Performing Department
(N/A)
Non Technical Summary
Range agroecosystems can be particularly sensitive to rainfall variability, since unlike most other contemporary agriculture they cannot be economically irrigated in response to drought. Consequently, forage available for range animals can vary dramatically with rainfall year to year. As such, ranchers often need to base stocking rates on the lower end of forage productivity to avoid losses in less productive years, reducing their ability to capitalize on high-productivity years.My overarching goal is to expand ecological knowledge of temporal dynamics in rangelands to better predict and manage forage productivity.Recent work suggests that previous-year rainfall is as important as current-year rainfall for rangeland dynamics, and may promote coexistence of different forage speciesTo test the effects of lagged precipitation on California rangelands, I conduct a field experiment with rainfall manipulation to parameterize modern coexistence theory models for communities of perennial and annual grasses under different patterns of dry and wet years. To extend these community models to consequent productivity and forage availability, I will test model predictions on long-term vegetation and productivity data from the site.This project aligns with the AFRI priority area of bioenergy, natural resources, and environment by increasing our understanding of rangeland dynamics and the role of plant diversity in the sustainable management of these systems. Additionally, the project directly supports the postdoctoral development of the PD, Chhaya Werner, in developing technical research and modeling skills and collaborating with rangeland managers and educating and mentoring students in rangeland science. I will communicate research findings through peer-reviewed papers, at conferences focused on the interactions between land managers and researchers such as the California Society for Ecological Restoration and the Natural Areas Association conference, and directly to local ranchers at the Sierra Foothill Research and Extension Center's field day for ranchers.?
Animal Health Component
50%
Research Effort Categories
Basic
40%
Applied
50%
Developmental
10%
Goals / Objectives
A strong predictive model for the role of these lagged effects would allow ranchers to use the past to anticipate future production. This project has three research-focused goals: (1) investigate differences in lagged drought responses of annual versus perennial grasses (2) understand the role of lagged rainfall effects for maintaining annual-perennial coexistence in California rangelands, (3) investigate the consequences of lagged rainfall effects on stability of grassland productivity. Additionally, this project has a general training and development goal: (4) support the postdoctoral development of the PD, Chhaya Werner, in developing skills in technical research, modeling, collaborating with rangeland managers, and educating and mentoring students in rangeland science.Corresponding to these goals, this project has three research objectives:1. Use field manipulations to collect annual and perennial grass demographic responses to current and lagged drought.2. Build modern coexistence theory models to predict when climate variability results in species coexistence.3. Model forage productivity and stability in drought and post-drought conditions, and test these models on past records.Additionally, this project has three training and development objectives:1. Develop and lead two course modules, including at least one rangeland field-focused module, with feedback from participating students, mentors Hallett and Shoemaker, and Southern Oregon University's Center for the Advancement of Teaching and Learning2. Network with the ranching community through SFREC's field day and small meetings such as the Natural Areas Association conference or other local meetings3. Mentor undergraduate and graduate students in rangeland research skills
Project Methods
Experimental Design.To test the interacting roles of precipitation and competition on perennial and annual grasses, I will establish a field experiment to measure productivity and demographic parameters ofS. pulchraandA. fatua. I will conduct this field experiment in an active rangeland at Sierra Foothill Research and Extension Center (SFREC) near Browns Valley, CA (39o 15' 04" N, 121o 18' 39" W, Elevation 202 m). This site experiences a typical California Mediterranean climate with hot, dry summers and cool, wet winters. Like much of California rangelands, it also experiences high interannual variation in precipitation (annual rainfall ranging from 220 mm to over 1200 mm, with an average of 720 mm; O.S.U. PRISM Climate Data). I will use the existing rainfall manipulation experiment at SFREC established through a University of California Agricultural and Natural Resource Infastructure grant, which consists of 16 precipitation reduction shelters measuring 50 ft x 16 ft with 16 paired controls. The seedbank in these rainfall manipulations was cleared in 2019 and 2020 by successive herbicide and mowing, which will allow me to directly manipulate densities of the target study species. I will monitor the resource dynamics under these treatments using soil moisture probes inserted vertically to measure average volumetric water content at 5-10 cm depth.Within the rainfall manipulation treatments, I will establish plots with combinations ofA. fatuaseeds (AF),S. pulchraseeds (SS), andS. pulchraplugs (SP) in Fall 2021 (Figure 3). To parametrize coexistence models, I will establish 0.5 m x 0.5 m plots each of these three (AF, SS, and SP) at observed ambient densities of 16 plugs/m2or 3200 seeds/m2, half-density of 8 plugs/m2or 1600 seeds/m2, and a no competition condition with no background planting. I will add in each of the target plants (AF, SS, and SP) at 2 plugs/m2or 320 seeds/m2in the varying density plots to measure population growth rates when rare (GRWR), a key parameter for species persistence. This experimental design will allow measurements of GRWR under high competition, low competition, and no competition.Field Measurements.I will collect key parameters forS. pulchraandA. fatuapopulations from Fall 2021 to Summer 2022. In December 2021 I will assessgerminationrates of AF and SS by subsampling seedling densities in a central 20 cm x 20 cm area in each plot. At peak biomass in April and May 2022 I will measuresurvivalby subsampling and counting stems in the same way as germination for AF and SS. For SP, all plugs in the full plot will be assessed for survival. I will additionally measure thegrowthof SP plugs at peak biomass by measuring their height, basal length, and basal width. I will measurefecundityin summer 2022 by counting awns for AF, which holds its awns and produces two seeds per awn. For SP I will measure awn lengths and collect awns from at least ten individuals outside of the plots to allometrically relate awn length and seed count.S. pulchraseedlings do not produce seeds in their first year.In addition to these measurements, at peak biomass in April and May 2023 I will clip the plots and sort, dry, and weigh theabove-ground biomassby species to measure total forage production in monoculture and combined species plots.Analysis.To test H1, that drought years have negative direct effects on both annual and perennial grasses but perennials are able to rebound more quickly, I will measure parameters from each species planted alone (without competition) under the different precipitation treatments. I will use ANOVA mixed models to verify the effects of treatments on resource conditions, germination rates, survival, and growth. I will use field data, combined with existing demographic data collected by Dr. Hallett, to parametrize population demography models. These models will simulate the responses of each species to drought events (H1a) and identify patterns of post-drought recovery (H1b).To test H2, that lower competition during drought years allowsS. pulchrato rebound more quickly after drought, I will additionally collect these demographic parameters from the species planted in combinations of different densities (Figure 3). In this way, I can directly measure the strength and consequence of competitive interactions under the different precipitation treatments. The different competition density treatments usingS. pulchraseeds (SS) or plugs (SP) and two densities ofA. fatua(AF) will provide information on the relative impacts of competition at different levels of species establishment and consequent competitive pressure.To test H3, that the lagged effects of drought promote long-term coexistence of rangeland annual and perennial grasses, I will test for coexistence using the mutual invasion criterion. Stable coexistence occurs if each species has a positive growth rate when rare (GRWR). With the data collected in the single species, low density, equal density, and high density comparisons, I will simulate the equilibrium abundance of each species (with no competitors). I will then test the growth rate of a single seed of the focal species in the equilibrium background of the other species, and calculate its GRWR. I will use discrete-time population growth equations to extend the coexistence method to account for perennial species. I will test for the stability of coexistence under variable environments using historic rainfall patterns, including long-term weather data from the SFREC field station site. I will also simulate different weather patterns with different drought frequencies or durations to see how this affects coexistence.To test H4, that mixtures of perennial and annual grasses promotes forage stability, I will simulate annual net productivity (ANPP) in varied climate conditions using the growth rate and biomass measured in the plots, for both monocultures and mixtures. I will compare these simulations to long-term observed ANPP in grasslands at the SFREC site. In addition to traditional measures of the mean ANPP and variation in ANPP through time, I will specifically test the time to recover after drought to at least the mean ANPP (lag time).Evaluation PlanThe experiment was established in Fall 2021, with data collection in 2021 - Spring 2023. An initial methods paper is in prep for publication and will be submitted in Summer 2023 andreceive direct feedback from editors and peer reviewers. In Spring 2024 I will complete the data collection and analysis for the forage stability study, and present it for feedback from a mixed community of researchers and managers at the SERCAL conference.In Spring 2023I designed and led a rangeland field course module. I will evaluate the success of this module through student course reviews, and modify it for future use. Finally, I will develop an Individual Development plans for my undergraduate assistants, and have monthly meetings with them to support their goals and progress.