Sus O, Martinez-Vilalta J, Poyatos R, Williams M (2012) Constraining key hydraulic parameters of Scots Pine through sapflow data assimilation along a climatic gradient. EGU Annual Meeting, Vienna, Austria, 22-27 April 2012. (Pòster).
Poyatos R, Aguadé D, Galiano L, Martínez-Vilalta J (2012) Defoliación inducida por sequía y límites hidráulicos a la asimilación asociados al agotamiento de carbohidratos de reserva en pino albar. II Coloquio de Primavera de Ecofisiología Forestal, Binifaldó (Mallorca), 19-23 Junio 2012.Comunicación oral.
Sterck F.J., Martínez-Vilalta J., Mencuccini M., Cochard H., Gerrits P., Zweifel R., Herrero A., Korhonen J.F., Llorens P., Nikinmaa E., Nolè A., Poyatos R., Ripullone F., Sass-Klaassen U. (2012) Understanding trait interactions and their impacts on growth in Scots pine branches across Europe. Functional Ecology. 26: 541-549.EnllaçDoi: 10.1111/j.1365-2435.2012.01963.x
Plants exhibit a wide variety in traits at different organizational levels. Intraspecific and interspecific studies have potential to demonstrate functional relationships and trade-offs amongst traits, with potential consequences for growth. However, the distinction between the correlative and functional nature of trait covariation presents a challenge because traits interact in complex ways. We present an intraspecific study on Scots pine branches and use functional multi-trait concepts to organize and understand trait interactions and their impacts on growth. Branch-level traits were assessed for 97 branches from 12 Scots pine sites across Europe. To test alternative hypotheses on cause-effect relationships between anatomical traits, hydraulic traits and branch growth, we measured for each branch: the tracheid hydraulic diameter, double cell wall thickness, cell lumen span area, wood density, cavitation vulnerability, wood-specific hydraulic conductivity, the leaf area to sapwood area ratio and branch growth. We used mixed linear effect models and path models to show how anatomical traits determine hydraulic traits and, in turn, how those traits influence growth. Tracheid hydraulic diameter was the best predictor of cavitation vulnerability (R 2=0·09 explained by path model) and specific conductivity (R 2=0·19) amongst anatomical traits. Leaf area to sapwood area ratio had the strongest direct effect on branch growth (R 2=0·19) and was positively associated with the tracheid hydraulic diameter (R 2=0·22). A number of bivariate correlations between traits could be explained by these functional relationships amongst traits. The plasticity in tracheid hydraulic diameter (10.0-15.1μm) and leaf area to sapwood area ratio (600-6051cm 2cm -2) and the maintenance of a minimum leaf water potential (between -2 and -2·5MPa) appear to drive the anatomical and hydraulic traits of Scots pine across Europe. These properties are major drivers of the functional trait network underlying the growth variation amongst pine branches and thus possibly contribute to the ecological success of pines at a local and continental scale. © 2012 The Authors. Functional Ecology © 2012 British Ecological Society.
Vanderklein D.W., Schäfer K.V.R., Martinez-Vilalta J. (2012) Crown conductance in dwarf, medium, and tall pitch pines in the Long Island Pine Plains. Trees - Structure and Function. 26: 1617-1625.EnllaçDoi: 10.1007/s00468-012-0736-1
The New York Pine Plains are a unique ecosystem with normal statured and a dwarfed variety of pitch pines (Pinus rigida Mill.). Growing interspersed with the dwarf pines are trees of intermediate height and features. Several hypotheses have been put forward as to why some of the trees are dwarfed, but none have been substantiated. In this study, we tested whether dwarf or medium trees are hydraulically limited compared to normally growing trees. Granier style sap flux sensors were installed in three to six trees of each tree type and sap flux was measured in early August 2004. Sap flux measurements were scaled to crown stomatal conductance using leaf area to sapwood area ratios for each tree. Contrary to expectation, dwarf and medium stature trees had very low leaf area to sapwood area ratios, but high crown stomatal conductances compared to normal trees. Analyses of leaf area, ring widths, and crown stomatal conductance indicate that differences between normal, and dwarf and medium pines are not due to hydraulic limitation, but that stunted growth may be due to other causes. © 2012 Springer-Verlag.
Vayreda J., Martinez-Vilalta J., Gracia M., Retana J. (2012) Recent climate changes interact with stand structure and management to determine changes in tree carbon stocks in Spanish forests. Global Change Biology. 18: 1028-1041.EnllaçDoi: 10.1111/j.1365-2486.2011.02606.x
Most temperate forests are accumulating carbon (C) and may continue to do so in the near future. However, the situation may be different in water-limited ecosystems, where the potentially positive effects of C and N fertilization and rising temperatures interact with water availability. In this study, we use the extensive network of plots of two consecutive Spanish national forest inventories to identify the factors that determine the spatial variation of the C stock change, growth, and mortality rate of forests in Peninsular Spain (below- and aboveground). We fitted general linear models to assess the response of C stock change and its components to the spatial variability of climate (in terms of water availability), forest structure (tree density and C stock), previous forest management, and the recent warming trend. Our results show that undisturbed forests in Peninsular Spain are accumulating C at a rate of ~1.4 Mg C ha -1 yr -1, and that forest structural variables are the main determinants of forest growth and C stock change. Water availability was positively related to growth and C accumulation. On the other hand, recent warming has reduced growth rate and C accumulation, especially in wet areas. Spatial variation in mortality (in terms of C loss) was mostly driven by differences in growth rate across plots, and was consistent with 'natural', self-thinning dynamics related to the recent abandonment of forest management over large areas of Spain, with the consequent increase in tree density and competition. Interestingly, the negative effect of warming on forest C accumulation disappears if only managed stands are considered, emphasizing the potential of forest management to mitigate the effects of climate change. However, the effect of forest management was weak and, in some cases, not significant, implying the need of further research on its impact. © 2011 Blackwell Publishing Ltd.
Vilà-Cabrera A., Rodrigo A., Martínez-Vilalta J., Retana J. (2012) Lack of regeneration and climatic vulnerability to fire of Scots pine may induce vegetation shifts at the southern edge of its distribution. Journal of Biogeography. 39: 488-496.EnllaçDoi: 10.1111/j.1365-2699.2011.02615.x
Aim Forest ecosystems dominated by fire-sensitive species could suffer shifts in composition under altered crown fire regimes mediated by climate change. The aims of this study were to: (1) study the spatio-temporal patterns and the climatic distribution of fires in Scots pine (Pinus sylvestris) forests during the last 31years in north-eastern Spain, (2) evaluate the climatic vulnerability to fire of these forests in Spain, (3) analyse the regeneration of Scots pine after fire, and (4) predict the mid-term maintenance or replacement of Scots pine in burned areas. Location Catalonia (north-eastern Spain): the southern distribution limit of Scots pine. Methods We characterized the spatio-temporal and the climatic distribution of fires that occurred in Catalonia between 1979 and 2009. We used a generalized linear model to characterize the climatic vulnerability to fire of Scots pine in the whole of Spain. We assessed the regeneration of the species after crown fires in nine burned areas in Catalonia. The resulting data were integrated into a stochastic matrix model to predict the mid-term maintenance or replacement of Scots pine in burned areas. Results During the last three decades, Scots pine forests distributed in dry sites were most affected by fire. Our assessment of the vulnerability to fire of Scots pine forests in Spain as a whole, based on climatic and topographical variables, showed that 32% of these forests are vulnerable to fire, and that this proportion could increase to 66% under a conservative climate change scenario. Field data showed almost no regeneration of Scots pine after crown fires, and a limited capacity to recolonize from unburned edges, even in relatively old fires, with 90% of recruits located in the first 25m from the edge. This process could be delayed by the elapsed time for new recruits to achieve reproductive maturity, which we estimated to be c.15years. Finally, our matrix model predicted the replacement of burned Scots pine forests by oak (Quercus sp.) forests, shrublands or mixed resprouter forests. Main conclusions Increased vulnerability to fire of Scots pine forests under future, warmer conditions may result in vegetation shifts at the southern edge of the distribution of the species. © 2011 Blackwell Publishing Ltd.
Yuste J.C., Barba J., Fernandez-Gonzalez A.J., Fernandez-Lopez M., Mattana S., Martinez-Vilalta J., Nolis P., Lloret F. (2012) Changes in soil bacterial community triggered by drought-induced gap succession preceded changes in soil C stocks and quality. Ecology and Evolution. 2: 3016-3031.EnllaçDoi: 10.1002/ece3.409
The aim of this study was to understand how drought-induced tree mortality and subsequent secondary succession would affect soil bacterial taxonomic composition as well as soil organic matter (SOM) quantity and quality in a mixed Mediterranean forest where the Scots pine (Pinus sylvestris) population, affected by climatic drought-induced die-off, is being replaced by Holm-oaks (HO; Quercus ilex). We apply a high throughput DNA pyrosequencing technique and 13C solid-state Nuclear Magnetic Resonance (CP-MAS 13C NMR) to soils within areas of influence (defined as an surface with 2-m radius around the trunk) of different trees: healthy and affected (defoliated) pines, pines that died a decade ago and healthy HOs. Soil respiration was also measured in the same spots during a spring campaign using a static close-chamber method (soda lime). A decade after death, and before aerial colonization by the more competitive HOs have even taken place, we could not find changes in soil C pools (quantity and/or quality) associated with tree mortality and secondary succession. Unlike C pools, bacterial diversity and community structure were strongly determined by tree mortality. Convergence between the most abundant taxa of soil bacterial communities under dead pines and colonizer trees (HOs) further suggests that physical gap colonization was occurring below-ground before above-ground colonization was taken place. Significantly higher soil respiration rates under dead trees, together with higher bacterial diversity and anomalously high representation of bacteria commonly associated with copiotrophic environments (r-strategic bacteria) further gives indications of how drought-induced tree mortality and secondary succession were influencing the structure of microbial communities and the metabolic activity of soils.©2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd.
Galiano L., Martínez-Vilalta J., Lloret F. (2011) Carbon reserves and canopy defoliation determine the recovery of Scots pine 4yr after a drought episode. New Phytologist. 190: 750-759.EnllaçDoi: 10.1111/j.1469-8137.2010.03628.x
Severe drought may increase physiological stress on long-lived woody vegetation, occasionally leading to mortality of overstory trees. Little is known about the factors determining tree survival and subsequent recovery after drought. We used structural equation modeling to analyse the recovery of Scots pine (Pinus sylvestris) trees 4yr after an extreme drought episode occurred in 2004-2005 in north-east Spain. Measured variables included the amount of green foliage, carbon reserves in the stem, mistletoe (Viscum album) infection, needle physiological performance and stem radial growth before, during and after the drought event. The amount of green leaves and the levels of carbon reserves were related to the impact of drought on radial growth, and mutually correlated. However, our most likely path model indicated that current depletion of carbon reserves was a result of reduced photosynthetic tissue. This relationship potentially constitutes a feedback limiting tree recovery. In addition, mistletoe infection reduced leaf nitrogen content, negatively affecting growth. Finally, successive surveys in 2009-2010 showed a direct association between carbon reserves depletion and drought-induced mortality. Severe drought events may induce long-term physiological disorders associated with canopy defoliation and depletion of carbon reserves, leading to prolonged recovery of surviving individuals and, eventually, to delayed tree death. © 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.
Gil D., Hernàndez-Sabaté A., Brunat M., Jansen S., Martínez-Vilalta J. (2011) Structure-preserving smoothing of biomedical images. Pattern Recognition. 44: 1842-1857.EnllaçDoi: 10.1016/j.patcog.2010.08.003
Smoothing of biomedical images should preserve gray-level transitions between adjacent tissues, while restoring contours consistent with anatomical structures. Anisotropic diffusion operators are based on image appearance discontinuities (either local or contextual) and might fail at weak inter-tissue transitions. Meanwhile, the output of block-wise and morphological operations is prone to present a block structure due to the shape and size of the considered pixel neighborhood. In this contribution, we use differential geometry concepts to define a diffusion operator that restricts to image consistent level-sets. In this manner, the final state is a non-uniform intensity image presenting homogeneous inter-tissue transitions along anatomical structures, while smoothing intra-structure texture. Experiments on different types of medical images (magnetic resonance, computerized tomography) illustrate its benefit on a further process (such as segmentation) of images. © 2010 Elsevier Ltd. All rights reserved.
Martínez-Vilalta J (2011) Què determina la demografia dels nostres arbres?. UAB Divulga 06/2011.
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