Contrasted effects of temperate forest closure on snake demography

Abstract Habitat modification is the main threat to biodiversity, but other causes are involved, such as climate change or pollution. To optimize conservation efforts, it is crucial to determine their respective contributions. An effective approach to disentangle causalities is to set up comparative or experimental monitoring in the field. In a temperate forest classified as an integral nature reserve, left unexploited, tree growth led to canopy closure and the progressive disappearance of semi‐open woodlands and associated thermophilic species. Past logging provided a semi‐experimental setting with contrasting patches in terms of canopy closure. A long‐term capture–mark–recapture study of two snake species (1995–2021), one thermophilic and the other less so, revealed which demographic parameters were affected and established a link between habitat closure and population decline. For the most thermophilic species ( Hierophis viridiflavus ), rapid increases in canopy cover drastically reduced the survival probability of very young individuals, neonates and snakes a few months old, likely by depriving them of essential thermophilic prey (i.e., small lizards). Juveniles and adults that feed mainly on rodents and less on thermophilic lizards were less affected. For the least thermophilic snake species ( Zamenis longissimus ) where all age groups feed on rodents, habitat closure had no major effect on survival. Importantly, open woodlands remained favorable for both species. Although closing habitat was detrimental to H. viridiflavus , we predict that the survival of Z. longissimus will also drop as the forest closure approaches 100%. Canopy closure and the disappearance of shrubby habitats are the main factors responsible for the decline of forest snakes. A lack of management in temperate forests may not be the best option to maintain healthy reptile populations.