Lecina-Diaz J., Alvarez A., Retana J. (2014) Extreme fire severity patterns in topographic, convective and wind-driven historical wildfires of mediterranean pine forests. PLoS ONE. 9: 0-0.EnllaçDoi: 10.1371/journal.pone.0085127
Crown fires associated with extreme fire severity are extremely difficult to control. We have assessed fire severity using differenced Normalized Burn Ratio (dNBR) from Landsat imagery in 15 historical wildfires of Pinus halepensis Mill. We have considered a wide range of innovative topographic, fuel and fire behavior variables with the purposes of (1) determining the variables that influence fire severity patterns among fires (considering the 15 wildfires together) and (2) ascertaining whether different variables affect extreme fire severity within the three fire types (topographic, convective and wind-driven fires). The among-fires analysis showed that fires in less arid climates and with steeper slopes had more extreme severity. In less arid conditions there was more crown fuel accumulation and closer forest structures, promoting high vertical and horizontal fuel continuity and extreme fire severity. The analyses carried out for each fire separately (within fires) showed more extreme fire severity in areas in northern aspects, with steeper slopes, with high crown biomass and in climates with more water availability. In northern aspects solar radiation was lower and fuels had less water limitation to growth which, combined with steeper slopes, produced more extreme severity. In topographic fires there was more extreme severity in northern aspects with steeper slopes and in areas with more water availability and high crown biomass; in convection-dominated fires there was also more extreme fire severity in northern aspects with high biomass; while in wind-driven fires there was only a slight interaction between biomass and water availability. This latter pattern could be related to the fact that wind-driven fires spread with high wind speed, which could have minimized the effect of other variables. In the future, and as a consequence of climate change, new zones with high crown biomass accumulated in non-common drought areas will be available to burn as extreme severity wildfires. © 2014 Lecina-Diaz et al.
Llusia J., Bermejo-Bermejo V., Calvete-Sogo H., Penuelas J. (2014) Decreased rates of terpene emissions in Ornithopus compressus L. and Trifolium striatum L. by ozone exposure and nitrogen fertilization. Environmental Pollution. 194: 69-77.EnllaçDoi: 10.1016/j.envpol.2014.06.038
Increasing tropospheric ozone (O3) and nitrogen soil availability (N) are two of the main drivers of global change. They both may affect gas exchange, including plant emission of volatiles such as terpenes. We conducted an experiment using open-top chambers to analyze these possible effects on two leguminous species of Mediterranean pastures that are known to have different O3 sensitivity, Ornithopus compressus and Trifolium striatum. O3 exposure and N fertilization did not affect the photosynthetic rates of O. compressus and T. striatum, although O3 tended to induce an increase in the stomatal conductance of both species, especially T. striatum, the most sensitive species. O3 and N soil availability reduced the emission of terpenes in O. compressus and T. striatum. If these responses are confirmed as a general pattern, O3 could affect the competitiveness of these species. © 2014 Elsevier Ltd. All rights reserved.
Llusia J., Sardans J., Niinemets U., Owen S.M., Penuelas J. (2014) A screening study of leaf terpene emissions of 43 rainforest species in Danum Valley Conservation Area (Borneo) and their relationships with chemical and morphological leaf traits. Plant Biosystems. 148: 307-317.EnllaçDoi: 10.1080/11263504.2013.770803
We have conducted a screening study of leaf terpene emissions for 43 rainforest woody species of Borneo. To the best of our knowledge, this study reports for first time the terpene emission capacity of 43 species belonging to 22 genera of rainforest woody plant species. We have used a general lineal model with phylogenetic control by the phylogenetic distance matrix when necessary. The proportion of the species that emitted terpenes in this set of Borneo woody species was 95% and the species average total terpene emissions of emitting species were 0.04-11.6 μg g-1 h-1, which is in the range of the reported emissions in similar screening studies conducted in other biomes. Altogether, 85 terpene compounds were detected, and 11 common monoterpenes and sesquiterpenes were identified and quantified. Only two of the terpenes, ocimene and γ-terpinene, of the 11 determined compounds showed a phylogenetic signal. No significant relationships were found between the terpene emissions and the physiological, chemical and morphological foliar traits and the data also showed a lock of constant applicability of the "excess carbon" hypothesis for this set of species. This evidence suggests multiple and diverse factors and conditions driving plant chemistry in the tropical forests. © 2013 © 2013 Società Botanica Italiana.
Loepfe L., Rodrigo A., Lloret F. (2014) Two thresholds determine climatic control of forest fire size in Europe and northern Africa. Regional Environmental Change. 14: 1395-1404.EnllaçDoi: 10.1007/s10113-013-0583-7
Fire weather indices predict fire extent from meteorological conditions assuming a monotonic function; this approach is frequently used to predict future fire patterns under climate change scenarios using linear extrapolation. However, the relationship between weather and fire extent may potentially depend on the existence of fuel moisture content thresholds above which this relationship changes dramatically, challenging this statistical approach. Here, we combine the continuous and the threshold approaches to analyze satellite-detected fires in Europe during 2001-2010 in relation to meteorological conditions, showing that fire size response to decreasing fuel moisture content follows a ramp function, i.e., with two plateaus separated by a phase of monotonic increase. This study confirms that at continental and high-resolution temporal scales, large fires are very unlikely to occur under moist conditions, but it also reveals that fire size stops to be controlled by fuel moisture content above a given threshold of dryness. Thus, fuel moisture content control only applies when fire is not limited by other factors such as fuel load, as large fires were virtually absent during the considered period in dry regions with less than 500 mm of average annual precipitation, i.e., low-productive areas where fuel amount would be scarce and discontinuous. In regions with sufficient fuel, other factors such as fire suppression or fuel discontinuity can impede large fires even under very dry weather conditions. These findings are relevant under current climatic trends in which the fire season length, in terms of number of days with drought code values above the observed thresholds (break points), is increasing in many parts of the Mediterranean, while it is decreasing in eastern Europe and remains unchanged in central Europe. © 2014 Springer-Verlag Berlin Heidelberg.
Longo A.F., Ingall E.D., Diaz J.M., Oakes M., King L.E., Nenes A., Mihalopoulos N., Violaki K., Avila A., Benitez-Nelson C.R., Brandes J., McNulty I., Vine D.J. (2014) P-NEXFS analysis of aerosol phosphorus delivered to the Mediterranean Sea. Geophysical Research Letters. 41: 4043-4049.EnllaçDoi: 10.1002/2014GL060555
Biological productivity in many ocean regions is controlled by the availability of the nutrient phosphorus. In the Mediterranean Sea, aerosol deposition is a key source of phosphorus and understanding its composition is critical for determining its potential bioavailability. Aerosol phosphorus was investigated in European and North African air masses using phosphorus near-edge X-ray fluorescence spectroscopy (P-NEXFS). These air masses are the main source of aerosol deposition to the Mediterranean Sea. We show that European aerosols are a significant source of soluble phosphorus to the Mediterranean Sea. European aerosols deliver on average 3.5 times more soluble phosphorus than North African aerosols and furthermore are dominated by organic phosphorus compounds. The ultimate source of organic phosphorus does not stem from common primary emission sources. Rather, phosphorus associated with bacteria best explains the presence of organic phosphorus in Mediterranean aerosols. © 2014. American Geophysical Union. All Rights Reserved.
Lonsdale J., Minunno F., Mencuccini M., Perks M. (2014) Bayesian calibration and Bayesian model comparison of a stand level dynamic growth model for Sitka spruce and Scots pine. Forestry. 88: 326-335.EnllaçDoi: 10.1093/forestry/cpv003
Growth models continue to be of importance in modern multi-functional forestry to provide forecasts. Bayesian calibrations allow both model structure and parameters to be assessed simultaneously in a probabilistic framework, providing a model with which forecasts and their uncertainty can be better understood and quantified using posterior probability distributions. A Bayesian calibration of a stand-level dynamic growth (SLeDG) model is carried out for both Sitka spruce and Scots pine in the UK for the first time. The calibration used the differential evolution Markov-Chain method to reduce the required number of iterations for inference. Two different model structures were considered for estimating local stand productivity: one using the measured height-age relationship, and one using estimated site yield class. The height-age relationship was shown to be more probable for both species in a Bayesian model comparison (total model probability$=$0.64 and 0.58 for Sitka spruce and Scots pine, respectively), although metrics of model performance were similar for both model structures ($R2 \geq 0.88$ in all variables). A complete calibration (using all data) of the more probable model structure was then completed, and excellent model fit was observed ($R2 >0.95$ for all variables in both species). Example forecasts using the output from the calibration were demonstrated, and are compatible with existing yield tables for both species. This method could be applied to other species or other model structures in the future. © Institute of Chartered Foresters, 2015.
Lopez-Bustins J.-A., Pla E., Nadal M., de Herralde F., Save R. (2014) Global change and viticulture in the Mediterranean region: A case of study in north-eastern Spain. Spanish Journal of Agricultural Research. 12: 78-88.EnllaçDoi: 10.5424/sjar/2014121-4808
Viticulture in the Mediterranean region has been improved by agronomic methods based on ecophysiological and genetic knowledge of the species and varieties cultivated. Plant growth, yield and quality are highly dependent on climate. Grape sugar content and wine alcohol content are considered as important quality parameters. The objective of our study is to analyse the effects of the current global change on the percentage of alcohol by volume (ABV) in red wines from vineyards located in the Montsant Designation of Origin (DO) (Priorat County, north-eastern Spain). We present an annual series of percentage of ABV in red wines over the 1984-2008 period (25 years), which is one of the longest series of this viticultural variable in Spain. We do not detect any significant trend of alcohol levels in red wines from the Montsant DO along the 1984-2004 subperiod, but a sharp increase about 1% (by volume) is observed after 2004; we statistically checked that the last four years constitute an outlier period in the series. We consider climate evolution over the 1984-2004 period in the study area in order to find some relation with alcohol levels in red wines. Agronomic practices and land cover changes are also taken into account. Results show that the interannual variability of the alcohol levels in red wines are partially explained by temperature and precipitation conditions few days before the vintage. The high percentages of ABV since 2005 may be associated with new trends in viticulture techniques rather than with climate change.
Manzano-Piedras E., Marcer A., Alonso-Blanco C., Pico F.X. (2014) Deciphering the adjustment between environment and life history in annuals: Lessons from a geographically-explicit approach in Arabidopsis thaliana. PLoS ONE. 9: 0-0.EnllaçDoi: 10.1371/journal.pone.0087836
The role that different life-history traits may have in the process of adaptation caused by divergent selection can be assessed by using extensive collections of geographically-explicit populations. This is because adaptive phenotypic variation shifts gradually across space as a result of the geographic patterns of variation in environmental selective pressures. Hence, large-scale experiments are needed to identify relevant adaptive life-history traits as well as their relationships with putative selective agents. We conducted a field experiment with 279 geo-referenced accessions of the annual plant Arabidopsis thaliana collected across a native region of its distribution range, the Iberian Peninsula. We quantified variation in life-history traits throughout the entire life cycle. We built a geographic information system to generate an environmental data set encompassing climate, vegetation and soil data. We analysed the spatial autocorrelation patterns of environmental variables and life-history traits, as well as the relationship between environmental and phenotypic data. Almost all environmental variables were significantly spatially autocorrelated. By contrast, only two life-history traits, seed weight and flowering time, exhibited significant spatial autocorrelation. Flowering time, and to a lower extent seed weight, were the life-history traits with the highest significant correlation coefficients with environmental factors, in particular with annual mean temperature. In general, individual fitness was higher for accessions with more vigorous seed germination, higher recruitment and later flowering times. Variation in flowering time mediated by temperature appears to be the main life-history trait by which A. thaliana adjusts its life history to the varying Iberian environmental conditions. The use of extensive geographically-explicit data sets obtained from field experiments represents a powerful approach to unravel adaptive patterns of variation. In a context of current global warming, geographically-explicit approaches, evaluating the match between organisms and the environments where they live, may contribute to better assess and predict the consequences of global warming. © 2014 Manzano-Piedras et al.
Margalef O., Martinez Cortizas A., Kylander M., Pla-Rabes S., Canellas-Bolta N., Pueyo J.J., Saez A., Valero-Garces B.L., Giralt S. (2014) Environmental processes in Rano Aroi (Easter Island) peat geochemistry forced by climate variability during the last 70kyr. Palaeogeography, Palaeoclimatology, Palaeoecology. 414: 438-450.EnllaçDoi: 10.1016/j.palaeo.2014.09.025
We analyze the geochemistry of Rano Aroi mire record (Easter Island) using bulk peat composition (C, N, S) and stable isotopes (δ13C, δ15N, δ34S) and major, minor and trace elemental compositions obtained by ICP-AES (Al, Ti, Zr, Sc, V, Y, Fe, Mn, Th, Ba, Ca, Mg and Sr). Peat geochemistry and the pollen record are used to reconstruct the environmental changes during the last 70kyr BP. Principal component analysis on ICP-AES data revealed that three main components account for the chemical signatures of the peat. The first component, characterized by lithogenic elements (combined signal of V, Al, Sc, Y, Cr, Cd, Ti, Zr and Cu), evidences long-term changes in the basal fluxes of mineral material into the mire. This component, in combination with stable isotopes and pollen data suggests a link between soil erosion and vegetation cover changes in the Rano Aroi watershed. The second component is identified by the signal of Fe, Mn, Th, Ba, Zr and Ti, and is indicative of strong runoff events during enhanced precipitation periods. The third component (tied mainly to Ca, Sr and Mg) reflects a strong peat oxidation event that occurred during an arid period with more frequent droughts, sometime between 39 and 31kyr BP. Correlation coefficients and a multiple regression model (PCR analysis) between peat organic chemistry and the principal components of ICP-AES analysis were calculated. Isotope chemistry of the peat organic matter further contributes to define Rano Aroi environmental history: δ13C data corroborates a vegetation shift documented by the palynological record from C4 to C3 between 55 and 45calkyr BP; the δ15N record identifies periods of changes in mire productivity and denitrification processes, while the δ34S peat signature indicates a marine origin of S and significant diagenetic cycling. The geochemical and environmental evolution of Rano Aroi mire is coherent with the regional climatic variability and suggests that climate was the main forcing in mire evolution during the last 70kyr BP. The coupling of geochemical and biological proxies improves our ability to decipher depositional processes in tropical and subtropical peatlands and to use these sequences for paleoenvironmental and paleoclimate reconstructions.
Marks E.A.N., Alcaniz J.M., Domene X. (2014) Unintended effects of biochars on short-term plant growth in a calcareous soil. Plant and Soil. : 0-0.EnllaçDoi: 10.1007/s11104-014-2198-2
Background and aims Biochar has demonstrably improved crop yields in weathered and acidic soils, but studies in calcareous soils are particularly lacking, so biochar effects on plant growth was investigated under these conditions. Methods Six biochars were obtained from different feedstocks and production technologies. Chemical characterization of fresh biochars included total and extractable nutrients, labile carbon, and Fourier transform infrared spectroscopy. Extractable nutrients were also evaluated in biochar-soil mixtures with a basic (pH >8.2) test soil. Bioassays with lettuce and ryegrass were carried out to relate biochar chemical properties to effects on plant biomass. Results A sewage sludge slow pyrolysis char was stimulatory to plant growth, as was a slow pyrolysis pine wood char at an intermediate concentration, while gasification and fast-pyrolysis pine and poplar wood chars were strongly inhibitory, with reductions in biomass at realistic application rates of 5-19 t ha-1. Conclusions Statistical comparison of plant responses with biochar composition led to the assessment that plant responses were most correlated with volatile matter content and total P content, whose availability was likely regulated by pH and Ca content. Potential effects of phytotoxins were considered, but these were seen to be much less probable than effects due to nutrient availability. © 2014 Springer International Publishing Switzerland.
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