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continent in summer. Chile appears to have slowly developed a MTC that began
about the same time as the initiation of the Andean uplift and continued until about
8 Ma when modern atmospheric circulation patterns were largely in place (Armesto
et al. 2007 ). A major effect of the Andean uplift was the drastic reduction in
lightning activity ( Fig. 10.4 ) and thus, from the late Miocene until humans arrived,
the western side of the Andes in northern and central Chile lacked a predictable
source of ignitions.
In summary, Tertiary climates have largely varied in the amount of landscape
that was potentially fire-prone. However, even during the most equable climatic
epoch of the Eocene, seasonally arid climates conducive to fire have existed in
some regions. On those landscapes that on average were aseasonal, longer decadal-
scale droughts could have contributed to fire-prone conditions. Seasonal distribu-
tion of drought appears to have varied spatially and temporally. In some regions
middle Tertiary aseasonal climates gave rise to winter-drought and summer-rain
regimes, whereas in other regions it is apparent that tendencies toward a MTC of
winter rain and summer drought appeared relatively early in the Miocene. Some
reports suggest alternating conditions of winter rain and summer rain at different
times since the Oligocene. From the middle Miocene on, it appears that the severity
of the summer drought component of the MTC intensified and there is little
evidence that it developed from a dramatic climatic shift at the end of the Tertiary.
The coupling of drought with high summer temperatures did not create qualitatively
different drought conditions, requiring an entirely new mode of adaptation. Rather
the MTC greatly expanded the portion of landscape subject to drought stress.
When combined with sufficient winter rainfall to produce a contiguous cover of
sclerophyll vegetation, fire regimes became more predictable and this represented
an important selective force. Late Tertiary increases in fire-prone landscape were
not restricted to MTC regions but were evident in other ecosystems such as
subtropical savannas under monsoonal climates (e.g. Keeley & Rundel 2005 ).
Origins of Mediterranean-type Vegetation
Our understanding of MTV origins is based on macrofossils of leaves, microfossils
of pollen and molecular clock estimates from genetic studies of contemporary
taxa. The quality and depth of record for these metrics vary greatly between
regions. Some parts of southern Australia and western North America have
extensive Tertiary vegetation records, whereas South Africa and Chile are not
well represented. The macrofossil record is the most extensive; however, it largely
pertains to woody species with annual leaf turnover, and herbaceous species are
not well represented. Palynology (study of fossil pollen) has provided some
insights into herbaceous origins, but pollen often cannot be recognized below
the generic or sometimes family level.
What is apparent from the fossil record is that some sclerophyllous MTV taxa
appear to predate the MTC, although the extent to which this is true is dependent
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