Lloret F., Peñuelas J., Prieto P., Llorens L., Estiarte M. (2009) Plant community changes induced by experimental climate change: Seedling and adult species composition. Perspectives in Plant Ecology, Evolution and Systematics. 11: 53-63.EnllaçDoi: 10.1016/j.ppees.2008.09.001
Experimental manipulation of climate provides a powerful tool for studying plant community dynamics with respect to current climate change. We experimentally investigated the vegetation dynamics of a Mediterranean shrubland under directional climate change by manipulating rain and temperature at stand level throughout 7 years. We focused on seedling establishment in relation to the between-year variability of drought conditions. We also compared seedling dynamics to changes in the established adult vegetation to assess the coupling between both dynamics. We used multivariate techniques (principal response curves (PRC) and redundancy analysis (RDA)) to explore changes in the whole community, and Generalized Linear Model (GLZM) to analyse the influence of drought on the abundance and survival of the most abundant species. Drought treatment induced significant changes in the species composition of the seedlings, via a differential decrease in the seedling density of most species. No species was particularly favoured in terms of seedling abundance under water-deficit conditions. Warming only explained a low percentage of the variability in seedling species composition. The emergence of seedlings in control plots - which may be considered an estimation of the between-year variability in the conditions for seedling establishment - was a better predictor of seedling emergence in experimental plots than climate manipulation treatments. The PRC analysis of the adults showed dynamics that were different from those recorded for seedlings, and it also showed that drought treatment significantly explained species composition. This result is reinforced by the change in the relative abundance of seedling and adults of the more common species in the drought and warming treatments, supporting the hypothesis that climatic directional change heightens discrepancies between recruitment and the adult performance. The RDA analysis applied to species composition at the end of the experiment failed, however, to attain any statistical significance. The warming treatment did not produce any significant shifts in adult vegetation. In conclusion, directional climate change - particularly drier conditions in Mediterranean shrublands - would result in a change in the recruitment of the plant community. This change in seedling recruitment tends to be different from the dynamics of adults, suggesting that potential adult mortality would not be compensated by actual seedling recruitment, thus enhancing shifts in community composition. © 2008 Rübel Foundation, ETH Zürich.
Prieto P., Peñuelas J., Lloret F., Llorens L., Estiarte M. (2009) Experimental drought and warming decrease diversity and slow down post-fire succession in a Mediterranean shrubland. Ecography. 32: 623-636.EnllaçDoi: 10.1111/j.1600-0587.2009.05738.x
Plant community recovery (species richness, diversity and composition) of a post-fire Mediterranean shrubland was monitored over a seven year period (1998-2005) under experimental drought and warming that simulated the environmental conditions forecast for this area in the coming decades. Species richness and Shannon's index were positively correlated with accumulated precipitation in the growing season and both variables were negatively affected by reduced water availability in drought plots. The relative abundance of the different species in both treatments was linearly correlated with their relative abundance in control plots. Moreover, we found species-specific responses to treatments. Drought and warming treatment reduced the competitive ability of the obligate seeder tree Pinus halepensis against native resprouter shrubs and consequently, the transformation from shrub to pine tree dominated vegetation was slowed down. Conversely, the water use strategy of Globularia alypum may allow this species to maintain a dominant position in drought plots. Therefore, future drier and warmer conditions in Mediterranean areas may severely affect plant community recovery after a disturbance, due to the existence of both abundance-dependent and species-specific responses that may change inter-specific competitive relationships. © 2009 Ecography.
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