Biology Reference
In-Depth Information
Eocene Gatuncillo fl ora from the canal region of Panama (Graham 1985).
They mostly serve to document the expected coastal mangrove to mid-
elevation tropical communities growing there during the Eocene. In the
middle Oligocene, there is a large fl ora of macrofossils (91 taxa; Hollick
1928) and microfossils (165 types; Graham and Jarzen 1969) known from
the San Sebastian Formation at the western end of the central cordillera of
Puerto Rico. At the time of deposition, the locality was near sea level, and
the deposits contain the mangroves Pelliceria and Rhizophora . Pelliceria is
presently found along the western coast of Central America and northern
Colombia. Its disappearance from the northern Caribbean region by the
Miocene, along with that of Nypa in the Eocene, represented a step in the
modernization of the mangrove ecosystem during the Tertiary. There was
also a lower to upper montane broad-leaved forest on the adjacent slopes
with Podocarpus , Acacia , and Bursera .
As a further note, recall from chapter 1 that the lower to upper montane
broad-leaved forest is designated to include midelevational forests in regions
of topographic and climatic diversity and at its lower limits grades either
into wetter and more tropical vegetation or into drier vegetation, and at its
upper limits into cooler deciduous or treeless communities (alpine tundra
or páramo). The many gradations within this formation, and between it
and other formations, cannot be consistently identifi ed in fossil fl oras, so
the more inclusive lower to upper montane broad-leaved forest formation
is recognized. In the Appalachian part of northern North America, the de-
ciduous forest is a prominent component of this formation that in the east
does not grade upward into a treeless alpine tundra because of the moderate
elevations, or downward into a tropical forest or drier shrubland or near-
desert vegetation. Hence, it is designated there as a separate, well-defi ned
formation. In western northern North America where there are alpine
and desert habitats, the deciduous forest is less extensive and well-defi ned
because it is often intermingled with gymnosperms to form a mixture of
deciduous angiosperm and evergreen coniferous forest, or it occurs as gal-
lery (streamside) vegetation through coniferous and drier-land communi-
ties. As noted, in Latin America, however, there are numerous instances
where warm-temperate deciduous forests grade into tropical forest or drier
woodland, or into ceja (stunted forest at its uppermost limits) or alpine tun-
dra / páramo. The designation lower to upper montane broad-leaved forest
is especially useful in the modern vegetation of Latin America, and in fossil
fl oras where more subtle distinctions are not warranted. In the Antilles, on
the slopes of Puerto Rico during San Sebastian times, the wet lower phase
of the formation grew there during the transition times of the Oligocene,
Search WWH ::




Custom Search