The Long-Term History of Oak Woodlands in California Scott Mensing University of Nevada, Reno

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1 The Long-Term History of Oak Woodlands in California Scott Mensing University of Nevada, Reno

2 Miocene ~20 5 MYA Ancestors of modern oaks present in western U.S. Pliocene ~5 2 MYA By end, oaks restricted to California Pleistocene 2MYA - 10,000 yr Oaks rare during glacial cycles Holocene last 10,000 years Oak abundance at a maximum Native Californian Period ~10, AD Manipulation of oak abundance through fires Spanish Mexican Period AD Slight impacts limited to coast live oak American Period 1850 AD to present Significant impacts due to cutting, grazing, fire suppression

3 Q. Lobata modern leaf Fossil of protolobata

4 20-16 MYA Early Miocene Valley Oak Early associates now extirpated from the western U.S.: Ginko Zelkova Carya (hickory) Liriodendron (tulip tree) Magnolia (magnolia) Ostrya (hornbeam) Fagus (beech) Crataegus (hawthorn)

5 16 10 MYA Middle Miocene Valley Oak

6 10 5 MYA Late Miocene Valley Oak

7 Q. Kellogii leaf and Q. pseudolyrata fossil

8 20 16 MYA Early Miocene Black Oak

9 16 10 MYA Middle Miocene Black Oak

10 10 5 MYA Late Miocene Black Oak

11 16-10 MYA Middle Miocene Coast live oak

12 10-5 MYA Late Miocene Coast live oak

13 Middle and Late Miocene ~16 5 MYA Ancestors of modern oaks present in west & California Pliocene ~5 2 MYA By end, native oaks restricted to California Pleistocene 2 MYA - 10,000 yr Oaks rare during glacial cycles Holocene last 10,000 years Oak abundance at a maximum Native Californian Period ~10, AD Manipulation of oak abundance through fires Spanish Mexican Period AD Slight impacts limited to coast live oak American Period 1850 AD to present Significant impacts due to cutting, grazing, fire suppression

14 Middle and Late Miocene ~16 5 MYA Ancestors of modern oaks present in west & California Pliocene ~5 2 MYA By end, oaks restricted to California Pleistocene 2 MYA - 10,000 yr Oaks rare during glacial cycles Holocene last 10,000 years Oak abundance at a maximum Native Californian Period ~10, AD Manipulation of oak abundance through fires Spanish Mexican Period AD Slight impacts limited to coast live oak American Period 1850 AD to present Significant impacts due to cutting, grazing, fire suppression

15 Pleistocene climate cool wet glacial periods and warm dry interglacials

16 Macrofossils rare in Pleistocene Evidence comes from pollen preserved in sediments

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23 The oak woodlands that characterize California today only came to be within the last 10,000 years Summer dry Mediterranean climate dominated by oaks appears to be confined to interglacial periods.

24 Middle and Late Miocene ~5 16 MYA Ancestors of modern oaks present in west & California Pliocene ~2 5 MYA By end, oaks restricted to California Pleistocene 10,000 yr 2 MYA Oaks rare during glacial cycles Holocene last 10,000 years Oak abundance at a maximum Native Californian Period ~10, AD Manipulation of oak abundance through fires Spanish Mexican Period AD Slight impacts limited to coast live oak American Period 1850 AD to present Significant impacts due to cutting, grazing, fire suppression

25 During the Holocene, climate variability has led to periods when oaks were more abundant

26 Middle and Late Miocene ~5 16 MYA Ancestors of modern oaks present in west & California Pliocene ~2 5 MYA By end, oaks restricted to California Pleistocene 10,000 yr 2 MYA Oaks rare during glacial cycles Holocene last 10,000 years Oak abundance at a maximum Native Californian Period ~10, AD Manipulation of oak abundance through fires Spanish Mexican Period AD Slight impacts limited to coast live oak American Period 1850 AD to present Significant impacts due to cutting, grazing, fire suppression

27 Oak woodlands increased in Yosemite when Indians who utilized acorns arrived, even though the climate cooled, which would have normally favored pines

28 Indirect evidence for expansion of black oaks comes from grinding stones. One site at 2100 m (near the upper limit of oaks today) had 34 mortar holes, indicating extensive acorn processing in a place where black oaks are now rare.

29 Middle and Late Miocene ~5 16 MYA Ancestors of modern oaks present in west & California Pliocene ~2 5 MYA By end, oaks restricted to California Pleistocene 10,000 yr 2 MYA Oaks rare during glacial cycles Holocene last 10,000 years Oak abundance at a maximum Native Californian Period ~10, AD Manipulation of oak abundance through fires Spanish Mexican Period AD Slight impacts limited to coast live oak American Period 1850 AD to present Significant impacts due to cutting, grazing, fire suppression

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31 Mensing and Byrne, 1998

32 American Spanish Native Californian Mensing and Byrne, 1998

33 Middle and Late Miocene ~5 16 MYA Ancestors of modern oaks present in west & California Pliocene ~2 5 MYA By end, oaks restricted to California Pleistocene 10,000 yr 2 MYA Oaks rare during glacial cycles Holocene last 10,000 years Oak abundance at a maximum Native Californian Period ~10, AD Manipulation of oak abundance through fires Spanish Mexican Period AD Slight impacts limited to coast live oak American Period 1850 AD to present Significant impacts due to cutting, grazing, fire suppression

34 Over much of their ranges oaks were removed for various purposes. Gallery forests of valley oaks were cut to supply cord wood for river boats.

35 Agricultural clearing leaves living dead trees, isolated solitary specimens that have little chance of reproducing.

36 Orchards and vineyards replaced many oak woodlands

37 Livestock grazing has affected oak regeneration and in the 1950s large areas of woodland were cut or poisoned to remove oaks for range improvement

38 Urban expansion has removed many hectares of oak woodland

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41 In recent decades ~400,000 ha of oaks have been cleared. In some areas, (Santa Barbara), fire suppression has allowed woodlands to increase in density At higher elevations where conifers and oaks co-occur, fire suppression has favored expansion of conifers Changes in understory annuals, livestock grazing, fire and other factors have reduced oak regeneration in some portions of their range Native Californians strongly influenced the range and abundance of oaks in the past. Our modern land use practices have had an even greater impact

42 NOT! California oaks