Biology Reference
In-Depth Information
tanea
(chestnut),
Fagus
(beech),
Juglans
(walnut),
Liquidambar
(sweetgum),
Platanus
(sycamore),
Prunus
(cherry),
Quercus
(oak), and
Ulmus
—brought
about largely by the disappearance of tropical forms. The deciduous forest
differed from its modern counterpart now in eastern North America by
the presence of a few more tropical holdovers, particularly in coastal areas,
and especially by a number of present-day Asian angiosperms (
Pachysandra
,
Platycarya
,
Pterocarya
) and deciduous gymnosperms (
Ginkgo
,
Glyptostrobus
,
Metasequoia
). Modernization of the New World deciduous forest would oc-
cur toward the end of the Miocene and in the Pliocene, when most of the
mesothermal to megathermal and present-day Asian genera disappeared.
To the south is the middle Eocene Princeton Chert fl ora of southern Brit-
ish Columbia, with representative Lauraceae,
Abies
(fi r), and
Pinus
(pine),
circa 50-45 Ma (Erwin and Stockey 1991; Crane and Stockey 1987; Pigg
and Stockey 1996; Smith et al. 2006; Little et al. 2009), along with the
Republic fl ora of northeastern Washington, with
Thuja
(arborvitae),
Abies
,
Picea
(spruce),
Tsuga
(hemlock), and
Betula
, circa 50-49 Ma (Wolfe and
Wehr 1987; Pigg et al. 2001). The Republic fl ora is important for tracing the
history of New World ecosystems because it is the fi rst assemblage where
fi r, spruce, pine, arborvitae, hemlock, and birch are recorded together in
one region. These elements were coalescing in the highlands of the north-
ern Rocky Mountains during the middle Eocene to form a recognizable co-
niferous forest ecosystem. From this site it would later spread northward
into the lowlands to form the boreal forest, and north and south into the
uplands to form the western montane coniferous forest with continued rise
of the Rocky Mountains and other western cordilleras.
The trends in climate, orogeny, and vegetation from this interval are
known in suffi cient detail that the kind of paleocommunity can often be
anticipated given its age, location, and the physical environment of the re-
gion, for example, at a western site of low to moderate elevation, close to
the coast, in the absence of signifi cant highlands to the west, near the early
to middle Eocene boundary. These parameters are met by the Clarno fl ora
in the John Day Basin of north-central Oregon (Manchester 1994; Wheeler
and Manchester 2002). The age (44 Ma), its location within 100 km of the
paleo-Oregon coastline, and the absence of highlands in the Coast Ranges
and the Cascade Mountains would suggest a paratropical forest beginning
the transition to a mixed deciduous angiosperm-gymnosperm forest. In fact,
among the approximately 145 genera and 173 species in this large and im-
portant fl ora, 52 percent have entire-margined leaves, 43 percent are lianas,
and broad-leaved evergreens are abundant. There are
Sabal
(palms),
Ensete
(Musaceae, banana family), other primarily tropical to subtropical fami-
