Andreas Y. Troumbis

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.

Consistent performance of invasive plant species within and among islands of the Mediterranean basin

Since the success of an invasive species depends not only upon its intrinsic traits but also on particular characteristics of the recipient habitat, assessing the performance of an invader across habitats provides a more realistic analysis of risk. Such an analysis will not only provide insights into the traits related to invasiveness, but also the habitat characteristics that underpin vulnerability to invasion that, taken together, will facilitate the selection of management strategies to mitigate the invader’s effect. In the present study, we considered the Mediterranean basin islands as an excellent study region to test how the same invasive species perform in different habitats within a single island, and to scale up differences among islands with similar climate. We tested how the performance of three widespread plant invaders with clonal growth but contrasting life-history traits, a deciduous tree Ailanthus altissima, a succulent subshrub Carpobrotus spp., and an annual geophyte Oxalis pes-caprae, varied depending upon the species identity, habitat, and invaded island. The environmental parameters considered were habitat type, elevation, species diversity in the invaded plot, and several soil traits (% C, % N, C/N, pH, and relative humidity). The study documents that the performance of these three important and widespread plant invaders is dependent mainly on species identity, and less upon the invaded island’s general features. Likewise, differences in performance among habitats were only significant in the case of Ailanthus, whereas Carpobrotus and Oxalis appear to perform equally well in different environments. Ailanthus thus appears to have a broader spectrum of invasiveness, being able to invade a larger number of habitat types. On the contrary, Carpobrotus spp. have not yet invaded habitats different from those where the species have been originally introduced and where they are still commonly spread by humans. Oxalis distribution is mainly related to agricultural activities and disturbed sites, and the total area infested by this geophyte may be more reflection of the extent of suitable habitats than of invasiveness or ecological impact. Our results confirm the potential for these species to significantly alter the functioning of ecosystems in the Mediterranean islands and highlight the risk to other islands not yet invaded.

The functioning of European grassland ecosystems: Potential benefits of biodiversity to agriculture

About half the farmland of Europe is grassland pasture or hay meadow, and much is impoverished in plant species due to the addition of fertilizers and pesticides, agricultural re-sowing, habitat fragmentation, land abandonment and changes in grazing and mowing regimes. Given this widespread reduction, it is important to understand the effect that loss of biodiversity is having upon our wider environment. Here the authors summarize the main results from the BIODEPTH project, the first multinational, large-scale experiment to examine directly the relationship between plant diversity and the processes that determine the functioning of ecosystems. The results suggest that preserving and restoring grassland diversity may be beneficial to maintaining desirable levels of several ecosystem processes, and may therefore have applications in land management and agriculture.

Observational evidence that diversity may increase productivity in Mediterranean shrublands

Abstract This paper reports field observational evidence on the diversity-biomass production relationship from eastern Mediterranean shrublands dominated by Cistus salviifolius. The main results are: (1) plant diversity and ecosystem primary production are positively correlated in the Cistus shrublands, which are multigrowth form systems; (2) the taxonomic and growth form diversity in Cistus shrublands suggests that there is strong differentiation along the structural niche axis, and thus functional redundancy is weak; (3) the performance of the dominant Cistus in terms of biomass production did not affect the overall diversity-biomass production of the studied communities.

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.

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.

Aspects of heterogeneity in the distribution of diversity of the European herpetofauna

Abstract In the western Palearctic, species richness decreases with increasing latitude for amphibians and reptiles. Hotspots are found in the southermost parts of the area for reptiles, while for amphibians they are in western middle latitude parts. Rapoports rule predicts that species range increases with latitude and that hotspots contain many species of small range. Both prediction are upheld in the case of reptiles, but the hotspots for amphibians contain mostly widespread species. Most amphibian species of small range are found in southern areas. The seasonal climatic variation hypothesis that has been proposed as an explanation for Rapoports rule is not verified for the Palearctic herpetofauna.

Functional shift hypothesis and the relationship between temperature and soil carbon accumulation

Recent experimental evidence on the relationship between temperature and litter or soil organic matter decomposition suggests that the simple assumption that temperature affects the rate constant of the processes may not be valid. Thermal conditions seem to influence the kinetics of C mineralization by changing, in a qualitatively predictable way, the estimated percentages of initial material that behave as labile or recalcitrant. The consequences of this shift in mineralization dynamics due to temperature, referred to as the functional shift hypothesis, for the long-term C accumulation potential of a soil were investigated using a modified version of Jennys model. It was concluded that if soils behave according to the functional shift hypothesis, then the utilization of Q10 or other temperature response functions by simulation models leads to significant overestimations of soil C losses due to temperature increase.

Use of a modified litterbag technique for the study of litter mixtures

Abstract The applicability of a modified, easily constructed litterbag is evaluated in this study. In this litterbag, designed for use in decomposition studies involving litter mixtures, litter species are decomposed in separated by mesh compartments so that they can interact with adjacent species and at the same time can be retrieved “non-contaminated” by them until late decomposition stages. The validity of the technique was examined by comparing mass loss rates of two litter species (Ailanthus altissima and Medicago sativa) incubated in single and mixed new litterbags, with rates in conventional litterbags. The results, referring to the disappearance of up to 65% of the material at constant moisture and temperature conditions, were not significantly affected by the use of the modified litterbag. Although differences between expected and measured decomposition rates of the mixture of the two species were not statistically significant, mixing resulted in a modification of decomposition rates of the individual components compared with their respective rates in single species litterbags.