Environmental Engineering Reference
In-Depth Information
Milankovich orbital forcing characteristics. There is also evidence for environmen-
tal change during both cold and warm stages, indicating heterogeneity rather than
homogeneity within each stage and the dynamic nature of the climate-ecosystem
relationship.
During the long glacial stages open habitats prevailed in regions and at altitudes
that were not snow/ice covered. Variations in erosion intensity, due in turn to cli-
matic variations, are reflected in the lake sediments. For example, in the record from
Lake Ohrid (Vogel
et al.,
2010) the last glacial stage was marked by variations in
particle size, ranging between coarse silt to fine sand, as well as low concentrations
of organic matter and calcite, which reflect low lake productivity. Moreover, the ex-
amination of the pollen content of hyena coprolites from the foothills of the Pyre-
nees (Gonzalez-Samperiz
et al.,
2003), which are between 50 700 and 39 900 years
old, shows that varied/mosaic vegetation communities prevailed. These included
juniper woodland and open habitats dominated by chenopods, grasses, etc.; the
presence of more warmth-demanding trees and shrubs also raises questions about
refugia, that is, loci of warmth-demanding species such as trees, from which they
spread when conditions ameliorated.
The existence of refugia has been questioned, notably in the context of tropi-
cal environments (for a discussion see Haffer, 1982), which have never experienced
glaciation and for which there is little evidence, but in temperate and Mediterranean
environments refugia must have existed and it is a matter of speculation as to where
the major tree species survived during the coldest periods of the Quaternary. This
is another important facet of past, present and future ecosystem dynamics that is
climate dependent and that can only be addressed through palaeoecology as a win-
dow to the past. Refugia relating to the last cold stage in the Mediterranean have
been identified on the basis of pollen, macrofossil and molecular records by Lopez
de Heredia
et al.
(2007), who have examined the possibility of multiple refugia for
the evergreen oak group of
Quercus suber
L.,
Q. ilex
L. and
Q. coccifera
L. They
suggest that refugia existed in southwestern, eastern and northern Iberia as well as
the Cantabrian Mountains of southeastern Spain. Beaudouin
et al.
(2007) have sum-
marized much of this work and have also identified the remains of
Abies, Picea and
deciduous
Quercus
from sediments in the Gulf of Lions c. 30 000 years old; this area
was part of the drainage basins of the Pyreneo-Languedocian rivers and may have
been linked to northeastern Spanish and southeastern French refugia/relicts. The
fact that several mountain regions provided refugia during Quaternary cold stages
is also considered likely by the analysis of Medail and Diadema (2009), who have
examined phylogeographical evidence (i.e. molecular evidence, notably molecular
markers within a species that reflect intraspecies relationships over time) for refu-
gia in the Mediterranean region as a whole and compared such data with proposed
'hotspots' of biodiversity. Hot spots have been delineated as having high species di-
versity, high endemism and intense habitat modification (Medail and Quezel, 1997).
Of special significance are the interglacial stages of the last 500 000 years
because they provide a record of interglacial progression similar to the present
Holocene but without any human impact. Investigations of such stages provide,
