“River phenomenon” in the Czech Republic
David Zelený, PhD Thesis – http://davidzeleny.net/doku.php/phd
In the middle elevations of the Czech Republic, deeply incised river valleys form distinct
geomorphological feature, with steep slopes and sharp upper edges contrasting to
the otherwise flat or softly undulating surrounding landscape. Most of these valleys
are of late Tertiary and early Quaternary origin, when the uplift of the Bohemian Massif
resulted into increased erosion power of rivers (Kopecký 1996). Geomorphology of
these valleys was further shaped during Pleistocene periods of glaciation, when intensive
frost weathering occurred as a result of periglacial climate (Kopecký 1996). Main
abiotic features of these valleys are related to rugged topography and specific microclimatic
conditions: steep slopes with exposed rocky outcrops, diversity of landform
shapes, variability in slope aspect with sharp contrast between warm south and cold
north facing slopes, and also frequent temperature inversions, resulting from the valley
shape and pronouncing the contrast between cold and wet valley bottom and dry continental
upper valley edges. Important biotic consequences of these features are (1) high
diversity concentrated in these valleys due to concentration of various, often ecologically
contrasting habitats, (2) occurrence of relict species, reflecting the role of valleys
as a refuge during glacial and postglacial period, (3) function of river valley as migration
corridors between mountains and lowlands, with migration of both downstream and upstream
direction (the latter facilitated due to the frequent occurrence of suitable dry and
warm habitats within the valleys in higher
altitude), and finally also (4) conservation of
vegetation less affected by human activities in
hardly accessible sections of the valleys.
Specific features of the vegetation pattern in
these valleys were summarized under the
heading “river phenomenon” in the
descriptions provided by Czech vegetation
scientists
in the 1960’s (Blažková 1964; Jeník &
Slavíková 1964).
Concentration of strong ecological gradients
within limited space of the valley together
with the fact, that these valleys are the main
source of the topographical heterogeneity
in the middle elevations of the Czech
Republic, makes them an interesting model
for studies searching for environmental
correlates of vegetation and plant diversity
patterns at the landscape scale.