Environmental Engineering Reference
In-Depth Information
Table 2.3
A summary of Holocene environmental change (based on Jalut
et al.,
2009)
Age (cal.
years BP)
Division
Climate
Vegetation, etc.
5500 to
present
Upper
Holocene
Aridification
A decline of deciduous
broad-leaved trees and
spread of evergreen
sclerophyllous taxa. This
was prompted by climatic
characteristics and
probably accelerated as
human activity intensified
7000-5500
Transition
phase
Decrease in insolation;
development of an
atmospheric system
similar to that of today
11 500-7000
Lower
Holocene
Humid with dry episodes
Spread of deciduous
broadleaved trees
change overall. They also showed that this was the case during later periods when
Mesolithic and Neolithic activity was occurring. It is also of interest that they iden-
tified a north-south gradient; that is, at the northern sites in Tuscany and Croatia
Quercus ilex
replaced deciduous forest species as conditions became drier; in con-
trast at the more southerly sites in Sicily
Q. ilex
replaced maquis or steppe as condi-
tions became wetter. This is because in wetter conditions, as in the early Holocene
of the north Adriatic region, deciduous species can outcompete
Quercus ilex
while
under drier conditions, as in the south,
Quercus ilex
is outcompeted by shrubs and
herb species. The sites investigated in this study are all at low altitude and how far
the results and inferences can be extrapolated in relation to the rest of the Mediter-
ranean Basin or its mountains requires further research. Nevertheless, it reflects the
complexity of climate-vegetation-fire relationships, which are just as important in
Mediterranean mountains. A further point of interest is the contrast between earlier
interglacial development and the Holocene. Tzedakis (2009) has reviewed this in
detail. He points out that sclerophyll species underwent a greater expansion dur-
ing the early part of the last interglacial than in the Holocene, which he attributes
to increased summer insolation in the interglacial. In comparison hazel (
Corylus
)
was more significant in the early Holocene in the western Mediterranean, with oak
(
Quercus
) in the east. Moreover, interglacial vegetation successions were more di-
versified than those of the Holocene and, of course, the latter half of the Holocene
was substantially affected by human activity not least by the spread of the olive
(
Olea
) and the creation of pasture and arable land during Neolithic times.
Notwithstanding these generalizations, examples of results from a few upland
sites illustrate specific vegetation/environmental changes. Table 2.4 summarizes
the environmental changes during the last 18 000 years at Tigalmamine in the
