Petrified Forest grasslands, status and trends: Vegetation and soils monitoring 2007–2018

Swan, Megan; McCoy, Lee; Norris, Jodi

This report presents results of upland vegetation and soil monitoring at Petrified Forest National Park (PEFO) 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 life form (e.g. perennial grass, shrub, forb), soil aggregate stability, and soil texture at 60 plots within two target grassland communities. The two communities were delineated using NRCS ecological site (ecosite) classifications and included clayey fan and sandy loam upland ecological sites. During the monitoring period, crews identified 165 plant species. Both ecosites were dominated by warm-season grasses, which comprised about three-quarters of the total cover of vegetation. Shrub cover was a small component of both ecosites, but cover was both greater and also more variable across sandy loam upland plots. Annual grasses were more common in the clayey fan ecosite. Less than 7% of the total species detected were nonnative. Russian thistle (Salsola tragus) was encountered most frequently, but frequency varied widely from year to year, occurring more commonly in the clayey fan ecosite. We detected seven species of plants new to the park during monitoring and added them to the park’s species list. Soils were generally deeper in the sandy loam ecosite, and contained less clay. Undifferentiated soil crust comprised the largest component of the soil surface. Cover of biological soil crust (cyanobacteria, lichen and moss) was low in both sites. Models revealed that temporal trends in indicator responses were weak or absent, implying that resources did not show directional change during the monitoring period. Soil aggregate stability was mid-range for both ecosites, but showed disparate trends, decreasing in the clayey fan and increasing in the sandy loam. Total foliar and perennial grass cover showed evidence of slight decreasing trends. There was evidence of increasing trend in species richness in both ecosites. Based on our results, we believe that the vegetation and soil in the monitored ecosites are in good condition. We did not detect strong trends in any category examined; species richness showed evidence of increasing over the period monitored; and there was low cover and frequency of nonnative species in both ecosites monitored.

Petrified Forest grasslands, status and trends: Vegetation and soils monitoring 2007–2018

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