Elevational variation in regional vegetation responses to late‐glacial climate changes in the Carpathians

Aim We used fossil records to explore patterns of change in vegetation composition, turnover and diversity along an elevational gradient during the late‐glacial to early Holocene, and to locate the elevations most sensitive to past climate changes. Location Romania. Methods Changes in the late‐glacial vegetation communities were inferred from seven published pollen records distributed within the main vegetation belts of the Romanian Carpathians, at elevations from 275 to 1840 m. Principal components analysis, detrended canonical correspondence analysis (DCCA) and rarefaction analysis were undertaken on these data. Results DCCA indicates that compositional change is strongest (SD 1.2, c. 70%) at the late‐glacial/Holocene transition (c. 11,500 cal. yr bp ), but significant shifts also occur at c. 14,700, c. 13,800 and c. 12,700 cal. yr bp (SD 0.4–0.8, 25–50%). Palynological turnover is greater for mid‐elevation records (730–1100 m) than at low and high elevations. Intervals of greater palynological richness occur between c. 13,800 and 12,500 cal. yr bp and after 11,500 cal. yr bp , and intervals of lower richness occur before c. 14,000 cal. yr bp and between c. 12,900 and 11,500 cal. yr bp . Main conclusions Variations in species composition during repeated climate changes of the late‐glacial suggest that community composition at a given time was not only a result of the environmental conditions of that period, but also the legacy of previous cumulative recruitment and extirpation events. Turnover estimates suggest that mid‐elevations have been the most sensitive to climate change during the late‐glacial and early Holocene. Palynological richness estimates show a less clear elevational pattern and no evidence for a greater sensitivity of this measure of biodiversity at high elevations to past climate change. However, results may have been affected by taxa with high pollen productivity and distance dispersability. Our finding concurs with other palaeoecological and local‐scale modelling studies in suggesting that small populations have survived in favourable microhabitats embedded within larger unsuitable areas during the late‐glacial, features not captured by broad‐scale model predictions.     

Alpine and subalpine snow patch vegetation on the Bogong High Plains,SE Australia

Abstract. Snow patch vegetation in Australia is rare, being restricted to the relatively small area of alpine and subalpine country in the highlands of southeastern Australia. Snow patch vegetation occurs on steeper, sheltered southeastern slopes, where snow persists until well into the growing season (December/January). We surveyed the vegetation of 33 snow patch sites in the alpine and subalpine tracts of the Bogong High Plains, within the Alpine National Park, in Victoria. The vegetation was dominated by herbs and graminoids, with few shrubs and mosses. Major structural assemblages identified included closed herb‐fields dominated by Celmisia spp, and grasslands dominated by Poa fawcettiae or Poa costiniana. These assemblages occurred on mineral soils. Open herb‐fields dominated by Caltha introloba and several sedge species occurred on rocky and stony substrata. Vegetation‐environment relationships were explored by ordination and vector fitting. There was significant variation in the floristic composition of snow patch vegetation as a function of duration of snow cover, altitude, slope and site rockiness. Alpine sites were floristically distinct from subalpine sites, with a greater cover of Celmisia spp. and a lesser cover of low shrubs in the former. There was floristic variation within some snow patches as a function of slope position (upper, middle or lower slope) but this was not consistent across sites. The current condition of snow patch vegetation on the Bogong High Plains is degraded, with bare ground exceeding 20% cover at most sites. Snow patch vegetation is utilized preferentially by domestic cattle, which graze parts of the Bogong High Plains in summer. Such grazing is a potential threat to this rare vegetation type.     

Late quaternary vegetation dynamics and human impact on Alexander Selkirk Island, Chile

Aim To reconstruct the history of vegetation and environments using pollen, charcoal and sediment analysis, and to identify the timing and nature of climate change and human impact on the vegetation of a remote Pacific island. Location Cerro de Los Inocentes, 1000 m above sea level, Alexander Selkirk Island (33°45′S, 80°45′W), Chile. The westernmost island of the Juan Fernandez Archipelago, south‐east Pacific Ocean. Methods A 150‐cm long sediment core comprising 87 cm dark brown peat overlying 63 cm of yellow grey clay was extracted from a shallow depression on the southern slopes of Cerro de Los Inocentes. Pollen, charcoal, sediment and accelerator mass spectrometry radiocarbon analyses were used to construct a record of vegetation change through time. Numerical analysis of multispecies data allowed the classification of fossil assemblages into distinct pollen zones. Results Pollen and spores are preserved throughout the sediment with high concentrations coinciding with the beginning of organic sediment accumulation at around 8000 ¹⁴C yr BP. Prior to 8000 ¹⁴C yr BP, the deposition of clays, presumably from upslope erosion, occurred in a landscape sparsely vegetated by grasses, ferns and Pernettya rigida heath, including several plants that are only found 100–200 m above the site today (Zone CI‐1). After 8000 ¹⁴C yr BP, a P. rigida heath was the dominant vegetation (Zone CI‐2). A shift to a wet heath–shrubland (Zone CI‐3) occurred at 6000 ¹⁴C yr BP and was followed by a transition to a treefern–shrubland mosaic accompanied by periodic burning (Zone CI‐4) after 4500 ¹⁴C yr BP. The impact of human occupation is evident in Zone CI‐5 at 450 ¹⁴C yr BP with the loss of forest species, increased burning and invasion of the exotic plant Rumex. Main conclusions The pollen and charcoal record provides the first evidence of vegetation changes spanning at least the last 8000 ¹⁴C yr BP from the high altitude environment of Alexander Selkirk Island. Prior to 8000 ¹⁴C yr BP, the altitudinal ranges of different plant species may have been suppressed by a cooler and drier climate. Increasing precipitation and temperatures at the end of the last glacial period may have mobilized exposed sediments in a sparsely vegetated upland environment, altering local drainage patterns, eventually leading to slope stabilization and deposition of organic detritus under an increasing density of heath and shrub vegetation. The subalpine heath–shrubland persisted until 4500 ¹⁴C yr BP when first evidence for sustained burning is found in association with the establishment of a more open treefern–shrubland vegetation pattern. In the absence of human occupation at this time, the influence of increased climatic variability associated with more frequent El Niño‐Southern Oscillation events during the mid to late Holocene is considered one of the main driving forces behind increased vegetation disturbance during this period. The record provides evidence that island vegetation patterns have been highly dynamic over millennial to decadal time‐scales and that the flora has persisted through periods of rapid and major climate change. This changed with the discovery of the island by European explorers in the late sixteenth century and the subsequent introduction of goats and exploitation and burning of forests, which resulted in the progressive destruction of native vegetation and the invasion of introduced plants. There is evidence that reduced burning and control of the goat population within the last 50 years has resulted in marginal recovery of some high altitude native plant species.     

A 40,000-year woodrat-midden record of vegetational and biogeographical dynamics in north-eastern Utah, USA

Aim A conspicuous climatic and biogeographical transition occurs at 40–45° N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time‐scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) middens to the south]. To overcome these limitations, we are extending the woodrat‐midden record northward into the lowlands of the central Rocky Mountains. Location Woodrat middens were collected from crevices and rock shelters on south‐facing slopes of Dutch John Mountain (2000–2200 m, 40°57′ N, 109°25′ W), situated on the eastern flanks of the Uinta Mountains in north‐eastern Utah. The site is near the regional limits for Pinus ponderosa, P. edulis, P. contorta, Cercocarpus ledifolius var. intricatus, Abies concolor, Ephedra viridis and other important western species. Methods We analysed pollen and plant macrofossils from the 40,000‐year midden sequence. The middens represent brief, depositional episodes (mostly years to decades). Four middens represent the early to full‐glacial period (40,000–18,000 cal‐yr bp ), eight middens are from the late‐glacial/early Holocene transition (13,500–9000 cal yr bp ), and 33 middens span the mid‐to‐late Holocene (last 7500 years). Temporal density of our Holocene middens (one every c. 210 years) is comparable with typical Holocene pollen sequences from lake sediments. Results Early to full‐glacial assemblages are characterized by low diversity and occurrence of montane conifers (Picea pungens, Pseudotsuga menziesii, P. flexilis, Juniperus communis) absent from the site today. Diversity increases in the late‐glacial samples with the addition of J. scopulorum, J. horizontalis, C. montanus, C. ledifolius var. intricatus and mesic understory species. The coniferous trees and J. communis declined and J. osteosperma appeared during the late‐glacial/Holocene transition. Juniperus osteosperma populations have occupied the site throughout the Holocene. Pinus ponderosa was established by 7500 cal‐yr bp , and has occurred at least locally ever since. Montane conifers and J. horizontalis persisted until c. 5500 cal‐yr bp . The signature events of the late Holocene were the invasions of P. edulis and Ephedra viridis and establishment of pinyon–juniper woodland in the last 800 years. Main conclusions The Dutch John Mountain midden record adds to an emerging picture in which mid‐elevation conifers (P. flexilis, Pseudotsuga menziesii, Picea pungens, J. scopulorum, J. communis) dominated vegetation over a wide area of the Colorado Plateau and adjacent Rocky Mountains. Rather than being fragmented, as often assumed in phylogeographical studies, these species had broader and more‐connected distributions than they do in the region today. Paradoxically, subalpine conifers (Picea engelmannii, A. lasiocarpa) occurred at higher elevations to the south, possibly representing declining precipitation from south to north owing to southward displacement of the polar jet stream. The Dutch John Mountain record displays a series of extinction and invasion events. Most of the extinctions were local in scale; nearly all constituents of fossil midden assemblages occur within a few kilometres of Dutch John Mountain, and some occur at least locally on its slopes. The sole exception is J. horizontalis, which is regionally extinct. In contrast to extinctions, Holocene invasions were regional in scale; J. osteosperma, P. ponderosa, P. edulis and Ephedra viridis immigrated from glacial‐age source populations far to the south.     

Post-glacial changes in spatial patterns of vegetation across southern New England

Aim We analysed lake‐sediment pollen records from eight sites in southern New England to address: (1) regional variation in ecological responses to post‐glacial climatic changes, (2) landscape‐scale vegetational heterogeneity at different times in the past, and (3) environmental and ecological controls on spatial patterns of vegetation. Location The eight study sites are located in southern New England in the states of Massachusetts and Connecticut. The sites span a climatic and vegetational gradient from the lowland areas of eastern Massachusetts and Connecticut to the uplands of north‐central and western Massachusetts. Tsuga canadensis and Fagus grandifolia are abundant in the upland area, while Quercus, Carya and Pinus species have higher abundances in the lowlands. Methods We collected sediment cores from three lakes in eastern and north‐central Massachusetts (Berry East, Blood and Little Royalston Ponds). Pollen records from those sites were compared with previously published pollen data from five other sites. Multivariate data analysis (non‐metric multi‐dimensional scaling) was used to compare the pollen spectra of these sites through time. Results Our analyses revealed a sequence of vegetational responses to climate changes occurring across southern New England during the past 14,000 calibrated radiocarbon years before present (cal yr bp ). Pollen assemblages at all sites were dominated by Picea and Pinus banksiana between 14,000 and 11,500 cal yr bp ; by Pinus strobus from 11,500 to 10,500 cal yr bp ; and by P. strobus and Tsuga between 10,500 and 9500 cal yr bp . At 9500–8000 cal yr bp , however, vegetation composition began to differentiate between lowland and upland sites. Lowland sites had higher percentages of Quercus pollen, whereas Tsuga abundance was higher at the upland sites. This spatial heterogeneity strengthened between 8000 and 5500 cal yr bp , when Fagus became abundant in the uplands and Quercus pollen percentages increased further in the lowland records. The differentiation of upland and lowland vegetation zones remained strong during the mid‐Holocene Tsuga decline (5500–3500 cal yr bp ), but the pattern weakened during the late‐Holocene (3500–300 cal yr bp ) and European‐settlement intervals. Within‐group similarity declined in response to the uneven late‐Holocene expansion of Castanea, while between‐group similarity increased due to homogenization of the regional vegetation by forest clearance and ongoing disturbances. Main conclusions The regional gradient of vegetation composition across southern New England was first established between 9500 and 8000 cal yr bp . The spatial heterogeneity of the vegetation may have arisen at that time in response to the development or strengthening of the regional climatic gradient. Alternatively, the differentiation of upland and lowland vegetation types may have occurred as the climate ameliorated and an increasing number of species arrived in the region, arranging themselves in progressively more complex vegetation patterns across relatively stationary environmental gradients. The emergence of a regional vegetational gradient in southern New England may be a manifestation of the increasing number of species and more finely divided resource gradient.     

Pinus cembra L. (arolla pine), a common tree in the inner French Alps since the early Holocene and above the present tree line: a synthesis based on charcoal data from soils and travertines

Aim In this study, charcoal‐based data for Pinus cembra L. (arolla pine) were gathered from soil and travertine sequences in order to reconstruct its historical biogeography at the landscape level in the inner western Alps during the Holocene. Location The study sites are located between 1700 and 2990 m a.s.l., in the southern (Queyras Massif and Ubaye Valley) and the northern (Maurienne Valley) parts of the inner French Alps. Methods Charcoal fragments were extracted from sediments by water sieving, using meshes of 5, 2, 0.8 and 0.4 mm. The charcoal mass of P. cembra was determined in each charcoal assemblage. Accelerator mass spectrometry and conventional ¹⁴C measurements were used to date the fragments. Results Supported by 40 ¹⁴C datings, the fragments show that, over 2000 m a.s.l., P. cembra accounts for around 40% (mean value) of identified fragments. Data reveal that arolla pine once extended between 260 and 375 m above the present‐day local tree lines. It was established in the southern and the northern French Alps from at least c. 9000 and 6000 cal yr bp , respectively. Main conclusions While present‐day populations of P. cembra are very fragmented in the inner French Alps, charcoal records indicate large past occurrences of this tree since the early Holocene. Human disturbance since the Neolithic seems to be the main reason for the regression of the arolla pine woodlands. On the south‐facing slopes of the study sites, currently deforested, this species extended up to 2800 m a.s.l. In the northern areas, charcoal records of the P. cembra expansion are consistent with the regional pollen archives, but in the southern massifs charcoal records indicate its presence c. 2600 years earlier than other palaeobotanical studies suggest. This discrepancy highlights the necessity to crosscheck data using several different proxies in order to assess the validity of conclusions regarding tree development in space and time.     

Holocene altitudinal shifts in vegetation belts and environmental changes in the Sierra Madre Occidental, Northwestern Mexico, based on modern and fossil pollen data

A modern pollen rain study was performed in a 300 km-long altitudinal transect (~ 28° N latitude) from 300 to 2300 m elevation. The higher elevation modern communities: epithermal oak–pines, pine–oak forest, pine forest, and mixed conifer forest were easy to distinguish from their pollen content. In contrast, lower elevation subtropical communities: thornscrub and tropical deciduous forest were difficult to separate, because they share many pollen taxa. Nevertheless we identify high frequencies of Bursera laxiflora as an important component of the tropical deciduous forest.Additionally, fossil pollen was analyzed at three sites located between 1700 and 1950 m altitude at ~ 28° latitude north in the Sierra Madre Occidental of northwestern Mexico. The sites were in pine–oak (Pinus–Quercus), pine, and mixed-conifer forests respectively. Shifts in the altitudinal distribution of vegetation belts were recorded for the last 12,849 cal yr BP, and climate changes were inferred. The lowest site (pine–oak forest) was surrounded by pine forest between 12,849 and 11,900 cal yr BP, suggesting a cold and relatively dry Younger Dryas period. The early Holocene was also cold but wetter, with mixed conifer forest with Abies (fir) growing at the same site, at 1700 m elevation, 300 m lower than today. After 9200 cal yr BP, a change to warmer/drier conditions caused fir migration to higher elevations and the expansion of Quercus at 1700 m. At 5600 cal yr BP Abies was growing above 1800 m and Picea (spruce) that is absent today, was recorded at 1950 m elevation. Fir and spruce disappeared from the 1950 m site and reached their present distribution (scattered, above 2000 m) after 1000 cal yr BP; we infer an episodic Holocene migration rate to higher elevations for Abies of 23.8 m/1000 cal yr and for Picea of 39.2 m/1000 cal yr. The late Holocene reflects frequent climate oscillations, with variations in the representation of forest trees. A tendency towards an openness of the forest is recorded for the last 2000 yrs, possibly reflecting human activities along with short-term climate change.     

Tree and shrub dynamics in northwestern Great Basin woodland and shrub steppe during the Late-Pleistocene and Holocene

During the last 12,000 to 30,000 years, a large proportion of the dominant trees and shrubs in modem assemblages of woodland and shrub steppe vegetation in the northwestern Great Basin have undergone relatively small changes in their geographic ranges. A woodland tree, Juniperus osteosperma, has an extensive temporal and spatial fossil record from 11 woodrat midden locales that were sampled in the northwestern Great Basin. Above 1,300 m elevation, J. osteosperma has been continuously present in that fossil record for at least the last 30,000 years. However, J. osteosperma was lost at elevations below 1,300 m sometime during the last 10,000 years, during the Holocene. Although the elevational ranges of six shrub taxa show changes during the Holocene, geographic ranges of 11 other shrub taxa have been largely static. Of the woodland and shrub steppe species examined, Pinus monophylla has experienced the greatest change in its geographic range during the late-Pleistocene and Holocene. Pinus monophylla has migrated northward across the Great Basin from Pleistocene refugia in the southern portions of this region. The rate of latitudinal migration was more rapid along the eastern side of the Great Basin than on the western side. Thus, the species that comprise modern woodland and shrub steppe communities of the northwestern Great Basin appear to have two strategies to cope with climate change. First are species, as exemplified by J. osteosperma, whose geographic ranges were relatively insensitive to climate change and are termed orthoselective species. High genetic variation within species and the formation of coenospecies likely allowed these species to cope with climatic change by genetic adaptation. Secondly, other species, as exemplified by P. monophylla, have experienced shifts in their geographic range during past climate changes and more clearly fit the migration model of species response to climate change.     

Holocene vegetation and climate change on the Colorado Great Plains,USA, and the invasion of Colorado piñon (Pinus edulis)

Aim To reconstruct the last c. 7000 years of vegetation and climate change in an unusual region of modern Great Plains grassland and scarp woodland in south‐east Colorado (USA), and to determine the late Holocene biogeography of Colorado piñon (Pinus edulis) at its easternmost extent, using a series of radiocarbon‐dated packrat (Neotoma sp.) middens. Location The West Carrizo Canyon drains the Chaquaqua Plateau, a plateau that projects into the western extent of the southern Great Plains grasslands in south‐eastern Colorado, USA. Elevations of the study sites are 1448 to 1525 m a.s.l. Today the plateau is mostly Juniperus scopulorum–P. edulis woodland. Methods Plant macrofossils and pollen assemblages were analysed from 11 ¹⁴C‐dated packrat middens. Ages ranged from 5990 yr bp (6839 cal. yr bp ) to 280 yr bp (485 cal. yr bp ). Results The results presented here provide information on the establishment and expansion of Juniperus–P. edulis woodland at its eastern limits. The analysis of both plant macrofossils and pollen from the 11 middens documents changes in plant communities over the last 7000 years, and the establishment of P. edulis at its easternmost limit. Though very minor amounts of P. edulis pollen occur as early as the middle Holocene, plant macrofossils were only recovered in middens dating after c. 480 cal. yr bp . Main conclusions Originally, midden research suggested a late glacial refuge to the north‐east of the Carrizo Canyon site, and a middle Holocene expansion of P. edulis. Results reported here are consistent with a late Holocene expansion, here at its eastern limits, but noted elsewhere at its northern and north‐eastern limits. In general, this late Holocene expansion is consistent with pollen data from sediments in Colorado and New Mexico, and suggests that P. edulis is still expanding its range at its present extremes. This has implications for further extension of its range due to changing climatic conditions in the future.     

Holocene vegetation history of the Sahel: pollen, sedimentological and geochemical data from Jikariya Lake, north-eastern Nigeria

Aim This study aims to separate regional and local controls on Holocene vegetation development and examine how well pollen records reflect climate change in a semi‐arid region. The relative importance of climate and human activity as agents of vegetation change in the Sahel during the late Holocene is also considered. Location Jikariya Lake, an inter‐dune depression in the Manga Grasslands of north‐eastern Nigeria. Methods Pollen and charcoal were used to provide a record of Holocene vegetation history. Palaeoclimate and hydrological changes were reconstructed from sedimentary and geochemical data. Regional and local influences were separated by comparing the evidence obtained from Jikariya Lake with previously published data from the Manga Grasslands. Results The Manga Grasslands experienced a prolonged wet period during the early and mid‐Holocene, during which swamp forest vegetation with Guinean affinities (Alchornea, Syzygium, Uapaca) occupied the inter‐dune depressions. However, variation in the pollen records between sites suggests that their establishment was dependent on conditions being locally favourable, rather than being directly coupled to regional climate. The pollen records from the Manga Grasslands are more consistent in suggesting the colonization of the dunefields by trees associated with Sudanian savanna (Combretaceae, Detarium) c. 8700 cal. yr bp . The Jikariya Lake pollen data are in accordance with the sedimentological and geochemical data from the region in indicating that the onset of arid conditions occurred progressively during the late Holocene (from c. 4700 cal. yr bp ). Abrupt changes in pollen stratigraphy, recorded at other Manga Grasslands sites 3500 cal. yr bp , appear to be the product of the local passing of ecological thresholds. The dunefield vegetation (Sahelian savanna) appears to have been resilient to (or at least palynologically silent regarding) to the climatic variability of the late Holocene. Main conclusions While climate appears to have been the primary control on vegetation development in the Manga Grasslands during the Holocene, local conditions (particularly depression size and sand influx) had a strong influence on the timing of pollen stratigraphic changes. Anthropogenic influences are difficult to detect, even during the late Holocene.     

Succession in sub‐boreal forests of West‐Central British Columbia

Abstract. Structural and compositional changes were analysed over the course of 400+ yr of post‐fire succession in the sub‐boreal forests of west‐central British Columbia. Using a chronosequence of 57 stands ranging from 11 to 438 yr in age, we examined changes in forest structure and composition with complementary PCA and DCA ordination techniques. To determine stand ages and timing of tree recruitment, approximately 1800 trees were aged. Most early successional forests were dominated by Pinus contorta, which established rapidly following fire. Abies lasiocarpa and Picea glauca × engel‐mannii were also able to establish quickly, but continued to establish throughout the sere. Few Pinus contorta survived beyond 200 yr, resulting in major changes in forest structure. In some stands P. contorta never established, which led to considerable variation among stands less than 200 yr old. The oldest forests converged on dominance by Abies lasiocarpa. Vascular plant diversity decreased during succession whereas canopy structure became more complex as gap dynamics developed. Although these sub‐boreal forests contain few tree species, successional changes were pronounced, with structure changing more than composition across the chronosequence.     

A long‐term record of Quercus decline,logging and fires in a southern Swedish Fagus‐Picea forest

Abstract. We reconstructed forest development and disturbance events (fire and logging) during the last 1000 yr with tree‐ring data, pollen and charcoal analysis from a semi‐natural Fagus sylvatica‐Picea abies forest (ca. 1 km²) in the hemiboreal zone. According to pollen analysis, Quercus robur together with Pinus sylvestris was abundant in the forest until the turn of the 18th/19th centuries when these species disappeared completely (Quercus) or nearly completely (Pinus) and were replaced by Fagus and Picea. The disappearance of Quercus was corroborated by the remarkable discovery of a single Quercus stump that had been cut in the 18th century and had become overgrown and preserved by a very old Picea. In total 11 fires were dated from 1555 to 1748 from fire scars in several Pinus stumps cut 100 ‐ 200 yr ago. Since the last fire in 1748, no Quercus or Pinus have regenerated in the core of the reserve apart from single pines in neighbouring managed forest (80 yr ago). During the period of documented fires Fagus was protected from fires in a refuge made up of large boulders. Picea colonized the region at the time when the fires ceased 250 yr ago. We hypothesize that most of the fires were probably of human origin because of their patchiness and high frequency compared to the natural background levels of lightning ignitions in the region. On a 300‐yr time scale, logging and fire suppression seem to strongly overshadow the effect of climate change on forest composition and dynamics.     

Tropical forest structure and diversity in relation to altitude and disturbance in a Biosphere Reserve in central India

Questions: Is species diversity affected in protected areas where human activities are permitted or tolerated? On plots of a fixed size, does stem density alone predict number of species? Are differences in density related to disturbance and altitude? Location: Achanakmar‐Amarkantak Biosphere Reserve, central India. Methods: 42 sites, each with three replicate 10‐m radius plots, were examined. All trees (≥ 30 cm GBH) in each plot were measured for girth at breast height. α‐diversity, species richness and evenness were calculated for each site. The sites were ordinated by Nonmetric Multidimensional Scaling (NMS) using relative importance values of component species. Correspondence Analysis was used to broadly delineate communities. Anthropogenic disturbances were recorded in terms of percentage of trees lopped, scale of lopping, number of domestic livestock dung piles and foot trails (both livestock and people) for each plot. Results: The NMS analysis exhibited a near linear arrangement of sites with no evidence of discrete vegetation zones. NMS axes were significantly related to altitude and disturbance scores. With increasing elevation, basal area increased but number of species, α‐diversity and its components declined monotonically. The number of species and indices of species diversity were positively associated with tree lopping and also with total disturbance. Number of species was controlled by stem density only in plots not dominated by Shorea robusta. Conclusions: Recent levels of human disturbance are associated with higher species diversity in this biosphere reserve. There is some evidence that stands at all altitudes follow the same successional pattern to dominance by Shorea, a successional pattern that also results in decreased diversity without disturbance.     

Late‐glacial and Holocene vegetation,climate and fire dynamics in the Serra dos Órgãos,Rio de Janeiro State,southeastern Brazil

We present a high‐resolution pollen and charcoal record of a 218 cm long sediment core from the Serra dos Órgãos, a subrange of the coastal Serra do Mar, located at 2130 m altitude in campos de altitude (high elevation grass‐ and shrubland) vegetation near Rio de Janeiro in southeastern Brazil to reconstruct past vegetation, climate and fire dynamics. Based on seven AMS ¹⁴C ages, the record represents at least the last 10 450 ¹⁴C yr bp (12 380 cal years bp ), The uppermost region was naturally covered by campos de altitude throughout the recorded period. Diverse montane Atlantic rain forest (ARF) occurred close to the studied peat bog at the end of the Late‐glacial period. There is evidence of small Araucaria angustifolia populations in the study area as late as the early Holocene, after which point the species apparently became locally extinct. Between 10 380 and 10 170 ¹⁴C yr bp (12 310–11 810 cal yr bp ), the extent of campos de altitude was markedly reduced as montane ARF shifted rapidly upward to higher elevations, reflecting a very wet and warm period (temperatures similar to or warmer than present day) at the end of the Younger Dryas (YD) chronozone. This is in opposition to the broadly documented YD cooling in the northern Hemisphere. Reduced cross‐equatorial heat transport and movement of the Intertropical Convergence Zone over northeastern Brazil may explain the YD warming. Markedly extended campos de altitude vegetation indicates dry climatic conditions until about 4910 ¹⁴C yr bp (5640 cal yr bp ). Later, wetter conditions are indicated by reduced high elevation grassland and the extension of ARF into higher elevation. Fire frequency was high during the early Holocene but decreased markedly after about 7020 ¹⁴C yr bp (7850 cal yr bp ).     

The influence of different grazing regimes on Phragmites‐ and shrub vegetation in the well‐drained zone of a eutrophic wetland

Abstract. The effects of grazing by cattle and horses on vegetation development were studied in the well‐drained border zone of the Oostvaardersplassen nature reserve, a managed eutrophic wetland in the young Zuidelijk Flevoland polder in The Netherlands. At the start of the study period, 12 yr after the area was enclosed by dykes, the vegetation was dominated by Phragmites australis and tall herbs, particularly Cirsium arvense. Over the next 8 yr, different plant communities developed under different grazing regimes. In all communities, C. arvense was gradually replaced by Urtica dioica, and stands dominated by these two species expanded at the expense of P. australis. The shrub Sambucus nigra invaded the stands of C. arvense and U. dioica. Grazing affected the rate of these developments and the degree to which the grass Poa trivialis became dominant. When cattle were enclosed at a relatively high stocking rate in an area of Phragmites australis and tall herbaceous vegetation during summer, P. trivialis became dominant within 4 yr. The introduction of herbivores led to a faster spread of S. nigra, which contains cyanogenic glycosides which only ruminants can detoxify. Horses, as hind‐gut fermenters, did not feed on S. nigra. Grazing pressure and herbivore species, therefore, are two important variables that can be used to manage the development of Phragmites‐ and shrub vegetation: the greater the grazing pressure by cattle or horses the greater the area dominated by grasses, and a relatively high grazing pressure by cattle will retard S. nigra expansion.     

Pollen-based reconstructions of biome distributions for Australia, Southeast Asia and the Pacific (SEAPAC region) at 0, 6000 and 18,000 14C yr BP

Aim This paper documents reconstructions of the vegetation patterns in Australia, Southeast Asia and the Pacific (SEAPAC region) in the mid‐Holocene and at the last glacial maximum (LGM). Methods Vegetation patterns were reconstructed from pollen data using an objective biomization scheme based on plant functional types. The biomization scheme was first tested using 535 modern pollen samples from 377 sites, and then applied unchanged to fossil pollen samples dating to 6000 ± 500 or 18,000 ± 1000 ¹⁴C yr bp . Results 1. Tests using surface pollen sample sites showed that the biomization scheme is capable of reproducing the modern broad‐scale patterns of vegetation distribution. The north–south gradient in temperature, reflected in transitions from cool evergreen needleleaf forest in the extreme south through temperate rain forest or wet sclerophyll forest (WSFW) and into tropical forests, is well reconstructed. The transitions from xerophytic through sclerophyll woodlands and open forests to closed‐canopy forests, which reflect the gradient in plant available moisture from the continental interior towards the coast, are reconstructed with less geographical precision but nevertheless the broad‐scale pattern emerges. 2. Differences between the modern and mid‐Holocene vegetation patterns in mainland Australia are comparatively small and reflect changes in moisture availability rather than temperature. In south‐eastern Australia some sites show a shift towards more moisture‐stressed vegetation in the mid‐Holocene with xerophytic woods/scrub and temperate sclerophyll woodland and shrubland at sites characterized today by WSFW or warm‐temperate rain forest (WTRF). However, sites in the Snowy Mountains, on the Southern Tablelands and east of the Great Dividing Range have more moisture‐demanding vegetation in the mid‐Holocene than today. South‐western Australia was slightly drier than today. The single site in north‐western Australia also shows conditions drier than today in the mid‐Holocene. Changes in the tropics are also comparatively small, but the presence of WTRF and tropical deciduous broadleaf forest and woodland in the mid‐Holocene, in sites occupied today by cool‐temperate rain forest, indicate warmer conditions. 3. Expansion of xerophytic vegetation in the south and tropical deciduous broadleaf forest and woodland in the north indicate drier conditions across mainland Australia at the LGM. None of these changes are informative about the degree of cooling. However the evidence from the tropics, showing lowering of the treeline and forest belts, indicates that conditions were between 1 and 9 °C (depending on elevation) colder. The encroachment of tropical deciduous broadleaf forest and woodland into lowland evergreen broadleaf forest implies greater aridity. Main conclusions This study provides the first continental‐scale reconstruction of mid‐Holocene and LGM vegetation patterns from Australia, Southeast Asia and the Pacific (SEAPAC region) using an objective biomization scheme. These data will provide a benchmark for evaluation of palaeoclimate simulations within the framework of the Palaeoclimate Modelling Intercomparison Project.     

Fire and late-Holocene expansion of Quercus ilex and Pinus pinaster on Corsica

Abstract. The natural origin of old Quercus ilex (holm oak) forests on the west coast of Corsica is a matter of dispute. This paper discusses the use of pedoanthracology, especially adapted to approach topics in palaeoecology requiring a high spatial precision. It also shows the importance of fire in vegetation change during the Holocene. Pedoanthracology relies on botanical identification and AMS ¹⁴C dating of micro-charcoal found in soil. Three test pits were dug in a forest currently protected within the ‘Man and Biosphere’ program. These pits yielded large quantities of charcoal. There is evidence that Pinus nigra ssp. laricio (laricio pine) and understorey heather species (Ericaceae) played an important role in the vegetation at the beginning of the Subatlantic (ca. 2500 BP). The importance of Pinus pinaster (maritime pine), Quercus ilex and a few mesophilic species increased between 2000 and 1000 BP. Charcoal fragments found in the soil show the role of fire in the vegetation changes recorded. The late expansion of P. pinaster results from a high fire frequency. The hypothesis proposed in the paper suggests that fires destroyed the remaining toxic humus that had accumulated during the millennia which preceded the arrival of Q. ilex to our study sites. The late development of holm oak forest is a combination of the migration of the species and the increase of fire frequency since 2500 BP, most probably resulting from slash-and-burn agriculture.     

Forest composition in Mediterranean mountains is projected to shift along the entire elevational gradient under climate change

Aim Species distribution models have been used frequently to assess the effects of climate change on mountain biodiversity. However, the value and accuracy of these assessments have been hampered by the use of low‐resolution data for species distributions and climatic conditions. Herein we assess potential changes in the distribution and community composition of tree species in two mountainous regions of Spain under specific scenarios of climate change using data with a high spatial resolution. We also describe potential changes in species distributions and tree communities along the entire elevational gradient. Location Two mountain ranges in southern Europe: the Central Mountain Range (central west of the Iberian Peninsula), and the Iberian Mountain Range (central east). Methods We modelled current and future distributions of 15 tree species (Eurosiberian, sub‐Mediterranean and Mediterranean species) as functions of climate, lithology and availability of soil water using generalized linear models (logistic regression) and machine learning models (gradient boosting). Using multivariate ordination of a matrix of presence/absence of tree species obtained under two Intergovernmental Panel on Climate Change (IPCC) scenarios (A2 and B2) for two different periods in the future (2041–70 and 2071–2100), we assessed the predicted changes in the composition of tree communities. Results The models predicted an upward migration of communities of Mediterranean trees to higher elevations and an associated decline in communities of temperate or cold‐adapted trees during the 21st century. It was predicted that 80–99% of the area that shows a climate suitable for cold–wet‐optimum Eurosiberian coniferous and broad‐leaved species will be lost. The largest overall changes were predicted for Mediterranean species found currently at low elevations, such as Pinus halepensis, Pinus pinaster, Quercus ilex ssp. ballota and Juniperus oxycedrus, with sharp increases in their range of 350%. Main conclusions It is likely that areas with climatic conditions suitable for cold‐adapted species will decrease significantly under climate warming. Large changes in species ranges and forest communities might occur, not only at high elevations within Mediterranean mountains but also along the entire elevational gradient throughout this region, particularly at low and mid‐elevations. Mediterranean mountains might lose their key role as refugia for cold‐adapted species and thus an important part of their genetic heritage.     

History of a Pinus strobus-dominated stand in northern New York

Abstract. Pollen, plant macrofossils and charcoal from a small forest hollow were analyzed to determine the formation and dynamics of a Pinus strobus-dominated forest stand on outwash soil in northern New York. P. strobus, Betula papyrifera and Abies balsamea colonized the upland surrounding the hollow following a major disturbance that occurred ca. 360 yr ago. Pre-disturbance vegetation consisted of shade-tolerant Tsuga canadensis, Fagus grandifolia and Picea ruhens. The size-class distribution of modern vegetation suggests continuing recruitment of A. balsamea and Acer rubrum at the site. The status of P. strobus and B. papyrifera in the stand is uncertain, but there is no evidence for recolonization of T. canadensis, F. grandifolia or P. rubens. Frequent windthrow has probably played a role in stand dynamics since ca. 310 yr BP due to the high wind-susceptibility of overstory and understory tree taxa in the modern forest patch. Vegetation change that occurred following fire(s) ca. 310 yr BP was recorded by plant macrofossils but not by pollen, indicating that the pollen assemblage was insensitive to vegetation change within at least 30 m (and potentially 60 m) of the hollow. The apparent insensitivity of this small-hollow pollen assemblage to local vegetation change may be related to the relatively large size of the hollow (75 m²) and/or to its close proximity to a 0.24 ha kettle pond.     

Fossil wood charcoal assemblages from Elands Bay Cave, South Africa: implications for Late Quaternary vegetation and climates in the winter-rainfall fynbos biome

Aim The aim of this paper is to analyse fossil charcoal deposits, largely identified to the species level and spanning a sequence from the late Holocene to < 40,000 BP , in order to reconstruct Late Quaternary vegetation and climatic patterns in the western (winter-rainfall) fynbos biome of South Africa. Location The charcoals were excavated from the Elands Bay Cave (32°19S, 18°20E) on the semiarid (200–250 mmyr^?1), winter-rainfall coastline of the western fynbos biome. Methods Patterns in the charcoal data set over time were sought by manual sorting of the charcoal×sample matrix, as well as by subjecting the data to multivariate analysis. Palaeoclimatic reconstruction was attempted by comparing the climatic controls on contemporary vegetation communities that resembled the fossil assemblages. Charcoal diversity was modelled using sample age and number of charcoal fragments as explanatory variables. Results The fossil assemblages ranged from xeric communities (similar to those presently occurring at the site) during the Holocene, to more mesic thicket and fynbos vegetation in the terminal Pleistocene, to Afromontane forest and riverine woodland communities after about 18,000 BP . Diversity of the charcoal samples increased monotonically with increasing sample age. Main conclusions The results suggest that, unlike the eastern fynbos biome, which is under fundamentally different climatic controls, soil moisture conditions in the western part of the biome were higher in the Last Glacial than during the Holocene. This scenario may help to explain the higher regional richness and associated diversification in the western than eastern part of the biome.