F. D. Pineda

Species diversity patterns in Mediterranean grasslands

. A field experiment involving herbivore exclusion, ploughing, and the combination of both was carried out over a period of 4 - 5 yr in Mediterranean grasslands located along an elevational gradient. The empirical results provide a general hierarchical framework for understanding patterns of plant species diversity in thesegrasslands. In grazed grasslands, plant species density decreased as altitude increased, and this pattern was maintained through time. The reduced seasonality along the climatic gradient is suggested as the extrinsic, indirect control factor. Ploughing caused species loss, but after 4 yr the original diversity was recovered in most grasslands. Our hypothesis is that a negative feedback mechanism regulates species increase towards a characteristic level. A trend of species density reduction was observed in ungrazed grasslands. Plant-herbivore interaction is considered to be essential for maintaining species diversity in grazed grasslands and for the recovery of diversity in mechanically disturbed grasslands.

Shrub encroachment in Argentinean savannas

Abstract In the Wet Chaco region of Argentina, increasing shrub encroachment in savannas over the last few decades has led to important changes in the structure and functioning of the landscape. Some sectors of this territory are characterized by the appearance of circular clusters of woody patches, dispersed throughout the grassland matrix. The increasing size of these patches leads to a gradual change from grassland to dense shrubland. We studied these circular woody patches in the eastern region of the Argentine province of Formosa and characterized the variation in terms of floristic composition, diversity and predominant seed dispersal mode in different size patches. We observed an increase in species richness, diversity and compositional heterogeneity among patches with increasing patch size. Seed dispersal by animals, especially birds, is an important factor in the expansion of these woody vegetation patches within the grassland matrix. Nomenclature: Zuloaga et al. (1994, 1996a, b). Some native names were included using quotation marks.

Relationship between landscape typology and socioeconomic structure. Scenarios of change in Spanish cultural landscapes

Abstract We formalized the canonical correspondence between the socioeconomic structure and the cultural landscape in a large county in the NE of Spain. The reference units consisted of a set of municipalities, at which scale the socioeconomic information is registered. We described the landscape using multivariate ordination analyses of data characterizing the physiognomy of the municipalities. We interpreted the dispersion of these municipalities on the plane obtained with the main ordination axes. The relationship between ‘landscape typology’ and ‘socioeconomic structure’ was expressed by multiple stepwise regression, where the independent variables were socioeconomic descriptors of the municipalities, and the dependent variable the coordinates of these on the ordination axes. We obtained a regression equation for each axis. Each of these allowed us to establish the optimum number of socioeconomic variables, and the importance and sign of these, in order to characterize the landscape variability. The relationship encountered is presented on maps as trend surface analysis, showing ‘classes’ or discrete types of landscape. We considered hypotheses of change in the main socioeconomic indicators and, using the trend surfaces as a base, we calculated the resulting changes in the landscape typology (the municipalities change position on the trend surfaces maps). We also tested, among others, scenarios based on the development of activities linked to the abandonment of agricultural activities. The procedure experimented shows a more or less high and significant dependence among different variation tendencies of the landscape in the county studied and its socioeconomic structure. Formalizing this dependence involves 12 variables of the set of descriptors used in the socioeconomic characterization of the county. The models experimented enable us to convey this relationship to simulated scenarios and to evaluate the implications of certain socioeconomic policies for landscape typology.

Influence of landscape complexity and land management on woody plant diversity in northern Spain

Abstract. Changes in land use, particularly the type of forest management, and their spatial pattern, especially woody plant diversity, were related to each other in an area in the Basque region (Spain). The number and diversity of boundaries between landscape patches is related to the development of the spatial complexity of the landscape, C(s), measured in bits and defined as: C(s) = H(b) H(l), where H(b) is the boundary diversity H(1) the spatial heterogeneity generated by these boundaries. As to the vegetation types, changes in land use over the last 50 yr have resulted in a less diversified and more fragmented landscape, especially on a small scale. Forest plantation has become the predominant land use. The frequency of land use changes is studied regarding its influence on the present levels of woody plant diversity.

Adaptation of ecological systems: compositional patterns of species and morphological and functional traits

. The species composition and morphological and functional traits of ecological systems are compared. The significance of the resulting relationship is interpreted considering the underlying spatial environmental variation. Using 60 morphological and functional traits, a gradient of ecological persistence was detected in Mediterranean grasslands along an altitudinal range of ca. 1200 m. This pattern coincides with the one expressed by its taxonomic composition and thus permits ‘styles of adaptation’ of ecological systems to be recognized. Species composition may represent one of the possible combinations which optimises its environmental fit. The relevance to ecological theory of this pattern of grassland organization is discussed in the context of a hypothetical model of evolution.

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.

Climate and vegetation at the Eurosiberian-Mediterranean boundary in the Iberian Peninsula

Abstract. The Northern Iberian Peninsula is dominated by various types of vegetation from deciduous oak and ash to evergreen oak woodlands. A recent vegetation map of Spain portrays vegetation series which are characterized in terms of their phytogeographic region or bioclimatic (altitudinal) belt. The aim of this paper is to determine whether the areas comprised by both phytogeographic regions (Eurosiberian and Mediterranean) in the study area, as established from the phytogeographic characterization of the vegetation, can be discriminated by climatic variables using multivariate methods, and to compare these with other conventional approaches. In addition, bioclimatic (altitudinal) belts and the main vegetation types were tested for discrimination by climatic variables. Conventional climatic criteria as well as discriminant and principal component analysis were applied to climatic data from 205 meteorological stations for which vegetation information had been taken from the vegetation map. Conventional criteria are good predictors of the phytogeographic division (Mediterranean and Eurosiberian regions) in the study area. Results were improved by multiple discriminant analysis based on climatic data of the dry period of the year (June to September). Both regions in the study area can be predicted with over 95 % accuracy. Using the same multivariate procedure and temperature data the bioclimatic (altitudinal) belts of the study area can be predicted with over 90 % accuracy. The main vegetation groups of the study area can also be predicted with over 80 % accuracy. Ordination analysis supported the results of the discriminant analysis. Empirical models have been generated to predict the phytogeographic- and belt character of any station in the area. The significance of the various periods of the year for discriminating regions and belts is evaluated. The responsiveness to climatic events during the year may be region specific. This study confirms the strong relationship between climate and vegetation in the Northern Iberian Peninsula, particularly regarding the Eurosiberian-Mediterranean boundary.

Production and spatial structure of Mediterranean pastures in different stages of ecological succession

The aim of this paper is to describe the changes of Mediterranean pasture phytomass and their dependence on succession, slope geomorphology and herbivore consumption. Four neighbouring slopes of similar aspect and steepness, located in a pasture area of Central Spain, were chosen for sampling. The slopes had not been cultivated for 1, 3, 8 and 40 years respectively. On each slope both the upper, erosion zone and the lower, accumulation zone were sampled during the months of plant growth (April to July), phytomass being recorded in plots where herbivore consumption was avoided with protection cages and in unprotected plots. Results from the protected plots show that the upper and lower parts of slopes undergo a different development during succession. The highest values of phytomass reached, tended to decrease during succession in the upper zones, the same being true for production. However in the lower zones both parameters tended to increase in time. The ratio P/B, widely known in ecology to decrease with time, did not seem to behave as a usual index of succession in the studied ecosystem. In the upper zone this ratio tended to decrease but in the lower zone it increased with succession after the first years. Phytomass consumption by herbivores was progressively concentrated during succession in the slope sectors of greater production, mainly in the lower zone, which increased its productivity as the slope-talweg system became functional. The evolution of the ecological structure of a slope should be interpreted not only as a result of the tolerance of species to phsysico-chemical factors. It may also reveal the existence of an important interaction between the pasture and the grazing behaviour of exploiting animals. Multivariate analysis of phytomass records revealed a trend of temporal variation which should be identified with the progress of succession.

Space-time variability in mediterranean pastures analyzed with diversity parameters

Different parameters of diversity and spatial niche amplitude (Piclou, 1975, Pineda et al., 1981b) have been used to describe the spatial organization of mediterranean grasslands in Central Spain. A slope sampled by 480 contiguous 8×8 cm quadrats proved to have a homogeneous floristic distribution when it was divided into 160 parts and maximum heterogeneity when divided into 4 sectors. These sectors corresponded to different geomorphological zones of the slope. The complexity of vegetation distribution on the slope was reflected by differences in organization — measured by diversity parameter A=H(P/E)/log2 N (number of plots) between the parts obtained by division. The presence of low-entropy species — specialists - and high entropy species — generalists — was related to the different scales of slope organization. The spatial distribution of plants was compared for different successional stages. Multivariate analysis of sampling plots confirmed previously identified organizational characteristics and clarified the nature of transitions between communities of different floristic composition or structure.

A fragmented landscape in northern Spain analyzed at different spatial scales: Implications for management

Changes in landscape pattern are analyzed through sampling plots of different size taken along a time series of aerial photographs at three scales of observation. The results indicate that variation in the landscape pattern shows a less pronounced change at the local scale than at larger scales and that appreciation of the structure of this landscape and descrip- tion of its temporal variation are scale-dependent. Analysis of the spatial complexity on different scales, measured by the C(s) index (Rescia et al. 1994), shows that the number of types of boundary between patches is the most important landscape component on all scales. Spatial com- plexity and the number of boundary types are related to woody plant diversity at a local scale. In the studied landscape, human activities on a local scale strongly influence the spatial configuration on a regional scale. This concerns territorial planning, the main problem of which is not found in selecting a correct observation scale, but in recognizing that the change under study occurs at various scales at the same time. This underlines the importance of analysing the landscape pattern at different scales with the design of plans and conservation programs in mind.