José M. de Miguel

Herbaceous plant richness and vegetation cover in Mediterranean grasslands and shrublands

Different types of relationship between herbaceous species richness and several parameters indicating abundance of plant material (herbaceous, woody plants, litter and bare ground cover) are presented. The data were obtained from 50 sites along a 300 km strip running from E to W within Spain and Portugal. Each site was representative of the silvo-pastoral landscape of the Mediterranean type ecosystems of the Iberian peninsula, and contained two neighboring patches, one of grassland and the other of shrubland. 3,600 20 × 20 cm subplots were randomly located (72 per site, 36 per patch) crossing the boundary grassland/shrubland. This approach allowed us to analyze the richness-occupation relationship of the space from different points of view: among and within the sites, and among and within the grassland and shrubland plant communities. We found a unimodal relationship between richness-cover similar to the one generally accepted between richness and biomass. Our results show that the dependence of this relationship varies depending on the spatial scale of the analysis and on the type of data used. When the whole region is taken into account, significant unimodal relationships are found between richness and herbaceous cover, litter and bare ground, and a negative linear relationship with woody plant cover. Within the sites there are mainly linear or non-significant relationships. But the results also depend on the type of communities analyzed. In pastures, the unimodal relationship represents the combination of positive and negative linear responses for low and high cover values, respectively. The value for herbaceous cover in which maximum richness occurs is around 60%. In shrublands, this value for cover also corresponds to maximum species richness, although the possibilities of reaching it are limited by other variables, such as woody plant cover. This implies that, on not considering variability at local scale, the relationship is linear and positive. This paper shows the existence of a common model related to herbaceous cover, but this model has multiple controlling factors that act differently in each type of community.

Matter transfer and land use by cattle in a dehesa ecosystem of Central Spain

The transfer of matter by cattle in a ‘dehesa’ patureland in Central Spain has been quantified by mapping the distribution of dung and different types of cattle behaviour in several areas distinguished by their geomorphological position, vegetation structure and management regime.

Understanding Mediterranean Pasture Dynamics: General Tree Cover vs. Specific Effects of Individual Trees

Abstract The study investigated the effect of general and homogeneous tree cover on grassland composition on an extensive Mediterranean rangeland with sparse oak trees in central Spain. We analyzed this effect together with other significant factors identified in this type of rangeland: topography and plowing. Data were collected in the 1984 growing season and they form part of a historical database on the characteristics of vegetation and livestock behavior; these data refer to grasslands below and away from the tree crowns of 91 individual trees, located in different topographical positions and in areas that were last plowed at different times. We used multivariate analyses to identify the main compositional trends of variation in pasture communities. The results indicate that the herbaceous community below tree crowns was more similar to that of the lowland areas than to the nearby areas away from the tree. This result supports the idea of tree cover in semiarid rangelands as a factor attenuating the effects on pastures of environmental conditions typical of high and intermediate topographical positions—generally presenting low soil moisture and fertility. Coupled with this, we also found effects of some individual trees related with the way livestock uses them as shelter and resting places. Our results indicate that the role played by dispersed trees in the management of this type of rangeland should be analyzed at two complementary spatial scales: the overall effect of tree cover as a factor acting at landscape scale and the specific effect of some individual trees acting at a more detailed scale.

La movilidad interurbana en la línea de alta velocidad Madrid-Sevilla: Rasgos definitorios a los 10 Años de su implantación

The success of the high speed train, in growing competition with other means of transport (especially the aeroplane and the car), has changed some of the standards of inter-city mobility between the principal cities on its route. The end of the first ten years of operation of the «AVE» high speed train Madrid-Seville is a good moment for a reflection on the impact that the high speed train has made on the growing demands of mobility in the post-industrial society of our country. The result of the analysis demonstrates a persistent increase in the number of travellers who use this means of transport, and growing satisfaction of the necessities of movement: professional, work-related, family-related, tourist, etc.; which have an ever more profuse effect on social collectives of varied and contrasting socioeconomic and demographic characteristics.

Ecotypic differentiation and phenotypic plasticity combine to enhance the invasiveness of the most widespread daisy in Chile, Leontodon saxatilis

Dispersal and reproductive traits of successful plant invaders are expected to undergo strong selection during biological invasions. Numerous Asteraceae are invasive and display dimorphic fruits within a single flower head, resulting in differential dispersal pathways - wind-dispersed fruits vs. non-dispersing fruits. We explored ecotypic differentiation and phenotypic plasticity of seed output and fruit dimorphisms in exotic Chilean and native Spanish populations of Leontodon saxatilis subsp. rothii. We collected flower heads from populations in Spain and Chile along a rainfall gradient. Seeds from all populations were planted in reciprocal transplant trials in Spain and Chile to explore their performance in the native and invasive range. We scored plant biomass, reproductive investment and fruit dimorphism. We observed strong plasticity, where plants grown in the invasive range had much greater biomass, flower head size and seed output, with a higher proportion of wind-dispersed fruits, than those grown in the native range. We also observed a significant ecotype effect, where the exotic populations displayed higher proportions of wind-dispersed fruits than native populations. Together, these patterns reflect a combination of phenotypic plasticity and ecotypic differentiation, indicating that Leontodon saxatilis has probably increased propagule pressure and dispersal distances in its invasive range to enhance its invasiveness.

The invasiveness of Hypochaeris glabra (Asteraceae): Responses in morphological and reproductive traits for exotic populations

Scientists have been interested in many topics driven by biological invasions, such as shifts in the area of distribution of plant species and rapid evolution. Invasiveness of exotic plant species depends on variations on morphological and reproductive traits potentially associated with reproductive fitness and dispersal ability, which are expected to undergo changes during the invasion process. Numerous Asteraceae are invasive and display dimorphic fruits, resulting in a bet-hedging dispersal strategy –wind-dispersed fruits versus animal-dispersed fruits–. We explored phenotypic differentiation in seed morphology and reproductive traits of exotic (Chilean) and native (Spanish) populations of Hypochaeris glabra. We collected flower heads from five Spanish and five Chilean populations along rainfall gradients in both countries. We planted seeds from the ten populations in a common garden trial within the exotic range to explore their performance depending on the country of origin (native or exotic) and the environmental conditions at population origin (precipitation and nutrient availability). We scored plant biomass, reproductive traits and fruit dimorphism patterns. We observed a combination of bet-hedging strategy together with phenotypic differentiation. Native populations relied more on bet-hedging while exotic populations always displayed greater proportion of wind-dispersed fruits than native ones. This pattern may reflect a strategy that might entail a more efficient long distance dispersal of H. glabra seeds in the exotic range, which in turn can enhance the invasiveness of this species.