Appendix S1. Average annual basal area increment (BAI) of old (>150; = 25) and young (<50; n = 11) Pinus hartwegii (Ph) (top panel) and Abies religiosa (Ar) (bottom panel) trees. Old trees are shown in the main panel and young trees in the top left panel, where lines represent a second order fitted curve. Equations for young trees are: Pinus y = −0.1336x2 + 531.21x – 527920 R2 = 0.72; Abies y = −0.0429x2 + 171.08x − 170 491 R2 = 0.37.

Appendix S2. Correlation between estimated source to product fractionation (∆13C) and tree ring δ18O at all study sites. Only Abies religiosa (Ar) trees at the Nevado de Toluca (NT) site (Fig. 1), the relationship between these variables was significant.

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