BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Achnatherum speciosum | Desert Needlegrass 



GENERAL BOTANICAL CHARACTERISTICS : 
Desert needlegrass is a native, cool-season, perennial bunchgrass with
stems 12 to 24 inches (30-60 cm) tall [10].  It grows in large dense
clumps that have persistent leaf bases [25,37].  The inflorescence is
compact and looks feathery due to the very hairy, bent awns [13,20].
Roots extend into the soil 3.3 to 3.9 feet (1-1.2 m) with most of the
roots located from 0 to 1 foot (0-0.3 m) deep [3].


RAUNKIAER LIFE FORM : 
   Hemicryptophyte


REGENERATION PROCESSES : 
Desert needlegrass reproduces asexually and sexually.  Vegetative
reproduction occurs with the annual growth of new tillers [7].  This
wind-pollinated grass may produce large amounts of seed [25].  From year
to year, desert needlegrass seed crops are variable in amount and
germibility in different populations [42].  Sexual reproduction is
closely tied to water availability.  Seed is not set if soil moisture is
low and temperatures are high [3].

Desert needlegrass has persistent seed and seedling banks [35].  Seeds
are self-planting.  Depending upon moisture conditions, the awn
alternately twists (dry) and untwists (wet), which drives the seed into
the ground [25].  Awns and calluses catch on animal fur, assisting in
seed dissemination [13].  The long awns may aid in wind dispersal.


SITE CHARACTERISTICS : 
Desert needlegrass typically occurs on coarse-textured soils with no
profile development, often on sandy or gravelly alluvial fans
[16,19,42,43].  It grows on dry rocky hills, talus slopes, and in
canyons [10,13,42].  Desert needlegrass is found at elevations from
4,025 to 5,249 feet (1,227-1,870 m) in California and Nevada
[5,19,25,31].  It is found from 3,000 to 7,000 feet (914-2,134 m) in
Arizona and up to 8,500 feet (2,590 m) in southwestern Colorado [10,13].

Desert needlegrass grows in warm to temperate mediterranean climates,
characterized by mild winters and warm to hot summers [4].  Young and
Evans [42] state that compared to other native needlegrasses, desert
needlegrass probably occurs in the most arid and harsh environments.

Associated species not mentioned in Distribution and Occurrence are
Joshua tree (Yucca brevifolia), white burrobrush (Hymenoclea salsola),
Indian ricegrass, bottlebrush squirreltail (Elymus elymoides), Thurber
needlegrass (Achnatherum thurberianum), and spiny phlox (Leptodactylon pungens)
[16,38,40].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Desert needlegrass is a stress-tolerant ruderal [35].  In disturbed
areas, such as abandoned town sites and roads, in Great Basin vegetation
(for example, spiney hopsage [Atriplex spinosa] communities), desert
needlegrass and Indian ricegrass seedlings were the first perennials to
appear [23].  In town sites abandoned for 30 to 73 years, desert
needlegrass and white burrobrush continued to dominate the vegetation
[35,36].

At the Nevada Test Site, vegetation in the crater from an aboveground
nuclear detonation was assessed after 14 and 24 years [24].  Desert
needlegrass and Indian ricegrass had gradually filled in after annual
plants.  After 24 years, desert needlegrass plants had advanced into the
crater 2,000 feet (610 m) and increased to 2.8 plants per square foot
(30 plants/sq m).


SEASONAL DEVELOPMENT : 
New leaves emerge from dormant desert needlegrass tufts in the spring.
Most vegetative growth occurs from late spring to early summer when
moisture conditions and temperatures are conducive to growth [3,38].
Florets are produced April to June [10,13].  Seed production and
dissemination occur May to June [25].  Tiller senescence begins in late
summer [3].

Related categories for Species: Achnatherum speciosum | Desert Needlegrass