Rosario G. Gavilán

Alpine cushion plants inhibit the loss of phylogenetic diversity in severe environments

Biotic interactions can shape phylogenetic community structure (PCS). However, we do not know how the asymmetric effects of foundation species on communities extend to effects on PCS. We assessed PCS of alpine plant communities around the world, both within cushion plant foundation species and adjacent open ground, and compared the effects of foundation species and climate on alpha (within-microsite), beta (between open and cushion) and gamma (open and cushion combined) PCS. In the open, alpha PCS shifted from highly related to distantly related with increasing potential productivity. However, we found no relationship between gamma PCS and climate, due to divergence in phylogenetic composition between cushion and open sub-communities in severe environments, as demonstrated by increasing phylo-beta diversity. Thus, foundation species functioned as micro-refugia by facilitating less stress-tolerant lineages in severe environments, erasing a global productivity - phylogenetic diversity relationship that would go undetected without accounting for this important biotic interaction.

Climatic classification and ordination of the Spanish Sistema Central: relationships with potential vegetation

Monthly precipitation and monthly mean temperature records from 255 meteorological stations in Central Spain (Spanish Sistema Central) were analyzed by cluster and principal component analyses. Classification separated 14 groups according to altitude, geographical distribution, as well as the combination of rainfall and temperature. The first cluster emerged as significantly higher and colder than the second. Then, two ordinations were carried out: one for the 14 groups extracted from the classification and a second for the total station pool. The second ordination was compared with potential natural vegetation data taken around each station. The first ordination summarized the principal climatic characteristics of the Spanish Sistema Central: its behaviour is that of a typical Mediterranean mountainous territory combining summer aridity and variation of temperature with altitude and the influence of winter winds. The ordination of all stations reflected a thermal, rainfall and summer aridity gradient. Meteorological stations situated at the highest altitude or with highest precipitation records characterized by scrub communities or pine woods and Quercus pyrenaica forests, appeared well-separated along the first two axes. Only the most thermophilous Q. rotundifolia associations could be clearly separated. The fourth axis was useful in clarifying some vegetation overlap of deciduous and sclerophyllous forests, along an east-west summer aridity gradient.Nomenclature: Tutin et al. (1964-1980) for plants; Rivas-Martínez (1987) and Rivas-Martínez et al. (1987) for syntaxa.

Climatic discrimination of Mediterranean broad‐leaved sclerophyllous and deciduous forests in central Spain

. Climatic differences between three types of deciduous (Quercus pyrenaica) and three types of sclerophyllous (Quercus rotundifolia) Mediterranean forests in the Spanish Sistema Central were analyzed by means of Canonical Discriminant Analysis and Janceys Discriminant Analysis, applied in successive steps to data from 252 meteorological stations. Climatic data included temperature and precipitation records as well as bioclimatic indices. Discriminant analysis was applied to broad-leaved sclerophyllous and deciduous forest communities sampled at each meteorological station using phytosociological methods. Annual and seasonal (summer, spring) water availability are the most important factor controlling the distribution of the two physiognomic forest types; southwestern associations of Quercus pyrenaica and Q. rotundifolia differ from their colder homologues by annual and monthly temperatures; western associations were separated from eastern ones in terms of annual and seasonal precipitation gradients. Discriminant analysis was a good technique to explore climatic gradients not shown by other general ordination or classification methods.

Are soil characteristics and understorey composition controlled by forest management

Data from 30 plots of Castanea sativa Miller stands were analysed to study the relationships among soil, understorey composition and management. Floristic cover percentage and edaphic features were separately studied by means of PCA. After that, correlations between floristic and edaphic axes were carried out by means of Pearson product‐moment correlation; and finally, correlations between floristic or edaphic axes and silvicultural characteristics were also calculated. PCA of soil variables showed differences between stands located on granitic rocks and floristic PCA showed a clear difference between managements. There were correlations between floristic axes and soil or silvicultural measurements, while correlations between soil axes and silvicultural measurements were not significant. The results indicated there were no general trends between soil properties and forest management probably due to deepness and development of soils. The management is the first source of variation on understorey composition: high forests were poorer than coppice stands. There were also differences within coppice stands related to the type of post-harvest practice. Finally temporal changes in nutrient rates were related to the understorey composition, as well. # 1999 Elsevier Science B.V. All rights reserved.

The expansion of thermophilic plants in the Iberian Peninsula as a sign of climatic change

Investigations conducted in the Iberian Peninsula over the last three decades show how some thermophilic plant species have extended their range. The native thermophilic species, Dittrichia viscosa (L.) W. Greuter, and Sonchus tenerrimus L., have expanded, apparently without any direct intervention by man. In addition, alien species have crossed biogeographical barriers to expand their range into new areas. These include taxa from the neotropics and the Cape Province of South Africa which have colonised areas close to the Mediterranean coast (Ageratina adenophora (Spreng.) King. & H. Rob., Araujia sericifera Brot., Tropaeolum majus L. and Arctotheca calendula (L.) Levyns). By analysing thermometric data series from 10 meteorological stations, we were able to correlate the expansion of the ranges of these species with mean temperature increases, particularly those of mean minimum temperatures. If other thermophilic species (native and introduced) also increase their range, this could have serious consequences for plant biodiversity.

Spatial patterns and interspecific relations analysis help to better understand species distribution patterns in a Mediterranean high mountain grassland

The aim of this study is to investigate distribution patterns of species occurring at definite spatial scales and to address the main ecological factors that structure a Mediterranean high mountain grassland community. Following the protocols of the GLORIA long-term study, four summits were sampled during the year 2006 and 2007 in Sierra de Guadarrama (Spain). The data recorded on two of those summits were analysed for spatial pattern of species, interspecific associations and environmental relationships were determined from the recorded data. This was done by multivariate analyses (ordinations), SADIE analyses (distance indices) and Pearson χ2 test, respectively. Results showed that chamaephyte species were more abundant in less disturbed situations whilst caespitose hemicryptophyte species and mosses were more abundant in disturbed ones. High mountain species were more abundant in less disturbed situations. Higher spatial heterogeneity was detected on northern and eastern slopes, which could be related to the increased environmental severity of northern exposures and to the greater intensity of the disturbances on eastern exposures. The frequent aggregated distribution of a few species may be related to facilitation processes due to their frequent participation in positive interactions. Finally we observed that positive pairwise associations of species were more frequent than negative associations. The relevance of the studied relationships lied in a better understanding of those threats on high mountain biodiversity induced by climate warming.

Plant functional strategies and environmental constraints in Mediterranean high mountain grasslands in central Spain

Background: The relationship between plant traits and environmental factors will be of value in understanding of functional strategies that plants have developed to cope with the environmental constraints on plant life in Mediterranean high mountain ecosystems. Aims: The aims of this study were (1) to explore the variation in plant traits in relation to environmental variability; (2) to analyse the functional strategies of species; and (3) to assess the habitat constraints for the species in the study area. Methods: We sampled the floristic composition of 76 1 m × 1 m plots on five summits over 2,100 m above sea level in the mountains of the Sistema Central, Spain. Soil properties and temperature and grazing disturbance parameters were recorded. Eight plant traits were assessed in 21 species. Environmental variability and the co-variation of functional traits were analysed by RDA and PCA, respectively. Plant traits and environmental variability were related using fourth-corner analysis. Results: Traits related to resource acquisition, such as leaf size and N concentration, varied with soil temperature and estimated summer water availability. Leaf dry matter content was found to be related to estimated water availability and soil pH. Seed mass was a factor of snow cover duration and water availability, and clonality to the duration of the vegetative period and estimated water availability. Grazing disturbance was related to the mean plant height of the species. Conclusions: The results suggest that low temperatures, rather than water shortage, may be the principal limiting factor for resource acquisition in plants. Nevertheless species establishment is limited by water shortage during summer in these Mediterranean high mountain communities.

Syntaxonomical update on the relict groves of Scots pine (Pinus sylvestris var. iberica) and Spanish black pine (Pinus nigra subsp. salzmannii) in the Gredos range (central Spain)

Pure and mixed high-mountain pine forest vegetation of the Gredos range (central Spain) was studied using 57 releves and multivariate analyses (hierarchical cluster analysis and detrended correspondence analysis). Classification of the releves resulted in 7 vegetation units, 3 of which were ranked as associations and only one as subassociation. DCA diagrams of releves and taxa indicated that floristic differentiation was attributed mainly to factors such as altitude. Differential taxa of vegetation units were chosen based on their phi coefficient values. The statistic discrimination of some of these vegetation units has allowed us to propose a new association and a new subassociation of other community described in a previous paper.

Is this the end? Dynamics of a relict stand from pervasively deforested ancient Iberian pine forests

Abstract A drier climate together with intense management can be detrimental for species when they are found at their xeric limit. We analyzed the dynamics of Pinus sylvestris in Central Spain in relation to colonization by more drought-tolerant Quercus pyrenaica. The studied forest presents high biodiversity and is one of the last stands relict from a widespread pine-dominated forest in West-Central Iberian Mountains demised by human deforestation. The observed age patterns could suggest a natural regeneration origin of the current stand for both species. However, while oaks regenerated continuously since the 1950s, there was almost no pine regeneration after the 1870s. Therefore, the lack of pine regeneration was previous to recent climatic changes. Pine stands with ongoing oak colonization were likely thinned in the 1920s in opposition to pure pine stands. Mixed and pure stands expressed certain differences in their response to climate. Pines suffered more from high temperatures from spring to fall, which would reflect their lower tolerance to drought than oaks. Cross-wavelet analysis showed that pine exhibited an increase in their sensitivity to drought intensity in the last years. However, the dominant pine canopy established in the nineteenth century does not show symptoms of growth decline in response to climate change. The factors determining the disruption of pine regeneration need to be determined. Management could have played a dominant role constraining stand dynamics, threatening pine sustainability through modifications of the understory vegetation and soil properties.

Una breve revisión de técnicas de análisis multivariantes aplicables en Fitosociología

ESUUOERO, A.: GAVILAN, R. & RUBIO, A. 1994. A brief review ef multivariate methods with Phytosociological applicability. Botan/ca Complutensis, 19: 9-38. A bricf review of multivariate methods used in Phytosociological studies is presented. Thcse methods have been grouped in twa items: gradient techniques arid numericai classifieaiions. Some general concepts like transtormation and standarization of data and similarity measures have been previously conmented. Gradient methods have been classified in regression, calibration, ordination and constrained ordination techniques and, in Ihe other hand, we have considered hierarchical and divisive methods under classification procedures. Finally, advanced numerical approaches, like partitions comparisons or consensus classifications, are treated.