Environmental Engineering Reference
In-Depth Information
for example, based on the genetic characteristics of modern pine populations in sev-
eral European mountain ranges including the Pyrenees has led Heuertz
et al.
(2010)
to state that 'The core regions of the Pyrenees
were probably recolonized
by
...
...
P
.
uncinata
...
from multiple glacial refugia that were well connected by pollen
flow within the mountain chains'.
One example of a site indicating the existence of a refugium is Siles in the moun-
tains of Segura, southern Spain. This is a lake at 1320m asl that has been investi-
gated by Carri on (2002) using a multidisciplinary approach involving pollen, mi-
crocharcoal, spores of terrestrial plants, fungi, and non-siliceous algae, and other
microfossils. The reconstructions for the 20 300 to 7400-year period are summa-
rized in Table 2.2. These data reflect considerable environmental changes within
the lake and in its catchment as the last ice age ended and they indicate that refu-
gia extended to higher elevations than previously thought. Carrion suggests that
Mediterranean and temperate tree species occupied the most sheltered habitats in a
forest belt that was fragmented in comparison with that of today. Moreover, Siles is
just 5-15 km from several river-cut gorges in the Parque Natural de Cazorla, Segura
y Las Villas, where microclimatic conditions today are favourable to relict popula-
tions of several tree species. This study lends support to the view that the degree
of shelter and/or favourable microclimatic conditions were more important than
altitude in determining the location of refugia in Mediterranean mountains. Such
conditions may also be more important than latitude given that Lamb
et al.
(1989)
have shown, on the basis of pollen analysis of sediments from Lake Tigalmamine
in the Middle Atlas Mountains at altitude 1628m asl, that despite the more south-
ern location in the Mediterranean Basin, sediments of the LGM were dominated by
open habitat species and that tree pollen, notably oak, did not become significant
until c. 14 000 years ago and persisted for c. 2000 years when a decline occurred
until a further increase in the early part of the Holocene.
The decline in oak at Tigalmamine was most likely due to a decline in temper-
ature, which is recognized as a global event during the climatically and ecologi-
cally complex period known as the Younger Dryas. This comprised a few thousand
years during which ice sheets oscillated prior to a major decline as the Holocene
opened (see below). There is evidence from ocean sediments as well as terrestrial
sites (see Robinson
et al.,
2006), including several in the Mediterranean mountains,
for late-glacial environmental change. For example, Hughes and Woodward (2009)
note the presence of late glacial moraines in the Italian Apennines, the Maritime
Alps and Pyrenees. Lakes with long sequences referred to in Table 2.1. and ac-
companying text also record this period. For example, at Lac du Bouchet/Praclaux,
1200m asl, steppe species expanded at the expense of forest species (Reille
et al.,
2000), while at Ioannina, at 470m asl in northwest Greece, Lawson
et al.
(2004)
reported that woodland contracted but was not entirely replaced by open habitat
species. At middle and high altitudes in the eastern Mediterranean, open habitat
xerophytic (dry) herb vegetation dominated, as Denefle
et al.
(2000) have shown
based on pollen evidence from Lake Maliq (Albania) at 818m asl in the Balkans
(see also Willis, 1994). At Lake Dolgoto at 2310m asl in the Pirin Mountains of
