Reduction of amphibian roadkill by one-side barriers

Amphibians are the most affected vertebrates by roadkill. Often, to minimise this problem mitigation barriers are installed. While two-side barriers effectiveness is well described in the literature, one-side barriers are poorly studied. The present study aimed to evaluate the effectiveness of one-side barriers installed by LIFE LINES project along the EM535 road in south-east Portugal. Two types of one-side barriers (one permanent and another temporary one made from tarp) were monitored through road surveys. For each barrier, the influence of interaction between the period (before and after the barrier installation) and road sector (control-no barrier, permanent or temporary barrier installed) on the number of amphibians was evaluated. The result showed that, contrary to the temporary barrier, the permanent one-side barrier appeared to be effective. Thus, the ineffectiveness of the temporary barrier may be related to (i) the tarp material that allows some amphibians to escape, (ii) the presence of vegetation that goes over the top of the barrier, or (iii) increased fence-end effects due to its short length. Even though less effective than two-side barriers, one-side barriers could be installed when there is budget limitation in conservation projects or if land use conflicts exist. Given that our study was the first to evaluate the effectiveness of one-side barriers, we discuss the potential constrains that may have affected our results.