Intra-site Variability Research Articles

Wood anatomy variability under contrasted environmental conditions of common deciduous and evergreen species from central African forests

Wood density profiles revealed significant differences in wood formation along a precipitation gradient in the Congo Basin. The response of trees to climate change varies depending on leaf phenology properties. Tropical forests face increasing pressures due to climate change and yet, the response of trees to varying climate conditions remains poorly understood. In the present study, we aim to fill some gaps by comparing the leaf phenology and the pith-to-bark wood anatomical variability of 13 common tree species of the Democratic Republic of Congo among three sites presenting contrasted rainfall regimes. We measured pith-to-bark density profiles on which we applied wavelet analyses to extract three descriptors, which we further used as proxies to describe and compare wood anatomical variability. They describe the growth periodicity, regularity and the amplitude of variations of the anatomical patterns. Our results show that evergreen species tend to have significantly higher anatomical variability where rainfall seasonality is more pronounced. Deciduous species, in spite of shedding leaves for longer periods in drier sites, did not show significant differences in their anatomical variability. The analyses of density profiles and phenology records suggest that the seasonality of precipitation influences both leaf phenology and cambial activity. The high intra-site variability in phenology and anatomy suggests that site-related micro-climate conditions also influence cambial activity.

Biomonitoring with mosses: Uncertainties related to sampling period, intra-site variability, and cleaning treatments

To assess the level of sampling period uncertainty and the main components of the measurement uncertainty, such as: sampling, preparation and analysis a total of 63 samples of Pleurozium schreberi (Brid.) Mitt. moss species and their duplicates were collected from the same sampling sites in September of 2014, and March and July of 2015. After each sampling campaign, the samples (primary sample – S1 and its duplicate – S2) were divided into two equal and homogenous samples (P1 and P2) for preparation. The P1 samples were subjected to dry cleaning whereas the P2 samples to wet cleaning. After digestion in a closed microwave system, Cu, Fe, Mn and Zn were determined in all these samples using FAAS and GFAAS techniques. The highest concentrations were noted in July samples. However, the average element contents were as follows: July > March ≈ September for Cu and Mn, July > March > September for Fe, and July ≈ March > September for Zn. The level of sampling period uncertainty was the highest for Fe and Mn, and the lowest for Cu. In 2014 the measurement uncertainty (srmeas) of Fe, Mn and Zn (expressed as a sum of sampling (srsamp), preparation (srprep) and analytical (sranal) uncertainty) was mainly affected by intra-site variability, so the contribution of sampling uncertainty to the srmeas values was the highest. In 2015 the cleaning procedure had the main impact of the measurement uncertainty of Fe and Zn, so the srmeas values were mainly loaded by the srprep values. For Cu and Mn the same relationship between the srsamp and srprep values was maintained in 2014 and 2015. In all cases, the sum of sampling, preparation and analytical uncertainty did not exceed 35%. However, high values of preparation uncertainty of Fe and Zn obtained in 2015 should make us more critical of the results from the analysis of mosses collected within different sampling periods and cleaned using different wet/dry cleaning methods.

Evaluating the carrying capacity at the archaeological site of Jerash (Gerasa) using mathematical GIS modeling

The carrying capacity represents an important module in tourism planning; it is one of the mechanisms for establishing standards for sustainable tourism and cultural heritage preservation. This study evaluates the carrying capacity at the site of Jerash (Gerasa), one of the Decapolis cities in Jordan. The methods of the study include mathematical modeling for evaluating the carrying capacity that was modified after Boullon (1985) within an ArcGIS 10.2 environment. The results show that the carrying capacity at the site of Gerasa is currently manifesting a serious issue, where the excessive number of tourists and Festival attendants put its archaeology in danger. The results also stress on the need for adopting intra-site variation in evaluating the physical carrying capacity. Accordingly, there is a need for further collaborations among decision makers, stakeholders, tour operators and the local community.

New Radiocarbon Dates from Nasera Rockshelter (Tanzania): Implications for Studying Spatial Patterns in Late Pleistocene Technology

AbstractLate Pleistocene and Holocene evidence from multiple rockshelters in north-central Tanzania suggests a regional pattern of changing technological behaviors through time. We use independent chronological evidence to test if the proposed technological patterns across space were also temporally equivalent. We applied AMS radiocarbon dating methods to the carbonate fraction of five ostrich eggshell fragments from Mehlman’s 1975-1976 excavations at Nasera rockshelter and compared our results to recent re-dating efforts of Mumba rockshelter. We document radiocarbon results >46 ka at Nasera in Level 5, indicating that associated and underlying technologies (including what Mehlman termed the ‘Nasera Industry’) are older than previously documented. Backed pieces first appear >46 ka at Nasera, which is in accordance with recent evidence from nearby rockshelters like Enkapune ya Muto, Panga ya Saidi, and potentially Kisese II. We also provide an age of 11,260-11,710 calBP for the ‘Silale Industry’ of Level 3B. Overall, the shifts in lithic technology previously considered to be shared between Mumba and Nasera rockshelters are not temporally aligned, emphasizing the possibility that intra-site variability was the norm throughout the Late Pleistocene in eastern Africa.

Isotopic evidence of diet variation at the transition between classical and post-classical times in Central Italy

This work examines the carbon and nitrogen composition of human and animal collagen from the Roman necropolis of Lucus Feroniae (Rome, 1st–3rd century AD) and the Longobard cemetery of La Selvicciola in northern Latium (Viterbo, 7th century AD), with a special focus on possible dietary variations at the transition between classical and post-classical times. A substantial isotopic difference between the two series reveals distinct dietary practices at the two sites, especially the consumption of cereals and contribution of other foodstuffs to a mainly grain-based diet. We argue that such differences are explained through the social and cultural background of the two populations examined, where the isotopic variance of the Roman data is in line with that of a group of heterogeneous origin and varied dietary practices, while the tight clustering of isotopic signatures for the Longobard people reflects the foodways of a homogeneous group. Intra-site variation shows no significant difference according to the sex of the deceased. Outlying individuals might be explained through cultural practices that call for further insight. Isotopic data have shown to successfully reflect social and cultural phenomena of human groups in a changing world, in a way that other archaeological proxies have sometimes failed to achieve.

A case for comprehensive analyses demonstrated by evaluating the yield benefits of neonicotinoid seed treatment in maize (Zea mays L.)

With increased scrutiny of the neonicotinoid class of chemistry and its negative impact on the pollinator community, ecological cost/benefit analyses of agronomic crops that use these insecticides are increasingly important. This study initially sought to address the question of yield benefit due to neonicotinoid seed treatment in maize (Zea mays L.), using North Carolina yield contest data from 2002 to 2006, the time period from initial neonicotinoid seed treatment adoption to nearly ubiquitous adoption. However, we recognized that several agronomic practices, including planting date, hybrid selection, and fertilization, could affect the yield of this crop; moreover, they could be collinear with one another and the analysis could be skewed by early adopters of new technology. Hence, we used all available data to compare among traditional approaches and a data-mining approach for analyzing the impact of neonicotinoid seed treatment on maize yield. At-planting insecticide treatment was not an important predictor of maize yield. When analyzed using the traditional approach (T-test), yields were significantly higher for fields planted with neonicotinoid treated seed compared to seed without neonicotinoid; however, data-mining approach (Decision tree analysis) that took into account other factors contributing to yield did not identify seed treatments as important. The contrast in these results highlights the need for future carefully designed studies that target to minimize inter- and intra-site variation; and include measurements of additional factors that may influence yield, such as seeding rate, tillage, and herbicide applications, as input variables that are largely lacking in current approaches on the subject.

Small mammals from Marine Isotope Stage 5 at Klasies River, South Africa–Reconstructing the local palaeoenvironment

Klasies River, a significant Middle Stone Age (MSA) site, preserves remains of anatomically modern humans and a 21 m sequence of human habitation that shows use of sophisticated lithic technology and systematic exploitation of marine and terrestrial resources. In this paper micromammals recovered from the lower MSA sequence (MSA I and MSA II) at Klasies River Main site have been analysed to provide proxy data for palaeoenvironmental reconstruction. Small mammals recovered from 183 separate layers ensure a detailed record of local climate and vegetation during Marine Isotope Stage (MIS) 5. Taphonomic analyses indicate that avian predators accumulated the micromammals. Analysis of post-depositional processes has provided information on intra-site variability and utilisation. The palaeoenvironmental reconstruction shows changes in rainfall seasonality within MIS 5. There was transient movement towards more aseasonal rainfall and significant alterations in the vegetation composition from MIS 5e to MIS 5a. Our study adds new insights to palaeoenvironmental conditions on the Cape coast during MIS 5.

Oxidative Stress Assessment in Alzheimer's Disease: A Clinic Setting Study.

Oxidative stress (OS) is a physiological age-related brain process, dramatically overexpressed in neurodegenerative disorders like Alzheimer's disease (AD). Nevertheless, the pathophysiological role of OS in AD pathology has not been clarified yet. OS as a biomarker for AD is a controversial issue. A comparison of previous data is difficult due to a remarkable methodological variability. Most of the previous studies have shown higher levels of OS markers and lower antioxidant power in patients with dementia when compared to mild cognitive impairment (MCI) and healthy controls. We followed a strict protocol in order to limit intrasite variability of OS assessment. In addition, we have taken into account possible confounding factors. In agreement with previous reports, we found both lower plasmatic OS and higher plasmatic antioxidant defenses when comparing patients with AD having dementia that is stably treated to patients with MCI-AD. A speculative hypothesis based on correlative data is provided.

Barley grain at Upp\xe5kra, Sweden: evidence for selection in the Iron Age

A metric analysis on hulled barley grain from the Iron Age regional centre of Uppåkra and surrounding sites in southern Sweden has identified a variation in the size of the grain found on these archaeological sites. Large, high-quality grain was found more frequently at Uppåkra when compared to sites in the surrounding area, where smaller grain was more frequent. The observed large grain found at Uppåkra was, however, restricted to only a few house contexts, including hall-buildings, while other contexts on the site, such as areas dedicated to craft production, had barley assemblages containing smaller grain, similar to the size range found on the surrounding sites. The intra-site variation between different contexts at Uppåkra points to a degree of sorting for larger grain and that this variation between grain assemblages was the result of selection after the crop processing was completed. The distribution of grain size at Uppåkra shows a pattern that indicates that the high-quality barley grain was indented for specific individuals or households. The different contexts at Uppåkra have together produced a record spanning the first millennium ad, representing almost the whole existence of the site. The evidence for selection of larger grain can be seen in the hall-buildings throughout most of the first millennium ad, although less prominently during the Late Roman Iron Age (ad 200–400), while during the Migration Period (ad 400–550) several houses on the main site Uppåkra had assemblages of large grain size. The distribution of grain size at the regional centre Uppåkra shows a pattern that indicates that the handling of large high-quality barley grain was part of a spatial organization, and such organization is similar to other functions observed on the site. The long-term record of grain size patterns across time shows that a structure for handling grain was already in place during the early phase of the settlement and that it remained for centuries. This study indicates that the affluence otherwise seen at the regional centre Uppåkra from an abundance of high-status objects, could also include agricultural wealth, with extensive access to high-quality grain.

UK audit of quantitative thyroid uptake imaging.

A national audit of quantitative thyroid uptake imaging was conducted by the Nuclear Medicine Software Quality Group of the Institute of Physics and Engineering in Medicine in 2014/2015. The aims of the audit were to measure and assess the variability in thyroid uptake results across the UK and to compare local protocols with British Nuclear Medicine Society (BNMS) guidelines. Participants were invited through a combination of emails on a public mailbase and targeted invitations from regional co-ordinators. All participants were given a set of images from which to calculate quantitative measures and a spreadsheet for capturing results. The image data consisted of two sets of 10 anterior thyroid images, half of which were acquired after administration of Tc-pertechnetate and the other half after administration of I-iodide. Images of the administration syringes or thyroid phantoms were also included. In total, 54 participants responded to the audit. The median number of scans conducted per year was 50. A majority of centres had at least one noncompliance in comparison with BNMS guidelines. Of most concern was the widespread lack of injection-site imaging. Quantitative results showed that both intersite and intrasite variability were low for the Tc dataset. The coefficient of quartile deviation was between 0.03 and 0.13 for measurements of overall percentage uptake. Although the number of returns for the I dataset was smaller, the level of variability between participants was greater (the coefficient of quartile deviation was between 0.17 and 0.25). A UK-wide audit showed that thyroid uptake imaging is still a common test in the UK. It was found that most centres do not adhere to all aspects of the BNMS practice guidelines but that quantitative results are reasonably consistent for Tc-based scans.

Carbon isotopic signature reveals the geographical trend in methane consumption and production pathways in alpine ecosystems over the Qinghai–Tibetan Plateau

ABSTRACTOn the Qinghai–Tibetan Plateau, isotopic signatures in soil–atmosphere CH4 fluxes were investigated in nine grasslands and three wetlands. In the grasslands, the fractionation factor for soil CH4 uptake, αsoil, was much smaller than the usually reported value of 0.9975–1.0095. Stepwise multiple variation analysis indicates that αsoil is higher for higher soil water contents but is lower for higher C/N ratios of soil surface biomass. In the three wetlands, the soil-emitted δ13C–CH4 was similar (−55.3 ± 5.5 ‰ and −53.0 ± 5.5 ‰) in two bogs separated by >1000 km but was lower (−63.4 ± 6.3 ‰) in a marsh. Environmental factors related to intrasite variations in soil-emitted δ13C–CH4 include the soil C/N ratio, oxidation–reduction potential, soil C concentration and soil water contents. Geographical isotopic surveys revealed environmental constraints on the CH4 consumption pathways in grasslands and the biome type-specific consistency in CH4 production pathways in wetlands.

Developments in Animal Husbandry and Food Supply in Roman Germania Inferior

The Roman province of Germania Inferior is characterized geographically by the river Rhine—the border of the Empire—and the forts along it. From the north-west to the south-east, there are significant differences in landscape and type of rural habitation. Whether these differences are also noticeable in animal husbandry forms the subject of this article. Are there any differences in species proportions and slaughter ages between the western and eastern parts of the province, and between urban, military, and rural sites? What does this say about farming and food supply? After presenting an overview of the zooarchaeological data from Germania Inferior, I shall discuss in detail onecivitas—thecivitasBatavorum, with the best known zooarchaeological dataset within the province. What changes in species proportions and cattle size can be detected over time from thiscivitas? Is there evidence for inter- and intra-site variability and changes in butchery methods? This article's further aim is to demonstrate what kind of questions a synthetic overview of zooarchaeological datasets can address.

Sociedad, identidad y variedad de los mausoleos de La Petaca, Chachapoyas

espanolLos chachapoya de la sierra nororiental de Peru utilizaron varios metodos para enterrar a sus muertos, pero casi todos estos se dieron en espacios sumamente visibles. Mientras que existe variacion regional entre diferentes espacios mortuorios chachapoya, hay evidencia de una cohesion estilistica dentro de cada sitio. Desafortunadamente, pocos complejos mortuorios han sido excavados, pero el complejo de La Petaca en el distrito de Leymebamba, nos provee una oportunidad de examinar cientificamente la variacion intra-sitio. En solamente medio acantilado del complejo mortuorio registramos un minimo de 125 construcciones incluyendo tumbas, plataformas y caminos, ademas de cavernas, nichos, y abrigos, todos con restos mortuorios. Utilizando arqueologia vertical, recuperamos restos culturales, muestras oseas y organicas para analisis bioquimico y para fechados. Desafortunadamente, muchos de los contextos han sido danados por la actividad de los huaqueros y los procesos tafonomicos naturales. Se ha hallado variabilidad en los metodos constructivos, materiales, disenos arquitectonicos y ubicacion en el sitio, pero en general la distribucion de rasgos comunes sugiere varias interpretaciones: 1) el estilo mortuorio fue adaptado a la locacion precaria, 2) habia muy pocos cambios a traves del tiempo, 3) habia pocos constructores de estas tumbas, o 4) este complejo refleja patrones constructivos de una sola tradicion. Sobre todo, estos datos nuevos nos pueden presentar valiosas interpretaciones sobre la accesibilidad, la complejidad en construccion y aspectos de la identidad social de los chachapoya. EnglishThe Chachapoya of the northeastern Peruvian highlands utilized various methods for disposing of their dead, but almost all involve highly visible spaces. While some regional variation is found among Chachapoya mortuary spaces, there is evidence for social cohesion within each site. While few mortuary complexes of the Chachapoya have been excavated, La Petaca mortuary complex in the Leymebamba district, provides the opportunity to scientifically study intrasite variation. On only half of the mortuary complex’s massive vertical wall we documented 125 constructions including tombs, platforms and walkways, as well as several caves, niches and rock shelters, all of which contained mortuary remains. By using techniques of vertical archaeology, we collected artifacts and skeletal and organic samples for analysis and radiocarbon dating. Unfortunately, many of the contexts had been damaged by looting and natural taphonomic processes. Here was some variability in construction methods, materials, architectural design, and location across the site, yet generally common features suggest several interpretations: 1) mortuary style was adapted to the precarious location, 2) there was little change over time, 3) few builders were involved, or 4) these practices reflect a single cultural tradition. Overall, these new, detailed data yield valuable information on the importance of mortuary spaces and the regional complexity of the Chachapoya.

The extreme 2013/2014 winter storms: Beach recovery along the southwest coast of England

Sand and gravel beaches naturally act as a coastal buffer, absorbing wave energy and dynamically adapting to the seasonal and long-term wave climate. Significant shifts in nearshore morphology can occur during extreme wave events, which can have a significant impact on coastal vulnerability. During the winter of 2013/14, the Atlantic coast of Europe received an unprecedented sequence of very energetic wave conditions (8-week mean offshore Hs=4.4m). These events caused extensive physical (beach and dune erosion) and socio-economic (flooding, damage to infrastructure) impacts throughout the west coast of Europe. Many monitored sites in the UK and France were in their most eroded state since morphological records began (5–10years). We consider the geomorphological significance of the storm response at 38 natural beaches in the southwest of England, ranging from semi-sheltered reflective gravel barriers to ultra-dissipative exposed sand beaches with dunes. The extent and patterns of post-storm recovery are examined in detail at three beaches with characteristic storm response behaviours. Exposed sandy beaches were dominated by cross-shore transport processes leading to significant loss of sediment offshore from the intertidal zone (>200m3/m); exposed gravel beaches were dominated by overwash with significant loss landward; and semi-sheltered sites exposed to more oblique wave forcing were dominated by a rotational response due to alongshore sediment redistribution. Due to these contrasting responses, mechanisms and timescales for beach recovery displayed strong inter-site and intra-site variations. In offshore and rotational cases, the recovery processes were multi-annual, comprising seasonal to decadal signals and were intrinsically linked to the storm response mechanisms, while permanent losses occurred when overwash dominated. We show that post-storm recovery does not necessarily occur during calm periods and that in many cases high-energy wave events appear to be essential for recovery of sediment (offshore and counter-rotation). Our results highlight the significance of dominant climatic oscillations, multi-annual storm sequencing, storm tracks and resultant variations in wave angle, in controlling the impact that extreme wave events have on contrasting sand/gravel beaches in exposed/sheltered locations.

Faunal acquisition, maintenance, and consumption: how the Teotihuacanos got their meat

The compilation of the last 40 years of zooarchaeological exploration at Teotihuacan, Mexico, provides a unique opportunity to create more nuanced models of New World vertebrate consumption that did not focus on domesticated animals (dog and turkey). Any single model of ancient food systems fails to represent how varied ecological and social contexts led to a complex web of adaptations, and here, it is argued that Teotihuacan’s arid, highland, and urban environment contributed to a distinct faunal acquisition strategy. Intra-site variation and diverse degrees of animal procurement and management were practiced throughout the site. For example, the low proportion of deer compared to the abundant evidence of rabbit/hare consumption suggests small-scale animal management and breeding programs in the residential complexes supplemented with opportunistic garden hunting and meat purchased through a market economy. Such foodstuffs would have been both more predictable and readily made available to organize large feasting events, a possibility that is strengthened by evidence of extraordinarily high abundances of rabbits in ceremonial contexts.

Low-cost sensors and crowd-sourced data: Observations of siting impacts on a network of air-quality instruments

Low-cost sensors offer the possibility of gathering high temporal and spatial resolution crowd-sourced data-sets that have the potential to revolutionize the ways in which we understand individual and population exposure to air pollution. However, one of the challenges associated with crowd-sourced data (‘citizen science’), often from low-cost sensors, is that citizens may use sites strongly affected by local conditions, limiting the wider significance of the data. This paper examines results from a low-cost network measuring ground-level ozone to evaluate the impact of siting on data quality. Locations at both reference stations and at private homes or research centers were used, and thought of as a typical ‘crowd-sourced’ network. Two instruments were co-located at each site to determine intra-site variability and evaluated by standard performance statistics and local-scale activity logs. The wider application of the data for both regional Inter-site variability was evaluated to show-case the wider value and usefulness of crowd-sourced data. Analysis of intra-site variability showed little differences at most sites (<5ppb). Large differences in intra-site variability were detected when sensors were exposed to direct sunlight (causing thermal variations within the instrument) and proximity to large emission sources. Short-term local activities, such as lawn-mowing, were identifiable in the data, but had minimal impact on standard reporting time-scales, and so did not pose as being significant limitations or errors. Inter-site evaluation demonstrated that dense networks of low-cost sensors can add value to existing networks, with minimal impact on the overall data-set quality. Sensors located in crowd-sourced locations nearby to regulatory analyzers were able to capture similar trends and concentrations, supporting their ability to report on wider conditions. Thus crowd-sourced approaches to monitoring (with suitable calibration and data quality control checks) may be an appropriate method for increasing the temporal and spatial resolution of air quality networks.

No accounting for taste: Palatability of variably defended Caribbean sponge species is unrelated to predator abundance

The antipredatory chemical ecology of Caribbean reef sponges has been well studied, with two distinct ecological strategies described: chemically defended species use secondary metabolites to deter fish predators, while palatable species lack chemical defenses, but grow, reproduce, or recruit fast enough to persist despite predation. While most palatable sponge species are consistently undefended from fish predators in laboratory feeding assays, there are some species that exhibit individual inter- and intra-site variation ranging from palatable to defended. The objective of this study was to better document the extent of chemical defense variability for 7 of these species over a wider geographic range and to test the dual hypotheses that variably defended sponge species would be (1) more palatable, and (2) exhibit greater variability in chemical defenses from reefs without sponge predators than from reefs where predators are abundant. Laboratory feeding assays using the bluehead wrasse confirmed intraspecific variability of chemical defenses for Clathria virgultosa, Cribrochalina vasculum, Desmapsamma anchorata, Dragmacidon reticulata, Iotrochota birotulata, Niphates digitalis, and Xestospongia muta for sites across the Caribbean. Surprisingly, logistic regression models relating levels of sponge chemical defense to a site-specific index of spongivorous fish abundance offered little support for the hypothesis that predator abundance alters palatability for any of these variably defended sponge species. The presence of symbiotic zoanthids in the tissue of I. birotulata and N. digitalis did not alter palatability. While the selective effect of predation has segregated most species of Caribbean reef sponges into chemically defended and undefended categories, this study concludes that the situation is more complex for variably defended sponge species, and suggests that automimicry is a possible explanation for this alternative strategy.

Improving the design of long-term monitoring experiments in forests: a new method for the assessment of local soil variability by combining infrared spectroscopy and dendrometric data

Near- and mid-infrared spectroscopy allows for the detection of local patterns of forest soil properties. In combination with dendrometric data, it may be used as a prospective tool for determining soil heterogeneity before setting up long-term forest monitoring experiments. Forest soils and stands generally exhibit higher spatial heterogeneity than other terrestrial ecosystems. This variability needs be taken into account before setting up long-term forest monitoring experiments to avoid multiple interactions between local heterogeneity and the factors tested in the experiment. We hypothesized that raw near- and mid-infrared spectra can be used as an integrated proxy of a large set of soil properties. The use of this method, in combination with dendrometric data, should provide a quick and cost-effective tool for optimizing the design of experimental forest sites. We assessed the local soil heterogeneity at 11 experimental sites in oak and beech stands, which belong to a new forest long-term ecological research (LTER) network. We used near- and mid-infrared spectroscopy in soil and litter samples. The spectra were subjected to principal components analyses (PCA) to determine the intra-site variability of the soil and litter layers. Based on mapped PCA coordinates and basic dendrometric data, it was possible to design the experiment and minimize the interactions between the treatment layout and the tested variables. The method was validated with chemical analyses of the soil. No interaction was detected at the set-up of the experiment between the treatment layout and chemical soil properties (C, N, C/N ratio, pH, CEC, Al, Mg, P2O5, Fe, Mn, Na, and K). Near-infrared (NIR) and mid-infrared (MIR) spectroscopy is a useful tool for characterizing the overall heterogeneity of soil chemical properties. It can be used without any preliminary calibration. In combination with dendrometric data, it provides a reliable method for optimizing LTER plots in different types of ecosystems.

Assessment of the uncertainty of trace metal and nitrogen concentrations in mosses due to sampling, sample preparation and chemical analysis based on the French contribution to ICP-Vegetation

Moss bio-monitoring is a convenient tool for establishing specific or large-scale exposure to atmospheric trace metals and nitrogen pollution. However, the uncertainty associated with sampling, sample preparation and chemical analysis of bio-monitors has been poorly documented, with the exception of one study dealing with lichens; thus, the uncertainty associated with moss bio-monitoring has never been assessed. Here, we propose following the Eurachem guidelines to determine the uncertainties associated with the concentrations of elements measured in mosses during the sampling survey across France in 2011. In addition, we assess the analytical method used in four surveys from 1996 to 2011. Uncertainties were expressed as linear functions of the element concentrations, with minimum and maximum slopes of 14 and 61%, corresponding to nitrogen and chromium, and a median of 32%. Although the data reveal that some steps of the protocol should be performed carefully, they also indicate that the protocol was executed properly and is reproducible. The chemical analyses contribute to a small proportion of the uncertainty associated with the protocol, except for the analysis of chromium. The sampling period, and intra-site variability largely contribute to this uncertainty. The moss species did not introduce additional uncertainty. This integrative assessment of measurement uncertainty will help improve the protocol for future surveys. Such studies could be useful for developing a standard operating procedure and could be used to improve comparisons between countries and to identify temporal trends across Europe.

Contrasted allometries between stem diameter, crown area, and tree height in five tropical biogeographic areas

Across five biogeographic areas, DBH-CA allometry was characterized by inter-site homogeneity and intra-site heterogeneity, whereas the reverse was observed for DBH-H allometry. Tree crowns play a central role in stand dynamics. Remotely sensed canopy images have been shown to allow inferring stand structure and biomass which suggests that allometric scaling between stems and crowns may be tight, although insufficiently investigated to date. Here, we report the first broad-scale assessment of stem vs. crown scaling exponents using measurements of bole diameter (DBH), total height (H), and crown area (CA) made on 4148 trees belonging to 538 species in five biogeographic areas across the wet tropics. Allometries were fitted with power functions using ordinary least-squares regressions on log-transformed data. The inter-site variability and intra-site (sub-canopy vs. canopy trees) variability of the allometries were evaluated by comparing the scaling exponents. Our results indicated that, in contrast to both DBH-H and H-CA allometries, DBH-CA allometry shows no significant inter-site variation. This fairly invariant scaling calls for increased effort in documenting crown sizes as part of tree morphology. Stability in DBH-CA allometry, indeed, suggests that some universal constraints are sufficiently pervasive to restrict the exponent variation to a narrow range. In addition, our results point to inverse changes in the scaling exponent of the DBH-CA vs. DBH-H allometries when shifting from sub-canopy to canopy trees, suggesting a change in carbon allocation when a tree reaches direct light. These results pave the way for further advances in our understanding of niche partitioning in tree species, tropical forest dynamics, and to estimate AGB in tropical forests from remotely sensed images.