• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

FIRE ECOLOGY OR ADAPTATIONS:

Fire adaptations: Black grama is reported to be fire sensitive [2,21]. It usually recovers from fire slowly, through vegetative spread. However, black grama grows quickly in response to summer moisture, and its postfire recovery can be good if the stand was healthy before fire and there is adequate precipitation in the 1st 2 growing seasons after fire [3,44,64].

Desert grassland fire regime: Knowledge of fire frequency and fire's ecological role in desert grasslands is uncertain. Grassland fires leave no direct evidence of historical frequency, such as tree scars [120]. Our general understanding comes from knowledge of plant community ecology, the physiology of individual plant species, and historical accounts. Scientific research has generated arguments to both support and contradict the idea that fire was a common disturbance in desert grasslands.

Several researchers suggest a fire frequency of 7 to 10 years for desert grasslands [17,120]. Fires in desert grasslands of the Chihuahuan Desert were probably less frequent than those in the Sonoran Desert [2]. Many researchers view fire as necessary to maintain desert grasslands, mainly due to the current level of invasion by woody species in the absence of fire. It is hypothesized that shrubs would not have achieved the current level of coverage in desert grasslands if stand-replacement fires had occurred at regular intervals [120]. Although fires may kill some grass plants and weaken others, establishment of shrub seedlings requires several years more than establishment of grasses [65]. Honey mesquite, a major invader of southwestern desert grasslands, shows low seedling establishment when subjected to frequent fire. Glendening and Paulsen [43] found that severe fires were required to kill established honey mesquite plants; honey mesquite seedlings were readily killed by low-severity fire [20]. Fires generally remove only a single year's growth from desert perennial grasses and do not burn deep into root crowns, enabling the grasses to resprout [69]. Most desert shrubs with perennating buds on the root crown cannot sprout until stems are at least 0.4 in (1 cm) in diameter. Most shrubs also require several growing seasons before fruiting can occur [43].

Other research suggests that competition for space and moisture is more important than frequent fire in controlling woody shrub invasion of desert ecosystems [18]. Glendening and Paulsen [43] observed that competition with annual grasses reduced germination and emergence of honey mesquite seedlings to the 1st true leaf. On healthy desert grassland sites, survival of mesquite seedlings through their 1st spring drought was rare [18]. Grama grasses have also been observed to outcompete snakeweed [65].

When cured and dried, desert grassland vegetation provides adequate fuel for ignition. Annual dry lightning storms mark the beginning of the southwestern rains, which take place late June or early July [120]. Once ignited, plant density is the limiting factor for fire spread. Annual productivity can vary from almost nothing to 1000 lbs/acre. If fuels are sparse, light winds may carry desert grassland fires [17,65]. Grazing may reduce fuels to the point where fire will no longer carry [65]. The Appleton-Whittell research sanctuary, a 7800-acre (3160 ha) semiarid grassland preserve in southeastern Arizona, experiences frequent wildfires associated with fuel accumulations resulting from domestic livestock exclusion [11].

Black grama can carry fire if cover is dense and conditions are windy. However, black grama's high reliance upon layering and stolons for expansion, along with its poor seed production, support arguments that historical fires were infrequent in areas dominated by black grama [18,34,120].

The invasion of shrub and subshrub species (for example, honey mesquite and burroweed) has increased the severity of fire in desert grasslands. Invasive plants such as burroweed provide extra fuel and increase fire temperatures, resulting in "hot spots" [3,22]. Cable [22] observed increased mortality of perennial grasses located adjacent to burroweed plants due to extra heat provided by the fine-stemmed, resinous burroweed crowns.

Invasive alien grasses have increased fire frequency on some desert grasslands sites. For example, some Sonoran Desert sites have been invaded by Lehmann's lovegrass (Eragrostis lehmanniana), buffel grass (Cenchrus cilaris), and/or foxtail chess (Bromus madritensis). These exotics generally increase with frequent fire, producing historically unprecedented fuel loads [2,3]. Exotic grasses are less common in the Chihuahuan than the Sonoran Desert [2].

The following table describes historic fire regimes for many communities where black grama occurs. For further information on fire regimes and fire ecology of communities and ecosystems where black grama occurs, see the "Fire Ecology and Adaptations" section of the FEIS species summary for the plant community and ecosystem dominant listed below.

Community or Ecosystem	Dominant Species	Fire Return Interval Range in Years
tobosa	Pleuraphis mutica	5-100
plains grasslands	Bouteloua spp.	< 35
blue grama-needle-and-thread grass-western wheatgrass	B. gracilis-Hesperostipa comata-Pascopyrum smithii	< 35
blue grama-buffalo grass	B. g.-Buchloe dactyloides	< 35
grama-galleta steppe	B. g.-Pleuraphis jamesii	< 35 to < 100
blue grama-tobosa prairie	B. g.-P. mutica	< 35 to < 100
creosotebush	Larrea tridentata	< 35 to < 100
pinyon-juniper	Pinus-Juniperus spp.	< 35
mesquite	Prosopis glandulosa	< 35 to < 100
mesquite-buffalo grass	P. g.-Buchloe dactyloides	< 35
Texas savanna	P. g. var. glandulosa	< 10 [17]

POSTFIRE REGENERATION STRATEGY [107]:

Tussock graminoid
Surface rhizome/chamaephytic root crown

Related categories for SPECIES: Bouteloua eriopoda | Black Grama