Distribution and regeneration strategies of major canopy dominants in species-rich subtropical/warm temperate rainforests in south-western Japan

The distribution and regeneration strategy of the major canopy dominants in species-rich subtropical/warm temperate rainforests in south-western Japan was studied in a hilly zone below 1100 m a.s.l. Using the patch sampling method, four dominance-community types were numerically identified and they corresponded to four habitats which represented a combination of topography and altitude (i.e. ridgesvs slopes, and belowvs above 500 m a.s.l.) Seven major canopy dominants had their respective distributional core in one of these topo-altitudinal habitats. The seven canopy dominants could be classified into three species groups according to their size structure and growth habits. Group A (Tsuga sieboldii andQuercus gilva) and group B (Quercus acuta, Quercus salicina, Machilus thunbergii) were restricted to the emergent and canopy layer, respectively. These two groups had only a few subcanopy trees and saplings. Saplings of group B showed a rapid growth rate in canopy gaps. Group C (Distylium racemosum) was characterized by many subcanopy trees and saplings that grew steadily under the closed canopy.Castanopsis sieboldii showed intermediate characteristics between group B and C in the size structure and growth habit of its saplings. The density ofD. racemosum canopy trees was markedly reduced on ridges and slopes above 500 m and on slopes below 500 m. In these marginal habitats, the three species groups coexisted by sharing different strata within a community. This situation was possible due to the differences in regeneration strategies among the canopy species.     

Canopy disturbance patterns and regeneration of Quercus species in two Ohio old-growth forests

This study was conducted to determine the abundance of Quercus species, the spatial pattern of Quercus regeneration, the current canopy disturbance pattern, and their interrelationship in two old-growth deciduous forests in Ohio (Goll Woods and Sears-Carmean Woods). Acer saccharum and Fagus grandifolia had the greatest density and basal area in both forests, yet the largest trees (by basal area) present at each site were Quercus spp. Quercus spp. appeared to be decreasing in abundance in both sites. Though Quercus seedlings were common, few Quercus saplings or subcanopy trees were present. The current disturbance regimes were dominated by small canopy gaps created by death of 1–2 trees; canopy gaps 100 m² in size were rare and only 2.5–2.8% of the forest area was covered by recognizable canopy gaps. No significant differences in the density of Quercus seedlings or saplings were found between gaps and non-gap areas at either site. Though no significant barrier to seedling establishment appeared to exist, the present disturbance regimes are not well suited for the growth of Quercus into the subcanopy size class or the recruitment of Quercus into the canopy. The most frequent gapmakers in Goll Woods were Tilia americana and Acer saccharum, and those in Sears-Carmean Woods were A. saccharum and F. grandifolia. The species most frequent as gap fillers were A. saccharum (in both sites) and F. grandifolia (in Goll Woods). These results suggest that A. saccharum will continue to increase in abundance, and Quercus decrease in abundance, in these two old-growth stands.     

Individual resource allocation to vegetative growth and reproduction in subgenus <Emphasis Type="Italic">Cyclobalanopsis</Emphasis> (<Emphasis Type="Italic">Quercus</Emphasis>, Fagaceae) trees

The resource allocation for vegetative growth and female reproduction in three tree species of subgenus Cyclobalanopsis (Quercus, Fagaceae), i.e., Q. salicina, Q. sessilifolia, and Q. acuta, were examined on a per-individual basis in two consecutive reproductive seasons, in order to test whether these trees fit the predictions of the masting hypotheses about resource matching versus resource switching. Since the three Quercus species have a biennial fruiting habit, it takes 3 years for the observation of two reproductive events. Female flower and acorn production per tree were investigated by using a seed-trap method and a numerical analysis of seed dispersal. The net production of each individual was estimated as the sum of the annual increase in the dry mass of vegetative organs and reproductive investment per tree. In the data analyses, the three species were pooled, since all 12 sample trees of the subgenus apparently showed masting in the same year, with no exceptions. Female flower and acorn production per individual tree changed considerably between years. The net production per tree increased with tree size, but did not differ between years. Therefore, the reproductive allocation (proportion of a plant’s annual assimilated resources which are used for reproduction) differed dramatically between years. On the other hand, within a year, the reproductive allocation increased with increasing net production per tree. These results suggest that the switching of resource allocation between years within an individual are occurring in subgenus Cyclobalanopsis species, and the intensity of the switching increases with increasing tree size.     

Seedling recruitment ofChamaecyparis obtusa andSciadopitys verticillata in different microenvironments in an old-growthSciadopitys verticillata forest

Seedling recruitment ofChamecyparis obtusa andSciadopitys verticillata in different microenvironments in an old-growthS. verticillata forest was studied for five years. Exposed mineral soil beneath a gap, which was newly created by a typhoon, supported the best seedling emergence forC. obtusa. S. verticillata seemed to require no specific microenvironment for its seedling emergence. Mortality of seedlings was higher for both species beneath a closed canopy, where all new seedlings ofC. obtusa died within a year after their emergence. Beneath the gap, mortality of seedlings was generally lower for both species, regardless of the presence of litter on the ground. The occurrence of saplings was more frequent forC. obtusa beneath the gaps and forS. verticillata beneath a closed canopy. Difference of seedling recruitment behaviour could maintain the coexistence ofC. obtusa andS. verticillata in the canopy layer of this forest in a non-equilibrium state caused by occasional disturbance.     

Shoot structure and dynamics of saplings and canopies of three deciduous broad-leaved trees of a coppice forest in central Japan

Three deciduous broad-leaved trees, Quercus serrata, Castanea crenata and Carpinus laxiflora, were the main constituents of a coppice forest in central Japan. The shoot elongation and leaf emergence modes of both saplings and the canopy of the three species were investigated. The shoot elongation modes of Q. serrata and C. crenata were the same in saplings and the upper layer of the canopy. The second shoots of these two species were formed after the first shoots were elongated. C. laxiflora was different between saplings and the upper layer of the canopy. In saplings, only the first shoots took a long time to elongate. In the upper canopy layer, higher order shoots were formed in the same way as in the other two species. In the lower layer of the canopy, all three species showed the same shoot elongation mode, in which only the first shoot and its duration of elongation was short. Leaf longevity, individual leaf area, leaf mass per unit leaf area and the stem mass per unit stem length of C. laxiflora were significantly shorter or significantly smaller than those of Q. serrata and C. crenata. The length of the stem per unit leaf area of C. laxiflora was three times that of Q. serrata and five times that of C. crenata. The elongation growth of C. laxiflora was highly efficient as it occurred with a small leaf area. The shoot dynamics and the shoot structure of C. laxiflora are more suitable for elongation growth than in Q. serrata and C. crenata. Furthermore, the shoot structures of the three species were compared and ecological characteristics of the three species are discussed. Received: 29 September 1998 / Accepted: 17 September 1999     

Spatial patterns and associations in a Quercus‐Betula forest in northern China

Question: Are species‐specific regeneration strategies and competition the dominant processes facilitating species coexistence in a Quercus liaotungensis dominated temperate deciduous forest? Location: Dongling Mountains, North China, 1300 m a.s.l. Methods: Ripley's K‐function was used to characterize the spatial patterns and spatial associations of two dominant tree species, Quercus liaotungensis and Betula dahurica, and a common subcanopy species, Acer mono, at different growth stages (adult, sapling, seedling). Results: Seedlings, saplings and adults of all three species exhibited clumped distributions at most spatial scales. Quercus seedlings and saplings were positively associated with conspecific adult trees and spatially independent of dead trees suggesting that seed dispersal and vegetative regeneration influenced the spatial patterning of Quercus trees. Betula seedlings and saplings were positively associated with both live and dead trees of conspecific adults at small scales (<5 m) but negatively associated with live and dead trees of other species indicating sprouting as an important mechanism of reproduction. Saplings of Acer had a strong spatial dependence on the distribution of conspecific adult trees indicating its limited seed dispersal range. Negative associations between adult trees of Betula and Quercus demonstrated interspecific competition at local scales (<5 m). Conclusions: Different regeneration strategies among the three species play an important role in regulating their spatial distribution patterns, while competition between individuals of Betula and Quercus at the adult stage also contributes to spatial patterning of these communities. The recruitment limitations of Betula and Quercus may affect the persistence of these species and the long‐term dynamics of the forest.     

Two-year cycles of synchronous acorn and leaf production in biennial-fruiting evergreen oaks of subgenus Cyclobalanopsis (Quercus, Fagaceae)

Many masting species switch resources between vegetative growth and reproduction in mast and non-mast years. Although masting of oak species is well known, there have been few investigations of the relationship between vegetative growth and reproduction based on long-term monitoring data, especially in evergreen oaks of subgenus Cyclobalanopsis. We investigated annual variations over 13?years in acorn and leaf production of three evergreen oak species in subgenus Cyclobalanopsis, genus Quercus (Fagaceae)??Q. acuta, Q. salicina and Q. sessilifolia??in western Japan. In these species, the maturation of acorns occurs in the second autumn after flowering, which is known as a biennial-fruiting habit. We found a pattern of acorn production and masting in alternate years that was synchronized in all three species. Masting was not correlated with temperature and precipitation. Annual leaf-fall also showed 2-year cycle in the three oak species; peak years were synchronized between species and peak leaf-fall alternated with acorn production in all three species. Furthermore, there was a significant negative correlation between acorn and leaf production in all three species. Data showing 2-year cycles of acorn and leaf production and the negative correlation between them supports the hypothesis of resource switching between vegetative growth and reproduction. The 2-year cycle might be the basic, intrinsic rhythm of resource allocation in biennial-fruiting Cyclobalanopsis species.     

Regeneration in subalpine coniferous forests

The regeneration process of a subalpine coniferous forest, a mixed forest ofTsuga diversifolia (dominant species),Abies veitchii, Abies mariessi, andPicea jezoensis var.hondoensis, was studied on the basis of annual ring data. The age class distribution was discontinuous and four age groups occurred in the study plot (30m×30m). The canopy layer was a mosaic of patches (83.8–133.7 m² patch area), which had different mean ages. The recruitment of canopy trees was carried out only by advance regeneration in the plot. The diameter growth ofAbies andPicea exceeded diameter growth ofTsuga in the gap.Abies lived for 200–300 years and their trunks were susceptible to heart rot.Picea lived for 300–400 years andTsuga for more than 400 years. The regeneration process derived from the analysis of the plot consisted of three phases leading to the development of a even-aged patch; (1) the establishment of saplings before a gap opening, (2) the opening of a gap in the canopy and repair of the canopy by advance regenerated saplings dominated by rapid growth species,Abies andPicea, and (3) the dying off of canopy trees as each species reached the end of its life-span, resulting in pure patches of long-livedTsuga.     

Initial regenerative processes ofDistylium racemosum andPersea thunbergii in an evergreen broad-leaved forest

We studied the initial regenerative processes ofDistylium racemosum andPersea thunbergii, major canopy species, in an old-growth evergreen broad-leaved forest, Kagoshima, southwestern Japan. Although the two species coexisted, the patterns of seed production, seedling emergence, and sapling survival were different between them. During the observation (1989–1991),P. thunbergii produced large numbers of seeds in alternate years, whileD. racemosum had no mast year. The density of established seedlings was high and increased with mass seed production forP. thunbergii, but was fairly low forD. racemosum. The mortality of seedlings and saplings ofP. thunbergii was higher than that ofD. racemosum. In a closed stand, the sapling bank was maintained by dense seedling supply forP. thunbergii, and by extremely low mortality of individuals germinated before the beginning of observation forD. racemosum. Since saplings ofD. racemosum showed continuous height growth beneath the closed canopy, the possibility of recruitment into the upper layer seems to be high. The strategy ofP. thunbergii might be to wait for suitable conditions favoring sapling growth on various site by means of frequent and large seed productivity and wide dispersal of seeds. Thus both species might be able to coexist through environmental heterogeneity.     

Coexistence of three canopy tree species in a riparian forest in the Chichibu Mountains, central Japan

Three canopy tree species (Fraxinus platypoda, Pterocarya rhoifolia, andCercidiphyllum japonicum) coexist in riparian forests in the Chichibu Mountains of central Japan. We compared the forest structure and the reproductive characteristics of these species.F. platypoda was the dominant canopy species. It produced many saplings and grew in abandoned channels and floodplains, and was able to invade both large and small disturbance sites.P. rhoifolia was a subdominant species that occurred on the deposits of large-scale landslides and grew in patches containing even-aged trees.C. japonicum was the other subdominant species that produced few saplings and invaded large disturbance sites together withP. rhoifolia. Establishment sites ofC. japonicum were restricted to fine mineral soils and fallen logs. We found tradeoffs in reproductive characteristics (seed size, seed number, irregular seed production, and sprouting) among the three canopy species.F. platypoda andP. rhoifolia had large seeds and produced fruits irregularly.C. japonicum produced many small seeds every year and sprouted prolifically around the main stem. The causes of the coexistence mechanism of the three riparian canopy tree species may be both niche- and chance-determined to varying degrees. In riparian areas, the three canopy species were well-adapted to disturbances throughout their life-history.     

Shoot growth and tree architecture of saplings of the major canopy dominants in a warm-temperate rainforest

Sapling density, shoot growth, and sapling architecture were studied in five major canopy dominants both under closed canopy and gaps in a warm-temperate rainforest. The five species showed wide variations in distribution, shoot growth, and sapling architecture. Distylium racemosum and Quercus acuta had significantly higher sapling densities under closed canopy than in gaps. Castanopsis sieboldii and Machilus thunbergii had significantly higher sapling densities in gaps than under closed canopy. Quercus salicina showed no significant difference in sapling density between the two habitats. Under closed canopy, C. sieboldii and M. thunbergii had wider crowns than the other species. Distylium racemosum had the greatest number of terminal shoots among the species. Quercus acuta had a branchless small crown. Quercus salicina showed intermediate values in crown width, depth and the number of terminal shoots among the species. Distylium racemosum showed the greatest height-growth rate among the species under the closed canopy, but was the slowest in gaps. Castanopsis sieboldii and M. thunbergii showed the greatest height-growth rates among the species in gaps. Quercus salicina showed the slowest height-growth rates both under closed canopy and gaps. All of the five species showed low mortality under closed canopy. For the major canopy dominants: (i) sapling architecture may not be an important factor in determining mortality but it may be important for height-growth rate; and (ii) sprouting helps saplings to survive until gap formation and facilitates rapid growth in the gaps.     

Genetic admixing of two evergreen oaks,Quercus acuta and Q. sessilifolia (subgenus Cyclobalanopsis), is the result of interspecific introgressive hybridization

In forests worldwide, Quercus is a major genus; however, the boundaries between the constituent species are relatively weak, and hybridization is reported frequently. In this study, we examined Quercus acuta and Quercus sessilifolia (subgenus Cyclobalanopsis), which have a putative hybrid—Q. x takaoyamensis. We investigated leaf morphological traits and microsatellites of Q. acuta and Q. sessilifolia in the area where the two species are both found. Although the leaf traits overlapped, the two species could be distinguished morphologically as demonstrated by principal component analysis based on a range of these traits. They were also genetically differentiated, with F _ST?=?0.104. However, they shared most of the alleles at all eight loci examined, and considerable genetic admixing was detected. Admixture analysis demonstrated that Q. acuta and Q. sessilifolia, respectively, contained 11 and 24 % of individuals with a probability of less than 0.9 of being correctly assigned to their species. Model-based testing showed that this admixing was created by not only shared ancestral polymorphism but also by hybridization. Effective population size and migration rate were estimated using the coalescent approach. We estimated 8.843 and 71.98 effective numbers of migrants per generation to Q. acuta and Q. sessilifolia, respectively. Theoretically, one to ten migrants per generation are required to prevent complete genetic differentiation. Based on the results of this study, it appears that genetic admixing, with sharing of most alleles, is probably common in the two species and is maintained by interspecific introgressive hybridization.     

Comparative study of leaf carbon gain in saplings ofThujopsis dolabrata var.hondai andQuercus mongolica var.grosseserrata in a cool-temperate deciduous forest

Seasonal courses of leaf CO₂ gas exchange in a growing season were examined in saplings ofThujopsis dolabrata var.hondai andQuercus mongolica var.grosseserrata in a cool temperate deciduous forest. Between the two tree species there were no large differences in the light compensation point of leaf photosynthesis, except for the season of new leaf expansion. However, light-saturated rates of net photosynthesis were obviously high inT. dolabrata var.hondai. EvergreenT. dolabrata var.hondai saplings had large photosynthetic production in two seasons, before the emergence of new foliage and after foliage fall of the overstory deciduous trees, because of the significantly high solar radiant energy penetrating under the forest canopy during the seasons. Saplings of deciduousQ. mongolica var.grosseserrata were heavily shaded throughout the growing season by foliage of the overstory trees, which resulted in a low daily surplus production. The annual surplus production of leaves in the growing season was estimated to be 2300 mmol CO₂ m⁻² inT. dolabrata var.hondai and −100 mmol CO₂ m⁻², slightly negative, inQ. mongolica var.grosseserrata. These results supported the high survivability ofT. dolabrata var.hondai saplings and the high mortality ofQ. mongolica var.grosseserrata in the deciduous forest.     

Mature tree effect ofAcer mono on seedling mortality due to insect herbivory

Mature tree effects on the mortality and herbivory of current-year seedlings were investigated in a common subcanopy species,Acer mono Maxim., in a cool temperature mixed forest. The mortality of natural seeldings under the canopy withA. mono layers was greater than that under the canopy without them. Also, the mortality of seedlings in planters located under the crown of anA. mono tree was at least 1.8 times greater than that of those in planters about 5 m away from the crown edge.Pyrrhalta fuscipennis (Coleoptera: Chrysomelidae) and other specialist insects, having probably dropped fromA. mono crowns, were more frequently observed in planters underA. mono crowns than in those far the crowns. Leaf area loss due to specialist herbivores was probably the main cause of increase in the mortality ofA. mono seedlings close to conspecific adults. It is implied that seedling predation by specialist herbivores coming from parent trees is a substantial factor promoting local seed dispersal ofA. mono.     

ITS sequences from nuclear rDNA suggest unexpected phylogenetic relationships between Euro-Mediterranean, East Asiatic and North American taxa ofQuercus (Fagaceae)

Nucleotide sequences from the internal transcribed spacer (ITS) regions of the 18S–26S nuclear ribosomal DNA have been studied from ten species ofQuercus (representing four subgenera),Castanea sativa andFagus sylvatica, as a preliminary molecular contribution to the still poorly understood systematics and evolution ofFagaceae. The resulting matrix has been used to calculate pair-wise sequence divergence indices and to construct a maximum parsimony tree forQuercus coding indels as a fifth state. Divergence is greater forQuercus vs.Fagus than forQuercus vs.Castanea. The tree for theQuercus taxa studied reveals two clearly divergent clades. In clade I the evergreen W MediterraneanQ. suber appears in a basal position as sister to more distal deciduous taxa, i.e. the E MediterraneanQ. macrolepis and the E AsiaticQ. acutissima (all formerly united as different sections under the apparently polyphyletic subg.Cerris), andQ. rubra (a representative of the N American subg.Erythrobalanus), forming a pair withQ. acutissima. In clade II the evergreen southeastern N AmericanQ. virginiana is basal and sister to the remaining three branches, i.e. a pair of evergreen Mediterranean taxa withQ. ilex andQ. coccifera (subg.Sclerophyllodrys), the deciduous but otherwise plesiomorphic SE European/SW AsiaticQ. cerris (type species of subg.Cerris), and the related but more apomorphic European pairQ. petraea andQ. robur (subg.Quercus). These results partly conflict with current taxonomic classification but are supported by some anatomical and morphological characters. They document polyphyletic lines from evergreen to deciduous taxa and suggest Tertiary transcontinental connections within the genus.     

Tree composition and structure in disturbed stands with varying dominance by Pinus spp. in the highlands of Chiapas,México

We studied soil and forest floor conditions, regeneration patterns oftrees, and forest structure and floristic composition along a gradient ofdominance by Pinus spp. in disturbed stands in thehighlands of Chiapas, southern Mexico. Seedlings, saplings, and adults of treespecies were counted and measured in 2-3 circular plots (1000m² each) in 36 forest stands (a total of 38 treespecies). Dominance of broadleaved trees other thanQuercusspp. was negatively correlated with basal area of Pinusspp. (P < 0.001). Soils of pine-dominated stands weremore compacted, less acidic, and less fertile (lower C.E.C., nitrogen, andorganic matter content). Numerous broadleaved trees may depend on anoak-dominated canopy to regenerate, and changes associated to pinelandsexpansion may compromise their long-term persistence. However, seedlings andsaplings of Quercus spp. were abundant in stands with bothan oak- or pine-dominated canopy. The results suggest that a plan forsustainable forest utilization in the study region, and in other similarpopulated tropical highlands, could take advantage of the abundant oakregeneration and coexistence with pines in the canopy.     

Differences in sapling architecture betweenFagus crenata andFagus japonica

The ecological significance of architectural patterns for saplings ofFagus crenata andFagus japonica co-occurring in a secondary oak forest were evaluated by comparing the size and shape of leaves, trunks and crowns.Fagus japonica saplings were different fromF. crenata saplings in some architectural properties: (i) the leaf area and specific leaf area were larger; (ii) the ratio of sapling height to trunk length was lower, indicating greater leaning of the trunk; and (iii) the projection area of the crown was larger and the leaf area index lower indicating less mutual shading of leaves. These architectural features indicated thatF. japonica saplings were more shade tolerant thanF. crenata andF. crenata saplings were superior toF. japonica for growth in height and could, therefore, utilize sunlight in the upper layer. An erect trunk inF. crenata and a leaning trunk inF. japonica may be important characteristics associated with the regenerations patterns of each species; regeneration from seedlings under canopy gaps in the former and vegetative regeneration by sprouting in the latter.     

Large-Scale Patterns of Quercus ilex, Quercus suber, and Quercus pyrenaica Regeneration in Central-Western Spain

In Central-Western Spain, forests and woodlands composed of Quercus sp. support outstanding levels of biodiversity, but there is increasing concern about their long-term persistence due to a lack of regeneration. We hypothesize that this regenerative lack is operating on a large geographic scale; that there are differences in the abundance of regeneration between three oak species; that oak regeneration is governed mainly by forest management and structure; and that shrubs act as important physical protectors of seedlings and saplings. We analyzed whether densities of oak seedlings and saplings in several size classes were related to stand-structure, understory, and physiographic variables potentially affecting regeneration. Data collected at a regional level (1 km × 1 km grid) by the Spanish Forest Inventory were evaluated from 2,816 plots. Results revealed that regeneration failure was common for all size categories, from small seedlings to large saplings, and for the three oak species studied, especially the evergreens. Of the Quercus ilex, Q. suber, and Q. pyrenaica plots studied, 49%, 62%, and 20% were lacking any small seedlings, and 82%, 96%, and 56% did not have any large saplings, respectively. Regeneration was positively correlated with tree cover and density, especially of small and medium-sized trees, and negatively correlated with the presence of large trees, indicating that regeneration failure is mostly associated with more open, uniform, and/or aged woodlands. Regeneration densities of Q. ilex and Q. suber were positively correlated with all understory variables, suggesting that the presence of pioneer shrubs represent a major safe site for early tree recruitment, independent from specific shrub species.     

The limited role of canopy gaps in the successional dynamics of a mature mixed Quercus forest remnant

Question: Are canopy gap dynamics responsible for driving the structural and compositional changes that have occurred over a 26‐year period in a mature Quercus forest remnant? Location: Dobbs Natural Area, an unlogged 3.6‐ha forest preserve in west‐central Indiana, USA. Methods: We analyzed mapped permanent plot data for a site that illustrates a trend common in Quercus‐dominated forests in eastern North America, where recruitment of new stems is dominated by mesophytic, shade‐tolerant species such as Acer saccharum, rather than Quercus. We developed a GIS database from stand census measurements taken in 1974 and 2000, employing it to conduct tree‐by‐tree comparisons that allow direct determination of ingrowth, mortality and survivorship, and to relate the spatial patterns of subcanopy dynamics to canopy gap occurrence. Results: The re‐census shows modest changes in canopy composition, but much greater turnover in the subcanopy. Nearly half of all individuals originally present died; much of this mortality resulted from a major decline in subcanopy Ulmus americana. While overall density remained fairly constant, the subcanopy experienced substantial ingrowth of shade‐tolerant Acer saccharum, Fagus grandifolia, and Tilia americana. Canopy gaps, although forming at rates in the upper range of regional averages, did not significantly benefit subcanopy populations of Quercus spp. or most other taxa with limited shade tolerance. Conclusions: Canopy gaps play a minor role in driving the recent demographic trends of this stand. The spatial and temporal scales of light availability in gaps do not support regeneration of most shade‐intolerant species. Compositional change parallels a historical shift in light regimes.     

Not only size matters: Acorn selection by the European jay (Garrulus glandarius)

A strong selection for acorn characteristics is expected to have evolved in the mutualistic relationship between the European jay (Garrulus glandarius) and the oak (Quercus spp.). Bossema's pioneer work suggested that jays do not select acorns randomly, but rather they preferentially select some size and species. Preference for some seeds over others may have implications on plant community dynamics by conferring advantages (or disadvantages) on the selected (avoided) seed characteristics. In this paper we test to what extent jays select acorns by species and/or by size and the relation between these two traits in Mediterranean oak species. The experiments consist of a set of field tests in which acorns from four different coexisting Mediterranean oak species (Quercus ilex, Quercus faginea, Quercus suber, and Quercus coccifera) were placed in artificial feeders accessible to wild jays. The acorns were previously measured to control individual acorn characteristics. Using video-recording techniques, we followed jay activity and the fate of each acorn (sequence of acorn selection and method of transport). Q. ilex acorns were preferred over other acorns, and Q. coccifera acorns were avoided when other acorns were available. Preference for Q. faginea and Q. suber acorns was intermediate, that is, they were preferred over Q. coccifera acorns but not over Q. ilex acorns. Large acorns were also preferred although acorn species selection was stronger than size selection. Jays selected species and size both by visual means and by using acorn area as an indicator of size. Acorns wider than 17–19 mm were carried in the bill because of throat limitation. Our results confirm Bossema's study on temperate oaks and extend it to Mediterranean oak species, revealing implications on mixed oak forest dynamics.