Frequent cytoplasmic exchanges between oak species that are not closely related: Quercus suber and Q. ilex in Morocco

Chloroplast (cp) and mitochondrial (mt) DNA variation were studied in 97 populations of cork oak (Quercus suber) in Morocco; in 31 of these populations, holm oak (Quercus ilex), a clearly distinct species, also occurred and was compared with Q. suber. Three cpDNA and one mtDNA primer pairs were used in the survey, each in combination with one restriction enzyme. Six haplotypes belonging to two very divergent lineages were detected; one lineage predominates in each species, and is probably ancestral, as inferred from comparisons with other oak species. In the mixed-species populations, cytoplasmic genomes were frequently shared across species, as indicated by an introgression ratio of 0.63. This index is a new measure of the propensity of species to share locally genetic markers, varying from zero (complete differentiation) to one (no differentiation). By contrast, more closely related deciduous oak species (Q. robur, Q. petraea and Q. pubescens) have introgression ratios varying from 0.82 to 0.97. The introgression events appear to have been more frequent in the direction Q. ilex (female) x Q. suber (male), a finding which seems attributable to the flowering phenology of these two species. This asymmetry may have favoured immigration of Q. suber beyond its main range, in regions already colonized by Q. ilex. There, rare hybridization and further introgression through long distance pollen flow have established populations that are morphologically indistinguishable from Q. suber but that have cytoplasmic genomes originating from the local Q. ilex populations.     

High variability of chloroplast DNA in three Mediterranean evergreen oaks indicates complex evolutionary history

Chloroplast DNA variation was studied in three evergreen Quercus species (Q. suber L., Q. ilex L. and Q. coccifera L.) from the Western Mediterranean Basin using PCR-RFLP. We studied five primer pair/enzyme combinations, four of them previously used in other European Quercus, obtaining a large number of haplotypes (81) grouped in three main types (suber type, ilex-coccifera I type and ilex-coccifera II type). Such level of haplotype diversity is higher than previously reported for the genus. Remarkable differences in haplotype richness between species have been found. Q. ilex and Q. coccifera usually share the same haplotypes, while a number of Q. suber populations possesses variants of the ilex-coccifera I type. This fact is interpreted as a result of genetic introgression between Q. suber and Q. ilex. Reproductive factors that could determine this exchange are discussed, as well as the influence of different species histories on the present structure of evergreen Quercus in the Western Mediterranean Basin.     

Natural hybridisation between kermes (Quercus coccifera L.) and holm oaks (Q. ilex L.) revealed by microsatellite markers

Hybridisation between species of the genus Quercus is a common phenomenon as a result of weak reproductive isolation mechanisms between phylogenetically close species that frequently co-occur in mixed stands. In this study, we use microsatellite markers to analyse introgression between kermes ( Quercus coccifera L.) and holm ( Q. ilex L.) oak, two closely related taxa that frequently dominate the landscape in extensive areas in the Mediterranean region. All tested microsatellites amplified and were polymorphic in both kermes and holm oaks. Bayesian admixture analyses showed a good correspondence between each species and one of the two inferred genetic clusters. Five sampled individuals were a priori tentatively identified as hybrids on the basis of intermediate morphological characteristics, and it was confirmed that they also presented mixed genotypes. However, we also detected different levels of genetic introgression among morphologically pure individuals, suggesting that successful backcrossing and/or reduced phenotypic expression of genetic variance in certain individuals may have resulted in strong convergence towards a single species phenotype.     

Molecular and palaeoecological evidence for multiple glacial refugia for evergreen oaks on the Iberian Peninsula

Aim  A multiple glacial refugia hypothesis for Mediterranean plant species was tested with the evergreen Quercus complex ( Quercus suber L., Quercus ilex L. and Quercus coccifera L.) from the Iberian Peninsula, using molecular and palaeobotanical data.
Location  The Iberian Peninsula, which is an ecologically and physiographically complex area located on the western edge of the Mediterranean Basin.
Methods  We sampled 1522 individuals from 164 populations of Q. suber , Q. ilex and Q. coccifera . A review of the recent literature on fossil pollen and charcoal records and a nested clade analysis on chloroplast DNA polymerase chain reaction-restriction fragment length polymorphism was carried out to infer demographic and historical processes.
Results  The analysis indicates at least one glacial refugium for Q. suber in south-western Iberia. Extensive introgression of Q. suber with Q. ilex indicates several potential refugia in eastern Iberia. Past fragmentation was followed by a restricted range flow/range expansion, suggesting multiple refugia for Q. ilex–Q. coccifera elsewhere in central and northern Iberia and multiple areas of secondary contact. This finding is consistent with fossil records.
Main conclusions  The predicted multiple refugia during glacial periods indicates the existence of secondary post-glaciation contact areas. These areas contained complex diversity patterns resulting mainly from range expansions followed by isolation by distance. To a lesser degree, traces of restricted and long-distance dispersal were also found.     

Endemic North African Quercus afares Pomel originates from hybridisation between two genetically very distant oak species (Q. suber L. and Q. canariensis Willd.): evidence from nuclear and cytoplasmic markers

Hybridisation is a potent force in plant evolution, although there are few reported examples of stabilised species that have been created through homoploid hybridisation. We focus here on Quercus afares, an endemic North African species that combines morphological, physiological and ecological traits of both Q. suber and Q. canariensis, two phylogenetically distant species. These two species are sympatric with Q. afares over most of its distribution. We studied two Q. afares populations (one from Algeria and one from Tunisia), as well as several populations of both Q. suber and Q. canariensis sampled both within and outside areas where these species overlap with Q. afares. A genetic analysis was conducted using both nuclear (allozymes) and chloroplastic markers, which shows that Q. afares originates from a Q. suber x Q. canariensis hybridisation. At most loci, Q. afares predominantly possesses alleles from Q. suber, suggesting that the initial cross between Q. suber and Q. canariensis was followed by backcrossing with Q. suber. Other hypotheses that can account for this result, including genetic drift, gene silencing, gene conversion and selection, are discussed. A single Q. suber chlorotype was detected, and all Q. afares individuals displayed this chlorotype, indicating that Q. suber was the maternal parent. Q. afares is genetically, morphologically and ecologically differentiated from its parental species, and can therefore be considered as a stabilised hybrid species.     

Phylogeographical variation of chloroplast DNA in holm oak (Quercus ilex L.)

Variation in the lengths of restriction fragments (RFLPs) of the whole chloroplast DNA molecule was studied in 174 populations of Quercus ilex L. sampled over the entire distribution of this evergreen and mainly Mediterranean oak species. By using five endonucleases, 323 distinct fragments were obtained. From the 29 and 17 cpDNA changes identified as site and length mutations, respectively, 25 distinct chlorotypes were distinguished, mapped and treated cladistically with a parsimony analysis, using as an outgroup Q. alnifolia Poech, a closely related evergreen oak species endemic to Cyprus where Q. ilex does not grow. The predominant role of Q. ilex as maternal parent in hybridization with other species was reflected by the occurrence of a single very specific lineage of related chlorotypes, the most ancestral and recent ones being located in the southeastern and in the northwestern parts of the species’ geographical distribution, respectively. The lineage was constituted of two clusters of chlorotypes observed in the ‘ilex’ morphotyped populations of the Balkan and Italian Peninsulas (including the contiguous French Riviera), respectively. A third cluster was divided into two subclusters identified in the ‘rotundifolia’ morphotyped populations of North Africa, and of Iberia and the adjacent French regions, respectively. Postglacial colonization probably started from three distinct southerly refugia located in each of the three European peninsulas, and a contact area between the Italian and the Iberian migration routes was identified in the Rhône valley (France). Chlorotypes identical or related to those of the Iberian cluster were identified in the populations from Catalonia and the French Languedoc region, which showed intermediate morphotypes, and in the French Atlantic populations which possessed the ‘ilex’ morphotype, suggesting the occurrence of adaptive morphological changes in the northern part of the species’ distribution.     

Differential and interactive effects of temperature and photoperiod on budburst and carbon reserves in two co-occurring Mediterranean oaks

Effects of temperature and photoperiod and their interactions on budburst and on the use of carbon reserves were examined in two Mediterranean oaks differing in wood anatomy and leaf habit. Seedlings of Quercus ilex subsp. ballota (evergreen and diffuse-porous wood) and Q. faginea (semi-deciduous and ring-porous wood) were grown under two temperatures (12 and 19 °C) and two photoperiods (10 and 16 h) in a factorial experiment. In the 16 h photoperiod at 19 °C, photosynthesis was suppressed in half of the seedlings by covering leaves with aluminium foil. The concentration of soluble sugars, starch and lipids in leaves, stems and roots was assessed before and after budburst. Under the 12 °C treatment (mean current temperature in early spring in the Iberian Peninsula), budburst in Q. faginea occurred earlier than in Q. ilex . Higher temperature promoted earlier budburst in both species, mostly under the 16 h photoperiod. This response was less pronounced in Q. faginea because its budburst was also controlled by photoperiod, and because this species needs to construct a new ring of xylem before budburst to supply its growth demands. Therefore, dates of budburst of the two species became closer to each other in the warmer treatment, which might alter competitive relations between the species with changing climate. While Q. ilex relied on carbon reserves for budburst, Q. faginea relied on both carbon reserves and current photoassimilates. The different responses of the two Quercus species to temperature and photoperiod related more to xylem structure than to the source of carbon used for budburst.     

Foliar trichornes of the evergreen and semideciduous species of the genus Quercus (Fagaceae) in the Iberian Peninsula

The leaf trichomes of the evergreen and semi-deciduous species of the genus Quercus living in the Iberian Peninsula were studied by means of SEM and LM. The SEM has been particularly useful because of the high quality of the illustrations and the possibility of recognizing the structures under I,M or the stereomicroscope afterwards. The studied species were: Quercus coccifera, Q ilex , Q rotundifolia, Q suber, Q canariensis, Q faginea, Q brateroi and Q lusitanica . All species show some exclusive particularities that permit their identification using these characters. The abaxial surface of the leaf always has more trichomes than the adaxial and hence provides more characters for identification. Quercus alpestris Boiss. shows the same features in the leaf trichomes as Q faginea Lam. A key for identification using these characters is provided.     

Seed-mass effects in four Mediterranean Quercus species (Fagaceae) growing in contrasting light environments

Three hypotheses have been proposed to explain the functional relationship between seed mass and seedling performance: the reserve effect (larger seeds retain a larger proportion of reserves after germinating), the metabolic effect (seedlings from larger seeds have slower relative growth rates), and the seedling-size effect (larger seeds produce larger seedlings). We tested these hypotheses by growing four Mediterranean Quercus species under different light conditions (3, 27, and 100% of available radiation). We found evidence for two of the three hypotheses, but none of the four species complied with all three hypotheses at the same time. The reserve effect was not found in any species, the metabolic effect was found in three species (Q. ilex, Q. pyrenaica, and Q. suber), and the seedling-size effect in all species. Light availability significantly affected the relationships between seed size and seedling traits. For Q. ilex and Q. canariensis, a seedling-size effect was found under all three light conditions, but only under the lowest light (3%) for Q. suber and Q. pyrenaica. In all species, the correlation between seed mass and seedling mass increased with a decrease in light, suggesting that seedlings growing in low light depend more upon their seed reserves. A causal model integrates the three hypotheses, suggesting that larger seeds generally produced larger seedlings.     

Foliar trichomes of the evergreen and semi-deciduous species of the genus Quercus (Fagaceae) in the Iberian Peninsula

The leaf trichomes of the evergreen and semi-deciduous species of the genus Quercus living in the Iberian Peninsula were studied by means of SEM and LM. The SEM has been particularly useful because of the high quality of the illustrations and the possibility of recognizing the structures under LM or the stereomicroscope afterwards. The studied species were-. Quercus coccifera, Q. ilex, Q. rotundifolia, Q suber, Q canariensis, Q. faginea, Q. broteroi and Q. lusitanica. All species show some exclusive particularities that permit their identification using these characters. The abaxial surface of the leaf always has more trichomes than the adaxial and hence provides more characters for identification. Quercus alpestris Boiss. shows the same features in the leaf trichomes as Q. faginea Lam. A key for identification using these characters is provided.     

Seasonal changes of root hydraulic conductance (KRL) in four forest trees: an ecological interpretation

This paper deals with the possibility of relating root hydraulic parameters to an ecological index describing the continentality/oceanicity of four forest trees. Root hydraulic conductance ($K_R$) of seedlings of Fagus sylvatica L., Quercus ilex L., Quercus suber L. and Quercus pubescens Willd. was measured in May, August and November 1996. $K_R$ was calculated in terms of the relation of the water flow through intact root systems in situ measured with the pressure chamber, and the pressure driving the flow. The sufficiency of the root system to supply the foliage was estimated by dividing $K_R$ by the seedlings leaf surface area ($A_L$) thus obtaining $K_RL$. In the spring, $K_RL$ was largest in F. sylvatica and smallest in Q. pubescens with intermediate values recorded in Q. ilex and Q. suber. All the species studied showed a large decline in $K_RL$ just prior to the winter rest except for Q. suber which mantained $K_RL$ approximately constant through the period of study. In most cases, $K_RL$ changed in accordance with analogous changes in the flow. When the total seedlings' leaf surface area ($A_L$) was plotted versus $K_RL$, it appeared that $K_RL$ of Q. pubescens increased with $A_L$, proportionally, while $K_RL$ of F. sylvatica was inversely related to $A_L$. This, together with the largest $K_RL$ recorded in the summer in Q. pubescens, was interpreted as advantageous to this species (which is adapted to semi-arid environments) in that: (a) roots could supply water to foliage efficiently even during the adverse season and (b) the foliage growth could be sustained even in summer.No statistically significant relation of $K_RL$ to the continentality index calculated for the four species studied on the basis of their European distribution, was found to exist. Nonetheless, our data appear to be encouraging for future research aimed at better interpreting the typical distribution areas of plant species.     

Ancient and current gene flow between two distantly related Mediterranean oak species, Quercus suber and Q. ilex

Background and Aims

Quercus suber and Q. ilex are distantly related and their distributions partially overlap. They hybridize occasionally, but the complete replacement of Q. suber chloroplast DNA (cpDNA) by that of Q. ilex was identified in two specific geographical areas. The objective of this study was to determine whether the contrasting situation reflected current or recent geographical interspecies gene flow variation or was the result of ancient introgression.

Methods

cpDNA PCR-RFLPs (restriction fragment length polymorphisms) and variation at ten nuclear microsatellite loci were analysed in populations of each species, in 16 morphologically intermediate individuals and the progeny of several of them. Interspecies nuclear introgression was based on individual admixture rates using a Bayesian approach with no a priori species assignment, and on a maximum-likelihood (ML) method, using allele frequencies in the allopatric populations of each species as controls. Gene flow was compared specifically between populations located within and outside the specific areas.

Key Results

High interspecies nuclear genetic differentiation was observed, with twice the number of alleles in Q. ilex than in Q. suber. According to Bayesian assignment, approx. 1 % of individuals had a high probability of being F₁ hybrids, and bidirectional nuclear introgression affected approx. 4 % of individuals in each species. Hybrid and introgressed individuals were identified predominantly in mixed stands and may have a recent origin. Higher proportions including allospecific genes recovered from past hybridization were obtained using the ML method. Similar rates of hybridization and of nuclear introgression, partially independent of cpDNA interspecies transfer suggestive of gene filtering, were obtained in the populations located within and outside the areas of complete cpDNA replacement.

Conclusions

The results did not provide evidence for geographical variation in interspecies gene flow. In contrast, historical introgression is supported by palynological records and constitutes the more reliable origin of cpDNA replacement in specific regions.Key words: cpDNA PCR-RFLPs, nuclear microsatellite (nSSR) variation, hybridization, interspecies genetic introgression, Quercus suber, Quercus ilex     

Variation in morphological traits in a recent hybrid zone between closely related Quercus liaotungensis and Q. mongolica (Fagaceae)

Aims Hybridization usually leads to gene introgression between related species in hybrid zones, associated with complex patterns of morphological variation. Nevertheless, previous studies have tended to ignore the effects of geographic variation in hybridization rates on species taxonomy. This study aims to investigate the variation of morphological traits between two sympatric and taxonomically confused oak species, Quercus liaotungensis and Q. mongolica, and reveal the effects of hybridization rates on morphological traits and the taxonomic boundary.Methods We used seven microsatellite loci to evaluate species status and measured 15 morphological traits in 26 trees in the recent hybrid zone between Q. liaotungensis and Q. mongolica, and we characterized the differences between the two oak species and their hybrids for the investigated traits.Important findings Molecular analyses indicated that 74% of 78 sampled maternal trees were hybrids between Q. liaotungensis and Q. mongolica although the observed morphological variation suggested that they had remained distinct species. Across all of the differentiated leaf and reproductive traits, the hybrids expressed patterns similar to Q. liaotungensis, which may suggest dominant expression of parental characters. These results are consistent with our expectation that hybrids will be difficult to distinguish from parental species in a recent hybrid zone.     

Potential host plants of Corythucha arcuata (Het., Tingidae) in Europe: a laboratory study

Abstract:  The oak lace bug Corythucha arcuata (Say) (Het., Tingidae), native to North America, was found in Europe on Quercus robur L. and other oaks in the spring of 2000. The potential host plant range of this species in Europe and its development time were investigated in a laboratory study. An assay was performed on leaf cuts of different plant species. On the deciduous European oaks ( Q. robur , Quercus pubescens Willd, Quercus petraea (Mattuschka) Liebl., Quercus cerris L.), as well as Rubus ulmifolius Schott. and Rubus idaeus L., most of the lace bugs (>50%) reached the adult stage; on Castanea sativa Mill., Rubus caesius L. and Rosa canina L., a reduced number of individuals (<25%) reached the adult stage. No nymphs survived on Quercus rubra L. (mentioned in literature as a host plant), on the evergreen oaks Quercus suber L. and Quercus ilex L., on Malus domestica Borkh. and four tested maple species. On plant species where the lace bug reached the adult stage, the development time varied from 13 to 27 days. On European deciduous oak species, the development time was longer on leaves taken in late summer (September) than on those of late spring (June); on the contrary, such differences were not observed on Rubus species, and Castanea sativa .     

Diversity and specificity of ectomycorrhizal fungi retrieved from an old-growth Mediterranean forest dominated by Quercus ilex

We analysed the ectomycorrhizal (ECM) fungal diversity in a Mediterranean old-growth Quercus ilex forest stand from Corsica (France), where Arbutus unedo was the only other ECM host. On a 6400 m2 stand, we investigated whether oak age and host species shaped below-ground ECM diversity. Ectomycorrhizas were collected under Q. ilex individuals of various ages (1 yr seedlings; 3-10 yr saplings; old trees) and A. unedo. They were typed by ITS-RFLP analysis and identified by match to RFLP patterns of fruitbodies, or by sequencing. A diversity of 140 taxa was found among 558 ectomycorrhizas, with many rare taxa. Cenococcum geophilum dominated (35% of ECMs), as well as Russulaceae, Cortinariaceae and Thelephoraceae. Fungal species richness was comparable above and below ground, but the two levels exhibited < 20% overlap in fungal species composition. Quercus ilex age did not strongly shape ECM diversity. The two ECM hosts, A. unedo and Q. ilex, tended to share few ECM species (< 15% of the ECM diversity). Implications for oak forest dynamics are discussed.     

Acorn removal and dispersal by the dung beetle Thorectes lusitanicus: ecological implications

Abstract.  1. Plant–animal interactions, and in particular the processes of seed predation and dispersal, are crucial for tree regeneration and forest dynamics. A novel and striking case of interaction between a dung beetle ( Thorectes lusitanicus ) and two Quercus species ( Q. suber and Q. canariensis ) in forests of southern Spain is presented here.
2. During the autumn, T. lusitanicus beetles (endemic to the southern Iberian Peninsula) bury and feed on single-seeded fruits (acorns) of Quercus , with important ecological implications.
3. Field experiments found differences in the removal rate of acorns by T. lusitanicus , depending on the type of microsite within the forest, the species of oak, the exclosure of large herbivores, and the forest site.
4. Acorn consumption by T. lusitanicus was studied under laboratory conditions, confirming for the first time that this dung beetle is a legitimate seed predator.
5. In addition, some buried acorns can be abandoned partially predated or even intact, and emerge as seedlings; thus, T. lusitanicus also has a potential role as secondary seed disperser.     

Differences in fine-scale genetic structure and dispersal in Quercus ilex L. and Q. suber L.: consequences for regeneration of mediterranean open woods

Cork oak (Quercus suber L.) and holm oak (Q. ilex L.) are among the most important tree species (economically and ecologically) in the Western Mediterranean region, where they define unique open woods (created and maintained by man) known as 'dehesas' in Spain. However, these formations are under increasing threat due to the lack of regeneration. We have analysed spatial genetic structure in a mixed parkland; inferences about gene dispersal have also been performed, according to the isolation by distance model. Noticeable differences have been detected between the species, despite their similar ecological roles. Restricted effective dispersal leads to kin structures in cork oak, up to 70 m, while no genetic structure is observed in holm oak. Our results suggest a very effective dispersal for the latter, with a local historical gene flow estimated between 55 and 95 m. This is the first time regeneration of Mediterranean oak parklands has been assessed from a genetic perspective. Effective gene flow detected for holm oaks allows us to discount the risk of inbreeding over successive generations. Thus, regeneration of Q. ilex dehesas will just require action directed to help the settlement of the saplings (such as limiting grazing). However, in those cases where densities are too low, more intense forestation (such as plantation and/or establishment of appropriate shelter) will be needed. The 'density threshold' for initiating regeneration will probably be higher for cork oak, due to its more limited dispersal and minor full-light tolerance.     

Comparative anatomical analysis of the cotyledonary region in three Mediterranean Basin Quercus (Fagaceae)

Anatomical changes at the cotyledonary node from the embryo to the seedling stage in Quercus coccifera, Q. ilex, and Q. humilis were investigated by light and scanning electron microscopy techniques. Mature embryos of Q. humilis possess 2-3 pairs of leaf primordia and a pair of cotyledonary buds, whereas in Q. coccifera and Q. ilex there are two incipient primordia, and cotyledonary buds are not observed until 1 wk after germination. In all three species the cotyledonary buds multiply, forming bud clusters, and a vascular connection is well established within 5-6 wk after germination. As development proceeds, the cotyledonary region becomes woody, but buds, which are exogenous in origin, never become embedded in the periderm. In comparison with Q. suber, another native Mediterranean Basin oak, the cotyledonary node is short and axillary buds are not present below the insertion of cotyledons. In addition, starch accumulation in the cotyledonary region is not observed from histological analysis in the three oaks. Therefore, in Q. coccifera, Q. ilex, and Q. humilis seedlings the cotyledonary node can be considered to be an important regenerative structure enabling them to resprout after the elimination of the shoot above the cotyledons, despite the absence of a lignotuberous structure.     

STUDIES IN THE QUERCUS UNDULATA COMPLEX. III. THE CONTRIBUTION OF Q. ARIZONICA

Tucker, J. M. (U. California, Davis.) Studies in the Quercus undulata complex. III. The contribution of Q. arizonica . Amer. Jour. Bot. 50(7): 699–708. Illus. 1903.—Of the 7 oak species involved in the Quercus undulata complex, Q. arizonica contributes the least of all. The latter has hybridized with Q. gambelii at a few widely separated localities (listed in Table 1) in central Arizona, and northern Sonora and Chihuahua, Mexico. The putative hybrids (identifiable as Quercus undulata) occur as isolated individuals with the parental species. The parents, although regionally sympatric, are usually ecologically isolated. They differ in a number of morphological characters, 6 of which were analyzed in detail. The resulting data, presented as pietorialized scatter diagrams, demonstrate that the putative hybrids are intermediate, in general. This is taken as evidence of their hybrid nature. Factors limiting hybridization in oaks are discussed. It is speculated that hybridization between Q. arizonica and Q. gambelii has occurred since the postglacial hypsithermal interval.     

Past distribution and ecology of the cork oak (Quercus suber) in the Iberian Peninsula: a pollen-analytical approach

Abstract.  This study presents pollen-analytical data from continental and offshore Iberian Peninsula sites that include pollen curves of Quercus suber , to provide information on the past distribution and ecology of the cork oak ( Q. suber ). Results centre on a new pollen record of Navarrés (Valencia, eastern Spain), which shows that the cork oak survived regionally during the Upper Pleistocene and was important during a mid-Holocene replacement of a local pine forest by Quercus -dominated communities. This phenomenon appears linked to the recurrence of fire and reinforces the value of the cork oak for reforestation programmes in fire-prone areas. In addition to Navarrés, other Late Quaternary pollen sequences (Sobrestany, Casablanca-Almenara, Padul, SU 8103, SU8113, 8057B) suggest last glacial survival of the cork oak in southern and coastal areas of the Peninsula and North Africa. Important developments also occur from the Late Glacial to the middle Holocene, not only in the west but also in the eastern Peninsula. It is suggested that, in the absence of human influence, Q. suber would develop in non-monospecific forests, sharing the arboreal stratum both with other sclerophyllous and deciduous Quercus and Pinus species.