Phytogeographical distribution of roadside flora along the plain to mountainous natural areas (Northern Khorasan Province, Iran)

- The native uni-regional taxa were dominant in roadside habitats of rangeland areas.
- The number of chorotypes decreased from native uni-regional to quadri-regional.
- Endemic species were notable in comparison with cosmopolitan taxa.
- The mid-altitude roadsides can act as a refuge for local endemic species.

Exploring the phytogeographical distribution of roadside flora in natural areas provides several original insights into plant dispersal. The roadside flora of the Irano-Turanian rangelands was studied in the northeast of Iran, along about 600 km of asphalt road. Sampling was performed in homogenous physiognomic-physiographic units along the altitudinal gradient from the plain to the mountainous areas. In a stratified random design, 38 sites on 12 asphalt roads were sampled, and 330 plant taxa of different chorotypes were identified. The altitudinal distribution of the chorotypes was examined fitting generalized linear models (GLM) and generalized additive models (GAM). The results showed that native uni-regional taxa (Irano-Turanian elements) were the dominant chorotype of the roadside habitats in the rangeland areas. The altitudinal response curve of multi-regional (bi-regional to quadri-regional) chorotypes reflected climatic conditions in their contributing phytochoria. Quadri-regional taxa, with an optimum of the Gaussian response curve at mid-altitudes, reflected a moderate climate. The proportion of endemic species (3.6%) was high compared to the pluri-regional (4.6%) and the cosmopolitan taxa (1.2%). While the pluri-regional taxa increased with altitude, cosmopolitan species decreased monotonically and were absent from the high altitudes. This study revealed the importance of the mid-altitude roadsides, both as a refuge for local endemic species and as a bed for local weeds and regional alien species.