Fig. 6
The change in tree dominance across the phases of pinyon and juniper expansion. In phase I, trees are present but shrubs and herbs are the dominant vegetation influencing ecological processes; in phase II, trees are codominant with shrubs and herbs and all three vegetation layers influence ecological processes; in phase III, trees are the dominant vegetation on the site and are the primary influence on ecological processes (Miller et al. 2005). The tree dominance index (TDI) is used as a quantitative measure of the relative dominance of pinyon and juniper based on the proportion of tree canopy cover to the summation of shrub and perennial grass (or herb) cover and is calculated as: tree cover / [tree + shrub + tall perennial grass cover]. Figure from Miller et al. (2019)