Geoscience Reference
In-Depth Information
Figure 6-8.
Red samphire, also known as saltwort
(
Salicornia rubra
; see Color Plate 6-8). Succulent stems
turn red in summer and may form bright maroon
carpets on saline mud l ats (see Color Plate 3-9). Cattle
relish the high salt content; as human food, it may be
eaten in salads and stews or used for pickling (Lahring
2003). Comb is
5 inches (12.5 cm) long; photo by J.S.
Aber at Frederick Lake, Saskatchewan, Canada.
∼
Figure 6-7.
Saltcedar (
Tamarix
sp.) growing beside an
irrigation canal near Fallon, Nevada, United States.
Saltcedar is a large bush or small tree, up to 4 m tall,
with attractive pink l owers, often used as an
ornamental garden tree. Saltcedar has become an
invasive plant that grows in dense thickets along
streams, rivers and wetlands in the western United
States. Photo by J.S. Aber.
among the fastest-growing plants in the world,
which explain its phenomenal success in Africa
(Dugan 2005). Another such plant is mosquito
fern (
Azolla
sp.), a small aquatic fern that has
worldwide distribution (Fig. 6-11). The plant
usually reproduces asexually by fragmentation
of the fronds as frequently as every two days
(Watanabe 1982), and it may also reproduce sexu-
ally under special, poorly dei ned conditions.
harmful compounds, which are often abundant
in anaerobic environments, are drawn into the
plant (Dugan 2005). Oligotrophic wetlands, par-
ticularly raised and blanket bogs, are severely
lacking in nutrients for plant growth. Few plants,
notably
Sphagnum
(see Color Plate 5-12), can
tolerate this situation. Some wetland plants have
become carnivores in order to supplement their
diets (Figs. 6-9 and 10).
In the general scheme of life, those species
that reproduce the most effectively are also the
most successful. Some plants reproduce sexu-
ally, usually via pollination, and others repro-
duce vegetatively by sending out runners or
growing from plant fragments. Certain hydro-
phytes can do both. Papyrus (
Cyperus papyrus
),
for example, reproduces in both ways and is
6.2 Ecological categories
Wetland vegetation may be grouped into four
general ecological categories, depending mainly
on growth position in relation to water level
(Fig. 6-12; Whitley et al. 1999). Of course, water
levels and chemistry tend to vary in wetlands
on seasonal and interannual time periods
according to climatic conditions, human man-
agement, and ephemeral events. Whereas some
wetland plants may tolerate substantial varia-
tions in soil moisture and water level, others
have strict water requirements for survival.
Thus, the following groups and illustrative
