Ecotone Boundaries Research Articles

A tree‐ring chronology and paleoclimate record for the Younger Dryas–Early Holocene transition from northeastern North America

ABSTRACTSpruce and tamarack logs dating from the Younger Dryas and Early Holocene (YD–EH; ∼12.9–11.3k cal a BP) were found at Bell Creek in the Lake Ontario lowlands of the Great Lakes region, North America. A 211‐year tree‐ring chronology dates to ∼11 755–11 545 cal a BP, across the YD–EH transition. A 23‐year period of higher year‐to‐year ring‐width variability dates to around 11 650 cal a BP, infers strong regional climatic perturbations and may represent the end of the YD. Tamarack and spruce were dominant species throughout the YD–EH interval at the site, indicating that boreal conditions persisted into the EH, in contrast to geographical regions immediately south and east of the lowlands, but consistent with the Great Lakes interior lowlands. This infers that Bell Creek was at the eastern boundary of a boreal ecotone, perhaps a result of its lower elevation and the non‐analog dynamics of the Laurentide Ice Sheet. This finding suggests that the ecotone boundary extended farther east during the YD–EH transition than previously thought.

A Holocene record of environmental change from Río Zeballos, central Patagonia

There are few continuous palaeoenvironmental records spanning the Holocene in Andean Southern Patagonia near the Northern Patagonian Ice Field (~47°S). Insights into the environmental context for human–landscape interactions have relied mostly on data extrapolated from distant extra-Andean locations that suggest limited environmental change during the Holocene. La Frontera (46°52′S), a high altitude site on the southern beech forest–steppe ecotone boundary in the Río Zeballos valley, provides lithostratigraphical and palaeoecological evidence, constrained by 14C dating and tephrochronology, for dynamic environmental change during the last ~8000 years. An initial amelioration in environmental conditions after c. 8210 cal. BP was followed by a reversal to colder conditions between c. 7420 and 6480 cal. BP, coincident with initial human occupation within the Paso Roballos and Lago Pueyrredón basin. Between c. 6480 and 3700 cal. BP, the woodland/steppe composition continued to fluctuate in response to climatic change. After c. 3700 cal. BP, a gradual shift to more stable and temperate conditions, punctuated by increased fire activity, is contemporary with the later phases of human occupation extending up into the Paso Roballos–Río Zeballos corridor.

Modeling the Boundaries of Plant Ecotones of Mountain Ecosystems

The ecological second-order phase transition model has been used to describe height-dependent changes in the species composition of mountain forest ecosystems. Forest inventory data on the distribution of various tree species in the Sayan Mountains (south Middle Siberia) are in good agreement with the model proposed in this study. The model was used to estimate critical heights for different altitudinal belts of vegetation, determine the boundaries and extents of ecotones between different vegetation belts, and reveal differences in the ecotone boundaries between the north- and south-facing transects. An additional model is proposed to describe ecotone boundary shifts caused by climate change.

Many species risk mountain top extinction long before they reach the top

Analyses of topography show that mountains do not monotonically decrease in area with elevation as is commonly believed and that in reality land area often increases at higher elevations. This finding bodes well for the future of biodiversity since it means that in many parts of the world there are sufficient upslope areas for low- and mid-elevation species to migrate into as temperatures increase. However, more attention needs to be given to determining if migrating species can actually reach these expansive high-elevation areas. Many factors can prevent species from migrating upslope including stable ecotones. Often ecotonal boundaries are not set by mean temperatures alone and thus are not shifting upslope with warming. An example of this are tropical alpine treelines, which are not shifting upslope despite rapid warming potentially due to the stabilizing influences of climatic factors other than mean temperatures (e.g., extreme cold events) or non-climatic factors (e.g., soil or human disturbances). Stable ecotones can potentially prevent species from expanding their ranges into upland areas in which case the amount of land at higher elevations is irrelevant and species may face “mountain top extinctions” long before they reach the actual tops of the mountains.

Evaluating the Potential of the Original Texas Land Survey for Mapping Historical Land and Vegetation Cover

This paper reports on research to evaluate the potential of Original Texas Land Survey (OTLS) to generate information that can be used to quantitatively map historical vegetation cover and analyse pertinent aspects of vegetation ecology. Research was conducted in Brazos County in east-central Texas. OTLS data are easy to acquire and convert to geo-referenced autecological information. Reconstructing and mapping vegetation and land cover, conducting vegetation- and species-site analyses with to soil-ecological maps, reconstructing vegetation assemblages and forest structure can be easily accomplished. Due to the irregular surveying framework used by OTLS, mapping gradational grassland-savannah ecotone boundaries is impracticable.

Moving beyond bioclimatic envelope models: integrating upland forest and peatland processes to predict ecosystem transitions under climate change in the western Canadian boreal plain

AbstractBy the end of this century, much of the climate space of western Canada's boreal forest is expected to shift northwards and be replaced by climates that are currently associated with aspen forest, parkland and grassland ecosystems. In this study, we review the various processes that will mediate ecological responses to these projected changes in climate. We conclude that ecological transitions are unlikely to involve a gradual wave‐like shift in ecotonal boundaries. Instead, we predict that ecological changes will lag substantially behind changes in climate and that individual ecosystem components will respond at different rates. In particular, if precipitation inputs are maintained as expected, then peatlands should exhibit considerable resilience to climate change and remain a dominant feature on the landscape in 2100. Because peatlands retain large amounts of water on the landscape their continued presence may in turn slow the rate of forest loss, especially the aspen component. Thus, ecological response to climate change in the western boreal region may involve a transition to a novel ecosystem that includes peatlands and aspen as dominant features – unlike anything that exists today. Moreover, this interim stage may remain in place well into the next century, potentially providing additional time for forest‐dependent species to adapt. Copyright © 2015 John Wiley & Sons, Ltd.

Complex Changes in Plant Communities across a Subarctic Alpine Tree Line in Labrador, Canada + Supplementary Appendix Table (See Article Tools)

As climate warms, abiotic factors, as well as plant community and biodiversity structure, may constrain or promote the movement of ecotone boundaries. Our study sought to examine how plant communities change across the tree-line ecotone of the Mealy Mountains in Labrador, Canada. We established eight transects (50–100 m in length) along an elevation gradient in three tree-line zones (forest, forest-tundra, and alpine-tundra) and recorded all species and cover of vegetation in contiguous 1 × 1 m quadrats. Companion abiotic parameters of nutrients and soil temperature were also measured. The absence of abrupt changes in important soil nutrients and growing season temperatures suggests that these factors do not limit tree species establishment beyond the current tree line. Vegetation cover and richness, however, were highly variable and in some cases changed non-linearly across the tree-line ecotone. Tree cover and species density generally decreased with elevation, while some field layer species (< 25 cm in height) increased; the latter change seems to be influenced by ground shrubs rather than herbaceous species. As expected, transects separated by the greatest difference in elevation were the least similar (higher beta diversity/species turnover); however, species turnover between the forest and forest-tundra transects was higher than it was between forest-tundra and alpine-tundra transects, even though the latter were separated by a greater elevation. Community structure and species turnover vary greatly across a tree line with the greatest differences between the forest and the forest-tundra, suggesting a biotic or abiotic barrier. While our ability to predict how the tree line will respond to continued climate change is complicated by these patterns in plant communities, the potential barriers investigated and others identified will be a useful focus for future studies.

Montane forest ecotones moved downslope in northeastern USA in spite of warming between 1984 and 2011

Ecotones are transition zones that form, in forests, where distinct forest types meet across a climatic gradient. In mountains, ecotones are compressed and act as potential harbingers of species shifts that accompany climate change. As the climate warms in New England, USA, high-elevation boreal forests are expected to recede upslope, with northern hardwood species moving up behind. Yet recent empirical studies present conflicting findings on this dynamic, reporting both rapid upward ecotonal shifts and concurrent increases in boreal species within the region. These discrepancies may result from the limited spatial extent of observations. We developed a method to model and map the montane forest ecotone using Landsat imagery to observe change at scales not possible for plot-based studies, covering mountain peaks over 39000km(2) . Our results show that ecotones shifted downward or stayed stable on most mountains between 1991 and 2010, but also shifted upward in some cases (13-15% slopes). On average, upper ecotone boundaries moved down -1.5myr(-1) in the Green Mountains, VT, and -1.3myr(-1) in the White Mountains, NH. These changes agree with remeasured forest inventory data from Hubbard Brook Experimental Forest, NH, and suggest that processes of boreal forest recovery from prior red spruce decline, or human land use and disturbance, may swamp out any signal of climate-mediated migration in this ecosystem. This approach represents a powerful framework for evaluating similar ecotonal dynamics in other mountainous regions of the globe.

Defining the next generation modeling of coastal ecotone dynamics in response to global change

Coastal ecosystems are especially vulnerable to global change; e.g., sea level rise (SLR) and extreme events. Over the past century, global change has resulted in salt-tolerant (halophytic) plant species migrating into upland salt-intolerant (glycophytic) dominated habitats along major rivers and large wetland expanses along the coast. While habitat transitions can be abrupt, modeling the specific drivers of abrupt change between halophytic and glycophytic vegetation is not a simple task. Correlative studies, which dominate the literature, are unlikely to establish ultimate causation for habitat shifts, and do not generate strong predictive capacity for coastal land managers and climate change adaptation exercises. In this paper, we first review possible drivers of ecotone shifts for coastal wetlands, our understanding of which has expanded rapidly in recent years. Any exogenous factor that increases growth or establishment of halophytic species will favor the ecotone boundary moving upslope. However, internal feedbacks between vegetation and the environment, through which vegetation modifies the local microhabitat (e.g., by changing salinity or surface elevation), can either help the system become resilient to future changes or strengthen ecotone migration. Following this idea, we review a succession of models that have provided progressively better insight into the relative importance of internal positive feedbacks versus external environmental factors. We end with developing a theoretical model to show that both abrupt environmental gradients and internal positive feedbacks can generate the sharp ecotonal boundaries that we commonly see, and we demonstrate that the responses to gradual global change (e.g., SLR) can be quite diverse.

Latitudinal range shifts of tree species in the United States across multi-decadal time scales

It is expected that some species will shift poleward in range due to climate change. However, despite numerous publications that project species distributions under climate change scenarios, there is less evidence for current latitudinal shifts by tree species, in part because ranges are dynamic and complex to measure. We developed a method to compare tree ranges using continental USDA Forest Service Forest Inventory and Analysis tree surveys during an interval of approximately 28 years. We analyzed compositional differences in ecological subsections within latitudinal bands using repeated measures ANOVA and considered differences in bands at the outer northern and southern range edges combined with increased area to indicate range expansion. Out of a pool of 74 relatively common species, we detected 12 species that had significant increases and expansion in the northern outer band, 13 species that had significant increases and expansion in the southern outer band, and one species that increased and expanded in both northern and southern bands. However, seven species with significant increases in the northern outer band in the contiguous United States had distributions that extended within Canada so that shifts do not represent increases in the northernmost latitudinal band for these species. Uniform poleward migration was not detectable and the number of species shifting southward suggests influence of other driving factors than climate change, including assisted migration of tree species through landscaping and a cascade of range shifts along ecotonal boundaries due to fire exclusion and land use.

Climate change and Ecotone boundaries: Insights from a cellular automata ecohydrology model in a Mediterranean catchment with topography controlled vegetation patterns

Regions of vegetation transitions (ecotones) are known to be highly sensitive to climate fluctuations. In this study, the Cellular-Automata Tree Grass Shrub Simulator (CATGraSS) has been modified, calibrated and used with downscaled future climate scenarios to examine the role of climate change on vegetation patterns in a steep mountainous catchment (1.3km2) located in Sicily, Italy. In the catchment, north-facing slopes are mostly covered by trees and grass, and south-facing slopes by Indian Fig opuntia and grass, with grasses dominating as elevation grows. CATGraSS simulates solar radiation, evapotranspiration, and soil moisture in space and time. Each model cell can hold a single plant type or can be bare soil. Plant competition is modeled explicitly through mortality and the establishment of individual plants in open spaces. In this study, CATGraSS is modified to account for heterogeneity in soil thickness and tested in the study catchment using the historical climate of the region. Predicted vegetation patterns are compared with those obtained from satellite images. Results of model under current climate underscore the importance of solar irradiance and soil thickness, especially in the uplands where soil is shallow, in determining vegetation composition over complex terrain. A stochastic weather generator is used to generate future climate change scenarios for the catchment by downscaling GCM realizations in space and time. Future increase in atmospheric CO2 concentration was considered through modifying the vegetation water use efficiency and stomatal resistance for our study site. Model results suggest that vegetation pattern is highly sensitive to temperature and rainfall variations provided by climate scenarios (30% reduction of the annual precipitation and a 2.8°C increase of the mean annual temperature). Future climate change is predicted to bring a considerable reorganization of the plant composition following topographic patterns, leading to a decrease of trees cover at the expenses of a grass expansion, which will cause loss of landscape vegetation diversity.

Responses of a small-mammal community to habitat management through controlled burning in a protected Mediterranean area

Fire is widely used as a management tool to achieve conservation goals. However, the consequences of such management on non-target species are frequently neglected and unknown. This study examines the effects of traditional management practices of scrubland clearance by controlled burning to improve menaced carnivores on non-target species: rodent and insectivores in Doñana National Park (SW of Iberian Peninsula). We used capture–recapture methods to examine changes in abundance in areas that were burnt one and three years ago, compared with unburnt areas. Results showed that burnt areas had higher species abundances, but mainly on the ecotonal boundaries. Species abundances showed dramatic seasonal differences with high abundances in autumn and winter, and very low abundance in summer. Our study revealed that scrubland management by controlled fires increases the abundance of small mammal species, mainly Mus spretus and Apodemus sylvaticus. We found only four small mammal species between the different treatments. However, some species that were formerly abundant in Doñana, such as Elyomis quercinus, were found only in burnt areas. Our results suggest that controlled burning is not contributing to the current loss of biotic diversity in this community.

Ecotones as Indicators of Changing Environmental Conditions: Rapid Migration of Salt Marsh–Upland Boundaries

Ecotones, the narrow transition zones between extensive ecological systems, may serve as sensitive indicators of climate change because they harbor species that are often near the limit of their physical and competitive tolerances. We investigated the ecotone between salt marsh and adjacent upland at Elkhorn Slough, an estuary in California, USA. Over a period of 10 years, we monitored movement of the ecotone–upland boundary, plant community structure, and physical factors likely to drive ecotone response. At three undiked sites, the ecotone boundary migrated about 1 m landward, representing a substantial shift for a transition zone that is only a few meters wide. Analysis of potential correlates of this upward migration suggests that it was driven by increased tidal inundation. Mean sea level did not increase during our study, but inundation at high elevations did. While the ecotone boundary responded dynamically to interannual changes in inundation at these undiked sites, the plant community structure of the ecotone remained stable. At two diked sites, we observed contrasting patterns. At one site, the ecotone boundary migrated seaward, while at the other, it showed no consistent trend. Diking appears to eliminate natural sensitivity of the ecotone boundary to interannual variation in oceanic and atmospheric drivers, with local factors (management of water control structures) outweighing regional ones. Our study shows that the marsh–upland ecotone migrated rapidly in response to environmental change while maintaining stable plant community structure. Such resilience, stability, and rapid response time suggest that the marsh–upland ecotone can serve as a sensitive indicator of climate change.

Mapping Ecotone Movements: Holocene Dynamics of the Forest Tension Zone in Central Lower Michigan, Usa

This paper presents a novel method for detecting and mapping movements of ecotone boundaries, over both time and space, using existing fossil pollen data. The method combines existing statistical techniques, including discriminant analysis and spatial interpolation, to generate statistically robust maps of ecotone boundaries over time. This method was applied to provide a comprehensive vegetative history of the forest tension zone in the Lower Peninsula of Michigan during the last 10,000 years. Pollen data for nine lakes in the Lower Peninsula were analyzed with discriminant analysis and spatially interpolated with inverse distance weighted to track ecotone movements of the forest tension zone. The forest tension zone has been in existence over the last 10,000 years and has been highly variable over space and time, with at least three major latitudinal shifts, spanning 320 km and 6° of latitude, as well as several less pronounced shifts. These shifts occurred primarily in response to millennial-scale oscillations in climate such as the warmer and dryer conditions associated with the mid-Holocene. A slighter shift was evident in association with the cooler and drier conditions of the Little Ice Age (600-100 cal yr BP). This research demonstrates the sensitivity of Great Lakes forest communities to Holocene climate change and suggests a similar sensitivity of future ecotone dynamics in response to modern global warming.

The 5.1 ka aridization event, expansion of piñon-juniper woodlands, and the introduction of maize (Zea mays) in the American Southwest

Pollen analysis is frequently used to build climate and environmental histories. A distinct Holocene pollen series exists for Chaco Canyon, New Mexico. This study reports linear modeling and hypothesis testing of long distance dispersal pollen from radiocarbon-dated packrat middens which reveal strong relationships between piñon pine ( Pinus edulis) and ponderosa pine ( Pinus ponderosa). Ponderosa pollen dominates midden pollen assemblages during the early Holocene, while a rapid shift to a much higher proportion of piñon to ponderosa pine pollen between c. 5440 and 5102 cal. yr BP points to an aridization episode. This shift is associated with higher δ18O values in Southwest speleothem records relative to the preceding millennium. The period of aridization is followed by a sharp increase in El Niño/Southern Oscillation events that would have caused highly variable precipitation and lasted until c. 4200 cal. yr BP. Bayesian change-point analysis suggests that this aridization episode led to stable ecotonal boundaries for at least 3000 years. The piñon/ponderosa transition may have been caused by punctuated multiyear droughts, analogous to those in the 20th century. The earliest documented instance of Zea mays cultivation on the Colorado Plateau is around c. 3940 14C yr BP ( c. 4364 cal. yr BP) (Hall SA (2010) Early maize pollen from Chaco Canyon, New Mexico, USA. Palynology 34(1): 125–137) in Chaco Canyon. The introduction of this labor-intensive cultigen from Mesoamerica may have been facilitated by changes in the regional ecosystems, specifically by an increase in piñon trees, that promoted increasing human territoriality. Linear modeling and hypothesis testing can complement traditional palynological techniques by adding greater resolution in vegetation patterning to climate/environmental histories.

Willows indirectly reduce arbuscular mycorrhizal fungal colonization in understorey communities

Summary1. Understanding mechanisms underlying species distributions is a central theme in ecology. This study identifies factors driving spatial variation in arbuscular mycorrhizal fungi (AMF). We conducted two experiments to test whether heterogeneity in AMF colonization of alpine perennial plants across a willow‐meadow ecotone is due to variation in (i) above‐ground competition with willows for light (experiment 1), (ii) below‐ground interactions with willows and their ectomycorrhizal fungi (EMF; experiment 1) or (iii) leaf litter deposition (experiment 2).2. In experiment 1, we tested the above‐ground interactions hypothesis by covering open meadow plots with 80% shade cloth to simulate willow shading (S). To test the below‐ground interactions hypothesis, we transplanted ectomycorrhizal (MW) and nonmycorrhizal willows (NW) into the open meadow. AMF colonization of herbaceous plants in the S, MW and NW treatments was compared to colonization of plants growing in unmanipulated open meadow (OC) and willow understorey (WC) control plots. In experiment 2, we tested the leaf litter hypothesis by manipulating leaf litter deposition in open meadow and willow understorey plots. AMF and EMF colonization was compared in plots with and without leaf litter.3. In experiment 1, AMF colonization was reduced in MW and WC plots compared to the other three treatments, suggesting that below‐ground interactions with EMF suppressed AMF colonization of herbaceous hosts. In experiment 2, the presence of leaf litter increased EMF colonization in the open meadow and reduced AMF colonization in both open meadow and willow understorey habitats, suggesting that willow‐derived leaf litter indirectly affected AMF colonization by promoting EMF colonization.4. Synthesis. Our results indicate that willows indirectly reduce AMF colonization of neighbouring herbaceous plants via feedbacks with leaf litter and EMF. These willow‐mediated effects could alter the distribution of mycorrhizal fungi in alpine communities, which could in turn impact the fitness and distribution of closely associated host species. Ultimately, this study demonstrates the potential for below‐ground interactions to drive variation in species associations across ecotonal boundaries.

Vegetation Zonation in a Neotropical Montane Forest: Environment, Disturbance and Ecotones

Gradual changes in vegetation structure and composition are expected to result from continuous environmental change with increasing elevation on mountains. Hence, the occurrence of abrupt or discrete ecotones in vegetation patterns is intriguing and may suggest key controls on community assembly in montane forests. We review tropical montane forest (TMF) zonation patterns focusing on a case study from the Cordillera Central, Hispaniola where a striking discontinuity in forest composition occurs consistently at ∼2000 m elevation, with cloud forest below and monodominant pine forest above. We propose that a discontinuity in climatic factors (temperature, humidity) associated with the trade-wind inversion (TWI) is the primary cause of this and other ecotones in TMFs that occur at a generally consistent elevation. Low humidity, fires and occasional frost above the TWI favor pine over cloud forest species. Fires in the high-elevation pine forest have repeatedly burned down to the ecotone boundary and extinguished in the cloud forest owing to its low flammability, reinforced by high humidity, cloud immersion and epiphytic bryophyte cover. Small-scale fire patterns along the ecotone are influenced by topography and where forest structure is impacted by hurricanes and landslides. Analogous patterns are observed worldwide in other TMFs where the TWI is important, high-elevation fires are frequent, and the flora contains frost-tolerant species (often of temperate lineage). The response of this and other TMFs to anthropogenic climate change is highly uncertain owing to potentially countervailing effects of different climatic phenomena, including warming temperatures and decreased frost; changes in the TWI, high-elevation drought or cloudiness; and increased frequency or intensity of hurricanes and El Niño-Southern Oscillation events. En zonas de montaña es de esperar que el cambio continuo que tiene lugar en las condiciones ambientales con la altitud se traduzca en cambios similarmente graduales de la estructura y composición de la vegetación. Por tanto, resulta llamativa la existencia de ecotonos abruptos o discretos en los patrones de vegetación de algunas montañas, los cuales pueden sugerir la existencia de factores clave que controlen el ensamblaje de las comunidades en bosques de montaña. En este trabajo revisamos los patrones de zonación en bosques montanos tropicales (BMTs) centrándonos como caso de estudio en la Cordillera Central, Hispaniola donde tiene lugar una consistente discontinuidad en la composición del bosque a 2000 m de altitud, con bosques de niebla por debajo de dicha cota y pinares monoespecíficos a mayor altitud. Proponemos que la causa principal de este y otros ecotonos en BMTs a similar altitud es la existencia de una discontinuidad en los factores climáticos (temperatura, humedad) provocada por una inversión térmica. La existencia de baja humedad, fuegos y heladas ocasionales por encima de la cota de inversión térmica favorece a los pinos en comparación con las especies de bosque nublado. Los fuegos que tienen lugar repetidamente en los pinares se extienden hasta llegar al ecotono, donde se extinguen debido a la baja flamabilidad del bosque de niebla, a la elevada humedad y a la cobertura de briófitos epífitos. Los patrones a pequeña escala de los fuegos a lo largo del ecotono están influenciados por la topografía y por cambios en la estructura del bosque causados por huracanes y deslizamientos de tierra. Patrones similares han sido observados en todo el mundo en otros BTMs donde la inversión térmica es importante, los fuegos a cotas altas son frecuentes, y la flora contiene especies tolerantes de las heladas (frecuentemente de origen templado). La respuesta de éste y otros BTMs al cambio climático es incierta debido a efectos potencialmente opuestos de diferentes fenómenos climáticos, incluyendo el aumento de temperatura y disminución de heladas, cambios en las inversiones térmicas, sequías o nubes en cotas altas, e incremento de la frecuencia e intensidad de huracanes y fenómenos el Niño. FIGURE S1. Map of study area and permanent vegetation plots established in 1999–2000, Bermúdez and Ramírez National Parks, Cordillera Central, Dominican Republic. FIGURE S2. View of the pine-cloud forest ecotone on a windward slope in the Cordillera Central, Dominican Republic. Please note: Wiley-Blackwell Publishing is not responsible for the content or functionality of any supporting materials supplied by the authors. Any queries (other than missing material) should be directed to the corresponding author for the article. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Tree Encroachment Impacts Carbon Dynamics in a Sand Prairie in Wisconsin

A sandy prairie remnant in the Lower Wisconsin River Valley, encroachment areas within the prairie, and an adjacent red pine (Pinus resinosa Aiton) plantation were studied to determine the influence of woody cover on C dynamics. Field transects, aerial imagery, and a geographic information system were used to quantify encroachment from 1979 to 2002. A linear encroachment model predicted 100% encroachment of the 6.0‐ha prairie in 50 yr. Four field plots in each of pine, prairie, and encroachment areas were sampled and soils collected (0–18, 18–38, and 38–75 cm) in 2004 and 2008. Total ecosystem C was greater in pine (126.6 Mg C ha−1) and encroachment areas (71.8 Mg C ha−1) than prairie (48.3 Mg C ha−1). In the 0 to 38 cm, coarse particulate organic matter (POM) (4.1, 6.3, and 7.5 Mg C ha−1) and the POM C/N ratio (15.1, 16.2, and 20.2) increased with woody encroachment (prairie, encroachment areas, and pine, respectively). Changes in POM suggest more organic inputs and slower decomposition, but due to minimal protection of C within aggregates, increased total soil C was not observed with woody advancement (46.4–47.2 Mg C ha−1). Microbial biomass (0–38 cm) was greatest in encroachment areas, followed by prairie, and then pine (108, 84, and 51 kg N ha−1, respectively), probably a result of more favorable microclimate and substrate at the ecotone boundary. Potential N mineralization (0.6, 2.8, and 4.8 kg N ha−1 d−1), extractable NH4+ (28, 33, and 57 kg ha−1), and Bray‐1 P (380, 402, and 541 kg ha−1) (0–38 cm) increased with woody cover, and increased nutrient availability could lead to a greater aboveground C sink through increased tree growth.

Variation in ecophysiological properties among conifers at an ecotonal boundary: comparison of establishing seedlings and established adults at timberline

Question: Environmental limitations on carbon acquisition and use can impact successful establishment and restrict a species range, such as for trees at timberline. How do ecophysiological properties associated with carbon uptake and allocation change along an elevation gradient for adult compared to seedling conifers in a timberline ecotone? Location: Teton Range in the Rocky Mountains, Wyoming, USA Methods: Photochemical efficiency (Fv/Fm), specific leaf area (SLA) and foliar nonstructural carbohydrates (NSC) were compared along an elevation gradient (2200-3050 m) among two age classes (seedling and adult) and species (Abies lasiocarpa and Pseudotsuga menziesii) at timberline during mid-summer. Results: F v/Fm values were relatively high in both seedlings and adults across the elevation gradient, with the exception of a low Fv/Fm for seedlings in the site having the lowest soil temperatures. SLA was surprisingly constant within each age class and species across the timberline ecotone. Foliar NSCs did not increase or decrease consistently with elevation in either age class. Nonetheless, NSCs were highly variable among sites, but only in seedlings and not in adults. Conclusions: Elevation effects on these indicators of the efficiency of interception and use of sunlight in the timberline ecotone were minimal during the optimum period of the growing season. However, establishing seedlings had a tendency to exhibit greater responses to the timberline environment, particularly in their allocation of photosynthate to NSC, which may be a constraint to tree establishment at high elevations.

The potential of high-resolution X-ray fluorescence core scanning: Applications in paleolimnology

PAGES news • Vol 17 • No 3 • October 2009 Sc ie nc e H ig hl ig ht s: P al eo lim no lo gy contributions herald a PAGES initiative aimed at the high-resolution reconstruction of climate history obtained through lake records from South America, Africa, and China. Another contribution focuses on deep-sediment drilling efforts in old crater lakes. These initiatives use a number of the techniques described above, which allow for the study of global teleconnections of climate variability at timescales of 105 to 102 years, while also revealing distinct regional and/or sub-continental climate features. Such regional syntheses are crucial for establishing the spatial and temporal patterns of climate change across climatic, hydrological, and ecotonal boundaries, thereby separating climatedriven and anthropogenic impacts on ecosystems at both the site-specific and landscape scales. Rioual and Wang (p. 110) provide a review of progress in Chinese paleolimnological studies, particularly highlighting records that trace the past dynamics of Asian monsoon systems and the Westerlies, which provide a better understanding of complex atmospheric teleconnections. Verschuren and Russell (p. 112) highlight the regionally different patterns of hydrological change during recent millennia, as reconstructed using novel temperature and moisture proxies in lakes across tropical Africa. They also demonstrate how paleogenetic tools can improve our understanding of climate-human-ecosystem interactions. Garcia-Rodriguez et al. (p. 115) demonstrate the value of integrating data obtained through paleolimnological studies in Argentinean and Uruguayan Holocene lake records. They focus particularly on the links between past monsoonal activity and regional hydrological variability since late Glacial times in the Pampas. Finally, Pienitz et al. (p. 117) provide an update on progress in the recovery of long sediment records from continental sites and, in particular, large and deep crater lake basins. They highlight three projects funded through the International Continental Scientific Drilling Program and other partners. The final contribution to this issue is a Program News by Gell et al. (p. 119). They report on the European Water Framework Directive and the important role paleolimnology can play in assessing ecological baseline conditions for lakes. Outlook The various contributions in this issue of PAGES news show that paleolimnology has reached a stage where high-precision data based on different proxies can be generated for lake records. Based on a vast amount of data gathered and standardized approaches, paleolimnologists are now in a position to document continentto hemispheric-wide sensitive responses of freshwater systems to ongoing global change.