Temporary ponds are seasonal wetlands annually subjected to extreme and unstable ecological conditions, neither truly aquatic nor truly terrestrial. This habitat and its flora have been poorly studied and documented because of the ephemeral character of the flora, the changeable annual weather that has a great effect on the small, herbaceous taxa and the declining abundance of temporary ponds. The objectives of this study are: (a) to define plant community diversity in terms of floristic composition of ephemeral wetlands in SW Portugal, (b) to identify temporary pond types according to their vegetation composition and (c) to identify those ponds that configure the European community priority habitat (3170* – Mediterranean temporary ponds). Vegetation sampling was conducted in 29 ponds, identifying 168 species grouped among 15 plant communities. Soil texture, pH, organic C and N content were measured, but only N and percent of clay appear to be related with the distribution of each community type. The results showed that ephemeral wetlands could be classified into four type: vernal pools, marshlands, deep ponds and disturbed wetlands. Vernal pools correspond to the Mediterranean temporary ponds (3170*), protected as priority habitat under the EU Habitats Directive. Submersed Isoetes species (Isoetes setaceum and Isoetes velatum) represents, together with Eryngium corniculatum, the indicator species for vernal pools. We identify also indicator plant communities of this priority habitat, namely I. setaceum and E. corniculatum–Baldellia ranunculoides plant communities. In this region, the conservation of temporary ponds has so far been compatible with traditional agricultural activities, but today these ponds are endangered by the intensification of agriculture and the loss of traditional land use practices and by the development of tourism.

The combined impact of soil tillage intensification and expansion of olive farming is resulting in soil degradation and biodiversity decline. We hypothesized that, instead of tilling, mowing to control the natural vegetation in spring can increase biodiversity and improve soil quality. We compared the effects of natural vegetation mowing (NVM) with those of tillage (NVT) on plant community composition and cover, soil water content and resistance to penetration, and olive yield over an 8-year period, in a Mediterranean rainfed olive orchard. NVM had an average of 28 more species and showed a strong positive correlation with Poaceae and Fabaceae, and also with geophytes and hemicryptophytes. In contrast, NVT was negatively correlated with species richness and diversity, with perennial life forms, and positively correlated with Convolvulaceae. Proportions of grass and straw cover in spring were higher in NVM from the beginning of the study (average difference was about 20%). In autumn, grass cover became higher in NVM than in NVT from year five (13% more) and straw cover from year two (30% more). Olive production did not differ between treatments in any of the years. Soil water was higher in NVM, at both soil depths, particularly in mid-summer and after the first autumn rains (1 to 2%). Soil resistance to penetration was 1 Mpa higher in NVM than in NVT. As compared to conventional tillage, natural vegetation cover mowed in spring seems to be an effective management practice to improve the overall rainfed olive orchard biodiversity and soil quality, without affecting production.

Assuming that dispersal modes or abilities can explain the different responses of organisms to geographic or environmental distances, the distance-decay relationship is a useful tool to evaluate the relative role of local environmental structuring versus regional control in community composition. Based on continuing the current theoretical framework on metacommunity dynamics and based on the predictive effect of distance on community similarity, we proposed a new framework that includes the effect of spatial extent. In addition, we tested the validity of our proposal by studying the community similarity among three biotic groups with different dispersal modes (macrofaunal active and passive dispersers and plants) from two pond networks, where one network had a small spatial extent, and the other network had an extent that was 4 times larger. Both pond networks have similar environmental variability. Overall, we found that environmental distance had larger effects than geographical distances in both pond networks. Moreover, our results suggested that species sorting is the main type of metacommunity dynamics shaping all biotic groups when the spatial extent is larger. In contrast, when the spatial extent is smaller, the observed distance-decay patterns suggested that different biotic groups were mainly governed by different metacommunity dynamics. While the distance-decay patterns of active dispersers better fit the trend that was expected when mass effects govern a metacommunity, passive dispersers showed a pattern that was expected when species sorting prevails. Finally, in the case of plants, it is difficult to associate their distance-decay patterns with one type of metacommunity dynamics.