Josep Piñol

CLIMATE WARMING, WILDFIRE HAZARD, AND WILDFIRE OCCURRENCE IN COASTAL EASTERN SPAIN

A climatic series (1941 to 1994) from a Mediterranean locality of NE Spain was used to calculate two wildfire hazard indices based on daily meteorological data. Both fire hazard indices increased over this period, as a consequence of increasing mean daily maximum temperature and decreasing minimum daily relative humidity. These trends were observed in both mean values of the indices and in the number of very high risk days. Annual data on the number of wildfires and burned area also show an increase from 1968 to 1994, and are significantly correlated with both fire hazard indices. Although other non-meteorological causes (e.g., human activities, fuel accumulation) have likely contributed to the observed increase of wildfires, an effect of climatic warming on wildfire occurrence is supported by this relationship.

Estimation of plant water concentration by the reflectance Water Index WI (R900/R970)

Abstract Water Index WI (R900/R970) was used for the estimation of plant water concentration (PWC) by ground-based, reflectance measurements. Reflectance and PWC were measured for adult plants growing in the field throughout an annual cycle and in potted seedlings submitted to progressive desiccation. The species studied were characteristicly Mediterranean: Pinus halepensis, Quercus ilex, Quercus coccifera, Arbutus unedo, Cistus albidus, Cistus monspeliensis, Phillyrea angustifolia, Pistacia lentiscus and Brachypodium retusum . WI was significantly correlated with PWC when all the species were considered together, and with almost all the species considered individually, especially when a wider range of PWC was obtained by extreme dessication of experimental plants. The correlations increased when normalizing WI by NDVI. The wavelength of the trough corresponding to water absorption band tended to shift from 970-980 nm to lower wavelengths 930-950 nm with decreasing PWCs. Infrared measurement of plant temp...

Drought-induced mortality and hydraulic architecture in pine populations of the NE Iberian Peninsula

Abstract 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. sylvestris populations in the Mediterranean basin.

The hydraulic architecture of Pinaceae – a review

We reviewed the literature to examine the vulnerability to water stress-induced embolism of Pinaceae relative to other conifers and to study the inter-relationships among the main traits involved in the hydraulic function within the Pinaceae. Results showed that Pinaceae (particularly the genus Pinus) are more vulnerable to xylem embolism, and show less variability in this character, than other conifers. Detailed data from 12 populations of Pinaceae (11 species) from three different areas (Piñol and Sala 2000; Martínez-Vilalta and Piñol 2002; Oliveras et al. 2003) was used to study the relationships among hydraulic properties of stems. These included: leaf-to-wood area ratio (AL:AW), wood- and leaf-specific hydraulic conductivity (KW and KL, respectively), vulnerability to xylem embolism (Ψ50PLC), carbon isotope composition of needles (δ13C) and minimum needle water potential (minimum ΨL). Results showed that hydraulic properties tended to be more correlated among each other than with indicators of environmental (precipitation to potential evapotranspiration ratio, P/E) or physiological water stress (minimum ΨL). The only exception was an increase of δ13C with decreasing minimum ΨL and P/E. Overall, AL:AW ratio decreased with increasing vulnerability to xylem embolism, and with increasing KW and KL (P<0.05). We found a strong positive relationship between carbon isotope composition and the estimated maximum loss of conductivity due to xylem embolism under field conditions, suggesting stronger stomatal control in more vulnerable species with higher levels of native embolism. Overall, results are consistent with a range of drought-avoidance strategies to minimise the gradient of water potential through the xylem, and show that different relationships among traits are possible depending on the scale of study (individual vs. species or populations). The strong interdependence among hydraulic traits implies that no single trait is a sufficient predictor of drought-resistance in Pinaceae. Finally, it is hypothesised that the intrinsically vulnerable xylem of pines may limit their survival under extremely dry conditions.

Unraveling the life history of successful invaders

Successful Invaders Invasive species have been integrated into ecosystems worldwide, and in many cases can cause significant ecological and economic damage. Not all non-native species, however, become invasive species; thus there has been much effort put toward understanding what makes a non-native “colonizer” an invader. It has been thought that, in general, successful invaders tend to be those that produce a large amount of offspring over a very short period of time, however, this pattern is absent in many successful invaders. Sol et al. (p. 580) looked at over 2700 invasions by bird species across the world and found no relationship between population growth rate and invasion success, although rapidly reproducing species could have an advantage when the new environment resembled their native environment. Furthermore, in many cases, those species that could prioritize survival, and delay reproduction, were much more successful than those forced to reproduce regardless of environmental conditions. Allocating resources to long-lived adults is one means by which birds succeed in new niches. Despite considerable current interest in biological invasions, the common life-history characteristics of successful invaders remain elusive. The widely held hypothesis that successful invaders have high reproductive rates has received little empirical support; however, alternative possibilities are seldom considered. Combining a global comparative analysis of avian introductions (>2700 events) with demographic models and phylogenetic comparative methods, we show that although rapid population growth may be advantageous during invasions under certain circumstances, more generally successful invaders are characterized by life-history strategies in which they give priority to future rather than current reproduction. High future breeding expectations reduce the costs of reproductive failure under uncertain conditions and increase opportunities to explore the environment and respond to novel ecological pressures.

A hydraulic model to predict drought-induced mortality in woody plants: an application to climate change in the Mediterranean

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.

Effects of a Severe Drought on Water and Nitrogen Use by Quercus ilex and Phyllyrea latifolia

A severe drought that took place in Spain and other Mediterranean countries in 1994 produced a dieback of Quercus ilex trees on south-facing conglomerates but only minor defoliations in trees on north-facing schists. The foliar Δ13C of damaged trees continued to decrease in the next two wet years probably indicating increasing water use efficiency, and their δ15N continued to increase indicating progressive ecosystem N saturation and/or N losses whereas there were no significant changes in undamaged trees. Pre-drought Δ13C values were reached in the third year after the drought, but δ15N values did not yet recover. Another co-occurring small tree, Phyllyrea latifolia, did not show any damage and gained dominance in the most affected stands.

Modelling the hydrological response of Mediterranean catchments, Prades, Catalonia. The use of distributed models as aids to hypothesis formulation

This paper attempts to extend the physical arguments underlying the distributed TOPMODEL concepts in an application to the strongly seasonal contributing area responses in two adjacent small mediterranean catchments in the Prades region of Catalonia, Spain. A perceptual model of hydrological response in these catchments is used to suggest possible modifications of the model in a hypothesis testing framework, including an attempt to modify the topographic index approach to reflect the expansion of the effective area of subsurface flow during the wetting-up sequence. It is found that slight improvements in modelling efficiency are possible but that different model parameter distributions are appropriate for different parts of the record. The model was much more successful for the catchment producing the higher runoff volumes.

Ki-ras mutations in exocrine pancreatic cancer: Association with clinico-pathological characteristics and with tobacco and alcohol consumption

The aims of this study were (i) to assess the prevalence and spectrum of codon 12 Ki‐ras mutations in patients diagnosed with exocrine pancreatic cancer (EPC) in 2 general hospitals between 1980 and 1990, (ii) to analyze the association of this genetic alteration with clinical and pathological characteristics, and (iii) to determine the association of Ki‐ras mutations with tobacco and alcohol consumption. DNA was amplified from paraffin‐embedded tissue samples and mutations in codon 12 of Ki‐ras were detected using the artificial RFLP technique. Cox proportional‐hazards regression and unconditional logistic regression were applied. Codon 12 Ki‐ras mutations were detected in 30 of 51 cases for which molecular results were available. The amino‐acid substitutions were Asp (8), Val (6), and Arg (3). A double mutation, including always a Val, was detected in 5 cases. None of the 4 non‐ductal pancreatic neoplasms were mutated. The mutation prevalence was 79% in metastases and 54% in primary tumors. The risk of a mutated tumor was 3 times higher in alcohol drinkers than in non‐drinkers, and a linear trend was apparent. When age, gender, hospital, and tobacco and alcohol consumption were taken into account, a high risk for mutations was detected in patients who only smoked and in patients who only drank, but less so in patients who both smoked and drank. These results raise novel hypotheses regarding the role of tobacco and alcohol in EPC. Int. J. Cancer, 70:661–667, 1997.

Hydraulic properties of Pinus halepensis, Pinus pinea and Tetraclinis articulata in a dune ecosystem of Eastern Spain

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.