Martínez-Vilalta J, Mangirón M, Ogaya R, Sauret M, Serrano L, Peñuelas J, Piñol J (2003) Sap flow of three co-occurring Mediterranean woody species under varying atmospheric and soil water conditions. Tree Physiology 23:747-758.
Oliveras I., Martínez-Vilalta J., Jimenez-Ortiz T., Lledó M.J., Escarré A., Piñol J. (2003) Hydraulic properties of Pinus halepensis, Pinus pinea and Tetraclinis articulata in a dune ecosystem of Eastern Spain. Plant Ecology. 169: 131-141.EnllaçDoi: 10.1023/A:1026223516580
The hydraulic properties of Pinus pinea, Pinus halepensis and Tetraclinis articulata were studied in a coastal dune area from Eastern Spain. The measured variables include vulnerability to xylem embolism (vulnerability curves), hydraulic conductivity and carbon isotopic discrimination in leaves. Leaf water potentials were also monitored in the three studied populations during an extremely dry period. Our results showed that roots had always wider vessels and higher hydraulic conductivity than branches. Roots were also more vulnerable to xylem embolism and operated closer to their hydraulic limit (i.e., with narrower safety margins). Although it was not quantified, extensive root mortality was observed in the two pines during the study period, in agreement with the high values of xylem embolism (> 75%) predicted from vulnerability curves and the water potentials measured in the field. T. articulata was much more resistant to embolism than P. pinea and P. halepensis. Since T. articulata experienced also lower water potentials, safety margins from hydraulic failure were only slightly wider in this species than in the pines. Combining species and tissues, high resistance to xylem embolism was associated with low hydraulic conductivity and with high wood density. Both relationships imply a cost of having a resistant xylem. The study outlined very different water-use strategies for T. articulata and the pines. Whereas T. articulata had a conservative strategy that relied on the low vulnerability of its conducting system to drought-induced xylem embolism, the two pines showed regulatory mechanisms at different levels (i.e., embolism, root demography) that constrained the absorption of water when it became scarce.
Piñol J, Salvador R, Beven K (2002) Model calibration and uncertainty prediction of fire spread. In Viegas DX (ed) Forest Fire Research & Wildland Fire Safety. Millpress, Rotterdam, pp. 1-13. ISBN 90-77017-72-0.
Martínez-Vilalta J., Piñol J. (2002) Drought-induced mortality and hydraulic architecture in pine populations of the NE Iberian Peninsula. Forest Ecology and Management. 161: 247-256.EnllaçDoi: 10.1016/S0378-1127(01)00495-9
The summers of 1994 and, to a lesser extent, 1998 were particularly dry in eastern Spain. As a result, several plant species were severely affected. We estimated drought-induced mortality in several populations of three pine species that co-exist in the study area (Pinus nigra, P. pinaster and P. sylvestris). Hydraulic conductivity, vulnerability to xylem embolism, and tree-ring width were also measured for each population. Results showed that mortality only affected P. sylvestris, and that there were significant differences between two populations of this species. Although maximum hydraulic conductivity and vulnerability to embolism were almost identical among species and populations, they differed in other aspects of their hydraulic architecture. In particular, (1) hydraulic conductivity per unit of leaf area was lower in the most acutely affected P. sylvestris population. Lower leaf specific conductivity causes higher water potential gradients and, hence, higher levels of embolism (if vulnerabilities are alike). We suggest that this difference was the main cause of the observed mortality pattern. (2) P. pinaster showed higher water-use efficiency (WUE) (inferred from δ13C data) than the other two species. Regarding the response to drought at the population level, the most affected P. sylvestris population slightly increased growth after the 1994 drought, which we relate to a relaxation of competition among surviving individuals. The important drought-induced mortality observed in the study area suggests that drier climate (as predicted by climate change simulations) may endanger several P. sytvestris populations in the Mediterranean basin. © 2002 Elsevier Science B.V. All rights reserved.
Martínez-Vilalta J., Piñol J., Beven K. (2002) A hydraulic model to predict drought-induced mortality in woody plants: An application to climate change in the Mediterranean. Ecological Modelling. 155: 127-147.EnllaçDoi: 10.1016/S0304-3800(02)00025-X
The potential effects of climate change on vegetation are of increasing concern. In the Mediterranean region, the dominant impact of climate change is expected to be through the modification of water balance. In this paper we present a model developed to predict drought-induced mortality of woody plants under different climatic scenarios. The model is physiologically-based and simulates water transport within individual woody plants, which can be isolated or competing for a common water resource. The model assumes that plant mortality is controlled by the carbon balance: when the plant is unable to transport water to the leaves it ceases to acquire carbon and, if this situation lasts long enough, it can no longer survive. In the particular application that we report in this study, two evergreen species are compared, Quercus ilex and Phillyrea latifolia, which were very differently affected by the acute drought that occurred in E Spain in summer 1994. While in some Q. ilex populations the amount of individuals that dried completely was up to 80%, P. latifolia showed almost no damage. During the years 1999 and 2000, canopy transpiration was monitored using sap-flow sensors in individuals of these two species in a Holm-oak forest from NE Spain. A Generalised Likelihood Uncertainty Estimation (GLUE) approach was used to calibrate the model against sap-flow measurements. The only difference between species that was introduced 'a priori' was that Q. ilex was more vulnerable to xylem embolism than P. latifolia (based on our own measurements in the study area). During the calibration process the information provided by the measured sap flows was used to retain the more likely parameter sets for each species. These parameter sets were used in all the following simulations. The model was able to accurately simulate transpiration dynamics of the two species in the study area. When the meteorological conditions of summer 1994 were introduced, the model outputs also reproduced the differential impact that drought had on the two species studied. In the simulations under climate change two factors were explored: the increase in mean temperature (+ 1.5, + 3 and + 4.5°C) through its effect on ET, and the duration of summer drought. Under any of the scenarios, mortalities were much higher for Q. ilex: while this species was predicted to survive with less than 5% mortality droughts of up to 84-94 days, the mortality of P. latifolia reached 5% between days 133 and 150. For droughts longer than 3 months, which is approximately the current drought duration in the study area for dry years, the mortality of Q. ilex increased sharply. These results are discussed in relation to the possible long-term impacts of climate change on Q. ilex-dominated forests. © 2002 Elsevier Science B.V. All rights reserved.
Martínez-Vilalta J., Prat E., Oliveras I., Piñol J. (2002) Xylem hydraulic properties of roots and stems of nine Mediterranean woody species. Oecologia. 133: 19-29.EnllaçDoi: 10.1007/s00442-002-1009-2
We studied the hydraulic architecture and water relations of nine co-occurring woody species in a Spanish evergreen oak forest over the course of a dry season. Our main objectives were to: (1) test the existence of a trade-off between hydraulic conductivity and security in the xylem, and (2) establish the safety margins at which the species operated in relation to hydraulic failure, and compare these safety margins between species and tissues (roots vs. stems). Our results showed that the relationship between specific hydraulic conductivity (Ks) and resistance to cavitation followed a power function with exponent ≈-2, consistent with the existence of a trade-off between conductivity and security in the xylem, and also consistent with a linear relationship between vessel diameter and the size of inter-vessel pores. The diameter of xylem conduits, Ks and vulnerability to xylem embolism were always higher in roots than in stems of the same species. Safety margins from hydraulic failure were narrower in roots than in stems. Among species, the water potential (Ψ) at which 50% of conductivity was lost due to embolism ranged between -0.9 and <-8 MPa for roots and between -2.0 and <-8 MPa for stems. Vulnerability to xylem embolism followed a pattern of: Quercus ilex=Acer monspessulanum=Arbutus unedo=Sorbus torminalis=Cistus laurifolius>Cistus albidus=Ilex aquifolium>Phillyrea latifolia>Juniperus oxycedrus. Gas exchange and seasonal Ψ minima were in general correlated with resistance to xylem embolism. Hydraulic safety margins differed markedly among species, with some of them (J. oxycedrus, I. aquifolium, P. latifolia) showing a xylem overly resistant to cavitation. We hypothesize that this overly resistant xylem may be related to the shape of the relationship between Ks and security we have found.
Martínez-Vilalta J, Mangirón M, Ogaya R, Lloret F, Mastrantonio M, Piñol J, Sardans J, Terradas J, Peñuelas J (1999) Effectes de la sequera sobre l'alzinar mediterrani a Prades. Treb. Cent. Hist. Nat. Conca de Barberà 2:49-60
Martínez-Vilalta J, Piñol J (1999) Arquitectura hidràulica, vulnerabilitat a l'embolisme i resistència a la sequera en plantes llenyoses. Orsis 14:129-157.
Martínez-Vilalta J, Piñol J, Sauret M (1998) Vulnerability to xylem embolism of two mediterranean sclerophylls and their ability to cope with extreme drought events. The Earth's Changing Land GCTE-LUCC Open Science Conference on Global Change Abstracts. Institut Cartogràfic de Catalunya, Barcelona, pp. 68.
Viegas DX, Piñol J, Viegas MT, Ogaya R (2001) Estimating live fine fuels moisture content using meteorologically-based indices. International Journal of Wildland Fire 10:223-240.
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