BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Panicum virgatum | Switchgrass 



GENERAL BOTANICAL CHARACTERISTICS : 
Switchgrass is a native, erect, coarse, warm-season perennial grass.
Foliage height of mature plants is mostly between 3 and 5 feet (0.9-1.5
m),; the inflorescence, a 6- to 18-inch-long (15-46 cm) open panicle,
often extends to a height of 5 to 7 feet (1.5-2.1 m) [76,77].
Switchgrass has both sodand bunch-forming ecotypes.  Bunch-forming
ecotypes are generally encountered on uplands, while sod-forming
ecotypes occur on lowlands [61,75].  Rhizomes of sod-forming switchgrass
on a floodplain in Iowa were 0.12 to 0.27 inch (3-7 mm) thick, 1 to 2
feet (0.3-0.6 m) long, and mostly 2 to 5 inches (5-12 cm) below the soil
surface [77].  In the Southeast, bunch-forming ecotypes have only short,
vertically oriented rhizomes averaging 0.5 inch (1.4 cm) in length,
while sod-forming ecotypes have both short, vertically-oriented rhizomes
and long horizontally-oriented rhizomes (2 to 4 times longer than
vertical rhizomes) [7].  Switchgrass growing on Valentine fine sand in
the Nebraska Sandhills is similar to sod-forming ecotypes of the
Southeast in that plants develop from both vertically and horizontally
oriented rhizomes [10].  Switchgrass roots may reach depths of 10 feet
(3 m) or more [75].


RAUNKIAER LIFE FORM : 
   Cryptophyte


REGENERATION PROCESSES : 
Switchgrass reproduces both sexually and vegetatively.  Rhizomes are
responsible for vegetative expansion, but spreading ability depends upon
growth form.  Some rhizomes of sod-forming ecotypes may extend to
lengths of 1 to 2 feet (0.3-0.6 m), while those of bunch-forming
ecotypes may extend only a few inches [7,77].  The primary site of
nonstructural carbohydrate storage is in the stem bases, roots, and
rhizomes [72].

Switchgrass generally produces abundant seed.  Natural stands often
yield 100 pounds of seeds per acre (112 kg/ha), and cultivated stands
may yield 300 to 500 pounds of seeds per acre (336-561 kg/ha) [78].  The
seeds are shed in fall or winter and require winter dormancy before they
germinate in the spring [61].  Germination begins when soil temperatures
reach 68 degrees Fahrenheit (20 deg C) [72].  Seed collected from
southeastern Montana and northeastern Wyoming had relatively high
germination rates; 70 to 90 percent at temperatures between 68 and 86
degrees Fahrenheit (20-30 deg C) [22].  Fulbright and others [26]
reported germinative capacity of 40 to 70 percent.

The importance of switchgrass seedling recruitment into prairie habitats
is scarcely discussed in scientific literature.  In tallgrass prairie,
switchgrass tillering and rhizome production generally begins 5 to 7
weeks after germination, unless competition is severe [77].  Three
months after germination, plants may be 12 to 20 inches (30-50 cm) tall,
and roots may be 12 to 30 inches (30-76 cm) deep [77].  

On sand dunes bordering Lake Erie, switchgrass maintains and expands
stands primarily through seedling establishment.  On the dunes,
seedlings emerged from seeds buried at depths of 0 to 4.3 inches (0-11
cm) and withstood considerable postemergence sand burial [79].


SITE CHARACTERISTICS : 
Switchgrass is a mesic grass that grows on a wide variety of soil
textures if soil moisture is adequate [74].  Studying its distribution
along a water gradient in Kansas, Knapp [40] found that switchgrass
favored mesic sites, and concomitant physiological studies showed it was
less able to adjust osmotically to drought than big or little bluestem.
In the tallgrass prairie region, switchgrass is generally most abundant
on low-lying areas that receive some upslope moisture [77].  It is
seldom found on dry uplands of the West [67] but does grow on
upper-elevation sand dunes in the Nebraska Sandhills.  Deep-rooted
switchgrass grows well on the sand dunes because even small amounts of
precipitation penetrate the coarse sand and thus subsurface moisture is
available throughout the growing season [6].

Besides mesic prairies, switchgrass also commonly grows in fresh and
brackish marshes, on dunes and along lakeshores, and in oak and pine
savannas.  Switchgrass is tolerant of spring flooding but not of high
water tables [74].  It is tolerant of moderate soil salinity and
acidity.  It grows in soils ranging in pH from about 4.5 to 7.6 [72,74].


SUCCESSIONAL STATUS : 
Obligate Climax Species

Switchgrass is a climax species of tallgrass prairie.  It is slow to
establish on abandoned agricultural lands because of limited seed
dispersal distances and relatively high soil fertility requirements
[61].


SEASONAL DEVELOPMENT : 
The stimulus for switchgrass to resume growth in the spring is warming
soil temperatures [52].  Thus the beginning of spring growth for a given
location may vary by a week or two from year to year.  In the Great
Plains, new shoots emerge in mid- to late spring about 1 week later than
associated warm-season grasses little bluestem, big bluestem,
indiangrass, and sideoats grama (Bouteloua curtipendula) [2,52,59].
Initiation of spring vegetative growth by location is as follows:

  Georgia - March [7]
  central Oklahoma - early to mid-April [2,59]
  eastern Nebraska - mid to late April [52]
  west-central Kansas - late April [3]

Vegetative growth is rapid after the initial spring flush.  In the
Missouri River Valley of eastern Nebraska and western Iowa, switchgrass
regrowth resumes in April, and by early June the foliage often exceeds
18 inches (46 cm) in height [76].  The peak of flowering generally
occurs in July in Colorado, Wyoming, Montana, North Dakota, South
Dakota, Minnesota, and Nebraska [50,52].  In Kansas, Missouri, and
Oklahoma flowering primarily occurs in August [52,59].  Risser and
others [61] stated that in the True Prairie, switchgrass seeds are shed
in late fall or winter.  However, a phenological study in southeastern
North Dakota found that most switchgrass seeds were shed by mid-August,
only 1 month after flowering occurred [50].

Related categories for Species: Panicum virgatum | Switchgrass