Jordi Carreras

Coarse-scale plant species richness in relation to environmental heterogeneity

Abstract We test to what extent mean environmental conditions and environmental heterogeneity are related to species richness in a regular geographical grid system (UTM) of 10 km × 10 km in the NE Iberian Peninsula (i.e. Catalonia, ca. 31900 km2). Species richness of each UTM quadrat was estimated by compiling a large database (more than a million records) from bibliographic references and atlases. Mean environmental conditions of each quadrat were derived from climatic maps. Environmental heterogeneity was estimated from the diversity of geological substrates and climatic classes in each quadrat. The increase in effective (real) area due to topographic complexity was also considered (derived from the digital elevation model). The statistical analysis was performed by a weighted analysis of deviance assuming a negative binomial error distribution. The results suggest that species richness in the study area is a function of both within-quadrat heterogeneity (specifically, effective area, heterogeneity of geological substrates, heterogeneity of January temperature) and mean environmental conditions (mean annual temperature, Thornthwaite moisture index and aspect). All these parameters showed a positive relationship with species richness. Quadrat heterogeneity accounted for ca. 2/3 of the explained deviance, suggesting the importance of environmental heterogeneity when using a geographical grid system. The study fits well with earlier results on the importance of climatic parameters on plant species richness and provides one of the few rigorous, quantitative, coarse-scale studies testing environmental heterogeneity in plant species richness.

THE EFFECT OF BEDROCK TYPE, TEMPERATURE AND MOISTURE ON SPECIES RICHNESS OF PYRENEAN SCOTS PINE (PINUS SYLVESTRIS L.) FORESTS

The relationship between environmental parameters (bedrock type, temperature and moisture index) and understorey species richness was studied from a large phytosociological data base on Pyrenean Scots pine (Pinus sylvestris L.) forests. Generalized linear models were used to test this relationship. Total species richness and species richness of the different life forms were considered. The results suggest different patterns for the different life forms, and that the richest forest was on the calcareous bedrock of north-facing slopes at low altitudes.

Timberline structure and limited tree recruitment in the Catalan Pyrenees

Background: Pyrenean timberlines, lowered to various extents through ancient land use, are expected to rise due to abandonment of land use and climate warming. Aims: To provide a comprehensive survey of the timberline in the Catalan Pyrenees, at the landscape, plant community, and tree population levels. Methods: We assessed the present location of timberlines by means of GIS techniques and characterised the treeline ecotone in 12 representative plots, where we took small phytosociological relevés (surface cover type, vegetation structure and species cover) and studied the regeneration of Pinus uncinata (seedlings and saplings). Results: The potential timberline was mostly found between 2300 and 2400 m a.s.l., with complex variation in these values due to bioclimatic and topographic diversity. Most of the present timberline was found at far lower altitudes than its potential location. Present forests reached the potential timberline about 25% along its total length. At natural or semi-natural treelines, the transition from subalpine forest to open alpine landscapes was relatively sharp. It was formed by the irregular alternation of two or three contrasting plant community types (forest, dwarf-shrub, grassland). Most Pinus regeneration was recorded where vegetation mosaics occurred on a fine scale. The highest numbers of Pinus seedlings and saplings were found emerging from bare ground or litter in small vegetation gaps. Over recent years Pinus recruitment showed very slow growth and a strong limitation in reaching the pole stage. Conclusions: In Pyrenean treeline ecotones situated near to their potential altitudes, recruitment and growth of existing Pinus uncinata seedlings and saplings is unlikely to produce pronounced infilling and thus perceptible changes in high-altitude forest cover.

Land cover classification at a regional scale in Iberia: separability in a multi-temporal and multi-spectral data set of satellite images

Earth observation at regional scales, such as of the Iberian Peninsula or Mediterranean Basin, is an important tool to understand the relationships between climate and surface properties. Among the different layers of information that can be derived from satellite imagery, land cover maps are important by themselves and as an aid to infer other variables. Land cover legends at regional scales require finer categories than those used at a global scale, which implies processing multi-spectral imagery acquired by Earth observing systems with daily acquisition rates. In this article we discuss several alternatives to analyse satellite image datasets that are both multi-temporal and multi-spectral, with spatial resolution of 1u2009km2. In order to facilitate the interpretation of our results, we restrict our analysis to pixels that correspond to cells with a uniform and known cover on the ground, as described by a detailed vegetation map, in Catalonia (NE Spain). Our results indicate that canonical redundancy analysis is efficient at reducing the multi-spectral and multi-temporal space while keeping high statistical separability among habitat types. The small fraction of uniform pixels (∼2%) suggests that, at least for the Mediterranean Region, data fusion techniques would be convenient to increase spatial resolution in the dataset, and that instruments keeping daily acquisition rates but with higher spatial resolution (∼1u2009ha) should be considered.

Drastic reduction in the potential habitats for alpine and subalpine vegetation in the Pyrenees due to twenty-first-century climate change

Recent climate change is already affecting both ecosystems and the organisms that inhabit them, with mountains and their associated biota being particularly vulnerable. Due to the high conservation value of mountain ecosystems, reliable science-based information is needed to implement additional conservation efforts in order to ensure their future. This paper examines how climate change might impact on the distribution of the main alpine and subalpine vegetation in terms of losses of suitable area in the Oriental Pyrenees. The algorithm of maximum entropy (Maxent) was used to relate current environmental conditions (climate, topography, geological properties) to present data for the studied vegetation units, and time and space projections were subsequently carried out considering climate change predictions for the years 2020, 2050 and 2080. All models predicted rising altitude trends for all studied vegetation units. Moreover, the analysis of future trends under different climate scenarios for 2080 suggests an average loss in potential ranges of 92.3–99.9xa0% for alpine grasslands, 76.8–98.4xa0% for subalpine (and alpine) scrublands and 68.8–96.1xa0% for subalpine forest. The drastic reduction in the potential distribution areas for alpine grasslands, subalpine scrublands and Pinus uncinata forests highlights the potential severity of the effects of climate change on vegetation in the highest regions of the Pyrenees. Thus, alpine grasslands can be expected to become relegated to refuge areas (summit areas), with their current range being taken over by subalpine scrublands. Furthermore, subalpine forest units will probably become displaced and will occupy areas that currently present subalpine scrub vegetation.

Assessing the natural interest of the landscapes of Andorra, a mountain country under contrasted land use changes

Abstract In this paper, we present a method for analysing the landscape, using the example of Andorra, through assessing the interest of the CORINE units recognised. The starting point was a map of habitats previously drawn at the 1:25,000 scale, on infrared orthoimages. It includes some 3,000 polygons, identified by 103 legend units based on the CORINE habitats. Diversity, naturalness, endemicity, rarity and other attributes of each habitat were evaluated a priori and then combined with site features (analysed through the GIS Arclnfo) to yield a global evaluation for each legend unit. This enabled us to produce a map showing a few levels of natural interest in the landscape of Andorra and to draw the attention to main tendencies of change, which are, when compared with similar neighbouring Pyrenean valleys, not so affected by human activity.

Multitemporal profiles of vegetation indices of Mediterranean habitats: an analysis of data provided by the VEGETATION instrument

Annual cycles of greenness, as observed from coarse satellite imagery, have proven to be a useful proxy of phenology of light interception. VEGETATION imagery has superior radiometric and geometric specifications compared to the commonly used NOAA-AVHRR images, which should result into a more accurate description of phenolgy. We have analyzed the annual cycles of VEGETATION reflectance quotients from 36 S10 products for a number of very detailed habitat types in the NW Mediterranean basin. We selected all VEGETATION pixels (1 km2) that were included within one single habitat patch, extracted their multi-temporal reflectance data and ancillary information, and analyzed the time series of normalized differences of near-infrared minus red and of near-infrared minus medium-infrared reflectance values. The distribution of habitats on the principal components plane indicated that individual time series tended to cluster by habitat type and that the main sources of variation were the average value of the time series and the position of the maximum value. The distribution of observations on the plane defined by both indices indicates a general linear correlation except if surface water is present. Our work shows the interest of the multi-temporal analysis of satellite imagery at detailed scales to fully understand the dynamics of light interception and the response of mixed multi-temporal VEGETATION image pixels.