Fine-root turnover rates of European forests revisited: An analysis of data from sequential coring and ingrowth cores

Brunner I., Bakker M.R., Björk R.G., Hirano Y., Lukac M., Aranda X., Børja I., Eldhuset T.D., Helmisaari H.S., Jourdan C., Konôpka B., López B.C., Miguel Pérez C., Persson H., Ostonen I. (2013) Fine-root turnover rates of European forests revisited: An analysis of data from sequential coring and ingrowth cores. Plant and Soil. 362: 357-372.
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Doi: 10.1007/s11104-012-1313-5

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Background and Aims: Forest trees directly contribute to carbon cycling in forest soils through the turnover of their fine roots. In this study we aimed to calculate root turnover rates of common European forest tree species and to compare them with most frequently published values. Methods: We compiled available European data and applied various turnover rate calculation methods to the resulting database. We used Decision Matrix and Maximum-Minimum formula as suggested in the literature. Results: Mean turnover rates obtained by the combination of sequential coring and Decision Matrix were 0. 86 yr-1 for Fagus sylvatica and 0. 88 yr-1 for Picea abies when maximum biomass data were used for the calculation, and 1. 11 yr-1 for both species when mean biomass data were used. Using mean biomass rather than maximum resulted in about 30 % higher values of root turnover. Using the Decision Matrix to calculate turnover rate doubled the rates when compared to the Maximum-Minimum formula. The Decision Matrix, however, makes use of more input information than the Maximum-Minimum formula. Conclusions: We propose that calculations using the Decision Matrix with mean biomass give the most reliable estimates of root turnover rates in European forests and should preferentially be used in models and C reporting. © 2012 The Author(s).

Llegeix més

Vegetation changes and human settlement of Easter Island during the last millennia: A multiproxy study of the Lake Raraku sediments

Canellas-Bolta N., Rull V., Saez A., Margalef O., Bao R., Pla-Rabes S., Blaauw M., Valero-Garces B., Giralt S. (2013) Vegetation changes and human settlement of Easter Island during the last millennia: A multiproxy study of the Lake Raraku sediments. Quaternary Science Reviews. 72: 36-48.
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Doi: 10.1016/j.quascirev.2013.04.004

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Earlier palynological studies of lake sediments from Easter Island suggest that the island underwent a recent and abrupt replacement of palm-dominated forests by grasslands, interpreted as a deforestation by indigenous people. However, the available evidence is inconclusive due to the existence of extended hiatuses and ambiguous chronological frameworks in most of the sedimentary sequences studied. This has given rise to an ongoing debate about the timing and causes of the assumed ecological degradation and cultural breakdown. Our multiproxy study of a core recovered from Lake Raraku highlights the vegetation dynamics and environmental shifts in the catchment and its surroundings during the late Holocene. The sequence contains shorter hiatuses than in previously recovered cores and provides a more continuous history of environmental changes. The results show a long, gradual and stepped landscape shift from palm-dominated forests to grasslands. This change started c. 450 BC and lasted about two thousand years. The presence of Verbena litoralis, a common weed, which is associated with human activities in the pollen record, the significant correlation between shifts in charcoal influx, and the dominant pollen types suggest human disturbance of the vegetation. Therefore, human settlement on the island occurred c. 450 BC, some 1500 years earlier than is assumed. Climate variability also exerted a major influence on environmental changes. Two sedimentary gaps in the record are interpreted as periods of droughts that could have prevented peat growth and favoured its erosion during the Medieval Climate Anomaly and the Little Ice Age, respectively. At c. AD 1200, the water table rose and the former Raraku mire turned into a shallow lake, suggesting higher precipitation/evaporation rates coeval with a cooler and wetter Pan-Pacific AD 1300 event. Pollen and diatom records show large vegetation changes due to human activities c. AD 1200. Other recent vegetation changes also due to human activities entail the introduction of taxa (e.g. Psidium guajava, Eucalyptus sp.) and the disappearance of indigenous plants such as Sophora toromiro during the two last centuries. Although the evidence is not conclusive, the American origin of V. litoralis re-opens the debate about the possible role of Amerindians in the human colonisation of Easter Island. © 2013 Elsevier Ltd.

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Geographical variability in propagule pressure and climatic suitability explain the European distribution of two highly invasive crayfish

Capinha C., Brotons L., Anastácio P. (2013) Geographical variability in propagule pressure and climatic suitability explain the European distribution of two highly invasive crayfish. Journal of Biogeography. 40: 548-558.
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Doi: 10.1111/jbi.12025

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Aim: We assess the relative contribution of human, biological and climatic factors in explaining the colonization success of two highly invasive freshwater decapods: the signal crayfish (Pacifastacus leniusculus) and the red swamp crayfish (Procambarus clarkii). Location: Europe. Methods: We used boosted regression trees to evaluate the relative influence of, and relationship between, the invader's current pattern of distribution and a set of spatially explicit variables considered important to their colonization success. These variables are related to four well-known invasion hypotheses, namely the role of propagule pressure, climate matching, biotic resistance from known competitors, and human disturbance. Results: Model predictions attained a high accuracy for the two invaders (mean AUC ≥ 0.91). Propagule pressure and climatic suitability were identified as the primary drivers of colonization, but the former had a much higher relative influence on the red swamp crayfish. Climate matching was shown to have limited predictive value and climatic suitability models based on occurrences from other invaded areas had consistently higher relative explanatory power than models based on native range data. Biotic resistance and human disturbance were also shown to be weak predictors of the distribution of the two invaders. Main conclusions: These results contribute to our general understanding of the factors that enable certain species to become notable invaders. Being primarily driven by propagule pressure and climatic suitability, we expect that, given their continued dispersal, the future distribution of these problematic decapods in Europe will increasingly represent their fundamental climatic niche. © 2012 Blackwell Publishing Ltd.

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Contrasting trait syndromes in angiosperms and conifers are associated with different responses of tree growth to temperature on a large scale

Carnicer J., Barbeta A., Sperlich D., Coll M., Penuelas J. (2013) Contrasting trait syndromes in angiosperms and conifers are associated with different responses of tree growth to temperature on a large scale. Frontiers in Plant Science. 4: 0-0.
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Doi: 10.3389/fpls.2013.00409

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Recent large-scale studies of tree growth in the Iberian Peninsula reported contrasting positive and negative effects of temperature in Mediterranean angiosperms and conifers. Here we review the different hypotheses that may explain these trends and propose that the observed contrasting responses of tree growth to temperature in this region could be associated with a continuum of trait differences between angiosperms and conifers. Angiosperm and conifer trees differ in the effects of phenology in their productivity, in their growth allometry, and in their sensitivity to competition. Moreover, angiosperms and conifers significantly differ in hydraulic safety margins, sensitivity of stomatal conductance to vapor-pressure deficit (VPD), xylem recovery capacity or the rate of carbon transfer. These differences could be explained by key features of the xylem such as non-structural carbohydrate content (NSC), wood parenchymal fraction or wood capacitance. We suggest that the reviewed trait differences define two contrasting ecophysiological strategies that may determine qualitatively different growth responses to increased temperature and drought. Improved reciprocal common garden experiments along altitudinal or latitudinal gradients would be key to quantify the relative importance of the different hypotheses reviewed. Finally, we show that warming impacts in this area occur in an ecological context characterized by the advance of forest succession and increased dominance of angiosperm trees over extensive areas. In this context, we examined the empirical relationships between the responses of tree growth to temperature and hydraulic safety margins in angiosperm and coniferous trees. Our findings suggest a future scenario in Mediterranean forests characterized by contrasting demographic responses in conifer and angiosperm trees to both temperature and forest succession, with increased dominance of angiosperm trees, and particularly negative impacts in pines. © 2013 Carnicer, Barbeta, Sperlich, Coll and Peñuelas.

Llegeix més

Improved empirical tests of area-heterogeneity tradeoffs

Carnicer J., Brotons L., Herrando S., Sol D. (2013) Improved empirical tests of area-heterogeneity tradeoffs. Proceedings of the National Academy of Sciences of the United States of America. 110: 0-0.
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Doi: 10.1073/pnas.1222681110

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[No abstract available]

Llegeix més

A unified framework for diversity gradients: The adaptive trait continuum

Carnicer J., Stefanescu C., Vila R., Dincǎ V., Font X., Peñuelas J. (2013) A unified framework for diversity gradients: The adaptive trait continuum. Global Ecology and Biogeography. 22: 6-18.
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Doi: 10.1111/j.1466-8238.2012.00762.x

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Aim Adaptive trait continua are axes of covariation observed in multivariate trait data for a given taxonomic group. These continua quantify and summarize life-history variation at the inter-specific level in multi-specific assemblages. Here we examine whether trait continua can provide a useful framework to link life-history variation with demographic and evolutionary processes in species richness gradients. Taking an altitudinal species richness gradient for Mediterranean butterflies as a study case, we examined a suite of traits (larval diet breadth, adult phenology, dispersal capacity and wing length) and species-specific habitat measures (temperature and aridity breadth). We tested whether traits and species-specific habitat measures tend to co-vary, whether they are phylogenetically conserved, and whether they are able to explain species distributions and spatial genetic variation in a large number of butterfly assemblages. Location Catalonia, Spain. Methods We formulated predictions associated with species richness gradients and adaptive trait continua. We applied principal components analyses (PCAs), structural equation modelling and phylogenetic generalized least squares models. Results We found that traits and species-specific habitat measures covaried along a main PCA axis, ranging from multivoltine trophic generalists with high dispersal capacity to univoltine (i.e. one generation per year), trophic specialist species with low dispersal capacity. This trait continuum was closely associated with the observed distributions along the altitudinal gradient and predicted inter-specific differences in patterns of spatial genetic variability (FST and genetic distances), population responses to the impacts of global change and local turnover dynamics. Main conclusions The adaptive trait continuum of Mediterranean butterflies provides an integrative and mechanistic framework to: (1) analyse geographical gradients in species richness, (2) explain inter-specific differences in population abundances, spatial distributions and demographic trends, (3) explain inter-specific differences in patterns of genetic variation (FST and genetic distances), and (4) study specialist-generalist life-history transitions frequently involved in butterfly diversification processes. © 2012 Blackwell Publishing Ltd.

Llegeix més

Mountain waters as witnesses of global pollution

Catalan J., Bartrons M., Camarero L., Grimalt J.O. (2013) Mountain waters as witnesses of global pollution. Living with Water: Targeting Quality in a Dynamic World. : 31-67.
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Doi: 10.1007/978-1-4614-3752-9_2

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Mountains lakes, streams, and rivers, collectively known as headwaters, are popularly seen as waters of the highest quality. However, human-related pollution has reached remote areas of the planet everywhere through atmospheric transportation. Mountain freshwater ecosystems are extreme environments for life and thus are particularly sensitive to some new stressors. This chapter begins by summarizing the main features of mountain freshwater ecosystems and then comments on the effects they have historically suffered. It focuses particularly on two environmental problems: (1) acidification and (2) contamination with persistent organic pollutants. These problems are at different stages of development and knowledge. Acidification mechanisms are well understood, and mitigation actions have been applied successfully. The pace of recovery and interaction with climate change are now focusing research interests. In contrast, the environmental problem of persistent organic pollutants in mountain waters has been unveiled only recently. Some initially unexpected findings, such as the increasing concentration of some pollutants with altitude, have stirred further investigations on bioaccumulation processes, which are summarized here. Actions against contamination of sites far from the pollution sources, such as mountains, require the development of international protocols. The fight against acidification constitutes a successful example of such actions, and efforts against other atmospheric pollutants are following suit. These large-scale actions require adequate long-term monitoring networks, models for interpretating the results, and sound understanding of the mechanisms that underlie the observed patterns. Research may focus on: (1) increasing understanding of biotransformation of organic pollutants in natural conditions; (2) better evaluation of toxicological effects on both organisms and ecosystems as a whole; and (3) the ways that climate change influences the transport, accumulation, and toxicity of pollutants, a subject that cuts across all freshwater quality issues. © 2013 Springer Science+Business Media New York. All rights are reserved.

Llegeix més

Global change revealed by palaeolimnological records from remote lakes: A review

Catalan J., Pla-Rabes S., Wolfe A.P., Smol J.P., Ruhland K.M., Anderson N.J., Kopacek J., Stuchlik E., Schmidt R., Koinig K.A., Camarero L., Flower R.J., Heiri O., Kamenik C., Korhola A., Leavitt P.R., Psenner R., Renberg I. (2013) Global change revealed by palaeolimnological records from remote lakes: A review. Journal of Paleolimnology. 49: 513-535.
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Doi: 10.1007/s10933-013-9681-2

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Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with respect to past, purely natural variability in lake systems. Fostering conceptual and methodological bridges with other environmental disciplines will upturn contribution of remote lake palaeolimnology in solving existing and emerging questions in global change science and planetary stewardship. © 2013 Springer Science+Business Media Dordrecht.

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Empirical and physical estimation of Canopy Water Content: From CHRIS/PROBA Data

Cernicharo J., Verger A., Camacho F. (2013) Empirical and physical estimation of Canopy Water Content: From CHRIS/PROBA Data. Remote Sensing. 5: 5265-5284.
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Doi: 10.3390/rs5105265

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Efficient monitoring of Canopy Water Content (CWC) is a central feature invegetation studies. The potential of hyperspectral high spatial resolution CHRIS/PROBAsatellite data for the retrieval of CWC was here investigated using empirical and physical based approaches. Special attention was paid to the spectral band selection, inversion technique and training process. Performances were evaluated with ground measurements from the SEN3EXP field campaign over a range of crops. Results showed that the optimal band selection includes four spectral bands: one centered about 970 nm absorption feature which is sensible to Cw, and three bands in green, red and near infrared to estimate LAI and compensate from leaf- and canopy-level effects. A simple neural network with a single hidden layer of five tangent sigmoid transfer functions trained over PROSAIL radiative transfer simulations showed benefits in the retrieval performances compared with a look up table inversion approach (root mean square error of 0.16 kg/m2 vs. 0.22 kg/m2). The neural network inversion approach showed a good agreement and performances similar to an empirical up-scaling approach based on a multivariate iteratively re-weighted least squares algorithm, demonstrating the applicability of radiative transfer model inversion methods to CHRIS/PROBA for high spatial resolution monitoring of CWC. © 2013 by the authors.

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Soil microarthropod community testing: A new approach to increase the ecological relevance of effect data for pesticide risk assessment

Chelinho S., Domene X., Andres P., Natal-da-Luz T., Norte C., Rufino C., Lopes I., Cachada A., Espindola E., Ribeiro R., Duarte A.C., Sousa J.P. (2013) Soil microarthropod community testing: A new approach to increase the ecological relevance of effect data for pesticide risk assessment. Applied Soil Ecology. : 0-0.
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Doi: 10.1016/j.apsoil.2013.06.009

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In the present study, a new complementary approach combining the use of the natural soil microarthropod community and conventional test methods was used. The effects of soil contamination with the insecticide carbofuran on two geographically distinct microarthropod communities (Mediterranean and Tropical) were evaluated in their soils of origin under controlled laboratory conditions. After contamination of two agricultural soils from Portugal and Brazil, a gradient of concentrations was prepared. Soil cores were taken from the respective uncontaminated surrounding areas and the mesofauna of three cores was extracted directly to the test soil. After extracting the microarthropod communities to the test soil, these were incubated under laboratory conditions for 4 weeks, after which the mesofauna was extracted again. The organisms were assorted into higher taxonomic groups and Acari and Collembola were respectively assorted into order/sub-order/cohort and family. Collembolans were still classified according to morphological traits and used as a case-study of trait based risk assessment (TERA; Baird et al., 2008) of pesticides. The exposure to insecticide contamination caused the impoverishment of the taxonomic diversity in both communities. Significant shifts in the microarthropod community structure in the different carbofuran treatments were found for both soils, although effects were more pronounced in the assay performed with the soil from Brazil. Collembolans were the most affected group with a strong decline in their abundance. A dose-response relationship was observed, showing a consistent decline on the relative abundance of Isotomidae, closely followed by an increase of Entomobryidae. Contrastingly, Acari (especially Oribatida) tended to increase their numbers with higher concentrations. Trait based analysis of Collembola data suggested that a shift in the functional composition of the communities occurred due to carbofuran soil contamination and that species adapted to deeper soil layers were more vulnerable to insecticide toxicity. © 2013 Elsevier B.V. All rights reserved.

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