Evaluating prescribed burn methods for controlling invasive Bromus diandrus, ripgut bromegrass

Background/Question/Methods

Invasive annual grasses dominate many ecosystems across the country, and present a different management challenge from perennial grasses because they quickly mature and produce seeds in a single growing season.  In California alone, more than 9 million hectares (22.2 million acres) of grasslands, chaparral, sage-scrub, and oak-savannah have been converted into exotic annual grasses.  One among these is Ripgut bromegrass (Bromus diandrus), which is cold hardy and drought tolerant, and produces copious amounts of seeds relative to native species, in addition to leaving behind a permanent litter layer that suppresses the growth of other species.  Aboveground management strategies such as mowing, weeding and herbicides are impractical when considering the scale at which B. diandrus and other invasive annual grasses are dominant, and these strategies are furthermore only effective in the short-term, as they fail to address the elimination of the larger seedbank.  Prescribed burning may be applied over larger areas and may offer improved control over these methods, by consuming invasive seeds while they are still curing in grass inflorescences, and by heat-treating soil seedbanks.  I am investigating the efficacy with which different intensity and frequency prescribed burns can achieve the latter.  How do differences in fuel-load at the time of burning affect B. diandrus seedbanks, and is there a difference between a single burn and repeat burns in back-to-back years?

Results/Conclusions

Thus far it has been found that B. diandrus seedbanks are concentrated more heavily in the aboveground litter than soil, and the reverse is true for native species, though the former has at least an order of magnitude higher density.  For the first year of burning, higher fuel-load prescribed burns more effectively destroyed or sterilized B. diandrus seeds in the litter and soil seedbanks than low fuel-load burns.  Longer fire duration and higher below-ground temperatures were responsible for the success of the higher fuel-load prescribed burns.  These findings suggest that high intensity prescribed burning can effectively control invasive annual grass seedbanks, and thereby facilitate native species restoration efforts.

See more of: Invasion: Control and Management II
See more of: Contributed Oral Papers

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