Commercial bunchgrass varieties used in post-wildfire rehabilitation differ from wildland populations

Photo Credit

Forest Service photo by Francis Kilkenny

Two bottlebrush squirreltail bunchgrasses growing in a post-wildfire seeding on the 2023 South Tom Fire in southern Idaho. These plants are from a commercial variety that was selected because the traits were well-matched to site conditions.

In the Intermountain West, and many regions around the world, native wildland populations rarely produce enough seed to meet the demands of most rehabilitation projects, making agricultural seed increase necessary. Commercial varieties of native plants are often marketed as being effective in places with conditions that are like those where they were originally sourced, and managers use this information in their seed purchasing and application decisions.

However, all commercial varieties go through a development process that takes several to many generations, where they are tested and selected based on performance within a narrow set of environmental conditions. This can lead to changes in the characteristics of commercial varieties during the plant material development process. 

Using seed transfer zones and common garden studies, Forest Service researchers have pioneered a unique and powerful method to characterize how similar the traits of six commercial varieties of bottlebrush squirreltail (Elymus elymoides), a native bunchgrass species commonly used in post-wildfire rehabilitation, are to wildland populations.

Bottlebrush squirreltail is one of the most used native bunchgrass species for post-wildfire rehabilitation of Intermountain West rangelands because of its high establishment rate, competitiveness with invasive grasses, and forage value. Collectively, federal, state, and local land management agencies spend as much as $2 million per year on commercial bottlebrush squirreltail varieties. The development of commercial varieties, and subsequent expansion in agricultural production, has significantly increased the availability of bottlebrush squirreltail seed over the last quarter century, leading to a drop in its inflation-adjusted price by nearly 70 percent. This price drop has led to greater cost-effectiveness and the ability to seed tens to hundreds of thousands of additional acres.

During the study, when bottlebrush squirreltail was grown side-by-side in three different environments, the traits, such as growth patterns, floral timing, and reproductive output of the commercial varieties differed significantly from what was expected. They were still within the broader range of variation found in wildland populations, which shows that while these commercial varieties are likely being used in the wrong places now, the methodology can be used to predict where they can be used most effectively in the future.

These results can provide managers with a better understanding of how these varieties will actually perform on the landscape. This unique approach can be applied by researchers and practitioners worldwide to determine whether commercial varieties differ from these expectations, and where they can be effectively planted if they do differ. This work allows for assessment of commercial varieties for trait differentiation, at any time and without the need for source material, by comparing these varieties to range-wide population variation.

While the empirical data comes from a large and logistically complex study, which requires significant resources to replicate, this study shows it is possible to gather usable data from much less resource-intensive studies. These statistical and modeling approaches can be widely usable and complimentary with other approaches.