Geoscience Reference
In-Depth Information
Table 12.4 Weighted correlation matrix values of DCA
analysis, presenting fluvial co-variables influence on
bryophyte species ordination axis 1 (r SP AX1). Only
co-variables with values greater than 0.3 are shown.
Bryophyte communities found in higher altitude
streams with acidic substrata of metamorphic
or magmatic origin, resemble high mountain
communities described for acid waters in the
Swiss Alps (Geissler, 1982) and European springs
(Zechmeister and Mucina, 1994). These bryophyte
communities, (TWINSPAN group B), usually
colonize spring peat areas, exposed springs or
ephemeral streams located in areas with high
levels of erosion and incident light. These habitats
are usually located in or influenced by extensive
cattle pastures and characterized by high annual
precipitation, lower temperatures, acidic soils and
water with the lowest pH and conductivity levels
(Table 12.5).
The aquatic rheophilic acidophilous to
slightly neutrophilous bryophyte communities
(corresponding to TWINSPAN groups C and D)
are similar to others described for Central Europe
(Marstaller, 1987), France (Denise-Lalande and
Touffet, 1987) and Northern Spain (Gil and
Guerra, 1985), but contain species endemic to the
Iberian Peninsula (e.g. Racomitrium lusitanicum ,
Racomitrium hespericum ) or western Europe (e.g.
Platyhypnidium lusitanicum, Fissidens polyphyllus,
Hyocomium armoricum , Radula holtii ). Usually these
communities are found in hillside streams with
highly heterogeneous but stable bedrock substrate
and turbulent, acidic, low conductivity running
water, surrounded by near-natural vegetation and
land use (Table 12.5).
The basophilic bryophyte communities were
found in limestone watercourses located in the
Sic o mountain range (TWINSPAN group A, with
Cinclidotus fontinaloides as an indicator species).
These communities are similar to those described
by Allorge (1947) for the base-rich watercourses
of the northern and central Iberian Peninsula
mountains, despite poorer representation of
orophilous species and greater occurrence of
desiccation-tolerant species in the Sic o mountain
communities. The most neutrophilic bryophyte
communities (TWINSPAN groups E and F)
were found in stream segments of the north-
west mountain valleys; here, higher average air
temperatures and levels of water mineralization
are caused by a combination of factors including
Parameter
r SP AX1
COND
0.8
RESI
0.7
DURZ
0.7
TISO
0.6
pH
0.6
MINE
0.4
POLU
0.4
INSO
0.3
BARR
0.3
LARG
0.3
TMARM
0.3
PRELP
0.3
ESCO
0.3
ALTI
0.5
substrate colonization (Douglas and Lake, 1994;
Barrat-Segretain, 1996).
Total macrophyte cover, itself highly correlated
with the presence and abundance of mosses and
liverworts in most of the sampled stream segments,
was negatively correlated with disturbance factors
such as soil erosion in the river catchment, water
pollution and an increase of incident light levels
reaching
the
stream
bed.
These
factors
affect
ecological
integrity
through
siltation,
nutrient
enrichment
and
an
increase
in
air
and
water
temperatures.
Bryophyte communities
The TWINSPAN classification of bryophyte
communities reveals geographical overlaps in
some of the study areas, suggesting that different
environmental and ecological conditions occur
in the same mountain range. Each TWNSPAN
community is dominated by a different assemblage
of
species
which
have
distinctive,
diverse
and
recognizable
ecological
preferences
(Dierssen,
2001).
 
Search WWH ::




Custom Search