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Aim Feedbacks between climate warming and fire have the potential to alter Arctic and sub-Arctic vegetation. In this paper we assess the effects and interactions of temperature and wildfire on plant communities across the transition between the Arctic and sub-Arctic. Location Mackenzie Delta region, Northwest Territories, Canada. Methods We sampled air temperatures, green alder ( Alnus viridis ssp. fruticosa) cover, growth, reproduction and age distributions, and overall plant community composition on burned and unburned sites across a latitudinal gradient. Results Mean summer temperature across the study area decreased by 3 °C per degree of increasing latitude (6 °C across the study area). In the northern part of the study area, where seed viability was low, alder was less dominant than at southern sites where seed viability was high. The age structure of alder populations across the temperature gradient was highly variable, except in the northern part of the forest–tundra transition, where populations were dominated by young individuals. Alder growth and reproduction were significantly greater on burned sites (38–51 years following fire) than on unburned sites. North to south across the temperature gradient, vegetation changed from a community dominated by dwarf shrubs and fruticose lichens to one characterized by black spruce ( Picea mariana), alder and willows ( Salix spp.). Regardless of the position along the temperature gradient, burned sites were dominated by tall shrubs. Main conclusions Temperature limitation of alder abundance and repro-duction, combined with evidence of recent recruitment on unburned sites, indicates that alder is likely to respond to increased temperature. Elevated alder growth and reproduction on burned sites shows that wildfire also has an important influence on alder population dynamics. The magnitude of alder’s response to fire, combined with observations that burns at the southern margin of the low Arctic are shrub dominated, suggest that increases in the frequency of wildfire have the potential to alter northern vegetation on decadal scales. By creating new seedbeds, fire provides opportunities for colonization that may facilitate the northward movement of tall shrubs. Feedbacks between the global climate system and low Arctic vegetation make understanding the long-term impact of increasing fire frequency critical to predicting the response of northern ecosystems to global change. [ABSTRACT FROM AUTHOR]

Aim Lianas differ physiologically from trees, and therefore their species-richness patterns and potential climate-change responses might also differ. However, multivariate assessments of spatial patterns in liana species richness and their controls are lacking. Our aim in this paper is to identify the environmental factors that best explain the variation in liana species richness within tropical forests. Location Lowland and montane Neotropical forests. Methods We quantified the contributions of environmental variables and liana and tree-and-shrub abundance to the species richness of lianas, trees and shrubs ≥ 2.5 cm in diameter using a subset of 65 standardized (0.1 ha) plots from 57 Neotropical sites from a global dataset collected by the late Alwyn Gentry. We used both regression and structural equation modelling to account for the effects of environmental variables (climate, soil and disturbance) and liana density on liana species richness, and we compared the species-richness patterns of lianas with those of trees and shrubs. Results We found that, after accounting for liana density, dry-season length was the dominant predictor of liana species richness. In addition, liana species richness was also related to stand-level wood density (a proxy for disturbance) in lowland forests, a pattern that has not hitherto been shown across such a large study region. Liana species richness had a weak association with soil properties, but the effect of soil may be obscured by the strong correlation between soil properties and climate. The diversity patterns of lianas and of trees and shrubs were congruent: wetter forests had a greater species richness of all woody plants. Main conclusions The primary association of both liana and tree-and-shrub species richness with water availability suggests that, if parts of the Neotropics become drier as a result of climate change, substantial declines in the species richness of woody plants at the stand level may be anticipated. [ABSTRACT FROM AUTHOR]

The vegetation of subantarctic Campbell Island consists mainly of lowland Dracophyllum scrub and upland tussock grassland and tundra. Soon after the island was discovered in 1810, occupation by sealers and whalers led to localized burning and cutting of scrub. Further burning and cutting took place as a result of sheep farming between 1894 and 1931. Since the earliest photographs and vegetation descriptions of the island in the late nineteenth century, scrub cover has expanded markedly. Also, since the 1960s, the island has become warmer and drier. The aim of this paper is to quantify scrub changes as depicted in photo-sequences from the island, and to establish if the spread of scrub is a result of the cessation of anthropogenic activities or a response to global warming. Campbell Island, an isolated island 600 km south of New Zealand mainland (52°33.7′S, 169°09′E). Changes in scrub cover in the island were established through analysis of 33 photographic sequences in the island, the earliest photos dating back to 1888. Visual estimates were made of percentage woody cover in matching areas of repeat photographs, and of changes in scrub distribution with altitude and landscape type. Dracophyllum scrub was restricted at the time of the first photographs (1888) relative to its present extent, and earlier written observations suggest that there had been little change from the 1840s. Scrub cover has subsequently increased in most areas. Most of the spread occurred after the cessation of farming. Change has mostly consisted of a thickening and expansion of pre-existing scrub patches. There is no indication that the upper elevational limit of scrub has increased. Initial reduction of scrub was probably due to anthropogenic fire in the early nineteenth century, although it is possible that less favourable climates had also restricted its distribution. Failure of the scrub to regenerate significantly between 1840 and c. 1895 may also have been a consequence of generally cooler, wetter climates at this time. Rapid scrub expansion began between the end of farming and burning in 1931 and 1988 when the remaining feral sheep were removed. Sheep grazing in the absence of fire reduced competition, and encouraged regeneration and growth of woody scrub. Spread was probably assisted by a pronounced shift to warmer, drier climates in the second half of the twentieth century. Upper elevational limits of scrub have not increased, suggesting that factors other than summer temperature are controlling scrub line in this superoceanic environment. [ABSTRACT FROM AUTHOR]

Aim: Tropical old‐growth grasslands are increasingly acknowledged as biodiverse ecosystems, but they are understudied in many aspects. Geoxyle species are a key component in many of these ecosystems, their belowground storage organs and bud banks are functionally diverse and contribute to the grasslands' resilience. However, the drivers of the geoxyles' evolution and (belowground) diversity are little understood. Thus, we combined analyses on the key aspects of diversity, belowground functionality, ancestry, and ecology of geoxyles to provide the first comprehensive understanding of this often overlooked growth form. Location: Southern hemisphere Africa, particularly Angola as a part of the Zambezian phytochorion. Taxon: Geoxyle species. Methods: We assessed belowground bud bank types and biogeographic origins of geoxyles in grass‐dominated vegetation types on the Angolan plateau, covering a broad altitudinal, climatic and geological range. Geoxyles were sampled extensively at three different sites, yielding 118 taxa covering about 59% of the Angolan geoxyle flora. Based on the current distribution of these species in Africa below the equator, we analysed their origins and environmental correlates in a taxonomic, functional and biogeographic context. Results: Geoxyle species numbers and species communities differed strongly among sites, but functional types showed very similar spectra. Geoxyles evolved in multiple lineages and originated in different biomes, and functional types were unevenly associated with lineages and biomes. Furthermore, functional types correlate to specific environmental driver combinations. Main conclusions: Functional diversity is not directly linked to species diversity, but is a result of multiple biogeographic origins that contributed functionally differently preadapted lineages to the Zambezian flora. Thus, geoxyles can occur under different environmental conditions, but require seasonal climates, and open grassy ecosystems subjected to fire, frost and likely herbivory. We highlight the importance of frost as a correlate of geoxyle diversity and emphasize the need for further studies to understand this important and complex growth form. [ABSTRACT FROM AUTHOR]

Aim: Climate‐induced range expansion ultimately implies recruitment at sites that were previously unoccupied by a species (i.e. colonization events). Using evidence on abiotic conditions and biotic interactions at these migration sites, we aimed to identify migration pathways from northern temperate to boreal forests for species showing northward range expansion. Location: Quebec, Canada. Taxon: Trees of northern temperate/boreal forests. Methods: Using past (1970–1977) and recently updated (2003–2015) forest inventories across 761,100 km2, we first quantified latitudinal shifts for saplings of eight tree species and investigated colonization events at migration sites. We used field evidence and a consensus modelling approach to determine environmental suitability and identify edaphic, climatic and disturbance conditions, as well as species co‐occurrence patterns, characterizing recent colonization events. The results were interpreted in relation to novel species associations facilitating species migration in unsuitable landscapes. Results: All species showed northward latitudinal shifts driven by increased recruitment and colonization northward. Colonization events occurred largely at historically unsuitable sites. Migration sites showed a shift towards humus types characteristic of the boreal forest and not typically found in the core range of most temperate species. Climatic conditions at migration sites were initially colder than at occupied sites, but warming suggests recent climatic suitability. A decrease in conifer basal area at migration sites following disturbances reduced priority effects that possibly constrained deciduous species establishment. Co‐occurrence patterns pointed to deciduous species tolerant of boreal edaphic conditions, leading the way for other temperate species. Main conclusions: Temperate tree species can recruit into sites typical of boreal forests, even under environmentally challenging conditions. Warming and disturbances open up the way for some novel species associations that in turn have the potential to facilitate the recruitment of temperate species into the boreal forest, revealing migration pathways. [ABSTRACT FROM AUTHOR]

Aim: To test the previously published hypothesis that there was widespread reforestation following the depopulation of Indigenous Peoples in the 16th and 17th centuries. Location: The central Appalachian Mountains of eastern North America. Taxon: Quercus alba, Liriondendron tulipifera Methods: To test for reforestation following depopulation, we used tree‐ring evidence of tree recruitment, early radial growth and growth releases from 18 historic log buildings (n = 361 logs) and eight old‐growth forest sites (n = 197 trees). We used inner‐ring dates to determine if a synchronous recruitment event(s) was present at historic sites but absent from old‐growth sites following depopulation. We used cluster analysis to determine if historic logs established in a clearing (fast early growth) or under a canopy (slow early growth). Similarly, we calculated disturbance rates (growth releases per 100 years) to determine if historic logs grew in a clearing (low disturbance) or under a canopy (high disturbance). Results: Historic log and old‐growth forest sites both document a period of elevated recruitment beginning in the 1670s. This event was observed in previous studies and across site types, suggesting that either climate variability or the absence of low‐intensity land use (e.g. fire) may have also contributed to forest establishment. Most historic sites (61%–83%) had fast early growth, indicating growth of trees in high‐light conditions. The rate of disturbance was lower at historic sites with fast early growth (5.3 events/century, 95% Cl [3.6, 7.0]) than at old‐growth sites with slow early growth (23.5 events/century, 95% Cl [17.5, 29.5]), consistent with the idea that most historic logs were harvested from fast‐growing, second‐growth forests that established after depopulation. Main Conclusions: Our results support the hypothesis of reforestation in upland forests of the central Appalachian Mountains following depopulation and suggest that upland forests, at the time of European immigration, were at least in part, a legacy of indigenous land use practices. However, the timing of a regional drought event, depopulation and subsequent recruitment of trees, all within the period of ~1650–1690 CE, warrants further research into interactions between indigenous land use and climate during a pivotal period in North American history. [ABSTRACT FROM AUTHOR]

Aim: In fresh waters, most biogeographical understanding of how extreme events such as drought modify biodiversity and ecosystem functioning derives from static, spatial comparisons of ecological communities, between intact and disturbed sites or along stress gradients. Impacts of drought on the development of ecological communities over time remain poorly resolved, with information on parallel trends in community structure and function particularly scarce. In theory, drought could progressively eliminate both species and functional traits, rendering communities increasingly taxonomically and functionally nested subsets of their pre‐existing counterparts. Alternatively, drought could create new niche opportunities, producing a continuous turnover of species and traits, or simply constrain natural community succession. Location: Dorset, UK. Taxon: Aquatic invertebrates. Methods: We studied temporal changes in community structure and function in artificial streams over 2 years, comparing drought (frequent drying) with control (constant flow) conditions. Temporal beta diversity was partitioned into turnover and nestedness components, calculated using both presence–absence and abundance data, and analysed using time‐lag and null modelling approaches. Results: Community development was comparable taxonomically under control and drought conditions, driven primarily by temporal turnover of species. Under control conditions, corresponding trends in functional composition were not apparent, and species turnover was characterized by the progressive replacement of some species by others of equivalent abundance. By contrast, species turnover in disturbed communities was accompanied by both functional turnover and greater loss of individuals, indicating that new colonists were not equivalent, either functionally or numerically, to those they replaced. Furthermore, functional dissimilarities between time points were greatest under drought, and more similar in magnitude to taxonomic dissimilarities, implying that drying reduced the stability and redundancy of functional attributes. Main conclusion: A shift to drier climate could disrupt the natural development of stream community structure, and undermine functional stability, at local and biogeographical scales, with potentially significant consequences for ecosystem services provisioning in fresh waters. [ABSTRACT FROM AUTHOR]

Abstract: Aim: The Mediterranean is characterized by diverse and spatially heterogeneous mosaic landscapes. Within this study, a cluster analysis‐based method is developed for the classification of Mediterranean vegetation types based on modern and fossil pollen datasets. The application of this approach to multiple pollen records spanning the Mediterranean region has allowed temporal variations in vegetation dynamics to be explored throughout the Holocene. We ask how far back stable baseline vegetation communities can be identified in the pollen record, and whether those types considered to be characteristic of the Mediterranean landscapes have been present in the past as well as at the present. Location: The research location includes the land areas surrounding the Mediterranean Sea. The pollen sites are principally located in mainland Spain, southern France, Greece and Turkey, Italy, North Africa, the Levant, and some Mediterranean islands. Methods: A total of 5,641 samples from 158 fossil pollen records (cores) and 1,799 modern pollen surface samples were harmonized taxonomically and pollen count data summed into 200‐year time windows on a common time‐scale from 11,000  bp to the present‐day. Cluster analysis and community classification were used to identify major vegetation types along with other approaches to explore patterns in ecological datasets, such as Simpson's diversity index and nonmetric multidimensional scaling. Results: The pollen datasets were classified into 11 closed forest/woodland and five open or scrubland vegetation types. Closed vegetation clusters declined from the mid‐Holocene with a marked increase in open or human‐modified vegetation types since 3,500  bp and with an increasing rate of vegetation change and habitat diversity through time. Main conclusions: The Mediterranean has been a dynamic landscape throughout the Holocene with frequent changes in land cover identified in the pollen datasets. The pollen‐inferred clusters reveal a wider range of Mediterranean vegetation types than identified in previous studies; for example, including both beech and alder woods. Evergreen Oleaceae‐dominated shrubland is much better represented in modern than in fossil samples while mesic forest was abundant in the past but is uncommon today. [ABSTRACT FROM AUTHOR]

Aim The aim of this study was to investigate the biogeography of plant zonation in salt marshes on the Pacific coast of South America; to examine whether salt marsh plant zonation varies with latitude; and to explore the relative importance of climatic, tidal, edaphic and disturbance factors in explaining large-scale variation in salt marsh plant community structure. Location A 2,000-km latitudinal gradient on the Pacific coast in Chile, with a climate shift from hyper-arid at low to hyper-humid at high latitudes. Methods Plant zonation was quantified in field surveys of ten marshes. Climate, tidal regimes, edaphic factors and disturbances (tsunami and rainfall floods) were determined. We used multivariate analyses to explore their relative importance in explaining large-scale variation in salt marsh plant community structure. Results Across latitude, marshes were dominated by distinct plant communities in different climate regions, especially at the extreme dry and wet latitudes. Intertidal plant species zonation was present in hyper-arid and semi-arid climates, but not in arid, humid and hyper-humid climates. Latitudinal variation in low-marsh plant communities (regularly flooded at high tide) was largely a function of precipitation, while at high marshes (never flooded at high tide) latitudinal variation was explained with precipitation, temperature, tidal cycles, soil salinity and disturbances. Main conclusions Salt marshes on the Pacific coast of South America belong to Dry Coast and Temperate biogeographic types. Salt marsh plant zonation varies across latitude, and is explained by climatic, tidal, edaphic and disturbance factors. These patterns appear to be mechanistically explained by extrapolating experimentally generated community assembly models and have implications for predicting responses to climate change. [ABSTRACT FROM AUTHOR]

Aim Our goal was to test the hypothesis that ancient humans substantially contributed to shaping the current distribution of Brazil nut ( Bertholletia excelsa), an Amazonian tree species that has been important for human livelihoods since pre-Columbian times. We scrutinized the putative association between Brazil nut and Amazonian Dark Earth soils ( ADE) and geometric earthworks called geoglyphs, and examined the existence of continental patterns in human footprints on Brazil nut stands. Location Amazon Basin. Methods We carried out a spatially explicit meta-analysis of the variation of Brazil nut stand metrics across the Amazon Basin based on 87,617 density estimates and 488 average stand diameter assessments, and related these to previously published datasets and suitability maps of Brazil nut, ADE and geoglyphs. Results We found consistently higher Brazil nut suitability scores, stand densities and average stand diameters in the vicinities of ADE than at larger distances, regardless of their position along a gradient from south-western to north-eastern Amazonia. For geoglyph sites such a pattern was only found for Brazil nut habitat suitability scores. The available data further revealed an accumulation of Brazil nut stands with increasing densities and average diameters from south-western to central and eastern Amazonia. Main conclusions Our findings suggest that the chance of encountering Brazil nut stands bearing the marks of past human influences increases from south-western to central and eastern Amazonia. In south-western Amazonia, the regeneration of Brazil nut seems to have been controlled predominantly by natural processes, whereas in central and eastern Amazonia, anthropogenic disturbance has been more important since pre-Columbian times. However, it remains challenging to disentangle human influences on the distribution and abundance of Brazil nut from existing environmental gradients across the Amazon Basin. In general, the results of this meta-analysis bode well for the future coexistence of Brazil nut with different forms of contemporary human land use. [ABSTRACT FROM AUTHOR]

Aim To identify the ecosystem features most important for differentiating leading edges from rear edges of plant population distributions, and for distinguishing both from contiguous-range sites. Location Eastern California, USA. Methods Habitats supporting multiple plant populations at their range edges were analysed, including 32 rear-edge, 32 leading-edge and 526 control sites within contiguous ranges. Multivariate modelling techniques, including general linear and additive modelling, ordination and classification trees were used to identify the biotic and abiotic factors that control range edges. Results Rear edges were associated with lower solar radiation and potential evapotranspiration, as would generally be expected as ranges shift in a warming climate regime. Leading edges were associated with lower topographical positions, such as canyon bottoms, and were characterized by recent disturbance and early successional stages. Rear edges occurred mainly in undisturbed sites. Main conclusions The interacting roles of biological and physical factors in determining population range limits have recently gained attention as the need to predict ecosystem shifts in a changing climate increases. Further understanding and recognition of disturbance in facilitating the expansion of native species' ranges and in conserving relict populations will enhance the ability of land managers to maintain biodiversity and ecosystem resilience as climate continues to change. [ABSTRACT FROM AUTHOR]

Aim Our aims were to: (1) reconstruct the fire history of pine-oak forests in the central Appalachian Mountains, USA, with an annual resolution over as long a time period as possible using dendroecological techniques; (2) estimate the frequency of fire in the study area before the fire-suppression era; and (3) investigate how variations in land use and climate have affected the occurrence of fire in the study area. Location Temperate forests at three study sites within the central Appalachian Mountains, Virginia, USA. Methods Cross-sections were taken (sawn) from fire-scarred pine ( Pinus L.) trees growing in pine-dominated patches within a hardwood forest matrix. Dendroecological techniques were used to date the scars, which were used to calculate fire intervals. A variety of analyses were carried out: Pearson correlation analysis, to investigate whether fire activity varied over time (under changing land uses); Kruskal- Wallis analysis, to examine whether fire frequency varied spatially (among study sites); chi-square analysis, to test whether scar seasonality changed temporally; and superposed epoch analysis, to explore whether fire activity was associated with interannual climatic variations in moisture, as characterized by the Palmer drought severity index ( PDSI). Results Fire scars dated back to the 17th or early 18th century (depending on site). The filtered composite fire interval, considered to be a particularly reliable estimate of fire interval, averaged between 6 and 8 years. Fire frequency remained fairly constant from the beginning of the record until effective fire suppression began in the early 20th century, after which burning virtually ceased. Fire occurred more frequently at the easternmost site, which was located in the Blue Ridge province of the Appalachian Mountains, than at the other two sites, in the Ridge and Valley province. Scar seasonality showed no discernible trend over time. Fire was associated with low PDSI (i.e. dry years) at two of the study sites. Main conclusions Fire occurred frequently at these central Appalachian study sites during the period of aboriginal depopulation that preceded European colonization, and throughout the periods of European settlement and industrialization (with mining, logging and railroads) that followed. Our results match those from other fire-history sites in the central and southern Appalachian Mountains, and suggest that fire was an important factor influencing vegetation development in the temperate forests covering this region. [ABSTRACT FROM AUTHOR]

Aim To evaluate the evidence for a small-island effect ( SIE) on insular floras, considering the effects of including islands without the species of interest, temporal variability and species composition. Location Small islands in the Andros, Exuma Cays and Abaco archipelagos of the Bahamas. Methods An information-theoretic multimodel inference approach was used, comparing the fit of a linear model versus two breakpoint models to species-area data. Corrected Akaike's information criterion ( AICc) scores were compared to determine the model(s) with the most support. Results Strong evidence for an SIE was found in the Andros and Exuma Cays archipelagos. At Andros, an SIE was always apparent, regardless of whether islands with no species were included or which time period was considered. In the Exuma Cays, the inclusion of islands with no species changed the inference of the existence of an SIE in one comparison, and the shape of the SIE (i.e. the best-fitting model) in two comparisons. Data from the Exuma Cays indicated that the existence of an SIE, as well as the shape of the SIE, may vary over time. Evidence for an SIE for the Abaco archipelago was equivocal, although fewer data were available. Main conclusions Even though it has been suggested that the exclusion of islands with no species may result in the erroneous detection of an SIE, the inclusion of islands with no species had little effect on the evidence for an SIE in this system. The finding that evidence for, and the shape of, the SIE can change over time suggests caution in interpreting SIE studies for systems that are not in equilibrium. Patterns of species composition as a function of island size support the hypothesis that disturbance events shape the habitat found on these islands, which limits the species pool that can survive on the smaller islands, resulting in an SIE. [ABSTRACT FROM AUTHOR]

Aim Top-down (climatic) controls of fire occurrence are expected to homogenize fire regimes in a given area over long (millennial) temporal scales. Previous investigations in south-eastern British Columbia have shown that bottom-up (local site) factors can override long-term climate as a dominant control. Here, we examine the interactions between fire regime controls using five 5000-year-long lake sediment records. Location All lakes are located in separate watersheds within a 550-km2 region of Engelmann spruce-subalpine fir forest in the Columbia Mountains, British Columbia, Canada. Methods Sedimentary macroscopic (> 150 μm) charcoal analysis was used to produce local fire history records. Fire events were identified by decomposing the charcoal concentration series using the program CharAnalysis. We analysed the temporal coherence of the reconstructed fire events and the distributions of the fire return intervals at all sites and pooled sites by their north-facing or south-facing aspect. Results Since 5000 cal. yr bp, fire frequency was highest between 4250 and 2750 cal. yr bp and lowest from 750 cal. yr bp to the present. Median fire return intervals were shorter on the warmer and drier south-facing slopes (135-190 years) and longer on the cooler and moister north-facing slopes (226-241 years). Significant synchrony existed between sites with similar aspect, but no synchrony was found at sites with opposing aspect, providing evidence for the importance of bottom-up controls. Smoothed fire frequencies suggested that the influence of aspect varied throughout the period and that the importance of aspect could be overridden by other controls. The asynchrony between sites with opposite aspects suggests that local conditions for fire are important spatial controls on the fire regime. Main conclusions Aspect is an important bottom-up control of fire regimes in mid-elevation forests and its influence varies through time. The variability of climate-fire-vegetation interactions in the region needs to be investigated to understand the importance of top-down and bottom-up controls. [ABSTRACT FROM AUTHOR]

Aim Our study aimed to identify and explore the main factors that influence tree recruitment of multiple species at a regional scale across peninsular Spain, an understanding of which is essential for predicting future forest species composition in the face of ongoing environmental change. The study focused on the dynamics of the key transition phase from saplings to adult trees. Location The forests of peninsular Spain. Methods We used the extensive network of plots sampled in two consecutive Spanish national forest inventories (> 30,000 plots) to identify the factors that determine regeneration patterns of the 10 most abundant forest species of Spain at relatively large temporal ( c. 10 years) and spatial scales (across Spain): five coniferous species of Pinus (pines) and five broadleaved species of the genera Fagus and Quercus. We fitted separate generalized linear models for the pine species and the broadleaved species to assess the response of sapling abundance and ingrowth rate to the spatial variability of climate (temperature, water availability and recent warming), forest structure (tree density, understorey and overstorey canopy cover, and basal area change) and disturbances (previous forest logging, wildfires and grazing). Results Mean sapling abundance was four times higher for broadleaved species than for pines, while mean annual ingrowth was twice as high. Sapling abundance and ingrowth rate were mainly determined by stand structure, both in pines and broadleaved trees. The direct effects of disturbances and climate were comparatively smaller, and there was no detectable effect of recent warming. Main conclusions The higher values of ingrowth rate of broadleaved species can be explained by their ability to maintain a higher sapling bank due to their greater shade tolerance. This differential response of pines and broadleaved species to canopy closure suggests a probable increase in broadleaved species at the expense of pines. This transition could occur earlier in stands with faster canopy closure dynamics. Spatially explicit, mixed-species demographic models incorporating both the ingrowth and the tree mortality components are needed for predicting the composition of future forests. [ABSTRACT FROM AUTHOR]

Urbanization is associated with strong changes in biodiversity, but the diversity of plant and animal assemblages varies among urban habitats. We studied effects of urban habitats on the diversity of vascular plants and land snails in 32 large cities. Central Europe, Belgium and the Netherlands. The species composition of all vascular plants that had not been planted by humans, and all land snails, was recorded in seven 1-ha plots within each city. Each plot contained one urban habitat type representing a different disturbance regime: historical city square, boulevard, residential area with compact building pattern, residential area with open building pattern, park, early successional and mid-successional site. For each plot, we obtained temperature and precipitation data. The effects of climate and habitat types on species composition were quantified using ordination methods with an adjusted variation partitioning algorithm. Differences in species composition among urban habitats were described using statistically determined diagnostic species, and differences in alpha, beta and gamma diversity were quantified. A total of 1196 plant and 87 snail species were recorded. Habitat type explained higher proportions of the total variation in both plant and snail species composition (11.2 and 8.2%, respectively) than did climate (4.6 and 6.3%). For both taxa, the main differences in species composition were observed between strongly urbanized sites in city centres and early successional and mid-successional sites. For vascular plants, the number of species was lowest in city squares and boulevards, and highest at successional sites and in residential areas with compact building patterns. Beta diversity of vascular plants calculated for the same habitat types among cities was highest for squares and successional sites. The number of snail species was lowest in city squares and at early successional sites, and highest at mid-successional sites. The highest beta diversity of snail assemblages among cities was observed within the city square and early successional habitat types, and the lowest within residential area habitat types. Urban habitats differ notably in the diversity of their vascular plant flora and land snail fauna. Understanding the habitat-related biodiversity patterns in urbanized landscapes will allow projections of future impacts of urban land-use changes on the biota. [ABSTRACT FROM AUTHOR]

Aim The spruce–moss forest is the main forest ecosystem of the North American boreal forest. We used stand structure and fire data to examine the long-term development and growth of the spruce–moss ecosystem. We evaluate the stability of the forest with time and the conditions needed for the continuing regeneration, growth and re-establishment of black spruce ( Picea mariana) trees. Location The study area occurs in Québec, Canada, and extends from 70°00′ to 72°00′ W and 47°30′ to 56°00′ N. Methods A spatial inventory of spruce–moss forest stands was performed along 34 transects. Nineteen spruce–moss forests were selected. A 500 m2 quadrat at each site was used for radiocarbon and tree-ring dating of time since last fire (TSLF). Size structure and tree regeneration in each stand were described based on diameter distribution of the dominant and co-dominant tree species [black spruce and balsam fir ( Abies balsamea)]. Results The TSLF of the studied forests ranges from 118 to 4870 cal. yr bp. Forests < 325 cal. yr bp are dominated by trees of the first post-fire cohort and are not yet at equilibrium, whereas older forests show a reverse-J diameter distribution typical of mature, old-growth stands. The younger forests display faster height and radial growth-rate patterns than the older forests, due to factors associated with long-term forest development. Each of the stands examined established after severe fires that consumed all the soil organic material. Main conclusions Spruce–moss forests are able to self-regenerate after fires that consume the organic layer, thus allowing seed regeneration at the soil surface. In the absence of fire the forests can remain in an equilibrium state. Once the forests mature, tree productivity eventually levels off and becomes stable. Further proof of the enduring stability of these forests, in between fire periods, lies in the ages of the stands. Stands with a TSLF of 325–4870 cal. yr bp all exhibited the same stand structure, tree growth rates and species characteristics. In the absence of fire, the spruce–moss forests are able to maintain themselves for thousands of years with no apparent degradation or change in forest type. [ABSTRACT FROM AUTHOR]

Aim To examine the relationship between diadromy and dispersal ability in New Zealand’s freshwater fish fauna, and how this affects the current environmental and geographic distributions of both diadromous and non-diadromous species. Location New Zealand. Methods Capture data for 15 diadromous and 15 non-diadromous fish species from 13,369 sites throughout New Zealand were analysed to establish features of their geographic ranges. Statistical models were used to determine the main environmental correlates of species’ distributions, and to establish the environmental conditions preferred by each species. Environmental predictors, chosen for their functional relevance, were derived from an extensive GIS database describing New Zealand’s river and stream network. Results In terms of geography, most diadromous species occur in a scattered fashion throughout extensive geographic ranges, and occupy large numbers of catchments of widely varying size. By contrast, most non-diadromous species show relatively high levels of occupancy of smaller geographic ranges, and most are restricted to a few large catchments, particularly in the eastern South Island. In terms of environment, there is marked separation of diadromous from non-diadromous species, with diadromous species generally caught most frequently in low-gradient coastal rivers and streams with warm, maritime climates. With a few notable exceptions, most diadromous species have lower occurrence in river segments that are located above obstacles to upstream migration. Non-diadromous species are usually caught in inland rivers and streams with cool, strongly seasonal climates, typified by a low frequency of high-intensity rainfall events. Main conclusions We interpret the contrasting biogeographies of New Zealand’s diadromous and non-diadromous species as reflecting interaction between their marked differences in dispersal ability and a landscape that is subject to recurrent, often large-scale, natural disturbance. While both groups are likely to be equally susceptible to local, disturbance-driven extinction, the much greater dispersal ability of diadromous species has allowed them to persist over wide geographic ranges. By contrast, the distributions of most non-diadromous species are concentrated in a few large catchments, mostly in regions where less intense natural disturbance regimes are likely to have favoured their survival. [ABSTRACT FROM AUTHOR]

Aim To understand the distribution pattern of endemic plant species in West African rain forests, one of the global priority areas for biodiversity conservation. Location Upper Guinean forests, West Africa (Senegal, Guinea-Bissau, Guinea, Sierra Leone, Liberia, Côte d'Ivoire, Ghana and Togo). Methods We used herbarium collections from the whole Upper Guinean region ( sensu White 1981) to analyse the distribution patterns of 216 vascular plant species (approximately one-third of the endemic flora ranging from herbs to trees) that are restricted to these rain forests. We related species distribution ranges and species commonness to the main environmental variables and species life-history traits. Results We found that most endemic species of West African forests have large distribution ranges and ruderal strategies. Among all plant life-forms, species with small ranges were restricted to very moist places whereas more widespread species were less dependent on the availability of water. These more common species seem able to tolerate drier conditions, indicated by the minimum rainfall conditions where they are found and the positive correlation with local habitat openness. Light-demanding endemics were more common and widespread than shade-tolerant species, and there was a trend towards wind-dispersed species having a higher proportion of records in open places. This suggests that how widespread and common an endemic species is depends on being able to tolerate open and drier conditions. Main conclusions A ruderal strategy seems to be key for understanding the success of endemics in the Upper Guinean forests, and indicates the important role of disturbances in shaping the composition of these tropical forests. Our results have large implications for predicting the potential effect of increasing drought on rare endemic plant species of West African forests. [ABSTRACT FROM AUTHOR]

Aim We tested the relative vulnerability of islands to Oxalis pes-caprae L. invasion compared to mainland regions. Oxalis pes-caprae is a South African annual geophyte that reproduces via bulbils, and has spread in many Mediterranean and temperate regions of the world where introduced. Our study is one of the first detailed regional analyses of the occurrence and local abundance of a non-native plant. Methods We conducted an extensive survey (2000 sampling points) to examine local and coarse-scale patterns in both the occurrence and abundance of O. pes-caprae on islands and in neighbouring mainland regions of Spain. Location We analysed occurrence (number of samples where present) and abundance (percentage cover) on two Balearic Islands (Menorca and Mallorca) and in two mainland administrative provinces of Spain (Murcia and València). Results Oxalis pes-caprae occurrence was consistently higher on islands. Occurrence varied among habitats, being the highest in tree groves and the lowest in forests and shrublands. It was never found in these two habitats on the mainland. Mean O. pes-caprae abundance was greatest in tree groves on the mainland, and in field margins and old fields on the islands. However, in general there were not significant differences in local abundances between island and mainland locations. Main conclusions These findings suggest that local processes (such as the biotic resistance of plant communities) are less important than coarse-scale phenomena (such as environmental driving forces) in explaining differences in the invasion patterns observed between islands and adjacent mainland regions. We suggest that O. pes-caprae has occupied a larger proportion of available habitats on islands due to: (1) its strong dependence on domestic animal and human-mediated dispersal which are probably greater on the islands than in mainland areas, and (2) the smaller area encompassed by islands that, over a comparable period of time, enables a greater proportion of available habitats to be colonized (and hence higher occurrence) than equivalent larger mainland areas. [ABSTRACT FROM AUTHOR]

Aim To explore: (1) the relative influences of site conditions, especially moisture relations, on pathways and rates of monsoon rain forest seedling and sapling regeneration, especially of canopy dominants, in northern Australia; and (2) contrasts between regeneration syndromes of dominant woody taxa in savannas and monsoon rain forest. Location Four monsoon rain forest sites, representative of regional major habitat and vegetation types, in Kakadu National Park, northern Australia. Methods A decadal study involved: (1) initial assessment over 2.5 years to explore within-year variability in seed rain, dormant seed banks and seedling (< 50 cm height) dynamics; and (2) thereafter, monitoring of seedling and sapling (50 cm height to 5 cm d.b.h.) dynamics undertaken annually in the late dry season. On the basis of observations from this and other studies, regeneration syndromes of dominant monsoon rain forest taxa are contrasted with comparable information for dominant woody savanna taxa, Eucalyptus and Corymbia especially. Results Key observations from the monsoon rain forest regeneration dynamics study component are that: (1) peak seed rain inputs of rain forest taxa were observed in the wet season at perennially moist sites, whereas inputs at seasonally dry sites extended into, or peaked in, the dry season; (2) dormant soil seed banks of woody rain forest taxa were dominated by pioneer taxa, especially figs; (3) longevity of dormant seed banks of woody monsoon rain forest taxa, including figs, was expended within 3 years; (4) seedling recruitment of monsoon rain forest woody taxa was derived mostly from wet season seed rain with limited inputs from soil seed banks; (5) at all sites rain forest seedling mortality occurred mostly in the dry season; (6) rain forest seedling and sapling densities were consistently greater at moist sites; (7) recruitment from clonal reproduction was negligible, even following unplanned low intensity fires. Main conclusions By comparison with dominant savanna eucalypts, dominant monsoon rain forest taxa recruit substantially greater stocks of seedlings, but exhibit slower aerial growth and development of resprouting capacity in early years, lack lignotubers in mesic species, and lack capacity for clonal reproduction. The reliance on sexual as opposed to vegetative reproduction places monsoon rain forest taxa at significant disadvantage, especially slower growing species on seasonally dry sites, given annual–biennial fires in many north Australian savannas. [ABSTRACT FROM AUTHOR]

Aim The Brazilian Atlantic forest covers c. 10% of its original extent, and some areas are still being logged. Although several ecological studies in Atlantic forest have been published over the past two to three decades, there has been little research on forest dynamics and there is a particular lack of information on the effects of disturbance. The aim of the present study was to assess the impact of selective logging on forest structure, floristic composition soil nutrients, litterfall and litter layer in a seasonally dry Atlantic forest . Location The Mata do Carvão is located in the Guaxindiba Ecological Reserve in São Francisco do ltabapoana district (21°24′ S, 41°04′ W), Rio de Janeiro, Brazil. Methods Four plots (50 × 50 m) were set up in 1995 in each of two stands: unlogged and logged. In each plot, all trees ≥ 10 cm d.b.h. were enumerated, identified and measured. Vouchers were lodged at UENF Herbarium. Five surface soil samples were collected in each plot in the dry season (in October 1995). Litterfall was collected in eight traps (0.50 m2) in each plot over a year from 14 November 1995 to 11 November 1996. The litter layer was sampled in eight quadrats (0.25 m2) in each plot in the dry and wet seasons. Soils were air-dried, sieved, and chemically analysed. The litter was dried (80 °C), sorted into six fractions, weighed and bulked samples analysed for nutrients. Results Forest stands did not differ in stem density and total basal area, with a total of 1137 individuals sampled in 1996 (564 unlogged and 573 logged), and a total basal area of 15 m2 (unlogged) and 13.0 m2 (logged). However, unlogged stands had more large trees (≥ 30 cm in d.b.h.) and greater mean canopy height. Among the families, Rutaceae and Leguminosae were the most abundant families in both sites, although the Rutaceae had a higher density in unlogged and Leguminosae in the logged stand. The species diversity index was similar between stands. Late-successional species, such as Metrodorea nigra var. brevifolia and Paratecoma peroba, were less abundant in the logged stand. Selective logging did not affect nutrient concentrations in the soil or in the litter. However, quantities of the nutrients in the total litterfall and in the leaf litterfall and litter layer were higher in unlogged than in logged stands, mainly as a result of fallen M. nigra leaves. Metrodorea nigra was considered a key species in the nutrients dynamics in Carvão forest. Main conclusions Despite the fact that effects on tree diversity and soil nutrients were not clear, selective logging in this Atlantic forest altered canopy structure, increased the relative abundance of some early-secondary species and decreased the litter input and stock of nutrients. Detailed information on the influence of logging on the distribution and structure of plant populations and in nutrient processes is fundamental for a sustainable logging system to be developed. [ABSTRACT FROM AUTHOR]

Aim To assess at a broad scale the vulnerability of Mediterranean vegetation to alien plant invasion under different climatic and disturbance scenarios. Location We simulated the vegetation biogeography and dynamics on five of the main islands of the Mediterranean Basin: Mallorca, Corsica, Sardinia, Crete and Lesvos. Methods We used LPJ-GUESS, a generalized ecosystem model based on dynamic processes describing establishment, competition, mortality and ecosystem biogeochemistry. We simulated the vegetation distribution and dynamics using a set of plant functional types (PFTs) based on bioclimatic and physiological parameters, which included tree and shrub PFTs defined especially for the Mediterranean. Additionally, two invasive PFTs, an invasive tree type and an invasive herb type, were defined and used to estimate the vulnerability to invasion of a range of different ecosystems. The model was used to simulate climate changes and associated changes in atmospheric [CO2] to 2050 according to two Special Report on Emissions Scenarios climate scenarios (A1Fi and B1) combined with mean disturbance intervals of 3 and 40 years. Results The simulations and scenarios showed that the effect of climate change alone is likely to be negligible in many of the simulated ecosystems, although not all. The simulated progression of an invasion was highly dependent on the initial ecosystem composition and local environmental conditions, with a particular contrast between drier and wetter parts of the Mediterranean, and between mountain and coastal areas. The rate of ecosystem disturbance was the main factor controlling susceptibility to invasion, strongly influencing vegetation development on the shorter time scale. Main conclusions Further invasion into Mediterranean island ecosystems is likely to be an increasing problem: our simulations predict that, in the longer term, almost all the ecosystems will be dominated by exotic plants irrespective of disturbance rates. [ABSTRACT FROM AUTHOR]

Climate, topography and soils drive many patterns of plant distribution and abundance across landscapes, but current plant communities may also reflect a legacy of past disturbance such as agricultural land use. To assess the relative influences of environmental conditions and disturbance history on vegetation, it is important to understand how these forces interact. This study relates the geographical distribution of land uses to variation in topography and soils; evaluates the consequences of land-use decisions for current forests; and examines the effects of agricultural land use on the chemical properties of forest soils.Tompkins County occupies 1250 km2 in central New York's Finger Lakes region. Like much of eastern North America, this area underwent forest clearance for agriculture during the 1800s and widespread field abandonment and forest recovery during the 1900s. The current landscape consists of a patchwork of forests that were never cleared, forests that developed on old fields and active agricultural lands.We investigated relationships among topography, soils and land-use decisions by gathering information about land-use history, slope, aspect, elevation, soil lime content, soil drainage and accessibility in a geographic information system (GIS). To assess the effects of agriculture on forest soil chemistry, we measured pH, organic matter content and extractable nutrient concentrations in field-collected soil samples from 47 post-agricultural and uncleared forests.Steeper slopes, less accessible lands and lower-lime soils tended to remain forested, and farmers were more likely to abandon fields that were steeper, farther from roads, lower in lime and more poorly drained. Slope had by far the greatest impact on patterns of clearance and abandonment, and accessibility had a surprisingly strong influence on the distribution of land uses. The effects of other factors varied more, depending for example on location within the county. Current forest types differed accordingly in topography and soil attributes, particularly slope, but they also showed much overlap. Post-agricultural and uncleared forest soils had similar chemical properties. Forests on lands abandoned from agriculture 80–100 years before had slightly higher pH and nutrient concentrations than adjacent, uncleared forests, but these changes were small compared to environmental variation across the county.Despite differential use of lands according to their topography and soils, the substantial influence of accessibility and the relatively small scale of land-use decisions allowed for broad similarity among forest types. Thus, the topography and soil differences created by land-use decisions probably contribute little to landscape-level patterns of diversity. Subtle changes in forest soil chemistry left from past agriculture may nevertheless affect plant distribution and abundance at finer scales. [ABSTRACT FROM AUTHOR]

To assess how ant species richness and structure of ant communities are influenced by island age (disturbance history) in a dynamic archipelago.Cabra Corral dam, Salta Province, north-west Argentina (25°08′ S, 65°20′ W).Ant species richness on remaining fragments (islands) of a flooded forest was determined, as well as island area, isolation and age. Simple linear regressions were performed to assess relationships between ant species richness and those insular variables. Furthermore, a stepwise multiple linear regression analysis was conducted in order to determine the relative influence of each insular variable on ant species richness. Islands were categorized in two age classes (old and young) and co-occurrence analyses were applied within each class to evaluate changes in community structure because of interspecific competition.Simple regression analyses indicated a moderate, positive effect of island area on ant species richness. Weak, marginally non-significant relationships were found between ant species richness and both island isolation and island age, showing the tendency for there to be a decrease in ant species richness with island isolation and that ant species richness might be higher in old islands. The multiple regression analysis indicated that island isolation and age had no significant effects on the number of ant species, island area being the only independent variable retained in the analysis. On the contrary, whereas a random pattern of species co-occurrence was found on young islands, ant communities in old islands showed a significantly negative pattern of species co-occurrence, suggesting that the effect of competition on community structure was stronger on older islands than on younger islands.Island area was the most important variable explaining ant species richness on the islands of Cabra Corral dam. However, both island isolation and island age (or disturbance history) might also contribute to shape the observed community patterns. The present study also shows that island age significantly affects the strength with which interspecific interactions structure ant communities on islands. [ABSTRACT FROM AUTHOR]

The impact of microscale frost disturbance on vegetation colonization and successionary trends was examined within patterned ground features of Little Ice Age chronosequences. The goal was to investigate and compare vegetation response to micro-site frost disturbance with that of previous studies done at a coarser landscape scale.The study sites occur on Little Ice Age glacier forelands within Jotunheimen, Norway (61°–62° N). The forelands of the glaciers Slettmarkbreen, Styggedalsbreen and Vestre Memurubreen have been well studied providing chronological controls for landscape studies. Sorted patterned ground features are found within the chronosequences, typically declining with frost intensity and disturbance with increasing terrain age.Micro-plots (8.3 × 8.3 cm) were placed at the inner borders and centres of patterned ground features. Species were identified and per cent species cover and per cent cover of life-form category were noted. Nonparametric Kruskal–Wallis and Mann–WhitneyU-tests were used to test for differences between percent cover of life-form categories within patterned ground features as well as to identify thresholds of successional change across the chronosequences.Significant relationships between life-from groups and patterned ground positions of varying ages were deduced using nonparametric statistics. Findings were then used to discuss trends of succession within patterned ground features and across the chronosequences. Vegetation establishment occurs at the border positions of young (< 30 years) patterned ground features. With time and distance from the ice margin, vegetation encroaches inwards toward the disturbed centres. Succession within patterned ground exhibits several stages: (1) bryophytes/crusts and lichens, (2) grasses/sedges and (3) woody shrubs. The occurrence of forbs was sporadic and generally non-significant.Frost disturbance in patterned ground appears to delay successional trends of vegetation communities when compared with previous studies on‘stable’ terrain, producing micro-site lag effects. These small patches of disturbed ground are therefore important regarding vegetation assemblages across the landscape and are unlikely to be detected at the landscape scale. [ABSTRACT FROM AUTHOR]

To evaluate whether seedlings of sugar maple ( Acer saccharum Marsh.) can establish beyond the species northern range limit in adjacent boreal forest. The hardwood–boreal forest transition zone on the north-east shore of Lake Superior, Ontario, Canada. Seed fall of sugar maple was monitored for 5 years in a stand of this species at its northern range limit, and seed from this stand was transplanted to five micro-habitat types in an adjacent boreal forest. The establishment and survival of sugar maple seedlings there, and in the seed-source stand, was monitored for the following 7–11 years. Soil-surface light levels were measured in both forest types. Most seed fell in the final year of monitoring, when c. 250 seeds m−2 were recorded. First-year seedling establishment rates in the maple stand, deriving from this mast seed year, was approximately double that deriving from seed transplanted to the boreal forest sites; this is tentatively attributed to seed predator satiation in the maple stand. However, subsequent seedling survivorship in the boreal forest was greater than that in the maple stand, resulting in comparable seedling densities by the end of 6 years. This difference is tentatively attributed to better illumination in the boreal forest sites, and canopy-opening disturbances appear to be especially facilitative of seedling survival. There is no fundamental impediment to sugar maple seedlings establishing in boreal forest communities if climate warming occurs and seed is available. If management intervention is needed to accelerate seed availability in a rapidly warming boreal forest, then diffuse seed application to disturbed boreal forest sites during mast years of local boreal tree species is recommended as the most effective way of avoiding seed predation and increasing seedling survival. [ABSTRACT FROM AUTHOR]

Abstract Aim There is increasing research attention being given to the role of interactions among natural disturbances in ecosystem processes. We studied the interactions between fire and spruce beetle (Dendroctonus rufipennis Kirkby) disturbances in a Colorado subalpine forest. The central questions of this research were: (1) How does fire history influence stand susceptibility to beetle outbreak? And conversely, (2) How does prior occurrence of a beetle outbreak influence stand susceptibility to subsequent fire? Methods We reconstructed the spatial disturbance history in a c. 4600 ha area by first identifying distinct patches in the landscape on aerial photographs. Then, in the field we determined the disturbance history of each patch by dating stand origin, fire scars, dates of mortality of dead trees, and releases on remnant trees. A geographical information system (GIS) was used to overlay disturbance by fire and spruce beetle. Results and main conclusions The majority of stands in the study area arose following large, infrequent, severe fires occurring in c . 1700, 1796 and 1880. The study area was also affected by a severe spruce beetle outbreak in the 1940s and a subsequent low-severity fire. Stands that originated following stand-replacing fire in the late nineteenth century were less affected by the beetle outbreak than older stands. Following the beetle outbreak, stands less affected by the outbreak were more affected by low-severity fire than stands more severely affected by the outbreak. The reduced susceptibility to low-severity fire possibly resulted from increased moisture on the forest floor following beetle outbreak. The landscape mosaic of this subalpine forest was strongly influenced by the interactions between fire and insect disturbances. [ABSTRACT FROM AUTHOR]

Abstract Aim The aim of this study was to document changes in forest composition, structure and distribution across Massachusetts, USA, from the time of European settlement (seventeenth century) to the present, and to investigate environmental and historical influences on regional patterns of variation. Location The study area encompasses the State of Massachusetts (69.9–73.5°E, 41.3–42.9°N), a 21,000-km2 area in the north-eastern United States. Methods A wide range of historical sources was used to document changes in land use and land cover for the historical period. Witness trees from early land surveys enabled us to evaluate vegetation patterns prior to widespread European settlement, and to compare historical and modern species composition. Nineteenth century maps of forest cover and contemporary agricultural censuses documented forest patterns during the peak agricultural period. Geographic Information System analyses were used to relate variation in climate, geology and land-use history to historical and modern forest composition. Results Massachusetts has a complex east-to-west environmental gradient involving changes in physiography, climate, geology and natural disturbance. Until the middle of the twentieth century, agriculture was the most important land-use across the region; although the percentage of land in agriculture and the timing of major land-use changes were remarkably consistent across the state, historical forest patch sizes varied locally and regionally in relation to physiography. Forest composition of both early historical and modern forests is most strongly related to environmental conditions, especially variation in climate. Historical land-use resulted in a state-wide increase in early successional tree species and a dramatic, although recovering, change in forest structure. Main conclusions At a regional scale, environmental conditions apparently control broad patterns of variation in vegetation... [ABSTRACT FROM AUTHOR]

Abstract Aim We use a retrospective approach to reconstruct the past distribution of fire in New England and to investigate the important drivers of this pattern across the period of European arrival to North America. Location Our study sites are in New England, and range from pitch pine and oak forests of coastal Massachusetts, pine and hardwood forests of central Massachusetts, and northern hardwood and spruce fir forests of northern Massachusetts and Vermont. Methods We collected sediment profiles from eighteen lakes across the study area to assess fossil charcoal and pollen abundance over the past 1000 years, including the time period of European arrival and settlement. Results Based on presettlement pollen composition, our study sites are divided into three vegetation types: (1) pitch pine and oak, (2) oak, pine and hardwood and (3) northern hardwoods. The abundance of presettlement charcoal in these lakes is closely related to climate and the composition of surrounding vegetation. Charcoal is most abundant in pitch pine forests and least common in northern hardwood forests. Following the arrival of Europeans, charcoal abundance increased at most sites substantially, and vegetation composition changed in a direction of either greater dominance by pitch pine or white pine, depending on whether the forests were located in the southern or northern part of New England. Main conclusions The major factor influencing the distribution of fire across New England is climate, which has a direct effect on the physical conditions conducive to fire ignition and spread and an indirect effect on fire through its control on the distribution of vegetation at this spatial scale. We find evidence that other factors exert some control over local fire regimes as well including landforms and their impact on vegetation composition, firebreaks and prevailing winds. Native Americans likely influenced the local occurrence of fire, but their impact on regional fire regimes in New... [ABSTRACT FROM AUTHOR]

Abstract Aim This study documents the vegetation history and age-structure of a rare, ridgetop dwarf pine–oak community and compares the dynamics of this unusual vegetation with similar dwarf pine communities found elsewhere in the north-eastern United States (US). Location The study area is located on the summit of Mt Everett in the Taconic Mountains of south-western Berkshire County, Massachusetts, USA (42°06′N 73°26′W). Methods Vegetation composition, tree age-structure, physical site characteristics, and evidence of fire and other disturbances were determined for twelve 15 × 15 m plots in dwarf pine–oak vegetation and two plots in oak forests on the summit. Age-structure analyses, tree-ring patterns, and historical records of human and natural disturbance were used to investigate the long-term history and dynamics of the summit vegetation. Results The summit of Mt Everett has been dominated by dwarf pines (1–3 m tall) and ericaceous shrubs similar to the modern vegetation throughout the historical period; there is no evidence that tall-stature forests occurred on the site at any point in the past few centuries. The summit supports uneven-aged stands; pitch pine (Pinus rigida ) recruitment began in the 1830s and occurred in every decade since the 1860s. Average pitch pine age is seventy-eight with a range of 12–170 years. Red oak (Quercus rubra ) and red maple (Acer rubrum ) increased in importance in the twentieth century, with most stems establishing from 1940 to 1980. Pitch pine radial growth rates averaged <0.5 mm year-1 while red oak and red maple averaged 1.0 and 0.8 mm year-1 , respectively. In some areas, hardwoods have overtopped pitch pines, apparently resulting in pitch pine mortality. Whereas most dwarf pitch pine communities occur on sites that burn frequently and have a high degree of cone serotiny, we found no evidence of recent fires or cone serotiny. Small... [ABSTRACT FROM AUTHOR]

Aim I investigated the determinants of plant species richness in two archipelagos, comparing the predictive power of different explanatory variables. I evaluated both conventional variables and alternative variables not commonly used in such analyses. I also investigated the effect of island location in relation to neighbouring landmasses on plant species richness and the predictive ability of regression models. Location Archipelagos of small islands in the central Exumas and near the north-east coast of Andros, Bahamas. Methods I surveyed plant species richness and obtained measures of seven predictor variables: total island area, the ratio of perimeter to total area, vegetated area, the ratio of vegetated area to total area, distance to the nearest large island, elevation and protection from surrounding islands. All seven predictor variables were evaluated as determinants of plant species richness in simple and stepwise multiple linear regressions. Analyses were conducted for each archipelago overall, and then separately for three categories of islands in the Exumas. Total area, elevation, and distance were evaluated as predictors of vegetation incidence in simple and stepwise multiple logistic regressions for both archipelagos. Results Some expression of insular area was always the best single predictor of plant species richness in the linear regressions. Total area was a relatively poor predictor compared with other expressions of insular area. Distance, elevation, and protection explained relatively little of the overall variation in plant species number, although all variables were selected as significant in some models. A greater amount of variation in plant species richness was explained by the linear regression models in the Exumas (69.0%) compared with Andros (60.9%). Different variables were entered into the models for the three categories of islands in the Exumas, and adjusted coefficients of multiple determination ranged from 68.9% to 85.7%. In the... [ABSTRACT FROM AUTHOR]

AimIn this study, we evaluated the fire-forest mosaic of a mixed conifer forest landscape by testing the hypothesis that pre-fire suppression fire regime parameters vary with species composition (tree species), and environment (i.e. slope aspect, slope position, elevation). LocationOur study was conducted in the 1587 ha Cub Creek Research Natural Area (CCRNA), Lassen National Forest, CA, USA. MethodsWe quantified the return interval, seasonal occurrence, size, rotation period, and severity of fires using dendroecology. ResultsSlope aspect, potential soil moisture, forest composition, and fire regime parameters in our study area co-vary. Median composite and point fire return intervals (FRI) were longest on higher, cooler, more mesic, north-facing (NF) slopes covered with white fir (Abies concolor), Douglas fir (Pseudotsuga menziesii)–white fir, and red fir (A. magnifica)–white fir forests, shortest on the dry, south-facing (SF) slopes covered with ponderosa pine (Pinus ponderosa)–white fir forests and intermediate on west-facing slopes dominated by white fir–sugar pine (P. lambertiana)–incense cedar (Libocedrus decurrens) forests. The spatial pattern for length of fire rotation (FR) was the same as that for FRI. Fires in CCRNA mixed conifer forests occurred mainly (90%) in the dormant season. Size of burns in CCRNA mixed conifer forests were generally small (mean=106 ha), however, during certain drought years widespread fires burned across fuel breaks and spread throughout the watershed. Fire severity was mainly high on upper slopes, low on lower slopes and moderate and low severity on middle slopes. Patterns of fire severity also varied with slope aspect. Fire frequency decreased dramatically in CCRNA after 1905. ConclusionsIn CCRNA, fire regime parameters [e.g. FRI, fire extent, FR, fire severity] varied widely with species composition, slope aspect and slope position. There was also temporal variation in fire extent with the most widespread fires occurring during drought years. The important contributions of topography and climate to variation in the fire regime indicates that exogenous factors play a key role in shaping the fire-forest structure mosaic and that the fire-forest structure mosaic is more variable, less predictable and less stable than previously thought. Finally, some characteristics of the fire regime (i.e. fire severity, season of burn) in CCRNA are different than those described for other mixed conifer forests and this suggests that there are geographical differences in mixed conifer fire regimes along the Pacific slope. [ABSTRACT FROM AUTHOR]

Abstract Aim This study compares human impacts and forest ecosystem response across geographical regions. Such a comparison allows us to evaluate the relationship between regional changes in forest composition and regional patterns of human activity. Location Four study areas in the north-eastern USA were investigated, two of which were dominated by oak-pine forests at the time of European settlement (Central Massachusetts, MA; Pike County, PA), and two of which were dominated by beech and hemlock (South Berkshire, MA; Wayne County, PA). Methods Trees recorded in early land survey records were compiled and compared with data on modern forest composition obtained from recent forest inventories. To assess the similarity of the four regions with regard to species composition, Euclidean Distances (ED) were calculated between the colonial and modern forest composition for each of the four regions. Information about the history of human impacts in the four study regions was used to interpret the changes in forest composition. Results General changes in forest composition through the historical period include a decline in beech, hemlock and chestnut, and an increase in maple and birch. Changes in pine and oak were minor by comparison. Supraregional human impacts are generally linked with supraregional trends in species composition, whereas regional patterns of land use caused regional patterns of change in species composition. Main conclusions These results suggest that human activities do not necessarily lead to more similar species composition between regions, especially if these activities show clear spatial patterns at about the same resolution that species composition is evaluated. Comparing species-specific changes in forest composition with species-specific human activities on the same spatial scale is crucial in order to evaluate human impacts on ecosystems and to make more robust generalizations about the temporal dynamics of landscapes. [ABSTRACT FROM AUTHOR]

Abstract Aim Spatial and temporal variation in fire regime parameters and forest structure were assessed. Location A 2630-ha area of mid- and upper montane forest in Lassen Volcanic National Park (LVNP). Methods Two hypotheses were tested concerned with fire-vegetation relationships in southern Cascades forests: (1) fire regime parameters (return interval, season of burn, fire size, rotation period) vary by forest dominant, elevation and slope aspect; and (2) fire exclusion since 1905 has caused forest structural and compositional changes in both mid- and upper montane forests. The implications of the study for national park management are also discussed. Results Fire regime parameters varied by forest compositional group and elevation in LVNP. Median composite and point fire return intervals were shorter in low elevation Jeffrey pine (Pinus jeffreyi) (JP) (4–6 years, 16 years) and Jeffrey pine–white fir (Abies concolor) (JP-WF) (5–10 years, 22 years) and longer in high elevation red fir (Abies magnifica)— western white pine (Pinus monticola) (RF-WWP) forests (9–27 years, 70 years). Median fire return intervals were also shorter on east-facing (6–9 years, 16.3 years) and longer on south- (11 years, 32.5 years) and west-facing slopes (22–28 years, 54-years) in all forests and in each forest composition group. Spatial patterns in fire rotation length were the same as those for fire return intervals. More growing season fires also occurred in JP (33.1%) and JP-WF (17.5%) than in RF-WWP (1.1%) forests. A dramatic decline in fire frequency occurred in all forests after 1905. Conclusions Changes in forest structure and composition occurred in both mid- and upper montane forests due to twentieth-century fire exclusion. Forest density increased in JP and JP-WF forests and white fir increased in JP-WF forests and is now replacing Jeffrey pine. Forest density only increased in some RF-WWP stands, but not others. Resource managers restoring fire to these now denser forests need to burn larger areas if fire is going to play its pre-settlement role in montane forest dynamics. [ABSTRACT FROM AUTHOR]

Spatial and temporal variations in fire frequency in the boreal forest of Wood Buffalo National Park (WBNP) were assessed using forest stand age, fire scar and historical data. I test the hypotheses that (1) fire frequency is higher in jack pine forests and aspen forests than in black spruce forests and white spruce forests, (2) these variations in fire frequency can be related to the mean waterbreak distance (MWD) around a site and (3) fire frequency has changed over the past 300 years. The fire cycles (the time required to burn an area equal in size to the entire study area) in jack pine forests (39 years) and in aspen forests (39 years) were significantly shorter than those in black spruce forests (78 years) and in white spruce forests (96 years). The length of the fire cycle varies inversely with the MWD around a site, and the MWD was significantly higher in jack pine and aspen forests than in black or white spruce forests. It is suggested that covariations between soil type and the MWD influence, respectively, variations in forest dominant and fire frequency. A change in fire frequency at 1860 was apparent in the fire history for all of WBNP, the black spruce dominated stands, and the near and medium MWD classes. The fire cycle estimates for these classes were all significantly shorter during the period 1750 to 1859 (fire cycles = 25-49 years) than they were in the period 1860 to 1989 (fire cycles = 59-89 years). The possible roles of changes in climate and aboriginal burning practices in causing the temporal change in fire frequency are discussed. [ABSTRACT FROM AUTHOR]