Shading and light interception in thickets of invasive Acer negundo and Sorbaria sorbifolia.
The purpose of the work was to establish how much the illumination conditions change under the crowns (canopy of leaves) of Acer negundo and Sorbaria sorbifolia, two invasive plant species in the Middle Urals. In June-August 2020, we performed 8370 illumination measurements in forest parks (at a height of 1.5 and 0.5 m, that is, above and below the canopy of the leaves of the invasive shrub S. sorbifolia and the local shrub Rubus idaeus; at random points under the crowns of Pinus sylvestris; in glades, trails, and near forest boundaries) and in urban habitats (at a height of 1.5 and 0.5 m in dense thickets of the invasive tree A. negundo and other tree species) using a portable light meter. The average illumination intensity was as follows: 4 ± 1 lx × 102 under S. sorbifolia; 7 ± 1 lx × 102 under R. idaeus; 13 ± 2 lx × 102 in stands of A. negundo; 25 ± 4 lx × 102 in urbanized plantations from other types of trees; 80 ± 10 lx × 102 under the canopy of urban pine forests; 96 ± 14 lx × 102 at the edge of the forest. Dense clumps of A. negundo intercept about 94% of the light from their crowns, and S. sorbifolia intercepts about 93%. This level is significantly higher than the level of light interception in control habitats: crowns of other tree species of highly urbanized habitats intercept about 89%, and thickets of R. idaeus intercept about 82%. Thus, invasive plants reduce the amount of light available to other species in communities significantly more strongly than native plants.