1a. Objectives (from AD-416)
The broad objective of this research is to use portions of the existing crested wheatgrass diversification infrastructure to simultaneously examine how multiple ecological processes interact to influence forb establishment in crested stands. Restoration research has traditionally examined the intensity of ecological processes such as competition. However, there is little effort placed on understanding the relative importance of these processes for determining plant community structure, which is ultimately the information practitioners want to know. For example, ecologists working in old fields have shown that root competition can be intense between species but that competitive interactions were relatively unimportant in determining old field community composition and diversity. In support of these findings, I have recently shown that while competition from annual grasses can interfere with native grass establishment following fire, interference was relatively insignificant in determining density and composition of seeded species compared to the effects of drought and seeding depth. Understanding the relative importance of various ecological processes in influencing forb establishment will provide the foundation for improving the ability of land managers to capitalize on the array of forb plant material available through the GBNPSIP.
1b. Approach (from AD-416)
Based on the results of a number of studies funded by the GBNPSIP, this study will examine the direct and indirect effects of disturbance, safe site availability, drought, crested wheatgrass and cheatgrass abundance, seeding depth, and seeding rate on forb establishment and diversity in a crested wheatgrass stand in southeast Oregon. Classical experimental designs and statistical tests do not allow the importance of direct and indirect effects and factor interactions to be easily evaluated. I will use structural equation modeling to quantify the relative importance of each of these factors and their interactions for forb establishment. For this experiment, 300, 6m x 6m plots will be established. One of five disturbance treatments (crested control) will be applied to each plot including: undisturbed, light till, herbicide, 1-way disking, 2-way disking. Half of these plots will be drill seeded with a rangeland drill. Seeds in the other half of the plots will be placed by hand in drill rows and buried 1/8 of an inch deep. Half of the plots also will receive supplemental watering in spring. Plots will be seeded at ½x, 1x, or 2x the recommend forb seeding rate. Eight forb species will be used based in recommendations from the GBNPSIP and land managers. Response variables including forb germination and establishment as well as first, second and third year survival and fecundity. Treatment effects on crested and cheatgrass density and cover and soil moisture availability will be quantified. The relative importance of each factor for forb establishment will be determined using path analysis and structural equation modeling in SAS.
3. Progress Report
Funding for the project was delayed so plot installation was postponed until this upcoming fiscal year (2012). The site has been selected and experimental design developed. Treatments and seedings will be applied this fall. This is a three year project with a five year funding window so no problems are anticipated.