Hogweed presence significantly reduced red/far-red light ratios but increased soil pH. Longer invasion history was associated with increasing soil conductivity and content of extractable phosphorus. There were also parameters that displayed opposite trends in different periods of invasion such as fungal/bacterial ratios or relative amount of photosynthetically active radiation (螖PAR). These parameters initially increased (fungal/bacterial ratio) or decreased (螖PAR), but after reaching a certain breakpoint they tended to return to pre-invasion conditions.
Differences in native species richness were best correlated with light availability and soil pH, and productivity with composition of soil microbial communities. Differences in hogweed cover were associated with soil pH and conductivity. The variation in hogweed performance in a common garden was related to the composition of soil microbial communities, soil conductivity and light availability of sites from which soil inocula were collected.
This study documents that ecosystem properties can be altered not only by an invasion event but are further modified as the invasion proceeds. These ecosystem changes likely underlie long-term impacts of invasive plants on native communities.