Status and trends in grassland vegetation at Chaco Culture National Historical Park: Upland vegetation and soils monitoring 2007–2018

Swan MC. 2022. Status and trends in grassland vegetation at Chaco Culture National Historical Park: Upland vegetation and soils monitoring 2007–2018. Natural Resource Report. NPS/SCPN/NRR—2022/2348. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/nrr-2288660

This report presents results of upland vegetation and soil monitoring at Chaco Culture National Historical Park (CHCU) by the Southern Colorado Plateau Inventory and Monitoring Network (SCPN) from 2007–2018. Crews collected data on composition and abundance of vegetation, both at the species level and by growth form (e.g., perennial grass, shrub, forb, soil aggregate stability, and soil texture at 30 plots within a target grassland community delineated using NRCS ecological site (ecosite) classification. From 2007–2018, SCPN crews identified 67 plant species. The ecosite was dominated by warm-season grasses, which comprised about three-quarters of the total cover of vegetation. Shrubs and forbs were a small component of total vegetation cover but were present in all plots monitored. Less than 4% of species detected were nonnative. Russian thistle (Salsola tragus), cheatgrass (Bromus tectorum) and kiss-me-quick (Portulaca oleracea) were the three nonnative species detected. Nonnative plant frequency varied from year to year and cover was very low. We did not detect any species of plants new to the park during monitoring. Soils in the sandy loam upland ecosite were generally deep and somewhat coarse-textured, although some plots had more clayey-textured horizons, especially in deeper layers. Undifferentiated soil crust comprised the largest component of the soil surface. Cover of biological soil crust (cyanobacteria, lichen and moss) was low. Soil aggregate stability was moderate. Models revealed that temporal trends for most responses were weak or absent, implying that resources did not show directional change over time other than those explained by precipitation covariates. There was evidence of a decreasing trend in species richness (0.25 species per year), however this may be due to the dry conditions we’ve encountered during sampling years since 2012 and warrants further examination. Spring season precipitation had the strongest positive effect on total foliar cover in these grasslands, as well as on the cover of the two dominant grass species. Nearly all the vegetation metrics we modeled increased with increasing spring precipitation. Grassland vegetation dependence on spring precipitation at CHCU is in agreement with another recent study (Andrews et al. 2019). This is a cause for concern given predictions of decreased spring precipitation and increased spring temperatures expected at CHCU in the coming decades (Monahan and Fisichelli, 2014, Andrews et al. 2019). Increasing drought stress in the spring months will almost certainly have a negative effect on the foliar cover of dominant species in these grasslands and could have wide-ranging implications including mortality and/or a shift in the species that these areas support.

Type
Published Report
Authors
Swan, Megan
Date of Issue
2022-01
Publisher
National Park Service
DOI
10.36967/nrr-2288660
Units
CHCU , NRSS , SCPN
Keywords
Bayesian hierarchical modeling, climate, covariates, Grasslands, invasive species, soil stability, soils, trend, upland vegetation
Subjects
Ecological Framework: Air and Climate | Weather and Climate | Weather and Climate , Ecological Framework: Geology and Soils | Soil Quality | Soil Function and Dynamics , Ecological Framework: Biological Integrity | Invasive Species | Invasive/Exotic animals , Ecological Framework: Biological Integrity | Focal Species or Communities | Grassland/Herbaceous Communities

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