Maron JL, Vilà M, Arnason J (2004) Loss of enemy resistance among introduced populations of St. John's Wort (Hypericum perforatum). Ecology 85:3243-3253.
Maron JL, Vilà M, Bommarco R, Elmendorf S, Beardsley P (2004) Rapid evolution of an invasive plant. Ecological Monographs 74:261-280.
Belmonte J, Vilà M (2004) Atmospheric invasion of non-native pollen in the Mediterranean region. American Journal of Botany 91:1243-1250.
Vicente-Serrano SM, Pons-Fernández X, Cuadrat-Prats JM (2004) Mapping soil moisture in the central Ebro river valley (northeast Spain) with Landsat and NOAA satellite imagery: a comparison with meteorological data. International Journal of Remote Sensing 25:4325-4350.
Vilà M, Weiner J (2004) Are invasive plants species better competitors than native plant species? — evidence from pair-wise experiments. Oikos 105:229-238.
Rodrigo A, Retana J, Picó X (2004) Direct regeneration is not the only response of Mediterranean forests to large fires. Ecology 85:716-729.
Avila A., Rodrigo A. (2004) Trace metal fluxes in bulk deposition, throughfall and stemflow at two evergreen oak stands in NE Spain subject to different exposure to the industrial environment. Atmospheric Environment. 38: 171-180.LinkDoi: 10.1016/j.atmosenv.2003.09.067
We compare here the bulk deposition, throughfall and stemflow fluxes of dissolved trace metals in two holm oak (Quercus ilex L.) forests in the Montseny Mountains (NE Spain) with the aim of: (1) applying different methods to distinguish between dry deposition and canopy leaching and (2) to add to the almost non-existing deposition measurements for dissolved Cu, Pb, Mn, V, Zn, Ni and Cd in two Spanish forests differentially exposed to the urban and industrial environment. No significant differences in mean bulk deposition concentrations or fluxes were found between sites, indicating little differential effect of the urban/industrial environment on bulk precipitation chemistry. At both sites, throughfall and stemflow fluxes increased relative to bulk deposition for all elements, except for Zn and Cd. The relative contribution of leaching and dry deposition was evaluated through: (1) the seasonal variability of throughfall, (2) regressions of element fluxes on water flux in net throughfall, (3) washing branches and metacrylate plates, and (4) the sequential washing of branches. Results indicated that leaching was the main enrichment process for Mn. For Ni, except the sequential washings, all other evidences also pointed to leaching. For Cu, Pb, Zn, Cd and V there was ample evidence for dry deposition. The fact that Zn and Cd had negative net throughfall fluxes indicated that canopy uptake was greater than deposition (wet plus dry). Net throughfall fluxes pointed to higher dry deposition onto the canopies in the more exposed site, but the occurrence of uptake impeached quantification. Therefore, dry deposition was estimated from the recovered quantities from experimental washings of foliage, taken to represent the impaction of small particles onto the canopy. The foliage-wash fluxes were, for Zn, Cu and Pb, respectively, 407, 25 and 16gha-1yr-1 at the sheltered site and 423, 38 and 26gha-1yr-1 at the exposed site. Deposition in bulk precipitation (wet deposition+an unknown fraction of dry deposition mostly accounted by coarse particles settling gravitationally) was lower: 222, 6.3 and 6.5gha-1yr-1 for Zn, Cu and Pb, respectively, averaged for the two sites. © 2003 Elsevier Ltd. All rights reserved.
Beier C., Emmett B., Gundersen P., Tietema A., Peñuelas J., Estiarte M., Gordon C., Gorissen A., Llorens L., Roda F., Williams D. (2004) Novel approaches to study climate change effects on terrestrial ecosystems in the field: Drought and passive nighttime warming. Ecosystems. 7: 583-597.LinkDoi: 10.1007/s10021-004-0178-8
This article describes new approaches for manipulation of temperature and water input in the field. Nighttime warming was created by reflection of infrared radiation. Automatically operated reflective curtains covered the vegetation at night to reduce heat loss to the atmosphere. This approach mimicked the way climate change, caused by increased cloudiness and increased greenhouse gas emissions, alters the heat balance of ecosystems. Drought conditions were created by automatically covering the vegetation with transparent curtains during rain events over a 2-5-month period. The experimental approach has been evaluated at four European sites across a climate gradient. All sites were dominated (more than 50%) by shrubs of the ericaceous family. Within each site, replicated 4-m X 5-m plots were established for control, warming, and drought treatments and the effect on climate variables recorded. Results over a two-year period indicate that the warming treatment was successful in achieving an increase of the minimum temperatures by 0.4-1.2°C in the air and soil. The drought treatment resulted in a soil moisture reduction of 33%-82% at the peak of the drought. The data presented demonstrate that the approach minimizes unintended artifacts with respect to water balance, moisture conditions, and light, while causing a small but significant reduction in wind speed by the curtains. Temperature measurements demonstrated that the edge effects associated with the treatments were small. Our method provides a valuable tool for investigating the effects of climate change in remote locations with minimal artifacts.
Belmonte J., Vilà M. (2004) Atmospheric invasion of non-native pollen in the Mediterranean region. American Journal of Botany. 91: 1243-1250.LinkDoi: 10.3732/ajb.91.8.1243
Most research on the impacts of plant invasion focuses on native plant performance, community structure, and ecosystem functioning. Some non-native species can also pose a risk to human health. One such risk is the allergenic nature of the pollen of some introduced plants. We examined whether patterns of airborne pollen differed between non-native and native taxa by summarizing data from seven Spanish Mediterranean localities monitored over 13 yr. The pollen spectra contained 27 native pollen taxa and 18 non-native taxa. Even though pollen from native taxa were more diverse and were present longer in the atmosphere than the non-native, in some years neither the prevalence of the two nor their weekly maximum pollen values differed significantly. However, maximum values for non-native taxa were found earlier in the season than for native pollen. A small percentage of non-native pollen includes pollen from introduced taxa that have not invaded natural habitats (e.g., ornamental plants). Non-native pollen has a larger proportion of allergenic pollen than native pollen. Therefore, the results reveal that the presence of non-native airborne pollen from naturalized and non-naturalized plant species increases the total amount of airborne allergenic pollen grains and the period of allergenic susceptibility.
Broncano M.J., Retana J. (2004) Topography and forest composition affecting the variability in fire severity and post-fire regeneration occurring after a large fire in the Mediterranean basin. International Journal of Wildland Fire. 13: 209-216.LinkDoi: 10.1071/WF03036
This study relates the spatial variability in tree regeneration generated by fire with topography and pre-fire vegetation composition, and analyses how the pattern of fire severities determines post-fire regeneration of the dominant tree species (Pinus halepensis and Quercus ilex) in a large fire that occurred in north-eastern Spain in summer 1994. At the fire level, the proportion of the different fire severities in the burned area was characteristic of large fires that burn with high severity. At the level of plot, the variability of fire severity in the study site depended on two topographic characteristics: elevation and aspect. Plots burned with high fire severity were distributed at higher altitude than less severely burned plots, which were mainly distributed in south- and east-facing slopes. Fire severity also increased with Q. ilex density in the stand. The mosaic of fire severities determined both plant mortality and seedling regeneration. Mortality of stems caused by fire was very high in both species, but many Q. ilex individuals resprouted after fire. Seedling regeneration of P. halepensis showed large differences among plots in the burned area, reflecting large spatial variability due to the elevation gradient, the variation in density of adult pine trees, and the spatial variability created by fire.
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