An interpretation of high montane conifers in western Tertiary floras

Abstract

Megafossil remains of conifers allied to taxa of the high montane fir-spruce-hemlock-white pine zone often occur in relatively lowland Tertiary floras together with taxa typical of the mixed-conifer and broadleaved sclerophyll forest zones. Even though these forests are now separated in elevation by fully 1,000 m and in distance by 10–20 km or more, it has been generally accepted that the structures of the high montane conifers were transported to the basins of deposition from distant, high mountains. Several lines of evidence show that montane conifers were regular members of both mixed-conifer and montane conifer forests. They were restricted to higher elevations in the late Neogene–Quaternary; as summers became drier and hotter, the germinating seedlings failed to become established in the mixed-conifer forest zone. They were further isolated from the broadleaved sclerophyll zone, which was confined to lower levels as winters became colder and snow more frequent.