General linear models (GLMs) were used to determine the
extent to which growth habit, moisture class, and flowering
season explain variance in root depth for the dataset as a whole
(n ¼ 125) and for each growth form group. Linear mixed models,
followed by Tukey’s pairwise comparisons, were used to test for
differences between specific plant groups (e.g., moisture groups)
while controlling accounting for effects of other factors (e.g.,
growth form). Only three of the woody species were exotic,
precluding statistical comparison with natives for this growth
form group. One outlier (53 m for Prosopis juliflora) was not
included in the statistical analysis. Root depths were square-root
transformed prior to analyses, which was conducted using
SYSTAT 13 software. Significance is set at a ¼ 0.05. Throughout,
plants with roots 0.5 m are referred to as shallow rooted, those
0.5e2 m as medium rooted, 2e5 m as deep rooted, and 5 m as
very deep rooted.