Biology Reference
In-Depth Information
In summer, the yellow flowers of gum-
plant (
Grindelia hirsutula
,
formerly
G.
stricta
var
. angustifolia
) lend color to the
green carpet of many bay tidal marshes.
Its bushy shape, deep-green leaves, and
daisylike flowers make this plant impos-
sible to miss along the meandering
edges of channels. Gumplant gets its
name from the sticky white resin that ac-
cumulates within the flower heads and
often varnishes the entire plant.
(Kathleen M. Wong)
trying to equalize salt concentrations on either side of their root mem-
branes. Some plants exclude salts when they absorb surrounding saline or
brackish water, and some shed extra salt via special glands on their
leaves—often evident as crystalline speckles or crusts—or when leaves die
and drop. Because live, green leaves are a plant's source of energy and food
production, dropping them can result in reduced growth. The most spe-
cialized halophytes deal with excess salt in their tissues with the help of
creative chemistry. They remove salts from cell sap, store salts in membra-
nous cell sacs called vacuoles, and balance the concentration of dissolved
solutes in sap with organic salt substitutes.
Only a small number of plant species can tolerate the higher levels of
salinity that occur in salt marshes, which range from the salinity of seawa-
ter (about 3.4 percent salt) to even higher concentrations due to evapora-
tion. A much larger number of plant species in the estuary can tolerate
diluted seawater, or less than about 2 percent of total dissolved salts. This
is why only about 16 plant species are associated with bay salt marshes,
versus about 100 species in brackish areas.
Another major challenge for tidal marsh vegetation is the wide fluctua-
tion in salinity due to seasons, drought, and climate cycles that deliver
extra rain. From the deluge of winter rain to the peak of summer drought,
salinity levels around a plant can triple over the course of a calendar year.
Stronger variations in climate can transform a cattail stand into a salt grass
meadow within a few months. Many marshes fluctuate regularly between
nearly fresh to seawater-salty over time, with extremes driving some plants
to local extinction.
The plants of the bay and its wetlands segregate themselves within hab-
itat zones. These include subtidal and intertidal zones in the bay, and low,
middle, and high marsh zones onshore. The boundaries between marsh
zones are seldom clear-cut. Tidal range, salinity, and drainage patterns
vary throughout the estuary, affecting both zone positions and the distri-
butions of marsh plant species (see Figure 6). Invasive non-native species,
such as perennial pepperweed, grow across the middle and high marsh
