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White-nose syndrome (WNS) is caused by the fungus Pseudogymnoascus destructans and has led to the deaths of millions of North American bats since it was first documented in New York in 2006. Since the first cases were recorded, WNS has spread rapidly across North America and is now confirmed or suspected in 40 US states and seven Canadian provinces. Often, the presence of P. destructans is detected in a cave or hibernaculum before signs of WNS manifest in the resident bat population, making presence of the fungus a more reliable assessment of potential epidemic spread than expansion of manifested WNS. An analysis of 43 cave internal climates across the state of Texas revealed a pattern of thermal suitability for P. destructans that correlated significantly with landscape (elevation, lithology) and external climate (mean surface temperature and precipitation). We generated a predictive model to assess the potential spread of P. destructans through Texas karst systems based on external features that correlate with suitable internal climates for fungal growth. Applications of this model to external climatic variables from 2019 showed seasonally varying patterns of suitability for fungal growth in select regions of Texas karst systems. Results from these surveys and models showed that internal climates of Texas caves are likely able to sustain the growth of P. destructans and could cause disease and resulting declines in Texas bats, and act as stepping-stones for the fungus, allowing it to travel southward into Mexican and Central American cave systems. The resulting work will inform researchers and natural resource managers of areas of significant concern to monitor for the spread of WNS.

Understanding how ecosystem engineers influence other organisms has long been a goal of ecologists. Woodpeckers select nesting sites with high food availability and will excavate and then abandon multiple cavities through their lifetime. These cavities are crucial to secondary cavity nesting birds (SCB) that are otherwise limited by the availability of naturally occurring cavities.Our study examined the role food resources have on the nest site location and home range size of woodpeckers, and the respective influence woodpeckers and the construction of cavities have on the nesting success of SCB.Using five years of avian point count data to locate golden-fronted woodpeckers (GFWO:Melanerpes aurifrons), we correlated insect availability with GFWO home range size and determined differences in insect availability between GFWO occupied and unoccupied sites, while recording nesting success (success: ≥ 1 fledgling) for the GFWO and common SCB in south Texas: Black-crested Titmouse (Baeolophus atricristatus), Ash-throated Flycatcher (Myiarchus cinerascens), Brown-crested Flycatcher (Myiarchus tyrannulus), and Bewick’s Wren (Thryomanes bewickii). We used model averaging to fit species-specific logistic regression models to predict nest success based on cavity metrics across all species.Sites occupied by GFWO had a higher biomass of insects in orders Coleoptera, Hymenoptera, and Orthoptera than unoccupied sites, and there was a negative correlation between the availability of these insect orders and home-range size. GFWO had increased nest success in trees with increased vegetation cover and lower levels of decay, whileSCB had higher levels of nesting success in abandoned GFWO cavities opposed to naturally occurring ones, and in trees with low decay.Our results suggest that SCB may be drawn to nest in abandoned woodpecker cavities where they have higher rates of nest success compared to natural cavities. Additionally, the prevalence for GFWO to excavate cavities in trees with lower levels of decay contradicts previous literature and may indicate a novel temperature trade-off, with live trees requiring more energy to excavate, but providing more protection from high breeding season temperatures in arid and semi-arid areas.

Recent climate warming and scenarios for further warming have led to expectations of rapid movement of ecological boundaries. Here we focus on the circumarctic forest-tundra ecotone (FTE), which represents an important bioclimatic zone with feedbacks from forest advance and corresponding tundra disappearance (up to 50% loss predicted this century) driving widespread ecological and climatic changes. We address FTE advance and climate history relations over the 20th century, using FTE response data from 151 sites across the circumarctic area and site-specific climate data. Specifically, we investigate spatial uniformity of FTE advance, statistical associations with 20th century climate trends, and whether advance rates match climate change velocities (CCVs). Study sites diverged into four regions (Eastern Canada; Central and Western Canada and Alaska; Siberia; and Western Eurasia) based on their climate history, although all were characterized by similar qualitative patterns of behaviour (with about half of the sites showing advancing behaviour). The main associations between climate trend variables and behaviour indicate the importance of precipitation rather than temperature for both qualitative and quantitative behaviours, and the importance of non-growing season as well as growing season months. Poleward latitudinal advance rates differed significantly among regions, being smallest in Eastern Canada (~10 m/year) and largest in Western Eurasia (~100 m/year). These rates were 1-2 orders of magnitude smaller than expected if vegetation distribution remained in equilibrium with climate. The many biotic and abiotic factors influencing FTE behaviour make poleward advance rates matching predicted 21st century CCVs (~103 -104 m/year) unlikely. The lack of empirical evidence for swift forest relocation and the discrepancy between CCV and FTE response contradict equilibrium model-based assumptions and warrant caution when assessing global-change-related biotic and abiotic implications, including land-atmosphere feedbacks and carbon sequestration.

A treeline can respond to climate change by shifting position, infilling, increasing recruitment, and increasing radial growth. More studies from understudied areas and their associated species are...

The alpine treeline ecotone is an important component of mountain ecosystems of the Nepal Himalaya; it plays a vital role in the livelihood of indigenous people, and provides ecosystem services. However, the region faces a problem of paucity of data on treeline characteristics at the regional and landscape scales. Therefore, we used Remote Sensing (RS), and Geographic Information Science (GIS) approaches to investigate cross-scale interactions in the treeline ecotone. Additionally, European Space Agency land cover map, International Center for Integrated Mountain Development (ICIMOD) land cover map, ecological map of Nepal, and United States Geological Survey Shuttle Radar Topography Mission-Digital Elevation Model were used to analyze treeline pattern at the regional scale. Digital Globe high-resolution satellite imagery of Barun (eastern Nepal) and Manang (central Nepal) were used to study treeline patterns at the landscape scale. Treeline elevation ranges from 3300-4300 m above sea level. Abies spectabilis, Betula utilis, and Pinus wallichiana are the main treeline-forming species in the Nepal Himalaya. There is an east to west treeline elevation gradient at the regional scale. No slope exposure is observed at the regional scale; however, at the landscape scale, slope exposure is present only in a disturbed area (Manang). Topography and human disturbance are the main treeline controlling factor in Barun and Manang respectively.

Conifer mountain forests influence a large portion of the World’s human population by providing a host of critical economic, sociological, and ecosystem services. Although the causes of the elevational, transitional boundaries of these forests (i.e. upper and lower timberlines) have been questioned for over a century, these investigations have focused predominately on the growth limitations of saplings or mature trees at the upper alpine boundary. Yet, the elevational movement of timberlines is dependent initially on new seedling establishment in favorable microsites that appear to be generated by ecological facilitation. Recent evidence suggests that this facilitation is critical during the initial 1-2 years of growth when survival may be less than a few percent, only cotyledons are present, and survival occurs only in favorable microsites created by inanimate objects (e.g. boulders, dead stems), microtopography, or already established vegetation. Dramatic changes in tree form (e.g. krummholz mats) across the timberline ecotone also plays an important role in generating microsite facilitation. These favorable, facilitated microsites have been characterized broadly as experiencing low sky exposure during summer (day and night) and leeward wind exposure during winter that generates protective snow cover, all of which are needed for new seedling survival. Thus, determining the specific microclimate and edaphic characteristics of favorable microsites, and their frequency at timberline, will provide a more mechanistic understanding and greater predictability of the future elevation and extent of conifer mountain forests. In addition, although the ecophysiological advantages of a needle-like leaf morphology is well established for adult conifer trees, the advantage of this phylogenetically unique trait in emergent seedlings has not been thoroughly evaluated. Understanding seedling ecophysiology and the functional morphology that contributes to survival, plus the nature and frequency of favorable microsites at timberline, will enable more reliable estimates of future elevational shifts in conifer mountain forests. This approach could also lead to the development of a valuable and sensitive tool for forest managers interested in evaluating future changes in these forests under increased large-scale infestation and drought mortality, as well as for current scenarios of predicted climate change.

The population structure and dynamics of high altitude, long-lived treeline species can be utilized as an indicator for climate change. This study was conducted in the treeline ecotone of the Barun Valley, eastern Nepal in order to understand the population dynamics of Abies spectabilis. The A. spectabilis population showed the reverse J-shaped size and age distribution curves indicative of undisturbed old growth forest. The age structure is mostly dominated by the young individuals, however, their mortality was found to be very high. Positive relationships between recruitment and high temperatures during winter months (January, February and December) and one summer month (August) were discovered. No significant relationship was found between precipitation and climate of the region. If warming condition prevails in summer and winter seasons in the near future, then there is chance that more individuals will be established above the treeline area, triggering the treeline advance.

A dendroclimatic study was conducted in the treeline ecotone of Barun Valley, eastern Nepal, to determine the tree-ring climate response and ring width trend of Abies spectabilis. A 160-year-old chronology, from 1850 to 2010, was developed from 38 tree-ring samples. No higher growth in recent decades was observed in tree-ring width in this area. The mean temperature of the current year in February and in the combined winter months of December, January, and February showed significant positive correlation with tree-ring width, although no significant correlation was found between tree-ring width and the precipitation pattern of the region. This tree-ring climate response result is different from that in other studies in Nepal, which could be attributed to location and elevation.

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала. Global change has become a major ecological concern that has the potential to dramatically alter plant distributions and assemblages worldwide. The specific response of plants to global change will depend on their ability to move, evolve, or adjust through phenotypic plasticity. Advances in biogeographic research are on the verge of a giant leap forward if we can take advantage of emerging tools in genetics and genomics. In this review, we appraise how new, post-Sanger, high-throughput sequencing and associated technologies can be used by next generation biogeographers to assess plant responses to global change. First, we briefly review the recent advances in genome sequencing and available approaches of genomic analysis. Secondly, we discuss the three main plant responses to global change: migration, adaptation, and phenotypic plasticity. This review is intended to spark the interest of biogeographers who do not traditionally use genetics but could benefit from including genetic and genomic tools into their research. Our goal is to illustrate that their use can contribute to new perspective and add an additional level of resolution into future biogeographic research.

The Arctic tundra is undergoing many environmental changes in addition to increasing temperatures: these changes include permafrost degradation and increased shrubification. Disturbances related to infrastructure can also lead to similar environmental changes. The Trans-Alaska Pipeline System (TAPS) is an example of infrastructure that has made a major imprint on the Alaskan landscape. This paper assesses changes in shrub presence along the northernmost 255 km of the TAPS. We used historical satellite imagery from before construction of the TAPS in 1974 and contemporary satellite imagery from 2010 to 2016 to examine changes in shrub presence over time. We found a 51.8% increase in shrub presence adjacent to the pipeline compared to 2.6% in control areas. Additionally, shrub presence has increased significantly more in areas where the pipeline is buried, indicating that the disturbances linked to pipeline burial have likely created favorable conditions for shrub colonization. These results are important for predicting potential responses of tundra vegetation to disturbance, which will be crucial to forecasting the future of Arctic tundra vegetation.

Biogeography is a multifaceted field that integrates geography, geology, ecology, and biology to investigate both historical and ecological questions of how spatial and temporal patterns of varying environmental factors impact the distribution of species and their evolutionary history. Genomes contain imprints of these impacts and, when such genomic imprints are rightly deciphered and interpreted, can help us address these questions. In the past 10 years, incredible advances have been made with respect to acquiring and deciphering genome sequences. The advances in genomics and bioinformatics and the decreasing costs of nucleotide sequencing have reduced many of the barriers to using genomics in biogeography. Here, we introduce some of the strategies and approaches from population genomics that can be integrated into biogeography research. First, we introduce the field of biogeography and define the two well-established broad subdisciplines of ecological and historical biogeography along with the traditional methods that they use. Next, we present examples of how population genomics approaches can be used to address biogeographic questions. To illustrate how both ecological and historical biogeography can benefit from adopting a population genomics approach, we outline our own research on mountain hemlock as a case study. We also briefly discuss the application of biogeography in biological conservation. We conclude the chapter by discussing some of the remaining challenges and future research avenues that become possible by integrating population genomics into biogeography research.

Treeline ecotone dynamics of Abies spectabilis(D. Don) Mirb.in the Barun valley, Makalu Barun National Park, eastern Nepal Himalaya were studied by establishing seven plots (20 m × variable length) from the forestline to the tree species limit: three plots on the south- and north-facing slopes each (S1-S3, N1-N3), and one plot on the east-facing slope (E) in the relatively undisturbed forests. A dendroecological method was used to study treeline advance rate and recruitment pattern. In all the plots, most trees established in the early 20th century, and establishment in the second half of the 20th century was confined to the forestline area. Treeline position has not advanced substantially in the Barun valley, with only 22 m average elevational shift in the last 130 years, and with average current shifting rate of 14 cm/yr. Moreover, no significant relationship was found between tree age and elevation on the south-, north-, and east-facing slopes. The number of seedlings and saplings in near the treeline area was negligible compared to that near the forestline area. Therefore, A. spectabilis treeline response to the temperature change was slow, despite the increasing temperature trend in the region. Beside the temperature change, factors such as high inter-annual variability in temperature, dense shrub cover, and local topography also play an important role in treeline advance and controlling recruitment pattern above the treeline.

Northern forested ecosystems are predicted to change dramatically in response to climate change during the next century. The purpose of this paper was to use logistic regression analysis to model the effects of climate and topography on the spatial distribution of the northern forest around Churchill, Manitoba, Canada. Climate maps were modeled using kriging interpolation of actual climate data collected from 34 long-term monitoring sites distributed throughout the study area, and topographic information was derived from commercially available digital elevation models. Five of the 18 independent variables contributed appreciably (p

Globally, alpine treelines are characterized as temperature-limited environments with strong controls on tree growth. However, at local scales spatially heterogeneous environments generally have more variable impacts on individual patterns of tree growth. In addition to the landscape spatial heterogeneity there is local variability in individual tree genetic diversity (level of individual heterozygosity). It has been hypothesized that higher individual heterozygosity will result in more consistent patterns of growth. In this article, we combine genomics and dendrochronology to explore the relationship between individual genetic diversity and tree growth at a mountain hemlock (Tsuga mertensiana Bong. Carr) alpine treeline on the Kenai Peninsula, Alaska, USA.We correlated average observed individual heterozygosity with average tree-ring width and variance in tree-ring width within individuals to test the hypothesis that trees with higher individual heterozygosity will also have more consistent growth patterns, suggesting that they may be more resilient to climate and environmental fluctuations at the alpine treeline. Our results showed that there was no significant relationship between tree growth and individual heterozygosity. However, there was a significant positive relationship between average tree-ring width and variance in tree-ring width implying that overall, fast growing trees in stressful environments, such as the alpine treeline, grow unstably regardless of the level of individual heterozygosity. peerReviewed

Alpine treelines are expected to advance to higher elevations in conjunction with global warming. Nevertheless, the importance of treeline reproductive patterns and seed dispersal within the alpine treeline ecotone remains unresolved. In this study, we address two research questions at mountain hemlock treelines on the Kenai Peninsula, Alaska: (1) What is the primary mode of reproduction and (2) are seeds leading to recruitment derived from within the local treeline populations or are they arriving from more distant seed sources? To answer these questions, we exhaustively sampled mountain hemlock individuals along a single mountain slope, and genotyped single nucleotide polymorphisms using doubledigest restriction site-associated DNA sequencing. First, we assessed mode of reproduction by determining the proportion of sampled individuals with identical multilocus genotypes that are the product of clonal reproduction. Second, we used a categorical parentage analysis to identify parent–offspring pairs, so that the proportion of treeline reproduction events could be spatially quantified and dispersal distance measured. We identified sexual reproduction as the primary mode of reproduction at our study site. Seedling establishment was characterized by extensive seed immigration and gene flow into the ecotone. The average dispersal distance was 73 m with long-distance dispersal identified as dispersal occurring at distances greater than 450 m. We found that production of seeds within the alpine treeline ecotone is not necessarily a requirement for treelines to advance to higher elevations in response to climate change. The extensive seed dispersal and gene flow into the alpine treeline ecotone is likely sufficient to propel the ecotone higher under more favorable climate. peerReviewed

Landscape genomics is a rapidly advancing research field that combines population genomics, landscape ecology, and spatial analytical techniques to explicitly quantify the effects of environmental heterogeneity on neutral and adaptive genetic variation and underlying processes. Landscape genomics has tremendous potential for addressing fundamental and applied research questions in various research fields, including ecology, evolution, and conservation biology. However, the unique combination of different scientific disciplines and analytical approaches also constitute a challenge to most researchers wishing to apply landscape genomics. Here, we present an introductory overview of important concepts and methods used in current landscape genomics. For this, we first define the field and explain basic concepts and methods to capture different hypotheses of landscape influences on neutral genetic variation. Next, we highlight established and emerging genomic tools for quantifying adaptive genetic variation in landscape genomic studies. To illustrate the covered topics and to demonstrate the potential of landscape genomics, we provide empirical examples addressing a variety of research question, i.e., the investigation of evolutionary processes driving population differentiation, the landscape genomics of range expanding species, and landscape genomic patterns in organisms of special interest, including species inhabiting aquatic and terrestrial environments. We conclude by outlining remaining challenges and future research avenues in landscape genomics.

Recent increases in deciduous shrub cover are a primary focus of terrestrial Arctic research. This study examined the historic spatial patterns of shrub expansion on the North Slope of Alaska to determine the potential for a phase transition from tundra to shrubland. We examined the historic variability of landscape-scale tall shrub expansion patterns on nine sites within river valleys in the Brooks Range and North Slope uplands (BRNS) between the 1950s and circa 2010 by calculating percent cover (PCTCOV), patch density (PADENS), patch size variability (CVSIZE), mean nearest neighbor distance (MEDIST) and the multi-scale information fractal dimension (d I ) to assess spatial homogeneity for shrub cover. We also devised conceptual models for trends in these metrics before, during, and after a phase transition, and compared these to our results. By developing a regression equation between PCTCOV and d I and using universal critical d I values, we derived the PCTCOV required for a phase transition to occur. All nine sites exhibited increases in PCTCOV. Five of the nine sites exhibited an increase in PADENS, seven exhibited an increase in CVSIZE, and five exhibited a decrease in MEDIST. The d I values for each site exceeded the requirements necessary for a phase transition. Although fine-scale heterogeneity is still present, landscape-scale patterns suggest our study areas are either currently in a state of phase transition from tundra to shrubland or are progressing towards spatial homogeneity for shrubland. Our results indicate that the shrub tundra in the river valleys of the north slope of Alaska has reached a tipping point. If climate trends observed in recent decades continue, the shrub tundra will continue towards homogeneity with regard to the cover of tall shrubs.

The alpine treeline in northern Fennoscandia is composed primarily of mountain birch (Betula pubescens ssp. czerepanovii), a deciduous tree that experiences episodic defoliation due to outbreaks of the autumnal moth (Epirrita autumnata) and winter moth (Operophtera brumata). Here, we use an extensive dendroecological data set to reconstruct historic defoliating outbreaks and relate them to climatic conditions. Our data are from 25 sites in eight valleys in northern Sweden. We used the computer program OUTBREAK to reconstruct moth outbreaks. The reconstructed outbreak record matches the historical record well. There is a significant, but weak relationship between the outbreak severity and temperatures in February, April, July, and August of the outbreak year. Temperatures in the previous May and November were also positively correlated with outbreak severity. For seasonally aggregated temperatures, only autumn temperatures are correlated with outbreak severity. There was no significant correlation...

Eastern hemlock (Tsuga canadensis Carriere) and the Carolina hemlock (Tsuga caroliniana Engelmann) are ecologically important tree species in eastern North America forests that are currently threatened by the hemlock woolly adelgid (HWA, Adelges tsugae Annand, Hemiptera: Adelgidae). HWA has spread rapidly from its original introduction site into new areas. Once present, HWA kills its hosts over a period of 4 to 10 years leading to a phenomenon that is known scientifically and colloquially as hemlock decline. To date, quarantine, chemical management, and biocontrol efforts have failed to curb the spread of the HWA. As such, forest management efforts are now being redirected towards developing an understanding of the effects of hemlock removal on vegetation dynamics, changes in forest composition, and changes in ecosystem function. In this study, we parameterize a spatially explicit landscape simulation model LANDIS II for a specific forested region of the southern Appalachians. Parameterization involves defining the life-history attributes of 37 tree species occupying 11 ecological zones and is based on knowledge of: current vegetation composition data, recent historic management and fire regimes, and life-history traits of each species. The parameterized model is used to explore a simple scenario of catastrophic hemlock mortality likely to occur as a result of HWA herbivory. Our results emphasize that hemlock is an important foundation species. When hemlock is removed from the system, forest composition changes considerably with a greater presence of shade intolerant pine and oak species. Additionally, hemlock removal leads to a period of transient, relatively unstable vegetation dynamics as the forest communities restructure.

Zonal patterns of salt marsh plants and physical conditions have been addressed primarily across the elevation gradient from inland to coastline rather than across tidal creeks in relation to their hydro-geomorphic processes such as bar formation and bank erosion. We found at a Danish marsh that by shaping major geomorphic features and providing sediments to the adjacent sites, fluvial-geomorphic processes of tidal creeks exert fundamental controls on the cross-channel distribution of abiotic and biotic factors. These results point to a need for biogeomorphic and landscape ecological perspectives to fully understand the underlying structure and geographic variability in salt marshes.

Coastal marshes are composed of distinct vegetation assemblages that contribute to ecosystem functions and services over time and space. In recent decades, natural and anthropogenic changes have led to large-scale marsh loss along the Chenier Plain of the Gulf of Mexico. An understanding of the composition and dominance of the vegetation assemblages that form these coastal marshes is necessary to effectively assess and monitor their stability under changing conditions. To investigate marsh vegetation assemblages along the Texas Chenier Plain, we analyzed the composition and dominance of 135 marsh plots distributed across two study areas bordering the East Bay of Galveston Bay in Chambers County, Texas using cluster analysis. Seven general vegetation assemblages were identified. The assemblages were evaluated using indicator species analysis and Multi-Response Permutation Procedures and compared to marsh vegetation assemblages found in the Louisiana Chenier Plain. Our data provide a foundation for better understanding of vegetation patterns found along the East Texas Chenier Plain allowing managers and conservationists the ability to better evaluate the effects of marsh change due to climatic and human driven pressures. © 2013 Society of Wetland Scientists.

Long-term eustatic sea-level variation has been recognized as a primary factor affecting the hydrological and geomorphic dynamics of salt marshes. However, recent studies suggest that wind waves influenced by atmospheric oscillations also may play an important role in many coastal areas. Although this notion has been conceptually introduced for the Wadden Sea, no modeling attempts have been made yet. As a proof of concept, this study developed a simulation model using the commercially available STELLA® software, based on long-term data on water level and sedimentation collected at a back-barrier marsh on the Skallingen peninsula in Denmark. In the model, the frequency (number year–1) of wind-driven extreme high water level (HWL) events (>130 cm Danish Ordnance Zero) was simulated in terms of the North Atlantic Oscillation (NAO) index. Then, surface accretion (cm year–1) and submergence duration (h year–1) were simulated for the period 1933–2007. The model showed good performances: simulated rates of surface accretion and simulated durations of submergence decreased from 1950 to 1980, the point at which the NAO shifted from its negative to its positive phase, and increased thereafter. Despite continuous increases in surface elevation, increases in simulated submergence duration were apparently due to wind-driven HWL events, which generally increased in frequency after 1980. These findings for the Danish Wadden Sea add to the growing body of evidence that the role of atmospheric oscillations—e.g., the NAO—as drivers of wind-generated water level variations merits more attention in assessing the impact of climate change on coastal marshes.

PREMISE OF THE STUDY Untangling alternative historic dispersal pathways in long-lived tree species is critical to better understand how temperate tree species may respond to climatic change. However, disentangling these alternative pathways is often difficult. Emerging genomic technologies and landscape genetics techniques improve our ability to assess these pathways in natural systems. We address the question to what degree have microrefugial patches and long-distance dispersal been responsible for the colonization of mountain hemlock (Tsuga mertensiana) on the Alaskan Kenai Peninsula. METHODS We used double-digest restriction-associated DNA sequencing (ddRADseq) to identify genetic variants across eight mountain hemlock sample sites on the Kenai Peninsula, Alaska. We assessed genetic diversity and linkage disequilibrium using landscape and population genetics approaches. Alternative historic dispersal pathways were assessed using discriminant analysis of principle components and electrical circuit theory. KEY RESULTS A combination of decreasing diversity, high gene flow, and landscape connectivity indicates that mountain hemlock colonization on the Kenai Peninsula is the result of long-distance dispersal. We found that contemporary climate best explained gene flow patterns and that isolation by resistance was a better model explaining genetic variation than isolation by distance. CONCLUSIONS Our findings support the conclusion that mountain hemlock colonization is the result of several long-distance dispersal events following Pleistocene glaciation. The high dispersal capability suggests that mountain hemlock may be able to respond to future climate change and expand its range as new habitat opens along its northern distribution.

Biogeographers emphasize the presence of scale-dependence in vegetation–environment relationships. This research addresses the issue of scale-dependence, focusing on spatial correspondence of floristic and edaphic gradients across salt marsh creeks at Skallingen, Denmark. We employed a hierarchical approach, which compared vegetation and soil gradients at both fine and coarse scales. At the fine scale, we used ordination techniques to identify the gradient structure of vegetation and soil data acquired in 1-m2 plots along transects across creeks. For the coarse-scale comparison, we systematically aggregated the fine-scale information (i.e., gradient structure) into larger blocks, or topographic zones such as point bar, cutbank edge, and marsh interiors. We found poor correlations between vegetation and soil at the fine scale but an improved correspondence at the coarse scale. The poor correspondence was caused by differential spatial extents that the vegetation and soil factors exhibited responding to env...

The annual growth rings of diffuse porous species such as mountain birch are often difficult to distinguish when samples are collected from trees that grow at treeline or in other harsh environments. In this study we document the differences in seedling and sapling ring counts obtained from two methods of analysis: a traditional analysis based on reflected light and low-power microscopy and one based on transmitted light with higher power magnification that uses thin-sections of the samples. Rings are easier to resolve using the more labor-intensive transmitted light method. Small rings are often missed when using the reflected light method, resulting in an underestimation of tree age. The dates estimated by the standard method agreed with those determined using the thin-sectioning method in 9.6% of the cases. Most commonly, the standard method gave a younger age than did thin-sectioning (72.4% of the trees). In only 18.03% of the cases did the standard method result in a greater age than did thin-sectioning. The reflected light method produced age estimations that were on average 1.37 years younger than those determined using the transmitted light method. The difference between the two methods was positively correlated with age and negatively correlated with mean ring-width. Age-class histograms based on the two methods show little difference at coarser aggregation levels (decades and pentads), but annualized age-class histograms have less agreement between the two methods. Therefore, we suggest using the more labor-intensive thin-sectioning method when annualized age counts are necessary in suppressed seedlings and saplings, for example, comparing tree establishment with annual climate conditions at treeline.

Small Footprint LiDAR (Light Detection And Ranging) has been proposed as an effective tool for measuring detailed biophysical characteristics of forests over broad spatial scales. However, by itself LiDAR yields only a sample of the true 3D structure of a forest. In order to extract useful forestry relevant information, this data must be interpreted using mathematical models and computer algorithms that infer or estimate specific forest metrics. For these outputs to be useful, algorithms must be validated and/or calibrated using a sub-sample of `known' metrics measured using more detailed, reliable methods such as field sampling. In this paper we describe a novel method for delineating and deriving metrics of individual trees from LiDAR data based on watershed segmentation. Because of the costs involved with collecting both LiDAR data and field samples for validation, we use synthetic LiDAR data to validate and assess the accuracy of our algorithm. This synthetic LiDAR data is generated using a simple geometric model of Loblolly pine (Pinus taeda) trees and a simulation of LiDAR sampling. Our results suggest that point densities greater than 2 and preferably greater than 4 points per m2 are necessary to obtain accurate forest inventory data from Loblolly pine stands. However the results also demonstrate that the detection errors (i.e. the accuracy and biases of the algorithm) are intrinsically related to the structural characteristics of the forest being measured. We argue that experiments with synthetic data are directly useful to forest managers to guide the design of operational forest inventory studies. In addition, we argue that the development of LiDAR simulation models and experiments with the data they generate represents a fundamental and useful approach to designing, improving and exploring the accuracy and efficiency of LiDAR algorithms.

Shrub expansion is a global phenomenon that is occurring on savannas, rangelands, and grasslands. In addition, this is an increasingly documented occurrence in the Arctic. Numerous recent studies have strived to pinpoint the drivers of this phenomenon, quantify the changes, and understand their implications for regional and global land use, disturbance regimes, and nutrient cycling. Inquiry into these topics has been facilitated by recent technological developments in satellite remote sensing, aerial photograph analysis, and computer simulation modeling. We provide a new review that accounts for more recent studies in these regions, Arctic shrub expansion, and technological and analytical developments. This four-part discussion focuses on observed patterns of shrub expansion in three rangeland types (desert grasslands, mesic grasslands, savannas) and the Arctic tundra, the primary causes of this expansion, critical comparisons and contrasts between these land types, and recommendations for future avenues of research. These new avenues can inform the development of future land management policies, as well as ongoing investigations to understand and mitigate the effects of climate change.

Coastal scientists postulate that salt marshes are significantly affected by dynamics of global climate. However, few studies have explicitly proposed a perspective that regards salt marshes as potential indicators of climate change. This review article evaluates the possibility of salt marshes as indicators of global climate change, focusing upon three major aspects: sedimentary, vegetation, and biogeochemical dynamics. The previous literature concerned with these aspects commonly argues that the primary impact of climate change on salt marshes occurs via sea-level variations, because hydrologic fluctuations regulate the frequency, duration, and depth of over-marsh flooding events. Sedimentary, floristic, and biogeochemical dynamics prove to be significantly influenced by sea-level changes regardless of climate zones, and hence, undoubtedly possess a potential for indicating climate signatures. However, where plant-plant interactions such as facilitation and competition are important, vegetation dynamics in salt marshes may not be an immediate, sole function of sea-level and climate variations. Also, specifically in the field of salt marsh biogeochemistry, enough long-term data have not been collected to convincingly conclude that biogeochemistry is a useful indicator of climate change. Therefore, while this review is concerned mainly with the possibility of salt marshes as indicators of climate change, their suitability or usefulness is a different matter to be resolved through further data collection and discussion in future investigations.

Long-term variation of mean sea level has been considered the primary exogenous factor of vegetation dynamics in salt marshes. In this study, we address the importance of short-term, wind-induced rise of the sea surface in such biogeographic changes. There was an unusual opportunity for examining field data on plant species frequency, sea-level variation, and sedimentation acquired from the Skallingen salt marsh in Denmark since the 1930s. The environmental and floristic history of Skallingen was summarized as (1) continuous sea-level rise with temporal variability (2.3–5.0 mm yr−1), (2) continuous sedimentation with spatial variability (2.0–4.0 mm yr−1), (3) increased frequency of over-marsh flooding events, and (4) contemporary dominance of Halimione portulacoides, indicating little progressive succession toward a later phase. Conventionally, recent eustatic sea-level rise was believed to drive the increased frequency of flooding and such retarded succession. Skallingen, however, has showed more or less...

Changing climate in the Arctic is expected to have significant effects on the pattern and distribution of terrestrial vegetation. Species characteristic of specific zones in the mountains of northern Sweden have been shown to migrate up- and down-slope with changes in climate over the Holocene. This study evaluates the potential for Scots pine (Pinus sylvestris L.) to become a treeline dominant at Fennoscandian treelines, replacing mountain birch (Betula pubescens subsp. czerepanovii (Orlova) Hämet-Ahti). Data from paired mountain birch and Scots pine tree-ring chronologies for eight locations in northern Sweden are used to develop climate – tree ring width index (RWI) relationships. Modeled climate–RWI relationships are then used to predict the relative RWI values of the two species under a suite of climate-forcing scenarios using an ensemble of three global climate models. Results indicate that mountain birch and Scots pine RWI are both correlated with summer temperatures, but Scots pine is more likely than mountain birch to be influenced by moisture conditions. Predictions of RWI under future climate conditions indicate that mountain birch is unlikely to be replaced by Scots pine within the next century.

Stochastic weather generators are useful tools for exploring the relationship between organisms and their environment. This paper describes a simple weather generator that can be used in ecological modeling projects. We provide a detailed description of methodology, and links to full C++ source code (http://weathergen.sourceforge.net) required to implement or modify the generator. We argue that understanding the principles of weather generation will allow ecologists to tailor a solution for their own requirements. The detailed, repeatable methodology we present demonstrates that weather generation is relatively straightforward for ecologists to implement and modify.

The response of treeline-forming species to global climate change is uncertain. While numerous treeline species have recently experienced range advance along their upper elevational boundary, this has been species- and region-dependent. Making an accurate prediction of how taxa will respond is essential for conservation and land management, as treeline advance is likely to result in a loss of alpine biodiversity through habitat change and fragmentation. Predicting any species response requires an understanding of the current physical and climatic determinants of its distribution. We used the Maxent species distribution modeling software to predict the likelihood of treeline advance in the Nepalese Himalayas by modeling the extent of suitable habitats for 3 dominant treeline species—Abies spectabilis, Betula utilis, and Pinus wallichiana—under present and projected climate conditions. Temperature-related climatic variables and elevation explained the greatest amount of variance in the distribution of the study species. Under projected climate conditions, we found a regional increase in suitable habitat for all 3 treeline species, predicting a potential for northward and upslope advance.

In coastal environments, biogeographic patterns are generally influenced by surface elevation and horizontal distance from sea water. However, it is still unclear whether these major topographic factors are significant controls of vegetation patterns across spatial scales at which different physical processes operate. This study investigated such a topography-vegetation relationship in a Danish salt marsh, focusing upon two scales: a macro-scale (ca. 500 m) across the marsh platform, encompassing seaward and landward areas, and a meso-scale (ca. 25 m) across tidal creeks. While long-term sea-level variation and grazing influenced the macro-scale pattern, short-term fluvial-geomorphic processes drove the meso-scale pattern. Despite these different underlying processes, similar floristic gradient structures between the two scales were identified by nonmetric multidimensional scaling. The gradient represented an ecological sequence from early to late succession, and strongly correlated with surface elevation...

Forest landscape models simulate forest change through time using spatially referenced data across a broad spatial scale (i.e. landscape scale) generally larger than a single forest stand. Spatial interactions between forest stands are a key component of such models. These models can incorporate other spatio-temporal processes such as natural disturbances (e.g. wildfires, hurricanes, outbreaks of native and exotic invasive pests and diseases) and human influences (e.g. harvesting and commercial thinning, planting, fire suppression). The models are increasingly used as tools for studying forest management, ecological assessment, restoration planning, and climate change. In this paper, we define forest landscape models and discuss development, components, and types of the models. We also review commonly used methods and approaches of modeling forest landscapes, their application, and their strengths and weaknesses. New developments in computer sciences, geographic information systems (GIS), remote sensing technologies, decision-support systems, and geo-spatial statistics have provided opportunities for developing a new generation of forest landscape models that are increasingly valuable for ecological research, restoration planning and resource management.

The Brazilian Cerrado is threatened by agricultural land use conversion. Accurate quantification of overall and subtype Cerrado distributions is essential for regional monitoring. In this research, unsupervised fuzzy ARTMAP was compared against conventional k-means classification of Cerrado and agriculture, based on Hyperion satellite data. We systematically tested a range of fuzzy ARTMAP parameters, determining the best parameter combinations. The effect of an additional surface liquid-water input vector was also tested. Similar results were obtained when only Hyperion apparent surface reflectance data were used; fuzzy ARTMAP, however, was generally markedly more accurate than k-means when the additional surface liquid-water input was included.

Matrix models have been used to model population growth of organisms for many decades. They are popular because of both their conceptual simplicity and their computational efficiency. For some types of organisms they are relatively accurate in predicting population growth; however, for others the matrix approach does not adequately model growth rate. One of the reasons for the lack of accuracy is that most matrix-based models implicitly assume a specific degree of variability in development times for the organism. Because the variability is implicit, the implied variances are often not verified with experimental data. In this paper, we shall present extensions to the stage-classified matrix models so that organisms with arbitrary means and standard deviations of development times can be modeled.

Many hypotheses have been put forward to explain the structure and position of alpine treelines. The spatial complexity of the ecotone, ranging from sharp boundaries to networks of tree patches wit ...

The forests of southeastern North America are influenced by a variety of disturbances including fire and insect outbreaks. In this paper, we discuss the role of disturbances in structuring forest landscapes with particular emphasis placed on the reciprocal interaction between forest structure and outbreaks of the southern pine beetle (Dendroctonus frontalis Zimmermann). We highlight work in which we are currently involved to illustrate the importance and utility of using spatially explicit forest modeling as a tool for understanding forest–insect interactions and its potential role in determining management strategies.

The reciprocal interaction of landscape structure and ecological processes is a cornerstone of modern landscape ecology. We use a simulation model to show how landscape structure and herbivory interact to influence outbreaks of southern pine beetle (Dendroctonus frontalis Zimmermann) in a landscape representative of the southern Appalachian Mountains, USA. We use LANDIS and its biological disturbance agent module to simulate the effects of landscape composition (proportion of landscape in host area) and host aggregation on the size and severity of insect outbreaks and the persistence of the host species, Table Mountain Pine (Pinus pungens Lamb.). We find that landscape composition is less important in the modeled landscapes than host aggregation in structuring the severity of insect outbreaks. Also, simulated southern pine beetle outbreaks over time tend to decrease the aggregation of host species on the landscape by fragmenting large patches into smaller ones, thereby reducing the severity of future outbreaks. Persistence of Table Mountain pine decreases throughout all simulations regardless of landscape structure. The results of this study indicate that when considering alternative restoration strategies for insect-affected landscapes, it is necessary to consider the patterns of hosts on the landscape as well as the landscape composition.

The alpine treeline is a potentially sensitive indicator of vegetation response to climate change. However, there is not a generally accepted single hypothesis that explains treeline position and pattern at multiple scales. Recently a set of five hypotheses has been proposed for treeline explanations (Korner, 2003b). The impacts of animals are not explicitly included in any of these hypotheses, however, they can and should be included. In this review we discuss Korner's five hypotheses and explain how animal activity can be included within them to make them more applicable to treeline environments experiencing a changing climate. We utilize the conceptual model proposed by Cairns and Moen (2004) as an organizing framework for the inclusion of animal activity with existing hypotheses. Finally we suggest that the equivocal nature of treeline response to climate change may be in part related to animal activity.

We used LANDIS, a model of forest disturbance and succession, to simulate successional dynamics of forests in the southern Appalachian Mountains. The simulated environments are based on the Great Smoky Mountains landscapes studied by Whittaker. We focused on the consequences of two contrasting disturbance regimes—fire exclusion versus frequent burning—for the Yellow pine (Pinus L., subgenus Diploxylon Koehne) and oak (Quercus L.) forests that occupy dry mountain slopes and ridgetops. These ecosystems are a conservation priority, and declines in their abundance have stimulated considerable interest in the use of fire for ecosystem restoration. Under fire exclusion, the abundance of Yellow pines is projected to decrease, even on the driest sites (ridgetops, south- and west-facing slopes). Hardwoods and White pine (P. strobus L.) replace the Yellow pines. In contrast, frequent burning promotes high levels of Table Mountain pine (P. pungens Lamb.) and Pitch pine (P. rigida Mill.) on the driest sites and reduces the abundance of less fire-tolerant species. Our simulations also imply that fire maintains open woodland conditions, rather than closed-canopy forest. For oaks, fire exclusion is beneficial on the driest sites because it permits oaks to replace the pines. On moister sites (north- and east-facing slopes), however, fire exclusion leads to a diverse mix of oaks and other species, whereas frequent burning favors Chestnut oak (Q. montana Willd.) and White oak (Q. alba L.) dominance. Our results suggest that reintroducing fire may help restore decadent pine and oak stands in the southern Appalachian Mountains.

Question: Can fire be used to maintain Yellow pine (Pinus subgenus Diploxylon) stands disturbed by periodic outbreaks of southern pine beetle? Location: Southern Appalachian Mountains, USA. Methods: We used LANDIS to model vegetation disturbance and succession on four grids representative of xeric landscapes in the southern Appalachians. Forest dynamics of each landscape were simulated under three disturbance scenarios: southern pine beetle, fire, and southern pine beetle and fire, as well as a no disturbance scenario. We compared trends in the abundance of pine and hardwood functional types as well as individual species. Results: Yellow pine abundance and open woodland conditions were best maintained by a combination of fire and southern pine beetle disturbance on both low elevation sites as well as mid-elevation ridges & peaks. On mid-elevation SE-W facing slopes, pine woodlands were best maintained by fire alone. Conclusions: Our simulations suggest that fire can help maintain open pine woodlands in stands affected by southern pine beetle outbreaks.

Summary 1 Transitions between major vegetation types, such as the tree line, are useful systems for monitoring the response of vegetation to climate change. Tree lines have, however, shown equivocal responses to such change. 2 Tree lines are considered to be primarily thermally controlled, although recent work has highlighted the importance of biotic factors. Dispersal limitation and the invasibility of the tundra matrix have been implicated and here we propose herbivory as an additional control at some tree lines. 3 We propose a conceptual model in which differing relative impacts of foliage consumption, availability of establishment sites, trampling, dispersal and seed predation can lead to very different tree-line responses. 4 The presence of large numbers of small trees above the current tree line at a site in northern Sweden that experiences limited reindeer (Rangifer tarandus) herbivory suggests range expansion. Other locations in the same region with higher reindeer populations have considerably fewer small trees, suggesting that range expansion is occurring much more slowly, if at all. 5 The use of tree lines as indicators of climate change is confounded by the activity of herbivores, which may either strengthen or nullify the impacts of a changed climate. Similar arguments are likely to be applicable to other ecotones.

Ecotones that are controlled by a single environmental gradient or a set of correlated environmental factors are hypothesized to show a sigmoid wave form in percentage cover as the ecotone is crossed. This study investigates the sigmoid wave hypothesis at the alpine treeline in Glacier National Park, Montana, USA. We find that approximately half of the sampled locations exhibit a sigmoid wave form in percentage cover across the ecotone. These results indicate that in some cases treeline is controlled by a single environmental gradient or a set of correlated environmental factors. However, in other cases, additional factors that are not correlated with the primary controlling gradient act to change the form of the transition. We investigated surficial geology as a possible controlling factor that would not be correlated with the primary climatic gradients found along transects across the alpine treeline. In at least some of the cases, surficial geology type was shown to be significantly associated with differences between sigmoidal and non-sigmoidal transitions. These results support previous evidence for sigmoid wave transitions at the boreal forest-tundra ecotone, but also show that the alpine treeline case is more complex. We argue that in cases where ecotones are used as sites for monitoring the effects of climate change on vegetation, care should be taken to utilize only sites that exhibit a sigmoidal transition so as to minimize the effects of non-climate-related controlling factors on the interpretations.

Spatial patterns of soil in alpine tundra just above timberline may determine patterns of advance by woody species. Patterns of advance since the Little Ice Age show spatial aggregation. If soil resources have similar patterns of aggregation, they might determine the pattern of vegetation change. Effective soil depth (ESD), which takes into account stoniness, was measured in tundra just above present timberline on regular grids at two scales and across solifluction treads and risers. No non-random spatial pattern was found, nor was there any difference related to relict solifluction patterns. Current patterns of woody vegetation could not have developed in direct response to the pattern of effective soil depth found in tundra. These patterns may develop in response to other soil factors, but may also include positive feedback.

Winter desiccation-induced foliage loss at high-elevation locations is an important determinant of positive carbon balance for trees and thus influences the location of the alpine treeline ecotone. In this study, data are presented that describe the amount of winter desiccation incurred by krummholz growth forms of subalpine fir (Abies lasiocarpa (Hook) Nutt.) at treeline locations in Glacier National Park, Montana, USA, for the winter of 1998/1999. An average 8.68% of the krummholz canopy was lost due to desiccation. Winter desiccation is not predictable based on any single environmental variable. When outliers are removed, winter desiccation shows a strong correlation with elevation (r= 0.97). Patch level winter desiccation amounts are, however, highly predictable from elevation, slope, aspect and topographic context when considered together. In general, injury increases with elevation and on more southwesterly facing hillslopes. High slopes and sheltered locations decrease winter desiccation. Within patches, most winter desiccation is located at the windward edge of the patch. This trend may be modified by the presence of leaders above the mean canopy surface of the krummholz patch, or by local microtopographic features such as dead branches or the proximity of large rocks. The winter of 1998/1999 was a high winter desiccation year compared to the two previous winters. The winter of 1998/1999 had high snowfall, and meltout did not occur until later than the previous two winters. The extended period of snow cover is hypothesized to be one of the causes of the increased winter desiccation for the 1998/1999 winter.