The impact of invasive Caucasian hogweeds on birds depends on areas of invaded and uninvaded habitats at various scales in Central European uplands
Abstract
The availability of various habitats increases biodiversity and provides niche opportunities for organisms, although greater habitat diversity may contribute to the spreading of invasive plants. In this study, we aimed to assess the impact of the extent of invasion on bird responses to the availability of their natural habitats.
Specifically, we asked whether the Caucasian hogweeds, herbaceous invasive plants spreading in abandoned lands, shape those responses by providing new niche opportunities or limitations and whether these invaders can be tolerated by the bird community. The research was conducted in south-eastern Poland in 2020 on 64 research sites, half of which were located near the Caucasian hogweeds' invasion.
The birds were counted from points within 100 m, while the areas of invaded and uninvaded habitats were measured within 100 and 500 m. The impact of the invaded area was negative for the overall bird abundance and species richness.
At the same time, the invasion affected birds differently depending on their nesting/foraging assemblages, the availability of various uninvaded habitats, and the extent of invaded areas. Specifically, the abundance of ground/herb dwellers non-linearly dropped even with small increases of the invaded area suggesting their high sensitivity to invasion.
These birds were supported by the agricultural land availability, but only when its area was lower than 1.0 ha and the habitat was fragmented, indicating the value of extensive croplands for ground/herb dwelling species. Ecotone birds benefited from small invaded areas mixed with bushes but suffered when the invaded areas were large.
Habitat homogenization by the invader physiognomically similar to shrubs was favoured by bush foragers. Tree foragers preferred forest partitioning near the largest invaded areas.
The invaded and uninvaded habitats influenced bird community at a fine scale (i.e. in a 100-m radius), while only crucial areas of meadows, forests and agriculture available in a 500-m radius remained important for the community. This study showed that even a small amount of plant invaders rapidly and negatively affect birds when they grow in open areas and are physiognomically different from these birds' habitats, while species living in ecotone or trees suffer from severely invaded areas.
It suggests the priority of invading weeds' removal in open areas, regardless of the invaded area, as well as the need to prevent weed development in overgrown areas.