Giandiego Campetella

Worldwide evidence of a unimodal relationship between productivity and plant species richness

Grassland diversity and ecosystem productivity The relationship between plant species diversity and ecosystem productivity is controversial. The debate concerns whether diversity peaks at intermediate levels of productivity—the so-called humped-back model—or whether there is no clear predictable relationship. Fraser et al. used a large, standardized, and geographically diverse sample of grasslands from six continents to confirm the validity and generality of the humped-back model. Their findings pave the way for a more mechanistic understanding of the factors controlling species diversity. Science, this issue p. 302 The humped-back model of plant species diversity is confirmed by a global grassland survey. The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity.

Patterns of functional clonal traits and clonal growth modes in contrasting grasslands in the central Apennines, Italy.

Abstract Aim: Patterns of plant functional traits related to clonality (clonal growth modes; CGM) in plant communities were studied and hypotheses on the importance of the selected traits in plant communities supported by soils differing in moisture and nutrient status were tested. Material and Methods: Selected plant functional traits, such as the position of the mother-daughter plants connections, length of spacers, frequency of multiplication, persistency of ramets connections, presence of storage organs and bud protection were studied in two contrasting plant communities (xeric and mesic abandoned pastures) typical of central Apennines, Italy. Results and Discussion: Clonality was shown to be of great importance in both mesic and xeric grasslands. The major differences between the two communities were due to the dominant CGMs: turf graminoids (having effective protection of growth meristems in dense tussocks) dominated xeric grasslands, while rhizomatous graminoids (typical of competitive resource-rich environments) dominated mesic grasslands. Below-ground CGOs (clonal growth organs), shorter spacers, higher multiplication potential, permanent ramet connection, large bud bank and increased importance of bud protection were found to be of importance in water stressed xeric grassland. Contrary to our expectations, the mesic (less stressed) grasslands have the higher number of clonal plants possessing storage organs. Nomenclature: Pignatti (1982) for taxa; Venanzoni & Kwiatkowski (1995) for the syntaxa mentioned in Table 1. Abbreviations: CGM = Clonal growth mode; CGO = Clonal growth organ.

Patterns of Clonal Growth Modes Along a Chronosequence of Post-Coppice Forest Regeneration in Beech Forests of Central Italy

Forest coppicing leads to changes in composition of the herbaceous understory through soil disturbance and alteration of the light regime. While the role of seed dispersal traits at the start of succession after coppicing has been extensively studied, the role of persistence traits such as clonal growth and bud banks is not yet sufficiently understood. To gain better understanding of this role, we studied the patterns of clonal growth organs and related clonal traits of species in a series of coppiced beech forests of the Central Apennines (Marches region, Italy) in various stages of recovery after the last coppicing event. We conducted stratified random sampling and established a chronosequence of recovery stages based on stand age (reflecting the number of years since the last coppicing). The beech stands were classified into three age groups (Post-logged, Recovering, and Old-coppice stands) according to the characteristic stages of beech coppice dynamics. Clonal growth organs and the corresponding clonal traits of plants in the forest understory vegetation were assessed with the help of a CLO-PLA1 database. We found no significant change in the proportion of clonal species along the studied chronosequence. In contrast, most of the traits and about the half of the clonal growth organs showed correlation with stand age or preference for a certain habitat (i.e., stage of regeneration). Clonal and bud bank traits proved to play an important role in the persistence of species subjected to forest coppicing cycles in the studied area.

Can management intensity be more important than environmental factors? A case study along an extreme elevation gradient from central Italian cereal fields

This paper aims to assess the importance of environmental and management factors determining the weed species composition along a strong elevation gradient. A total of 76 cereal fields (39 low input and 37 intensively managed) were sampled along an elevation gradient in central Italy. Explanatory variables were recorded for each field to elucidate the role of large-scale spatial trends, of site-specific abiotic environmental conditions and of field management characters. Redundancy analysis was used to assess the relative importance of each environmental variable in explaining the variation in species composition. Our results indicate that variation in weed species composition is strongly determined by altitude, mean annual precipitation, mean annual temperature and also by soil characteristics. However, the level of intensification proved to be the most influential variable. There was a significant difference in species richness and composition between low-input and intensively managed fields. Intensification leads to considerable species loss at both lower and higher elevations. Low-input fields had 296 species in total, while intensively managed fields had only 196.

Fine‐scale spatial pattern analysis of the herb layer of woodland vegetation using information theory

Abstract The scale dependence of vegetation patterns and processes is generally accepted, but few long‐term studies have directly and explicitly considered scaling aspects in their sampling designs. In order to optimise data collection, particular emphasis must be given to the spatial scales at which maximum diversity, maximum heterogeneity, and maximum spatial dependence appear. The spatial pattern of the herb layer of woodland vegetation (old Quercus cerris coppice) in the central Apennines (Italy) was studied using information theory models. Inside a permanent plot, ground layers of vegetation were sampled along three circular transects. Data were analysed along a series of scales between 0.1 and 60 m. Detected patterns were tested against neutral models generated by Monte‐Carlo simulations. The maximum diversity of species combinations was found between 1 and 4 m, while the maximum heterogeneity and the highest degree of spatial dependence of populations appeared around 10 m. Complete randomisation de...

Mapping local and global variability in plant trait distributions

Significance Currently, Earth system models (ESMs) represent variation in plant life through the presence of a small set of plant functional types (PFTs), each of which accounts for hundreds or thousands of species across thousands of vegetated grid cells on land. By expanding plant traits from a single mean value per PFT to a full distribution per PFT that varies among grid cells, the trait variation present in nature is restored and may be propagated to estimates of ecosystem processes. Indeed, critical ecosystem processes tend to depend on the full trait distribution, which therefore needs to be represented accurately. These maps reintroduce substantial local variation and will allow for a more accurate representation of the land surface in ESMs. Our ability to understand and predict the response of ecosystems to a changing environment depends on quantifying vegetation functional diversity. However, representing this diversity at the global scale is challenging. Typically, in Earth system models, characterization of plant diversity has been limited to grouping related species into plant functional types (PFTs), with all trait variation in a PFT collapsed into a single mean value that is applied globally. Using the largest global plant trait database and state of the art Bayesian modeling, we created fine-grained global maps of plant trait distributions that can be applied to Earth system models. Focusing on a set of plant traits closely coupled to photosynthesis and foliar respiration—specific leaf area (SLA) and dry mass-based concentrations of leaf nitrogen (Nm) and phosphorus (Pm), we characterize how traits vary within and among over 50,000 ∼50×50-km cells across the entire vegetated land surface. We do this in several ways—without defining the PFT of each grid cell and using 4 or 14 PFTs; each model’s predictions are evaluated against out-of-sample data. This endeavor advances prior trait mapping by generating global maps that preserve variability across scales by using modern Bayesian spatial statistical modeling in combination with a database over three times larger than that in previous analyses. Our maps reveal that the most diverse grid cells possess trait variability close to the range of global PFT means.

Adaptation of the Canadian Fire Weather Index to Mediterranean forests

The Canadian Fire Weather Index (FWI) is one of the most used tools to forecast forest fire hazard. In this paper, we propose an adaptation of the FWI to take into account the Mediterranean vegetation and climate, to improve FWI performances for areas with these characteristics. In particular, the FWI has been calibrated for two Mediterranean regions (Algarve, Portugal and Peloponnese, Greece) by fitting the experimental data, collected in the field, for the forest fuel moisture content, with the values expected by the application of the original Canadian FWI. Field data were collected during the 2010 and 2011 fire seasons. The satisfactory results obtained by the adaptation of parameters from the original FWI, in spite of the small sample areas and limited time of collection, allowed us to verify the usefulness of the method in describing the fuel moisture dynamics and obtaining indexes closer to the characteristics of the Mediterranean forests considered. The adapted FWI, if further tested and extended to other sample areas, may help in a more detailed and precise application of the FWI index by improving the daily forest fire hazard forecast, to become also a better support for the Civil Protection Agency of Mediterranean countries.

Spatial patterns of plant species, guilds and biological types in the regenerative phase of a beech coppice (Torricchio Mountain Nature Reserve, Apennines, Italy).

Abstract This work explores and compares horizontal models of some textural categories in the herb layer of an aged beech coppice wood in Torricchio Nature Reserve, Apennines (Italy). Vegetation was analysed using multi-species models of information theory, considering the relationships of diversity and spatial dependence in the categories. Frequency data on circular transects were analysed along a series of scales. Detected patterns were tested against neutral models by Monte-Carlo simulations. Most of the species show a high degree of aggregation and heterogeneity levels which were often maximal over 10 m. The guilds have a much weaker structure. The life forms have the most spatially aggregated groups, and intermediate spatial dependence and units complexity. These results show that the spatial distribution of the understory is guided by effects of previous management that have modified the community structure, creating static centres of shoot development, and sharp environmental heterogeneity.

Unravelling mechanisms of short-term vegetation dynamics in complex coppice forest systems

The silvicultural management of coppicing has been very common in deciduous forests in many European countries. After decades of decline of this practice, socio-economic changes might induce a revival valuing the biomass as a resource. New insights in the ecological processes that regulate plant diversity are relevant for a sustainable forest management. While studies on long-term changes are available, the short-term dynamics of the coppice forest understorey has not yet been explored. In this context, it is interesting to evaluate the species compositional changes, including the processes of species turnover and species impoverishment (nestedness) and to investigate the role of plant functional traits. For this purpose, we resampled a chronosequence of complex coppice beech forests of the Central Apennines (Italy) monitoring the short-time species dynamics of five years (i.e. from 2006 to 2011) in three age classes, i.e. post-logged, recovering and old coppice stands (0–16, 17–31 and > 32 years, respectively). In contrast to our expectation, declining species richness appeared only in the recovering stands, while the landscape scale (between-stand) heterogeneity, except for post-logged and recovering stands in 2011, did not change over five years. Significant temporal nestedness was found in each stage of succession. However, the rate of species turnover and species impoverishment do not significantly differ among the three age classes, indicating their constant importance along the forest regeneration after disturbance. Only in the early stage of forest regeneration after coppicing, species compositional changes are reflected by functional changes with surviving understorey species having clonal regeneration traits. Our results suggest an overall landscape-scale stability (and sustainability) of this coppice forest system. We conclude with management indications, highlighting the importance of maintaining the traditional local approach (coppicing with standards in small 0.5–1.0 ha sized management units with a ca 30-year rotation cycle) where active coppice parcels are interspersed by abandoned stands.

Clonal Growth Modes in Plant Communities Along a Stress Gradient in the Central Apennines, Italy

A simplification from species to functional groups using the concept of clonality is particularly attractive for predictive modelling of vegetation processes and preparing guidelines for nature conservation. This important functional trait based on a modular structure including resource-acquiring units (ramets, feeding sites) and spacers, has been studied in three plant communities (xeric grassland, mesic grassland, and beech forest) under different levels of environmental stress (related to soil moisture and fertility) in the Montagna di Torricchio Nature Reserve near Camerino, Central Apennines, Italy. The study sought to reveal patterns of clonal growth modes (CGMs) in the three plant community types, and to test a series of hypotheses on the importance of selected CGMs along the stress gradient. Clonality was shown to have different importance in the grassland communities, due to differences in the importance of various CGMs (representing syndromes of clonal traits). Below-ground positioning of CGOs, shorter spacers, higher multiplication potential, permanent physical connection between ramets, large bud bank, and increased importance of bud protection were frequently found in water-stressed xeric grasslands, suggesting the adaptive value of these clonal traits. The major differences between grassland communities were due to the dominant CGMs: turf graminoids (with an effective way of protecting growth meristems in dense tussocks) dominated xeric grasslands, whereas rhizomatous graminoids (typical of competitive resource-rich habitats) dominated mesic grasslands. The beech forest had fewer clonal species (67%) and lower CGM diversity. Based on the assumption that different environments promote different selection pressures, the tests revealed the following results: (1) Plants with clonal organs below ground have significantly higher cover values in stressed habitats. (2) Species with short spacers are more frequent in less favourable environments, and their importance is almost ten times higher in the xeric grassland than in the forest (71% to 7.6%). (3) The number of species able to produce numerous ramets is highest in the most stressed habitat. (4) The number of species with a potential for longlasting connection between ramets increases towards stressed environments. In contrast to our expectations, the mesic grasslands (occupying the central position along the studied stress gradient) have the highest number of species with storage organs. (6) In stressed habitats, species with forms of bud protection were the most frequent.