Sándor Bartha

Spatiotemporal dynamic models of plant populations and communities

The idea of relating spatial patterns and temporal processes in plant community dynamics is not new, but its transformation into realistic spatiotemporal models is the result of quite recent methodological developments. There are now two classes of analytical model and a broad class of simulation models pertaining to the role of spatial structure in vegetation dynamics. They indicate that any community-dynamical theory intended to be predictive should not omit the spatial aspects of plant population dynamics, because these may radically change the conditions of persistence and coexistence.

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.

A grid-based, satellite-image supported, multi-attributed vegetation mapping method (MÉTA)

In this paper we present the main characteristics of a new, grid-based, landscape-ecology-oriented, satellite-image supported, field vegetation mapping method, called MÉTA (MÉTA stands for Magyarországi Élőhelyek Térképi Adatbázisa: GIS Database of the Hungarian Habitats). The goals of the MÉTA method based vegetation mapping program (MÉTA mapping) include the following: (1) to map the actual (semi-)natural vegetation of Hungary; (2) to evaluate Hungarian (semi-)natural vegetation heritage for conservation purposes; (3) to evaluate the present state of Hungarian landscapes from a vegetation point of view; (4) to collect vegetation and landscape ecological data for the prognosis of future changes of vegetation and the landscape. Spatial resolution, mapped attributes and mapping methods were developed to meet these goals.The MÉTA method uses a hexagon grid with cells of 35 hectares. In the hexagons, habitat types are listed, then the area, naturalness-based habitat quality, spatial pattern in the hexagon, effect of the neighbourhood, connectedness, and threats are recorded for each habitat type. Other attributes are recorded in the hexagons: potential natural vegetation, area occupied by invasive plant species, area of old fields, land use of grasslands, and landscape health status (naturalness and regeneration potential of the landscape in general). One hundred hexagons form a quadrat — mainly for practical, organizational reasons, but also for collecting certain vegetation data at this spatial scale. For standardization of mapping, three different pre-printed data sheets and two different kinds of guides have been composed (Mapping Guide and Habitat Guide) and field trainings were organized. For standardization of estimation of naturalness-based habitat quality and regeneration potential field examples were prepared for each habitat type and each category of these attributes.

The effect of spatial pattern on community dynamics; a comparison of simulated and field data

The effect of the spatial limits of dispersal and competition on plant community dynamics was studied using Monte-Carlo simulation. The model generates community point patterns, using life-table data, dispersion parameters and radii of competitive effects. These data have been estimated in a field situation, for the 11 most abundant weed species growing on the refuse soil dumps of a strip coal mine. In a simulation experiment, the patterns produced by two versions of the model were compared. The first was based on the field situation as much as possible; the other used the same input parameters except for dispersal, which was randomized in this case. We found considerable differences regarding the temporal changes of species abundances, the realized competitive abilities and the spatial patterns generated by the two versions. An important conclusion of this comparison is that the realized competitive effect (both intra-and interspecific) of a species is dependent not only on constant competition parameters, but on the abundance relations and on the spatial patterns of the competing populations as well. It is concluded that the spatial limits of dispersal and competition may result in the increased persistence of weak competitors, moderate the realized competitive effects of strong species, and shape the spatial coalition structure of the community.

Advances in the conservation of dry grasslands: Introduction to contributions from the seventh European Dry Grassland Meeting

Abstract Dry grasslands in Europe are mostly of zoo-anthropogenic origin, but nevertheless they are among the most diverse plant communities of the world at small spatial scales, and they support a significant proportion of the biodiversity of the continent. Both agricultural intensification and abandonment of former dry grasslands caused dramatic losses in area and quality of this habitat type during recent decades. Here we report from the 7th European Dry Grassland Meeting, organised by the European Dry Grassland Group (EDGG) in Smolenice, Slovakia, in 2010. Under the motto “Succession, restoration and management of dry grasslands” one hundred researchers from throughout Europe discussed conservation issues of this threatened habitat type. We give a brief introduction to those nine articles that are included in this Special Feature. With contributions from many different countries and various dry grassland types, they address issues of conservation value, succession, management as well as regeneration and restoration. We conclude that the diversity of dry grasslands and their conservation problems require further research to develop adequate management techniques under changing frame conditions. However, also the frame conditions, such as the incentives for certain land use practices provided by the Common Agricultural Policy of the European Union need to be addressed if long-term success in conservation of dry grasslands is intended.

Seminatural grassland management by mowing of Calamagrostis epigejos in Hungary.

Abstract Regeneration of seminatural grasslands are often threatened by the invasion of Calamagrostis epigejos, which can slow down or arrest secondary succession. Here we report the results of a 9-year mowing experiment designed to suppress the spread of C. epigejos in mid-successional grasslands in Hungary. The experimental design consisted of 16 permanent plots of 3 × 3 m. Half of the plots were mowed twice a year (in June and September), the other half was left as control. Vegetation was sampled in 2 × 2 m quadrates before mowing in each year between 2001 and 2009. The effects of mowing were tested using repeated–measure analyses of variance (ANOVA) and Tukey HSD for post hoc tests. Significant decrease of C. epigejos appeared after 2 years of mowing. Species richness increased after 4 years, while diversity after 8 years. By this time the target native species Brachypodium pinnatum become dominant. Similar trends appeared in the control plots during spontaneous succession but at much slower rates. Our results suggest that C. epigejos disappears spontaneously in secondary grassland succession after ca. 40–50 years. However, mowing twice a year can speed up this process by opening a “colonization window” to the valuable target species. For successful control, mowing should be maintained for approximately 8 years.

Past Trends, Present State and Future Prospects of Hungarian Forest-Steppes

In Hungary a countrywide vegetation mapping project carried out between 2003 and 2006 provided immense, detailed data on the current status of the forest-steppe vegetation (META database). In addition, two fundamentally important historical sources from the late eighteenth century have been analyzed recently. Using these sources we reconstruct and evaluate the past history and current status, and forecast the expected future of the vegetation types within the forest-steppe zone.

Spatial constraints masking community assembly rules: A simulation study

The effect of competition on species coexistence is usually strongly modified by other factors especially in non-equilibrium systems of sessile organisms with limited availability of propagules. As a consequence, competition-based assembly rules (even if their existence seems to be unambiguously detected) would result in incomplete understanding of the coexistence of species in plant communities. J. Bastow Wilson suggested measuring variance deficit in the number of co-occurring species as a means to detect niche limitation in a community. The method provides a relatively simple and quick “snap-shot” analysis of a community. However, it has been questioned whether niche limitation is the only factor which might account for variance deficit.The paper presents a spatially explicit simulation experiment in which artificial communities are produced by pre-defined rules for competitive interactions. Then we examine whether these rules can be detected by a proposed method for pattern analysis. Two limiting cases are simulated: (A) all the species share the same niche, and (B) all the species have different niches. The difference between these cases in the variance of species numbers is examined. Using the simulation results, some basic spatial constraints upon species assembly are emphasized.It is argued that the assumptions of Wilson’s approach confine its applicability to species-saturated equilibrium communities. The study of assembly rules in dynamically changing, spatially structured communities requires the consideration of a set of coenological characteristics and the use of careful spatio-temporal scaling to detect their patterns. The use of spatially explicit individual-based models to study the mechanisms and constraints limiting species coexistence at different scales is suggested.

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.

Chamber series and space-scale analysis of CO2 gas-exchange in grassland vegetation: A novel approach

Significant part of our work was developing a new type of CO2 and H2O gas exchange chambers fit for measuring stand patches. Ground areas of six chambers (ranged between 0.044–4.531 m2) constituted a logarithmic series with doubling diameters from 7.5 to 240.0 cm. We demonstrate one of the first results for stand net ecosystem CO2 exchange (NEE) rates and temporal variability for two characteristic Central European grassland types: loess and sand. The measured mean NEE rates and their ranges in these grasslands were similar to values reported in other studies on temperate grasslands. We also dealt with the spatial scale dependence from ecophysiological point of view. Our chamber-series measurement was performed in a perennial ruderal weed association. The variability of CO2-assimilation of this weed vegetation showed clear spatial scale-dependence. We found the lowest variability of the vegetation photosynthesis at the small-middle scales. The results of spatial variability suggest the 0.2832 m2 patch size is the characteristic unit of the investigated weed association and there is a kind of synphysiological minimi-area with characteristic size for each vegetation type.