Season of prescribed fire determines grassland restoration outcomes after fire exclusion and overgrazing
Fire exclusion and mismanaged grazing are globally important drivers of environmental change in mesic C4 grasslands and savannas. Although interest is growing in prescribed fire for grassland restoration, we have little long-term experimental evidence of the influence of burn season on the recovery...
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Zusammenfassung: | Fire exclusion and mismanaged grazing are globally important drivers of
environmental change in mesic C4 grasslands and savannas. Although
interest is growing in prescribed fire for grassland restoration, we have
little long-term experimental evidence of the influence of burn season on
the recovery of herbaceous plant communities, encroachment by trees and
shrubs, and invasion by exotic grasses. We conducted a prescribed fire
experiment (seven burns between 2001 and 2019) in historically
fire-excluded and overgrazed grasslands of central Texas. Sites were
assigned to one of four experimental treatments: summer burns (warm
season, lightning season), fall burns (early cool season), winter burns
(late cool season), or unburned (fire exclusion). To assess restoration
outcomes of the experiment, in 2019, we identified old-growth grasslands
to serve as reference sites. Herbaceous-layer plant communities in all
experimental sites were compositionally and functionally distinct from
old-growth grasslands, with little recovery of perennial C4 grasses and
long-lived forbs. Unburned sites were characterized by several species of
tree, shrub, and vine; summer sites were characterized by certain C3
grasses and forbs; and fall and winter sites were intermediate in
composition to the unburned and summer sites. Despite compositional
differences, all treatments had comparable plot-level plant species
richness (range 89–95 species/1000 m2). At the local-scale, summer sites
(23 species/m2) and old-growth grasslands (20 species/m2) supported
greater richness than unburned sites (15 species/m2), but did not differ
significantly from fall or winter sites. Among fire treatments, summer and
winter burns most consistently produced the vegetation structure of
old-growth grasslands (e.g., mean woody canopy cover of 9%). But whereas
winter burns promoted the invasive grass Bothriochloa ischaemum by
maintaining areas with low canopy cover, summer burns simultaneously
limited woody encroachment and controlled B. ischaemum invasion. Our
results support a growing body of literature that shows that prescribed
fire alone, without the introduction of plant propagules, cannot
necessarily restore old-growth grassland community composition.
Nonetheless, this long-term experiment demonstrates that prescribed burns
implemented in the summer can benefit restoration by preventing woody
encroachment while also controlling an invasive grass. We suggest that
fire season deserves greater attention in g |
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DOI: | 10.5061/dryad.mcvdnck06 |