Stefanescu C., Peñuelas J., Filella I. (2005) Butterflies highlight the conservation value of hay meadows highly threatened by land-use changes in a protected Mediterranean area. Biological Conservation. 126: 234-246.EnllaçDoi: 10.1016/j.biocon.2005.05.010
Butterfly assemblages were used to characterize and evaluate the conservation value of the main habitat types in the Aiguamolls de l'Empordà Natural Park (north-eastern Spain), an important protected wetland area on the Mediterranean coast. Butterfly data were obtained from a number of transects walked as part of the Catalan Butterfly Monitoring Scheme, which uses a standardized methodology for monitoring butterflies. A Mantel test indicated a strong association between habitat types and the composition of butterfly assemblages and a principal component analysis ordinated individual butterfly species along a gradient from woodland to open areas, thereby indicating various degrees of shade tolerance. In addition, cluster analysis distinguished two main groups of habitats based on the similarities of their butterfly fauna: woodland and bramble clumps and a group of three different kinds of grasslands (traditionally hay meadows, pastures, and alfalfa fields). Hay meadows flooded in winter (the so-called closes) appeared always as the highest ranked habitat in terms of conservation evaluation: they have more butterflies and a slight tendency to harbor more and generally rarer species. This conclusion coincides with that of previous investigations that have indicated that the most diverse and rare plant communities in the whole Natural Park are present in the closes, and highlights the importance of traditionally managed hay meadows for wildlife. However, these hay meadows - one of the rarest habitats in the Mediterranean region - are in alarming decline and have become the most threatened habitat in this protected area: no longer profitable, we believe that the future of the closes will depend ultimately on the existence of agri-environmental schemes. © 2005 Elsevier Ltd. All rights reserved.
Filella I., Peñuelas J. (2004) Indications of hydraulic lift by Pinus halepensis and its effects on the water relations of neighbour shrubs. Biologia Plantarum. 47: 209-214.EnllaçDoi: 10.1023/B:BIOP.0000022253.08474.fd
We measured the stable deuterium isotopic composition of xylem sap, the shoot predawn and midday water potentials, and the leaf δ13C of Mediterranean shrubs Pistacia lentiscus, Globularia alypum and Rosmarinus officinalis in a south-oriented transect from a large (12 m tall) Aleppo pine tree, Pinus halepensis. We aimed to study the possibility of hydraulic lift from the deep roots of this pine tree to the shallow soil layers and its influence on these neighbour shrubs. These same traits were also studied in several individuals of the shrub Pistacia lentiscus growing with different types of neighbours: just shrubs, a small (3-4 m) pine tree, and the above mentioned large pine tree. The greater the distance from P. halepensis the plants grew, the higher xylem water SD, the lower the soil water content, and, the lower the predawn and midday water potentials were found. These results suggest the existence of an hydraulic lift from deep roots to shallow soil in this big tree. Further indication of this existence is provided by the improved water status of P. lentiscus (higher water potentials and δD, and lower δ13C and, therefore, lower water use efficiencies) when growing close to the big pine in comparison with the same shrub species growing close to small pines or just surrounded by other shrubs. Moreover, all these trends occurred in the dry summer season, but disappeared in the wet spring season.
Filella I., Peñuelas J., Llorens L., Estiarte M. (2004) Reflectance assessment of seasonal and annual changes in biomass and CO2 uptake of a Mediterranean shrubland submitted to experimental warming and drought. Remote Sensing of Environment. 90: 308-318.EnllaçDoi: 10.1016/j.rse.2004.01.010
We aimed to evaluate how the remote sensing vegetation indices NDVI and PRI responded to seasonal and annual changes in an early successional stage Mediterranean coastal shrubland canopy that was submitted to experimental warming and drought simulating predicted climate change for the next decades. These conditions were obtained by using a new non-intrusive methodological approach that increases the temperature and prolongs the drought period by using roofs that automatically cover the vegetation after the sunset or when it rains. On average, warming increased air temperature by 0.7°C and soil temperature by 1.6°C, and the drought treatment reduced soil moisture by 22%. We measured spectral reflectance at the canopy level and at the individual plant level seasonally during 4 years. Shrubland NDVI tracked the community development and activity. In control and warming treatments, NDVI increased with the years while it did not change in the drought treatment. There was a good relationship between NDVI and both community and individual plant biomass. NDVI also decreased in summer seasons when some species dry or decolour. The NDVI of E. multiflora plant individuals was lower in autumn and winter than in the other seasons, likely because of flowering. Shrubland PRI decreased only in winter, similarly to the PRI of the most dominant species, G. alypum. At this community scale, NDVI was better related than PRI to photosynthetic activity, probably because photosynthetic fluxes followed canopy seasonal greening in this complex canopy, which includes brevideciduous, annual and evergreen species and variable morphologies and canopy coverage. PRI followed the seasonal variations in photosynthetic rates in E. multiflora and detected the decreased photosynthetic rates of drought treatment. However, PRI did not track the photosynthetic rates of G. alypum plants which have lower LAIs than E. multiflora. In this community, which is in its early successional stages, NDVI was able to track biomass, and indirectly, CO2 uptake changes, likely because LAI values did not saturate NDVI. Thus, NDVI appears as a valid tool for remote tracking of this community development. PRI was less adequate for photosynthetic assessment of this community especially for its lower LAI canopies. PRI usefulness was also species-dependent and could also be affected by flowering. These results will help to improve the interpretation of remote sensing information on the structure and physiological status of these Mediterranean shrublands, and to gain better insight on ecological and environmental controls on their ecosystem carbon dioxide exchange. They also show the possibility of assessing the impacts of climate change on shrubland communities. © 2004 Elsevier Inc. All rights reserved.
Peñuelas J, Munné-Bosch S, Llusià J, Filella I (2004) Leaf reflectance and photo- and antioxidant protection in field-grown summer-stressed Phillyrea angustifolia. Optical signals of oxidative stress? New Phytologist 162:115-124.
Peñuelas J., Filella I., Zhang X., Llorens L., Ogaya R., Lloret F., Comas P., Estiarte M., Terradas J. (2004) Complex spatiotemporal phenological shifts as a response to rainfall changes. New Phytologist. 161: 837-846.EnllaçDoi: 10.1111/j.1469-8137.2004.01003.x
• Climatic warming produces significant gradual alterations in the timing of life-cycle events, and here we study the phenological effects of rainfall-pattern changes. • We conducted ecosystem field experiments that partially excluded rain and runoff during the growing season in a Mediterranean forest and in a mediterranean shrubland. Studies of time-series of leaf-unfolding, flowering and fruiting over the last 50 yr in central Catalonia were carried out, and greenup onset in the Iberian Peninsula was monitored by satellite images. • Experimental, historical and geographical changes in rainfall produced significant, complex and strongly species-specific, as well as spatially and temporally variable, phenological effects. Among these changes, it was found that in the Iberian Peninsula, greenup onset changes from spring (triggered by rising temperatures) in the northern cool-wet regions to autumn (triggered by the arrival of autumn rainfalls) in the southern warm-dry regions. Even in the mesic Mediterranean central Catalonia (NE of the peninsula) rainfall had a stronger relative influence than temperature on fruiting phenology. • The results show that changes in rainfall and water availability, an important driver of climate change, can cause complex phenological changes with likely far-reaching consequences for ecosystem and biosphere functioning and structure. The seasonal shift in the Iberian Peninsula further highlights this importance and indicates that vegetation may respond to climate change not only with gradual, but also with abrupt temporal and spatial, changes in the timing of greenup onset.
Filella I., Peñuelas J. (2003) Partitioning of water and nitrogen in co-occurring Mediterranean woody shrub species of different evolutionary history. Oecologia. 137: 51-61.EnllaçDoi: 10.1007/s00442-003-1333-1
We studied the interspecific and intraspecific variation in the development of water stress and in the use of different water and nitrogen sources during the spring (wet season) and summer (dry season) in a shrub community in NE Spain. We measured shoot water potentials, stable deuterium isotopic composition (δD) of xylem sap, leaf mass per area, leaf N and C concentrations, gas exchange, leaf δ13C, and leaf δ 15N of the dominant species (Quercus coccifera, Arbutus unedo, Pistacia lentiscus, Erica multiflora, Globularia alypum). The δD, the δ13C and the shoot water potential values showed diurnal, seasonal, intraspecific and interspecific variation in the source and use of water. There was also seasonal, intraspecific and interspecific variation in the foliar δ15N and N concentrations. In summer, some species (A. unedo, P. lentiscus and E. multiflora) presented significantly different δD values in morning and afternoon measurements likely indicating that they used different sources of water during the day, and a dual root system in these species. We conjecture that dew may be one of these water sources. Species predawn water potential was negatively correlated with species xylem water δD. There was also a positive correlation between δ 13C and δD in P. lentiscus, species for which we took additional samples from nearby sites. These results suggest that the access to water from greater depths allowed the maintenance of more favourable plant water supply. Multivariate principal component analysis based on the studied hydrological and isotope variables clearly separated the seasons (wet spring and dry summer) and the species. The species resulted separated according to their evolutionary history (Pre-Mediterranean and Mediterranean) and the associated root and functional traits. These results show water (and nitrogen) partitioning among coexisting species of the same functional type (Mediterranean woody shrubs). They also show the great intraspecific plasticity of responses to resource availability.
Filella I, Peñuelas J (2003) Indications of hydraulic lift by Pinus halepensis and its effects on the water relations of neighbour shrubs. Biologia Plantarum 47:209-214.
Llorens L., Peñuelas J., Filella I. (2003) Diurnal and seasonal variations in the photosynthetic performance and water relations of two co-occurring Mediterranean shrubs, Erica multiflora and Globularia alypum. Physiologia Plantarum. 118: 84-95.EnllaçDoi: 10.1034/j.1399-3054.2003.00101.x
Diurnal and seasonal fluctuations in the photosynthetic performance and water relations of two co-occurring Mediterranean shrubs, Erica multiflora and Globularia alypum were monitored throughout two consecutive years at Garraf Natural Park in north-east Spain. Leaf gas exchange rates, chlorophyll fluorescence and shoot water potentials were measured once each season. Leaf nitrogen and carbon concentrations, leaf δ13C and δ15N and specific leaf area (SLA) were also measured once a year (August) on well developed mature leaves. Globularia alypum experienced seasonal fluctuations in their water potential, with the lowest values recorded in summer, whereas E. multiflora did not show significant differences in water potential among seasons. Moreover, lower water potentials were found in G. alypum than in E. multiflora throughout the entire study, suggesting that the latter behaved as a drought-avoiding species, whereas the former tolerated lower water potentials. In both species, maximum leaf gas exchange rates were observed in autumn and secondarily in spring; in contrast, photosynthetic and transpiration rates reached absolute minima in summer. The stronger fluctuations in water potential and leaf gas exchange rates found in G. alypum compared to E. multiflora, suggest that G. alypum is, sensu Levitt (1980), a water spender, whereas E. multiflora is a water conservative. This hypothesis is further supported by a higher integrated water-use efficiency (higher δ13C values) and a higher degree of sclerophylly (lower SLA) in E. multiflora in comparison with G. alypum. Globularia alypum showed higher leaf gas exchange rates and higher predawn potential photochemical efficiency (Fv/Fm) than E. multiflora during most of the study. In spring and autumn, predawn Fv/Fm values were within the optimal range, whereas chronic photoinhibition in summer and winter was detected in both species. However, whereas both species could maintain positive photosynthetic rates in winter, frequent negative values were found in summer, suggesting higher levels of stress during the drought period. These results together with the high correlations that were found between the net photosynthetic rates and several parameters of water availability (accumulated rainfall, soil moisture or midday water potential) provided further evidence of the key role of water availability in the regulation of the photosynthetic rates in these Mediterranean species. Warmer and drier conditions in future decades, as a consequence of climate change, may alter the present, slight competitive advantage of G. alypum and the fitness of both shrub species within semi-arid Mediterranean environments.
Peñuelas J., Filella I. (2003) Deuterium labelling of roots provides evidence of deep water access and hydraulic lift by Pinus nigra in a Mediterranean forest of NE Spain. Environmental and Experimental Botany. 49: 201-208.EnllaçDoi: 10.1016/S0098-8472(02)00070-9
We studied the tree access to deep water sources and the possibility of hydraulic lift from the deep roots of a Pinus nigra tree to the shallow soil layers in a Mediterranean forest of NE Spain. We also studied the use of hydraulically lifted water by neighboring trees, shrubs, and sprouts. We enriched the roots of a large P. nigra (10 m tall) with deuterium by accessing them from a below ground cave. During the next 3 days we measured stable deuterium isotopic composition of xylem sap, shoot predawn and midday water potentials, and the leaf δ13C and δ15N of the P. nigra tree, neighboring Quercus ilex ballota trees and sprouts, and Juniperus oxycedrus shrubs. The study was conducted both in dry summer and in wet spring. In summer, deuterated water absorbed by deep roots of P. nigra appeared in the stem water of neighboring plants and in surface soil. The most δD-enriched plant xylem sap was found in the enriched P. nigra tree, followed by the Q. ilex sprouts, the small Q. ilex trees and the surface soil (15 cm). All these trends disappeared in the wet spring season, when HDO only slightly appeared in the surface soil. The results show that the studied P. nigra tree accesses deep water source and conducts hydraulic lift in this Mediterranean forest in dry summer but not necessarily in wet spring. © 2002 Elsevier Science B.V. All rights reserved.
Stefanescu C., Penuelas J., Filella I. (2003) Effects of climatic change on the phenology of butterflies in the northwest Mediterranean Basin. Global Change Biology. 9: 1494-1506.EnllaçDoi: 10.1046/j.1365-2486.2003.00682.x
Phenological changes in response to climatic warming have been detected across a wide range of organisms. Butterflies stand out as one of the most popular groups of indicators of climatic change, given that, firstly, they are poikilothermic and, secondly, have been the subject of thorough monitoring programmes in several countries for a number of decades. Here we provide for the first time strong evidence of phenological change as a consequence of recent climatic warming in butterflies at a Spanish site in the northwest Mediterranean Basin. By means of the widely used Butterfly Monitoring Scheme methodology, three different phenological parameters were analysed for the most common species to test for trends over time and relationships with temperature and precipitation. Between 1988 and 2002, there was a tendency for earlier first appearance dates in all 17 butterfly species tested, and significant advances in mean flight dates in 8 out of 19 species. On the other hand, the shape of the curve of adult emergence did not show any regular pattern. These changes paralleled an increase of 1-1.5°C in mean February, March and June temperatures. Likewise, a correlation analysis indicated the strong negative effect of spring temperature on phenological parameters (i.e. higher temperatures tended to produce phenological advances), and the opposite effect of precipitation in certain months. In addition, there was some evidence to indicate that phenological responses may differ between taxonomic lineages or species with similar diets. We discuss the consequences that these changes may have on species' population abundances, especially given the expected increase in aridity in the Mediterranean Basin caused by current climatic warming. We predict that varying degrees of phenological flexibility may account for differences in species' responses and, for multivoltine species, predict strong selection favouring local seasonal adaptations such as diapause phenomena or migratory behaviour.
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