Two-scale modelling of Saponaria bellidifolia Sm. (Caryophyllaceae) abundance on limestone outcrops from its northern range periphery (Southeastern Carpathians)

We modelled the effect of habitat heterogeneity on the abundance of the submediterranean Saponaria bellidifolia, a red list species in Romania. The study was designed at two scales: 100 and 0.5 m². At larger scale, generalized additive models and canonical correspondence analysis were used to model the density of ramets, whereas at microscale, binomial logistic regression was employed to model the species’ occurrence. S. bellidifolia abundance responded sensitively to habitat type (classified as “grassy”, “rocky” and “scree”), rather than to microclimatic variables. At both scales, habitat type was the best predictor of ramet abundance, followed by slope and vegetation cover. At 0.5 m², soil depth was also a good predictor of species occurrence. The data revealed that screes are the most suitable habitats for hosting relatively large populations of this rare species, because of occasional natural disturbances and presumably lower interspecific competition.     

Trends in single trait dispersion between early-mid successional stages: the importance of species pool extension and habitat scale

Aims Are there trends of increasing/decreasing dispersion of single, categorical traits related to early/late-successional species between stages of community development? If yes, are these trends dependent on species pool extension and habitat scale? Is there a consistent reduction in single trait convergence or divergence in any seral stage when scaling down from ecological to local species pool?Methods Presence of all vascular species rooted within plots of 5 × 5 m was recorded in assemblages of exposed mining spoils (EMS) and heathlands (HTL), which form a chronosequence on two abandoned ore tailing heaps located close to each other in the south-eastern Carpathians (Romania). Fifteen nominal, trait attributes of plant species co-occurring in the two seral assemblages were collected from available databases and subsequently classified as either successionally 'pioneer' or 'mature'. The strength of single trait convergence or divergence was estimated by comparison with null plant assemblages at patch type (meta-community) level by reference to the ecological or local species pool, and at community level.Important findings At patch type level, all pioneer and mature trait attributes (apart from short life span), with significant variation between the two seral stages, increased and, respectively, decreased in dispersion irrespective of species pool extension. However, these trends were more conspicuous when using the ecological species pool, very likely due to relaxation in abiotic filtering and dispersal limitation. At community level, no consistent trends were observed between EMS and HTL assemblages, probably because most trait attributes were sorted by microenvironmental filters displaying high variation, like topography or habitat patch geometry. In both seral stages, there was a general weakening of trait convergence or divergence at patch type level when scaling down from the ecological to the local species pool, which was due to niche space contraction. At community level, there was a trend of rise in dispersion of pioneer attributes along the observed chronosequence, presumably imputable to increasing competition for light and underground water, but an opposite trend of dispersion drop in mature attributes was not so evident. Based on these findings, we proposed two rules of thumb concerning the expected changes in dispersion of trait attributes at patch level along successions and between levels of species pool extension. In conclusion, trends in the successional dynamics of pioneer and mature trait dispersion are clearly detectable at meta-community level, especially by reference to the ecological species pool. Habitat scale and species pool extension are key factors to consider and report when estimating the magnitude of single trait dispersion.     

Associations between canopy and understory species increase along a rainshadow gradient in the Alps: habitat heterogeneity or facilitation?

Spatialassociations among overstory and understory species tend to increase ongradients from wet to dry climates. This shift in the strength of spatialassociations has usually been attributed to shared abiotic requirements betweencanopy species and understory assemblages within communities and/or to anincrease in habitat heterogeneity in dry climates and therefore higher betadiversity. On another hand, more important positive effects of tree canopies onunderstory species in drier climates may also explain stronger associations andhigher beta diversity. We examined these three hypotheses along a strongrainshadow gradient that occurs from the wet external Alps to the dry innerAlpsby analyzing with correspondence analysis and canonical correspondence analysisthe species composition of 290 relevés of forests dominated to differentdegrees by Abies alba and Piceaabies.We found important differences in climatic requirements forAbies and Picea, withAbies occurring in warmer and drier habitats thanPicea. The understory species associated with these twospecies showed similar correlations with temperature but not with moisture,withunderstory species of Picea-communities having strongerxeric affinities than understory species ofAbies-communities. We found no significant associationsbetween canopy species and understory composition in the external Alps despitethe fact that Abies and Piceaoccurredin substantially different environments. In contrast,Abiesand Picea occurred in more similar environments in theinner Alps, but the understory assemblages associated with eitherAbies or Picea were significantlydifferent. This increase in canopy-understory associations was in partdetermined by strong differences in moisture between southern and northernaspects in the inner Alps, which affected both canopy and understory speciesdistributions. However, differences between the canopy effects ofPicea and Abies also appeared tocontribute to stronger associations between canopy and understory species, andconsequently to increase beta diversity. This pattern only occurred on southernaspects of the inner Alps but was highly significant. Our results suggest thatspecies distributions may be continuous on the wet ends of moisture gradientsbut discrete on dry ends. Relatively discrete communities at stressful ends ofgradients appear to develop as a result of both habitat differentiation and thepositive effects of overstory species.     

Eco-coenotic conditions and structure of Trollius europaeus L. populations in an extrazonal habitat complex (Transylvanian Carpathian foothills)

To estimate the importance of community structure and environmental factors for maintenance and in situ conservation of populations of European Globeflower (Trollius europaeus subsp. europaeus) in four sites (one within a natural reserve) in a low elevation but cool valley of the Transylvanian Carpathian foothills, an inventory of all globeflower individuals was performed and floristic relevés were recorded in different community types (meadow, fen and scrub). As a surrogate for habitat conditions, we used plant species indicator values for light, moisture and nitrogen. Globeflower density is highest in mesic habitats, the ecological optimum estimated (about 6 on Ellenberg's scale) being slightly lower than that indicated for Central Europe (7). The juvenile:fertile plants ratio (J:F) declines with increasing soil moisture. Larger flower production in hygrophilous communities does not result in a higher proportion of juveniles or J:F ratio. Despite the presumed strong competition determined by high species richness in some host communities, the most dynamic population (large proportion of juveniles) was found in mesophilous, mown meadows. A clumped distribution of fertile plants under the open scrub canopy seems to be responsible for the significantly larger number of flowers per individual observed, as compared with the relative amount of flowers produced in the adjacent sward. Irrespective of host community, the juveniles display an aggregated distribution with respect to fertile plants, which is probably related to short-distance dispersal of seeds. Our results reveal the importance of host community species richness and soil moisture for the target population stage structure and reproductive investment.