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.
Llorens P, Álvarez-Cobelas J, Latron J, Martínez-Vilalta J, Moreno G. (2011) Hydrology and biogeochemistry of Mediterranean forests. 2011. In: D Levia, D Carlyle-Moses, T Tanaka. Forest Hydrology and Biogeochemistry: Synthesis of Research and Future Directions. Springer-Verlag.
Martínez-Vilalta J (2011) Què determina la demografia dels nostres arbres?. UAB Divulga 06/2011.
Martínez-Vilalta J, Sol D, Terradas J. (2011) Un planeta a la deriva. Converses sobre el canvi global. Barcelona: RBA – La Magrana.
Mencuccini M, Hölttä T, Martinez-Vilalta J. (2011) Design Criteria for Models of the Hydraulic Systems of Tall Trees. 2011. In: FC Meinzer, T Dawson and B Lachenbruch. Size- and Age-Related Changes in Tree Structure and Function. Springer-Verlag.
Loepfe L., Martinez-Vilalta J., Piñol J. (2011) An integrative model of human-influenced fire regimes and landscape dynamics. Environmental Modelling and Software. 26: 1028-1040.EnllaçDoi: 10.1016/j.envsoft.2011.02.015
Fire regimes depend on climate, vegetation structure and human influences. Climate determines the water content in fuel and, in the longer term, the amount of biomass. Humans alter fire regimes through increased ignition frequency and by hindering the spread of fire through fire suppression and fuel fragmentation. Here, we present FIRE LADY (FIre REgime and LAndscape DYnamics), a spatially explicit fire regime model that takes into account daily weather data, topography, vegetation growth, fire behaviour, fire suppression and land use changes. In this model, vegetation growth depends on water availability, and stem diameter and stand density are the fundamental parameters. Fire behaviour is modelled using the Rothermel equations and taking into account both crown fire and spotting. Human influences on fire regime, such as ignition frequency, fire suppression and land use changes, are explicitly modelled. The model was calibrated for three regions in NE Spain and reproduces fire regimes, changes in land cover distribution and tree biomass with promising accuracy. The explicit modelling of human influences makes the model a useful and unique tool for assessing the impacts of climate change and informing local fire regime management strategies. © 2011 Elsevier Ltd.
Quero J.L., Sterck F.J., Martínez-Vilalta J., Villar R. (2011) Water-use strategies of six co-existing Mediterranean woody species during a summer drought. Oecologia. 166: 45-57.EnllaçDoi: 10.1007/s00442-011-1922-3
Drought stress is known to limit plant performance in Mediterranean-type ecosystems. We have investigated the dynamics of the hydraulics, gas exchange and morphology of six co-existing Mediterranean woody species growing under natural field conditions during a drought that continued during the entire summer. Based on the observed minimum leaf water potentials, our results suggest that the six co-existing species cover a range of plant hydraulic strategies, from isohydric to anisohydric. These differences are remarkable since the selected individuals grow within several meters of each other, sharing the same environment. Surprisingly, whatever the leaf water potentials were at the end of the dry period, stomatal conductance, photosynthesis and transpiration rates were relatively similar and low across species. This result contradicts the classic view that anisohydric species are able to maintain gas exchange for longer periods of time during drought stress. None of the plants showed the expected structural acclimation response to the increasing drought (reduction of leaf-to-sapwood area ratio), thereby rejecting the functional equilibrium hypothesis for our study system. Instead, three of the six species increased photosynthetic area at the branch level. The observed dissimilar patterns of gas exchange, hydraulics and morphology across species seem to be equally successful given that photosynthesis at the leaf level was maintained at similar rates over the whole dry period. © 2011 Springer-Verlag.
Vila-Cabrera A., Martinez-Vilalta J., Vayreda J., Retana J. (2011) Structural and climatic determinants of demographic rates of Scots pine forests across the Iberian Peninsula. Ecological Applications. 21: 1162-1172.EnllaçDoi: 10.1890/10-0647.1
The demographic rates of tree species typically show large spatial variation across their range. Understanding the environmental factors underlying this variation is a key topic in forest ecology, with far-reaching management implications. Scots pine (Pinus sylvestris L.) covers large areas of the Northern Hemisphere, the Iberian Peninsula being its southwestern distribution limit. In recent decades, an increase in severe droughts and a densification of forests as a result of changes in forest uses have occurred in this region. Our aim was to use climate and stand structure data to explain mortality and growth patterns of Scots pine forests across the Iberian Peninsula. We used data from 2392 plots dominated by Scots pine, sampled for the National Forest Inventory of Spain. Plots were sampled from 1986 to 1996 (IFN2) and were resampled from 1997 to 2007 (IFN3), allowing for the calculation of growth and mortality rates. We fitted linear models to assess the response of growth and mortality rates to the spatial variability of climate, climatic anomalies, and forest structure. Over the period of;10 years between the IFN2 and IFN3, the amount of standing dead trees increased 11-fold. Higher mortality rates were related to dryness, and growth was reduced with increasing dryness and temperature, but results also suggested that effects of climatic stressors were not restricted to dry sites only. Forest structure was strongly related to demographic rates, suggesting that stand development and competition are the main factors associated with demography. In the case of mortality, forest structure interacted with climate, suggesting that competition for water resources induces tree mortality in dry sites. A slight negative relationship was found between mortality and growth, indicating that both rates are likely to be affected by the same stress factors. Additionally, regeneration tended to be lower in plots with higher mortality. Taken together, our results suggest a large-scale self-thinning related to the recent densification of Scots pine forests. This process appears to be enhanced by dry conditions and may lead to a mismatch in forest turnover. Forest management may be an essential adaptive tool under the drier conditions predicted by most climate models. © 2011 by the Ecological Society of America.
Arnan X, López BC, Martínez-Vilalta J, Estorach M, Poyatos R (2011) The age of monumental olive trees (Olea europaea) in northeastern Spain. Dendrochronología doi: 10.1016/j.dendro.2011.02.002.
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