Research

​Applegate's milkvetch (Astragalus applegatei)  is a critically endangered plant species that is a narrow endemic of the Lower Klamath Basin in Southern Oregon, within the city of Klamath Falls. Once thought to be extinct, it is now know to exist at only a few sites within the Lower Klamath Basin. The lab has been conducting research on Applegate's milkvetch since 2013. We have several completed and ongoing projects related to different aspects of Applegate's milkvetch conservation: 

• The United States Fish and Wildlife Service (FWS) has worked with a local nursery to improve propagation techniques. In 2012, 2013, and 2014, volunteers and biologists from the FWS augmented one of the protected populations by out-planting  hundreds of A. applegatei  seedlings that have been propagated in the greenhouse.  To date, no thorough demographic monitoring program has established the success of this out-planting program. We monitored all out-planted individuals at this site over six years, tracking seedling survival, reproduction, and recruitment, and compared vital rates of the out-planted individuals to extant individuals at the same site as they aged (Stewart and Byrne, 2025).

• ​​We conducted annual demographic monitoring in four extant populations from 2016 - 2022 and have developed population models to predict future population dynamics of each population (Stewart, Byrne, & Jules, in prep). 

• With Catalina Cuellar-Gempeler (Cal Poly Humboldt Biology) we are investigating the role of the microbial community in the success of Applegate's milkvetch population growth.

• Also with Catalina Cuellar-Gempeler, we are assessing the efficacy of three land management techniques (burning, mowing, and scraping) on survival and recruitment of Applegate's milkvetch and impacts on the mycorrhizal community.

Each of these projects will assist Federal, State, and Local agencies in planning future conservation efforts, and are vital for the recovery of this imperiled species.​

Ranchers and land managers in the United States spend billions of dollars annually to control invasive plants, such as cheatgrass and medusahead – invasive annual grasses that can outcompete native plant species and increase wildfire risk on western rangelands.

Efforts to restore native perennial species through seeding projects are also costly, often with low and unpredictable germination rates. A growing body of evidence suggests that livestock grazing, particularly fall and spring targeted grazing, may reduce invasive annual grass abundance through biomass and litter removal of annual grass while perennial species are dormant. However, treatment of invasive species in isolation will be unsuccessful if there is no longer a sufficient seed source for native species to return without further assistance.

The soil seed bank is a critical and understudied component of rangeland plant communities. Seed banks contribute to plant species persistence and recovery after disturbance and provide a signature of past, present, and future characteristics of the aboveground plant community. Furthermore, the seed bank can be used as a resource for restoration efforts after undesirable species (such as exotic annual grasses) have been removed.

The lab currently is involved in two projects related to targeted grazing in annual grass invaded rangelands. Here is a 2023 talk Dr. Byrne gave with the Idaho Native Plant Society and a 2025 talk she gave with the California Native Plant Society about this work.

1) Seeds underhoof: can the soil seed bank facilitate restoration of sheep-grazed, cheatgrass-invaded rangelands?
In this project with collaborator Kelly Hopping (Boise State University), we are examining relationships between aboveground vegetation composition and belowground seed bank composition across a range of cheatgrass invasion levels spanning different targeted grazing treatments by sheep in high elevation sagebrush steppe in Idaho.
Funding: Western Sustainable Agriculture Research and Education sabbatical grant program SW23-944
Educational video about the project

2) Quantifying the effects of herbicide and targeted grazing on medusahead thatch and the soil seed bank over time
In collaboration with the Bureau of Land Management, we seek to understand how the combined impacts of herbicide (impazapic) and fall targeted grazing by cattle affect the quantity of medusahead thatch, soil microclimate, and seed bank dynamics of a winter annual dominated grazing allotment located within the sagebrush steppe in eastern Oregon.
Funding: Bureau of Land Management Invasive and Noxious Plant Management Program grant L22AC00317

Extreme droughts are expected to become more frequent and intense in the future. Although drought impacts will vary by ecosystem type, as water-limited systems, grasslands and shrublands will likely be particularly sensitive. Indeed, experimental and observational studies in grass- and shrub-dominated systems have linked the direct impacts of drought to reductions in plant biomass and drought-induced plant mortality and dormancy (Byrne et al., 2013; Hoover et al., 2014; Weaver, 1954). 

Understanding the impacts of extreme drought in grasslands and shrublands and providing land managers with suggestions to increase resiliency of plant communities to drought is a major research goal in the Byrne lab, and we have participated in several research projects related to drought impacts across western North America.

1) Assessing the impacts of extreme drought on forage quality and quantity in California rangelands

In this new project with PI Robert Griffin-Nolan (Chico State), Justin Luong (UC Berkeley), and Yamina Pressler (Cal Poly SLO), we are establishing a network of drought shelters across CA rangelands to experimentally test how extreme drought impacts forage quality and quantity, root production, and soil aggregate stability.
Funding: California Agricultural Research Institute

2) Predicting the impacts of drought and drought recovery on the quality and quantity of livestock forage production in northeastern California

With Dr. Kristen Kaczynski (California State University, Chico) and Dr. Justin Luong (UC Berkeley) we investigated the impacts of intense, long-term drought (Byrne et al., 2025; Nunes and Byrne 2022) and recovery (Chavez and Byrne, in prep) on the western Great Basin sagebrush ecosystem. The experiment was part of a large network of concurrent drought experiments, called Drought-Net. This project aims to help inform future management decisions for the Bureau of Land Management. 

Funding: Bureau of Land Management L16AS00178, California Agricultural Research Institute (18-06-004 and 22-06-101) 

3) Effects of drought and water addition on Great Plains Plant Communities

Dr. Byrne's dissertation research examined the effects of precipitation changes on plant species composition and community structure in native grassland communities in the Great Plains of North America. She used a field experiment to manipulate rainfall in three treatments- control, water addition, and drought - and measured changes in species composition (Byrne et al. 2017) and aboveground (ANPP) and belowground (BNPP) net primary production (Byrne et al. 2013) in each treatment over 3-4 years. This research improved our understanding of ecosystem dynamics under climate change, especially BNPP dynamics, which are infrequently studied and not well understood. 

Grassland restoration has the potential to return valuable ecosystem services and stability to the restored area, yet restoration outcomes are often context-dependent and rarely monitored over time (at a relevant timescale for many ecosystem services). For this project, we are collaborating with Dr. Monica Sheffer (Biological Sciences) to assess ecosystem services across a restoration chronosequence in Northern California coastal prairie. Specifically, we are assessing restoration impacts on: plant and insect biodiversity, forage production, root biomass, soil carbon, and duration and intensity of vegetation greenness (an indicator of forage quality).

Funding: Bureau of Land Management L22AC00223, California Agricultural Research Institute (25-06-100 and 26-99-101)