TY - JOUR A1 - Brose, Ulrich A1 - Tielbörger, Katja T1 - Subtle differences in environmental stress along a flooding gradient affect the importance of inter-specific competition in an annual plant community N2 - Empirical evidence suggests that the direction and intensity of plant-plant interactions may depend on the favourability of the environment. Previous studies have mainly focused on steep gradients of environmental stress or disturbance, while the interplay of competition and environment has not been tested for subtle environmental differences. Here, we present results from a study on plant communities of temporary wetlands in East-German farmland. Due to yearly ploughing in autumn, the vegetation is composed of annual species. Flooding does not affect adult plants and the elevation on the gradient expresses differences in the length of the growing season rather than in disturbance intensity or severe environmental stress. We tested whether such subtle differences in environmental stress may affect the importance of interspecific competition by the dominant species. Two treatments were applied at two elevations: removal of the dominant species (Matricaria maritima ssp. inodora) and reciprocal transplants of the seed-bank of the two elevations. At both elevations, removal of Matricaria inodora led to an increase in total species richness and number of wetland species, but the effects were substantially stronger at high elevations. Removal and the elevation on the flooding gradient significantly influenced the plant community composition. In particular, the weed communities became more similar to the wetland communities after the removal. Transplanted weed species did not emerge at low elevations. While two of four target species had significantly higher densities after the removal at high elevations, none of them was influenced by removal at low elevations. This indicates that, consistent with previous studies from other habitat types, competition by the dominant species was more intense under conditions of low environmental stress. The overall results suggest that both flooding as well as interspecific competition are important in structuring the plant communities along the freshwater gradient studied Y1 - 2005 SN - 1385-0237 ER - TY - JOUR A1 - Tielbörger, Katja A1 - Prasse, Rüdiger A1 - Bornkamm, Reinhard A1 - Kadmon, Ronen A1 - Tsoar, H. T1 - Sukzessionsprozesse in einem Sanddünengebiet nach Ausschluß von Beweidung Y1 - 2000 ER - TY - JOUR A1 - Tielbörger, Katja A1 - Kadmon, Ronen T1 - Temporal environmental variation tips the balance between facilitation and interference in desert plants N2 - Recently, numerous studies have pointed to the importance of positive interactions in natural communities. There is now a broad consensus that the balance between negative and positive interactions should shift along environmental gradients, with competition prevailing under environmentally benign conditions and positive interactions dominating under harsh conditions. A commonly cited example of the importance of facilitation in harsh environments is the preference of desert annual plants for the areas under the canopy of shrubs. The recognition of apparently positive effects of desert shrubs on annuals, however, has been mostly based on density measurements, while fitness parameters of the understory plants have been ignored. Also, the temporal consistency of such effects has not been previously tested. Based on conceptual ideas about the balance between interference and facilitation, we predicted that positive effects of the shrubs on the understory should dominate in dry years, while in favorable years, negative effects would be stronger. We tested our hypothesis by measuring the direction and magnitude of the shrub effect on demographic responses of four desert annual plant species during four consecutive seasons of differing rainfall. The results contradicted our initial hypothesis. Depending on the species, the effect of the shrubs shifted from either negative to neutral or from neutral to positive with increasing annual rainfall. However, this trend was stronger for the effect of shrubs on plant reproductive success than on their densities. Our data highlight the importance of measuring fitness parameters in studies of plant-plant interactions. We suggest that the negative effects of shrubs on plant fitness were due to rainfall interception, while positive effects were related to increased nutrient availability beneath shrubs. However, the mechanisms by which the shrubs and annuals interact can only be resolved using an experimental approach. Our results contradict previous hypotheses about the relative importance of positive and negative interactions along environmental gradients. A simple conceptual model summarizing the proposed role of rainfall in determining the direction of shrub effects on their understory annuals is presented. Y1 - 2000 ER - TY - JOUR A1 - Kadmon, Ronen A1 - Tielbörger, Katja T1 - Testing for source-sink population dynamics : an experimental approach exemplified with desert annuals N2 - Theoretical models indicate that natural populations may be structured in such a way that many individuals occur in habitats where reproduction is insufficient to balance mortality. The persistence of such 'sink' populations depends on immigration from neighboring 'source' habitats where local reproduction exceeds mortality. While source-sink dynamics has become a fundamental concept in ecological theory, there has been virtually no experimental test for the existence of sources and sinks in natural populations. This paper reports the results of a four-year study that was designed to experimentally test for source-sink population dynamics in desert annual communities. Based on evidence from a variety of desert ecosystems indicating that patchiness caused by the presence of shrubs is important in structuring desert annual communities, we distinguished between two types of habitats: areas beneath the canopy of shrubs and the open areas between the shrubs. If, as suggested in previous studies, source-sink dynamics is important in structuring such annual communities, one would expect that removal of populations from one habitat leads to extinction of some species in the other habitat. We tested this prediction using removal experiments. Specifically, we monitored density responses of annual populations inhabiting open areas to the repeated removal of conspecific populations from the shrubs and vice versa. Four years after establishment of the experiment, none of the studied 34 species responded to the removal treatments with habitat-specific extinction. Only one species exhibited a significant habitat-specific decrease in density in response to the removal of conspecific populations from the other habitat. These findings contradict our expectations and point to the importance of applying an experimental approach in studies of source-sink dynamics. Y1 - 1999 ER - TY - JOUR A1 - Tschöpe, Okka A1 - Tielbörger, Katja T1 - The role of successional stage and small-scale disturbance for establishment of pioneer grass Corynephorus canescens N2 - Question Which mechanisms promote the maintenance of the protected pioneer grass Corynephorus canescens in a mosaic landscape? Which are the interactive effects of small-scale disturbances, successional stage and year-to-year variation on early establishment probabilities of C. canescens? Location Brandenburg, NE Germany. Methods We measured emergence and survival rates over 3 yr in a sowing-experiment conducted in three successional stages (C. canescens- dominated site, ruderal forb site and pioneer forest) under two different regimes of mechanical ground disturbance (disturbed versus undisturbed control). Results Overall, disturbance led to higher emergence in a humid year and to lower emergence in a very dry year. Apparently, when soil moisture was sufficient, the main factor limiting C. canescens' establishment was competition, while in the dry year, water became the limiting factor. Survival rates were not affected by disturbance. In humid years, C. canescens emerged in higher numbers in open successional stages while in the dry year, emergence rates were higher in late stages, suggesting an important role of late successional stages for the persistence of C. canescens. Conclusions Our results suggest that small-scale disturbances can promote germination of C. canescens. However, disturbances should be carefully planned. The optimal strategy for promoting C. canescens is to apply disturbances just before seed dispersal and not during dry years. At the landscape scale, a mosaic of different vegetation types is beneficial for the protected pioneer grass as facilitation by late-successional species may be an important mechanism for the persistence of C. canescens, especially in dry years. Y1 - 2010 UR - http://onlinelibrary.wiley.com/doi/10.1111/j.1654-109X.2009.01072.x/full U6 - https://doi.org/10.1111/j.1654-109X.2009.01072.x SN - 1402-2001 ER - TY - JOUR A1 - Tielbörger, Katja T1 - The vegetation of linear desert dunes in the north-western Negev, Israel N2 - In 1992, the flora and vegetation of an area of linear sand dunes at Nizzana, western Negev desert, Israel, was investigated. Seven different plant communities were found and a vegetation map of the research area was produced. The plant communities were distinguished by only the dominating perennial species. Nevertheless, the results of the study indicate, that also annual species may be suitable as a tool to distinguish between desert plant communities. Y1 - 1997 ER -