Procesos ecológicos implicados en el ensamblaje de comunidades en taludes de carretera y su aplicación a la restauración ecológica

Abstract

The present doctoral thesis examines some ecological processes that determine both species and community functions on roadslopes under Mediterranean climate conditions, and its implications for ecological restoration. In the first two chapters, we assess whether a standard measure of revegetation such as woody ornamental plantings provide ecological functions. Specifically, in Chapter I we evaluate if these plantings may act as attractors for frugivorous birds in the area, enhancing the process of seed dispersal. For this purpose, we surveyed bird populations to analyse bird community composition and spatial distribution patterns on embankments with and without plantings. We estimated seed dispersal by recording seed abundance, richness and viability in bird droppings. We also measured the density of woody plants with and without fleshy fruits in the surrounding matrices. As a result, we found that the local bird community was dominated by granivorous species, and did not use the roadside plantings. However, plantings acted as selective bird attractors, providing perch and food, for some individuals of locally frugivorous species. The number of frugivorous birds was rather low within the total bird community. Moreover, the structure of the surrounding landscape showed a high correlation between frugivorous bird density on embankments and woody plants with fleshy fruits in their surrounding matrices. Nevertheless, frugivorous birds did not increase seed dispersal as no seeds of the surrounding matrices species where found at the roadsides. We argue that plantings did not enhance bird dispersal and roadside connectivity because of a mismatch between local actions and the agricultural landscape. In Chapter II we analyse whether the same plantings may act as environmental filters through changes in local soil properties, improving fertility under plantings and therefore lead to differences in species composition between inside and outside plantings. To this end, we monitored soil variables and vegetation dynamics (cover, richness, diversity and species composition) inside and outside of the plantings on embankments. We also evaluated the relative importance of the surrounding matrices in the community assembly on the roadslopes. Our results revealed that the woody ornamental plantings had some effects on soil variables during the first year but were disappearing over time. Species composition was not affected by plantings. In summary, the results of the first two chapters indicate that the effects of revegetation measures on local community assembly (both birds and plants) are strongly influenced by the surrounding landscape. In addition, the specific soil properties determine the herbaceous vegetation of the embankments. Chapter III seeks to know the response "in situ" of a common species growing on roadslopes, Dactylis glomerata, in order to identify morpho-physiological response of plants to air enriched in CO2 and metal particles. Firstly, we analysed field A/Ci Response Curves, SLA, pigment pools, foliar nitrogen and carbohydrates in plants growing at three different distances from the road and two different traffic intensities. Secondly, we selected plants at two different distances and two different traffic intensities to assess six metals (Pb, Zn, Cu, Sr, Sn and Cd) in leaves, roots and soil. Plants submitted to high traffic intensity did not show any positive effect on their morphological or photosynthetic variables. Therefore, our results do not support the “CO2-fertilization hypothesis” under field conditions on the roadside where soils are extremely poor in nutrients and water. Leaf starch content was almost double at high traffic intensity, and maximum catalytic activity of the enzyme RuBisCo and Maximum rate of electron transport were lower, which suggests a down photosynthetic response, suggesting negative effects on plants. Additionally, Dactylis glomerata plants can bioaccumulate metals such as Pb, Cu, Zn, Sr in their tissues, decreasing their biological fitness through reduction of inflorescences. In Chapters IV and V we research microclimate regulations by ground covers (vegetation, litter and bare ground) at different timescales on the roadsides. In Chapter IV, a technique to estimate ground covers was optimized using digital photographs. We selected object-based image analysis, using a software program called eCognition Developer, to relate the percentage of ground covers to microclimatic data in Chapter V. The hypothesis of Chapter V was that different ground cover percentages modulate microclimatic conditions of roadslopes under Mediterranean conditions. We monitored photosynthetically active radiation, temperature and moisture in soil and temperature and relative humidity in air, and we calculated thermal oscillation from the corresponding soil and air temperature. The microclimatic data were analysed using three approaches. First, we compared the temporal pattern of microclimatic variables in plots with different initial vegetation cover. Subsequently, we evaluated the correlations between ground covers and microclimatic variables. Finally, we analysed which variable or variables were the most important in determining the microclimatic dynamic. Our results indicate that regional climate with strong seasonal pattern influence the interactions between the ground cover and microclimatic variables, which themselves depend on timescale. Despite this complexity, the results showed that the percentage of vegetation and litter affected variables associated to soil and air temperatures. These correlations were stronger in autumn and winter, when the vegetation cover was higher. Not only vegetation cover but also and mainly litter reduced soil thermal oscillation, indicating a dampening effect on soil temperature during seasons. Our results support that the maintenance of cover derived from plants (litter and vegetation) has an important role in regulating the microclimate in roadside environments, improving the conditions for the establishment of vegetation.