Mirijam Gaertner

Impacts of alien plant invasions on species richness in Mediterranean-type ecosystems: a meta-analysis

Besides a general consensus regarding the negative impact of invasive alien species in the literature, only recently has the decline of native species attributable to biological invasions begun to be quantified in many parts of the world. The cause-effect relationship between the establishment and proliferation of alien species and the extinction of native species is, however, seldom demonstrated. We conducted a meta-analysis of studies in Mediterranean-type ecosystems (MTEs) to examine: (1) whether invasion of alien plant species indeed causes a reduction in the number of native plant species at different spatial and temporal scales; (2) which growth forms, habitat types and areas are most affected by invasions; and (3) which taxa are most responsible for native species richness declines. Our results confirm a significant decline in native species richness attributable to alien invasions. Studies conducted at small scales or sampled over long periods reveal stronger impacts of alien invasion than those at large spatial scales and over short periods. Alien species from regions with similar climates have much stronger impacts, with the native species richness in South Africa and Australia declining significantly more post-invasion than for European sites. Australian Acacia species in South Africa accounted for the most significant declines in native species richness. Among the different growth forms of alien plants, annual herbs, trees and creepers had the greatest impact, whereas graminoids generally caused insignificant changes to the native community. Native species richness of shrublands, old fields and dune vegetation showed significant declines, in contrast to insignificant declines for forest habitats.

Effects of Alien Plants on Ecosystem Structure and Functioning and Implications for Restoration: Insights from Three Degraded Sites in South African Fynbos

We investigated the type and extent of degradation at three sites on the Agulhas Plain, South Africa: an old field dominated by the alien grass Pennisetum clandestinum Pers. (kikuyu), an abandoned Eucalyptus plantation, and a natural fynbos community invaded by nitrogen fixing—Australian Acacia species. These forms of degradation are representative of many areas in the region. By identifying the nature and degree of ecosystem degradation we aimed to determine appropriate strategies for restoration in this biodiversity hotspot. Vegetation surveys were conducted at degraded sites and carefully selected reference sites. Soil-stored propagule seed banks and macro- and micro-soil nutrients were determined. Species richness, diversity and native cover under Eucalyptus were extremely low compared to the reference site and alterations of the soil nutrients were the most severe. The cover of indigenous species under Acacia did not differ significantly from that in reference sites, but species richness was lower under Acacia and soils were considerably enriched. Native species richness was much lower in the kikuyu site, but soil nutrient status was similar to the reference site. Removal of the alien species alone may be sufficient to re-initiate ecosystem recovery at the kikuyu site, whereas active restoration is required to restore functioning ecosystems dominated by native species in the Acacia thicket and the Eucalyptus plantation. To restore native plant communities we suggest burning, mulching with sawdust and sowing of native species.

Does land abandonment decrease species richness and abundance of plants and animals in Mediterranean pastures, arable lands and permanent croplands?

BackgroundObscured by the more prevalent discussion of intensification and expansion of agricultural land, the impacts of the abandonment of many grasslands and croplands of the world in recent decades have received limited attention in the literature. Land abandonment is a common phenomenon in the Mediterranean Basin, a global biodiversity hotspot, but little is known about the impacts of this process on biodiversity. To upscale existing case-study insight to a Pan-Mediterranean level, we plan to perform a systematic review of the effects of land abandonment on plant and animal richness and abundance in pastures, arable lands and permanent crops of the Mediterranean Basin. In particular, we ask (1) which taxonomic groups are most affected by land abandonment; (2) whether different spatial and temporal scales of studies influence species richness and abundance outcomes; (3) whether previous land use and current anthropogenic impacts on abandoned lands determine differences in the number and abundance of species; and (4) whether landscape context modifies the impacts.MethodsOur review will be based on searching scientific databases as well as the internet for empirical studies on the effects of land abandonment on biodiversity in the Mediterranean Basin. Study selection follows a three-stage process and includes study quality assessment. Extracted data will be synthesized through meta-analysis. Results will be presented in the form of a quantitative (e.g. figures indicating effect sizes, tables summarizing heterogeneity statistics) and narrative synthesis. Additional aspects will be addressed through meta-regression and sub-group analyses.

Der ehemalige Panzerschießplatz Dauban

Landschaftlicher Kontext. Das Oberlausitzer Heide- und Teichgebiet in Ostsachsen ist eine der grosten und okologisch vielfaltigsten Teichlandschaften Mitteleuropas und erstreckt sich vom Oberlauf der Schwarzen Elster ostwarts bis uber die Neise. Nach Suden schliest das durch Lossanwehung periglazial beeinflusste Oberlausitzer Gefilde an und geht in das Oberlausitzer Bergland uber. Im Norden finden sich die ausgedehnten Sandgebiete des Niederlausitzer Grenzwalls.