Effects of post-fire seedings on plant cover and annual grass invasion in the Great Basin: A chronosequence approach

Background/Question/Methods

Federal land management agencies, particularly the Bureau of Land Management (BLM), have invested heavily in post-fire seedings in Great Basin sage steppe ecosystems of the western U.S. These seedings are typically implemented to reduce both soil erosion and post-fire dominance of non-native annual grasses while also mitigating the probability of recurrent fire. Although post-fire seedings are currently monitored for three years, few scientific studies or monitoring strategies have examined long-term effects of these seedings on plant community characteristics and fuel structure. We recently initiated a chronosequence study (Joint Fire Science study 09-S-02) of post-fire seeding projects scattered amongst seven ecoregions within the Great Basin. In 2011, we evaluated 100 post-fire seedings on BLM lands sown between 1990 and 2004. We investigated effects of post-fire aerial and drill seedings on plant community composition and structure relative to adjacent burned-unseeded areas as well as unburned locations. We hypothesized that these post-fire seedings would have greater perennial and lower annual grass cover, less gaps between perennial plants, and greater density of desirable shrubs (primarily Artemisia species) relative to burned and unseeded locations on similar soil types.

Results/Conclusions

Preliminary results indicate mean cover of deep-rooted perennial grasses at drill seedings (14.3%) was increased compared to burned-unseeded (6.2%) or unburned (5.6%) treatments (p < 0.01). Mean cover of Bromus species was greater in burned-unseeded areas (56.5%) relative to drill-seeded locations (48.7%) but not significantly different (p > 0.05). Mean percentage of canopy gaps between perennial plants in burned-seeded areas (67.1%) was lower than burned-unseeded areas (75.3%), and both were greater than unburned areas (55.9%, p < 0.001). With annual grasses included, the decrease in mean percentage of canopy gaps was greatest in burned-unseeded locations (47.6% compared to 36.7% in burned-seeded and 22.0% in unburned areas, p < 0.001), suggesting Bromus continuity is most extensive in burned-unseeded areas. Shrub cover and density were no different in aerial seedings relative to unseeded areas (p > 0.1). There was a positive association between Artemisia tridentata density and age of aerial-seeded areas (p < 0.01, R² = 0.38), suggesting that sagebrush seedings initiate and contribute to further recruitment over at least the first 20 years post-seeding. Overall, post-fire seedings may improve perennial grass cover and slightly reduce Bromus continuity, but factors such as post-seeding precipitation or drought warrant further investigation of seeding performance.