BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Uniola paniculata | Sea Oats 



GENERAL BOTANICAL CHARACTERISTICS : 
Sea oats is a native, perennial, semitropical, rhizomatous C4 grass
[12,14].  Culms are stout and 3.3 to 6.6 feet (1-2 m) tall [2,4].
Leaves are both basal and cauline; leaf blades are up to 24 inches (60
cm) long.  The inflorescence is a narrow condensed panicle 8 to 20
inches (20-50 cm) long [21].  Spikelets are very flat, 10- to
20-flowered, and 0.6 to 1.2 inches (1.5-3.0 cm) long [2,14]; they
disarticulate below the glumes and fall entire.  The fruit is a
caryopsis [10].  Rhizomes are elongated and extensively creeping [2,14],
readily rooting at the nodes when buried by sand [4].  Sea oats develops
a dense concentration of surface roots as well as a penetrating system
of deep roots [12].


RAUNKIAER LIFE FORM : 
   Hemicryptophyte
   Geophyte


REGENERATION PROCESSES : 
Sea oats sprouts from rhizomes and from perennating buds at the bases of
culms [14]; growth and tillering is stimulated by sand burial [15], and
new shoots and roots arise from the nodes of both rhizomes and aerial
stems [5].  Sea oats also reproduces by seed [10].  

Sea oats is wind pollinated.  Florets open and close in the early
morning; they open only once.  Cross-pollination may be required for sea
oats to produce an appreciable number of seeds.  The very small sea oats
populations on the Louisiana coast west of the Mississippi Delta produce
average seed numbers of 0 to 9.53 per culm, depending on the population.
Seeds that are produced have high germination rates [11].

Sea oats shows a trend toward lower seed production with decreasing
latitude.  Seeds from Bogue Bank, North Carolina, produced an average of
2.24 seeds per spikelet, which was about 30 percent of pollinated
ovaries; the remaining ovaries aborted.  In southern Florida 0.6 seeds
per spikelet were found [11].

Sea oats spikelets are rapidly disseminated by wind, and are usually
soon buried where sand is accreting [6].  Wind, ocean currents, and
animals may disperse seeds to island and mainland beaches [3,15].  In
storms, seeds and plant parts can be carried great distances [20].

The cold treatment required to break seed dormancy decreases southward
along the range of sea oats, and is nonexistent for the south Atlantic
coast Florida populations.  Seeds from North Carolina gave optimal
germination when cold-layered moist for 30 days at 40 degrees Fahrenheit
(4.4 deg C) before being given an alternating thermoperiod (conditions
of no light and alternating temperatures of 65 degrees Fahrenheit [18.3
deg C] for 17 hours followed by 95 degrees Fahrenheit [35 deg C] for 7
hours).  No cold and/or moist treatment was required for seeds from
Louisiana; room temperature treatment gave highest germination, but
moist cold (40 degrees Fahrenheit [4.4 deg C]) pretreatment gave rates
almost as high.  Exposure of seeds to 30 days of dry cold at 40 degrees
Fahrenheit (4.4 deg C) adversely affected germination.  Louisiana seeds
collected October 1981 and tested in April 1982 had germination rates of
78.0 to 88.8 percent under the alternating thermoperiod described above
[11].

Seedlings establish during the first growing season and produce
extensive tillers by the second season [16].


SITE CHARACTERISTICS : 
Sea oats is found on upper beaches, dunes, and loose sands near
seashores in the southeastern United States [2,4,10,14,15,21,29] but it
is seldom found in the forb zone of lower beaches [26].  Sea oats is one
of the most important grasses on dunes and continuous dune ridges [15]
because it helps build and maintain the sites on which it grows.  Sea
oats is dominant on the ocean facing part of fore dunes, often dominant
at the top of the more stable second dune system, and much less
prominent in the depression between the two [1,15,16,23].  This reflects
the close zonal relationship of sea oats to the deposition of salt
spray.  On Bogue Bank, North Carolina, sea oats was dominant where salt
spray was greatest.  The highest salt concentration was on the windward
side of the fore dune; the crest of the rear dune had a somewhat lower
concentration, and the depression between the dune systems received much
less salt depostion [20].

Sea oats sites have in common exposure to wind, salt spray, storms,
drought [1], often deep and shifting sand, and occasional fires and salt
water inundation.  These unstable habitats suffer wind and water
erosion.  The soil has low water retaining ability and excellent
drainage.  Evaporation rates are high due to constant air movement, high
temperatures, and full sunlight [20].

Sea oats is found on the Upper Keys of Florida, where sands are of coral
origin, and on the Lower Keys which are limestone and have carbonate
sands.  The Atlantic seaboard beaches and dunes have siliceous sands.
Soils of the Gulf Coast islands are fine to medium sand, with almost no
organic content.  On Cat Island, Texas, the organic content of the soil
in the sea oats zone was measured at 0.07 percent [20].

Soils on the Coastal Plain are strongly leached, rich in aluminum and
iron oxides, and usually deficient in many nutrients.  However, salt
spray carries some essential micronutrients to beach and dune plants
[13,23].

Sea oats occurs on sands with the following reactions:  Bogue Bank,
North Carolina, pH 7.4 to 7.9; Jupiter, Florida, pH 7.5; Cat Island,
Texas, pH 6.9 [3,20].

Climate in the maritime communities of the southeastern United States is
one of mild winters with high humidity and long, hot, humid summers.
The July mean temperature is about 81 degrees Fahrenheit (27 deg C).  On
the Atlantic coast most rainfall occurs during summer and early fall.
Rainfall averages over 39 inches (1,000 mm) per year, and in some places
considerably more.  In Florida, Miami receives 60 inches (1,524 mm) of
precipitation annually; Key West receives 38 inches (965 mm); Tortugas
receives 33 inches (838 mm).  There is a steady decrease in rainfall
from Pensacola, Florida, west to Brownsville, Texas, where rainfall is
27 inches (680 mm) per year.  October and November are the driest months
on the northern and eastern Gulf coast.  March is the driest month at
Brownsville, Texas [19,20,23].

Soil temperature variation on sea oats sites is greatest in the surface
inch of soil.  In the early afternoon soil surface temperatures of 125
to 127 degrees Fahrenheit (52-53 deg C) are common in the early
afternoon when air temperature is 95 to 100 degrees Fahrenheit (35-38
deg C) [20].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Sea oats is a pioneer species [15].  It spreads locally through
vegetative reproduction; it colonizes new areas primarily through seed
dispersal [11], but sea oats plant parts can also be dispersed by ocean
currents.  Of 17 surveyed small islands near Key West, Florida, sea oats
had colonized 14 [15].

Sea oats is also a climax species because of its high tolerance for salt
spray.  Succession in the salt spray community is limited primarily by
the intensity of the spray, and does not show the usual climatically
controlled pattern [20].  Sea oats is dominant on ocean-facing primary
dunes even if the dunes are stable because it tolerates more salt spray
than other species.  If the shoreline is rising, however, the beach in
front of the primary dunes may accrete and new dunes form in front of
old ones.  Then distance from the ocean to the original dunes will
increase, the effect of salt spray will diminish [23], and sea oats may
be replaced by other vegetation [16].  Eventually, succession to a
climax forest of subtropical mixed hardwood may occur [23].

Rather than rising, most of the shoreline of the southeastern United
States is subsiding.  On the Gulf coast west of the Mississippi Delta to
Texas, the rate of coastal retreat is 3.3 to 164 feet (1-50 m) per year.
Sea oats can achieve vegetative lateral spread of 2 to 6 feet (0.6-1.8
m) per year, but this is generally not sufficient to keep pace with the
high rate of subsidence.  Sea oats is not dominant in this area and is
reduced to a few sparse, scattered populations [11].


SEASONAL DEVELOPMENT : 
Sea oats growing season is May 1 to September 4 on Currituck Bank, North
Carolina.  The germination period of sea oats seeds there is late May to
the middle of June [26].

Spikelets fall from the plant and disperse in late fall and early winter
[16].

Sea oats flowers and sets fruit (combined) at the following times:
                    
      Carolinas              June-November             [21] 
      Florida         
        central              spring-fall               [29]
        panhandle            October-November          [2]
      Texas                  April-November            [18,9]
      General range          June-September            [4]

Related categories for Species: Uniola paniculata | Sea Oats