Habitat Changes Across a Forest-Steppe Ecotone in Central Montana

Abstract

Woody encroachment, the expansion of woody vegetation into open range/cropland, is caused by a variety of factors, including lack of disturbance. At our central Montana site, Douglas Fir (Pseudotsuga menziesii), Ponderosa Pine (Pinus ponderosa), and Rocky Mountain Juniper (Juniperus scopulorum) encroach into the montane sagebrush steppe. The long-term effects of woody encroachment are not fully understood in many regions. By examining the relationship between woody encroachment and ground cover vegetation, we can examine habitat dynamics within a changing climate. Our objective is to establish preliminary data at our Canyon Creek site and examine changes in percent cover and tree canopy density over an ecotone transition transect. Historical aerial imagery was used to determine the study site by showing locations of woody encroachment over the past decades. We surveyed a 150-meter transect across the forest-steppe ecotone with sample points at randomized distances on either side. At each point, we conducted a visual estimate of percent cover, broken into cover classes by functional group. Camera traps were used to survey wildlife use. Data showed a high abundance of litter (mean = 69.6%, sd = 30.9%), high visual obstruction (mean = 34.1 cm, sd = 36.3 cm), and a lack of sagebrush (mean = 1.5%, sd = 0.7%) under the forested area. Percent cover grass (-3.2%) and forbs (-6.1%) decreased under the forested area. Results from this study will inform management decisions and further understanding of woody encroachment’s long-term impact on understory vegetation.