Elisa Santi

Anthropogenic drivers of plant diversity: perspective on land use change in a dynamic cultural landscape

Changes in land use are among the forces shaping Earth’s surface. In many industrialized areas, the loss of a traditional state of dynamic equilibrium between traditional management and natural dynamics is followed by abandonment to regeneration processes. This can reduce ecological complexity at the landscape scale and negatively affect biodiversity patterns. In this study, we investigate the relation between land use change and plant species diversity in the network of protected areas (PAs) of the province of Siena (Tuscany, Central Italy). This is an area characterized by long-lasting human activities and highly renowned cultural landscapes. We used remotely sensed, mapping and ground based plant compositional data, to investigate the present pattern of plant species diversity, the changes of landscape structure and changes in forest habitats. Most of the plant diversity present in this network of PAs is due to broad scale gradients due to ecological diversity but also to human management. Most of the area is currently covered by forests and analysis of a historical sequence of spatial data reveals that this is largely a consequence of the abandonment of traditional management during the last decades. Finally, focusing on forest succession as a consequence of land use change, we demonstrate that species richness significantly declines with increasing age of forest stands. Taken together, our results confirm that the recent trends of rural abandonment are leading to homogenization and biodiversity loss in traditional landscapes of Mediterranean Europe. We discuss implications for policy, and suggest that PA management in cultural and historical landscapes should pay increasing attention traditional anthropic practices.

Bias in topographic thresholds for gully heads

Abstract The topographic threshold for overland flow gully head represents a promising tool for both research development and users. Nevertheless, some of the basic assumptions that were used to derive the threshold equation are also at the base for errors, including systematic ones, which introduce bias in the evaluations. Particularly, the assumption that the gully head catchment (GHC) area is a synonym for runoff causes is often false. This cause errors when calculating the threshold equation parameters (i.e. exponent and coefficient of the power equation linking critical slope gradient near the gully head to the GHC area). The assumption implies that every part of the GHC is connected via continuous overland flow paths to the outlet at the moment of peak discharge. Larger areas require larger concentration times, hence longer rainfall duration. This makes the occurrence of a rainfall intensity of the right duration to allow the total connectivity of the GHC less frequent (i.e. less probable). Also the land use (characterized by a specific vegetation type) and the soil conditions could have an effect on the probability that the previous assumption is verified. In order to show this, a distributed model developed in R was used to analyse where the conditions for gully erosion are actually verified. The hydrological part was developed based on the curve number (CN) approach, including the simulation of peak discharge with a few modifications/adaptations to a spatially distributed environment. A small routine was added to simulate concentrated flow erosion and condition for gully head formation. Then, a set of simulations were run using a series of daily rainfall amount and different land use/soil scenarios. Results show a clear effect of the vegetation distribution and patterns on gully head position in the simulated landscapes. From these results, it becomes evident that CN-weighted average in composite catchments needs to be replaced by a different averaging procedures, where the fraction of catchment area as CN weight is completed by an additional weight based on distances to the catchment outlets of the different land uses.

The impact of land abandonment on the plant diversity of olive groves

We investigated the effect of woody species’ encroachment on plant diversity changes with regard to vascular plants and bryophytes in traditional olive groves of the Maremma Regional Park (Tuscany, Italy) and assessed cross-taxon correlation between these two taxa. We classified the olive groves into four land use types, representing different successional stages. To describe the evenness of species distribution within a community, we plotted rank-abundance diagrams for each taxon and each land use type. The relationship between the number and cover of vascular plants, therophytes, bryophytes, colonists and phanerophytes in each plot was examined using linear regression. The effects of land use type on vascular plant and bryophyte richness and assemblages were assessed by permutational uni- and multivariate analysis of variance. The congruence in species composition between the two taxa was evaluated using Procrustes analysis. The number of vascular plants, bryophytes and therophytes decreased linearly with increased phanerophyte species cover. The number of species belonging to Thero-Brachypodietea progressively decreased throughout succession. Rank-abundance diagrams and multivariate analysis showed differences between the land use types, which were statistically significant for vascular plants between the traditional olive groves and the other land use types, and for bryophytes between the traditional olive groves and woodlands. PROTEST analysis and NMDS graphs showed a correlation between vascular plant and bryophyte communities. The results suggested that conservation measures are needed in the study area in order to ensure both the maintenance of traditional olive groves of conservation interest and high levels of environmental heterogeneity.

Development of Biological Diversity in Farmland Ponds

ABSTRACT To describe the rate of pond diversity development and how the age of ponds affects diversity of plants, amphibians, and aquatic insects, eight recently created artificial ponds (four young ponds created in the year 2003 and four new ponds created in the year 2007) were compared to four reference ponds. For each pond, we recorded the presence of plants and the abundance of amphibians and aquatic insects in plots of 0.25 m2 along two orthogonal transects. Data were analyzed using rarefaction technique, permutation tests for multivariate analysis of variance (PERMANOVA), and rank-abundance diagrams. The new and young ponds showed lower plant and aquatic insect species richness than the reference ponds, and the communities showed gradual changes over time in all three taxa Amphibians, which were absent from new ponds, reached the same species richness as in reference ponds five years after pond creation. PERMANOVA wormed on presence/absence data showed no significant differences in community composition for aquatic insects and amphibians among pond age but showed significant differences among ponds belonging to, the same age classes for all taxa studied.

Methodological issues in exploring cross-taxon congruence across vascular plants, bryophytes and lichens

The effectiveness of surrogate taxa as ecological indicators for biodiversity assessment and monitoring depends on different factors, such as the spatial scale of analysis. In this study, we explored the effects of the grain size and the choice of predictor variables on the strength of the community congruence relationships among vascular plants, bryophytes and lichens. Community data for these taxa were collected using a restricted random sampling applied in the Bosco di Sant’Agnese Nature Reserve (Tuscany, Italy). Co-correspondence analysis (Co-CA) was performed on two different response communities (e.g. bryophytes and lichens), considering three predictors (presence/absence of vascular plant, abundance of vascular plants and data on the vegetation structure in each plot) for three grain sizes (1 m2, 100 m2 and 10,000 m2). The effects of spatial grain and the type of predictor variable on the strength of the congruence among the considered taxonomic groups were twofold: (i) the amount of explained variance depends on the grain size and on the analysed taxon; it increased with increasing grain size for bryophytes while showing, in general, an opposite pattern for lichens; and (ii) the observed relationships mainly depend on the choice of predictor variables. The highest predictive power for bryophytes was shown by the vegetation structure predictor, while for lichens it was shown by the presence/absence of vascular plants. Our results highlight the importance of plot dimension, the choice of type of data used as predictors and taxon identity in evaluating cross-taxon relationships and provide further insights into the limitations of cross-taxon estimates among vascular plants and cryptogams for biodiversity assessment and conservation planning.

Slope Dynamics and Climatic Change Through Indirect Interactions

The rapid variation of climate can cause direct changes in slope dynamics due to a modified rainfall regime. Variations in evapotranspiration regime determines changes in soil moisture, modifies shrinking-swelling cycles, creeping, surface mass movement, and soil erosion, including gully erosion. All these effects can be considered as direct consequences of any climate modification. Besides them, other indirect effects should be considered to fully determine climate change impact on slope dynamics. This is the case of the effects of climate change on vegetation, that strongly controls slope instability phenomena. Here we will concentrate on the effect of increased danger due to forest fire, and in particular we discuss the changes in the hydrogeological hazard linked to the effect of drought on wild fires in a case-study in Umbria (Italy), mainly considering field observations and simulations with LANDPLANER (LANDscape, Plant, LANdslide and ERosion) model. This study shows that when discussing of climate changes particular emphasis must be put on side effects that can influence slope dynamics and basin behavior. In particular the understanding of where threats can come, requires the identification of complex framework describing the dynamic interaction of all the elements coexisting in a slope.