subnival
/ˌsʌbˈnʌɪvl/adjective
1Designating the uppermost mountain zone in which regular plant growth is still possible, immediately below the permanent snow line.
2Existing, living, or carried out underneath snow; = subnivean.
Origin
Mid 19th century; earliest use found in Hewett Watson (1804–1881), botanist and phrenologist. From sub- + nival, after German subnival, itself after post-classical Latin subnivalis.