Figure 1.
Transects were replicated 20 times along each of the 3 roads. Each plot (road, mid, far) measured 2×50 m, with the roadside plot parallel to the road, and the mid and far plots perpendicular. Mid and far plots both are divided in two subplots of 2×25 m each (mid1, mid2, far1 and far2).
Figure 2.
Native species richness as a function of elevation and distance to the road.
(A) Average native species richness (±1 SE) in plots across the elevational gradient. Different letters indicate significant differences (p<0.05) in a Tukey’s post-hoc test. (B) Native species richness (number of species per plot) as a function of elevation. •, black full line: roadside plots; •, grey full line: mid plots; ○, broken line: far plots (see Fig. 1 for plot types).
Figure 3.
Plot coverage as a function of distance to the road.
Percentage of the plots (± 1 SE) covered with (A) total vegetation, (B) bryophytes, (C) the dominant species (E. nigrum) and (D) bare ground, as a function of distance to the road. Different letters indicate significant differences (p<0.001).
Figure 4.
DCA-ordination of plots (•) based on total species coverage. Ellipses indicate the standard deviations for different subgroups as a function of elevation and distance to the road. Elevation: H = highest third, M = middle third, L = lowest third of the gradient; road distance: A = roadside, B = mid, C = far (see Fig. 1 for plot types). The arrow represents the vector of increasing elevation. Eigenvalues of DCA1 and 2 are 0.3479 and 0.2771 respectively.
Figure 5.
Changes in total species composition between roadside and far plots with elevation.
Left column: number of species that were present in the natural plant communities but lost in the roadsides ( = species unique for the natural plant communities). Middle column: species newly gained in the roadsides ( = species unique for the roadsides). Right column: shared species between roadsides and natural plant communities. A-C = all species, D-F = competitive species, G-I = stress-tolerant species, J-L = ruderals, derived from Grime’s triangle. Significance of linear regressions: ***: p<0.001; **: p<0.01; *: p<0.05;.: p<0.1; otherwise higher than 0.1.
Figure 6.
Alien species richness as a function of elevation and distance to the road.
(A) Alien species richness (number of species per plot) as a function of elevation. Roadside plots (•, black line), intermediate plots (•, grey line) and far plots (○, dashed grey line). (B) Ratio of alien species richness in the natural plant communities to that in the roadside plot, with mid/roadside (•, grey line) and far/roadside (○, dashed grey line). Significance of linear regressions: see text. Symbols of different variables were slightly shifted to avoid overlap.
Figure 7.
Elevational range of native and alien species.
Relationship between elevational range and maximum elevation reached by native (•, dashed line) and alien (○, thick solid line) species. Symbols are constrained to the lower right of the graph (marked by the thin solid line), since the elevational range cannot exceed the maximum elevation.