1a. Objectives (from AD-416):
The first and primary research goal of this project is to improve our systems approach to restoration for annual grass management in the sagebrush steppe of North America. In 2013, we provided a systems approach that advances ecological restoration beyond conceptual and phenomenological descriptions to quantitative process-based models that can be used to address specific applied questions (James et al. 2013a). Our systems approach uses life histories to identify transitions important to seedling establishment and maturation. It links those transitions to ecological processes directing establishment and management practices that can favorably impact those processes. Our technology transfer goal is to use the research results for developing tools aimed at assisting land managers in selecting seeds based on their quality, guidelines for determining when and what species to broadcast during restoration, and guidelines on assessing and managing defoliation of newly emerged seedlings at risk to herbivory. Specifically, during the next five years we will focus on the following objectives: Objective 1: Enhance rangeland restoration processes by improving the establishment of seedlings of desirable plant species (such as increasing seed quality and seedling survival), acquiring and implementing basic knowledge to match naturally occurring physical safe-sites with seed traits, identifying and quantifying the effects of herbivory on seedling survivorship, and developing threshold guidelines for mitigation. Sub-objective 1A: Improve rangeland restoration success by enhancing seed quality and emergence survival of desired restoration species and develop simple seed quality selection criteria. Sub-objective 1B: Develop the basic knowledge to match naturally occurring physical safesites with seed traits to maximize seedling establishment during restoration. Sub-objective 1C: Identify and quantify the effects of herbivory on seedling survivorship to develop threshold guidelines for mitigation during restoration. Objective 2: Integrate research into an ecological systems approach to restoration with current cost/benefit models and link to site-specific best management practices. Sub-objective 2A: Develop decision-support tools for 1) choosing seeds based on quality characteristics, 2) matching seed size, number, and physical safe-site availability during restoration, and 3) identifying and managing risk to seedlings associated with herbivory. Sub-objective 2B: Inform and update our systems approach to include important aspects of seed quality, maximizing physical safe-site capture, and minimizing seedlings risk of herbivory and link this model with existing cost/benefit models.
1b. Approach (from AD-416):
Rangelands cover nearly one-half of the earths land surface and provide life sustaining goods and services to about one-third of the global population. Low and variable rainfall combined with often infertile soil make the world’s rangelands highly susceptible to degradation, invasion, and global climate change (Millennium Ecosystem Assessment 2005). The inability to establish healthy plant communities is cited by stakeholders as the single largest barrier to implementing restoration and turning the tide against the hundreds of thousands of hectares of sagebrush steppe lost to invasive plants each year. Despite over a century of research, rangeland science lacks a comprehensive understanding of the ecological processes influencing seedling establishment. The goal of this project is to improve restoration for annual grass management in the sagebrush steppe of North America. Using a series of field and laboratory tests, our first study attempts to improve rangeland restoration success by enhancing seed quality and emergence survival of desired restoration species and develop simple seed quality selection criteria. Our second study is aimed at developing the basic knowledge to match naturally occurring physical safe-sites with seed traits to maximize seedling establishment during restoration. Third, we plan to identify and quantify the effects of herbivory on seedling survivorship to develop threshold guidelines for successful restoration. Finally, we will integrate this research into an ecological systems approach to restoration with current cost/benefit models.
3. Progress Report:
For Objective 1, studies have been initiated to improve rangeland restoration success by enhancing seed quality and emergence survival of desired restoration species and developing simple seed quality selection criteria. ARS scientists extended a short-term study assessing how seed mass enhances seedling emergence potential to cover a one-year period and determine seedling survivorship, with results currently drafted into a manuscript. A study to determine if seed mass enhances wintertime seedling emergence and establishment under varying soil water conditions is completed and currently drafted into two manuscripts. The two other studies to enhance seedling success by using high quality seeds are in various stages of progress. A preliminary study that focused on matching naturally occurring physical safe-sites with seed traits to maximize seedling establishment was completed. Based on this study, the procedures for quantifying safe sites were improved and the larger study is underway. Both a low elevation site and a high elevation site have been selected and plots have been established. Treatments have been applied to half the plots and the resulting seedlings sampled. The experiment has been extended so that the other half of the plots will be treated and sampled in the coming year. Abiotic characteristics of safe sites and non-safe sites (temperature and moisture) were also collected to allow for better characterization of safe sites. The effects of herbivory on newly established seedlings were monitored on nine sites in Oregon and Idaho this spring. To improve effectiveness of insect exclusions, treatments were modified and now include only two exclusions, both applied with mesh netting (no exclusion, mammal exclusion, and insect and mammal exclusion. Plots used to test the effects of timing and frequency of herbivory on seedlings were seeded last fall, and a subset of emerged seedlings was selected to receive one of five clipping treatments (no defoliation, 30% defoliation once, 30% defoliation twice, 70% defoliation once, 70% defoliation twice). First year survival of seedlings was monitored, and surviving plants were marked to allow tracking through winter and into next year. A large number of photos of safe-site microtopographical conditions have been collected for Objective 2, and are currently being processed to assess safe-site characteristics. This information will be used to create a safe-site ranking system.
1. Optimizing season of seeding and seed rate to improve seedling recruitment during restoration of invaded grassland. High disturbance frequency, low water availability, and advantageous growth mechanisms of invasive annual compared to native perennial grasses reduce native grass establishment throughout arid rangelands. Modifying seeding dispersal processes, including seeding rate and time, may increase native grass recruitment by influencing safe site occupation. Scientists in Burns, Oregon tested the effects of spring versus fall annual grass seeding times, adding water, and varying annual and perennial grass propagule pressure on perennial and annual grass recruitment in an eastern Oregon shrub-steppe ecosystem. Perennial grass recruitment was generally low, especially when annual grass propagule pressure was higher than 150 seeds per square meter. Although, by the second growing season, perennial grasses had the highest density when perennials were seeded with annuals in autumn and water was added. Land managers can improve native perennial grass establishment by seeding in autumn and increasing seeding rate in sagebrush-steppe rangeland.
Schantz, M.C., Sheley, R.L., James, J.J., Hamerlynck, E.P. 2016. Role of dispersal timing and frequency in annual grass-invaded Great Basin ecosystems: how modifying seeding strategies increases restoration success. Western North American Naturalist. 76(1):36-52. doi: 10.3398/064.076.0106.
Svejcar, T., Boyd, C.S., Davies, K.W., Hamerlynck, E.P., Svejcar, L. 2017. Challenges and limitations to native species restoration in the Great Basin, USA. Plant Ecology. 218:81-94. doi: 10.1007/s11258-016-0648-z.