In semiarid Mediterranean areas, the widespread environmental impact caused by the construction of motorways, railways, and pipelines has created an increasing need for effective restoration. We examined the influence of slope characteristics on vegetation and water erosion on 71 motorway slopes in a semiarid Mediterranean region. Specifically, we studied the effect of slope angle, type (roadfill vs. roadcut) and aspect (north vs. south) on soil properties, vegetation cover, species richness, floristic composition, and water-caused erosion. Temporal dynamics of soil water content was monitored and related to the soil water potential in order to explain possible differences in vegetation cover between slope types. The main factors influencing vegetation on motorway slopes were the angle, type, and aspect of the slope. Vegetation was almost completely lacking on roadcuts with slopes greater than 45 . On gentler slopes, vegetation cover was 4478% on roadfills but did not reach 10% on roadcuts, regardless of aspect. The main soil properties affected by the slope type and aspect were the organic matter content, soil available P, and water content. Rill erosion, gully erosion, and mass movement were all significantly higher on roadcuts than roadfills. A total of 308 spontaneous colonizers and seeded species were recorded. The type and aspect of the slope also controlled species composition. The short duration of available water in the soil with respect to soil water potential proved to be a limiting factor to plant colonization on roadcuts and southfacing slopes as well as the low soil fertility in the case of roadcuts. Our results underscore the difficulty of revegetating slopes with angles greater than 45 , where the probability of seeds moving downhill is high. Future efforts should focus on increasing the surface roughness or building terraces at regular intervals in order to reduce slope angle to less than 45 and favor seed trapping and germination. On gentler slopes, adjusting of seed mixes according to dominant species associated with each slope type and aspect should improve considerably the success of roadside revegetation.

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The evergreen-sclerophyllous vegetation associated to the mediterranean-type ecosystems shares common characteristics that have been explained invoking an evolutionary convergence driven by the mediterranean climate. Mediterranean climate originated in the Quaternary but the plant 'convergent' characteristics are also present in tropical-like lineages that evolved along the Tertiary, before the mediterranean climate appeared. Because evergreen-sclerophyllous vegetation was broadly distributed across the world in the Tertiary, current trait similarities among the mediterranean taxa may be due to historical and phylogenetical constraints and not to evolutionary convergence. We tested historical and phylogenetical vs. convergence hypotheses to explain present ecological attributes found in woody plant species in mediterranean areas. Multivariate analyses were performed on the matrix of genera ¥ life-history reproductive characteristics in three mediterranean-type ecosystems and a tropical system as an outgroup, the Mexical shrubland. These analyses indicate that character syndromes in mediterranean plants may largely be explained in relation to the age of the lineage (Tertiary vs. Quaternary). We also found that the similarities shown among mediterranean vegetations are due to Tertiary (pre-mediterranean-) and not to Quaternary (true mediterranean-) taxa. Furthermore, the similarities among mediterranean taxa are due to phylogenetical inertia because similarities in the character syndromes disappear when common genera are excluded from the analysis.

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Previous studies report that the low colonisation success on eroded roadslopes of semiarid environments is controlled by microsite limitations. We predicted that soil water availability, through its effect on seed germination, is a determinant factor in the colonisation process of roadslopes in semiarid environments. Moreover, we predicted that the success of species establishment on the harshest roadslope conditions (i.e., south-facing roadcuts) is either due to the ability of seeds to germinate fast at low water potentials (colonising species) or to the ability of plants to sprout (resistant species). Specifically we present evidence for: (1) soil drying occurs faster on roadcuts than on roadfills after a rainfall event;(2) germination is a filtering process that influences the success of species establishment on roadslopes; (3) species able to colonise successfully south-facing roadcuts have higher germination rates and a shorter time to germination under water-stress conditions than species able to colonise successfully but exclusively the most favourable roadslopes (i.e., roadfills); (4) species that live on south-facing roadcuts and have the ability to sprout do not necessarily germinate with germinating rates and speeds as high as species that colonise successfully these slopes but are unable to sprout. To test these hypotheses we compared water dynamics in the soil among roadslope types and aspects as well as the seed ability to germinate at low water potentials among species showing different regeneration strategies and establishment success on roadslopes. Soil water availability after rainfalls occurring during the germination period played a major role in the germination of seeds. The patterns of seed germination under water-stress conditions were consistent with the success of colonising species on roadslopes and with the distribution of adult plants in the roadslopes 8 years after these latter were built. We discuss the usefulness of these results for the improvement of revegetation projects in semiarid areas by means of an appropriate selection of species adapted to the local environmental conditions. We suggest that the ability of species to germinate under water stress could be an indication of a species' potential for success under semiarid conditions.

Abstract. The possible causes for the lack of vegetation in five badland sites from southeast Spain were experimentally tested. The main factors affecting seed germination and seedling survival considered were seed availability, regolith water dynamics in relation to rain events, regolith salinity, seedling predation by herbivores and seedling removal by erosion. Four issues are addressed: 1. Both rainfall and the temporal and spatial dynamics of regolith water during the seedling emergence period were monitored in five different zones at one site (Petrer, Alicante). 2. Effects of salinity and water potential on the rate and speed of germination of local seeds were determined. 3. Seed reserve and seedling emergence and mortality were followed throughout one season. 4. Regolith characteristics of all five sites were compared and the consequences for plant colonization discussed. The main factor limiting plant colonization in these sites was the very short duration of available water in the soil, due to the physical and chemical characteristics of the regolith. In addition, high regolith salinity and its effects on seed germination, the aspect of the site and the pattern of rain events, played a very important role reducing germination and survival. Herbivory and erosion were seldom responsible for seedling mortality. However, there were no highly erosive rain events during the study period, although several have been measured during the past few years.

Soil erosion plays an important role in plant colonization of semi-arid degraded areas. In this study, we aimed at deepening our knowledge of the mechanisms that control plant colonization on semi-arid eroded slopes in east Spain by (i) determining topographic thresholds for plant colonization, (ii) identifying the soil properties limiting plant establishment and (iii) assessing whether colonizing species have specifi c plant traits to cope with these limitations.Slope angle and aspect were surrogates of erosion rate and water availability, respectively. Since soil erosion and water availability can limit plant establishment and both can interact in the landscape, we analysed variations in colonization success (vegetation cover and species number) with slope angle on 156 slopes, as a function of slope aspect. After determining slope angle thresholds for plant colonization, soil was sampled near the threshold values for soil analysis [nitrogen, phosphorous, calcium carbonate (CaCO 3 ), water holding capacity]. Plant traits expressing the plant colonizing capacity were analysed both in the pool of species colonizing the steep slopes just below the threshold and in the pool of species inhabiting gentler slopes and absent from the slopes just below the threshold.Results show that the slope angle threshold for plant colonization decreased from north to south. For the vegetation cover, threshold values were 63°, 50°, 46°, 41° for the north, east, west and south slope aspect classes, respectively, and 65°, 53°, 49° and 45° for the species richness and the same aspect classes. No differences existed in soil properties at slope angle threshold values among slope aspects and between slope positions (just below and above the threshold) within slope aspect classes. This suggests that variations between slope aspect classes in the slope angle threshold result from differences in the colonizing capacity of plants which is controlled by water availability. Long-distance dispersal and mucilage production were preferably associated with the pool of colonizing species.These results are discussed in the perspective of a more effi cient ecological restoration of degraded semi-arid ecosystems where soil erosion acts as an ecological fi lter for plant establishment.