Poyatos R., Martínez-Vilalta J., Čermák J., Ceulemans R., Granier A., Irvine J., Köstner B., Lagergren F., Meiresonne L., Nadezhdina N., Zimmermann R., Llorens P., Mencuccini M. (2007) Plasticity in hydraulic architecture of Scots pine across Eurasia. Oecologia. 153: 245-259.EnllaçDoi: 10.1007/s00442-007-0740-0
Widespread tree species must show physiological and structural plasticity to deal with contrasting water balance conditions. To investigate these plasticity mechanisms, a meta-analysis of Pinus sylvestris L. sap flow and its response to environmental variables was conducted using datasets from across its whole geographical range. For each site, a Jarvis-type, multiplicative model was used to fit the relationship between sap flow and photosynthetically active radiation, vapour pressure deficit (D) and soil moisture deficit (SMD); and a logarithmic function was used to characterize the response of stomatal conductance (G s) to D. The fitted parameters of those models were regressed against climatic variables to study the acclimation of Scots pine to dry/warm conditions. The absolute value of sap flow and its sensitivity to D and SMD increased with the average summer evaporative demand. However, relative sensitivity of G s to D (m/G s,ref, where m is the slope and G s,ref is reference G s at D = 1 kPa) did not increase with evaporative demand across populations, and transpiration per unit leaf area at a given D increased accordingly in drier/warmer climates. This physiological plasticity was linked to the previously reported climate- and size-related structural acclimation of leaf to sapwood area ratios. G s,ref, and its absolute sensitivity to D (m), tended to decrease with age/height of the trees as previously reported for other pine species. It is unclear why Scots pines have higher transpiration rates at drier/warmer sites, at the expense of lower water-use efficiency. In any case, our results suggest that these structural adjustments may not be enough to prevent lower xylem tensions at the driest sites. © 2007 Springer-Verlag.
Poyatos R., Villagarcía L., Domingo F., Piñol J., Llorens P. (2007) Modelling evapotranspiration in a Scots pine stand under Mediterranean mountain climate using the GLUE methodology. Agricultural and Forest Meteorology. 146: 13-28.EnllaçDoi: 10.1016/j.agrformet.2007.05.003
Canopy transpiration (Ec) and soil evaporation (Es) in a Mediterranean Scots pine stand were simulated using a two-layer model, with a Jarvis-type submodel of canopy stomatal conductance (Gs) and a soil resistance to evaporation expressed as a function of superficial soil moisture. Sap flow measurements and soil evaporation data, together with meteorological and soil moisture variables were used to calibrate the model. Gs was calibrated using the generalized likelihood uncertainty estimation (GLUE) methodology, first with data from the year 2004, a year characterised by mild meteorological conditions. Then, data from the year 2003, which included an intense summer drought, was used to update the results from the previous calibration. The discrepancy between the diurnal courses of modelled and measured Ec using best-fit parameters was not related to any particular situation of meteorology or soil moisture. Model performance improved at the daily scale, but the model failed to simulate Ec adequately during the year 2005. Maximum modelled Es rates were 0.7 mm day-1 with the ratio Es/Ec being typically under 0.3 during the growing season. The GLUE analysis revealed that parameters representing reference stomatal aperture at a vapour pressure deficit (D) value equal to 1 kPa (Gs,ref), and sensitivity to D (m) were the most relevant, and were consistent with the hydraulic theory of stomatal regulation. Parameters controlling the response to superficial soil moisture deficit only appeared sensitive in the calibration with data from the year 2003, suggesting that response to deeper soil layers should also be considered in the model. Updating the original calibration reduced predictive uncertainty and constrained the value of some parameters. Nevertheless, it seems that representations of variable plant and soil hydraulic resistances, are required to simulate long-term Ec in seasonally-dry Mediterranean forest stands. © 2007 Elsevier B.V. All rights reserved.
Quevedo L., Rodrigo A., Espelta J.M. (2007) Post-fire resprouting ability of 15 non-dominant shrub and tree species in Mediterranean areas of NE Spain. Annals of Forest Science. 64: 883-890.EnllaçDoi: 10.1051/forest:2007070
Post-fire resprouting ability of the non-dominant tree and shrub species of the Mediterranean Basin has not yet been experimentally tested, although this group contributes to maintain the richness of Mediterranean plant communities. In this study, we have analyzed the post-fire recovery ability of 15 woody species that occur in relatively low abundance in dry and sub humid Mediterranean areas in NE of Spain. The main goals have been: (i) to determine experimentally the post-fire resprouting ability of these species and (ii) to compare the abundance of these species in areas affected by wildland fires and in unburned areas. We have observed a high resprouting ability after prescribed burning of most species except for Juniperus communis and J. phoenicea which showed a null resprouting. As the species with high resprouting ability showed similar presence in burned and unburned areas, we can conclude that wildfires are not a factor that constrains the presence of these species in Mediterranean woodlands. However, we found a reduction in the abundance of J. communis and J. phoenicea at the regional level after wildland fires. © INRA, EDP Sciences, 2007.
Riera P., Peñuelas J., Farreras V., Estiarte M. (2007) Valuation of climate-change effects on Mediterranean shrublands. Ecological Applications. 17: 91-100.EnllaçDoi: 10.1890/1051-0761(2007)017[0091:VOCEOM]2.0.CO;2
In general, the socioeconomic analysis of natural systems does not enter into the realms of natural science. This paper, however, estimates the human-welfare effects of possible physicochemical and biological impacts of climate change on Mediterranean shrublands over the coming 50 years. The contingent choice method was applied to elicit the trade-offs in perceived values for three climate-sensitive attributes of shrubland (plant cover, fire risk, and soil erosion) and for the costs of programs designed to mitigate changes. Soil erosion was found to be the attribute of shrubland that most concerned the population, followed by fire risk and then plant cover. An increase of 1% in the shrubland area affected by erosion was estimated to cost each person on average 2.9 euros per year in terms of lost welfare, a figure that is equivalent in terms of perceptions of social welfare to an increase of 0.24% in the shrub area burned annually and a decrease of 3.19% in the area of plant cover. These trade-off values may help ecologists, policy makers, and land managers to take social preferences into account. © 2007 by the Ecological Society of America.
Rodrigo A., Quintana V., Retana J. (2007) Fire reduces Pinus pinea distribution in the northeastern Iberian Peninsula. Ecoscience. 14: 23-30.EnllaçDoi: 10.2980/1195-6860(2007)14[23:FRPPDI]2.0.CO;2
This study analyzes the recovery of Pinus pinea in forested areas that have burned in the last 30 years. The main objectives of the study were (i) to analyze the success of the regeneration of P. pinea in areas with the presence or absence of surviving adult trees and (ii) to investigate whether or not the post-fire response of P. pinea may affect its present distribution. We analyzed the survival of adult P. pinea trees and the regeneration of P. pinea seedlings in 8 areas burned by wildfires in Catalonia (northeast Spain) between 1979 and 2001. This study shows that the inability of seedlings to establish after fire, together with the short seed dispersal distance of this species and the low level of seedling survival, renders the natural regeneration of P. pinea in burned areas difficult. A comparison of the presence of P. pinea in plots located in burned and unburned areas throughout its distribution area in Catalonia indicates that its presence at the regional level is clearly reduced after fire. Moreover, in the areas where it persists, tree density and cover are smaller than in unburned areas. This decrease of P. pinea forests is exacerbated by the increase in surface area burned by forest fires during recent decades in the Mediterranean basin and by decreasing profits associated with this species as a consequence of the falling value of its pine kernel.
Rydgren K., Økland R.H., Picó F.X., De Kroon H. (2007) Moss species benefits from breakdown of cyclic rodent dynamics in boreal forests. Ecology. 88: 2320-2329.EnllaçDoi: 10.1890/06-1634.1
Bryophytes have increased in abundance in northern regions, and climate changes have been proposed to account for this change. However, changes in the population dynamics of microtine rodents may also contribute to changes in bryophyte abundance. New evidence indicates a tendency for microtine rodent population oscillations to change from periodicity of 3-5 years to become irregular or acyclic. The impact on ecosystem functioning is potentially great. We study the impact of variation in microtine rodent population characteristics, such as cycle length and amplitude, on the population dynamics of the boreal, clonal moss Hylocomium splendens. We use experimental and observational demographic data to construct 127 scenarios representing all combinations of disturbance type (gap formation and/or clipping), period (cyclic with 4, 6, 12, or 24 years between rodent peaks; or acyclic with constant or stochastically varying annual disturbance severity) and disturbance severity (fraction of individuals affected by disturbance in each year relative to the maximum disturbance carried out in the field experiment; seven levels). Population data collected in the field during 13 years were used as a baseline scenario. By subjecting all scenarios to stochastic matrix modeling, we demonstrate considerable impact of microtine rodent on the population dynamics of H. splendens, most notably when rodent populations fluctuate with short periods and high peak disturbance severities. Under the same average disturbance severity, H. splendens population growth rates are highest in acyclic scenarios and are progressively reduced with increasing peak disturbance severities (i.e., with increasing period). Stochastic elasticity analyses show that in less variable environments mature segment survival contributes more to the population growth rate, while in more variable environments the regeneration pathway (branching of older parts of the plant) plays a stronger role, inevitably leading to lower population fitness. Our results support the hypothesis that breakdown of cyclic rodent population dynamics accentuates increase in the abundance of H. splendens and other large bryophytes in boreal forests in Norway, observed empirically in recent years and primarily ascribed to climatic change. © 2007 by the Ecological Society of America.
Réale D., Reader S.M., Sol D., McDougall P.T., Dingemanse N.J. (2007) Integrating animal temperament within ecology and evolution. Biological Reviews. 82: 291-318.EnllaçDoi: 10.1111/j.1469-185X.2007.00010.x
Temperament describes the idea that individual behavioural differences are repeatable over time and across situations. This common phenomenon covers numerous traits, such as aggressiveness, avoidance of novelty, willingness to take risks, exploration, and sociality. The study of temperament is central to animal psychology, behavioural genetics, pharmacology, and animal husbandry, but relatively few studies have examined the ecology and evolution of temperament traits. This situation is surprising, given that temperament is likely to exert an important influence on many aspects of animal ecology and evolution, and that individual variation in temperament appears to be pervasive amongst animal species. Possible explanations for this neglect of temperament include a perceived irrelevance, an insufficient understanding of the link between temperament traits and fitness, and a lack of coherence in terminology with similar traits often given different names, or different traits given the same name. We propose that temperament can and should be studied within an evolutionary ecology framework and provide a terminology that could be used as a working tool for ecological studies of temperament. Our terminology includes five major temperament trait categories: shyness-boldness, exploration- avoidance, activity, sociability and aggressiveness. This terminology does not make inferences regarding underlying dispositions or psychological processes, which may have restrained ecologists and evolutionary biologists from working on these traits. We present extensive literature reviews that demonstrate that temperament traits are heritable, and linked to fitness and to several other traits of importance to ecology and evolution. Furthermore, we describe ecologically relevant measurement methods and point to several ecological and evolutionary topics that would benefit from considering temperament, such as phenotypic plasticity, conservation biology, population sampling, and invasion biology. © 2007 Cambridge Philosophical Society.
Sala A., Verdaguer D., Vilà M. (2007) Sensitivity of the invasive geophyte Oxalis pes-caprae to nutrient availability and competition. Annals of Botany. 99: 637-645.EnllaçDoi: 10.1093/aob/mcl289
• Background and Aims: Invasion by alien plants may be partially related to disturbance-related increases in nutrient availability and decreases of competition with native species, and to superior competitive ability of the invader. Oxalis pes-caprae is an invasive winter geophyte in the Mediterranean Islands that reproduces vegetatively via bulbs. An investigation was made into the relative responses of O. pes-caprae and the native annual grass Lolium rigidum to nutrient availability and to competition with each other in order to understand patterns of invasion in the field. Because Oxalis accumulates oxalic acid in its leaves, which could ameliorate soil phosphorous availability, field observations were made to determine whether the presence of Oxalis alters soil P availability. • Methods: A full-factorial glasshouse experiment was conducted with nutrient availability (high and low) and competition (Lolium alone, Oxalis alone, and Lolium and Oxalis together). Plant performance was assessed by determining (1) above- and below-ground biomass at the time of Oxalis maximum biomass and (2) reproductive output of Oxalis and Lolium at the end of their respective growth cycles. Measurements were also taken for leaf N and P content. Soil samples were taken in the field from paired Oxalis-invaded and non-invaded plots located in Menorca (Balearic Islands) and available P was determined. • Key Results: High nutrient availability increased Oxalis and Lolium vegetative biomass and reproductive output to a similar degree. Competition with Lolium had a much stronger negative effect on Oxalis bulb production than reduced nutrients. Lolium was a superior competitor than Oxalis; the latter did not affect Lolium maximum biomass and spike production. Significantly greater soil-P availability in Oxalis-invaded field soils relative to paired non-invaded soils suggest that Oxalis influences soil P cycling. • Conclusions: Oxalis is a poor competitor. This is consistent with the preferential distribution of Oxalis in disturbed areas such as ruderal habitats, and might explain its low influence on the cover of native species in invaded sites. The results also suggest that certain disturbances (e.g. autumn ploughing) may greatly enhance Oxalis invasion. © The Author 2007. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.
Sardans J., Peñuelas J. (2007) Drought changes the dynamics of trace element accumulation in a Mediterranean Quercus ilex forest. Environmental Pollution. 147: 567-583.EnllaçDoi: 10.1016/j.envpol.2006.10.008
We conducted a field drought manipulation experiment in an evergreen oak Mediterranean forest from 1999 to 2005 to investigate the effects of the increased drought predicted for the next decades on the accumulation of trace elements that can be toxic for animals, in stand biomass, litter and soil. Drought increased concentrations of As, Cd, Ni, Pb and Cr in roots of the dominant tree species, Quercus ilex, and leaf Cd concentrations in Arbutus unedo and of Phillyrea latifolia codominant shrubs. The increased concentration of As and Cd can aggravate the toxic capacity of those two elements, which are already next or within the levels that have been shown to be toxic for herbivores. The study also showed a great reduction in Pb biomass content (100-135 g ha-1) during the studied period (1999-2005) showing the effectiveness of the law that prohibited leaded fuel after 2001. The results also indicate that drought increases the exportation of some trace elements to continental waters. © 2006 Elsevier Ltd. All rights reserved.
Sardans J., Peñuelas J. (2007) Drought changes phosphorus and potassium accumulation patterns in an evergreen Mediterranean forest. Functional Ecology. 21: 191-201.EnllaçDoi: 10.1111/j.1365-2435.2007.01247.x
1. Climate models predict more extreme weather in Mediterranean ecosystems, with more frequent drought periods and torrential rainfall. These expected changes may affect major process in ecosystems such as mineral cycling. However, there is a lack of experimental data regarding the effects of prolonged drought on nutrient cycling and content in Mediterranean ecosystems. 2. A 6-year drought manipulation experiment was conducted in a Quercus ilex Mediterranean forest. The aim was to investigate the effects of drought conditions expected to occur over the coming decades, on the contents and concentrations of phosphorus (P) and potassium (K) in stand biomass, and P and K content and availability in soils. 3. Drought (an average reduction of 15% in soil moisture) increased P leaf concentration by 18.2% and reduced P wood and root concentrations (30.9% and 39.8%, respectively) in the dominant tree species Quercus ilex, suggesting a process of mobilization of P from wood towards leaves. The decrease in P wood concentrations in Quercus ilex, together with a decrease in forest biomass growth, led to an overall decrease (by approximately one-third) of the total P content in above-ground biomass. In control plots, the total P content in the above-ground biomass increased 54 kg ha-1 from 1999 to 2005, whereas in drought plots there was no increase in P levels in above-ground biomass. Drought had no effects on either K above-ground contents or concentrations. 4. Drought increased total soil soluble P by increasing soil soluble organic P, which is the soil soluble P not directly available to plant capture. Drought reduced the ratio of soil soluble inorganic P : soil soluble organic P by 50% showing a decrease of inorganic P release from P bound to organic matter. Drought increased by 10% the total K content in the soil, but reduced the soil soluble K by 20.4%. 5. Drought led to diminished plant uptake of mineral nutrients and to greater recalcitrance of minerals in soil. This will lead to a reduction in P and K in the ecosystem, due to losses in P and K through leaching and erosion, if the heavy rainfalls predicted by IPCC (Intergovernmental Panel on Climate Change) models occur. As P is currently a limiting factor in many Mediterranean terrestrial ecosystems, and given that P and K are necessary for high water-use efficiency and stomata control, the negative effects of drought on P and K content in the ecosystem may well have additional indirect negative effects on plant fitness. © 2007 The Authors.
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