2013 Annual Report
1a.Objectives (from AD-416):
To investigate (1) the potential for Great Basin native annual forbs to effectively compete with B. tectorum and facilitate the establishment success of native perennial grasses (2) the germination ecology of key Great Basin native annual forbs. The ultimate goal of this work is to determine whether it would be useful to include native annuals in postfire rehabilitation seed mixes.
1b.Approach (from AD-416):
1. Greenhouse competition study: This aspect of the research is being conducted in combination with scientists at UNR. We have completed one greenhouse experiment to look at competition of the two native species with B. tectorum and establishment of E. multisetus with native annual forbs, with B. tectorum , and with annual forb-B. tectorum mix. Growing with competitors decreased the size of E. multisetus, however the largest decrease in size was found when grown with B. tectorum and A. tesselata. In contrast, E. multisetus grew best with M. veatchiana. When in competition with B. tectorum, E. multisetus performed best when M. veatchiana was also present. These results support the idea that the presence of certain native annual forbs can enhance the establishment of E. multisetus in B. tectorum invaded rangelands.
2. Buried seed bank experiments for Amsinckia tesselata, Amsinckia intermedia, Blepharipappus scaber, and Mentzelia veatchiana: For each species, I prepared artificial seed bank buried bags. Bags are being retrieved monthly for one year, then in early spring and late summer for up to 5 years or until there is no evidence of seed carryover. For each bag, the number of recently field-germinated seeds, seeds germinable at 2/15°C for 4 weeks are being determined.
3. Field study: Amsincka intermedia and Bromus tectorum demography. I have collected three years of demographic data quantifying plant density and seed output for B. tectorum and Amsinckia intermedia at a field site. We will resample the plots and add seed bank sampling to determine how long-term fluctuations in adult and seed bank densities relate to amount and timing of precipitation for the native and the invasive annual.
4. Field competition study: This experiment also is being conducted in combination with two scientists at UNR. Last fall, we planted small plots with combinations of native annuals and Bromus tectorum. The experiment looks at the performance of B. tectorum or E. multisetus target plants in annual native forb monocultures, B. tectorum monoculture, or a mixture of annual native forbs and B. tectorum.
This agreement was established in support of objective 4 of the in-house project, "Develop restoration methodologies to prevent the invasion of annual grasses (such as cheatgrass, medusahead rye, and/or red brome) following destructive events (such as fire) in rangeland ecosystems". Two common garden experiments were completed that measured the success of late seral and early seral native seed mixes when planted with an invasive annual grass, either cheatgrass or medusahead. Each seed mix consisted of two forbs (herbaceous flowering plant), two perennial grasses, and one shrub. The use of native annual and early seral species in Great Basin rangeland reseeding efforts may improve restoration/rehabilitation success by increasing ecological resistance to invasion by exotic annual grasses and by facilitating succession to desirable late seral vegetation. Early seral species may be similar to exotic annual grasses in growth rates and resource acquisition strategies. As a result, ecological theory predicts that early serals would compete more strongly against invasives like cheatgrass (Bromus tectorum) and medusahead (Taeniatherum caput-medusae). Because the invasion and success of exotic grasses appears to be associated with soil type, competitive interactions between exotic and native plants may also depend on soil type. We used a common garden approach to evaluate the performance of two exotic annual grasses (either cheatgrass or medusahead) and mixtures of native species growing in two soil types of contrasting texture (sandy loam and clay loam). Performance of an early seral seed mix (native annual forbs, early seral grasses and shrubs) was compared with that of a late seral seed mix representative of species commonly used in restoration. We found that the early serals generally outperformed late serals when growing with exotic annual grasses, both in terms of seedling emergence and early survival, though results differed among functional groups (i.e., native grasses, forbs, and shrubs) and soil types. Performance of the native grasses was generally higher than the performance of native forbs and shrubs. During early life stages, the presence of native species did not have a suppressive effect on the exotics. In terms of soil preference, cheatgrass survival was higher in sandy loam compared to clay loam, but survival of medusahead was high on both soil types. The response of native plants to soil type depended on whether natives were growing with exotics. Given their generally higher survival, the early seral natives may have a greater chance of persisting in the presence of cheatgrass or medusahead in comparison to the late seral natives. Success of seeded natives at the seedling stage is likely critical in determining the eventual success of native reseeding efforts. Our findings suggest that use of early serals in reseeding efforts may result in greater density of natives in communities where exotics are present, though additional studies will be needed to assess whether these species are able to persist in the long-term. The high survival of medusahead in both soil types underscores the need for greater efforts to prevent its further spread in the Great Basin. One manuscript has been submitted and another two manuscripts are in preparation.