Martinez-Vilalta J, Mencuccini M, Alvarez X, Camacho J, Loepfe J, Pinol J (2012) Spatial distribution and packing of xylem conduits. 7th Plant Biomechanics International Conference, Clermont-Ferrand, France, 20-24 August 2012. (Comunicació oral).
Martínez-Vilalta J, Aguadé D, Banqué M, Barba J, Curiel Yuste J, Galiano L, Garcia N, Gómez M, Heres; AM, López BC, Lloret F, Poyatos R, Retana J, Sus O, Vayreda J, Vilà-Cabrera A (2012) Las poblaciones ibéricas de pino albar ante el cambio climático: con la muerte en los talones. Ecosistemas 21: 15-21.
Martínez-Vilalta J, Aguadé D, Banqué M, Barba J, Yuste JC, Galiano L, Garcia N, Gómez M, Hereş AM, López BC, Lloret F, Poyatos R, Retana J, Sus O, Vayreda J, Vilà-Cabrera A (2012) Las poblaciones ibéricas de pino albar ante el cambio climático: con la muerte en los talones. Revista Ecosistemas 21: 15–21.
Sus O, Martínez-Vilalta J, Poyatos R, Williams M (2012) Constraining key hydraulic parameters of Scots pine through sapﬂow data assimilation along a climatic gradient. Geophysical Research Abstracts 14: 10170. EGU General Assembly 2012,Vienna (Austria), 22-27 Abril 2012. Póster.
Lloret F., Escudero A., Iriondo J.M., Martínez-Vilalta J., Valladares F. (2012) Extreme climatic events and vegetation: The role of stabilizing processes. Global Change Biology. 18: 797-805.EnllaçDoi: 10.1111/j.1365-2486.2011.02624.x
Current climatic trends involve both increasing temperatures and climatic variability, with extreme events becoming more frequent. Increasing concern on extreme climatic events has triggered research on vegetation shifts. However, evidences of vegetation shifts resulting from these events are still relatively rare. Empirical evidence supports the existence of stabilizing processes minimizing and counteracting the effects of these events, reinforcing community resilience. We propose a demographic framework to understand this inertia to change based on the balance between adult mortality induced by the event and enhanced recruitment or adult survival after the event. The stabilizing processes potentially contributing to this compensation include attenuation of the adult mortality caused by the event, due to site quality variability, to tolerance, phenotypic variability, and plasticity at population level, and to facilitative interactions. Mortality compensation may also occur by increasing future survival due to beneficial effect on growth and survival of the new conditions derived from global warming and increased climatic variability, to lowered competition resulting from reduced density in affected stands, or to antagonistic release when pathogens or predators are vulnerable to the event or the ongoing climatic conditions. Finally, mortality compensation may appear by enhanced recruitment due to release of competition with established vegetation, for instance as a consequence of gap openings after event-caused mortality, or to the new conditions, which may be more favorable for seedling establishment, or to enhanced mutualistic interactions (pollination, dispersal). There are important challenges imposed by the need of long-term studies, but a research agenda focused on potentially stabilizing processes is well suited to understand the variety of responses, including lack of sudden changes and community inertia that are frequently observed in vegetation under extreme events. This understanding is crucial for the establishment of sound management strategies and actions addressed to improve ecosystem resilience under climate change scenarios. © 2011 Blackwell Publishing Ltd.
Loepfe L., Martinez-Vilalta J., Piñol J. (2012) Management alternatives to offset climate change effects on Mediterranean fire regimes in NE Spain. Climatic Change. 115: 693-707.EnllaçDoi: 10.1007/s10584-012-0488-3
Fire regime is affected by climate and human settlements. In the Mediterranean, the predicted climate change is likely to exacerbate fire prone weather conditions, but the mid- to long-term impact of climate change on fire regime is not easily predictable. A negative feedback via fuel reduction, for instance, might cause a non-linear response of burned area to fire weather. Also, the number of fires escaping initial control could grow dramatically if the fire meteorology is just slightly more severe than what fire brigades are prepared for. Humans can directly influence fire regimes through ignition frequency, fire suppression and land use management. Here we use the fire regime model FIRE LADY to assess the impacts of climate change and local management options on number of fires, burned area, fraction of area burned in large fires and forest area during the twenty-first century in three regions of NE Spain. Our results show that currently fuel-humidity limited regions could suffer a drastic shift of fire regime with an up to 8 fold increase of annual burned area, due to a combination of fuel accumulation and severe fire weather, which would result in a period of unusually large fires. The impact of climate change on fire regime is predicted to be less pronounced in drier areas, with a gradual increase of burned area. Local fire prevention strategies could reduce but not totally offset climate induced changes in fire regimes. According to our model, a combination of restoring the traditional rural mosaic and classical fire prevention would be the most effective strategy, as a lower ignition frequency reduces the number of fires and the creation of agricultural fields in marginal areas reduces their extent. © 2012 Springer Science+Business Media B.V.
Martínez-Vilalta J., Lloret F., Breshears D.D. (2012) Drought-induced forest decline: Causes, scope and implications. Biology Letters. 8: 689-691.EnllaçDoi: 10.1098/rsbl.2011.1059
A large number of episodes of forest mortality associated with drought and heat stress have been detected worldwide in recent decades, suggesting that some of the world's forested ecosystems may be already responding to climate change. Here, we summarize a special session titled 'Drought-induced forest decline: causes, scope and implications' within the 12th European Ecological Federation Congress, held in Ávila (Spain) from 25 to 29 September 2011. The session focused on the interacting causes and impacts of die-off episodes at the community and ecosystem levels, and highlighted recent events of drought- and heat-related tree decline, advances in understanding mechanisms and in predicting mortality events, and diverse consequences of forest decline. Talks and subsequent discussion noted a potentially important role of carbon that may be interrelated with plant hydraulics in the multi-faceted process leading to drought-induced mortality; a substantial and yet understudied capacity of many forests to cope with extreme climatic events; and the difficulty of separating climate effects from other anthropogenic changes currently shaping forest dynamics in many regions of the Earth. The need for standard protocols and multi-level monitoring programmes to track the spatiotemporal scope of forest decline globally was emphasized as critical for addressing this emerging environmental issue. © 2011 The Royal Society.
Martínez-Vilalta J., López B.C., Loepfe L., Lloret F. (2012) Stand- and tree-level determinants of the drought response of Scots pine radial growth. Oecologia. 168: 877-888.EnllaçDoi: 10.1007/s00442-011-2132-8
Characterizing the responses of key tree species to extreme climatic events may provide important information for predicting future forest responses to increased climatic variability. Here we aimed at determining which tree- and stand-level attributes were more closely associated with the effect of a severe drought on the radial growth of Scots pine, both in terms of immediate impact and recovery after the drought event. Our dataset included tree-ring series from 393 plots located close to the dry limit of the species range. Time series analysis and mixed-effects models were used to study the growth of each tree and its detailed response to a severe drought event that occurred in 1986. Our results showed that the radial growth responses of Scots pine were determined primarily by tree-level characteristics, such as age and previous growth rate, and secondarily by stand basal area and species richness, whereas local climate had a relatively minor effect. Fast-growing trees were more severely affected by the drought and retained proportionally lower growth rates up to three years after the episode. In absolute terms, however, fast-growing trees performed better both during and after the event. Older trees were found to be less resilient to drought. The effect of stand basal area and species richness indicated that competition for resources worsened the effects of drought, and suggested that the effect of interspecific competition may be particularly detrimental during the drought year. © 2011 Springer-Verlag.
Martínez-Vilalta J., Mencuccini M., Álvarez X., Camacho J., Loepfe L., Piñol J. (2012) Spatial distribution and packing of xylem conduits. American Journal of Botany. 99: 1189-1196.EnllaçDoi: 10.3732/ajb.1100384
Premise of the study: The hydraulic properties of the xylem determine the ability of plants to transport water from the soil to the leaves and to cope with important stress factors such as frost and drought. Hydraulic properties have usually been studied as a function of the anatomy of xylem conduits and their pits, but recent studies have proposed that system-level properties, related to the topology of the xylem network, may also play a role. Here we study how the spatial arrangement of conduits in xylem cross sections affects the relationship between mean conduit lumen area and conduit density (packing function) across species.Methods: Point pattern analysis was used to describe the spatial distribution of xylem conduits in 97 woody species. The effect of conduit aggregation on the packing function was tested using phylogenetic generalized least squares. A hydraulic model with an explicit description of the topology of the xylem network was used to interpret the functional significance of our findings.Key results: The spatial arrangement of conduits affected the packing function across species, so that species with aggregated distributions tended to have lower conduit densities for a given conduit size and lower conduit lumen fractions. According to our modeling results, the higher conduit-to-conduit connectivity of species with aggregated distributions allows them to achieve higher hydraulic conductivity. Species with aggregated conduits, however, pay a cost in terms of increased vulnerability to embolism.Conclusions: The spatial arrangement of conduits affects the fundamental structural and functional attributes of the xylem. © 2012 Botanical Society of America.
Mencuccini M, Martínez-Vilalta J, Hölttä T (2012) Structural limitations of water and sugar transport in trees during drought: Model characterization of the relative importance of xylem embolism, carbon starvation, and lack of phloem transport. ESA Annual Meeting 2012, Portland, OR, United States of America, 5-10 August 2012. (Comunicació oral convidada).
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