Expansion Of Beech Research Articles

Enemy release from beech bark disease coincides with upslope shift of American beech

Upslope shifts in plant distributions are often attributed to warming climate and lengthening of the growing season; however, biotic interactions may also contribute. The impacts of pests and pathogens are often sensitive to climate change and can vary along the climatic gradient associated with elevation. American beech ( Fagus grandifolia) has moved upslope throughout the northeastern United States. Meanwhile, beech growth and longevity have decreased as a result of beech bark disease (BBD), a decline disease caused by the introduced European felted beech scale insect ( Cryptococcus fagisuga) and native fungi from the genus Neonectria. Within a forested landscape spanning 250–1150 m elevation, we examined the relationships between elevation, beech demography and BBD to explore whether release from BBD at higher elevation may contribute to the upslope expansion of beech. Beech has shifted upslope at a rate of 1 m⋅year−1 coincident with lower mortality, higher recruitment, faster growth, lower BBD severity, and higher sapling densities at higher elevations. We suggest that climatic constraints on the beech scale insect at high elevations has led to a lower impact of BBD, which contributed to higher rates of beech growth, survival, and recruitment and in turn facilitated the regional upslope shift of beech.

Toward a Beech-Dominated Alternative Stable State in Dinaric Mixed Montane Forests: A Long-Term Study of the Pecka Old-Growth Forest

In the last century, a synchronous beech expansion has been observed for many mixed mountain forests in southeastern Europe. This change is associated with the interaction of various disturbances. We analyzed structural changes in the Pecka old-growth forest in Slovenia during the last century, using several inventories of the tree layer, regeneration, and site factors. Throughout the observation period, the density of silver fir in the regeneration layer and in the overstory steadily decreased. In 1893, silver fir accounted for about 60% of the growing stock, whereas in 2013 it accounted for less than 13%. This is likely because of silver fir’s decline in the canopy layer due to air pollution, successive windthrows, and overbrowsing. However, climate change may also have played an important role, as silver fir also declined in southeastern European old-growth forests where air pollution was less pronounced and ungulate densities were low. A gradual decline of silver fir in the overstory resulted in a decrease of overall tree density to 231 trees ha–1, while growing stock remained relatively high at 712 m3 ha–1. Median diffuse light at 1.3 m was 3.7% and regeneration density was 19,954 ha–1. Beech was dominant (94%), followed by silver fir (4%), and sycamore maple (2%). No silver fir seedlings larger than 0.2 m were recorded. Silver fir, sycamore maple, and beech regeneration showed 87, 76, and 45% browsing damage, respectively. Regression models indicated some evidence of niche partitioning between silver fir and beech. However, many processes may be masked by the silver fir’s avoidance strategy. Given current red deer densities, climate change, and existing forest structure, the Pecka old-growth forest will likely reach an alternative stable state dominated by beech in a few decades. This calls for immediate reduction of ungulate populations. Despite the interaction of multiple disturbances, the Pecka old-growth forest has maintained a relatively high overall growing stock, a favorable microclimate, and succession pathway with shade-tolerant beech. This indicates the intrinsic resilience of natural forests. The mechanisms discussed here can be applied to the future governance of old-growth and managed montane mixed forests.

Fine-Scale Spatial Patterns of the Genetic Diversity ofEuropean Beech (Fagus sylvatica L.) around a Mountainous Glacial Refugium in the SW Balkans

Beech (Fagus sylvatica L.) is one of the most important forest trees in Europe and its current broad expanse over the continent is believed to be the outcome of the Holocene postglacial expansion of lineages originating from different glacial refugia. Studies using gene markers, pollen profiles and fossils suggest the main locations of glacial refugia in Southern Europe. In this study, we conduct a fine-scale genetic study on the beech populations surrounding the Almopia basin, an area that is said to have hosted one of the main European glacial refugia for several plant and animal species during the Pleistocene Epoch. We test the hypothesis of the existence of a local refugium in the study area for beech to understand the spatial genetic pattern of the putative refugial beech populations in the area and to investigate possible genetic connections between the local beech populations and the European expansion of the species. The genetic diversity of 100 sampled trees in 20 plots representing the expansion of beech in the area was studied using chloroplast and nuclear DNA microsatellites (cpSSR and nSSR, respectively). All three cpSSR regions were polymorphic, resulting in eight haplotypes, separated spatially in two distinct groups (one on the western and the other on the eastern part of the Almopia basin) that correspond to two different postglacial beech lineages. Furthermore, the cpSSR sequences of the eastern lineage are genetically identical to those of beech populations extending over central and northern Europe. The nSSR markers were highly polymorphic, and the trees studied were separated into two genetic groups that coincided with the cpSSR ones in locations where the topography is more pronounced. These results indicated that the Almopia region was indeed a major refugium for beech that possibly produced two main postglacial lineages for Europe, one of which is connected with the majority of beech populations growing on the continent. These southern refugial populations are important diversity centers that need to be the subject of special management and conservation.

ДИНАМИКА ЛАНДШАФТОВ И КЛИМАТА В ЦЕНТРАЛЬНОЙ И ВОСТОЧНОЙ ЕВРОПЕ В ГОЛОЦЕНЕ – ПРОГНОЗНЫЕ ОЦЕНКИ ИЗМЕНЕНИЯ ПРИРОДНОЙ СРЕДЫ

The paper presents a review of the Holocene landscape and climate reconstructions for the forest zone of Central and Eastern Europe revealed from various proxies and comparison of the data obtained with the main stages of relief development and sedimentation during the Holocene. Projections of expected climate change are discussed according to IPCC scenarios (Coupled Model Intercomparison Project, Phase 5; Representative Concentration Pathways for possible range of radiative forcing). Analysis of the data showed that in the Early Holocene (11.7–8.2 ka BP), a rapid climate warming led to crucial transformation when all of landscape components were transformed, and relief-forming processes underwent significant changes. In the Middle Holocene, the time interval of 8.2–5.7 ka BP was characterized by the maximum heat supply in comparison with the whole Holocene and the weakening of the temperature gradient in the direction from west to east. At this time, a continuous zone of broad-leaved forests occupied the mid-latitude regions of Europe. Starting from 5.7 ka BP, the climatic cooling led to the sectoral differentiation of vegetation cover. In the western regions, the expansion of beech and hornbeam began, in the east, and the role of spruce in forest communities increased. Climate reconstructions for the Late Holocene (4.2 ka BP – present) have shown that against the background of the general climate trend towards a decrease in heat supply, periods of warming and cooling are distinguished. During the late Holocene the modern landscape cover was formed, the influence of the anthropogenic factor increased. According to paleobotanical, isotope-geochemical and paleohydrological studies in various regions of Central and Eastern Europe, the climate was drier than at present during periods of warming, mainly due to changes in the precipitation/evaporation balance, and climate cooling was accompanied by an increase in moisture. Bearing in mind the Holocene climate reconstructions as a possible scenario of climate changes during the current century, one can expect that an increase in temperatures, especially in the summer period, will cause the increase in the frequency of droughts and natural disasters, associated with irregular rainfall.

Climate–growth relationships at the transition between Fagus sylvatica and Pinus mugo forest communities in a Mediterranean mountain

Species interactions implicate a complex balance of facilitation and competition, which may shift during community development, thus structuring the subalpine ecotone of Mediterranean mountain ranges through time and space. This study highlights that encroachment of grasslands and simultaneous downward/upward movement of forest tree species involve species interferences and environmental feedbacks, with differential effects on mountain pine and European beech, and the grassland communities of the Majella Massif. The transitional ecotone from the European beech closed forest to the mountain pine krummholz vegetation in the Majella Massif (Apennines, Italy) is a sensitive area to climate and land-use changes. Vegetation shifts in these ecotonal zones may cause a negative impact on the spatial distribution and survival of rare or endemic herbaceous species, thus influencing the appearance, structure, and productivity of the subalpine ecotone of the Majella National Park. We focused on determining the structures and dynamics of this Mediterranean tree line, and the climate–growth relationships of European beech and mountain pine. We investigated the upward and downward movement of pine into areas potentially suitable for beech expansion, and the concurrent beech encroachment upward. Growth dynamics and canopy cover of European beech closed forest and mountain pine krummholz vegetation were analyzed in relation to disturbances at four different sites. Spring and summer temperatures and summer precipitation affected stem radial growth of both species. In details, spring and summer temperatures negatively affected tree ring width (TRW) of European beech, except for the highest site, whereas spring temperatures affected positively and summer temperatures negatively TRW of mountain pine. Mountain pine expanded upward, encroaching formerly grazed pastures and harvested areas, especially where the soil is shallow and rocky; downward expansion is also occurring, following progressive abandonment of forest management practices. At the same time, European beech recruitment is moving upward, interspersed within mountain pine krummholz, taking advantage from canopy shelter and higher temperature. Climate and land-cover simultaneous changes induce species interactions and a complex balance of facilitation and competition, which may shift during community development and structure the subalpine European beech-mountain pine ecotone of the Majella Massif through time and space.

Dark Ages woodland recovery and the expansion of beech: a study of land use changes and related woodland dynamics during the Roman to Medieval transition period in northern Belgium

AbstractThe results from analyses of botanical remains (pollen, wood, charcoal, seeds) from several archaeological features excavated in Kluizen (northern Belgium) are presented. The region was largely uninhabited until the Iron Age and Roman period when a rural settlement was established, resulting in small-scale woodland clearance. The site was subsequently abandoned fromc.AD 270 till the High Middle Ages. The results of the archaeological and archaeobotanical analyses provide information on changes in land use and resulting dynamics of woodland cover and composition betweenc.600 BC and AD 1200, with a spatial and temporal resolution unrivalled in northern Belgium. Especially the long period of woodland regeneration following abandonment of the site around AD 270, covering the Late Roman and Early Medieval period, could be reconstructed in detail. Abandoned fields were first covered with pioneer woodland (Salix,CorylusandBetula), thenQuercus-dominated secondary forest and finally a late-successional forest withFagus sylvatica,Carpinus betulusandIlex aquifolium, an evolution that took over 300 years. The results also indicate that the observed increase ofFagusduring the Early Middle Ages, which was never an important element in the woodland vegetation in northern Belgium before, was related to climatic changes rather than anthropogenic factors.

RESTRICTING CLIMATIC CONDITIONS ON THE EASTERN DISTRIBUTION LIMIT OF EUROPEAN BEECH (FAGUS SYLVATICA) IN NORTH-EASTERN ROMANIA FOR THE MARCH – JUNE INTERVAL

The meteo-climatic arguments for the eastern biogeographic limit of beech in Romania are of particular interest to forestry, but also to geographers and climatologists. This limit marks the transition from the temperate humid climate of Western and Central Europe to the temperate continental climate of Eastern Europe. Our paper provides improved knowledge on climatic conditions that restrict the longitudinal distribution of beech at temperate latitudes in north-eastern Romania. Results show that rainfall scarcity and high temperature in the March-June interval, added to temperature drop below the freezing point in April-June are the main climatic conditions that limit beech expansion eastward of this biogeographic limit.

Adaption of Norway spruce and European beech forests under climate change: from resistance to close-to-nature silviculture

Abstract In time of climate change, close-to-nature silviculture is growing in importance as a tool for future forest management. The paper study the tree layer and natural regeneration of monospecific Norway spruce (Picea abies [L.] Karst.), trough mixed spruce-beech to dominant European beech (Fagus sylvatica L.) forests in Jizerské hory Mts., the Czech Republic. In the locality, shelterwood and selection system have been applied since 2000. The research objectives were to evaluate production parameters, structural diversity, species richness, natural regeneration dynamics and radial growth of individual tree species in relation to climatic factors and air pollution. The stand volume on permanent research plots amounted to 441 – 731 m3 ha−1 in initial stage of transformation. Natural regeneration showed high expansion of beech and decrease of spruce compared to mature tree species composition. Radial growth of spruce was in significant negative correlation with SO2 and NOX concentrations compared to no effect on beech increment. Moreover, spruce was more sensitive to significant years with extreme low radial growth. Beech was more stable in radial growth. Spruce was more resistant to air pollution and climatic stress in mixed stands. Low temperature was limiting factor of radial growth together with climate extremes (such as strong frosts and more frequent droughts) and biotic factors (bark beetle, beech scale). Close-to-nature management supporting admixed tree species should lead in future to diversification of stand structure toward higher species, spatial and age structure to mitigate negative effect of climatic change.

Four decades of the coexistence of beech and spruce in a Central European old-growth forest. Which succeeds on what soils and why?

The dynamics of forests dominated by European beech (Fagus sylvatica) and Norway spruce (Picea abies) have been studied intensively. However, mainly due to a lack of long-term data, little is known about how these dynamics interact with soil conditions. In an old-growth spruce-beech forest with high soil diversity we studied how the development of tree populations differs among different soils. Data from tree censuses carried out in 1972, 1996 and 2010 in the Boubin Primeval Forest in the Czech Republic were combined with detailed soil sampling to assess the relative abundance of beech and spruce and the role of the main drivers of population dynamics (tree growth, mortality and recruitment) in changes with respect to soils. The spatial distribution of populations of the two species primarily reflected a gradient of soil hydromorphism, with beech dominating drier soils and spruce dominating wetter soils. Over the 38 years, beech expanded on all major soils, yet the most important drivers differed. The only driver acting in favour of spruce on certain terrestrial soils was its faster radial growth. However, the effect was weaker than the effect of drivers that prioritized beech, mainly tree mortality. Fine-scale mortality (deaths of individual trees) was more significant on terrestrial soils, while the effect of coarse-scale mortality (deaths from a single severe windstorm event) increased towards hydromorphic soils. Certain soils (Histosols and Albic Podzols) diverged from the general trends because of their different disturbance regimes and specific tree–soil interactions. Soils play an important role in the dynamics of an old-growth spruce-beech forest. Their physical and chemical properties together with specific disturbance regimes determine fine-scale differences in tree species composition. At the same time, soils themselves are affected by trees, e.g. through acidification. The current expansion of beech is expected to continue on terrestrial soils but will probably slow down with increasing soil wetness.

Beech forests as world heritage in aspect to the next extension of the ancient and primeval beech forests of the Carpathians and other regions of Europe world heritage site

Beech forests were first protected under the World Heritage Convention in 2007 as the Primeval Beech Forests of the Carpathians (Slovakia and Ukraine). After two latter extensions in 2011 and 2017, the Natural World Heritage site is currently named the Ancient and Primeval Beech Forests of the Carpathians and Other Regions of Europe (Albania, Austria, Belgium, Bulgaria, Croatia, Germany, Italy, Romania, Slovakia, Slovenia, Spain and Ukraine) and consists of 78 component parts in 12 European countries. It aims to ensure the preservation of beech gene pool, ecosystem and species diversity of beech forests, their future renewal and expansion, in regard to the development and use pressures they encounter and the biodiversity they support. Additionally, this World Heritage site aims to depict the beech expansion after the last Ice Age, spreading over a large percent of the continent to form one of the most significant forest ecosystems in Europe. The third extension nomination has been developed in 2020 and proposes the inscription of additional 30 component parts, a considerable step towards the complete overall picture of post-glacial beech re-colonization process and beech ecosystem diversity across Europe. With this extension 8 additional European countries would join this property, including the Republic of Serbia. The extended property would consist of over 100 component parts in 20 European countries, a pan-European network of protected areas with joint protection and management goals to represent a platform for policy making and knowledge exchange. This paper presents the genesis of this extremely complex World Heritage property and the work done to expand it over the protected beech forests in Serbia, in preparation of the first Natural World Heritage nomination for the Republic of Serbia.

Holocene vegetation history of the Jeseníky Mts: Deepening elevational contrast in pollen assemblages since late prehistory

AbstractQuestionsHow did the vegetation of a Central European mountain region with a fragmented alpine zone develop during the Holocene? When did human land use start to alter summit grasslands? Which gradient in pollen assemblages was strongest and was it consistent through time?LocationJeseníky Mountains, Czech Republic.MethodsSixteen pollen records were subjected to DCA in order to explore patterns of compositional similarities in the fossil pollen data. Because only the last 6,000 years were recorded in the study sites from mountain summits, we restricted further analysis to this period. Twelve radiocarbon‐dated pollen records were subjected to DCCA constrained by modelled calibrated age. Responses of individual pollen types to the principal DCCA gradients were tested with GAMs.ResultsIn the DCA, Early Holocene samples were located close to recent ones due to abundant pollen of herbs, Poaceae, Betula, Pinus sylvestris type and rare pollen of climax deciduous trees. In the DCCA for the last 6,000 years, the sorting of sites along the first unconstrained axis correlated with altitude, which is a complex factor corresponding to temperature and geomorphology (flat summits vs alluvia of mountain rivulets). This elevational differentiation became more pronounced after 2,250 cal BP when summit peatlands started to contain more Vaccinium, Calluna vulgaris, Amaranthaceae, Plantago lanceolata and Rumex acetosa type pollen. In contrast, mid‐elevation pollen spectra started to contain more meadow herbs (Caltha, Potentilla type, Cirsium/Carduus). Picea pollen was surprisingly more associated with mid‐elevation than high‐elevation sites, unlike Fagus.ConclusionIncreasing contrast between summits and middle elevation alluvia seems to be a major feature of vegetation development over the last 6,000 years. While alluvial areas were encroached by Alnus–Picea forests, and later locally transformed into wet grasslands, grazing and forest burning at summits gradually increased abundance of acidophytic dwarf shrubs and peatlands, especially since the Iron Age. Human impact might facilitate beech expansion at high elevations, with Picea‐dominated forests being restricted to alluvia and around mid‐elevation basin peatlands prior to establishment of modern Picea plantations.

Seven decades of change in a European old-growth forest following a stand-replacing wind disturbance: A long-term case study

Understanding long-term successional changes in old growth forests affected by stand-replacing disturbance is particularly important in the context of contemporary changes in climate and disturbance regimes. We analyzed seven decades of succession following a stand-replacing wind disturbance (in 1947) in Badínsky prales, one of the best preserved old-growth fir-beech forests in western Carpathians (Central Europe), and contrasted the post-disturbance development with changes that occurred in the adjacent undisturbed old-growth forest. Both the disturbed and undisturbed sections of the old-growth forest showed compositional and structural changes that differed in their starting point, magnitude, and ecological mechanisms, but forest composition, structure and light conditions appeared to be converging across the two disturbance histories. The windthrow was initially dominated by early-successional goat willow (Salix caprea L.) that declined in abundance, basal area, and growth over time as beech (Fagus sylvatica L.) gradually increased in both abundance and basal area to dominate all canopy layers by 2015. This increase in beech dominance over time within the windthrow mirrored increasing beech dominance in the undisturbed old-growth forest which was caused by the gradual decline of silver fir (Abies alba Mill.). The fact that old-growth forests originally co-dominated by fir and beech appear to be transitioning to forests dominated by beech regardless of the disturbance history suggests that beech expansion may be a robust process that should be considered in both old-growth conservation and forest management where timber harvest with low canopy retention may have similar effects on forest dynamics as a stand-replacing windthrow.

Soil fertility and charcoal as determinants of growth and allocation of secondary plant metabolites in seedlings of European beech and Norway spruce

Climate-change is predicted to drive a migration of European beech (Fagus sylvatica) into the boreal Norway spruce (Picea abies) zone. Still, the mechanisms underpinning beech success on novel soils is little understood. Further, projected increasing summer temperatures will increase risk of fire and subsequent charcoal deposition. Here we investigate how soil type and presence of charcoal affect growth and key plant traits of beech and spruce seedlings.Beech and spruce seedlings were grown in pots with forest soils of beech- or spruce origin to which beech- or spruce derived charcoal was added. Concentrations of phenolic compounds, carbon (C) and nitrogen (N) were analysed separately for root, stem, and leaf tissues.Our spruce forest soil contained more N than the beech forest soil, and both beech- and spruce seedlings grew bigger in spruce forest soil. Beech seedlings also had overall lower tissue concentrations of phenolic compounds when grown in spruce soil. For both species, shoots and roots displayed opposite phenolic responses. The addition of charcoal had no effect on growth, while effects on phenolic compounds were largely idiosyncratic.Our results indicate that beech expansion is not limited by soil factors in the study area, nor is it facilitated by increased levels of charcoal.

Effects of thinning and canopy type on growth dynamics of Pinus sylvestris: inter-annual variations and intra-annual interactions with microclimate

We assessed the effects of thinning (0, 20 and 30 % extraction of basal area) and canopy type (pine–beech vs. pine plots, beech accounting for 12 % of total basal area) on radial growth of dominant and codominant Scots pine at inter-annual scale and on microclimatic conditions, radial growth and xylogenesis 9 years after thinning at intra-annual scale. Thinning weakly affected pine growth, which was enhanced 3 years after harvesting. Over time, a gradual reduction in pine growth in mixed canopy relative to pure canopy occurred only in unthinned plots apparently due to beech expansion. Indeed, 9 years after thinning, a higher seasonal radial increment and a greater number of tracheids were produced under pine canopy in the unthinned plots, whereas no differences between canopy types were observed in the thinned plots. Radial increment and tracheid production were mainly affected by tree water status (air and soil humidity, throughfall). The differences of tree water status caused by treatments, and plausibly disparities in tree size and tree-to-tree competition, were the main drivers explaining the patterns observed for radial increment and xylogenesis. Our results suggest that the negative effects of beech competition on Scots pine growth in similar mixed forest may be controlled to some extent by thinning.

Spatiotemporal dynamic of European beech ( Fagus sylvatica L.) in Slovenia, 1970–2005

Based on data acquired from the spatial information system Silva-SI, the majority of the entire forest area in Slovenia (22,220 forest compartments with a total area of 7446 km 2, classified into eight forest categories) was analysed for changes in the distribution of European beech ( Fagus sylvatica L.) in the period 1975–2005 using a binary logistic regression model in terms of selected site, stand and management variables. Additionally, changes in the abundance of beech in forest stands in which beech was present at the beginning and the end of the analysed period were analysed. Beech expanded its area by more than 1200 ha per year on average, i.e. the annual expansion rate amounted to 0.24%. Among the 18 studied variables, three site, four stand and no management variables were included in the binary logistic regression model of beech expansion. Beech expansion was more pronounced at lower altitudes, on sites with steep topography, and on sites with a higher proportion of beech in potential natural vegetation. The probability of beech expansion reduced by a factor of 0.54 when the distance to the nearest compartment with beech increased by 1 km. Among other stand variables, the proportion of early successional phases and the proportion of silver fir ( Abies alba Mill.) and Norway spruce ( Picea abies (L.) Karst.) also influenced the expansion of beech. During the observed period the growing stock of beech almost doubled, its proportion in total growing stock increasing from 27% to 32%. Significant differences were found in changes of beech proportion in the total growing stock among different forest categories; a decrease in the beech proportion was registered in alpine coniferous forests and thermophilous deciduous forests, while in other forest categories the proportion of beech increased. The recent development of forest stands and their current structure indicate a further expansion of beech and an increase in the proportion of beech in forest stands.

Stratigraphy, pollen and 14C dating of Johnston's Gum Hole, a late Quaternary fossil kauri (Agathis australis) site, Northland, New Zealand

AbstractJohnston's Gum Hole provides a discontinuous pollen record commencing late in Marine Isotope Stage 5 (MIS 5). In combination with other published records from the region, the Aupouri Peninsula is reconstructed to have been continuously forested through much of the last glacial cycle with the oscillation of Agathis‐ and Nothofagus‐dominated forest corresponding to stadials and interstadials, respectively. A northward latitudinal expansion of beech forest to 35° S is demonstrated. Kauri demise at the close of MIS 5 appears to have been due to flooding of the site. The elimination of kauri in MIS 3 was also associated with rewetting of the substrate, but could have been a more catastrophic event. The presence of both MIS 5 and MIS 3 kauri wood at the site suggests that other Aupouri peat swamps may also preserve timber of these ages, and demonstrate the potential of this area for providing MIS 3 and MIS 5 tree ring records. Copyright © 2008 John Wiley & Sons, Ltd.

Leaf Size and Leaf Area Index in Fagus sylvatica Forests: Competing Effects of Precipitation, Temperature, and Nitrogen Availability

Plants across diverse biomes tend to produce smaller leaves and a reduced total leaf area when exposed to drought. For mature trees of a single species, however, the leaf area–water supply relationship is not well understood. We tested the paradigm of leaf area reduction upon drought by a transect study with 14 mature Fagus sylvatica forests along a steep precipitation gradient (970–520 mm y−1) by applying two independent methods of leaf size determination. Contrary to expectation, average leaf size in dry stands (520–550 mm y−1) was about 40% larger and SLA was higher than in moist stands (910–970 mm y−1). As a result of increased leaf sizes, leaf area index significantly increased from the high- to the low-precipitation stands. Multiple regression analyses suggested that average leaf size was primarily controlled by temperature, whereas the influence of soil moisture and soil C/N ratio was low. Summer rainfall of the preceding year was the most significant predictor of total leaf number. We assume that leaf expansion of beech was independent of water supply, because it takes place in May with ample soil water reserves along the entire transect. In contrast, bud formation, which determines total leaf number, occurs in mid-summer, when droughts are severest. We conclude that leaf expansion and stand leaf area of beech along this precipitation gradient are not a simple function of water availability, but are controlled by several abiotic factors including spring temperature and possibly also nitrogen supply, which both tend to increase toward drier sites, thus overlaying any negative effect of water shortage on leaf development.

The migration of beech (Fagus sylvatica L.) up the Rhone: the Mediterranean history of a “mountain” species

New anthracological data on the beech (Fagus sylvatica L.), obtained through rescue excavations, allows the proposal of a new pattern of population by beech of the South of France since the Lateglacial. Due to its current ecology and distribution it is considered to be a mountain species in the Mediterranean area despite the presence of beech forests, usually described as glacial relicts, at low altitudes in the South of France and in the Rhone valley (Sainte-Baume, Valbonne and Grand Fays). Our results, combined with previous pollen and charcoal data, show both an early spread from glacial refuges and a late disappearance of the species. During the glacial period, the beech remained in the southernmost zones. From there, it first spread during the Preboreal towards outposts in the Rhone delta, and during the Atlantic along the rhodanian corridor. During the Subboreal, a retreat of beech towards the Pre-Alps and the Rhone delta can be traced. The Iron Age and the Classical period experienced the maximal concentration of beech along the Rhone river, while it became more rare in the North and in the South. During the Middle Ages, it first disappeared from these distal areas, and later also in the valley (around A.D. 1000), finally settling in its present mountainous distribution area (probably around the 14th century A.D.). Some crucial points of the proposed dynamics are further analysed: the paradoxical regression of beech in the valley during the Subboreal, the factors determining the expansion of beech from refuge areas during the Subatlantic and finally, the disappearance of the beech in the middle Rhone valley in rather recent times, a disappearance attributed to the strong human impact on the landscape.

Rôle de l'homme dans l'histoire de la végétation de la vallée Ellero (Alpes maritimes, Italie)

The pollen analysis of a sediment core from a peat bog (Rifugio Mondovı̀) at the mountain belt (1760 m) in the Ellero Valley (Italian Maritime Alps) shows the postglacial vegetation history. The sequence starts at 12000 BP during a peak of pine pollen; this first phase shows a low representation of birch and the presence of Tilia. Younger Dryas is characterised by increasing percentages of Artemisia, showing the presence of deciduous Quercus, fir and beech. Elm appears at the beginning of the Holocene during the second pine peak (9800 BP). A 3000-year hiatus is present. Sedimentation resumes at 6000 BP in a Rhododendron fir-wood. The present timberline at 1500 m, at the limit of the beech wood, is a result of the decline of the fir-wood at 2600 BP, which allowed an expansion of beech. During this period, there was a continual increase in Gramineae and deciduous oak and the first occurrences of evergreen oak are observed. The development of larch occurs at 1800 BP, together with walnut, chestnut, cereals and vine. To cite this article: E. Ortu et al., C. R. Biologies 326 (2003).

Towards the reconstruction of the Holocene vegetation history of Lower Provence: two new pollen profiles from Marais des Baux

Two new14C-dated Holocene pollen profiles from Marais des Baux, Bouches-du-Rhone, France, are presented. The record begins in the Younger Dryas, when the vegetation consisted mainly of grasses and mugwort (Artemisia). The Preboreal was marked by a transitory expansion of pine forests and was followed by the establishment of a rich deciduous oak-forest that included hazel (Corylus) and elm (Ulmus). During the Boreal, hazel played a dominant role within the oak-forest. The oak forests, which includedQuercus ilex, achieved a major expansion during the Atlantic period. The Subboreal was characterised by the regional establishment of, firstly, fir (Abies) and then beech (Fagus). The spread and expansion of beech coincides with the first clear evidence for farming. Agricultural activities brought about the decline of deciduous oak-forest. During the Subatlantic, forests in the vicinity of Marais des Baux were cleared for farming. Cereal growing, which included rye cultivation, was of considerable importance. Three noteworthy characteristics that serve to differentiate the Holocene vegetation history of the low-lying Provence region from other French regions are as follows: 1) the early establishment (from the onset of Preboreal) of low altitude mixed forest; 2) the expansion during the Subboreal of fir and beech in low altitude areas with a Mediterranean climate and, 3) the exceptional taxonomic richness of the pollen assemblages (120 identified taxa) and the presence of borealalpine and Euro-Siberian taxa that no longer exist in Lower Provence.