Vilà-Cabrera A., Saura-Mas S., Lloret F. (2008) Effects of fire frequency on species composition in a Mediterranean shrubland. Ecoscience. 15: 519-528.EnllaçDoi: 10.2980/15-4-3164
The effect of high fire frequency on the species composition of Mediterranean-type plant communities is reported on the basis of shrubland stands located in Catalonia (Spain) that have experienced from 1 to 5 fires over the last 31 years. We focused on changes in the abundance of species, grouped according to post-fire regenerative traits (resprouting and seed germination) and life form (shrubs, herbaceous graminoids, and herbaceous non-graminoids). High fire frequency was related to a low abundance of obligate resprouter and obligate seeder shrubs. In the latter group, Cistus sp. disappeared in stands with high fire frequency and showed a maximum abundance in stands with low fire frequency. The abundance of facultative resprouter shrubs did not change with fire frequency. This group thus became dominant in the shrub layer at high fire frequency due to the low abundance of obligate resprouter and obligate seeder shrubs. These changes in the abundance of shrub species involve changes in the patterns of relative dominance of regenerative syndromes, in line with fire frequency. An examination of life forms revealed that the abundance of herbaceous non-graminoids and herbaceous graminoids was higher in stands with high fire frequency and the graminoid Brachypodium retusum was dominant at all fire frequencies. These results suggest a loss in the resilience of shrubs after frequent fires, leading to a simplification of vegetation structure with a shift from shrubland to grassland-type communities, thereby probably enhancing a potential positive herb-fire feedback.
Wiegand T., Naves J., Garbulsky M.F., Fernández N. (2008) Animal habitat quality and ecosystem functioning: Exploring seasonal patterns using NDVI. Ecological Monographs. 78: 87-103.EnllaçDoi: 10.1890/06-1870.1
Many animal species have developed specific evolutionary adaptations to survive prolonged periods of low energy availability that characterize seasonal environments. The seasonal course of primary production, a major aspect of ecosystem functioning, should therefore be an important factor determining the habitat quality of such species. We tested this hypothesis by analyzing the relationship between habitat quality and ecosystem functioning for brown bears (Ursus arctos), a species showing hyperphagia and hibernation as evolutionary adaptation to seasonal peaks and bottlenecks in ecosystem productivity, respectively. Our unique long-term data set comprised data from two brown bear populations in northern Spain on historical presence, current presence, and reproduction. The data were classified on a grid of 5 x 5 km pixels into five classes: frequent reproduction, sporadic reproduction, frequent presence, sporadic presence, and recent extinction. We used the long-term average of the seasonal course of NDVI (normalized difference vegetation index) as a proxy for ecosystem functioning and investigated the relationship between habitat quality and ecosystem functioning with methods borrowed from statistical point-pattern analysis. We found that brown bears indeed selected habitat with specific ecosystem functioning (i.e., the variance in all habitat classes was smaller than in the landscape overall) and the relationship between habitat quality and ecosystem functioning was ordered. First, the average distance in ecosystem functioning between two habitat classes was larger if the difference in habitat quality was larger. Second, habitat for which there was the greatest need (i.e., breeding habitat) occupied the narrowest niche regarding ecosystem functioning and showed the most pronounced seasonality. Progressively poorer classes occupied wider niches that partly overlapped those of better classes. This indicated that nonbreeding animals are less selective. Our methodology provided new insight into the relationship between ecosystem functioning and habitat quality and could be widely applied to animal species living in seasonal environments. Because NDVI data are continuously collected, our methodology allows for continuous monitoring of changes in habitat quality due to global change. © 2008 by the Ecological Society of America.
Cremer S, Ugelvig LV, Drijfhout FP, Schlick-Steiner BC, Steiner FM, Seifert B, Hughes DP, Schulz A, Petersen KS, Konrad H, Stauffer C, Kiran K, Espadaler X, d’Ettore P, Aktaç N, Eilenberg J, Jones G, Nash D (eds) (2008) The Evolution of Invasiveness in Garden Ants. PLoS ONE 3(12): e3838. doi:10.1371/journal.pone.0003838
Zabala A., Pons X., Aulí-Llinàs F., Serra-Sagristà J. (2008) Image compression effects in visual analysis. Proceedings of SPIE - The International Society for Optical Engineering. 7084: 0-0.EnllaçDoi: 10.1117/12.798572
This study deals with the effects of lossy image compression in the visual analysis of remotely sensed images. The experiments consider two factors with interaction: the type of landscape and the degree of lossy compression. Three landscapes and two areas for each landscape (with different homogeneity) have been selected. For every of the six study area, color 1:5000 orthoimages have been submitted to a JPEG2000 lossy compression algorithm at five different compression ratios. The image of every area and compression ratio has been submitted to on-screen photographic interpretation, generating 30 polygon layers. Maps obtained using compressed images with a high compression ratio present high structural differences regarding to maps obtained with the original images. On the other hand, the compression of 20% obtains values only slightly different from those of the original photographic interpretation, but these differences seem owed to the subjectivity of the photographic interpretation. Therefore, this compression ratio seems to be the optimum since it implies an important reduction of the image size without determining changes neither in the topological variables of the generated vector nor in the obtained thematic quality.
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