Klára Virágh

The effect of the expansion of the clonal grass Calamagrostis epigejos on the species turnover of a semi-arid grassland

ABSTRACT Question: How does the dominance of Calamagrostis epigejos influence species turnover of a grassland? Location: Loess grassland at the foothills of Bükk Mountains, Hungary (47°54′ N, 20°35′ E). Methods: Presence/absence of vascular plants and different performance attributes of C. epigejos were recorded in a plot-subplot system between 2002 and 2005. Appearance and disappearance rates of grassland species were calculated for pairs of consecutive years. 1. Mean appearance and disappearance rates were compared in grassland plots dominated by C. epigejos and in plots free from this species, based on Monte Carlo randomization. 2. Mean appearance rates were assessed for categories of C. epigejos performance and their confidence intervals were calculated via Monte Carlo randomization. For two performance variables (percentage cover and shoot number) analyses were performed at two spatial scales. Results: 1. C. epigejos-dominated plots differed from unaffected ones by significantly lower appearance rates. 2. Change in appearance rates was best explained by differences in percentage cover of C. epigejos. Coarse-scale C. epigejos performance had a closer correspondence with appearance rate change than fine-scale performance. Low level C. epigejos performance enhanced appearance rate compared to intact stands, while high level performance decreased it, regardless of the choice of performance measure. Conclusions: C. epigejos lowers species number by hindering reappearance of species of the original grassland. This is best explained by the increased shading effect at the coarse scale. The marked non-linear initial enhancement in appearance rate, however, can also be taken as an early sign of future species loss. Nomenclature: Tutin et al. (1964–1993).

Plasticity of leaf and shoot morphology and leaf photochemistry for Brachypodium pinnatum (L.) Beauv. growing in contrasting microenvironments in a semiarid loess forest-steppe vegetation mosaic

Summary After clearcutting xerothermic oakwoods once natural in semiarid temperate loess regions of Hungary the perennial understorey grass Brachypodium pinnatum(L.) Beauv. may persist through decades and often dominates grasslands maintained by grazing and/or cutting in the place of former oakwoods. This grass also successfully establishes from low- to high-light microenvironments co-ocurring as forest regeneration commences after pasture abandonment. It was assumed that B. pinnatum must possess a high degree of phenotypic plasticity for such an ecological versatility. This assumption was tested by comparing leaf and sho ot morphology and leaf photochemistry in the species’ three typical microenvironments (full shade under oak canopy, half shade near shrubs, and full sun in unshaded grassland) for plants growing in situ and for those reciprocally transplanted between these microhabitats. Aboveground standing crop of B. pinnatum was greatest near shrubs, indicating that in this microhabitat light limitation (typical in oak shade) and water stress (appearing temporarily in the grassland) are ameliorated. Average leaf lifes pan was greatest under oak canopy, while leaf senescence was highest in the grassland. An efficient adjustment to low light was observed both in leaf morphology (specific leaf mass, leaf thickness and bulk tissue density were lowest in oak shade) and in leaf photochemistry (quantum yield of PSII ( ΦPSII), photochemical quenching (qP), and non-photochemical energy dissipation (NPQ) were lower, while PSII antenna efficiency (Fv’/Fm’) was higher for leaves in oak shade than for others). Transplanted plants showed remarkable phenotypic plasticity since after one year of transfer their leaves did not differ in photochemistry and/or morphology from those growing in situ in the new microenvironment. However, transplants appeared to be more sensitive to the high radiation load in the grassland than in situ ones. Our results confirm the high capacity of B. pinnatum for phenotypical adjustment to habitat light environment, that is consistent with the species’ original forest-steppe coenological affi nity and also may contribute to the species’ persistence after deforestation. Nevertheless, temporary water stress associated with hi gh radiation load in the unshaded grassland appear to pose a limitation on the ecological distribution of this species in Central Europe.

Static and dynamic approaches to landscape heterogeneity in the Hungarian forest‐steppe zone

. This paper describes the successional status of the vegetation in a clear-felled dry oak woodland at the edge of the Hungarian forest-steppe zone on the basis of a vegetation map. Due to a varied geomorphology of the colline landscape several so-called landscape units can be distinguished. The patchwork on the vegetation map is evaluated using several, morphology-based attributes (static morphological indices) traditionally applied in landscape ecology. In the ca. 100 years that elapsed since forest clear-cut, xeric grassland species and steppe elements became more abundant and the former xeromesophilous vegetation – containing even some woodland components – is slowly turning into xeric grassland communities. The vegetation units mapped can be arranged into a hypothetical succession scheme in which successional distances (the number of steps between two stages) are determined. Based on the distances thus obtained, a new dynamic morphological index is introduced. This is applied to each landscape unit for the dynamic evaluation of successional vegetation, its results being compared with those obtained by static morphological indices.

The effect of herbicides on vegetation dynamics: A five year study of temporal variation of species composition in permanent grassland plots

In a semi-natural, species-rich perennial grassland community permanent plots during secondary succession induced by herbicides selective to dicots and monocots and herbicides of total effect. The effectiveness of using different similarity matrices in detecting vegetation dynamic changes was investigated.Differences caused by treaments in (1), the coenological similarity relations, (2) the direction of secondary succession, (3) the rates of change measured as floristic change (Sörensen index) and as change of species cover (Czekanowski’s coefficient), (4) the reestablishment of the original state, (5) the seasonal dynamics, (6) the responses to stress situation (drought) have been analysed.The vegetation dynamic processes of the community near stable state were mainly influenced by the differences between years. During the 5 years of study the changes referred to the first sampling date showed a trend induced by changing climatic conditions. In the intact community, seasonal fluctuations can be detected very well. The community rich in species has been proved to be resistant to drought, but resilience referring to its recovery following disturbance was relatively small.After having been drastically disturbed from its dynamically stable state, the grassland community regenerated very slowly. In fact, the community could not recover its original state within five years.The direction and rate of change of the secondary successional and regeneration processes have been determined primarily by the species first occupying the bare ground after herbicide treatment, and the vegetative regeneration of the species present, namely the “competition for space”. The main differences between treatments lie in the behaviour of the constituent species in the different coenostates developed following the disturbance.

Effect of slight vegetation degradation on soil properties in Brachypodium pinnatum grasslands

The interrelationship of soil and vegetation degradation is an emerging issue, where most studies have addressed severe degradation so far. We aimed at revealing changes in soil accompanying slight vegetation degradation in a case study involving xeromesophilous grasslands from Hungary. Slight degradation is of special interest here because the target community (Euphorbio pannonicae—Brachypodietum pinnati association) has great nature conservation value. Vegetation status was related to chemical and structural soil properties by principal component analysis and redundancy analysis. Vegetation conditions were assessed by species abundances and by fine-scale spatial structure, which is proposed here for soil-vegetation studies. Slight vegetation degradation clearly manifested itself in soil properties. Differences in vegetation status when assessed by species abundances were mirrored in chemical soil properties. When structural vegetation descriptors were used, a soil structure property (bulk density) was responsible for the segregation according to naturalness. Vegetation-soil relationships were more consistent over biogeographic regions, when vegetation structural descriptors were used. Differences in chemical soil properties reflected species abundance pattern, as was found in most non-grazing related degradation studies. However, changes to soil structure also accompanied slight degradation, and their importance was revealed when vegetation structure was taken into account.

A Bayesian MCMC approach to reconstruct spatial vegetation dynamics from sparse vegetation maps

In studies of vegetation dynamics, data points describing the changes are often sparse, because changes were not recognized in early stages or investigations were part of different projects. The snapshots at hand often leave the nature of the dynamics unrevealed and only give a rough estimation of the directions of changes. Extrapolation of the dynamics with traditional cellular automaton modeling is also complicated in such cases, because rules often cannot be deduced from field data for each interaction. We developed a Bayesian MCMC method, using a discrete time stochastic cellular automaton model to reconstruct vegetation dynamics between vegetation maps available and provide estimation of vegetation pattern in years not surveyed. Spread capability of each vegetation type was characterized by a lateral spread parameter and another for establishment from species pool. The method was applied to a series of three vegetation maps depicting vegetation change at a grassland site following abandonment of grazing in north-eastern Hungary. The Markov chain explored the missing data space (missing maps) as well as the parameter space. Transitions by lateral expansion had a greater importance than the appearance of new vegetation types without spatial constraints at our site. We estimated the trajectory of change for each vegetation type, which bore a considerable non-linear element in most cases. To our best knowledge, this is the first work that tries to estimate vegetation transition parameters in a stochastic cellular automaton based on field measurements and provides a tool to reconstruct past dynamics from observed pattern.