Revegetating After a Wildfire

By Michael Amaranthus and David Russell

Wildfires are a typical, even beneficial, event in the life cycle of many plant communities. However, decades of fire suppression and human encroachment into areas with large accumulations of fuel have resulted in dramatic increases in fire severity. The results have been soils burned so hot that soil erosion and plant recovery is of great concern.

Resource managers and erosion control specialists are then forced into frantic action to quickly establish protective ground cover, often with native grasses that stabilize soils and help alleviate the destructive power of high-intensity rainfall. This goal can be achieved more easily with an understanding of how plants have naturally restored damaged ecosystems. This article explores the use of mycorrhizal fungi, symbiotic partners with most plant species in the post-fire reestablishment of native plants.The Root of the Problem

Wildfires burned over half a million acres in Oregon and California in 2002.
Hidden from view beneath the soil surface are a multitude of beneficial soil organisms that are key to plant establishment but strangers to many resource professionals. Over the last decade we have learned much regarding the role of soil organisms in the recovery and establishment of post-wildfire vegetation. Mycorrhizal fungi are a vital group of beneficial soil organisms critical for plant survival and growth in many communities. Mycorrhizal fungi should be familiar to us; they form a symbiotic relationship with approximately 90% of all plant species in their native habitats. Even though mycorrhizae are as common to the roots of plants as chloroplasts are to the leaves, they are commonly left out of assessments for revegetation of severely disturbed lands. Fortunately, recent studies have examined the impact of wildfire on mycorrhizal colonization of post-fire plant communities (Amaranthus et al. 2004, Amaranthus and Trappe 1993, Vilarino and Arines 1991, Bellgard et al. 1994). Other studies have examined the successful use of mycorrhizal inoculum to encourage the reestablishment of post-fire native vegetation (Amaranthus et al. 2003; Bellgard et al. 1994; Rashid et al 1997; Pattinson et al. 2001a, 2001b). In 2002, more than 500,000 acres burned in wildfire in northern California and southern Oregon. We report recent data on natural revegetation and seeded native-grass-community establishment following two of these fires, Squires Peak and Antelope, on Bureau of Land Management (BLM) lands in southwest Oregon.Fire’s Effects on Soil and Flora

Figure 1. Mean mycorrhizal colonization of three species of pioneering vegetation in a severely burned area of the Squires Peak fire.The overall effects of fire on ecosystems are complex, ranging from the reduction or elimination of aboveground biomass to impacts on below-ground physical, chemical, and microbial mediated processes. Because a key component of overall ecosystem sustainability occurs below ground, recovery is tied to the soil’s physical, chemical, and biological functions and processes. Depending on several fire-severity measures, changes in below-ground components can be either beneficial or harmful to the entire ecosystem.

Figure 2. Mean foliar phosphorous levels of three species of pioneering vegetation in a burned area of the Squires Peak fire.For example, low-intensity burning can promote a herbaceous flora, increase various plant nutrients, and thin overcrowded forests, all of which can foster healthy soil microbial systems. Severe fire, however, can cause changes in successional rates, alter above- and below-ground species composition, produce rapid or decreased mineralization rates, alter carbon/nitrogen ratios, and cause subsequent nutrient losses through volatilization, accelerated erosion, leaching, or denitrification. Other effects include changes in soil hydrologic functioning, degradation of soil physical properties, decreases in micro- and macro fauna, and dramatic reductions in beneficial soil microbial populations. The Mycorrhizal Relationship

Mycorrhizal root tip with radiating mycorrhizal filaments.

Squires Peak fire area, where seeding mycorrhizal inoculation was implemented.Mycorrhizae are the symbiotic association between specific soil fungi and plant roots that exists for the vast majority of the world’s plant species in their native habitats. The mycorrhizal relationship is the “norm” in native habitats. Mycorrhizal populations, however, are often reduced or eliminated in severely burned soils following wildfire. Research has established that the growth of mycorrhiza-dependent plants are significantly affected by availability of mycorrhizal fungi (Steinfeld and Amaranthus 2003; Allen 1991; Amaranthus and Perry 1987, 1989; Trappe and Luoma 1992). Mycorrhizae and their interactions profoundly affect plant reestablishment through capture and uptake of nutrients, protection against pathogens, maintenance of soil structure, and buffering against moisture stress. Mycorrhizae are critically important following wildfire because the tiny filaments of the fungus radiate out from the plant roots to occupy large expanses of the soil volume, allowing plants to stabilize soil resources and establish. The filaments actually attach to and penetrate the outer cells of the plant root, effectively becoming extensions of the root itself by taking up water and plant nutrients. Both angiosperm and gymnosperm plant species that recolonize burned areas belong to families that dominantly form mycorrhizae (Trappe 1987). Two broad groups of mycorrhizal fungi are involved: ectomycorrhizal fungi (EMF) species and arbuscular mycorrhizal fungi (AMF) species, formerly known as “endomycorrhizal” fungi (Marx and Kuslowski 1976, Sanders et al. 1975). The approximately 200 described AMF species are the dominant mycorrhizal types worldwide, forming mycorrhizae with approximately 80% of all plant species. AMF propagules, which form new mycorrhizae, are spores, hyphal filaments, and colonized root fragments. AMF propagules are produced beneath the soils surface and disperse slowly after disturbance, primarily with movement of soil (Harley and Smith 1983). The approximately 5,000 species of EMF form mycorrhizae with only about 5% of the world’s species of vascular plants. These, however, include the following important forest, ornamental, and nut crops: most species of Pinaceae, Fagaceae, Betulaceae, Salicaceae, and Tiliaceae, as well as many members of the Rosaceae, Leguminosae, Ericaceae, and Juglandaceae. EMF associates include many fire-dependent species. Most EMF propagules are spores associated with specific mushrooms, puffballs, and truffles dispersed primarily by wind and animals (Trappe and Luoma 1992).Mycorrhizal Colonization and Nutrient Uptake: The Squires Peak Wildfire

Figure 3. Mean foliar calcium levels of three species of pioneering vegetation in a severely burned area of the Squires Peak fire.

Figure 4. Mean foliar nitrogen levels of three species of pioneering vegetation in a severely burned area of the Squires Peak fire.

Figure 5. Mean percent cover of seeded native grass species in a severely burned area after 20 months.

Large acreages of summer wildfire have become increasingly more common across the western United States in the last decade. Steep terrain and high winter precipitation lead to the potential for severe surface erosion following fire in many locations. In July 2002, the Squires Peak wildfire burned thousands of acres of conifer forests and oak woodland in the Siskiyou Mountains of southwestern Oregon, much of it on steep, erosion-prone slopes. This wildfire produced an opportunity to study grass seeding and mycorrhizal inoculation of a severely burned forest soil on steep slopes. In October 2002, we established 0.1-hectare plots to evaluate the success of seeded grasses and mycorrhizal inoculations following wildfire. The seeded grasses consisted of three natives-Lemons needle grass, melaca onion grass, blue wild rye-and sterile wheat. The mycorrhizal treatment consisted of Glomus mosseae, Glomus aggregatum, and Glomus intraradices at 44,000 propagules each per kilo on an expanded clay carrier. Each 0.1-hectare plot received one of four possible treatments in September 2002: mycorrhiza treatment at 20 kilos/hectare (designated MYCO)mycorrhiza treatment at 20 kilos/hectare and native grass seeding at 10 kilos/hectare (MYCO/SEED)native grass seeding only (SEED)no mycorrhiza inoculations and no native grass seeding (No MYCO/No SEED) In May 2003, we selected three plant species that occurred across all treatment plots to determine their mycorrhizal status and foliar nutrient levels.

Figure 6. Mean surface cover and mycorrhizal colonization of the native grass Elymus glaucus with and without a mycorrhizal seed inoculant in a disturbed area of the Antelope fire.

Results

Round arbuscular spores cling to developing root from germinating mycorrhizal-inoculated Elymus seed.

Comparison of Elymus glaucus cover with (left) and without (right) the additions of a mycorrhizal seed coat.AMF colonization was significantly higher for all three post-fire plant species in both MYCO and MYCO/SEED treated plots compared to SEED only plots and NO SEED/NO MYCO plots (Figure 1; p< 0.05). All three plant species, the forbs Claytonia parviflora and Clarkia rhomboidea, and the native grass Trisetum spicatum responded similarly to the treatments in terms of mycorrhizal colonization.Foliar nutrient levels for the three plant species were also determined by treatment. Foliar phosphorous levels were significantly higher for all three post-fire plant species in both MYCO and MYCO/SEED treated plots compared to SEED only plots and NO SEED/NO MYCO plots (Figure 2; p<0.05). Foliar calcium levels were significantly higher for all three post-fire plant species in both MYCO and MYCO/SEED treated plots compared to SEED only plots and NO SEED/NO MYCO plots (Figure 3; p<0.05). Foliar nitrogen concentrations were significantly higher for Claytonia in MYCO and MYCO/SEED plots compared to SEED only plots NO SEED/NO MYCO (Figure 4; p< 0.05). Foliar nitrogen concentrations increased significantly for Trisetum for MYCO/SEED treated plots compared to MYCO only, SEED only, and NO MYCO/NO SEED plots. There were no significant differences in foliar nutrient concentrations for sulfur, potassium, magnesium, sodium, iron, aluminium, boron, copper, zinc, and manganese for any of the plant species.In May 2004, we examined percent surface cover of seeded native grasses using transects and quadrant data. Not surprisingly, percent cover was significantly higher for SEED and MYCO/SEED plots compared to MYCO only plots and NO MYCO/NO SEED plots (Figure 5; p<0.05). MYCO/SEED treated plots had significantly higher grass cover compared to GRASS only plots. Restoring Native Grasses and Cover After the Antelope Wildfire

Often government agencies use grass-seeding activities to mitigate the erosion potential of severely burned lands but fail to monitor the effectiveness of post-fire seeding. The Antelope wildfire burned conifer forests and oak woodland in the Southern Cascade Mountains of southwestern Oregon. Soil erosion from the fire area was a concern because of the fire’s close proximity to the city of Ashland, OR, and to a steelhead and salmon spawning stream. The Antelope wildfire produced an opportunity to study native grass seeding and mycorrhizal seed inoculation in an area where rapid vegetative cover was a priority. In October 2002, we established three replicates of 7-square-meter plots for evaluating the success of the seeded native grass blue wild rye (Elymus glaucus) with and without the addition of mycorrhizal powder to the seed before outplanting. The plots were established on a highly disturbed firebreak area that had been mechanically cleared of vegetation. For three plots, 15 grams of a mycorrhiza seed treatment consisting of Glomus mosseae, Glomus, aggregatum, and Glomus intraradices at 65 propagules each per gram was hand-mixed with 225 grams Elymus glaucus seed. Paired plots were seeded with 225 grams Elymus glaucus without a mycorrhizal seed inoculant. In May 2003, we measured percent Elymus glaucus cover and excavated root systems to examine mycorrhizal colonization.Results

Elymus arbuscular mycorrhizal colonization was significantly higher for Elymus seed with mycorrhizal inoculant plots than plots with Elymus seed only (Figure 6). Elymus cover was also significantly higher for Elymus seed with mycorrhizal inoculant plots than plots with Elymus seed only. Overall, mycorrhizal colonization was six times higher and Elymus cover was two times higher on Elymus seed with mycorrhizal inoculant plots compared to plots with Elymus seed only.Conclusions Wildfires are a typical event in many plant communities, and we are beginning to understand the role of mycorrhizal fungi in the recovery of post-fire vegetation. Recent studies have examined the impact of wildfire on erosion control, mycorrhizal colonization, and establishment of post-fire plant communities. Our data from the 2002 Squires Peak and Antelope fires in southwest Oregon indicate severely burned and disturbed areas lose their ability to rapidly form the mycorrhizal relationship. Post-fire mycorrhizal inoculation can improve mycorrhizal colonization of pioneering vegetation and improve the cover and nutrition of seeded native grass species. Even though the role of mycorrhizal fungi in plant establishment is well documented, these “familiar strangers” are seldom considered as treatments in post-fire restoration activities. Resource managers must consider the effects of fire on mycorrhizal fungi with emphasis placed on the consequences these changes have for reestablishment of post-fire plant communities.

Michael Amaranthus, P.h.D., is an associate professor (adjunct) in the Department of Forest Science at Oregon State University and president of Mycorrhizal Applications Inc. David Russell is a forester with the Bureau of Land Management in Medford, OR.