Comparing soil organic carbon, infiltration, and bulk density in various grass communities and management practices on Confederated Salish and Kootena

The Bison Range is located in the Mission Valley of Montana and includes a low-rolling mountain, wetlands, a creek, and intermontane Palouse-type grasslands (Gilles & Coffman, 2019). This variety of ecosystems allows for a variety of vegetation and wildlife. Bluebunch wheatgrass and rough fescue are some of the important cool-season grasses on the Bison Range. (Garcia Neto, 2014). There are other grasses, small shrubs, and forb such as Koeleria macrantha (prairie junegrass), Symphoricarpos albus (snowberry), and Balsamorhiza sagittate (arrowleaf balsamroot). (Gilles & Coffman, 2019). Invasive species on the Bison Range include Cirsium arvense (Canada thistle), Bromus tectorum (cheatgrass), Potentilla recta (Sulphur cinquefoil), Dipsacus fullonum (teasel), Ventenata dubia, Lepidium draba (whitetop), (Gilles & Coffman, 2019) The main ungulates on the Bison Range putting grazing pressure on the grasslands are bison, elk, white-tailed deer, mule deer, bighorn sheep, and pronghorn, (Garcia Neto, 2014). 

The intermountain valley where the Bison Range is located was created by glacier action and was once a large glacial lake. Soil Valley sediments, lakebed silt, and glacier debris are the main soils in the valley (Smith, 2001). The north side of the mountain tends to be moister than the south side (Gilles & Coffman, 2019). Ventenata can be found in all aspects but it tends to dominate southern aspects. 

The majority of precipitation is in the spring and early summer averaging about 2.5 inches per month in May and June (Gilles & Coffman Gilles & Coffman, 2019). Climate projections for the next several decades predict a rise in temperature of about 2 to 4 degrees globally with a local, 2019).

The grassland environment on the CSKT Bison Range is currently subjected to numerous environmental and climatic variabilities. Since the Bison Range was returned to the Confederated Salish, Kootenai, and Pend d’Oreilles Tribes, the tribes have decided to let the bison choose where to graze within the Bison Range (Peter Bugoni, Personal Communication, 2023). Future changes from climate change are projected to include an increase in annual invasive grasses and loss of cool season grass production (Abatzoglou and Kolden, 2011, & Loka et al., 2018). 

Site selection

The study sites have been selected on the northeastern side of the Bison Range, at the base of a small rolling mountain. The desirable aspects of the site are the presence of ventenata dubia and native grasses, no recent herbicide applications, and no western cedar nearby. The site is relatively flat with few if any gullies and small hills. The soil type is primarily the Ronan series. (USDA, 1978). Each site will be one of two main management groups; bison grazed and a bison exclosure. According to Bison Range staff, the exclosed area has been fenced off from the rest of the Bison Range for the past 50 years. Deer, elk, and possibly pronghorns have been the only ungulate grazers in the fenced area. These sites are in triangles fenced off at the base of Red Sheep Mountain on the Northeast corner of the Bison Range. The grazed area is just northwest of the enclosers and has been grazed by Bison since the Bison Range was established in 1908 (CSKT, Bison Range). 

Step 1 Mapping Focal Groups

  The grassland communities were stratified in 2023. The researcher walked through the sites to visually assess patches of vegetation and designate them into general vegetation focal groups. Ventenata dubia, an annual invasive grass prevalent on the Bison Range, will be one focal group (Gilles & Coffman, 2019). Other vegetation focal groups included native grasses such as bluebunch wheatgrass (Pseudoroegneria spicata), rough fescue (Festuca campestris Rydb), prairie junegrass (Koeleria macrantha), western wheatgrass (Pascopyrum smithii), (Gilles & Coffman, 2019). Researchers will use GIS technology to map focal groups. 

Step 2 Vegetation Sampling 

Researchers selected three of the most prominent focal groups; bunch grasses, rhizomatous grasses, and annual invasive grasses. Three plots out of each focal group made up a study site. Researchers estimated vegetation cover and diversity within each plot. They also took five soil samples, and five bulk density samples, and perform three soil infiltration tests from each plot. 

 In June and part of July, vegetation percent cover was estimated using a 15 m line-point intercept (LPI)(De Stephano et al. 2021, and Rangeland Gateways, 2023). A 15 m radius circular plot was placed in the center of the focal groups and split into quadrants. The Researcher walked back and forth, documenting plants not identified with the LPI, such as trees and shrubs, and plants not picked up with the LPI (Sherman and Anderson, 2023 p. 61).

Step 3 Soil Sampling

In August and September, the researchers took infiltration rates and soil samples from five random points selected in each plot, using ArcGIS Pro and Google random number generator. The closest microsite (a small patch of vegetation of interest) to the random point was used for sampling. Sarah Holloway and sometimes Jarod Swan or Brad Mitchell took infiltration rates first using the Mini-Disk Infiltrometer. Infiltration rates took from 12 to 80 minutes. The researchers dug micro pits for soil sampling within the same microsite while avoiding the moisture from the infiltration test. Each pit was about 30cmX30cm. The researchers hammered a 4cmX4cm cylinder into the side of the pit at 1 cm and 15 cm below the surface then used a Hori Hori knife to remove the cylinder. The researchers collected small chunks of soil at 30 cm to keep the hole small rather than using the cylinder. They stored soil samples in labeled Ziplock bags. After returning to the office, each soil sample collected that day was weighed and dried in a dehydrator at 160 F for 12 hours. The following day, the soil samples were weighed and re-bagged.

In January 2025, Holloway took the soil to the Desert Research Institute in Reno, Nevada. Holloway worked in the soils lab, with the assistance of Sally Houseman, Kristine Lu, and Alan Villanueva, to test for soil organic carbon (SOC) using the loss on ignition (LOI) method. Holloway split the samples and placed them in a 105-degree Celsius oven the day before LOI testing. The samples remained in the warm oven until each batch was tested. Small batches were weighed and put in a muffle furnace at 400 degrees Celsius for an hour. Holloway cooled the samples for 20 min in a desiccator before weighing them. After the LOI testing, Holloway split several more samples for a laser particle size analysis. She took one surface sample from each plot. Houseman ran the laser particle size analysis and emailed the results.

Data collection

   Soil and vegetation data collection forms were signed, time and date recorded, and original copies stored at the SKC Extension Office.

Schedule of activities

• Fall 2023 -Stratify three grass communities within triangle areas.
• Spring and summer 2024- Sample Sites
• Fall 2024- Analyze Data
• Winter 2025-LOI testing
• Spring and summer 2025- Data analysis and write up

Research Objectives

• The first objective is to sample vegetation and soils in three mapped grassland functional groups in one season. We will compare SOC, infiltration, and bulk density and determine which functional group is the most beneficial to soil health.
• The second objective is to sample soil and vegetation in a bison grazed and un-grazed grassland in one growing season. We will compare the SOC, infiltration, and bulk density to determine whether Bison Range stocking rates are maintaining soil health.

Data Management Plan

Data collection

        The collected soil was moved directly from the cylinder into a new bag. Soil was stored in a secure draw in a filing cabinet or in a locked cabinet. Data collected was signed or initialed, timed, and dated. The team was trained to properly identify the common grasses.        

       To protect the data, soil data was written on waterproof paper and researchers used pencil or a waterproof pen. Pictures were taken of data sheets for backup. When the research team returned to the office, they entered the data onto data sheets onto a computer that has a good security system in place including passwords and a firewall. Data sheets are backed up on Google Drive. More than one team member has access to the data so it remains accessible in case someone leaves the team unexpectedly.

To maintain quality control consistent methods were be used at each site. Researchers will measure the completeness if any data is found to be invalid (Holmes et al., 2021). They will ensure it is comparable and is a representative data set by documenting variabilities (Holmes et al., 2021).