BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Scolochloa festucacea | Whitetop 



GENERAL BOTANICAL CHARACTERISTICS : 
Whitetop is an emergent, perennial, rhizomatous cool-season grass which
grows 2.6 to 4.9 feet (0.8-1.5 m) tall.  The stout culms are hollow and
0.1 to 0.2 inches (3-5 mm) in diameter near the base.  The extensive
rhizomes are soft, thick, and succulent [13,23,36].  Some authors [5,17]
suggest whitetop is an introduced species to the United States because
of its scattered distribution.  However, abundant collection of whitetop
in North Dakota over a long period of time suggests that it is native
[13].


RAUNKIAER LIFE FORM : 
   Hemicryptophyte


REGENERATION PROCESSES : 
Whitetop regenerates and spreads primarily by shallow rhizomes.  In
North Dakota, a road grader removed the vegetation from a site dominated
by hardstem bulrush (Scirpus acutus).  The following growing season, the
cleared area was dominated by whitetop with 90 stems per square foot
(998 stems/sq m) while water was still 16 inches (40 cm) deep.  Whitetop
regenerated from rhizomes in the substrate [36].

Although whitetop generally produces abundant seeds, it does so only if
wetlands contain water early in the spring [18].  Seeds are dispersed by
water movement and accumulate in the seedbank [34,43].

Smith [38] tested the effects of stratification temperatures and times
on germination of wet and dry whitetop seeds.  Results were variable.
Galinato and van der Valk [11] reported that stratification does not
improve whitetop germination.

Seed burial, which occurs with inundation, is required for whitetop
emergence.  Anaerobic conditions stimulate fermentation which increases
the germination rate.  In summer, anaerobic conditions increase as water
levels decrease and potholes stagnate.  Seeds, which have been
stimulated by early season anaerobic conditions, germinate when light
reaches the substrate and the ground is no longer submerged [11,36].  A
seed burial depth of 0.4 inches (1 cm) maximizes emergence and seedling
length and weight [38].  Seedlings can reach the soil surface from a
maximum depth of 2 inches (5 cm) [11].  Smith [36] found no seedlings in
areas with heavy litter accumulation.

Few whitetop seedlings become established.  A seedling must have a
rhizome to survive the winter.  Seedlings produce a rhizome 30 to 60
days after emergence.  The window of time between germination and
dormancy is often too short to produce a rhizome [36].

Merendino and others [29,30] investigated whitetop establishment and
success on artificially created mudflats subject to reflooding 1 year
later at different depths.  Mudflats were created at four drawdown
dates:  May 15, June 15, July 15, and August 15.  Seedling density,
measured on August 30, was highest with the June 15 and July 15
drawdowns.  The soil may have been too cold for germination in May.  The
plots were reflooded the following May with four depths:  0, 6, 12, and
20 inches (0, 15, 30, and 50 cm).  By August 30, most 1-year-old
whitetop seedlings had died with 12 inches (30 cm) or more of continuous
flooding [29,30].

McKee and others [28] investigated root metabolic response of whitetop
to flooding.  Whitetop has insufficient air space development in the
roots to allow complete aerobic metabolism during prolonged flooding.
It is not as tolerant of flooding as hybrid cattail (Typha glauca),
hardstem bulrush, softstem bulrush (Scirpus validus), or common reed [28].


SITE CHARACTERISTICS : 
Whitetop grows in northern climates where the winters are cold.  It
occurs in seasonally flooded wetlands including wet depressed meadows,
prairie potholes, and lake and river margins [4,20,36].  Whitetop shoots
have been observed elongating in 32 degree Fahrenheit (0 deg C) water
[36].

Whitetop occurs in freshwater and saline wetlands, with optimal
occurrence in oligosaline water [20,26].  Whitetop germination is
substantially reduced by soil sodium chloride concentrations of 1,000
parts per million and higher [11,38].  Optimal seedling emergence
occurred in soil containing 250 parts per million sodium chloride.
Seedling emergence decreased steadily as magnesium chloride
concentrations increased from 0 to 6,000 parts per million [38].
Whitetop has been reported in water with specific conductivity as low as
0.1 and as high as 12.1 millisiemens per centimeter, with a mean of 3.4
[20,38].

Whitetop occurs in the shallow marsh zone which is inundated by snowmelt
water until June or July [36].  The soil surface does not dry out except
possibly at the end of the growing season [26].  The thick, corky
epidermis of the rhizomes prevents desiccation by drying or freezing
[36].  Established whitetop is generally tolerant of continuous flooding
for 1 to 2 years, with individual plants surviving as many as 5 to 6
years [31].

Whitetop grows on mineral soils high in clay with some organic matter
[15,36].  In the Peace-Athabasca Delta of Alberta, average particle
distribution of the mineral fraction of whitetop sites was 5 percent
sand, 49 percent silt, and 46 percent clay.  Organic content in the
upper 12 inches (30 cm) averaged 23 percent, and soil pH averaged 6 [4].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Whitetop colonizes exposed mud flats [14,20,43].  Once established, it
persists under a seasonally flooded regime.  Whitetop occupies a fairly
specific environment with respect to water level.  It is replaced by
cattail and bulrush when average water levels rise and by sedge (Carex
spp.) and American mannagrass when average water levels drop [4,32].
On nutrient-rich saline sites with stable water levels, whitetop and
slough sedge replace cattail as the pond bottom gradually builds up with
silt and organic matter [24].


SEASONAL DEVELOPMENT : 
Whitetop shoot emergence is initiated from mid-April to mid-May while
the ground is still inundated with water.  Deeply submerged plants break
the water surface at the same time as plants in shallow water.  Flowers
develop in May.  Seeds mature from mid-June to late July.  Germination
of 1-year-old or older seeds occurs from mid-July to late August when
the ground surface is no longer inundated.  Rhizomes are produced from
late August to mid-September.  Dormancy begins in late September and
early October [36].

Related categories for Species: Scolochloa festucacea | Whitetop