Pacific Southwest Research Station

Publication Information

Title: Tertiary vegetation history

Author: Millar, C. I.

Date: 1996

Source: Sierra Nevada Ecosystem Project, Final report to Congress, Volume II, Assessments and Scientific Basis for Management Options, Centers for water and Wildland Resources, Report No. 37, University of California, Davis California

Description: The Tertiary period, from 2.5 to 65 million years ago, was the time oforigin of the modern Sierra Nevada landscape. Climates, geology,and vegetation changed drastically in the Sierra Nevada during thistime, and analyses of this period provide both context for and insightinto vegetation dynamics of the current and future Sierra. During theearly Tertiary, warm-humid, subtropical to tropical conditions prevailedon the low, rolling plains of the area now the Sierra Nevada. Fossiltaxa with tropical adaptations and affiliations were widespreadthroughout the region. In the Sierra Nevada, ginkgo (Ginkgo biloba),avocado (Persea), cinnamon (Cinnamomum), fig (Ficus), and treefern (Zamia) were common. At the end of the Eocene epoch, about34 million years ago, global climates changed rapidly from warmequableto cool-seasonal temperate conditions. In response, vegetationalso shifted enormously; cool-dry-adapted conifers andhardwoods, which had been refugial during the early Tertiary in uplandareas of the Great Basin–Idaho region, migrated into newly hospitablehabitats of the Sierra Nevada. These floras contained manyof the taxa now native to the Sierra, plus relicts from the subtropicalforests of the earlier Tertiary and species adapted to temperate conditionswith summer rain—mixes that seem incompatible under modernconditions. Until late in the Pliocene epoch (about 1 million yearsago), adequate but diminishing rainfall distributed through the yearsupported many taxa now extinct in the Sierra Nevada. By the lateTertiary, in response to continued drying, winter cooling, and increasingsummer drought, and to gradual uplift of the Sierra Nevada, replacementof early Tertiary floras by modern taxa and associationshad occurred. With the development of a Mediterranean climate bythe late Pliocene, floras of the Sierra Nevada became segregatedecologically into elevational, latitudinal, and orographic zones

Key Words: management, tertiary period, vegetation

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Millar, C. I.   1996.  Tertiary vegetation history  Sierra Nevada Ecosystem Project, Final report to Congress, Volume II, Assessments and Scientific Basis for Management Options, Centers for water and Wildland Resources, Report No. 37, University of California, Davis California.