Panayiotis G. Dimitrakopoulos

Ecosystem effects of biodiversity manipulations in European grasslands.

We present a multisite analysis of the relationship between plant diversity and ecosystem functioning within the European BIODEPTH network of plant-diversity manipulation experiments. We report results of the analysis of 11 variables addressing several aspects of key ecosystem processes like biomass production, resource use (space, light, and nitrogen), and decomposition, measured across three years in plots of varying plant species richness at eight different European grassland field sites. Differences among sites explained substantial and significant amounts of the variation of most of the ecosystem processes examined. However, against this background of geographic variation, all the aspects of plant diversity and composition we examined (i.e., both numbers and types of species and functional groups) produced significant, mostly positive impacts on ecosystem processes. Analyses using the additive partitioning method revealed that complementarity effects (greater net yields than predicted from monocultures due to resource partitioning, positive interactions, etc.) were stronger and more consistent than selection effects (the covariance between monoculture yield and change in yield in mixtures) caused by dominance of species with particular traits. In general, communities with a higher diversity of species and functional groups were more productive and utilized resources more completely by intercepting more light, taking up more nitrogen, and occupying more of the available space. Diversity had significant effects through both increased vegetation cover and greater nitrogen retention by plants when this resource was more abundant through N2 fixation by legumes. However, additional positive diversity effects remained even after controlling for differences in vegetation cover and for the presence of legumes in communities. Diversity effects were stronger on above- than belowground processes. In particular, clear diversity effects on decomposition were only observed at one of the eight sites. The ecosystem effects of plant diversity also varied between sites and years. In general, diversity effects were lowest in the first year and stronger later in the experiment, indicating that they were not transitional due to community establishment. These analyses of our complete ecosystem process data set largely reinforce our previous results, and those from comparable biodiversity experiments, and extend the generality of diversity–ecosystem functioning relationships to multiple sites, years, and processes.

Hypotheses, mechanisms and trade-offs of tolerance and adaptation to serpentine soils: from species to ecosystem level.

Understanding 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.

Species adaptation in serpentine soils in Lesbos Island (Greece): metal hyperaccumulation and tolerance

Serpentine (ultramafic) soils, containing relatively high nickel and other metal concentrations, present a stressful environment for plant growth but also a preferred substrate for some plants which accumulate nickel in their tissues. In the present study we focused on: (1) the relationships between serpentine soils of Lesbos Island (Greece) and serpentinophilic species in order to test their adaptation to the ‘serpentine syndrome’, and (2) the Ni-hyperaccumulation capacity of Alyssum lesbiacum, a serpentine endemic, Ni-hyperaccumulating species, recorded over all its distribution for the first time. We sampled soil and the most abundant plant species from the four serpentine localities of Lesbos Island. Soil and leaf elemental concentrations were measured across all the sites. Our results confirmed our hypothesis that serpentinophilic species are adapted to elevated heavy metal soil concentrations but restricting heavy metal concentration in their leaves. We demonstrated that different A. lesbiacum populations from Lesbos Island present differences in Ni hyperaccumulation according to soil Ni availability. Our results highlighted the understanding of serpentine ecosystems through an extensive field study in an unexplored area. Alyssum lesbiacum and Thlaspi ochroleucum emerge as two strong Ni hyperaccumulators with the former having a high potential for phytoextraction purposes.

Incorporating Ecosystem Function Concept in Environmental Planning and Decision Making by Means of Multi-Criteria Evaluation: The Case-Study of Kalloni, Lesbos, Greece

Nature provides life-support services which do not merely constitute the basis for ecosystem integrity but also benefit human societies. The importance of such multiple outputs is often ignored or underestimated in environmental planning and decision making. The economic valuation of ecosystem functions or services has been widely used to make these benefits economically visible and thus address this deficiency. Alternatively, the relative importance of the components of ecosystem value can be identified and compared by means of multi-criteria evaluation. Hereupon, this article proposes a conceptual framework that couples ecosystem function analysis, multi criteria evaluation and social research methodologies for introducing an ecosystem function-based planning and management approach. The framework consists of five steps providing the structure of a participative decision making process which is then tested and ratified, by applying the discrete multi-criteria method NAIADE, in the Kalloni Natura 2000 site, on Lesbos, Greece. Three scenarios were developed and evaluated with regard to their impacts on the different types of ecosystem functions and the social actors’ value judgements. A conflict analysis permitted the better elaboration of the different views, outlining the coalitions formed in the local community and shaping the way towards reaching a consensus.

Grazing effects on plant functional group diversity in Mediterranean shrublands

Grazing is one of the prevalent human activities that even today are taking place inside protected areas with direct or indirect effects on ecosystems. In this study we analyzed the effects of grazing on plant species diversity, plant functional group (PFG) diversity and community composition of shrublands. We analyzed plant diversity data from 582 sampling plots located in 66 protected areas of the Greek Natura 2000 network, containing in total 1102 plant species and subspecies. We also classified a priori all plant species in seven PFGs: annual forbs, annual grasses/sedges, legumes, perennial forbs, perennial grasses/sedges, small shrubs and tall shrubs. For each site, grazing intensity was estimated in four classes (no grazing, low, medium and high grazing intensity). We found that, at the spatial and temporal scale of this study, as grazing intensity increased, so did total species richness. However, each PFG displayed a different response to grazing. Short-lived species (annual grasses or forbs and legumes) benefited from grazing and their species richness and proportion in the community increased with grazing. Perennial grasses and forbs species richness increased with grazing intensity, but their dominance decreased, since their proportion in the community declined. Short shrub species richness remained unaffected by grazing, while tall shrub diversity decreased. Finally, in sites without grazing the spatial pattern of species richness of the different PFGs was not congruent with each other, while in grazed sites they were significantly positively correlated (with the exception of tall shrubs). This finding may imply that grazing is a selective pressure organizing the community structure, and imposing a certain contribution of each PFG. So, in Mediterranean shrublands in protected areas with a long historical record of grazing, it seems that grazing promotes species diversity and its continuation on a portion of the landscape may be a necessary part of an effective management plan.

Short-term invasibility patterns in burnt and unburnt experimental Mediterranean grassland communities of varying diversities

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.

Investigating knowledge and perceptions of citizens of the National Park of Eastern Macedonia and Thrace, Greece

The designation and management of protected areas (PAs) is a challenging task significantly influenced by numerous parameters, both economic and social. In this paper, these issues are explored by means of an empirical survey in a PA of international importance in Greece: the National Park of Eastern Macedonia and Thrace (NPEMT). In particular, the survey explored the knowledge and perceptions of different interest groups concerning environmental issues in general, awareness of the restrictions imposed by the current management framework, benefits connected with the designation of the PA and willingness of individuals to pay for protection of the NPEMT. These interest groups were created depending on their level and type of involvement with PA issues. The results revealed a low level of awareness, indicating that further efforts should be conducted, both by the state and non-governmental organisations, to inform the local community and visitors about the existence of the PA and also the social and economic benefits resulting from its creation. Furthermore, the level of knowledge and perceptions of individuals about the NPEMT varies according to the social groups examined. Finally, individuals are willing to pay €94.08 annually for protection of the park, although there was a high percentage of protest responses.

Comparative patterns of plant invasions in the mediterranean biome

The objective of this work was to compare and contrast the patterns of alien plant invasions in the world’s five mediterranean-climate regions (MCRs). We expected landscape age and disturbance history to have bearing on levels of invasion. We assembled a database on naturalized alien plant taxa occurring in natural and semi-natural terrestrial habitats of all five regions (specifically Spain, Italy, Greece and Cyprus from the Mediterranean Basin, California, central Chile, the Cape Region of South Africa and Southwestern - SW Australia). We used multivariate (hierarchical clustering and NMDS ordination) trait and habitat analysis to compare characteristics of regions, taxa and habitats across the mediterranean biome. Our database included 1627 naturalized species with an overall low taxonomic similarity among the five MCRs. Herbaceous perennials were the most frequent taxa, with SW Australia exhibiting both the highest numbers of naturalized species and the highest taxonomic similarity (homogenization) among habitats, and the Mediterranean Basin the lowest. Low stress and highly disturbed habitats had the highest frequency of invasion and homogenization in all regions, and high natural stress habitats the lowest, while taxonomic similarity was higher among different habitats in each region than among regions. Our analysis is the first to describe patterns of species characteristics and habitat vulnerability for a single biome. We have shown that a broad niche (i.e. more than one habitat) is typical of naturalized plant species, regardless of their geographical area of origin, leading to potential for high homogenization within each region. Habitats of the Mediterranean Basin are apparently the most resistant to plant invasion, possibly because their landscapes are generally of relatively recent origin, but with a more gradual exposure to human intervention over a longer period.

Intra-specific variation in Ni tolerance, accumulation and translocation patterns in the Ni-hyperaccumulator Alyssum lesbiacum.

A hydroponic experiment was conducted to investigate inter-population variation in Ni tolerance, accumulation and translocation patterns in Alyssum lesbiacum. The in vitro results were compared to field data (soil bioavailable and leaf Ni concentrations) so as to examine any potential relationship between hydroponic and natural conditions. Seeds from the four major existing populations of A. lesbiacum were used for the cultivation of plantlets in solution cultures with incrementally increasing Ni concentrations (ranging from 0 to 250 μmol L(-1) NiSO4). Ni accumulation and tolerance of shoots and roots, along with initial seed Ni concentration for each population were measured. The ratio of root or shoot length of plantlets grown in NiSO4 solutions to root or shoot lengths of plantlets grown in the control solution was used as tolerance index. For the range of metal concentrations used, A. lesbiacum presented significant inter-population variation in Ni tolerance, accumulation and translocation patterns. Initial seed Ni concentration was positively correlated to shoot Ni accumulation. A significant positive relationship between tolerance and accumulation was demonstrated. Initial seed Ni concentration along with physiological differences in xylem loading and Ni translocation of each population, appear to be the determining factors of the significant inter-population variation in Ni tolerance and accumulation. Our results highlight the inter-population variation in Ni tolerance and accumulation patterns in the Ni-hyperaccumulator A. lesbiacum and give support to the suggestion that the selection of metal hyperaccumulator species with enhanced phytoremediation efficiency should be considered at the population level.

The effect of harsh abiotic conditions on the diversity of serpentine plant communities on Lesbos, an eastern Mediterranean island

Background: Diversity patterns of plant communities are related to the environment, including productivity and patchiness of habitat. Aims: To determine differences in diversity patterns between serpentine and non-serpentine communities. Methods: A two-year study was conducted in native eastern Mediterranean grasslands. For each year 40 0.25 m2 plots were sampled across four pairs of sites, each of which contained a serpentine and an adjacent non-serpentine plant community. Alpha and beta diversity (variation in species composition among plots within localities), species composition and biomass production were determined. Total soil elemental concentrations and pH were also measured. Results: Serpentine habitats were shown to support a lower alpha diversity relative to non-serpentine habitatas on a per plot basis. Differences in alpha diversity between the two substrates were associated with variation in soil chemistry rather than above-ground biomass production. Serpentine habitats also exhibited lower beta diversity, which was unrelated to variation in biomass production. The two contrasting communities presented distinct species composition. Conclusions: Differences in diversity patterns between serpentine and non-serpentine communities in the eastern Mediterranean are influenced by soil chemistry rather than biomass production.