Year of Award


Document Type

Thesis - Campus Access Only

Degree Type

Master of Science (MS)

Degree Name


Department or School/College

Department of Geosciences

Committee Chair

Marco Maneta

Commitee Members

Solomon Dobrowski, Andrew Wilcox, Zach Holden


hydrology, ecohydrology, mortality, plant hydraulics


University of Montana

Subject Categories



Drought influences the extent of forests through large-scale die-offs and reductions of seedling recruitment and survival. We examined the spatial distribution of drought stress in seedlings to evaluate its influence on regeneration at the lower treeline in the northern Rockies. We used a novel ecohydrologic model (Ech2o-SPAC) combined with a vegetation dynamic stress index that incorporates intensity, duration, and frequency of stress, to examine mortality from loss of hydraulic conductivity in Pinus ponderosa seedlings. We calibrated our model using a glasshouse drought experiment; tested our model using in situ monitoring data on seedling mortality from reforestation efforts; and simulated high-resolution drought stress in seedlings within the Bitterroot River watershed of western Montana. Our model successfully simulated drought responses and mortality of seedlings in the glasshouse and within monitored stands. Low elevation, south-facing, non-convergent locations with high atmospheric demand and limited upslope water subsidies experienced the highest rates of modeled mortality in our study watershed. Modeled drought mortality in seedlings from 2001-2015 correlated tightly with the current distribution of forest cover near the lower treeline, suggesting that drought limits recruitment and ultimately constrains the low elevation extent of conifer forests within the region.

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