Vegetation trends in pinyon-juniper woodlands in Southern Colorado Plateau Network parks
Swan M . 2025. Vegetation trends in pinyon-juniper woodlands in Southern Colorado Plateau Network parks. Science Report. NPS/SR—2025/307. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/2312771
The Southern Colorado Plateau Network has monitored vegetation and soils in pinyon-juniper woodlands at Bandelier National Monument (BAND), Grand Canyon National Park (GRCA), and Mesa Verde National Park (MEVE) since 2007. This report analyzes 15 years of data on site characteristics and changes in selected indicators. Overall, MEVE and GRCA exhibited similar conditions in Pinyon-Juniper woodlands, with sparsely vegetated understories and dense canopies dominated by Utah juniper (Juniperus osteosperma) and two-needle pinyon pine (Pinus edulis). In contrast, BAND had a more diverse understory with a greater variety of forb and shrub species, and a less dense overstory primarily of one-seed juniper (Juniperus monosperma). Seedling and sapling presence was noted at all sites but was least common at BAND. Soils differed in texture, development, and depth across parks. Aggregate stability was generally moderate across all sites. While plant species richness was generally low, it was highest at BAND. Nonnative plants were uncommon except for cheatgrass (Bromus tectorum), which had up to 40% cover at some BAND plots. Vegetation analysis revealed a pattern of stability and slight positive changes over the 15-year monitoring period. Species richness increased at all sites, and cover of shrubs and cactus/succulents rose at three out of four locations. However, exotic cheatgrass (Bromus tectorum) also increased significantly at BAND—averaging about 2% per year—while it slightly decreased at GRCA (< 1% annually). Climate variables influenced plant trends, with increasing water stress negatively impacting vegetation cover, particularly perennial grasses. Although tree mortality was generally low, it was highest for pinyons at GRCA. Limiting disturbance in pinyon-juniper woodlands to prevent the introduction of invasive grasses is recommended; stand thinning in old-growth woodlands designed to potentially increase drought resilience requires further study and is not recommended.
- Type
- Published Report
- Authors
- Swan, Megan
- Date of Issue
- 2025-06
- Publisher
- National Park Service
- DOI
- 10.36967/2312771
- Units
- BAND , GRCA , MEVE , NRSS , SCPN
- Keywords
- Bandelier National Monument, Grand Canyon National Park, Mesa Verde National Park, pinyon-juniper, SCPN, Southern Colorado Plateau Network, trend report, upland vegetation