• Energy Research

Most grazing lands in Mediterranean ecosystems that support extensive sheep farming systems are characterized by unfavorable edapho-climatic conditions, especially in semi-arid areas. Often, though, their use is far from sustainable, causing erosion and ecosystem degradation impacts. In this paper, we explore the use, productivity, and flora diversity of typical Mediterranean grazing lands in four farms at the Agra locality in the western part of Lesvos Island, Greece. For a period of two consecutive growing seasons (September to June), we recorded herbage biomass on 16 plots of grazing lands with three measurements per season of land cover and plant productivity (biomass) inside small exclosures (cages) protected from grazing. We recorded the species richness of herbaceous plant communities within and outside the cages at the end of every growing season, the period of maximum growth of herbaceous species. We also chemically analyzed the biomass for crude protein at the end of each season. Results show sizable productivity differences among pasture plots as well as seasons and an overall medium to high degree of productivity and species richness considering the relatively intensive grazing, with little differences over the different cages and the degree of grazing intensity. These results suggest that the “history” of the fields is important, as grazing lands that had been used for arable crops in the past, as well as those leveled and in favorable locations, were the most productive and diverse ones, while shallower soils and inclined grazing lands showed signs of overuse and degradation. Overall, though, these ecosystems showed a high degree of resilience despite their intensive use.

AbstractUnderstanding the relative importance of the abiotic environment and species interactions in determining the distribution and abundance of organisms has been a challenge in ecological research. Serpentine substrata are stressful environments for plant growth due to multiple limitations, collectively called the “serpentine syndrome”. In the present review, our aim is not only to describe recent work in serpentine ecology, but also to highlight specific mechanisms of species tolerance and adaptation to serpentine soils and their effects on community structure and ecosystem functioning. We present hypotheses of the development of serpentine endemism and a description of functional traits of serpentine plants together with a synthesis of species interactions in serpentine soils and their effects on community structure and ecosystem productivity. In addition, we propose hypotheses about the effects of the ‘serpentine syndrome’ on ecosystem processes including productivity and decomposition.

This paper reports the findings of a short-term natural invasibility field study in constructed Mediterranean herbaceous communities of varying diversities, under a fire treatment. Three components of invasibility, i.e. species richness, density and biomass of invaders, have been monitored in burnt and unburnt experimental plots with resident diversity ranging from monocultures to 18-species mixtures. In general, species richness, density and biomass of invaders decreased significantly with the increase of resident species richness. Furthermore, the density and biomass of invading species were significantly influenced by the species composition of resident communities. Although aboveground biomass, leaf area index, canopy height and percent bare ground of the resident communities explained a significant part of the variation in the success of invading species, these covariates did not fully explain the effects of resident species richness. Fire mainly influenced invasibility via soil nutrient levels. The effect of fire on observed invasibility patterns seems to be less important than the effects of resident species richness. Our results demonstrate the importance of species richness and composition in controlling the initial stages of plant invasions in Mediterranean grasslands but that there was a lack of interaction with the effects of fire disturbance.

We conducted a field experiment using constructed communities to test whether species richness contributed to the maintenance of ecosystem processes under fire disturbance. We studied the effects of diversity components (i.e., species richness and species composition) upon productivity, structural traits of vegetation, decomposition rates, and soil nutrients between burnt and unburnt experimental Mediterranean grassland communities. Our results demonstrated that fire and species richness had interactive effects on aboveground biomass production and canopy structure components. Fire increased biomass production of the highest-richness communities. The effects of fire on aboveground biomass production at different levels of species richness were derived from changes in both vertical and horizontal canopy structure of the communities. The most species-rich communities appeared to be more resistant to fire in relation to species-poor ones, due to both compositional and richness effects. Interactive effects of fire and species richness were not important for belowground processes. Decomposition rates increased with species richness, related in part to increased levels of canopy structure traits. Fire increased soil nutrients and long-term decomposition rate. Our results provide evidence that composition within richness levels had often larger effects on the stability of aboveground ecosystem processes in the face of fire disturbance than species richness per se.

By shifting the structure and function of forest ecosystems, global change threatens their ability to provide key ecosystem services for human well-being. Lowland and mountainous Mediterranean forests are experiencing climate-related pressures that lead to changes in tree mortality, fire regime and their primary productivity. Understanding and mapping Mediterranean forest vulnerability to climate change is thus important for designing efficient adaptive management policies at the regional and country-level scale. In this project we developed an integrated framework that accounts for four (4) key components of forest vulnerability, i.e. drought mortality, wildfire frequency change, habitat suitability shrinkage and primary productivity shift. To do so, we combine dendro-ecological tree-ring data, fire risk and species distribution modelling, as well as regionally parameterized process-based simulations of forest gross and net primary productivity under two climate change scenarios, for the ten most ecologically and economically important tree-taxa in Greece, including evergreen needleleaf (EN), deciduous broadleaf (DB) and evergreen broadleaf (EB) representative species. In terms of drought triggered mortality, a relatively higher vulnerability of EN species (compared to DB and EB species), particularly at lower elevation emerged from the analysis of tree-ring data. Wildfire vulnerability was projected to be higher at lowland forests. Vulnerability related to habitat suitability changes was greater for mountainous DB and EN species. Simulated changes in primary productivity suggest a higher vulnerability at the lower elevation limits of species distribution. By combining the different vulnerability components, we provide species-specific vulnerability maps at a spatial resolution of ca 9 km, suitable for designing forest mitigation policies under different climate change scenarios.

Fluctuations in nutrient ratios over seasonal scales in aquatic ecosystems can result in overyielding, a condition arising when complementary life-history traits of coexisting phytoplankton species enables more complete use of resources. However, when nutrient concentrations fluctuate under short-period pulsed resource supply, the role of complementarity is less understood. We explore this using the framework of Resource Saturation Limitation Theory (r-strategists vs. K-strategists) to interpret findings from laboratory experiments. For these experiments, we isolated dominant species from a natural assemblage, stabilized to a state of coexistence in the laboratory and determined life-history traits for each species, important to categorize its competition strategy. Then, using monocultures we determined maximum biomass density under pulsed resource supply. These same conditions of resource supply were used with polycultures comprised of combinations of the isolated species. Our focal species were consistent of either r- or K-strategies and the biomass production achieved in monocultures depended on their efficiency to convert resources to biomass. For these species, the K-strategists were less efficient resource users. This affected biomass production in polycultures, which were characteristic of underyielding. In polycultures, K-strategists sequestered more resources than the r-strategists. This likely occurred because the intermittent periods of nutrient limitation that would have occurred just prior to the next nutrient supply pulse would have favored the K-strategists, leading to overall less efficient use of resources by the polyculture. This study provides evidence that fluctuation in resource concentrations resulting from pulsed resource supplies in aquatic ecosystems can result in phytoplankton assemblages' underyielding.

This study evaluated the short-term responses of physiological and psychological indices and examined the human senses that are mostly engaged during a green space and urban exposure in residents of Athens, Greece. The forest had beneficial effects for human physiology, anxiety and mood states and was also associated with all five senses and positive reactions, while the opposite was observed in the urban center. The difference of pre- and post-green space exposure salivary cortisol was correlated with the participants’ environmental profile and body mass index. Green spaces can alleviate stress and improve overall mood, while helping individuals experience their surroundings with all five senses.

The COVID-19 pandemic has highlighted the importance of incorporating nature-based solutions in urban design, in order to create sustainable and resilient cities. Inspired by these events, the present study aims at exploring the mental health benefits of nature exposure during the outbreak. Secondarily, we investigate changes in use patterns towards urban green spaces (UGS) and urban blue spaces (UBS) and whether extreme conditions, such as these of a lockdown, can lead to an increase in people’s appreciation of urban nature. Through an online survey, we observed that the pandemic resulted in a decrease in the frequency of visitation to UGS/UBS (p < 0.001). Significant differences were found for exercise (p < 0.001) and socialization (p < 0.05) as main drivers for visiting urban nature pre- and post-lockdown. Accordingly, visitation rates for forests (p < 0.05), playgrounds (p < 0.001), and the sea (p < 0.001) differed significantly when comparing the two periods. In people’s perception, UGS/UBS are important for the urban fabric (89%). Our structural equation model indicated that nature exposure had a beneficial effect on participants’ mental health (p < 0.001). Pathways that explain the relationship between nature exposure and post- lockdown value were nature relatedness, motivation, and perceived importance of UGS/UBS. No mediation could be extracted for nature exposure and mental health. Our findings show the positive association between nature exposure and mental health improvement, especially in times of crisis, as well as a shift in the “value domain” towards urban nature.