Statistical analysis of fire frequency models for Catalonia (NE Spain, 1975-1998) based on fire scar maps from Landsat MSS data

Díaz-Delgado R., Lloret F., Pons X. (2004) Statistical analysis of fire frequency models for Catalonia (NE Spain, 1975-1998) based on fire scar maps from Landsat MSS data. International Journal of Wildland Fire. 13: 89-99.
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Doi: 10.1071/WF02051

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This paper estimates fire frequency in Catalonia (NE Spain) for the last quarter of the 20th Century (1975-1998) from historical burned area maps. Remote sensing images provided perimeters of fires ≥30 ha, which were used to characterize the temporal patterns of fire occurrence in Catalonia. Several fire frequency models were used to reproduce the observed pattern of wildfires occurrence in the study period. Natural fire rotation period was estimated to be 133 years. Poisson tests were carried out to check random fire occurrence either along the time period or across the analysed region. Observed fires were not randomly generated either in space or in time, despite being sampled using two different plot sizes. This sampling design was also used for Mean Fire Interval (MFI) analysis, which allowed us to significantly fit a Weibull distribution to the observed proportion of fire intervals (for both sample sizes), enabling us to estimate the hazard of burning, mortality, and survivorship functions. Finally, MFI was also applied to forest regions of Catalonia, which are defined according to forest management plans based on their homogeneous climatic conditions. Such an analysis revealed relevant differences in forest management and their consequences on fire occurrence.

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Spatial patterns of fire occurrence in Catalonia, NE, Spain.

Díaz-Delgado R, Lloret F, Pons X (2004) Spatial patterns of fire occurrence in Catalonia, NE, Spain. Landscape Ecology 19:731-745.

Fire recurrence effects on the structure and composition of Mediterranean Pinus halepensis communities in Catalonia (northeast Iberian Peninsula).

Eugenio M, Lloret F (2004) Fire recurrence effects on the structure and composition of Mediterranean Pinus halepensis communities in Catalonia (northeast Iberian Peninsula). Ecoscience 11:446-454.

Establishment of co-existing Mediterranean tree species under a varying soil moisture regime.

Lloret F, Peñuelas J, Ogaya R (2004) Establishment of co-existing Mediterranean tree species under a varying soil moisture regime. Journal of Vegetation Science15:237-244.

Maximal species richness: an empirical approach for evaluating woody plant forest biodiversity.

Terradas J, Salvador R, Vayreda J, Lloret F (2004) Maximal species richness: an empirical approach for evaluating woody plant forest biodiversity. Forest and Ecology and Management 189:241-249.

Local and regional abundance of exotic plant species on Mediterranean islands: Are species traits important?

Lloret F., Médail F., Brundu G., Hulme P.E. (2004) Local and regional abundance of exotic plant species on Mediterranean islands: Are species traits important?. Global Ecology and Biogeography. 13: 37-45.
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Doi: 10.1111/j.1466-882X.2004.00064.x

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Aim We assess the importance of three relevant and readily obtainable life-history traits (dispersal syndrome, stem height and growth form) and biogeographical origin (European vs. non-European) on the local and regional abundance of over 400 exotic plant species across eight Mediterranean islands. Location The Mediterranean islands of Lesbos, Rhodes, Crete, Malta, Corsica, Sardinia, Majorca and Minorca. Methods We adopt two abundance criteria for each exotic species: the proportion of islands in which the species occurs (regional abundance), and a qualitative estimate of species abundance within each of five islands (local abundance). Subsequently, we assess the relationship between local and regional abundance, as well as the role of key life-history traits on both regional and local abundance. These analyses were undertaken separately for the European exotics and the non-European exotics. Results Only 10.9% of the species occur on more than four islands, and only four species are present on all eight islands. Both local and regional abundances were higher for the non-European than the European species. Local and regional abundances were positively correlated, particularly for exotics with non-European origins. Wind-dispersed species tended to have higher regional abundance than species dispersed by other means but this trend only occurred for local abundance on two islands - Corsica and Majorca. Neither a species' growth form nor its stem height explained trends in regional or local abundance. Conclusions Although wind-dispersed exotics are more widespread in the Mediterranean, plant life-history traits appear to play a lesser role in invasion success than area of biogeographical origin. In general, exotic species of non-European origin were more abundant at both local and regional scales. Invasion patterns should be interpreted at both local and regional scales, but the stochastic nature of biological invasions may limit deterministic interpretations of invasion patterns, especially if islands are studied in isolation. © 2004 Blackwell Publishing Ltd.

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Experimental evidence of reduced diversity of seedlings due to climate modification in a Mediterranean-type community

Lloret F., Penuelas J., Estiarte M. (2004) Experimental evidence of reduced diversity of seedlings due to climate modification in a Mediterranean-type community. Global Change Biology. 10: 248-258.
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Doi: 10.1111/j.1365-2486.2004.00725.x

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We are still lacking in experimental evidence of the effects of climate change on the richness of plant species under field conditions. We report a decrease in the species richness of recruited seedlings in a Mediterranean shrubland in experimentally induced drought and warming over 4 consecutive years. Drought decreased the number of emerging seedlings and their respective species richness. Warming also decreased seedling species richness, but it did not affect the number of emerging seedlings. Species that produce fewer recruits are more likely to disappear in drier or warmer scenarios. However, when the effect of induced climate treatment was greatest, the more abundant species in control stands were not necessarily the ones least affected by treatment; in other words, species-idiosyncratic responses may occur. These results show that demographic processes are sensitive to minor climate changes, with probable consequences on the diversity and structure of the future plant communities. © 2004 Blackwell Publishing Ltd.

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Canopy recovery after drought dieback in holm-oak Mediterranean forests of Catalonia (NE Spain)

Lloret F., Siscart D., Dalmases C. (2004) Canopy recovery after drought dieback in holm-oak Mediterranean forests of Catalonia (NE Spain). Global Change Biology. 10: 2092-2099.
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Doi: 10.1111/j.1365-2486.2004.00870.x

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Climate change is likely to produce more frequent and longer droughts in the Mediterranean region, like that of 1994, which produced important changes in the Quercus ilex forests, with up to 76% of the trees showing complete canopy dieback. At the landscape level, a mosaic of responses to the drought was observed, linked to the distribution of lithological substrates. Damage to the dominant tree species (Q. ilex) and the most common understorey shrub (Erica arborea) was more noticeable on the compact substrates (breccia) than on the fissured ones (schist). This result was consistent with observations documenting deeper root penetration in schist than in breccia materials, allowing the plants growing on fissured substrates to use water from deeper soil levels. Smaller plants were more vulnerable to drought than larger plants in the trees, but not in the shrubs. Overall, Q. ilex was more affected than E. arborea. The resilience of the system was evaluated from the canopy recovery 1 year after the episode. Stump and crown resprouting was fairly extensive, but the damage pattern in relation to substrate, plant size, and species remained similar. The effect of recurrent drought episodes was studied on vegetation patches of Q. ilex located on mountain slopes and surrounded by bare rock. We observed that plants that resprouted weakly after a previous drought in 1985 were more likely to die or to produce poor regeneration in 1995 than plants that had resprouted vigorously. Vegetation patches located on the lower part of the slope were also less damaged than patches situated uphill. The study provides evidence of relevant changes in forest canopy as a consequence of extreme climate events. The distribution of this effect across the landscape is mediated by lithological substrate, causing patchy patterns. The results also support the hypothesis that recurrent droughts can produce a progressive loss of resilience, by depleting the ability of surviving plants to regenerate. © 2004 Blackwell Publishing Ltd.

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Effects of sewage sludge on plant community composition in restored limestone quarries

Moreno-Peñaranda R., Lloret F., Alcañiz J.M. (2004) Effects of sewage sludge on plant community composition in restored limestone quarries. Restoration Ecology. 12: 290-296.
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Doi: 10.1111/j.1061-2971.2004.00310.x

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The effects of sewage sludge, used to improve fertility of replaced soil, on vegetation were studied in limestone quarry restoration. Plant community growing in the first stages after sludge application was surveyed in six quarries of NE Spain. Areas with a mixture of sewage sludge and residual soil were compared to areas where the application consisted only of residual soil (a mixture of previous top soil and mine spoils). Sewage sludge was hypothesized to increase total biomass and cover, modifying species composition and delaying the early successional recover of the community. The results showed that both biomass and plant cover increased because of sewage sludge addition. The floristic composition was dominated by ruderal species that did not show any dependence on sewage sludge application. Convergence on similarity between sludge and control plots was not detected along a 5-year period. Although species richness was significantly lower in sludge plots, diversity and equitability indexes did not show differences between treatments. The results did not show differences in the proportion of non-native species. The proportion of legumes was lower in sludge plots. These results show that the plant communities resulting from the addition of sewage sludge to the soil used in limestone quarry restoration have more biomass and cover, but less number of species, and they do not show a clear trend to converge to those areas restored only with non-amended soil. © 2004 Society for Ecological Restoration International.

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Complex spatiotemporal phenological shifts as a response to rainfall changes

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.
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Doi: 10.1111/j.1469-8137.2004.01003.x

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• 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.

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