Abstract
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.
Highlights
Ash-leaved maple (Acer negundo L.) is an invasive tree in the territory of Northern Eurasia that is currently colonising disturbed and semi-natural territories[1,2,3,4]
In ANOVA, with fixed effects "plot type" and "year" and a random effect "site", the differences between plots dominated by invasive A. negundo (An +) and dominated by other tree species (An −) in canopy cover were significant (Fplot type(1; 54) = 11.09; P = 0.0016), as well as the effect of the year of observation (Fyear(2; 54) = 3.55; P = 0.0356).The interaction of factors with fixed effects was insignificant (Fplot type × y ear(2; 54) = 0.33; P = 0.7186)
We observed decreased ground cover plant species in large and small vegetation areas dominated by the alien maple Acer negundo compared to areas dominated by native tree and shrub species
Summary
Ash-leaved maple (Acer negundo L.) is an invasive tree in the territory of Northern Eurasia that is currently colonising disturbed and semi-natural territories[1,2,3,4]. Shading is often considered a valid mechanism of the invasive plant influence on native communities[33,34,35] This hypothesis seems easy to understand but has no absolute experimental support. In addition to the hypothesis about the strong shading of A. negundo, it is possible that even with the same canopy cover, the ash-leaved maple has a stronger effect on ground cover than other trees (Fig. 1b,c). This suggestion implies that the reduced richness of the ground cover under A. negundo is associated with
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