• IMMEDIATE FIRE EFFECT ON PLANT
• DISCUSSION AND QUALIFICATION OF FIRE EFFECT
• PLANT RESPONSE TO FIRE
• DISCUSSION AND QUALIFICATION OF PLANT RESPONSE
• FIRE MANAGEMENT CONSIDERATIONS

IMMEDIATE FIRE EFFECT ON PLANT:

Black grama is generally top-killed by fire [21]. Fire typically causes little if any mortality in desert grasses [116]. Within the southwestern United States, fire usually consumes black grama to within 0.2 to 0.8 inch (3-19 mm) of the root crown. Culm bases and stolons located near the soil surface are susceptible to damage by fire [73,100]. Fire effects, however, are largely determined by relative levels of humidity and precipitation. Periods of hot, dry weather increase black grama's susceptibility to serious damage [64,72,73]. Hot fires due to relatively large amounts of fine-stemmed, dry herbaceous fuels may result in high mortality for black grama [21].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

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PLANT RESPONSE TO FIRE:

Black grama postfire response is variable. Both positive and negative effects are observed. Black grama recovery is best when above-average summer precipitation occurs after fire. Recovery is very slow when plants are subject to drought and grazing after fire, or if plant vigor was low prior to fire [84]. In the long term, stoloniferous expansion may be enhanced by fire under some conditions [1].

Studies monitoring postfire recovery potential of black grama in the Southwest suggest a recovery period from 2 to 8 years [47,64]. Postfire drought can lengthen recovery time considerably [123]; in some extremes, estimated recovery time is 50 years [120]. Allen [3] reported that black grama populations in the malpais area of the Arizona Sonoran Desert recover from fire faster than lower-elevation populations that receive less precipitation.

In some situations, little or no recovery is observed in the short term [52,74]. A study in the Chihuahuan Desert of southern Arizona found that black grama had not recovered prefire density 4 years after a June 1950 prescribed fire [100]. Further north near Tucson, under cooler and wetter conditions, black grama recovered prefire coverage 2 years after January and June prescribed burning [63].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

A positive postfire response was observed in mountain shrub habitats of the Chihuahuan Desert. The frequency of black grama was 2 times that of unburned controls 3 growing seasons after fires [1]. The opposite was seen in a Sonoran Desert shrub range in southern Arizona. Observations of black grama coverage after a June fire in the Sonora Desert are summarized below [100].

	Prefire cover (%)		Postfire cover (%)
Treatment	June 1950	October 1950	October 1951	October 1953	October 1954
Control	0.81	0.60	0.80	0.74	0.62
Burn	1.36	0.23	0.40	0.46	0.23
Percent of Control	167.9	38.3	50.0	62.2	37.1

On southern plains grasslands and plains grassland-desert grassland transition zones, blue grama may recover from fire more quickly than black grama. Because blue grama is more resistant to grazing, livestock grazing may retard black grama recovery even further. The October after late June prescribed burning or clipping treatments on a Chihuahuan Desert-southern plains grassland transition zone in New Mexico, growth of blue grama exceeded that of black grama on burned, clipped, and control plots. The contrast in plant height was greatest on burned plots. Mean plant height (cm) in the 1st posttreatment growing season was [44]:

In New Mexico black grama had less mean plant height on June-burned plots compared to unburned areas. Biomass was also significantly (p < 0.05) greater in unburned compared to burned plats [44].

Following April and May prescribed fires in the Sierrita Mountains of southern Arizona, black grama not occur on burned plots at postfire year 2; however, black grama density on adjacent unburned control plots was also low (mean=0.31 plant/m²⁾ [63].

FIRE MANAGEMENT CONSIDERATIONS:

Drought lengthens black grama recovery time after fire, and drought in combination with grazing may result in extremely high postfire mortality [8]. Recovery is best if grazing is deferred until plants receive at least 2 consecutive years of above-average summer rainfall [64]. Black grama response was poor, with density reduced by half, following a fall burn in Arizona. The fire was initiated following a summer of average rainfall and a 40-day rain-free period. Results were partly attributed to postburn grazing pressure [70]. According to Gosz and Gosz [44], infrequent fires in conjunction with light grazing may allow persistence of black grama within New Mexico desert grassland communities on sandy loam or loamy sand soils.

Related categories for SPECIES: Bouteloua eriopoda | Black Grama