Agriculture Reference
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this is that lineages were stimulated by apparently different triggers at different
times in the Miocene, Pliocene and Pleistocene. In the relatively short time since
the beginning of the Pliocene a substantial amount of diversification has occurred
as the MTC intensified and presumably the amount of fire-prone landscape
increased.
In the third southern hemisphere MTC region in central Chile, temperate
woodland communities extended across the continent in the Oligocene, and left
biogeographic evidence of their past presence in the disjunctions of numerous
woody plant genera between central Chile and southeastern Brazil. Examples of
such disjunctions include
Araucaria
,
Bomarea
,
Crinodendron
,
Lithraea
,
Mutisia
,
Myrceugenia
,
Perezia
,
Persea
,
Podocarpus
,
Quillaja
,
Viviana
,and
Weinmannia
(Landrum
1981
). These Tertiary forests gave rise to a mixed sclerophyllous
forest by early Miocene, remnants of which survive today in relict patches
throughout the coastal ranges (Hinojosa
et al.
2006
). Taxa with affinities to
contemporary MTC
Kageneckia
(Rosaceae) were present in a Paleocene fossil
flora of southern Chile (Axelrod
et al.
1991
). Miocene matorral bordered more
mesic forest and occurred in small, isolated pockets, but relatively little is known
of the late Tertiary vegetation changes that led to its spread. Sclerophyll forests
of the Coast Ranges of central and southcentral Chile today show strong legacies
of the pre-Pleistocene structure and composition of sclerophyll forest paleo-
floras. These forests and woodlands have been biogeographically isolated for
several million years, but had relatively limited impact from glacial events in the
Pleistocene. The similarity between these contemporary forests and late pre-
Pleistocene paleofloras indicates evolutionary stability of surviving lineages
under relatively moderate climate cycles (Villagra´ nandArmesto
2005
; Hinojosa
et al.
2006
).
In summary, as in the northern hemisphere, sclerophyllous taxa that gave rise to
MTV lineages developed gradually during the mid- to late Tertiary and were
widely distributed by the mid-Miocene. Sclerophyll shrubs persisted in pockets
of stressful substrates with limited nutrient and/or water resources. However, the
widespread persistence of highly weathered low-fertility soils in southwestern
Australia potentially gave rise to an earlier dominance of sclerophylls (Hopper
2009
). It is widely believed that the Quaternary Period was a time of rapid
speciation in all MTC regions, presumably due to rapid climate changes, alternat-
ing glacial and interglacial episodes, increasing aridity and mountain building, and
fires. However, the uniqueness of these changes has been questioned (Bennett
2004
; Sauquet
et al.
2009a
) and molecular studies fail to support a model of
sudden Quaternary radiations in most southern hemisphere MTC lineages. More
broadly, Willis and Niklas (
2004
) tested whether Quaternary speciation rates were
substantively higher than for previous periods and found no evidence to support
this assertion. The evidence for MTV origins in both the northern and the
southern hemispheres shows that species radiations varied in their timing between
different lineages. Some groups radiated throughout the Tertiary and others
appear to have radiated more recently in the Quaternary.
