Previous models of understory loss as pinyon and juniper tree cover increases indicated that perennial herbaceous loss precedes that of shrubs. On 10 western or Utah juniper and one or two needle pinyon pine sites across the Great Basin, we found that shrub cover was more sensitive to tree infilling than perennial herbaceous cover. Shrub cover was decreased to 50% of maximum when tree dominance (tree cover/ (tree + shrub + tall grass cover) exceeded 0.25, while perennial herbaceous cover decreased to 50% of maximum when tree dominance exceeded 0.5. Additional soil moisture from tree reduction, even 8 years after treatment, supported increases in both desirable and weedy understory cover. Six years after treatment, shrub cover averaged 4% on burned and 14% on tree cut plots compared to 7.8% on untreated plots. Tall grass cover averaged 16% on burn plots, 23% on tree-cut plots, and 12% on untreated plots. Cheatgrass cover was highest on burned plots at high initial tree dominance (9.6-14% cover at 0.65-1 initial tree dominance). Perennial herbaceous cover responded best to tree cutting even at high initial tree dominance (38 to 33.8% cover at 0 to 1 initial tree dominance). Perennial grass cover is a key component in these systems in avoiding the crossing of a biotic threshold by reducing weed dominance and avoiding crossing of an abiotic threshold by reducing interspace erosion. Continued monitoring will be important in determining if perennial bunchgrasses will dominate and suppress cover of cheatgrass over time.
Oral presentation and poster titles, abstracts, and authors from the Society for Range Management (SRM) Annual Meetings and Tradeshows, from 2013 forward.