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).