Věra Hadincová

Small-scale spatial dynamics of plant species in a grassland community over six years

. In a species-rich mountain grassland in the Krkonosse Mts., Czechoslovakia, data from four permanent plots of 50 cm x 50 cm were recorded annually from 1985 to 1990 to study the spatial dynamics of the species. Plots were divided into 15 x 15 subplots and the number of vegetative units of all plants within each subplot was determined. There was not much net change at the plot level, but the subplots were very dynamic. Two aspects of the spatial dynamics of the species were followed: (1) persistence, i.e. the tendency of the species to remain in the same subplot, and (2) long-distance spreading, i.e. movement to subplots beyond the immediate neighbourhood. Species differed widely in their persistence and longdistance spreading and were classified into mobility types: long-range guerrilla, short-range guerrilla, phalanx and sitting’. The mobility types were, to a certain extent, correlated with the growth form of plants, but some species of one growth form showed different types of small-scale dynamics and some species with different growth forms had the same spatial dynamics.

Small‐scale variability as a mechanism for large‐scale stability in mountain grasslands

. Data from a 7-yr permanent plot study of grassland dynamics were used to address the relationship between processes at two levels of resolution (3.3 cm x 3.3 cm, 50 cm x 50 cm). Grasslands mown and manured in the traditional way in the Krkonose Mts. (Riesengebirge) were used as a model system. Spatial dynamics at the finest scale were very high, as demonstrated by turnover of individual species in 3.3 cm x 3.3 cm subplots and year-to-year transition matrices of the same subplots. The direction of these dynamics was not correlated with grassland treatment, although there was some correlation within years. An extrapolation of such year-to-year dynamics to larger time scales would result in big large-scale changes on the community level, and large shifts in species composition of the whole sward. However, dynamics at larger spatial or temporal scales were generally small. Some directional change occurred in manured plots, whereas little change occurred in unmanured plots. Large-scale dynamics were not correlated with small-scale dynamics in plots without manuring, but some correlation was detectable in manured plots. There are probably several processes that drive small-scale dynamics, such as non-linear interactions and environmental fluctuations. We argue that within certain limits these forces act on species composition so as to make small-scale dynamics non-directional. This results in both large-scale species diversity and apparent large-scale stability of these grasslands. However, if these forces are beyond these limits, the small-scale dynamics may become directional, resulting in rapid changes at larger spatial scales.

Within population genetic differentiation in traits affecting clonal growth: Festuca rubra in a mountain grassland

Festuca rubra , a clonal grass of mountain grasslands, possesses a considerable variability in traits related to spatial spreading (rhizome production, length and branching; tussock architecture). Since these traits highly influence the success of the species in a spatially heterogeneous system of grasslands, a combined field and growth chamber approach was adopted to determine the within‐population variation in these parameters. Clones were sampled in a mountain grassland (The Krkonoše Mts., Czech Republic); the environment (mean neighbour density) of individual clones varied highly. Before the clones were collected, shoot demography and tussock architecture within these clones were recorded in the field for four seasons. Their clone identity was determined using DNA RAPD. Vegetatively propagated plants from these clones were cultivated in a common garden experiment to demonstrate variation in tussock growth and architecture. Their response to change in red/far red light ratio was determined in the growth chamber.

Is a grassland community composed of coexisting species with low and high spatial mobility

Patterns of grasslands species mobility were compared between communities and within plant species. Data from high spatial resolution permanent plots with fine scale recording system, experiment with removal of the dominant recorded also at a fine scale were used. The permanent plots showed large variation within a community in the patterns of species mobility. The species mobility was partly dependent on the site and was higher in a more nutrient rich and climatically more favourable community. Mobility also varied within species. In some species (Nardus stricta, Anthoxanthum spp.) it differed between communities (it was higher in more nutrient rich and climatically more favourable community) and did not respond to removal of the dominant species. In another species,Festuca rubra, mobility also differed between plots; in contrast, it did not show consistent variation attributable to community type and showed strongly increased spatial persistence in plots with the dominant species removed. In this species the mobility seems to be dependent on the competitive pressure of the coexisting species.

Climatic variability and grassland community composition over 10 years : separating effects on module biomass and number of modules

1. Data from permanent grassland plots, collected yearly over a 10 year period were analysed for correlation between weather variables and plant performance. Number of modules and mean biomass of the module were recorded separately. Because the two variables are inter-related, both with each other and with the values in preceding years, regression residuals were used to quantify the response in the particular year. The performance variables were correlated with the monthly averages of temperature and bimonthly averages of precipitation. 2. There was a large year-to-year component of variation in species performance. For biomass, the year-to-year variation is largely explained by correlations with weather ; in number of modules, some species show variation which is not explained by the weather variables studied. Weather variables of both current and preceding years showed significant correlations with species performance. 3. Species responded characteristically to weather variables and in any one species, the number of modules and the biomass do not necessarily respond in the same way. This may be an important mechanism creating time lags in the community response to weather variables and, more generally, may be responsible for non-linearity of the community response to the weather.

Fine-scale species interactions of clonal plants in a mountain grassland : a removal experiment

A removal experiment (one species removed per treatment) in a species poor mountain grassland community was established to (1) determine the horizontal competitive effect at the fine scale, and distinguish them from the effects at the plot level, (2) identify species specific competition effects and (3) determine the overall structure of competitive network within a community. Observation of the species response at the fine spatial scale was done using the grid of 3.3 x 3.3 cm cells. The competitive effects at the level of cells were measured by the correlation between the presence of the removed species in the cell before the removal and the density change of the target species in the cell. Significance of the correlation was estimated by a permutation procedure. At the level of the whole 25 x 25 cm plot, there was no clear tendency in the response to removal of any species except for Nardus stricta, which increased significantly in treatments with Deschampsia flexuosa and Anthoxanthum alpinum removed. Anthoxanthum alpinum increased its biomass per shoot in the treatments with other species removed. At the fine scale level of 3.3 x 3.3 cm cells, some species began to occupy the empty space made by the removal of their neighbours, indicating release from competition following removal. The most pronounced change was the increase of Deschampsia flexuosa following removal of Nardus stricta. Some responses were species-pair specific. Two species pairs (Deschampsia-Anthoxanthum, Deschampsia-Fesiuca) showed reciprocal response at the fine scale; each species increased if the other one was removed. In two species (Nardus stricta, Deschampsia flexuosa) the effects observed at the level of the whole plot and at the level of the individual cells differed. This is attributed to (1) different role of belowground competition (which has wider horizontal range and appears at the scale of the plot) and aboveground competition (which is rather short range and appears already at the scale of the cell) and (2) different plasticity in their clonal growth architecture.

Variability in the Contribution of Different Life Stages to Population Growth as a Key Factor in the Invasion Success of Pinus strobus

Background Despite the increasing number of studies attempting to model population growth in various organisms, we still know relatively little about the population dynamics of long-lived species that reproduce only in the later stages of their life cycle, such as trees. Predictions of the dynamics of these species are, however, urgently needed for planning management actions when species are either endangered or invasive. In long-lived species, a single management intervention may have consequences for several decades, and detailed knowledge of long-term performance can therefore elucidate possible outcomes during the management planning phase. Methodology and Principal Findings We studied the population dynamics of an invasive tree species, Pinus strobus, in three habitat types represented by their position along the elevation gradient occupied by the species. In agreement with previous studies on the population dynamics of long-lived perennials, our results show that the survival of the largest trees exhibits the highest elasticity in all of the studied habitats. In contrast, life table response experiments (LTRE) analysis showed that different stages contribute the most to population growth rates in different habitats, with generative reproduction being more important in lower slopes and valley bottoms and survival being more important on rock tops and upper slopes. Conclusions The results indicate that P. strobus exhibits different growth strategies in different habitats that result in similar population growth rates. We propose that this plasticity in growth strategies is a key factor in the invasion success of the white pine. In all of the investigated habitats, the population growth rates are above 1, indicating that the population of the species is still increasing and has the ability to spread and occupy a wide range of habitats.