SPECIES: Nassella pulchra


Nassella pulchra: INTRODUCTORY

INTRODUCTORY

SPECIES: Nassella pulchra
photos courtesy of Hastings Natural History Reservation
AUTHORSHIP AND CITATION:
Steinberg, Peter D. 2002. Nassella pulchra. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

FEIS ABBREVIATION:
NASPUL

SYNONYMS:
Stipa pulchra A.S. Hitchc. [37,51]

NRCS PLANT CODE [66]:
NAPU4

COMMON NAMES:
purple needlegrass
purple stipa
purple tussockgrass

TAXONOMY:
The currently recognized scientific name of purple needlegrass is Nassella pulchra (A.S. Hitchc.) Barkworth (Poaceae) [5,36,41].

LIFE FORM:
Graminoid

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
No entry


DISTRIBUTION AND OCCURRENCE

SPECIES: Nassella pulchra
GENERAL DISTRIBUTION:
Purple needlegrass occurs on the west side of the Coast Ranges from northern Baja California north to the Oregon border. The species also occurs in the Central Valley and foothills of the Cascade Range and Sierra Nevada, and on the Channel Islands [36,51]. Cal Flora provides a distributional map of purple needlegrass.

ECOSYSTEMS [29]:
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES27 Redwood
FRES28 Western hardwoods
FRES34 Chaparral-mountain shrub
FRES42 Annual grasslands

STATES:
CA MEXICO

BLM PHYSIOGRAPHIC REGIONS [11]:
3 Southern Pacific Border
4 Sierra Mountains

KUCHLER [44] PLANT ASSOCIATIONS:
K006 Redwood forest
K009 Pine-cypress forest
K029 California mixed evergreen forest
K030 California oakwoods
K033 Chaparral
K035 Coastal sagebrush
K036 Mosaic of K030 and K035
K037 Mountain-mahogany-oak scrub
K047 Fescue-oatgrass
K048 California steppe

SAF COVER TYPES [25]:
229 Pacific Douglas-fir
232 Redwood
234 Douglas-fir-tanoak-Pacific madrone
244 Pacific ponderosa pine-Douglas-fir
245 Pacific ponderosa pine
246 California black oak
248 Knobcone pine
249 Canyon live oak
250 Blue oak-foothills pine
255 California coast live oak

SRM (RANGELAND) COVER TYPES [59]:
201 Blue oak woodland
202 Coast live oak woodland
204 North coastal shrub
205 Coastal sage shrub
206 Chamise chaparral
207 Scrub oak mixed chaparral
208 Ceanothus mixed chaparral
214 Coastal prairie
215 Valley grassland

HABITAT TYPES AND PLANT COMMUNITIES:
Purple needlegrass occurs in grasslands, oak and pine woodlands, mixed evergreen forests, chaparral, and coastal scrub. It is most prominent in the vegetation type known as the California prairie or valley grassland. This community is similar to the palouse prairie of Washington and Oregon in that Idaho fescue (Festuca idahoensis), prairie Junegrass (Koeleria macrantha), Sandberg bluegrass (Poa secunda) and bottlebrush squirreltail (Elymus elymoides) are present, but purple needlegrass is dominant in place of bluebunch wheatgrass (Pseudoroegneria spicata) [34]. Other important perennial associates in California prairie are California oatgrass (Danthonia californica), California fescue (Festuca californica), tussockgrass (Nassella lepida), beardless wildrye (Leymus triticoides), and melicgrass (Melica spp.). Mediterranean annuals such as wild oat (Avena fatua), slender oat (A. barbata), ripgut brome (Bromus diandrus), soft chess (B. hordeaceus), mouse barley (Hordeum murinem), and rattail fescue (Vulpia myuros) have replaced native perennial grasses in some areas (see Successional Status). Forbs present include fiddleneck (Amsinckia spp.), shooting star (Dodecatheon spp.), goldenpoppy (Escholzia spp.), lupine (Lupinus spp.), malacothrix (Malacothrix spp.), phacelia (Phacelia spp.), and sage (Salvia spp.) [46].

Purple needlegrass is dominant in northern coastal prairie, and present in coastal areas from San Francisco Bay north to the Oregon border. Associated grasses include Pacific reedgrass (Calamagrostis nutkaensis), Idaho fescue, red fescue (F. rubra), and California oatgrass; forbs present are rockcress (Arabis spp.), Mariposa lily (Calochortus spp.), hairy goldenaster (Heterotheca villosa), congested snakelily (Dicholstemma congestum), hairy gumweed (Grindelia hirsutula), Douglas iris (Iris douglasiana), lupine, and pineforest woodrush (Luzula subsessilis) [35,46,62]. Mediterranean annuals are also prominent in this prairie type, especially on nonserpentine soils [35]. 

Coastal prairie occurs in association with northern coastal scrub; here purple needlegrass cover is lower or more intermittent. This vegetation type is present from southern Oregon south to San Mateo County. Associated species include San Diego bush monkeyflower (Diplacus auranticus), Monterey Indian paintbrush (Castilleja latifolia), Pacific dewberry (Rubus vitifolius), open lupine (Lupinus varicolor), cow parsnip (Heracleum lanatum), seaside woollysunflower (Eriophyllum staechadifolium), salal (Gaultheria shallon), western pearlyeverlasting (Anaphalis margaritacea), coastal wormwood (Artemisia suksdorfi), and seaside fleabane (Erigeron glaucus) [51,60,67].

Coastal sage scrub occurs on slopes in the Coast Ranges; purple needlegrass, tussockgrass, and giant wildrye (Leymus condensatus) are present in areas of lower shrub density. Associated shrubs include California sagebrush (Artemisia californica), white sage (Salvia apiana), black sage (S. mellifera), purple sage (S. leucophylla), coyote bush (Baccharis pilularis), eastern Mojave buckwheat (Eriogonum fasciculatum), lemonade sumac (Rhus integrifolia), and California brittlebrush (Encelia californica) [4,19]. Purple needlegrass is slightly less common in chaparral. Chaparral shrubs include chamise (Adenostoma fasciculatum), toyon (Heteromeles arbutifolia), California coffeeberry (Rhamnus californica), Nuttall's scrub oak (Quercus dumosa), birchleaf mountain-mahogany (Cercocarpus betuloides), Our Lord's candle (Yucca whipplei), California flannelbush (Fremontodendron californicum), hollyleaf cherry (Prunus ilicifolia), ceanothus (Ceanothus spp.), manzanita (Arctostaphylos spp.), and chaparral pea (Pickeringia montana) [10,12,51].

Among wooded types, purple needlegrass is common in the understory of oak woodlands of blue oak (Q. douglasii), California black oak (Q. kelloggii), canyon live oak (Q. chrysolepis), coast live oak (Q. agrifolia), interior live oak (Q. wislizenii), and valley oak (Q. lobata) [17]. It is also present in some successional stages of woodlands and forests dominated by gray pine (Pinus sabiana), Coulter pine (P. coulteri), California bay (Umbellularia californica), California buckeye (Aesculus californica), or bishop pine (P. muricata), Monterey pine (P. radiata), Mexican pinyon (P. cembroides), Monterey cypress (Cupressus macrocarpa), and Gowen cypress (C. goveniana), tanoak (Lithocarpus densiflorus), Pacific madrone (Arbutus menziesii), coast Douglas-fir (Pseudotsuga menziesii var. menziesii), golden chinkapin (Chrysolepis chrysophylla), California bay, and canyon live oak [51].

Vegetation classification systems describing purple needlegrass-dominated communities include: [13,34,38,46,54].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Nassella pulchra
GENERAL BOTANICAL CHARACTERISTICS:
Purple needlegrass is a caespitose perennial native grass [23,36]. Culms are 24 to 39 inches (60-100 cm) tall, producing an open, nodding panicle 4 to 8 inches (10-20 cm) long [51]. Leaves are 0.031 to 0.14 inch (0.8-3.5 mm) wide [36]. The species expands vegetatively when tussocks are fragmented. Stands with fire and grazing exclusion are likely to be low density with larger individuals and more litter accumulation. With fragmenting disturbance, stands are higher density with smaller size tussocks and less litter accumulation, at least in the short term [21,45]. Bunches are roughly circular when undisturbed and more irregular with fragmenting disturbance [23,45]. Purple needlegrass is apparently long lived: 1 study found mortality of mature individuals was 2 to 6% annually over a 7-year period [20]. Purple needlegrass is arbuscular mycorrhizal and has a rooting depth of at least 25 inches (64 cm) on deep soils. 

RAUNKIAER [56] LIFE FORM:
Hemicryptophyte

REGENERATION PROCESSES:
Breeding system: Purple needlegrass is monoecious [51].

Pollination: Purple needlegrass is pollinated by wind.

Seed production: Purple needlegrass produces large quantities of viable seed. Under favorable conditions 2-year-old plants are able to produce seed. In dense healthy stands seed production may be up to 227 pounds per acre (200 kg/ha). Defoliation during periods of rapid growth or flowering may decrease seed production [6].

Seed dispersal: Purple needlegrass seeds have a twisting awn and pointed seed, which increases self-burial [6].

Seed banking: Seed banking of purple needlegrass is relatively low compared to that of associated nonnative annual grasses [1,66].

Germination: Reported germination rates are varied. Gulmon [31] reported germination rates from 80 to 93.7% on leached litter, fresh litter, and topsoil. Ahmed [1] found mean germination rates of 30 to 75% for seed collected in summer and germinated in petri dishes in October. Germination is reduced and slower in the presence of annual competitors [9,58]. This further reduces competitive ability in the presence of nonnative annuals [9]. Fire may increase germination and emergence in the 1st postfire growing season [1,22].

Seedling establishment/growth: Seedling success is influenced by climate, competition from annuals, grazing intensity and duration, and fire. One study found a 94% decrease in abundance between the 1- and 2-tillered seedling stages, and a 26% decrease between the 2- and 3-tillered seedling stages [45]. Another study found <1% survival of purple needlegrass following 20% germination of "precision planted" seed [20]. Dyer and others [22] found 0.01% 4-year survival, with various grazing and prescribed fire treatments improving survival only during the 1st year. The authors noted that survival to this age "appeared to be more strongly influenced by factors not manipulated or monitored in this study," such as climatic variation. Generally individuals greater than 0.8 inch (2 cm) in diameter are able to survive summer drought [2]. Early spring drought is more detrimental to nonnative annual grass seedlings than to purple needlegrass seedlings. Purple needlegrass seedling growth in shade is poor; in field plots experimental removal of nonnative annuals increased seedling density by 88% and increased biomass by 90% [32]. Annual seedlings' roots grow faster than those of purple needlegrass; 1 study found soft chess root elongation rates under controlled conditions were 50 to 100% greater than purple needlegrass [1]. Rapid growth of annual grass roots causes rapid water depletion in surface soil and interacts with shading to cause high purple needlegrass seedling mortality in spring [9].

Asexual regeneration: Purple needlegrass regenerates by tillering and fragmentation of bunches. Fragmentation is an important form of regeneration for purple needlegrass; it is an adaptation that allows recovery from defoliation by high-intensity, short-duration grazing and/or fire [6,21,45].

SITE CHARACTERISTICS:
Purple needlegrass habitats occur in areas with a Mediterranean climate of mild, moderately wet winters and warm to hot summers with drought. The growing season is 7 to 11 months long with 205 to 325 frost-free days. Mean annual precipitation ranges from 5.9 to 19.7 inches (150-500 mm), with peaks from October through March and from late April to early May [15].

Purple needlegrass occurs on a variety of soil types but is well adapted to those with high clay content. Robinson [58] reports purple needlegrass dominant on sites in Monterey County, California with high clay content, and a "sudden and dramatic" change in vegetation to nonnative annuals where clay content decreases. Stromberg and Griffin [63] also found clay content in soils supporting native perennial grasses (purple needlegrass and Sandberg bluegrass) higher than on sites supporting nonnative annual grasses. Purple needlegrass often grows in mound topography wherein a claypan exists approximately 7.9 inches (20 cm) below intermounds and 25.6 inches (65 cm) below mounds. Deeper soil on mounds often gives purple needlegrass an advantage over annual  grasses [20].

Purple needlegrass grows well where nonnative annuals are suppressed and, for this reason, is generally more dominant on serpentine-derived soils than on other soil types [14]. In northern coastal prairie, pure stands often occur on serpentine ridges [35]. A vegetation survey at Jasper Ridge Experimental Area on the San Francisco peninsula found purple needlegrass more dominant on serpentine than on sandstone areas; on sandstone soils it was best developed on drier sites with lower aboveground standing crop. Conversely, it had highest cover on wetter serpentine areas [48]. These patterns are generally consistent throughout the species' range [8].

Purple needlegrass occurs from sea level to 5,000 feet (1,500 m) [36,51].

SUCCESSIONAL STATUS:
Purple needlegrass is difficult to classify as a climax or seral species. Many researchers, following Kuchler [44], have described the species as a climax that was historically dominant with other perennial grasses throughout the valley and coastal grassland and was displaced by nonnative annual grasses with overgrazing in the mid-1800s [7]. More recently the former extent of purple needlegrass has been debated, primarily because of limited physical evidence of the composition of presettlement grasslands. Stromberg and others [62] state classification of purple needlegrass as a climax species is not supported by long-term studies or critical review of existing evidence. This group and others argue that large areas of the interior valley grassland may have been occupied by native annual forbs that were quickly replaced by nonnative annual forbs and grasses [15,62]. Holstein [39] has also criticized the climax classification of purple needlegrass, noting that in the valley and foothill grasslands there are "at least an order of magnitude" more prairie remnants dominated by rhizomatous beardless wildrye than by native bunchgrasses. He suggests that beardless wildrye was more dominant on heavier soils, while sandy areas were dominated by purple needlegrass. Keeley [43] has stated purple needlegrass was historically more abundant and widespread, but in southern California it was likely in isolated patches in dry areas similar to its current habit.

There are several possible origins of nonnative annual communities. Some current annual grasslands, both native and nonnative, were created sometime prior to about 1920 when prescribed fire was used to remove shrubs and improve forage production in chaparral or coastal scrub [42,43]. Additionally, some nonnative annual grasslands are likely the results of overgrazing of native annual grasslands [15]. While early vegetation will not be known, it is apparent that the assumption that all nonnative annual grasslands were dominated by perennial bunchgrasses has led to many failed restoration attempts [39].

Despite disagreement about the former extent of purple needlegrass, there is agreement that it is now suppressed by competition with nonnnative annuals. Invasion by nonnative grasses and forbs has been less complete on serpentine soils; these soils frequently support vigorous stands of purple needlegrass [14,26]. Dyer and Rice [23] observed competition effects by weeding nonnatives, planting purple needlegrass at different densities, and measuring growth and flowering for 3 years. Competition from nonnative annuals restricted growth and flowering of purple needlegrass more than intraspecific competition; intraspecific competition decreased productivity only in the absence of nonnative annuals. Both inter- and intraspecific competition affected flowering culm production more than vegetative production.

Purple needlegrass response to disturbance is unique. It is seldom present on formerly cultivated sites regardless of grazing history; these sites are commonly occupied by relatively stable communities of native and nonnative annuals [63]. Purple needlegrass and other native bunchgrasses are well adapted to light grazing and defoliation by fire but not to high-intensity continuous grazing, particularly under drought conditions [6]. Pocket gophers occur in high density (10 to 50 per acre (26-125/ha)) in some valley grasslands, sometimes disturbing up to 30% of the soil surface annually. This disturbance has important implications for nitrogen cycling and generally favors annual grasses over native perennials [63].

Where purple needlegrass occurs in mesic grasslands or in the understory of woodlands, chaparral and coastal scrub, shrubs may gradually exclude herbaceous vegetation in the absence of periodic disturbance (See the 'Fire Ecology' section of this species summary). In a wide-ranging survey of northern California, very few purple needlegrass individuals were found in areas with more than 50% cover of woody species [9].

SEASONAL DEVELOPMENT:
Summer drought and cold temperatures in winter induce dormancy. Vegetative growth of purple needlegrass is greatest from March through late May or early June, depending on onset of drought. Vegetative growth increases with precipitation in the fall, which occurs in September or October. Freezing temperatures in December generally stop growth [40,63]. Flowers begin to develop in early May, and seed is mature and dispersed by late July. The length of time from flowering to seed ripening in purple needlegrass is similar to that of nonnative annual grasses, but those species begin flowering approximately 1 month earlier [40].

FIRE ECOLOGY

SPECIES: Nassella pulchra
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: After fire, cover, density, and seedling establishment of purple needlegrass often increase as a result of increased soil temperature, light intensity, and nutrient release, and decreased standing litter [1,15,21,22,45]. Regeneration occurs from tillers at the soil surface, fragmentation of bunches, and/or by seedling establishment. Stands that experience severe fire have larger decreases in individuals' basal area and foliage height in the 1st postfire year but are more likely to increase by fragmentation. These patterns are more pronounced with short-duration grazing, particularly in early spring [21,45]. Annual grasses have larger seeds than purple needlegrass and are better adapted to establishing in litter layers. For this reason, fire can increase purple needlegrass seedling establishment, particularly in old stands where litter accumulation is highest [1,21,45]. Adult individuals are also benefited by reduction of competition from annual grasses. Even though fire during periods of rapid growth can be detrimental to purple needlegrass, it is generally more damaging to nonnative annuals [1,6]. Some studies, however, have found fire and/or grazing effects on cover, density, or seedling establishment of purple needlegrass were highly variable or insignificant, suggesting a large influence of climate on purple needlegrass' response to fire [22,33].

Fire regimes: There is little direct physical evidence of the historical extent of purple needlegrass, and less about historic fire frequencies in the communities where it occurs. Most agree, however, that purple needle grass' abundance was historically greater, and fire exclusion has been a factor in its decline [6,15,45]. In the coastal scrub, chaparral, and woodland fire frequency declined in the early 1900s with restrictions against burning; in grasslands fire frequency declined in the 1840s when heavy grazing and intermittent drought reduced fuels [15,30]. Before Spanish settlement, California prairie was used by tule elk, pronghorn, and mule deer, but grazing was intermittent enough to allow dominant grasses to regrow and support fire [15]. In many areas where purple needlegrass and nonnative annuals now coexist, purple needlegrass and native annuals were historically mixed. Here, the interaction of fire and grazing likely reduced competition from annual grasses, reduced woody species encroachment, and improved purple needlegrass regeneration [20,45].

One study of vegetation dynamics in coastal sage scrub, chaparral, and coast live oak woodland near Santa Barbara found that without fire or livestock grazing, coastal sage scrub was replaced by oak woodland at a rate of 0.3% annually. Grassland to coastal sage scrub transition occurred at a rate of 0.69% per year, and oak woodland reverted to grassland at a rate of 0.08% per year. On burned areas without livestock grazing or on unburned sites with livestock grazing, rates of transition of grassland to coastal scrub and coastal scrub to oak woodland were lower. On areas burned without grazing or grazed without burning the rate of oak woodland reversion to grassland was higher than on areas with neither burning nor grazing [16].

In chaparral and coastal scrub, early postfire vegetation is dominated by native and nonnative annuals. Herbaceous vegetation is greatest in areas where fire eliminates nonsprouting shrubs [42,49]. Purple needlegrass and other perennial grasses are more abundant after fire in coastal scrub than in chaparral. Fire repeated in less than approximately 3-year intervals often causes the herbaceous sere to persist [42]. Conversion of purple needlegrass grassland to coyote bush/ripgut brome communities has been observed with 24 years of fire exclusion [45].

Purple needlegrass is present in oak and pine woodlands and in the early seral stages of mixed evergreen forests, redwood and coast Douglas-fir forests. Generally, purple needlegrass and other herbaceous species are present in later successional oak woodlands only in intercanopy areas. Closed stands have up to 5 inches (12.7 cm) of oak litter that essentially eliminates grass growth [55]. Generally tree establishment is better after some shrubs have established in grasslands excluded from fire or grazing. In these cases, transition from grassland/coastal scrub mosaic to mixed evergreen forest can occur in 50 years. In other cases, however, fire exclusion does not result in type conversion but rather maintenance of a system wherein reversion and succession allow both vegetation types to persist [16].

Fire return intervals: Greenlee and Langenheim [30] described fire regimes in purple needlegrass associated communities in the Monterey Bay area between aboriginal time and present. Their results, presented below, show the large decline in fire frequency in coastal sage, chaparral, and forests, and savannas in the recent era (1929 was chosen to demarcate the recent fire regime because of restrictions that were put in place against burning in the Santa Cruz area). "Probable mean fire interval" refers to estimates of fire intervals that are derived from historical or very limited physical evidence. Estimates of presettlement fire return intervals in coastal terrace grasslands are similar to those reported below for prairie [62].

Fire regime Vegetation where burning concentrated Vegetation where burning incidental Recorded or calculated mean fire intervals (years) Probable mean fire intervals (years)
Lightning   Prairie   1-15
  Coastal sage   1-15
  Chaparral   10-30
  Oak woodland   10-30
Mixed evergreen     15-30
Redwood forest   135  
Aboriginal (until approximately 1792) Prairies   1-2  
Coastal sage   1-2  
  Chaparral 18-21  
Oak woodland   1-2  
  Mixed evergreen   50-75
  Redwood forest 17-82  
Spanish (1792 to 1848)   Prairies   1-15
  Coastal sage   1-15
Chaparral   19-21  
  Oak woodland   2-30
  Mixed evergreen   50-75
  Redwood forest 82  
European-American (1847 to 1929)   Prairies   20-30
  Coastal sage   20-30
  Chaparral 10-27  
  Oak woodland 50-75  
Mixed evergreen   7-29  
Redwood forest   20-50  
Recent (1929 to present)   Prairies   20-30
  Coastal sage 155  
  Chaparral 155  
  Oak woodland 225  
  Mixed evergreen 215  
  Redwood forest 130  

Fire regimes for plant communities and ecosystems in which purple needlegrass occurs are presented below. More information regarding fire regimes and fire ecology of these communities can be found in the 'Fire Ecology and Adaptations' section of the FEIS species summary for the plant community or ecosystem dominants below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
California chaparral Adenostoma and/or Arctostaphylos spp. < 35 to < 100 
coastal sagebrush Artemisia californica < 35 to < 100 
California steppe Festuca-Danthonia spp. < 35 [52,62]
pine-cypress forest Pinus-Cupressus spp. < 35 to 200 
Pacific ponderosa pine* Pinus ponderosa var. ponderosa 1-47 [3]
coastal Douglas-fir* Pseudotsuga menziesii var. menziesii 40-240 [3,50,57]
California mixed evergreen Pseudotsuga menziesii var. m.-Lithocarpus densiflorus-Arbutus menziesii < 35 
California oakwoods Quercus spp. < 35 [3]
coast live oak Quercus agrifolia 2-75 [30]
canyon live oak Quercus chrysolepis <35 to 200 
blue oak-foothills pine Quercus douglasii-Pinus sabiniana <35 [3]
California black oak Quercus kelloggii 5-30 [52
redwood Sequoia sempervirens 5-200 [3,27,64]
*fire return interval varies widely; trends in variation are noted in the species summary

POSTFIRE REGENERATION STRATEGY [61]:
Tussock graminoid
Ground residual colonizer (on-site, initial community)

FIRE EFFECTS

SPECIES: Nassella pulchra
IMMEDIATE FIRE EFFECT ON PLANT:
Factors that influence immediate severity of damage and subsequent recovery of purple needlegrass include fuel loading, landscape position, fire seasonality, grazing, and abundance of annual grasses. Older, decadent individuals, and/or those growing on mounds with litter accumulation, support more severe fire with more immediate damage [21]. Burned material senesces soon after fire but bunches often retain some green foliage in the center and at culm bases until fall rain allows new growth. Carbohydrate reserves decrease with burning, particularly with fire during periods of active growth [45].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
No entry

PLANT RESPONSE TO FIRE:
With rain after defoliation by fire, purple needlegrass grows new tillers from meristems at the ground surface [45]. Often, growth the fall after fire is limited because of carbohydrate loss, and increases in growth rates (relative to unburned sites) are not observed until spring [1,45]. Mowing treatments have produced similar, though less pronounced effects, suggesting an important effect of postfire nutrient release. One study comparing mowing and burning found that production of purple needlegrass tillers was increased 3- to 4-fold by burning and 2-fold by mowing [1].

Recovery rate depends on the type and extent of damage to purple needlegrass relative to the reduction in competition from annuals. Where fire is relatively severe, particularly in mound topography, individuals have an immediate reduction in basal area and are likely to fragment [6,45]. In such stands, increased density and decreased basal area are noticeable for about 3 years after fire [45]. One study found little effect of fire on density but a large increase in basal area on sites with high density of nonnative annuals. This was primarily because purple needlegrass competition with nonnative annuals had been severe before density of annuals was greatly reduced by fire, allowing expansion of purple needlegrass basal area via increased tillering [1]. Mean foliage height (or mean maximum foliage height) is often reduced for 1 year after fire even if total productivity increases. This results because burned and unburned plants initiate new growth from different heights: burned plants regrow from basal meristems and unburned plants regrow from buds on culm bases in the bunch interior. Growth is also shorter on burned areas if fire burns the center of bunches where the tallest growth originates [45].

Tussocks that are old and/or growing on mounds generally have higher litter accumulations and greater immediate damage from fire than young and/or intermound plants. Fire temperatures are hottest on mounds and may kill basal meristems in the centers of purple needlegrass bunches. This process creates 2 or more clones from 1 individual, which initiate tillers on their exteriors. Postfire grazing greatly increases fragmentation. Many researchers state that, prior to heavy continuous grazing by domestic livestock in the 1800s, intermittent grazing and periodic fire interacted as important means of purple needlegrass regeneration [1,6,21,45,68].

There is some debate about the effect of fire seasonality. Some have cautioned against prescribed burning in spring because this causes greatest carbohydrate loss and reduces purple needlegrass seed production by removing flowerstalks [6,45]. Fire in spring, however, also burns nonnative annuals in their period of rapid growth and may therefore be a net benefit to purple needlegrass. One study compared burning in June, August, and September and found each produced significant (p<0.05) increases in growth rates and basal area of purple needlegrass with no significant effect of fire seasonality [1].

Purple needlegrass density prior to fire influences postfire responses. Ahmed [1] observed effects of fire in June, August, and September on purple needlegrass when planted at low (40 individuals per 96.8 square foot (9 m2) plot), medium (70 plants per plot), and high (100 plants per plot) density.  Fall growth was reduced by all fire treatments; growth rates and basal area the following spring were higher than on control plots. On plots with low density of purple needlegrass, spring growth increased 109%; on high density plots growth increased only 38% (percentages are based on the aggregate data set from fires in June, August, and September). The author concluded on low-density sites, reduction of competition from nonnatives is more important than on high-density sites. These results could indicate that fire regrowth is greater without conspecific competition [1].

Several researchers have noted short term increases in purple needlegrass seedling establishment and seed viability following fire [1,22,45]. Dyer and others [22] tested prescribed burning and domestic sheep grazing effects on planted seedlings and natural seedling establishment. Fire slightly increased purple needlegrass emergence for 1 year, but only 0.01% of seedlings survived 4 years. No treatment had any significant effect on 4-year survival, indicating that in some cases, establishment and survival to maturity may be influenced more by annual climatic variation than by management practices.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
No entry

FIRE MANAGEMENT CONSIDERATIONS:
Prescribed fire has been used to reduce dominance of nonnative annuals and to limit encroachment of woody species [28]. Prescribed fire also is used to limit coast Douglas-fir invasion of oak woodlands, a process that reduces herbaceous diversity and abundance [14].

Most research regarding fire effects on purple needlegrass has pertained to its recovery in inland habitats. Few have studied its response to fire in coastal grasslands. Hatch and others [33] found that prescribed burning and grazing in purple needlegrass-dominated coastal prairie had no significant effect on foliar cover or frequency of purple needlegrass. The authors commented that fire and grazing differentially affected California oatgrass, tussockgrass, and purple needlegrass, making restoration efforts in coastal prairie difficult because treatments that improve 1 species' status may be detrimental to other native species. They concluded that, in contrast to inland habitats, fire and grazing manipulation are likely to be of limited value in restoring oatgrass/needlegrass (Nassella spp.) coastal prairie.

FIRE CASE STUDIES

SPECIES: Nassella pulchra
CASE NAME:
Responses of purple needlegrass to fire and short-duration grazing

REFERENCES:
Dyer, A. R.  1993. [21]
Langsroth, R. P.  1991. [45]

FIRE CASE STUDY AUTHORSHIP:
Steinberg, Peter. 2002.

SEASON/SEVERITY CLASSIFICATION:
Fall/moderate

STUDY LOCATION:
Eighteen 4,300-square-foot (400 m2) plots were established at Jepson Prairie Reserve in Solano County in the California Central Valley.

PREFIRE VEGETATIVE COMMUNITY:
Purple needlegrass (Nassella pulchra) was the most prominent native grass; others included saltgrass (Distichlis spicata), beardless wildrye (Leymus triticoides), Lemmon's canarygrass (Phalaris lemmonii), and meadow barley (Hordeum brachyantherum). Native forbs included common stickyseed (Blennosperma nanum), triphysaria  (Triphysaria eriantha ssp. eriantha), and clover (Trifolium spp.). Nonnative grasses were all annuals; species present were slender oat (Avena barbata), soft chess (B. hordeaceus), ripgut brome (B. diandrus), mouse barley (Hordeum murinum), and medusahead (Taeniatherum caput-medusae). Nonnative forbs present were filaree (Erodium spp.), dovefoot geranium (Geranium molle), and smooth catsear (Hypochoeris glabra).

TARGET SPECIES PHENOLOGICAL STATE:
Fire was prescribed in early September near the end of purple needlegrass drought dormancy.

SITE DESCRIPTION:
The site was characterized by mound topography with intermound areas having poor drainage. Cover of native species was highest in intermound areas because nonnative grasses' growth is limited by poor aeration in spring. 

Purple needlegrass individuals were marked on mound and intermound sites and subjected to 6 treatments: prescribed fire or fire exclusion in combination with short-duration domestic sheep grazing in early season, summer, and or excluded. Early spring grazing consisted of 14 ewes per plot for 2 to 4 days in late March or early April. Summer grazed plots had 15 ewes per plot in late August. Grazing durations were determined by ocularly estimating when herbaceous biomass was reduced to 570 pounds per acre (500 kg/ha) for the spring grazing treatment and 1,360 pounds per acre (1,200 kg/ha) for the summer grazing treatment. Grazing treatments were applied in seasons preceding and following fire.

FIRE DESCRIPTION:
Plots were burned at mid-day on September 1, 1988. Air temperature ranged from 75 to 82 degrees Fahrenheit (24-28 C), and relative humidity ranged from 47 to 61%. Winds ranged from 6 to 16 miles per hour (10-25 km/h) with gusts of up to 25 miles per hour (40 km/h). Fuel loading was highest on ungrazed mounds and lowest on summer grazed intermound areas.

FIRE EFFECTS ON TARGET SPECIES:
Many burned plants senesced shortly after fire, but individuals retained some green leaf material in bunch interiors and bases for the rest of the summer. During the growing season burned plants grew from basal meristems at the soil surface. Plants that were grazed but not burned grew from bunch interiors and were therefore generally taller. Langsroth [45] observed changes in average and maximum foliage heights, live crown cover, fragmentation, basal area, seed production, seedling establishment, and community composition for 2 years. Dyer [21] commented on general trends in the purple needlegrass population several years thereafter.

Foliage height: Average and maximum foliage heights were reduced by fire for 2 seasons. Fire reduced December 1988 average foliage height 71% (p<0.001), and maximum foliage height was reduced 65% (p=0.013). Foliage height was most reduced by fire on mounds where the highest fuel loading was present during fire. Grazing had no effect on burned plant foliage heights. On unburned plots, summer and spring grazing both had reduced foliage heights compared to ungrazed and unburned plots, but spring and summer grazing were not significantly different from each other. By January 1990, foliage heights were similar across all treatments.

Live crown cover: Measured in December 1988, fire had no significant effect on live crown cover of early-spring grazed intermound plants, while fire did significantly (p=0.001) reduce live crown cover on summer grazed plots and ungrazed plots. Plants growing on mounds that were burned had reduced live crown cover, irrespective of grazing treatment. Importantly, by January 1990, the immediate postfire effect had reversed: burned plants had higher mean live crown cover (p=0.005) than unburned plants (except on summer grazed intermounds and mounds (p=0.053)).

Fragmentation: Because of high litter accumulations and fire temperatures, fragmentation was highest on mounds; grazing was important in causing fragmentation in the 1st postfire year. Ungrazed plots that were burned showed no fragmentation at all. Without fire, grazing did not increase fragmentation significantly. The highest rate of fragmentation was on spring grazed, burned plots, most likely because summer grazing lessened fire severity by removing fuel.

Basal area: Basal area of burned plants, measured in 1989, averaged 40% less than unburned plants. Basal area of ungrazed or summer-grazed plants on mounds was most strongly (p=0.042) reduced by fire. Mean basal area of intermound plants increased under all treatments.

Seed production: One year after fire, burned plots had 32% fewer mature reproductive tillers per plant (p=0.048). Early spring grazing also reduced mature reproductive tiller numbers, particularly on intermound plants. Grazing and burning had no significant (p>0.05) effects on average number of seeds per tiller. Fire reduced seed output but increased seed mass. Fire caused a 45% reduction in mean number of seeds per plant (p=0.01). Fire increased mean seed weight by 14% (p=0.002). Early spring grazed plants had lower seed weights than summer grazed plants; this pattern was most pronounced with grazing in combination with burning.

Seedling establishment: Seedling numbers (assessed in April following fire) were variable, particularly for 2-tillered seedlings. On intermound areas, ungrazed, unburned plots had higher seedling establishment (12.3 m2) compared to early spring grazed (3.7 m2) or early spring burned plots (3.1 m2). Intermound areas with other treatments had 5.8 to 8.1 seedlings per m2. Seedling establishment trends were reversed on mounds: early spring grazed, burned plots had 13.1 seedlings per m2 compared to 1.9 m2 on ungrazed, unburned plots.

Community composition: On summer grazed plots, fire reduced total native grass cover (p=0.048 for interaction of fire and grazing). With the exception of purple needlegrass, native grasses individually had no significant (p>0.05) trends in response to any treatments. For nonnative annual grasses fire reduced total cover only on spring grazed or ungrazed plots. Without fire, nonnative grasses' cover was most reduced by spring grazing. Fire significantly (p=0.004) increased native forb frequency, particularly on ungrazed plots where frequency increased 250%. Few native forbs had significant individual responses to treatments. On plots with early spring grazing or no grazing, fire increased exotic forb cover. In the absence of fire, early spring grazed plots had higher exotic forb cover (grazing and fire treatments were both significant, interaction term was not significant (p=0.09)) [45].

Long-term responses: Monitoring after 3 postfire years showed that many fire effects were short lived, perhaps reflecting the sudden change in management from exclusion of fire and grazing to introduction of both practices in the same year. Increased fragmentation and decreased basal area of purple needlegrass because of burning and grazing were no longer perceptible. After 3 years it was evident that while summer grazing reduced purple needlegrass more than spring grazing did, burned plots with summer grazing had more native forb species [21].

FIRE MANAGEMENT IMPLICATIONS:
This study highlights the value of prescribed fire and seasonal grazing for improving purple needlegrass seedling establishment and competitive ability. One notable result was the dramatic increase in purple needlegrass seedling establishment on burned mounds, most likely because of reduction of competition from annual grasses. In the absence of litter removal, nonnative grasses have a competitive advantage on mounds because they, unlike purple needlegrass, are able to germinate in litter and extend roots into soil. Seedling establishment and fragmentation of purple needlegrass compensated for short-term decreases in live crown cover, basal cover, and foliage height. Also notable were the decreases in cover of native grass and forbs, indicating that management to maximize purple needlegrass cover and minimize that of nonnative annuals may be detrimental to other native species.

MANAGEMENT CONSIDERATIONS

SPECIES: Nassella pulchra
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Purple needlegrass was an important source of food for herds of pronghorn, mule deer, and Tule elk that were present in much of the California prairie; some areas were intermittently occupied by herds of several hundred to 3,000 individuals. Purple needlegrass-dominated prairie was heavily used by livestock throughout the 1800s, with cattle numbers peaking in about 1862 and domestic sheep numbers in about 1876. Jackrabbits, Beechey ground squirrels, kangaroo rats, and pocket gophers are numerous throughout the valley grassland [34]. Purple needlegrass is an important source of forage for livestock in California. Valley and foothill grasslands and savannas comprise only 15% of California's land area but are now about 80% of the land used by livestock [7,15].

Palatability/nutritional value: Purple needlegrass has moderate protein value and is highly palatable to livestock and wildlife [66].

Cover value: No information

VALUE FOR REHABILITATION OF DISTURBED SITES:
Purple needlegrass is used in restoration projects and established by transplants, drilled seed, or broadcasted seed [65]. Purple needlegrass has been used for competitive reseeding after prescribed burning of grasslands invaded by yellow starthistle (Centaurea solstitialis) and nonnative annual grasses [47]. One project in the Santa Monica Mountains used seeded and transplanted purple needlegrass, tussockgrass, California brome (B. carinatus), and smallflower melicgrass (Melica imperfecta) for replacement of ripgut brome [53]. Irrigation has been used to reduce purple needlegrass seedling mortality in summer [2].

OTHER USES:
No information

OTHER MANAGEMENT CONSIDERATIONS:
Livestock grazing can increase purple needlegrass cover and reduce that of nonnative annuals [9,24]. One study noted a decrease in purple needlegrass cover from 65 to 10% with only several years of grazing exclusion. Large increases in cover have been reported for winter and spring grazing on sites studied in southern California. Grazing in spring may be more detrimental to mature individuals. However, because nonnative annuals are better adapted to development under their canopies than purple needlegrass, spring grazing generally increases purple needlegrass seedling establishment [6,45].

Davis and Sherman [18] studied the remaining population of Sonoma spineflower ( Chorizanthe valida), a plant listed by the state of California as endangered. The population is located in Marin County. The authors state that though grazing maintains purple needlegrass and reduces shrub invasion, it may be detrimental to Sonoma spineflower and other rare endemic forbs.

Nassella pulchra: References


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