• GENERAL BOTANICAL CHARACTERISTICS
• RAUNKIAER LIFE FORM
• REGENERATION PROCESSES
• SITE CHARACTERISTICS
• SUCCESSIONAL STATUS
• SEASONAL DEVELOPMENT

GENERAL BOTANICAL CHARACTERISTICS

Black grama is a solid-stemmed [27,96], long-lived [30], native perennial [45,61]. It has wiry, spreading stems that reach 8 to 24 inches (20-60 cm) in length [45,46]. The growth habit is generally caespitose but occasionally stoloniferous. It has smooth, narrow [91], flexuous and pointed, mostly basal leaves [108]. Leaf blades are 1 to 3 inches (2-7cm) long [91,108] and 0.08 to 0.02 inch (0.5-2 mm) wide [108]. Crown foliage is compact, producing dense ground shade [122]. The inflorescence is a panicle consisting of 3 to 8 spicate, unilateral branches [96,108].

Black grama possesses a well-developed, finely divided root system, with the greatest concentration of roots found within the uppermost 10 inches (25 cm) of soil [26]. In sand, roots may extend 4 feet (1.2 m) or more vertically [96]. At low soil moisture levels (1/4^th field capacity), the greatest concentration of roots is found near the soil surface. At intermediate levels of soil moisture (1/3^rd field capacity), roots are arranged evenly throughout the soil column. When moisture levels are high, greater concentrations of roots are found toward the bottom of the soil profile [35].

Once established black grama is tolerant of short droughts. Under prolonged periods of water stress black grama tufts dry out from the center breaking into smaller tufts. With good rainfall, broken tufts may coalesce [91]. The water-regulating physiology and root morphology of black grama place it in the 'intensive exploiter' classification. Intensive exploiters are plants that derive the majority of moisture through dense rooting networks situated within the shallower soil horizons. Periodic rainfalls are exploited with rapid root growth and water absorption. Intensive exploiters are good competitors for limited, shallow soil moisture and recover rapidly from stress or damage with readily available soil moisture [19].

RAUNKIAER [99] LIFE FORM:

Hemicryptophyte

REGENERATION PROCESSES:

Vegetative: Black grama primarily regenerates asexually through tillering, layering, and stoloniferous expansion, all of which are effective under arid conditions [59,64,85,91,108]. Parent plants provide support to new plants during establishment. Stoloniferous expansion [114] and tillering [29] increases black grama coverage slowly; therefore, black grama does not show quick colonization into adjacent areas. Black grama's reliance upon vegetative reproduction does not promote extensive migration [16]. Successful production of newly rooted stolon sets is directly related to the current and upcoming growing season. A year of favorable growth is required for stolon production, followed by another favorable year for rooting to take place [91]. Surface soil layers consisting of loose sand that is high in organic matter provide good conditions for stolons to successfully root [29]. Once established, plants may survive several decades through stoloniferous reproduction [13].

Layering is another form of regeneration used by black grama. Layering occurs when flowerstalks or vegetative stems bend to the ground and produce nodal roots. Small clusters of leaves form at axillary buds, nodes, or joints and take root under favorable environmental conditions, growing into new plants [85].

Seeding: Black grama does not seed well because the majority of spikelets produce sterile florets [70]. A 53-year study monitored black grama seed regeneration; black grama seedlings were produced in only 7 of the 53 years [89]. Germination of black grama under different summer growing conditions was monitored in New Mexico for 9 years (1917-1926). Results are summarized below [91].

Year	Summer growing conditions	Germination (%)
1917	poor (droughty)	27.5
1919	excellent	10.5
1920	excellent, poor seed maturity	2.0
1921	fairly good	---
1922	poor (droughty)	4.0
1923	fairly good	40.7
1924	poor	0
1925	fairly good	2.0
1926	intermittently good and poor	2.0

Although summer growing conditions were adequate in 1920, extremely poor germination was observed. The poor performance was attributed to precipitation distributed over the year, and low September moisture levels that allowed seedlings to dry out. Requirements for the production of viable seed remain misunderstood [91], although the effect of drought on seedling establishment is well recognized. Reseeding trials in New Mexico have found similar trends, noting difficulty in establishing black grama seedlings in arid rangelands due to frequent drought [13]. Black grama has shown good establishment in the northern Chihuahuan Desert when summer precipitation was favorable [6].

Black grama seed may not survive cattle grazing. In a seeding trial in the northern Chihuahuan Desert, alkali sacaton (Sporobolus airoides), blue panic grass (Panicum antidotale), and fourwing saltbush (Atriplex canescens) seed survived cattle grazing with little loss in germination, but black grama seeds were more completely digested and did not germinate [6].

SITE CHARACTERISTICS:

Black grama is a major grass within western desert grassland areas receiving 12 to 18 inches (300-457 mm) mean annual precipitation [67]. It occurs on rocky or sandy mesas and dry, open ground with well-drained sandy and gravelly soils [40,61,108]. Black grama is rarely found on clay loams or adobe flats [91]. The majority of precipitation (> 50%) within sites dominated by black grama occurs from July to September [21]. In desert grasslands of New Mexico, black grama sites usually receive low rainfall [91], occupying the 8- to 17-inch (200-430 mm) precipitation belt [34]. Low rainfall is often accompanied by high temperatures and extreme winds [91].

Several studies have evaluated black grama distribution in relation to edaphic factors. Black grama prefers sandy but firm soils [14,40]. Good stands are rarely found on shifting soils [40]. In California, black grama occupies sandy to rocky slopes [60]. In desert grasslands of New Mexico, greatest coverage is achieved on coarse soil of low clay and high sand content [119]. Black grama is common on sandy soils possessing a lower caliche profile of a few inches to depths of 6 to 7 feet (1.8-2.1 m) [9,28,58]. An association between percent organic matter and nitrogen was observed for black grama in the Chihuahuan Desert. Greatest coverage was achieved in areas with relatively higher organic matter and nitrogen [105]. In southern Arizona higher frequencies of black grama were found where nitrate was readily available in conjunction with trace amounts of organic matter [93].

On some sites, cover of black grama may be related to topographical aspect. In New Mexico, basal cover was highest on south- and west-facing slopes [39]. In a grassland valley in southeastern Arizona at the upper limits of black grama's elevational range, black grama showed a preference for low, south-facing slopes [12].

Elevational range of black grama is as follows:

Arizona - 3,000 to 5,000 feet (914-1524 m) [76]
California - 2,600 to 6,200 feet (800-1900 m) [60]
Colorado - 4,400 to 4,800 (1340-1460 m) [51]

SUCCESSIONAL STATUS:

Black grama occurs on both seral and late-successional communities [10,25,96]. It was a dominant component of early succession during a 3-year natural revegetation of mesquite sand dunes in southern New Mexico. The site received light grazing and adequate rainfall [25]. Black grama increased with grazing on arid southeastern Arizona rangelands that were dominated by tall grasses such as plains lovegrass (Eragrostis intermedia), beardgrass (Bothriochloa spp.), and sideoats grama (Bouteloua curtipendula) [10].

SEASONAL DEVELOPMENT:

Growth of black grama corresponds with season and amount of precipitation. Precipitation received between July and September is more important than total annual precipitation [96]. Stems remain green throughout the year [15,19,89], with carbohydrate reserves stored in the stem, root, and root crown [59]. Rapid development and growth occur under periods of relatively abundant moisture and high nighttime temperature. Growth is suspended during dry periods until the next saturating rain [27]. Flowering, fruiting, and seed dispersal occur during late summer and fall rains. Early seedling establishment may also occur after these rains [89]. A general description of black grama phenology in the Chihuahuan Desert is as follows [77]:

growth begins - late April to early May
flowering - late August to early September
fruiting - late September to early October

In arid ranges of southern New Mexico, the start of the growing season corresponds with the beginning of the summer rainy period (early July, sometimes May or June possibly mid-August). With adequate rainfall, growth continues until the end of September or October. If fall, spring, and winter precipitation is high and temperatures are not too low, leaves may start growth in March and April. With continued moisture, growth may extend into the main summer growing period. Flowering is generally initiated 5 to 7 weeks after summer growth starts, so time of flowering and fruiting varies with the beginning of the growing season. Flowering usually takes place in early August, with fruiting occurring in late September. Dissemination begins in October and extends into November. The possibility for 2 flowering stages exists if adequate moisture is available. High amounts of early spring rains may induce an early flowering, and a second flowering may occur if July rainfall is high [91].

Development of black grama in relation to precipitation during the growing season was monitored from 1925 to 1935 within the Jornada Experimental Range in New Mexico. Results are summarized below [28].

Year	Growth began	Growth ended	Period of Growth (days)	Total rainfall for growth period
1925	July 21	Oct 17	89	7.01 (inches)
1926	May 18	Nov 9	176	11.95
1927	July 25	Oct 1	69	5.58
1928	July 20	Oct 5	78	3.75
1929	July 22	Oct 14	85	3.91
1930	Aug 11	Nov 3	85	3.35
1931	July 1	Nov 4	127	5.79
1932	Aug 9	Nov 1	85	4.16
1933	July 20	Oct 17	120	6.52
1934	no growth	no growth	0	1.57
1935	Aug 13	Oct 15	64	5.14

 

Related categories for SPECIES: Bouteloua eriopoda | Black Grama