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Ring width decreases with increasing VPD. VPD values are annual totals. Solid lines represent linear regression models with 95% confidence intervals (shaded colors). All slopes are significant: Southwest (SW), β = −2.985, P < 0.001; California (CA), β = −1.084, P < 0.001; southern Rockies (SR), β = −2.295, P < 0.001; central Rockies (CR), β = −0.8704, P = 0.023; northern Rockies (NR), β = −2.068, P < 0.001; Pacific Northwest (PNW), β = −0.994, P = 0.002.
