Positive effects of large‐scale mire restoration on breeding of brown frogs continue 5 years after rewetting

Introduction Wetland rewetting is costly and often involves conservation trade‐offs. Therefore, it is important to understand the extent to which it supports wetland‐dependent species. Objectives We assessed the effects of large‐scale mire restoration on the breeding of brown frogs: the moor frog ( Rana arvalis ) and the common frog ( R . temporaria ), dominant and functionally important amphibians in the studied ecosystems. Methods We used a before‐after‐control‐impact design in six mire landscapes in Estonia. Our study focused on the peripheral areas of bogs, including lagg zones and swamp forests. Results The number of spawn clumps of both species increased sharply immediately after restoration. The abundance of moor frog spawn continued to increase until the end of the study, exceeding the pre‐restoration level by more than two orders of magnitude. The increase in spawn abundance was slower in sites where trees were not removed, probably due to the gradual mortality of trees. The development of birch thickets in some logged areas did not yet degrade breeding conditions. The change in the frequency of tadpole occurrence was more positive in restoration sites than in drained reference sites. A post‐restoration decrease in water pH weakened, but did not eliminate, the positive effect of restoration on tadpole occurrence. Although restoration created novel aquatic habitats (impounded ditches, borrow pits), brown frogs—especially the moor frog—bred predominantly in flooded areas that resembled natural water bodies. Conclusions Large‐scale mire restoration strongly supports brown frog populations, especially the moor frog, which tolerates water acidification better.