Penuelas J., Boada M. (2003) A global change-induced biome shift in the Montseny mountains (NE Spain). Global Change Biology. 9: 131-140.EnllaçDoi: 10.1046/j.1365-2486.2003.00566.x
Shifts in plant species and biome distribution in response to warming have been described in past climate changes. However, reported evidence of such shifts under current climate change is still scarce. By comparing current and 1945 vegetation distribution in the Montseny mountains (Catalonia, NE Spain), we report here a progressive replacement of cold-temperate ecosystems by Mediterranean ecosystems. Beech (Fagus sylvatica) forest has shifted altitudinally upwards by ca. 70 m at the highest altitudes (1600-1700 m). Both the beech forests and the heather (Calluna vulgaris) heathlands are being replaced by holm oak (Quercus ilex) forest at medium altitudes (800-1400 m). This beech replacement has been observed to occur through a progressive isolation and degradation of beech stands. In 'isolated' (small and surrounded by holm oaks) beech stands, beech trees are 30% more defoliated, beech recruitment is 41% lower, and holm oak recruitment is three times higher than in 'continental' (large and continous) beech stands. The progressively warmer conditions, complemented by the land use changes (mainly the cessation of traditional land management) are the apparent causes, providing a paradigmatic example of global change affecting distributions of plant species and biomes.
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.
Peñuelas J., Llusià J. (2003) BVOCs: Plant defense against climate warming?. Trends in Plant Science. 8: 105-109.EnllaçDoi: 10.1016/S1360-1385(03)00008-6
Plants emit a substantial amount of biogenic volatile organic compounds (BVOCs) into the atmosphere. These BVOCs represent a large carbon loss and can be up to ∼10% of that fixed by photosynthesis under stressful conditions and up to 100 g C m-2 per year in some tropical ecosystems. Among a variety of proven and unproven BVOC functions in plants and roles in atmospheric processes, recent data intriguingly link emission of these compounds to climate. Ongoing research demonstrates that BVOCs could protect plants against high temperatures. BVOC emissions are probably increasing with warming and with other factors associated to global change, including changes in land cover. These increases in BVOC emissions could contribute in a significant way (via negative and positive feedback) to the complex processes associated with global warming.
Picó F.X., Retana J. (2003) Seed ecology of a Mediterranean perennial herb with an exceptionally extended flowering and fruiting season. Botanical Journal of the Linnean Society. 142: 273-280.EnllaçDoi: 10.1046/j.1095-8339.2003.00172.x
Lobularia maritima is a Mediterranean short-lived herb with a flowering and fruiting season that lasts for ten months. Previous studies have shown that recruitment in periods other than autumn of the flowering season has few demographic implications; that is contributes little to the population growth rate. Since environmental conditions in periods other than autumn would allow recruitment, we examined to what extent the seed ecology of L. maritima accounts for recruitment shortage for the greater part of the year. To this end, we studied the effects of selfing and outcrossing on seed production and germination, within- and between-year variation in seed mass and germination, seed characteristics in the soil seed bank throughout the year, and the effect of temperature as a factor controlling seed germination. Results indicate that selfing does not decrease recruitment, and thus the observed changes in visitation rate and pollinator composition throughout the year cannot account for differences in recruitment. Germinability decreases throughout the year, suggesting a possible cost in reproduction associated with extended flowering. L. maritima has a transient seed bank whose seeds also experience a decrease in their germination throughout the year. Finally, temperature affects seed germination patterns, indicating the existence of quiescence mechanisms that prevent germination in the months prior to the summer drought. Overall, the results obtained support and, at least partly, explain the recruitment patterns of L. maritima observed in the field. © 2003 The Linnean Society of London.
Ribas A., Peñuelas J. (2003) Biomonitoring of tropospheric ozone phytotoxicity in rural Catalonia. Atmospheric Environment. 37: 63-71.EnllaçDoi: 10.1016/S1352-2310(02)00696-9
The ozone (O3) phytotoxicity in rural areas of Catalonia (NE Spain) and the biomonitoring capacity of Bel-W3 tobacco (Nicotiana tabacum) cultivars were assessed by determining the percentage of leaf area injured by ozone in plants of this cultivar exposed from spring to autumn since 1995-1999. The study was conducted simultaneously on nine field sites where ground level ozone concentrations and meteorological parameters were continuously monitored. Geographical, seasonal and annual variations of ozone damage rate and their links with meteorological conditions were studied. Ozone concentrations and leaf damage increased at the end of spring and the beginning of summer. Coastal sites generally presented higher O3 concentrations than inland and mountain sites. These mountain sites were the most sensitive ones to ozone toxicity. The ozone concentrations correlated well with ozone injury. However, at this local scale the ozone levels did not fully account for all the observed injury (only 11%). The response of tobacco plants to ozone concentrations and therefore its biomonitoring capacity depended also on different environmental conditions, mainly those linked to stomatal behaviour such as vapour pressure deficit. The categorization of leaf damage in 10% intervals and its averaging throughout the whole study period and the whole region, strongly improved (99% of variance accounted) the relationship with ozone concentrations expressed as AOT20 (accumulated over a cut-off of 20ppbv). N. tabacum cultivar Bel-W3 is thus a very good biomonitor of ozone concentrations in the long term at the regional scale. Taking into account the phytotoxical response of this sensitive tobacco cultivar, we propose the 1.28ppmvh biweekly AOT40 (with a solar radiation threshold of 50Wm-2) as a damage threshold level for sensitive species. © 2002 Elsevier Science Ltd. All rights reserved.
López B, Sabaté S, Gracia C (2003) Thinning effects on carbon allocation to fine roots in a Quercus ilex L. forest. Tree Physiology 23:1217-1224.
Serra P., Pons X., Saurí D. (2003) Post-classification change detection with data from different sensors: Some accuracy considerations. International Journal of Remote Sensing. 24: 3311-3340.EnllaçDoi: 10.1080/0143116021000021189
Change detection from remote sensing data is often done by simple overlay of classified maps. However, such analyses can contain a significant proportion of boundary errors, especially when combining data from different sensors. This paper presents a protocol that allows reliable post-classification comparisons by taking into account classification accuracies, landscape fragmentation, planimetric accuracies, pixel sizes and grid origins. The proposed protocol has been applied, with little extra effort, in a fragmented agricultural Mediterranean zone using MSS (1970s) and TM (1990s) images. Applying the protocol, change detection had an accuracy of 85.1%, while for a direct overlay it was only 43.9% accurate. The drawback of this method is that it reduces the useful area of comparison. As the accuracy of individual classifications is critical, the paper also describes and tests a hybrid classifier that combines an unsupervised classification approach with training areas. This approach has proved more successful than maximum likelihood classifiers.
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.
Boet O, Arnan X, Rodrigo A (2003) Efectes dels incendis forestals sobre les comunitats de formigues. Monografies del Montseny 18:145-161.
Espadaler X, Bernal V (2003) Exotic ants in the Canary Islands (Hymenoptera, Formicidae). Vieraea 31:1-7.
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