Post fire seeding

Wildfires consume live and died fuels, destabilize physical and ecological landscapes, and impact human social and economic systems. [Pyne, S.J. Fire in America. 1982. A Cultural History of Wildland and Rural Fire. Princeton University Press. 654 p. [ISBN 0-295-97592-X] ] Post fire seeding was initially used to stabilize soils. More recently it is being used to recover post wildfire plant species, manage invasive non-native plant populations and establish valued vegetation compositions.

oil Stabilization

Water Erosion

Post fire seeding evolved from a desire to stabilize hillslope soils in hilly terrain after a wildfire and prevent downstream flooding and debris/mud flows. The assumption being supplemental seeding immediately after a wildfire would provide vegetation cover lost in the wildfire. Some of the earliest seedings were in Southern California after wildfires burned through fire prone foothills and alluvial fans developed with homes. Although recent studies confirm that the probability of flooding and debris/mud flows significantly increase following a wildfire [Moody, J.A. and D.A. Martin. 2001. Post-fire, rainfall intensity-peak discharge relations for three mountainous watersheds in the western USA. Hydrological Processes, 15(15):2981-2993] and that rainfall intensity, burn severity and ground cover reduction accounts for most hillside erosion, [Pietraszek, J.H. 2006. Controls on post-fire erosion at the hillslope scale, Colorado, M.S. Thesis. Colorado State Univ. Ft. Collins Co. 124p.] post fire seeding is not the most effective treatment.

A review of 37 publications and 25 monitoring reports on soil stabilization seeding discovered that less than half showed any reduced sediment movement with seeding. [Beyers, J. L. 2004. Postfire seeding for erosion control: effectiveness and impacts on native plant communities. Conservation Biology 18(4):947-956.] Seeding was not found to be effective in increasing cover or reducing sediment yields on burned areas in the Colorado Front Range compared to controls, even for storms with return periods of less than one year. [Waggenbrenner, J.W. 2003. Effectiveness of burned area emergency rehabilitation treatments, Colorado Front Range. M.S. Thesis, Department of Earth Resources, Colorado State University, Fort Collins, CO.] A comparison of commonly used soil stabilization treatments found that wood and straw mulch reduced water erosion rates by 60 to 80%, contour-felled log erosion barriers 50 to 70%, hydromulch 19% and grass seeding had little effect the first year during low intensity rainfall events and all were relatively ineffective in high intensity rainfall events. [Robichaud, P.R. and W.J.Elliot. 2006. Protection from erosion following wildfire. Written for presentation at the 2006 ASABE Annual International Meeting. Sponsored by ASABE, Portland Convention Center, Portland, OR. 9 - 12 July 2006. ASABE Paper No. 068009. American Society of Agricultural and Biological Engineers.] Vegetation cover from supplemental seeding was not significantly different from natural vegetation recovery. [Robichaud, P.R., T.R. Lillybridge, and J.W. Wagenbrenner. 2006. Effects of post fire seeding and fertilizing on hillslope erosion in northern-central Washington, Catena 67(1):56-67.]

Wind Erosion

In arid communities post fire seeding is attempted to reduce wind erosion and deposition. There is little objective evidence that supplemental seeding is any better than natural vegetation recovery from the post fire seedbank. After the Railroad Fire in Utah, neither seeded (drilled or aerial) or unseeded areas showed significant signs of wind erosion or deposition as evidenced by little difference (<2mm) in the height of washers on erosion measurement stakes. [Thompson, T.W., B.A. Roundy, E.D. McArthur, B. D. Jessop, B. Waldron, and J.N. Davis. 2006. Fire Rehabilitation Using Native and Introduced Species: A Landscape Trial. Rangeland Ecol. Manage. 59:237-248.] . Soil wind erosion was observed to have been moderated to some degree after the Command 24 Fire in Washington by natural site recovery alone. [Evans, J.R., and M.P. Lih. 2005. Recovery and rehabilitation of vegetation on the Fitzner-Eberhardt Arid Lands Ecology Reserve, Hanford Reach National Monument, following the 24 Command Fire. The Nature Conservancy of Washington, 217 Pine St. Suite 1100, Seattle, Wa. 246p.] .

Ecological Stabilization

Seeding especially with native seed mixes is increasingly being proposed to recover post wildfire plant species, manage invasive non-native plant populations and establish valued vegetation compositions. Compared to seeding for soil stabilization, ecosystem recovery and restoration is far more complex and take several decades to fully evaluate. Some recent comparison studies provide early evidence on seeding’s contribution to overall post wildfire recovery. A study at Mesa Verde National Park compared seeded burned areas with unseeded burned areas and unburned areas and found that seeded burned areas had significantly less non-native plants than unseeded burned areas but significantly more than unburned areas except there was no significant difference in cheatgrass ("Bromus tectorum") between seeded or unseeded burned areas. [Floyd, M.L., D. Hanna, W.R.Romme, and T.E. Crews. 2006. Predicting and mitigating weed invasion to restore natural post-fire succession in Mesa Verde National Park, Colorado, USA. International Journal of Wildland Fire 15:247-259.] . In northwestern Nevada from 1984 – 1997 cheatgrass density was altered by changing the seeding rates of a variety of native and non-native perennial grass and forb seed mixes. Cheatgrass densities were reduced to 2.6 plants per sq. m with seeding rates of 22.5 – 25 PLS per sq ft. Cheatgrass densities of 4.07 and 3.58 plants per sq. m were obtained with seeding rates of 10 and 35 PLS per sq. ft., respectively. [ Eiswerth, M.E. and J.S. Shonkwiler. 2006. Examining post-wildfire reseeding on arid rangeland: a multivariate tobit modeling approach. Ecological Modeling 192:286-298.] On three burned areas in Colorado and New Mexico where native grass seeding was hand, drilled or aerially applied, there was a positive relationship between native species richness and non-native species cover and negative relationship between dominant native plant cover and non-native species cover. [ Hunter M.E., P.N. Omi, E.J. Martinson and G.W. Chong. 2006. Establishment of non-native plant species after wildfires: effects of fuel treatment, abiotic and biotic factors, and post-fire grass seeding treatments. International Journal of Wildland Fire 15:771-281.] In a Utah study, all native perennial seeded plots had lower cover of annual species than unseeded plots; however, by the third year following seeding there was little change in seeded native species density, but the density of annuals more than doubled with cheatgrass and three annual forbs making up the majority of plant density. [ Thompson, T.W., B.A. Roundy, E.D. McArthur, B. D. Jessop, B. Waldron, and J.N. Davis. 2006. Fire Rehabilitation Using Native and Introduced Species: A Landscape Trial. Rangeland Ecol. Manage. 59:237-248] .

It is possible that native plant seeding subsidies are not actually needed. Great Basin native big squirreltail ("Elymus multisetus") appears to has evolved competitive advantage traits in the presence of cheatgrass. [ Leger E.A. 2005. The adaptive value of remnant native plants in invaded communities: an example from the Great Basin. Ecological Applications 8(5):1226–1235 ]

Unintended Consequences

Some unintended consequences have been observed from post fire seeding. Seed mixes, even “certified weed free” seed mixes, have been contaminate with invasive species and initiated new infestations. [Hunter M.E., P.N. Omi, E.J. Martinson and G.W. Chong. 2006. Establishment of non-native plant species after wildfires: effects of fuel treatment, abiotic and biotic factors, and post-fire grass seeding treatments. International Journal of Wildland Fire 15:771-281.] Successful growth of seeded grasses (i.e., enough to affect water erosion) have displace native or naturalized species, including shrub and tree seedlings. [Beyers, J. L. 2004. Postfire seeding for erosion control: effectiveness and impacts on native plant communities. Conservation Biology 18(4):947-956.] [ Hunter M.E., P.N. Omi, E.J. Martinson and G.W. Chong. 2006. Establishment of non-native plant species after wildfires: effects of fuel treatment, abiotic and biotic factors, and post-fire grass seeding treatments. International Journal of Wildland Fire 15:771-281.] [ Keeley, J.E. 2004. Ecological impacts of wheat seeding after a Sierra Nevada wildfire. International Journal of Wildland Fire 13:73-78.] Seed bed preparation and the seeding process has facilitated the growth and expansion of naturalized non-native species. [Erickson, H.E. and R. White. 2007. Invasive plant species and the Joint Fire Science Program. USDA Forest Service Pacific Northwest Research Station. Gen, Tech. Rep. PNW-GTR-707. 18p.] The machinery used in landscape seeding operations (e.g., drill seeders and chains) impact surviving native plants and disturb microbial soil crusts. [Shaw, Nancy L.; Pellant, Mike; Monsen, Stephen B., comps. 2005. Sage-grouse habitat restoration symposium proceedings; 2001 June 4–7, Boise, ID. Proc. RMRS-P-38. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 130 p.]

Other Factors

Other land management activities can affect the effectiveness of post fire seeding. Grazing seeded burned areas exacerbates the problem of non-native annual grass invasions, even when conducted after a two year hiatus. [Eiswerth, M.E. and J.S. Shonkwiler. 2006. Examining post-wildfire reseeding on arid rangeland: a multivariate tobit modeling approach. Ecological Modeling 192:286-298.] Historic post logging seed treatments had a significant influence on the effectiveness of post Rodeo-Chediski fire seeding. [Kuenzi, A.M., P.Z. Fule and C.H. Sieg. 2007. Effects of fire severity and pre-fire stand treatment on plant community recovery after a large fire. Forest Ecology and Management 255:855-865.]

References