Increasing aridity threatens the sexual regeneration of Quercus ilex(holm oak) in Mediterranean ecosystems

Knowledge of the recruitment of dominant forest species is a key aspect for forest conservation and the ecosystem services they provide. In this paper, we address how the simultaneous action of climate change and the intensity of land use in the past influence the recruitment of a forest species that depends on the provision of nurse plants to recruit. We compared the number of saplings (up to 15 years old) and juveniles (16 to 50 years old) of Quercus ilex in 17, 5.3 ha plots in the Iberian System (eastern Spain). We used a gradient of past deforestation intensity crossed with two levels of average annual precipitation, one of them at the lower limit of the species'' precipitation niche (semi-arid) and the other at the optimum (sub-humid). We also examined the association between recruits and nurse plants and the effect on this association of plot-scale factors, such as seed abundance (reproductive Q. ilex), microsites (nurse species and soil availability), and large herbivores. The increase in aridity in the last decades has drastically reduced the recruitment of new individuals in the forests of Q. ilex located in the lower limit of their precipitation niche, regardless of the intensity of past deforestation that they suffered. Recruitment in these climatic conditions depends almost exclusively on large trees and shrubs whose abundance may also be limited by aridity. The lack of regeneration questions the future of these populations, as the number of individuals will decrease over time despite the strong resistance of adult trees to disturbance and drought

Characterization of the natural variation in Arabidopsis thaliana metabolome by the analysis of metabolic distance

Metabolite fingerprinting is widely used to unravel the chemical characteristics of biological samples. Multivariate data analysis and other statistical tools are subsequently used to analyze and visualize the plasticity of the metabolome and/or the relationship between those samples. However, there are limitations to these approaches for example because of the multi-dimensionality of the data that makes interpretation of the data obtained from untargeted analysis almost impossible for an average human being. These limitations make the biological information that is of prime importance in untargeted studies be partially exploited. Even in the case of full exploitation, current methods for relationship elucidation focus mainly on between groups variation and differences. Therefore, a measure that is capable of exploiting both between- and within-group biological variation would be of great value. Here, we examined the natural variation in the metabolome of nine Arabidopsis thaliana accessions grown under various environmental conditions and established a measure for the metabolic distance between accessions and across environments. This data analysis approach shows that there is just a minor correlation between genetic and metabolic diversity of the nine accessions. On the other hand, it delivers so far in Arabidopsis unexplored chemical information and is shown to be biologically relevant for resistance studies

Conservation of Mediterranean oak woodlands: understorey dynamics under different shrub management

The effect of experimental disturbances on the dynamics of a shrub community was studied on a ‘Montado’ ecosystem, in southern Portugal. The evolution of the community physiognomy, composition and diversity were monitored after shrub clearing followed by biomass removal, deposition on soil surface and incorporation with the soil, over a 9-year period. Maximum shrub density was recorded in the first year after the disturbances, excepting in mulched plots which showed the greatest number of individuals 1 year later. The increment of shrub leaf biomass was very fast in the first 3 years, whereas wood production was slower but occurred along the whole study period. At the end of the study, leaf and wood biomass was still significantly lower than in the predisturbance situation. The variation pattern of leaf area index was similar to that of leaf biomass. The evolution of total plant cover and diversity was similar across treatments. The highest species richness and diversity were recorded 2 years after cutting, decreasing afterwards with the increasing dominance of shrubs. Thus it seems likely that, although a 9 year period is too short for these communities to reach steady equilibrium, they are very resistant and resilient to disturbances, as regeneration was fast and vegetation dynamics was not influenced by differences among treatments. We can conclude that shrub clearing promotes biodiversity and the time of permanence of shrub patches depends on the particular goal we want to achieve

Conservation of Mediterranean oak woodlands: understorey dynamics under different shrub management

The effect of experimental disturbances on the dynamics of a shrub community was studied on a ‘Montado’ ecosystem, in southern Portugal. The evolution of the community physiognomy, composition and diversity were monitored after shrub clearing followed by biomass removal, deposition on soil surface and incorporation with the soil, over a 9-year period. Maximum shrub density was recorded in the first year after the disturbances, excepting in mulched plots which showed the greatest number of individuals 1 year later. The increment of shrub leaf biomass was very fast in the first 3 years, whereas wood production was slower but occurred along the whole study period. At the end of the study, leaf and wood biomass was still significantly lower than in the predisturbance situation. The variation pattern of leaf area index was similar to that of leaf biomass. The evolution of total plant cover and diversity was similar across treatments. The highest species richness and diversity were recorded 2 years after cutting, decreasing afterwards with the increasing dominance of shrubs. Thus it seems likely that, although a 9 year period is too short for these communities to reach steady equilibrium, they are very resistant and resilient to disturbances, as regeneration was fast and vegetation dynamics was not influenced by differences among treatments. We can conclude that shrub clearing promotes biodiversity and the time of permanence of shrub patches depends on the particular goal we want to achieve

Erosion, water availability and plant characteristics control plant colonization on semiarid eroded slopes

The objective of this study was to understand the mechanisms that control spontaneous plant colonisation on severely eroded slopes in a semiarid badland area of East Spain. More specifically, we aimed at (1) determining topographic thresholds for plant colonisation, (2) identifying the soil properties that limit plant establishment and (3) identifying plant traits that enable colonising species to cope with these limitations. We used slope angle and aspect as surrogates of erosion rate and water availability respectively. Since soil erosion and water availability can limit plant establishment and both interact in the landscape, we analysed variations in colonisation success with slope angle and aspect. Vegetation success was measured in terms of total vegetation cover on 156 different slopes. After determining slope angle thresholds for plant colonisation, soil was sampled on slopes just above and just below the threshold values for soil analysis in order to test for differences in soil properties related to plant establishment and development. Plant traits related to plant colonising capacity were analysed in two different groups of species: the group of species colonising the steep slopes near the threshold and the group of noncolonising species present on more gentie slopes but unable to colonise the slopes just below the threshold. The identified slope angle threshold values for plant colonisation clearly decreased from North to South. No differences were found in soil properties neither among slope aspects at the slope angle threshold values nor between slope positions (just below and above the threshold) within slope aspect classes. Long-distance dispersal mechanisms and ability of seeds to segregate mucilage in contact with water were more frequent characteristics in colonising species than in non-colonising ones. It is concluded that water availability for plants which, in turn, is controlled by the solar radiation can explain the differences in the slope angle threshold values for plant colonisation among slope aspect classes. Some important implications of these results in the context of ecological restoration of these severely eroded areas are also discussed.status: publishe

Road slope revegetation in semiarid mediterranean environments. Part I: Seed dispersal and spontaneous colonization

9 páginas, 2 figuras, 2 tablas.The importance of neighboring vegetation as a seed reservoir for spontaneous colonization of adjacent road slopes was analyzed in a semiarid region of east Spain. Two independent methodological approaches were used to examine the relative contribution of seed from neighboring vegetation and the efficiency of different seed dispersal strategies in plant colonization. We first used a randomization test to compare floristic similarity between road slopes, neighboring flora, and local flora (the regional species pool found in the same climate and soil conditions as the road slopes). Second, we compared seed dispersal mechanisms of road slope vegetation with those of the surrounding area using frequency analysis. Species composition of road slopes was more similar to that of the flora of adjacent surrounding areas than expected by chance. Anemochorous (wind-dispersed) plants were over-represented in road slopes 8 years after road slopes were built. We concluded that seed dispersal from neighboring vegetation is an important factor in the vegetative colonization of road slopes. However, this initial species pool was also strongly shaped by the harsh environmental conditions of roadcuts and southern aspect. These results have important implications in road slope restoration because they suggest that naturally vegetated areas should be maintained adjacent to road slopes to enhance seed immigration from species adapted to local site conditions, which will accelerate the successional process. The application of this single reclamation strategy and mixed strategies that combine the use of natural colonization and soil amendment for road slope restoration in Mediterranean environmental conditions is discussed.This research was supported by the Ministerio de Ciencia y Tecnología (projects FEDER and TALMED). We are grateful to Hans Jacquemyn (KUL, University of Leuven, Belgium) for providing the simulation procedure and to Olga Cueto (CEA-Commissariat à l’Énergie Atomique, Grenoble, France) for modifying the procedure to match our experimental design. We would also like to acknowledge the field assistance of José Antonio Bellido, Daniel Montesinos, Manuel Monsalve, and David Correa (CIDE–Centro de Investigaciones sobre Desertificatión, Valencia, Spain). We are also grateful to Cynthia Jones and Jenny Brown for language editing this article.Peer reviewe