Population and clonal level responses of a perennial grass following fire in the northern Chihuahuan Desert

Abstract

Relationships involving fire and perennial grasses are controversial in Chihuahuan Desert grasslands of southern New Mexico, USA. Research suggests that fire delays the resprouting of perennial grasses well after two growing seasons. However, such results are confounded by livestock grazing, soil erosion, and drought. Additionally, post-fire grass responses may depend on initial clone size. We evaluated the effects of fire, grazing, and clone size on Bouteloua eriopoda (black grama) in southern New Mexico grasslands. Four 2-ha plots were established in each of four sites. Fire and grazing were applied or not applied in 1999 such that four treatment combinations were assigned randomly to plots within each site. Within each plot, small (0-10 cm(2) basal area), medium (10-30 cm(2)), and large ( > 30 cm(2)) clones were initially mapped in five 0.91-m(2) quadrats where grass attributes and litter cover were evaluated before and at the end of two growing seasons following fire. Maximum fire temperature was also measured. At a population level, canopy and litter cover were each approximately 50% less in burned than unburned areas. However, compared to initial levels, canopy height had increased by 10% at the end of the study, regardless of fire. At a clonal level, basal cover reductions were attributed mostly to large clones that survived fire. Smaller clone densities had decreased by as much as 19% in burned compared to unburned areas, and fire reduced the basal cover of medium clones. Basal and canopy cover, recruitment, and clone basal area decreased with increased fire temperatures. Almost all responses were independent of grazing, and interactive effects of grazing and fire were not detected. Fire did not kill all perennial grass clones, regardless of size. However, rapid responses were likely influenced by above-average precipitation after fire. Future studies in desert grasslands should examine how perennial grass dynamics are affected by fire, precipitation patterns, and interactions with grazing.

Response of dominant grass and shrub species to water manipulation: an ecophysiological basis for shrub invasion in a Chihuahuan Desert Grassland

“…Reichmann, unpublished data). See Drewa et al (2006) for additional details on vegetation and soils at the site.…”

“…Plots were 2.5 £ 2.5 m, and each was centered around a single mature mesquite shrub that was similar in size to other mesquite on this ecological site (mean height 0.5 m, canopy diameter 1.1 m; Drewa 2003). Shrubs were surrounded by black grama (mean basal area 11.48 cm 2 ; Drewa et al 2006); black grama individuals selected for measurements were >0.75 m from plot edges. Reductions in PPT were achieved via passive rainout shelters; supplementation was achieved via a sprinkler irrigation system.…”

Ecophysiological responses of Chihuahuan desert grasses to fire

“…(Drewa and Havstad, 2001;Valone and Kelt, 1999) and other vegetation (McGlone and Huenneke, 2004). However, responses of B. eriopoda to fire evaluated at the clonal scale showed a reduction in basal area and cover, but overall survivorship was dependent upon clone size, large clones having increased survivorship in comparison to small clones (Drewa et al, 2006).…”

“…Drewa et al (2006) suggested that the patterns of precipitation immediately following fire may be a considerable factor in regrowth and recovery. Precipitation event size and frequency in post-fire conditions may substantially alter soil water recharge (Noy-Meir, 1973;Reynolds et al, 2004), ultimately affecting aboveground vegetation and post-fire recovery.…”

Effects of fire on belowground biomass in Chihuahuan desert grassland

“…In addition, Parmenter (2008) found that aboveground cover of B. eriopoda required 7-10 years to return to pre-fire abundance following a management burn. However, if large amounts of precipitation follow a burn, B. eriopoda canopy height can be equivalent in both burned and unburned areas after as little as one year of regrowth (Drewa et al 2006), but such conditions are rare. Just as favorable conditions can decrease recovery time, drought or grazing likely delay regeneration of B. eriopoda and other perennial grasses following disturbance (Reynolds and Bohning 1956, Cable 1967, Drewa et al 2006.…”