Manuscript Title: Slow Lifelong Growth Predisposes Populus Tremuloidestrees to Mortality

Manuscript Title:Slow Lifelong Growth Predisposes Populus tremuloidesTrees to Mortality

Authors: Kathryn B. Ireland, Margaret M. Moore, Peter Z. Fulé, Thomas J. Zegler, and Robert E. Keane

Corresponding Author: Kathryn B. Ireland, Email:, Phone: 801-718-9497/fax: 406-994-3190

Appendix S2. Overstory aspen mortality by forest type.

We used one-way analysis of variance (ANOVA) to testfor differences in percent overstory aspen mortality by both basal area (BA m2 ha-1) and, separately, by trees per hectare (TPH; tree ha-1), among forest types, using the R Statistical Package version 2.1.5.2 (R Development Core Team 2012). We also tested for differences in live conifer BA among forest types using a one-way ANOVA. Since competition with other aspen stems could also account for differences in mortality among forest types, we also tested for differences in live aspen BA among forest types using one-way ANOVA.

Overstory aspen mortality was higher in lower elevation PIPO-type and PIPO/PSME-type forests than in the highest elevation, more mesic PSME/ABCO-type forests. Aspen mortality was statistically different among forest types by both BA (df = 2, 11; F = 5.97; p = 0.02) and by TPH (df = 2, 11; F = 5.14; p = 0.02). The lowest elevation PIPO-type forests had higher mortality than the highest elevation PSME/ABCO-type forests, for both overstory aspen mortality by BA and by TPH (Fig. 1). Aspen overstory mortality was not different between any other pairwise comparisons of forest types.

Live conifer BA did not differ by forest type, but live aspen BA increased in higher elevation, more mesic forest types. We found no statistically significant differences in conifer BA (df = 2, 11; F = 1.50; p = 0.27) among forest types. However, forest types had significantly different levels of aspen BA (df = 2, 11; F = 16.42, p = 0.0004). The highest elevation PSME/ABCO-type forests had the highest aspen BA (33.6 m2 ha-1), followed by the mid-elevation PIPO/PSME-type forests (13.4 m2 ha-1) and low elevation PIPO-type forests (3.8 m2 ha-1). The PSME/ABCO-type forests had significantly higher aspen BA than both the PIPO/PSME-type forests (Bonferonni-corrected p = 0.0067) and the PIPO-type forests (p = 0.0005), but the PIPO-type and PIPO/PSME-type forests were not significantly different from one another (p = 0.31).

Figure 1. Differences between overstory aspen mortality (mean ± SE) by a) percent basal area and b) trees per hectare among forest types. Asterisks indicate significant differences in Bonferonni-adjusted p-values (α=0.05).