResultsModel selection using the Fisher'sCinformation criterion supported a causal direction from total shrub cover to diversity in this landscape. Interestingly, the best supported model also supported a positive relationship between species richness and the number of functional types, which in turn is driven by the total shrub cover along the elevation gradient.ConclusionsOur results suggest that more species might not necessarily boost productivity. On the contrary, ongoing warming temperatures and aridity, which are characteristic of low elevations compared to highlands, might significantly reduce the number of species (victim rather than rescuer) through deleterious effects on productivity.

From the city to the countryside: indicators of artisanal glass production in the central Iberian Peninsula (8th-9th centuries)

The current work presents the production and distribution of glass in the Emiral period in Spain. The study of the rural areas of the central Iberian Peninsula allows to identify some forms of production in large rural towns. Through the systematic study of the Dehesa de Navalvillar, including some archaeometric analyses, we have been able to establish that in the early Emiral period glass was produced in metallurgical workshops that left traces of occasional glass manufacture, probably carried out by itinerant craftsmen. With this article, we would like to contribute to the debate on glass production by introducing a new, multidisciplinary study of the rural world and the transformations that took place in the 8th century with the arrival of the Arabs in the Iberian Peninsula. The findings indicate artisanal production, circulation, and recycling of materials during the Emiral Period, where for the first time we find regional production in rural centres in addition to production in urban centres.

La Piquera (central Iberian Peninsula): A new key vertebrate locality for the Early Pliocene of western Europe

La Piquera (central Iberian Peninsula): A new key vertebrate locality for the Early Pliocene of western Europe

Nature and evolution of the lower crust under central Spain: Inferences from granulite xenoliths (Calatrava Volcanic Field-Spanish central system)

So far, the nature and evolution of the lower crust under central Spain have been constrained mainly on the basis of a heterogeneous suite of granulite xenoliths from the Spanish Central System (SCS). In recent years, ultramafic volcanics from the Calatrava Volcanic Field (CVF) have also provided deep-seated crustal xenoliths which have not been studied in detail. Our data, combining mineral, whole-rock and isotopic geochemistry with U–Pb–Hf isotope ratios in zircons from the CVF and SCS xenoliths, highlight the felsic composition of the lower crust under central Iberia. A number of the Calatrava xenoliths represents Variscan igneous protoliths, which are a minor population in the SCS, and were likely formed by crystallisation of intermediate and felsic melts in the lower crust during the Variscan orogeny (leucodiorite protolith age of 314 ± 3 Ma and leucogranite protolith age of 308 ± 2.5 Ma). U–Pb data of metamorphic zircons show that granulite-facies metamorphism mainly occurred from 299 to 285 Ma in both areas. These ages are slightly younger than those of granitic intrusions that could be genetically related to the granulitic residue, which points to a main role of U–Pb isotope resetting in lower crustal zircons during HT or UHT conditions. The zircon U–Pb–Hf isotopic ratios support the idea that the lower crust in central Iberia consists mainly of Ordovician–Neoproterozoic metaigneous and metasedimentary rocks associated with the Cadomian continental arc of northern Gondwana. These rocks provide evidence of mixing between juvenile magmas and an enriched crustal component, ultimately extracted from an Eburnean crust. Other more evolved components present in detrital zircons are likely related to recycling of Archean crust derived from North Africa cratonic terranes.

New insights on patterns of genetic admixture and phylogeographic history in Iberian high mountain populations of midwife toads.

Multiple Quaternary glacial refugia in the Iberian Peninsula, commonly known as "refugia within refugia", allowed diverging populations to come into contact and admix, potentially boosting substantial mito-nuclear discordances. In this study, we employ a comprehensive set of mitochondrial and nuclear markers to shed light onto the drivers of geographical differentiation in Iberian high mountain populations of the midwife toads Alytes obstetricans and A. almogavarii from the Pyrenees, Picos de Europa and Guadarrama Mountains. In the three analysed mountain regions, we detected evidence of extensive mito-nuclear discordances and/or admixture between taxa. Clustering analyses identified three major divergent lineages in the Pyrenees (corresponding to the eastern, central and central-western Pyrenees), which possibly recurrently expanded and admixed during the succession of glacial-interglacial periods that characterised the Late Pleistocene, and that currently follow a ring-shaped diversification pattern. On the other hand, populations from the Picos de Europa mountains (NW Iberian Peninsula) showed a mitochondrial affinity to central-western Pyrenean populations and a nuclear affinity to populations from the central Iberian Peninsula, suggesting a likely admixed origin for Picos de Europa populations. Finally, populations from the Guadarrama Mountain Range (central Iberian Peninsula) were depleted of genetic diversity, possibly as a consequence of a recent epidemic of chytridiomycosis. This work highlights the complex evolutionary history that shaped the current genetic composition of high mountain populations, and underscores the importance of using a multilocus approach to better infer the dynamics of population divergence.

Characterising Mitochondrial Capture in an Iberian Shrew.

Mitochondrial introgression raises questions of biogeography and of the extent of reproductive isolation and natural selection. Previous phylogenetic work on the Sorex araneus complex revealed apparent mitonuclear discordance in Iberian shrews, indicating past hybridisation of Sorex granarius and the Carlit chromosomal race of S. araneus, enabling introgression of the S. araneus mitochondrial genome into S. granarius. To further study this, we genetically typed 61 Sorex araneus/coronatus/granarius from localities in Portugal, Spain, France, and Andorra at mitochondrial, autosomal, and sex-linked loci and combined our data with the previously published sequences. Our data are consistent with earlier data indicating that S. coronatus and S. granarius are the most closely related of the three species, confirming that S. granarius from the Central System mountain range in Spain captured the mitochondrial genome from a population of S. araneus. This mitochondrial capture event can be explained by invoking a biogeographical scenario whereby S. araneus was in contact with S. granarius during the Younger Dryas in central Iberia, despite the two species currently having disjunct distributions. We discuss whether selection favoured S. granarius with an introgressed mitochondrial genome. Our data also suggest recent hybridisation and introgression between S. coronatus and S. granarius, as well as between S. araneus and S. coronatus.

The role of habitat features in patterns of population connectivity of two Mediterranean amphibians in arid landscapes of central Iberia

ContextMediterranean wetland ecosystems are in continuous decline due to human pressure. Amphibians are key elements of biotic communities of Mediterranean temporary ponds and streams, and their persistence depends on the availability and inter-connectivity of breeding sites.ObjectivesWe investigated the role of different factors potentially driving functional connectivity patterns in two amphibian species at the landscape and local scales. We focused on two Mediterranean endemic pond-breeding amphibians inhabiting semi-arid landscapes of central Spain, the common parsley frog (Pelodytes punctatus) and the common midwife toad (Alytes obstetricans).MethodsWe genotyped 336 individuals of P. punctatus and 318 of A. obstetricans from 17 and 16 breeding populations at 10 and 17 microsatellite loci, respectively. We used remotely sensed vegetation/moisture indices and land use/cover data to derive optimized resistance surfaces and test their association with estimates of gene flow and migration rates across populations.ResultsWe found evidence for higher population connectivity in common midwife toads than in common parsley frogs, with a strong effect of water availability in patterns of population connectivity of both species. However, the two species differ in the role of landscape features on population connectivity, with the distance and spatial distribution of artificial land-use types positively influencing connectivity in A. obstetricans and meadows/pastureland favouring P. punctatus. This is in line with reported breeding site preferences for the two species, with A. obstetricans successfully breeding in artificial water bodies that P. punctatus generally avoid.ConclusionsThis study highlights the importance of assessing species–habitat relationships shaping connectivity when developing and implementing conservation and management actions to benefit fragmented amphibian populations in the Mediterranean region. Our results show that amphibian species respond differently, even contrastingly to landscape features and thus require alternative, complementary strategies to improve population connectivity and ensure long-term viability.

Orogenic reworking and reactivation in Central Iberia: A record of Variscan, Permian and Alpine tectonics

Interference between orogenic systems and deformation phases within them may lead to reworking and reactivation of previous structures. The eastern sector of the Spanish-Portuguese Central System holds evidence of two orogenic systems, Variscan and Alpine, plus a stage of Permian extension. We perform an integrated structural analysis to identify reworking and reactivation processes throughout the geological record. The Variscan record starts with crustal thickening (D1; E-verging overturned folds). A second phase features the intra-orogenic collapse of an overthickened crust (D2; top-to-the-SE ductile extensional shear zone), which produced intense structural reworking at the core of the shear zone and moderate reworking at its hanging wall. During subsequent strike-slip tectonics, crustal thickening parted transpressional deformation into a dextral shear zone and upright folds (D3). Variscan deformation did not reactivate previous structures, but exploited a weak rheological boundary defined by contrasted lithologies (sedimentary versus igneous rocks) to accommodate D2 shearing. Reactivation played a role afterwards: Variscan strike-slip shear zone acted as a transfer fault to accommodate Permian extension (post-orogenic collapse), and then Alpine contraction. The Permian extension record is blurred by Alpine inversion, although the trend of Alpine structures in Central Iberia, and the Spanish-Portuguese Central System, may result from Permian structural inheritance.

Rock surface luminescence dating of prehistoric rock art from central Iberia

AbstractRock art paintings are notoriously difficult to date numerically. Recently, luminescence dating has been shown to provide reliable rock surface burial ages in various archaeological settings. Here we use the cross‐cutting relationship between a fallen rock and two paintings of the Iberian Levantine (older) and Schematic (younger) styles to constrain the age of the paintings by dating the rockfall event using rock surface luminescence dating. Infrared‐stimulated luminescence (IRSL) signals as a function of depth into the buried face of the talus border indicate that the IRSL signal measured at 50°C (IR50) was sufficiently reset to a depth of about 1.6 mm prior to burial. An uncorrected IR50 age of 1.6 ± 0.2 ka was calculated for the rockfall event by dividing the surface equivalent dose (De) by the total dose rate. This age was corrected using both conventional and field‐to‐laboratory saturation approaches to yield indistinguishable ages of 2.7 ± 0.5 and 2.9 ± 0.3 ka, respectively. Since the panel with Schematic art was first available to the artist after the rockfall, we conclude the Schematic rock art at Villar del Humo is younger than ~2.9 ka. The Levantine rock art was painted on a panel constrained by the talus boulder before detachment, and so it is likely to be older than ~2.9 ka.

Reasons to move far away: studying the drivers of Carpetania matritensis (Hormogastridae: Crassiclitelatta) dispersal behaviour

Dispersal is a crucial process for animal populations as it allows the colonisation of new habitats and the maintenance of genetic diversity. However, it has not been studied enough for soil fauna, which is the basis for a wide variety of ecosystem services. Therefore, the study of their dispersal and the factors that trigger this behaviour is a relevant area of knowledge for the maintenance of the services they provide. For this work, Carpetania matritensis, an endogeic earthworm species endemic to the central Iberian Peninsula, has been used as a model to study the effect of habitat quality and conspecific density on dispersal and exploratory behaviour. The experiment was carried out in horizontal mesocosms divided into three sectors of the same dimensions: an inoculation section (left), a crossing section (centre) and a target sector (right). Those sectors were occupied by soil, a favourable habitat for earthworms, or sand, which represents an unsuitable habitat for earthworms and a physical barrier for their displacement. Earthworms were inoculated at two different densities (2 and 6 individuals per mesocosm; 848.86 and 2546.58 individuals/m3 respectively) and at two experimental durations (4 and 8 days) for each of the three different experimental treatments (unsuitable-unsuitable-suitable (U-U-S), suitable-unsuitable-suitable (S-U-S) and suitable-suitable-suitable (S-S-S), depending on the habitat type filling the inoculation, crossing and target section respectively). The results showed a large effect of treatment on the dispersal rate, being higher when earthworms were inoculated in an adverse environment, establishing habitat quality as a driver of the species’ dispersal behaviour. No significant effects of conspecific density, experimental duration or its interactions were found. Further studies are needed to clarify the species dispersal behaviour with a view to its conservation.

A warm and humid paleoecological context for the Neanderthal mountain settlement at the Navalmaíllo rockshelter (Iberian Central System, Madrid)

Neanderthals have been claimed to have had a selective adaptation to rugged, wooded landscapes that would have partially compensate their high basal metabolic rate and locomotor energetic costs through reducing search time and increasing diet breadth. The archaeological site of the Navalmaíllo rockshelter (Pinilla del Valle, Madrid), located in a mountain environment in central Iberian Peninsula, has been interpreted as a repeated short-term occupation hunting camp by Neanderthal groups, mainly focused on primary access to large bovids and cervids. Navalmaíllo rockshelter has also furnished fish, toads, frogs, tortoises, lizards and snakes remains. This association of amphibians and reptiles suggests a much warmer climate (+2.8 °C) for layer F than at present, with similar temperatures during the summer but higher temperatures throughout the remaining months. Rainfall was slightly more abundant (+180.6 mm) than today, with a more contrasted regime during the year, with rainier winters and drier summers. A two-month period of aridity is observed during summer, representing a similar duration to present-day climatic conditions. Reconstructed landscapes are mainly constituted by open areas with dry grassland and rocky or stony areas, evolving laterally to humid meadows, probably close to the aquatic and peri-aquatic areas, such as rivers or ponds with riverside vegetation. Woodland environments are also well represented around the site, with medium scrublands to forest formations. Fish complete this reconstruction by documenting the presence of a pre-mountain well-developed river system characterized by relatively cold, permanent, oxygen-rich, and running waters. Such reconstruction is in disagreement with previous pollen interpretation for Layer F that suggested a very open and cold environment. Our new interpretation suggests that the Neanderthal occupation of the Navalmaíllo rockshelter occurred during a somewhat temperate and humid period, probably within the later part of the Marine Isotope Stage 5, effectively favouring the presence of a high biodiversity around the site.

Azimuthal anisotropy of the westernmost Mediterranean: New constraints on lithospheric deformation and geodynamical evolution

A new high-resolution azimuthally anisotropic Vs model beneath the westernmost Mediterranean is constructed based on Rayleigh wave dispersions obtained from 1186 broadband seismic stations. The model reveals several prominent features, including: (1) Anisotropy beneath Iberia inferred from surface waves is generally consistent with the results independently deduced from the analysis of SKS splitting, with fast velocity directions aligned close to E-W in most of the investigated area. (2) Vertically coherent mantle deformation is found across the vast majority part of the westernmost Mediterranean, namely, lithospheric deformation is coupled with the underlying asthenosphere. (3) Two anisotropic mantle layers are required to fit the data in a region in central Iberia, including part of the Duero and Tagus basins and the Central System. This is interpreted as denoting deformation in the mantle lithosphere related to the Alpine compressional regime. (4) The anisotropy in the Alboran Basin is complex and can be related to a deflected mantle flow pattern around the Alboran slab.

Crustal Imbrication in an Alpine Intraplate Mountain Range: A Wide‐Angle Cross‐Section Across the Spanish‐Portuguese Central System

AbstractIntraplate ranges are topographic features that can occur far from plate boundaries, the expected position of orogens as described in the plate tectonics theory. To understand the lithospheric structure of intraplate ranges, we focused on the Spanish‐Portuguese Central System (SPCS), the most outstanding topographic feature in the central Iberian Peninsula. The SPCS is an Alpine range that exhumes Precambrian‐Paleozoic rocks and is located at >200 km from the northern border of the Iberian microplate. Here, we provide a P‐wave velocity model based on wide‐angle seismic reflection/refraction data of the central SPCS (Gredos sector). Our results show: (a) a layered lithosphere characterized by three major interfaces: Conrad, Mohorovicic, and Hales discontinuities, (b) an asymmetry of the crust‐mantle boundary under the SPCS, (c) the extent of the Variscan batholith forming the main outcrops of Gredos, and (d) the thinning of the lower crust toward the south. This model suggests that the exhumation of the SPCS basement was driven by a south‐vergent thick‐skinned thrust system, developed in the southern part of the SPCS and that promoted crustal imbrication and a Mohorovicic discontinuity's offset under the SPCS. Thus, the deformation mechanisms of the crust seem to be controlled by the presence of the late‐ to post‐Variscan granitoids that assimilated the Variscan mid‐crustal detachment creating a new rheological boundary. This tectonic structure allowed the formation of Alpine crustal‐scale thrust systems that eased coupled deformation of the upper and lower crust, leading to limited underthrusting of both crustal layers.

Juan Labranz cave: a Quaternary deposit in the central Iberian Peninsula

ABSTRACT Here we report the preliminary results from the 2015–19 s prospecting explorations, excavations, and research from Juan Labranz Cave, a new Quaternary palaeontological deposit rich in mammals that offers information on the faunal context of the southern sub-plateau. This cave is located on the border of the Iberian range, at the Sierra de Valdecabras, Cuenca, at 1.279 metres above sea level. This study includes the first georeferenced digital map of the cave and a preliminary analysis of its chronology, palynology, macro- and microvertebrate palaeontology, and taphonomy. The cave is interpreted as a hyena den, and this would represent one of the highest elevation cavities where the activity of this taxon is recorded. Moreover, we consider this site important and unique because it constitutes one of the very few Pleistocene cave sites in the southern sub-plateau. It is strategically located on the border between the Iberian range and the Tajo Tertiary Basin, at the Júcar River valley, which represents the only great natural corridor that covers hundreds of kilometres and connects two very important palaeoecological areas, the interior of the Iberian Peninsula and the Mediterranean basin.

Ability of the WRF-ARW and HARMONIE-AROME models to detect turbulence related to mountain waves over Central Iberia

Aircraft turbulence is one of the most dangerous meteorological phenomena that can affect aviation safety. This study is focused on the turbulence associated to mountain lee waves in the vicinity of Adolfo Suárez Madrid-Barajas airport (Spain). Sixty-eight mountain lee waves events are selected to simulate the turbulence with the Weather Research and Forecasting (WRF-ARW) and the HARMONIE-AROME numerical weather prediction models. To study and characterize the turbulence associated, the vertical wind speeds are selected as an important variable and the Eddy Dissipation Rate is estimated. Both models have properly simulated the turbulence and the clear air turbulence, obtaining higher values of turbulence intensity by WRF-ARW than HARMONIE-AROME in the mountain lee waves events. Finally, these results are used to enhance a mountain wave warning decision tree, including the turbulence warning which is validated through several turbulence reports.

Herders and Pioneers: The Role of Pastoralism in the Neolithization of the Amblés Valley (Ávila, Central Iberia)

Abstract In recent years, the notion of landscape learning has been the object of increasing attention when discussing the neolithization of Europe. The landscape learning model stresses the necessity of gathering environmental information about a previously unfamiliar region. Therefore, it is particularly relevant in cases where the beginning of a farming economy is better explained in relation to the movements of peoples (colonization), rather than to the adoption of crops and livestock by pre-existing hunters and gatherers (acculturation). Unlike other Iberian regions, where the adoption of agriculture runs parallel to that of animal husbandry, the available data on the neolithization process of the Sierra de Gredos mountain range seem to suggest that raising livestock may have preceded plant cultivation. Based on an interdisciplinary and multi-proxy approach, this paper explores the idea that the adoption of a food-producing economy in the Amblés Valley (Ávila, Central Iberia) may have been connected with pastoralism. In this context, landscape learning provides a model for analyzing how Early Neolithic herders in their seasonal movements were capable of wayfinding by memorizing spatial features that functioned as visual landmarks.

Seismic structure and composition of the southern central Iberian crust: The ALCUDIA wide angle seismic reflection transect

The nature of the crust beneath central Iberia was estimated by a wide-angle seismic reflection/refraction transect, ALCUDIA-WA, which sampled the southern half of the Variscan Central Iberian Zone, covered in the north by the Cenozoic Tajo Basin. The shot gathers recorded by vertical component sensors revealed well defined P- and S-wave phases. These arrivals were modeled by an iterative forward approach providing 2D crustal models showing variations in the velocity distribution with upper crustal P- and S-wave velocities increasing northwards. The lower crust P-wave velocities are homogeneous along the profile while the S-wave velocities slightly increase northwards. The Moho is placed at 32 km depth in the southern edge of the profile, deepening northward down to 35 km beneath the Tajo Basin. The Poisson's ratio, calculated from P- and S-wave velocities, varies along the profile at upper crustal depths. The highest values are located below the Mora and Pedroches batholiths. These resulting physical properties can serve to constrain the crustal composition by comparing them with laboratory measurements on rock samples. Our results suggest that the upper crust in the southern and central segments of the ALCUDIA profile is made up of low-grade metasedimentary rocks, while the northern segment is dominated by igneous rocks, in agreement with the surface geology. Separated by a sharp boundary located between 12 km (south) and 18 km (north) depth, the lower crust is more homogeneous and shows low Poisson’ ratios compatible with a rather felsic composition. However, outstanding lamination described in coincident vertical incidence data indicates some degree of intercalation with mafic components.

Palynological and sedimentological implications of the sauropterygian Upper Triassic site of El Atance (Central Iberian Peninsula)

This study presents new palynological and sedimentological data concerning the Upper Triassic outcrop El Atance (Guadalajara province, Spain). This fossil site has provided a unique and unprecedented concentration of reptile skeletons from the Late Triassic in the Iberian Peninsula, which are almost complete, articulated and preserved in three dimensions. It is the type locality of the simosaurid nothosauroid Paludidraco multidentatus and the henodontid placodont Parahenodus atancensis, being the only species of these clades represented with some certainty in the Iberian record.Although these reptiles are often linked to shallow marine environments, little is known about the sedimentary environment where they became fossilized. Furthermore, to compare these remains with those from other areas of Europe, greater precision in their age assignment is necessary.The new palynological data provided in this study allows us to assign a precise age, in addition to other data such as a probable plant community, palaeoecology, and palaeoclimatic conditions. This information together with the geological and sedimentological data and the new isolated sauropterygian remains studied, allow a better understanding of the local palaeogeography and the evolutionary history of the vertebrates found in the El Atance fossil site.

Phylogeography of Hyalomma (Euhyalomma) lusitanicum (Acarina, Parasitiformes, Ixodidae) in Andalusia based on mitochondrial cytochrome oxidase I gene

The genetic population structure relationships of Hyalomma (Euhyalomma) lusitanicum in Andalusia (the south of the Iberian Peninsula) were examined using mtDNA sequence data from 887 bp of cytochrome oxidase subunit I (COI) gene. The sequence for the COI region was determined for 84 individuals collected in several localities of Andalusia, and 10 for other localities (i.e., five from Toledo, central Iberian Peninsula, four from Sicily (Italy) and one from Canary Island). Seventeen haplotypes were detected, including 27 polymorphic sites. The number of amino acid substitutions per site from mean diversity calculations for the entire population was 0.017. AMOVA analysis revealed a low gene flow that characterises the genetic population structure of this species in South Iberian Peninsula, with a haplotype diversity (h) value of 0.815. No geographically induced differentiation was observed, and separate evolutionary units were not detected. Our results indicate low genetic diversity across the geographical range of H. lusitanicum tick in Andalusia. Our data do not show any genetic discontinuity between the tick populations studied, including specimens from Canary Island and Sicily (Italy).

Measuring recent effective gene flow among large populations in Pinus sylvestris: Local pollen shedding does not preclude substantial long-distance pollen immigration.

The estimation of recent gene flow rates among vast and often weakly genetically differentiated tree populations remains a great challenge. Yet, empirical information would help understanding the interaction between gene flow and local adaptation in present-day non-equilibrium forests. We investigate here recent gene flow rates between two large native Scots pine (Pinus sylvestris L.) populations in central Iberian Peninsula (Spain), which grow on contrasting edaphic conditions six kilometers apart from each other and show substantial quantitative trait divergence in common garden experiments. Using a sample of 1,200 adult and offspring chloroplast-microsatellite haplotypes and a Bayesian inference model, we estimated substantial male gametic gene flow rates (8 and 21%) between the two natural populations, and even greater estimated immigration rates (42 and 64%) from nearby plantations into the two natural populations. Our results suggest that local pollen shedding within large tree populations does not preclude long-distance pollen immigration from large external sources, supporting the role of gene flow as a homogenizing evolutionary force contributing to low molecular genetic differentiation among populations of widely distributed wind-pollinated species. Our results also indicate the high potential for reproductive connectivity in large fragmented populations of wind-pollinated trees, and draw attention to a potential scenario of adaptive genetic divergence in quantitative traits under high gene flow.