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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.

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The aim of the work is to establish how greatly the light conditions change under the leaf canopy of two invasive plant species in the Middle Urals - Acer negundo and Sorbaria sorbifolia . In June - August 2020, using a portable light meter, 8370 measurements of illumination were performed in forest parks (at a height of 1.5 and 0.5 m, i.e. above and below the canopy of the leaves of the invasive shrub S. sorbifolia and the native shrub Rubus idaeus ; in random points under the canopies of Pinus sylvestris ; on glades, paths and forest edges) and in urban habitats (at a height of 1.5 m and 0.5 m in dense thickets of the invasive tree A. negundo and other tree species). The average illumination intensity was as following: under S. sorbifolia - 4 ± 1 lux × 10; under R. idaeus - 7 ± 1 lux × 10; in A. negundo thickets - 13 ± 2 lux × 10; in thickets of other tree species - 25 ± 4 lux × 10; under the canopies of urban pine forests - 80 ± 10 lux × 10; in the forest edges - 96 ± 14 lux × 10. In dense thickets, A. negundo intercepts about 94% of the light falling on its canopies, S. sorbifolia - about 93%. This is significantly higher than the light interception level in habitats used as control: other tree species canopies of greatly urbanized habitats intercept about 89%, the thickets of R. idaeus - about 82%. Thus, invasive plants reduce the amount of light available to other plant species in communities significantly more than native plants.

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We assessed the link between canopy cover degree and ground vegetation diversity under alien the 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 completed over three years, we recorded canopy cover and plant diversity 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 diversity 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 diversity among vascular ground plant species by 40% (inter-habitat) and 20% (intra-habitat) in areas dominated by the 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.

We assessed the link between canopy cover degree and ground vegetation diversity 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 diversity 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 diversity 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 diversity 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.