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Long-term vegetation recovery and invasive annual suppression

Date: May 24, 2019

Seed mixes used for postfire seeding in the Great Basin typically focuses on the short-term rehabilitation objectives. Longer-term considerations are also important.


Background

Although introduced species such as crested wheatgrass (Agropyron cristatum) have been widely used for post-fire rehabilitation seedings in semiarid Great Basin ecosystems, native species such as bluebunch wheatgrass (Pseudoroegneria spicata), western wheatgrass (Pascopyrum smithii) and big sagebrush (Artemisia tridentata) now play an increasingly important role in seeding efforts. Seed mixes containing only native species are ideal for areas where natural vegetation recovery is a long-term objective, but the ability of native seedings to meet other objectives such as weed suppression has often been questioned.

Research

An operational-scale seeding experiment was initiated at two study sites following the 1999 Railroad wildfire in Tintic Valley, Utah, to compare native seed mixes with conventional mixes dominated by introduced species. Short-term effects of these seed mix treatments during the first three years of seedling growth were examined and reported by Thompson et al. (2006). In 2015, a team of researchers from the USDA Forest Service Rocky Mountain Research Station and Utah Department of Natural Resources returned to the study site to examine longer-term effects. They were interested in documenting changes in cover and density of key plant species to determine whether the seed mix treatments had been effective at re-establishing perennial cover and suppressing exotic annuals over the longer term.

Examples of unburned sagebrush and sagebrush/juniper vegetation in Tintic Valley, Utah where the study was carried out.

Key Findings:

  • This is the first long-term experimental study comparing conventional seed mixes, which include introduced grasses, forbs and shrubs, to native-only post-fire seeding mixes in the Great Basin.
  • Seeding treatments had a lasting effect on vegetation cover and composition regardless of seed mix. Although responses of individual species varied, seed mix species collectively came to dominate seeded treatments and increased 2-fold or more between 2002 and 2015, even in experimental blocks where initial establishment had been minimal.
  • Performance of native seed mixes varied according to site and mix characteristics. Native seed mixes had lower establishment than conventional mixes when seeded at standard rates at a dry low-elevation site, but establishment was not significantly different at a higher elevation site. Using higher seeding rates and a more diverse mix of species compensated for the lower establishment of the native seed mix at the low-elevation site.
  • By 2015 there was clear evidence that both conventional and native seed mixes were suppressing invasive exotic annuals. Cheatgrass suppression was greatest in the conventional seed mix treatments where cheatgrass cover did not exceed 2%. The native seed mix treatments had 3-6% cheatgrass cover, which also indicated significant suppression relative to unseeded controls where cheatgrass cover reached 9-15%.

Cover by plant group at the drill-seeded study site in Tintic Valley, Utah, as recorded 3 years (2002) and 16 years (2015) following fire and seeding. Treatments are a mix of conventional mixes and native

 

Featured Publications

Ott, Jeffrey E. ; Kilkenny, Francis F. ; Summers, Daniel D. ; Thompson, Tyler W. , 2019
Thompson, Tyler W. ; Roundy, Bruce A. ; McArthur, E. Durant ; Jessop, Brad D. ; Waldron, Blair ; Davis, James N. , 2006


Principal Investigators: 
Principal Investigators - External: 
Daniel D. Summers - Habitat Restoration Coordinator - Utah Division of Wildlife Resources - Ephraim - UT 84627 - USA
Tyler W. Thompson - Watershed Program Director - Utah Department of Natural Resources - Salt Lake City - UT 84114 - USA
External Partners: 
Utah Division of Wildlife Resources, Ephraim, UT 84627, USA
Utah Department of Natural Resources, Salt Lake City, UT 84114, USA
Research Location: 
Great Basin ecosystems Tintic Valley, Utah