Restoration of C₄ grasses with seasonal fires in a C₃/C₄ grassland invaded by Prosopis glandulosa, a fire‐resistant shrub

Abstract

Questions: Can prescribed fire restore C 4 perennial grasses in grassland ecosystems that have become dominated by fire-resistant C 3 shrubs (Prosopis glandulosa) and C 3 grasses? Do fires in different seasons alter the direction of change in grass composition? Location: Texas, USA. Methods: We quantified short-and long-term (12 yr post-fire) herbaceous functional group cover and diversity responses to replicated seasonal fire treatments: (1) repeated-winter fires (three in 5 yr), (2) repeated-summer fires (two in 3 yr), and (3) alternate-season fires (two winter and one summer in 4 yr), compared with a no-fire control. Results: Summer fires were more intense than winter fires, but all fire treatments temporarily decreased Prosopis and C 3 annual grass cover. The alternateseason fire treatment caused a long-term increase in C 4 mid-grass cover and functional group diversity. The repeated-summer fire treatment increased C 4 short-grass cover but also caused a long-term increase in bare ground. The repeated winter fire treatment had no long-term effects on perennial grass cover. Mesquite post-fire regrowth had increasingly negative impacts on herbaceous cover in all fire treatments. Conclusions: Summer fire was necessary to shift herbaceous composition toward C 4 mid-grasses. However, the repeated-summer fire treatment may have been too extreme and caused post-fire herbaceous composition to ''over-shift'' toward less productive C 4 short-grasses rather than C 4 mid-grasses. This study provides some of the first long-term data showing a possible benefit of mixing seasonal fires (i.e., the alternate-season fire treatment) in a prescribed burning management plan to restore C 4 mid-grass cover and enhance overall herbaceous diversity.

Soil Moisture, Grass Production and Mesquite Resprout Architecture Following Mesquite Above-Ground Mortality

“…Because of this, historically, there has been a continual use of less expensive treatments such as chaining, prescribed fire or general "weed" herbicides that have the effect of "top-killing" mesquite. This provides temporary suppression, but stimulates multi-stemmed regrowth that, if allowed to grow for more than a few years, can be extremely competitive with grasses and visually obstructive for livestock herding [15]. Much of the reason why mesquite has become dominant in grasslands is because these suppression treatments have not been applied at adequate frequency [16].…”

Patch-burn grazing (PBG) as a livestock management alternative for fire-prone ecosystems of North America

“…[59][60][61] . Fire may also restore the C4 grass component in areas dominated by C3 annual grasses 62 . Fire has also been effectively restored in areas that are invaded by naturalized C3 grasses but additional information is currently lacking on if or how fire may reduce exotic C3 grasses 39 .…”

Invasion promotes invasion: Facilitation of C3 perennial grass dominance in mixed C3/C4 grassland by an invasive C3 woody sprouter (Prosopis glandulosa)

“…The Prosopis/Nassella association, or similar C 3 shrub/C 3 grass associations, may alter our view of state-and-transition dynamics in semi-arid savanna ecosystems (Briske, Fuhlendorf, & Smeins, 2003;Westoby, Walker, & Noy-Meir, 1989). Because P. glandulosa is a prolific resprouter, it is uncertain whether resumption of the presettlement mechanism of frequent suppression by fire could shift the Prosopis/Nassella association back to C 4 dominant grassland (Ansley, K E Y W O R D S coppice, drought, grassland restoration, rangeland, resprouting, shrubs, state-and-transition, woody plant encroachment Boutton, Mirik, Castellano, & Kramp, 2010). Moreover, few if any models have considered subcanopy/interspace microsite responses.…”