PLJV Expands Woody Encroachment Study

A recent Audubon North American Grasslands and Birds report highlights the need to not only protect our remaining grasslands but also to prioritize and direct our conservation efforts to areas that will support grassland birds now and into the future. Within the PLJV, one of the best ways we can do that is to remove invasive woody shrubs. While this issue affects all North American rangelands, short- and mixed-grass prairies are particularly hard hit, and woody species encroachment is of top concern for many conservation partners and landowners. To help us be more effective, PLJV uses the Integrated Monitoring in Bird Conservation Regions (IMBCR) program to learn where to focus our work.

“IMBCR is a very adaptive program which helps PLJV answer management questions about grassland bird habitat and target our conservation delivery work while continuing to collect bird monitoring data,” explains PLJV Biologist Kyle Taylor. “Before each sampling season, we poll our partners to learn what are the most pressing management questions for landbirds in the western Great Plains and then align about a third of our monitoring work to answer those questions through off-year studies.”

Annualized rate of change for mesquite and eastern redcedar across the PLJV region from 2003-2017 NAIP imagery. Darker colors are decreases in woody species occupancy. Lighter colors are increases in woody species occupancy. Click to enlarge.

This past spring was the first season PLJV used IMBCR to look at woody encroachment by sampling birds in mesquite hotspots within New Mexico, Texas, and Oklahoma. The first step was to map mesquite and eastern redcedar encroachment over the last 15 years using high-resolution satellite imagery from USDA Natural Resources Conservation Service and Farm Service Agency. The figure to the right demonstrates mesquite and eastern redcedar encroachment hotspots across the PLJV region using landscape models fit to both species from 2003-2017.

We then sent crews out to sample birds in grasslands experiencing low, medium, or high rates of mesquite encroachment to assess canopy thresholds that lead to changes in grassland bird communities. As part of the 2019 study, we also partnered with Texas Parks and Wildlife to launch IMBCR sampling at the Matador Wildlife Management Area, tracking the efficacy of long-term mesquite removal and how grassland planting efforts influence abundance for Northern Bobwhite and other grassland birds. The data from these efforts are being analyzed with results available later this fall.

In 2020, PLJV will expand the woody encroachment study to include grasslands affected by eastern redcedar in Oklahoma, Kansas, and Nebraska. Similar to the 2019 mesquite study, we will send crews out to measure grassland bird densities across a gradient of woody encroachment levels in shortgrass and mixed-grass prairie. Using the data from the two studies and the land cover modeling, we will be able to predict how grassland bird communities change across the region and determine areas of high priority for shrub management.

From our 2019 land cover modeling work, we observed roughly 700,000 acres of grassland adjacent to woodlands and forests experiencing the early stages of woody encroachment in each state. For common grassland birds experiencing steep declines that have been tracked with IMBCR, such as Eastern Meadowlark, we estimate that treating encroached grasslands on an annual basis would result in a habitat capacity increase of 26,960 individuals per year.

According to Taylor, “By aligning local, project-scale bird sampling with large-scale monitoring efforts, we will be able to provide refined targeting tools showing where eastern redcedar is — and how effective specific treatments are at removing it — to our partners who are on the front lines of dealing with eastern redcedar encroachment.”

Photo credit: Mesquite and juniper encroachment (Jill Wussow/BCR).

Posted: October 13, 2019