Rodent acorn selection in a Mediterranean oak landscape

Quercus suber, Quercus ilex and Quercus coccifera (Cork, Holm and Kermes oaks, respectively) are common evergreen oak species that coexist in the landscapes of the western part of the Mediterranean basin. Rodents are the main acorn predators and thus one of the main factors for understanding recruitment patterns in oaks. In this paper we analyse to what extent mice prefer acorns from one oak species over another in three oak species studied using acorn removal experiments and video tape recordings. Twenty labelled acorns from each of the three Quercus species (60 acorns) were placed in 40 cm×40 cm quadrats on each plot. Because selection might vary as a result of the vegetation context, we performed the trials in the five main vegetation types within the study area (four replicates in each vegetation type) in order to control for habitat influences on rodent acorn preferences (a total of 20 plots). The removal of 1,200 acorns occurred within 68 days. Mice removed 98.7% of the acorns. Q. ilex acorns were preferred over Q. suber and Q. coccifera in all vegetation types except in pine forest, where no acorn preferences were detected. Acorn removal rates differed with vegetation type, correlating positively with shrub cover. The distance at which acorns were displaced by rodents (mean =4.6 m±5.1 SD) did not differ between acorn species, but varied among vegetation types. Bigger acorns of Q. coccifera were selected only after Q. ilex and Q. suber acorns were depleted, while no size selection was detected for the latter two species. Thus, we conclude that rodents show preference for some oak acorns and that landscape context contributes significantly to rodent activities and decisions.     

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.     

Acorn dispersal estimated by radio-tracking

Bird-dispersed seeds are difficult to track, especially in the case of long-distance dispersal events. To estimate the oak dispersal distance and the seed shadow generated by the European jay (Garrulus glandarius), we inserted radio-transmitters in 239 acorns, placed them in bird-feeders and then located them by radio-tracking. Using this methodology we located the exact caching site of 94 Quercus ilex and 54 Q. suber acorns and determined the caching habitat characteristics (vegetation type, distance, spatial distribution). The results show that: (1) there is no differences in the dispersal distance distribution between the different acorn species or sizes, (2) dispersal distances range from approximately 3 m up to approximately 550 m (mean = 68.6 m; median = 49.2 m), (3) recently abandoned fields and forest tracks were the sites preferred by jays to cache acorns, whereas fields and shrublands were avoided and (4) seed shadows showed acorn aggregation zones (i.e. clusters of caches) close to the feeder as well as isolated caches at longer distances. The results also suggest that radio-transmitters are a cheap and reliable way to determine seed shadows and quantify both seed dispersal and post-dispersal seed predation for medium to large seeds.     

Guild structures of seed insects in relation to acorn development in two oak species

We investigated patterns of acorn growth in Quercus variabilis Blume and Quercus serrata Thunb., seasonal trends in emergence of seed insects found in the acorns, oviposition periods of the insects and falling periods of insect-infested acorns. In Q. variabilis, two insect guilds were associated with acorn development: (i) the immature acorn feeding (IAF) guild [Curculionidae sp., Poecilips cardamomi (Schaufuss), and Characoma ruficirra (Hampson)]; and (ii) the mature acorn feeding (MAF) guild [Curculio robustus (Roelofs), Curculio sikkimensis (Heller), and Cydia glandicolana (Danilevsky)]. In Q. serrata, there were three guilds: (i) the pistillate flower feeding (PFF) guild (cynipid wasp); (ii) the IAF guild [sap absorption by Mechoris ursulus (Roelofs)]; and (iii) the MAF guild (M. ursulus, C. sikkimensis, Cydia danilevskyi (Kuznetzov), C. glandicolana and Autostichidae sp.). The succession of guilds during acorn development may be a consequence of the use by different species of the limited food resource. The lack of a PFF guild in Q. variabilis that was found in our field site would have a positive effect on IAF guilds in utilizing the acorns.     

Effectiveness of rodents as local seed dispersers of Holm oaks

In this study we assessed the effectiveness of rodents as dispersers of Quercus ilex in a patchy landscape in southeastern Spain. We experimentally followed the fates of 3,200 marked and weighed acorns from dispersal through the time of seedling emergence over three years. Rodents handled about 99% of acorns, and dispersed 67% and cached 7.4% of the dispersed acorns. Most caches were recovered and consumed, and only 1.3% of the original experimental acorns were found alive in caches the following spring. Dispersal distances were short (mean = 356.2 cm, median = 157 cm) and strongly right-skewed. Heavier acorns were dispersed further and were more likely to be cached and survive than lighter acorns. All caches were in litter or soil, and each contained a single acorn. Rodents moved acorns nonrandomly, mostly to oaks and pines. Most surviving acorns were either in oaks, a poor microhabitat for oak recruitment, or shrubs, a suitable microhabitat for oak recruitment. Our results suggest that rodents, by burying a relatively high proportion of acorns singly in shrubs and pines, act as moderately effective dispersers of Q. ilex. Nonetheless, this dispersal comes at a very heavy cost.     

Hoarding behaviors of two wood mouse species: Different preference for acorns of two Fagaceae species

Two species of wood mouse, Apodemus argenteus and A. speciosus, were observed consuming and hoarding acorns of Quercus serrata and Castanopsis cuspidata. When each species of acorn was supplied individually, both species of mice used each species of acorn for eating and hoarding. When both species of acorn were supplied, A. argenteus consumed or hoarded only C. cuspidata, whereas A. speciosus tended to eat C. cuspidata acorns at the feeding site, and disperse or hoard Q. serrata acorns. Apodemus speciosus is unlikely to disperse C. cuspidata acorns (their utilization was biased towards consumption) when Q. serrata acorns are also available. Apodemus argenteus will make almost no contribution to the dispersal of Q. serrata when the two acorn species coexist.     

Effects of acorn masting on population dynamics of three forest-dwelling rodent species in Hokkaido,Japan

The effects of the abundance of acorns of the oak, Quercus crispula, on the population dynamics of three rodent species (Apodemus speciosus, A. argenteus, and Clethrionomys rufocanus) were analyzed using time series data (1992–2006). The data were obtained in a forest in northern Hokkaido, Japan, by live trapping rodents and directly counting acorns on the ground. Apodemus speciosus generally increased in abundance following acorn masting. However, the clear effect of acorn abundance was not detected for the other two rodent species. Acorns of Q. crispula contain tannins, which potentially have detrimental effects on herbivores. Apodemus speciosus may reduce the damage caused by acorn tannins with tannin-binding salivary proteins and tannase-producing bacteria, whereas such physiological tolerance to tannins is not known in the other two rodent species. The differences in the effects of acorns between the three species may be due to differences in their physiological tolerance to tannins.     

Selective consumption of acorns by the Japanese wood mouse according to tannin content: a behavioral countermeasure against plant secondary metabolites

We examined the presence of selective consumption against tannins in acorns as a pre-ingestive countermeasure to plant secondary metabolites by using the Japanese wood mouse (Apodemus speciosus) and acorns of Quercus serrata, which contained ca. 6.4% tannins on a dry weight basis. In addition, the presence of selective consumption against proteins was also examined. In the acorn-feeding experiment, 18 wood mice were allocated to two groups: the experienced group (N = 9), which had previous experience in feeding on acorns, and the inexperienced group (N = 9), which had no experience. Mice of both groups were fed only acorns for 3 nights. Selectivity against tannins (an index estimated from the tannin content in control, remaining, and ingested acorns) was significantly positive in the experienced group, indicating the presence of selective consumption against tannins. In contrast, mice in the inexperienced group did not show significant selectivity against tannins. Comparing the selectivity indices directly between two groups, however, they did not differ significantly. Selective consumption against proteins rather than that for proteins also occurred in the experienced group, but it was thought to be a byproduct resulted from the selectivity against tannins. Selective consumption against tannins can mitigate the negative effects of tannins by decreasing tannin intake.     

Nutrient compositions of acorns and horse chestnuts in relation to seed-hoarding

Nutritional compositions of acorns (Quercus serrata Thunb. and Quercus mongolica Fisch. var. grosseserrata Rehd. et Wils.) and horse chestnuts (Aesculus turbinata Blume) were analyzed. Major nutrients of acorns and horse chestnuts were carbohydrate, protein and fat. They proved to contain considerable amounts of tannins (7.28–11.72% dry mass^–1) and saponins (6.20%), respectively. The nutrients and the secondary metabolites of seeds buried for either 1 month or 3 months were analyzed to evaluate effects of seed-caching by animals. Noticeable changes were not observed, which suggested that caching may not bring any advantages to the seed-hoarders with respect to nutrition.     

Predating strategy of rodents on acorns of Quercusaliena var. acuteserrata under different predating risks and fate of acorns

The effects of rodents on forest regeneration have been highlighted in many ecological studies. In 2002 and 2003, the acorns of Quercus aliena var. acuteserrata were subjected to 12 different treatments. The daily dynamics and the amount of acorns that were finally left intact, predated in situ, or removed off were examined and documented. The ratios of acorns that were infested by bugs before and after predation by rodents were carefully documented. It was found that: (1) the ratios of acorns infested by bugs before and after predation by rodents showed significant difference (P > 0.05), suggesting that rodents would not prey on acorns during the predating process if acorns had been already infested by bugs. (2) When compared with the controls, the fate of acorns could be roughly classified into four types: acorns that were simply buried or placed on black paper showed no significant differences with the controls in their response to rodents, suggesting that rodents have no sensitivity to the little change of odor resulting from burying and may be more adapted to black background. Acorns attached with strings, dyed with black ink, cut into halves, or placed on white/green/red paper were predated in situ with much lower predation rates and lasted the same duration. Compared with the controls, the acorns were removed away by rodents with the same first day rate and the removal lasted longer. The final removal rate of the acorns by rodents was increased, whereas that of predation in situ was decreased, and none were left in the spot. This may suggest that rodents in this case increased their predation risk expectation and adopted a strategy of “less predation proportion in situ”. Acorns that were burnt were not predated in situ as well as removed in the first day, but the rates were raised to the maximum in the forth and fifth day and then declined to zero. Consequently, the final ratios of predation in situ and removal considerably decreased with many acorns, nearly 50%, being left intact. It can be hypothesized that the rodents responded to the change in odor of acorns by using the strategies of “less predation proportion in situ” and “less predating activities”, thereby resulting in larger number of acorns remained intact. Acorns that were enwrapped were barely predated in situ, removed in the first day with a normal predation rate, which declined to nearly zero in the second day and then increased till it declined again from the fourth day to the final day. The final rate of predation in situ was lower than 5% without acorns remained intact, and the rate of removal of acorns showed a considerable relative increase. This suggests that when there was a change in both odor and status of acorns, rodents also adopted the “spying” and “less predation proportion in situ” strategy, Because the predation risk is critical, the sense of sight would play an important role in rodent's living. (3) Definite amounts of acorns were predated in situ, discarded, removed away, predated ex situ, lost and hoarded separately.     

Production-dependent reproductive allocation of a tall tree speciesQuercus serrata

The reproductive allocation (allocation of net production to acorns) of a tall tree speciesQuercus serrata was estimated by a method combining branch diameter distribution and the sampling of acorns per branch. Acorn production per branch of 0.5-cm diameter significantly varied among individuals and years, but not significantly across tree size. Leaf production per branch of 0.5-cm diameter had little annual fluctuation, while that of acorns fluctuated about 6 times between the maximum and minimum. The reproductive allocation was regressed against vegetative allocation, following the general model of klinkhameret al. (1992); the reproduction had a beginning threshold and reproductive allocation increased drastically at relatively young stage after the tree began reproduction. With its small threshold production, coppicing traits and large maximum size,Q. serrata seemed adaptive to infrequent but large-scale disturbances like fires.     

Removal and predation of Quercus liaotungensis acorns by animals

Two types of acorns (fresh, current-year acorns and old, previous-year acorns) of Quercus liaotungensis were used under two different situations (night and day) to examine the removal and predation by animals in the field. The acorns disappeared very fast. During the day, all of the 280 this-year acorns (TA) and all of the 140 last-year acorns (LA) were removed by animals within 6 h and 5 h, respectively, after acorns were put in place. At night, all of the 280 TA acorns were removed by animals within 10 h after acorns were distributed, and 71 out of 140 LA acorns were removed within 10 h. Animals consumed a small proportion of acorns in situ (11.8%). The number of TA acorns consumed in situ at night was higher than that during the day. During the day, the number of LA acorns consumed in situ was significantly higher than TA acorns. This result suggests that the most important harvesters of Q. liaotungensis during the day were visually orientated diurnal animals, and the most important harvesters at night were olfactorily orientated nocturnal animals. Furthermore, the latter are more efficient than the former at finding and harvesting acorns, because they spend less energy on harvesting the same number of sound acorns.     

Different responses to shade of evergreen and deciduous oak seedlings and the effect of acorn size

An evergreen oak species, Cyclobalanopsis multinervis, and a deciduous oak species, Quercus aliena var. acuteserrata were grown from acorns under two light levels (full sunlight and shade at about 18 % of full sunlight, simulating the light intensities in forest clearings and gaps, respectively) for one growing season. Three hypotheses were tested: (i) the deciduous species grows faster than the evergreen species in forest gaps and clearings; (ii) the deciduous species responds more strongly in terms of growth and morphology to variation in light climate than the evergreen species; and (iii) seedling size is positively correlated to acorn size. The results showed: (i) at both light levels, the deciduous seedlings gained significantly more growth in biomass and height than the evergreen seedlings; (ii) both species produced significantly more biomass in full sunlight than in shade, without showing any significant difference in height between treatments. Increase in light intensity improved the growth of the deciduous seedlings more strongly; (iii) at a similar age, the deciduous seedlings showed a greater response in leaf morphology and biomass allocation to variation in light levels, but when compared at a similar size, biomass allocation patterns did not differ significantly between species; (iv) bigger acorns tended to produce larger seedlings, larger leaf sizes and more leaf area, between and within species. These differences demonstrate that the deciduous species is gap-dependent and has the advantage over the evergreen species in forest gaps and clearings.     

Facilitation of Quercus ilex recruitment by shrubs in Mediterranean open woodlands

Question: Insufficient tree regeneration threatens the long‐term persistence of biodiverse Mediterranean open oak woodlands. Could shrubs, scarce due to decades of management (clearing and ploughing), facilitate holm oak recruitment at both acorn and seedling stages? Location: Open oak woodlands in Central Spain. Methods: Plots with four acorns were planted: (1) under the canopy of the spiny shrub Genista hirsuta, (2) in a small cage, protecting against ungulates, (3) in a shaded cage, protecting against ungulates and sun, and (4) in open grassland. Sets of these four treatments were spatially grouped according to a randomised block design, with 16 blocks near (< 10 m) and 16 away from (> 20 m) parent trees to test for distance‐related survival. Plots were regularly checked for seed removal. After emergence one seedling per plot (97 in total) was selected and its survival monitored. Results: Three months after sowing, 199 of 512 acorns were removed, predominantly by rodents. Acorn removal occurred at each treatment but was highest under shrubs. Eight months after sowing, seedling survival was highest under shrubs (50%), followed by shaded cages (16%), open grassland (4%) and cages (0%). Main mortality cause was drought (90%), killing most seedlings between June and July. No seedlings died from ungulate browsing. Conclusion: Shrubs demonstrated clear net facilitative effects for Quercus ilex recruitment, despite higher seed removal. Shading appears the crucial factor facilitating seedling survival. We therefore propose that lack of shrubs contributes largely to tree recruitment failure in Mediterranean open woodlands; management should aim at conserving shrubs.     

两种象甲幼虫肠道微生物组成及对高单宁食物的适应

【目的】象甲是栎属植物橡子中主要的寄生昆虫,但其适应高单宁食物(橡子)的肠道微生物基础尚待揭示。本研究分析了蒙古栎和辽东栎橡子中两种柞栎象(Curculio arakawai和C.dentipes)幼虫的肠道菌群结构和多样性,试图阐明柞栎象幼虫适应高单宁食物的肠道微生物基础。【方法】分别提取蒙古栎和辽东栎橡子中象甲幼虫各50头的肠道DNA,利用Illumina MiSeq技术对肠道菌群的V3–V4区序列进行16S rRNA测序,统计样品操作分类单元(OTU)数量,分析物种组成丰度、α多样性和β多样性。【结果】结果表明,可用于物种分类的OTU分别有2054和2308个,C. arakawai和C. dentipes共有的OUT 481个。在两种柞栎象C. arakawai和C. dentipes肠道菌群中,共注释到的主要分类阶元有27个门、145个科和274个属。变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)和厚壁菌门(Firmicutes)在两种象甲肠道菌群中占优势;假单胞菌属Pseudomonas(63.8%)、沙雷氏菌属Serratia(6%)和不动杆菌属Acinetobacter (5.2%)是C. arakawai肠道中的主要类群,而沙雷氏菌属Serratia (32%)、拉恩菌属Rahnella(24.2%)、气单胞菌属Aeromonas(6.8%)和立克次体属Rickettsia(6.6%)在C.dentipes肠道菌群中占主导优势。C. arakawai和C. dentipes肠道菌群α多样性无显著差异,β多样性则差异显著。具有单宁酶活性的肠道细菌,如粘质沙雷菌Serratia marcescens、乳球菌Lactococcus lactis、假单胞菌Pseudomonas spp.在C. arakawai和C. dentipes之间差异不显著。【结论】寄生在蒙古栎和辽东栎橡子中的C. arakawai和C.dentipes肠道菌群组成迥异,这可能与遗传因素和食物特点有关。具有单宁酶活性的粘质沙雷氏菌Serratia marcescens和乳球菌Lactococcus lactis等菌类可能是两种象甲幼虫适应高单宁食物的肠道微生物基础。     

Spatial patterns of dispersal, seed predation and germination during colonization of abandoned grassland by Quercus petraea and Corylus avellana

Key processes during recruitment of Quercus petraea and Corylus avellana were investigated in abandoned calcareous grasslands and adjacent scrub using the following methods: (1) observation of hoarding animals during the main period of ripening of acorns and hazel nuts, (2) exposition of seeds on the soil surface and in 5–6 cm depth to test differences in predation and germination, and (3) mapping of seedlings in the grasslands. European jays (Garrulus glandarius) and mice were the main disperser of seeds. Jays preferred acorns, whereas the rodents were less selective, but probably more important for dispersal of nuts. The maximum dispersal distance was about 10–20 m for mice and was estimated several hundred metres for jays. Mice collected hoards of several seeds in about 2 cm depth in the soil, whereas jays stored single seeds. Seed predation and probably hoarding by mice were highest under scrub and in unmown grassland, while jays preferred mown sites for hoarding. However, hiding of seeds in the soil reduced losses in all sites. Predation of nuts was slightly less intensive than that of acorns. Seeds of Corylus were more sensitive to desiccation than Quercus, but in both species germination was lower for seeds exposed on the soil surface and in drier sites. Quercus and Corylus were the most abundant woody species in the fallow grasslands, probably due to the effective multi-staged dispersal by jays and mice, whereas wind-dispersed and fleshy-fruited species were less common; the latter restricted to margins of adjacent scrubland. The study provides several examples for discordance in suitability of patches for seeds and seedlings due to different habitat requirements of successive developmental stages. This result emphasizes the need for studies in the multiple stages during recruitment of vertebrate-dispersed plants.     

Spatial and temporal variations in insect-infested acorn fall in a <Emphasis Type="Italic">Quercus liaotungensis</Emphasis> forest in North China

Three plots with different aspects and slope characteristics were surveyed in 1999 and 2000 to clarify the spatial and temporal variations in insect-infested acorn fall patterns in a Quercus liaotungensis Koidz. forest in the Dongling Mountain region, North China. There was a significant difference in the proportion of infested acorns in the three plots in a low crop year, but not in a mast year. Within oakwoods on the southeast-facing slope, the insect infestation rate on the upper slope was significantly higher than on the lower slope, but not in the northwest-facing plot. Infestation rate in the low crop year in all three plots was significantly higher than infestation in the mast year. Most of the early fallen acorns had a higher proportion of insect infestation, and in the mast year it was much more obvious than in the low crop year. The proportion of infested acorns in seed bank along the topographic gradient showed a similar decreasing trend with acorn fall time, but the proportion on the upper slope was the highest and the proportion on the lower slope was the lowest. Larval emergence from acorns commenced just after acorns fell from the trees and lasted for 40–50days, with peak emergence occurring from 24 to 32days after acorn rain began. We conclude that insect-infested acorn distribution in Q.liaotungensis shows spatial and temporal heterogeneity, and an early drop of infested acorns can be a short-term defensive strategy against insect infestation.     

Importance of microhabitat and acorn burial on Quercus ilex early recruitment: non-additive effects on multiple demographic processes

This study investigates the effect of microhabitat and seed burial on the main demographic processes operating during the early recruitment of Quercus ilex, such as postdispersal seed predation, seed germination, and seedling emergence, survival and growth. The effect of burial was positive over all the processes analysed in this study, since predation rate was lower (63.6% vs. 88%), whereas germination (53.1% vs. 21.8%) and emergence (32.0% vs. 5.5%) were higher for buried acorns. The quality of some microhabitats remained similar throughout the stages and processes studied. Thus, afforestation provided especially suitable microhabitats for oak establishment, since seed predation was lower, while germination, emergence and seedling survival were higher, than in any other microhabitat. By contrast, the quality of some microhabitats, such as open sites and Holm oaks, differed between recruitment stages. Acorns in open sites escaped predation and germinated easily, but most seedlings died due to summer drought. Similarly, although acorns under Holm oaks can germinate and survive drought, they cannot survive to postdispersal predators. This uncoupling results in a post-dispersal change in the spatial distribution of Q. ilex recruits. Furthermore, there were significant interactions between burial and microhabitat for some demographic processes. The recruitment was in afforestations high irrespective of burial, suggesting that burial is not as beneficial in high-quality habitats as it is in lower-quality ones. An accurate understanding of plant recruitment requires the determination not only of the direct effects of limiting factors but also the potential interactions occurring between them.     

Variation of stand structure and regeneration of Mediterranean holm oak along a grazing intensity gradient

Mediterranean ecosystems are traditionally influenced by human disturbance. In the mountain chains of south-eastern Spain, holm oak forests representing the potential natural vegetation are currently highly fragmented and subjected to extensive grazing by goats and sheep. This grazing activity by large herbivores has important impacts on community structure and dynamics of the remaining remnants because several processes associated with reproduction are affected. The present research analyses the variation of stand structure and regeneration of six forests dominated by Quercus ilex along a gradient of increasing grazing intensity. Stands of higher grazing intensity are characterized by a lower trunk number. Particularly, trees > 1.3 m height and diameter classes < 20 cm are clearly less represented. In addition, more intensively grazed forests show a highly aggregated dispersion of trees, which might be explained by an increase of clonally produced ramets by silvipastoral use. On the other hand, no Quercus ilex seedlings were found in any of the stands examined, although acorn production was high and did not correlate with grazing intensity. However, grazing clearly influences the quality of acorn harvest. We found a significant negative correlation between acorn length, acorn mass and grazing intensity and a positive correlation between the percentage of aborted acorns, acorn predation and herbivore activity. Thus, management of grazing in holm oak forests must take the high influence that livestock exerts on the regeneration of Quercus ilex into account, and maximum sustainable grazing intensity should be significantly lower than 0.8 animals per ha.     

Notes on Quercus ilex L. in Liguria (NW Italy)

The climatic characteristics of the Liguria region have been outlined by means of raw data and derived indices (water balance related to potential evapotraspiration, Rivas-Martinez's index of mediterraneity and thermicity, De Martonne's index of dryness, and Emberger's pluviothermic quotient and index of summer dryness). Their interpretation suggests that Liguria is a boundary region between two different climatic areas: the Mediterranean and that of Central Europe.The distribution of Quercus ilex communities in Liguria have suffered the heavy consequences of human activity on the coastal belt of the region. There is, however, sufficient evidence to show that their presence is closely linked to climatic conditions. Quercus ilex communities are absent from the western coastal belt where the annual water balance is below –50 mm and high mean temperatures occur. They are also absent from marly limestone dominated areas where annual water balance is below 300 mm. Quercus ilex woods show a preference for water balance values between 0 and 600, with the better developed forests being found in central and eastern coastal Liguria.The Ligurian Quercus ilex woods are ascribed to Quercetum ilicis Br.-Bl. 1915. Given that the presence within their floristic composition of a group of species of Querco-Fagetea (more species in eastern stands, few in western ones) is an almost constant characteristic, the subass. fraxino-ostryetosum Mariotti 1984 can be retained for many of them. Quercus ilex is not present in the initial succession stages of Mediterranean Liguria vegetation. It can be found in later stages when the vegetation is more fully developed towards a maquis type structure. In this case it tends to become dominant and the community develops (if no fire or other human interference occurs) into a Quercus ilex forest. Frequently, this succession takes place under an old tree layer cover (generally Pinus sp.), a remanant of man's past management of the vegetation in the area.