Biotic factors
Because character of the data (observation for 2x2 km grid), we had no detailed information regarding invaded habitats. However the data still allowed testing the hypothesis regarding species co-occurrence at landscape scale and the effect of dominant land cover/land use forms. Results from other region of Central Europe revealed existence of large areas dominated by a single invasive Solidago species, where presence of another was unlikely. This spatial pattern results, most likely, from priority effect (Szymura & Szymura 2016). In the studied region we had no evidences for such phenomenon: the presence of one species did not explain the absence of the other. The species rarely formed mixed stands (Szymura & Szymura, 2016), but considering grain size used in this examination (square 2 × 2 km) it can be assumed that they could co-occurred in the same landscape. We also found that the presence of S. canadensis is rather unlikely in a landscape dominated by agricultural areas. It could be linked to high use of herbicides and a small amount of available area for invasive goldenrod habitats (e.g., abandon fields, meadow, pastures) in lands with intense, large-scale agriculture (Szymura et al., 2016; Szymura & Szymura, 2016).
The relatively low importance of variables that can be related to biotic interactions does not necessarily mean that biotic interactions did not shape invasion pattern. It is more likely related to the grid size in this study (2 × 2 km), while the biotic interactions occur mostly in the closest vicinity of the studied individuals. Such data can potentially be derived from other sources of information, namely phytosociological relevés, which document species composition and abundance in small plots (~25 m2 for herbal vegetation).