High canopy cover of invasive Acer negundo L. affects ground vegetation taxonomic richness.

We assessed the link between canopy cover degree and ground vegetation taxonomic richness under alien ash-leaved maple (Acer negundo) and other (native or alien) tree species. We investigated urban and suburban forests in the large city of Yekaterinburg, Russia. Forests were evaluated on two spatial scales. Through an inter-habitat comparison we recorded canopy cover and plant taxonomic richness among 13 sample plots of 20 × 20 m where A. negundo dominated and 13 plots where other tree species dominated. In an intra-habitat comparison, we recorded canopy cover and ground vegetation taxonomic richness among 800 sample plots measuring 1 m2 in the extended urbanised forest, which featured abundant alien (308 plots) and native trees (492 plots). We observed decreased taxonomic richness among vascular ground plant species by 40% (inter-habitat) and 20% (intra-habitat) in areas dominated by A. negundo compared to areas dominated by native tree and shrub species. An abundance of A. negundo was accompanied by increased canopy cover. We found a negative relationship between canopy cover and the number of understory herbaceous species. Thus, the interception of light and the restriction of its amount for other species is a main factor supporting the negative influence of A. negundo on native plant communities.

[The impacts of permanent irradiation on the flora of the eastern ural radioactive trace].

In the Eastern Ural Radioactive Trace, concentrations of 90Sr, the main contaminant, in the upper topsoil was estimated to be 40-17000 times over the global level. The density of contamination decreased with the distance from the accident plot according to exponential law. The resulting doze loads shown an excess over the background level of about 1-3 orders of magnitude. Vegetation in the head part of the EURT is represented with synanthropic and seminatural communities undergoing different phases of degradations and recovery successions. Phytocenosis degradation is caused by the failures during the accident, subsequent reinstatement and restoration activities and also by the initial anthropogenic load. The ecological and genetic effects of permanent ionizing radiation on plants are evident from a wider spectrum of variability for all indicators of the living ability of seed posterity and their increased mutability. The effect of radioadaptation, i.e. increased the resistance to the additional irradiation, in the EURT plants was not found.