Evaluating the Effects and Effectiveness of Post-fire Seeding Treatments in Western Forests
High-severity wildfires can profoundly affect soils and plant communities, thus requiring emergency rehabilitation treatments such as post-fire seeding. Intended to stabilize soils, reduce erosion, and combat non-native species invasions, post-fire seeding is typically one of the first treatments used by most U.S. natural resource agencies. But despite its widespread use, there is still doubt about the treatment’s actual effectiveness and ecological impacts.
Therefore, researchers conducted a study to gain more definitive insight on the ecological effects and usefulness of post-fire seeding. The first part of the study involved an evidence-based review of scientific articles, theses, and government publications to address questions on soil erosion, non-native plant invasion, and native plant community recovery. Researchers then analyzed Forest Service Burned Area Reports to assess seeding trends related to species, costs, and area seeded.
- In studies that evaluated soil erosion in seeded versus unseeded controls, 78 percent revealed that seeding did not reduce erosion relative to unseeded controls. Even when seeding significantly increased vegetative cover, there was insufficient plant cover to stabilize soils within the first two years after fire.
- Sixty percent of the studies reported that seeding deterred native plant recovery in the short-term.
- Out of 11 papers that evaluated the ability of seeding to curtail non-native plant species invasions, 54 percent stated that seeding treatments were effective and 45 percent stated they were ineffective.
- Forty papers and 67 Burned Area Reports dated between 1970 and 2006 revealed an increased use of native species and annual cereal grains/hybrids during seeding treatments over time, with native species dominating seed mixes.
- From 2000 to 2007, total Burned Area Emergency Response (BAER) seeding expenditures have increased substantially, reaching an average of $3.3 million per year—a 192 percent increase compared to the average spent over the previous 30 years.
The need for seed
As the number, size, and severity of wildfires escalate across the western U.S., so does the need for post-fire rehabilitative efforts. In fact, U.S. land management agencies such as the Bureau of Land Management (BLM), forest Service, and National Park Service, are required by federal policy to conduct emergency post-fire rehabilitation measures to stabilize soils and prevent further degradation to the landscape. For this purpose, the most commonly used treatment is broadcast seeding.
Broadcast seeding, which includes aerial or ground-based seeding treatments, is applied to reduce soil erosion and increase vegetative cover, while minimizing the growth and spread of non-native plant species. Non-native perennials or short-lived annuals are often used for these treatments; however, the use of seed from native species is preferred, as there is concern that non-native species will hinder native plant recovery. In addition, contaminated seed mixes can introduce invasive species and stimulate competition with recovering native plant communities. While native species use has increased over time, it is not always possible, due to high costs and inadequate availability.
With the increase in post-fire seeding, it became necessary to examine and quantify the effectiveness and ecological effects of these treatments. To accomplish this objective, researchers conducted a study that included an evidence-based review of post-fire seeding literature and an assessment of Forest Service Burned Area Reports to examine seeding trends.
Assessing post-fire seeding success
Systematic reviews are commonly used in the medical sciences industry but are a relatively new approach for natural resource disciplines. The methodology used is rigorous and includes a predetermined protocol to ensure that the synthesis of available literature is unbiased, thorough, and evidence-based. For this study, researchers began their evidence-based review by conducting an extensive search of theses, scientific articles, agency monitoring reports, and government publications related to post-fire seeding. By targeting appropriate literature, researchers hoped to answer the following questions:
- Does seeding after severe forest fires reduce soil erosion?
- Is seeding effective at reducing non-native plant invasion in burned areas?
- Does post-fire seeding affect native plant community recovery?
Criterion were used to rate the quality of the evidence—from highest to lowest—based on design and statistical robustness. In addition, researchers evaluated post-wildfire seeding effectiveness based on the treatment’s effectiveness in reducing: (1) erosion and sedimentation; (2) non-native species invasion; and (3) effects on native plant community recovery. Each study or individual site within a study was given an effectiveness rating.
The second part of the study focused on the overall trends of post-fire seeding costs, area seeded, and use of native seed over time. Researchers reviewed unpublished documents, theses, scientific literature, government publications, and summaries of 1,164 Forest Service Burned Area Reports. Only specific quantitative information on evolving seeding trends was accepted, including area and amounts of seed used, seed sources and species selected, total seeding costs, and cost per hectare seeded.
Types of plant species seeded were characterized as non-native or native, typically based on the author’s classifications. Consequently, definitions of “native” differed between papers. To help determine nativity, researchers used the Natural Resource Conservation Service (NRCS) Plants Database. In addition, when available, information on the geographic origin of seed sources was extracted.
After the review: Results revealed
After applying specific inclusion criteria, 94 of approximately 19,455 studies were considered relevant for the evidence-based review portion of this study. Research results related to soil erosion, non-native plant invasions, and native plant community recovery are as follows:
- According to 78 percent of the studies that evaluated soil erosion in both seeded and unseeded areas, seeding did not reduce erosion relative to unseeded controls. Even when seeding significantly increased vegetative cover, there was not enough plant cover to stabilize soils within the first 2 years after fire.
- Out of 11 papers that evaluated the effectiveness of seeding to curtail non-native plant invasions, 54 percent indicated that seeding treatments were effective and 45 percent indicated that the treatments were ineffective. Of those treatments that were regarded as effective, however, 83 percent used non-native species (i.e., grasses and cereal grains).
- Sixty percent of the studies indicated that seeding suppressed native plant recovery. However, long-term impacts were not studied.
To determine trends in post-wildfire seeding, conducted in forested ecosystems. From these reports, data researchers selected 380 Forest Service Burned Area Reports, out of a total of 1,164, because they contained information on seeding treatments that had been specifically conducted in forested ecosystems. From these reports, data indicated an increase in the use of native species and annual cereal grains/hybrids, with native species dominating seed mixes over non-native species in recent years.
In addition, total Burned Area Emergency Response (BAER) seeding expenditures have increased exponentially, by 192 percent over the past decade (compared to the average spent during the previous 30 years), reaching an average of $3.3 million spent annually. In the 1970s, the percentage of total burned area that was seeded averaged 21 percent compared to only 4 percent between 2000 and 2007, however the cost per acre seeded has risen over time. This inflated cost is likely due to the increased use of more expensive native species.
“Our results are well in-line with previous reviews but the big difference versus the last major review, published in 2000, is that there has been a wealth of new, well-documented studies. These studies used statistically sound experimental designs to provide more rigorously tested information about post-fire seeding. Incorporating all the new data in our review, we found that earlier reviews describing the lack of efficacy of seeding were supported, but now with much more solid evidence,” stated Donna Peppin, Co-Principal Investigator.
According to the literature review and monitoring data, seeding is not a reliably effective post-fire treatment for short-term soil protection or native plant recovery. Therefore, it is critical for land managers to carefully consider the tradeoffs associated with these treatments. For example, seeding with non-native species, sterile hybrids, or cereal grains may provide quick vegetative cover, however, the species may persist longer than desired and therefore suppress native plant community recovery. In addition, non-local genotypes of native species are available and still used, but these types of species can compromise the diversity and composition of local gene pools. And, even though use of native seed has increased, costs remain high and supplies are limited.
When considering post-fire seeding treatments, researchers recommend:
- Weighing treatment costs/benefits and using alternative rehabilitation methods that have been proven to be more effective, such as various types of mulch that are free of non-native seed.
- Monitoring post-fire environments closely to detect the invasion of non-native species and using rapid response methods to contain, deny reproduction of, and eliminate these invasions.
- Using locally-adapted, genetically appropriate plant materials whenever and wherever possible.
To be continued…
The collaboration between researchers and land managers helped provide this study with a solid blend of scientific and on-the-ground experience. Yet, research on post-fire seeding treatments is far from over. Specifically, a greater understanding of long-term effects is needed. Peppin stated, “Our findings underscore the importance of further research in this arena. Of critical importance is the need for well-designed studies addressing long-term effects and effectiveness of seeding, in particular the use of native species and cereal grains or cereal/grass hybrids on burned landscapes.” Research on the genetic implications of using non-local genotypes of native species for post-fire seeding is also critical.
- Weigh the costs/benefits of seeding treatments and consider using alternative rehabilitation methods shown to be more effective, such as mulching (using mulch that is free of non-native seed).
- Encourage the development of locally-adapted, genetically-appropriate seed sources and limit use of non-local, or unknown, genotypes until seed transfer zones of species used during post-fire seeding are defined.
- Monitor post-fire environments closely and use rapid response methods to help detect, contain, and potentially eliminate invasions of non-native species.
“Our findings underscore the importance of further research in this arena.”
Publications and Web Resources
Peppin, D.L., P.Z. Fule, C.H. Sieg, J.L. Beyers, and M.E. Hunter. 2010. Post-wildfire seeding in forests of the western United States: An evidence-based review. Forest Ecology and Management 260:573-586.
Peppin, D.L.,P.Z. Fulé, C.H. Sieg, M.E. Hunter, J.L. Beyers, and P.R. Robichaud. Recent trends in post-wildfire seeding: Analysis of costs and use of native seed. International Journal of Wildland Fire. In press.
USDA Natural Resource Conservation Service Plants Database: http://plants.usda.gov/