Physiological Constraints of Assisted Migration of Coast Redwoods (Sequoia Sempervirens) to Washington’s Western Cascade Region

Abstract

There is broad interest in moving the iconic Sequoia sempervirens (D. Don) Endl. to western Washington to assist in the climate pressured species’ habitat shift northward as well as provide cultural, ecological, carbon, and timber value. This research investigates the ecophysiological constraints of young redwoods in comparison with native species, Pseudotsuga menziesii (Mirb.) Franco and Thuja plicata (Donn.) through testing of S. sempervirens cultivars under controlled greenhouse drought conditions and across a soil moisture gradient in a field study outside of its native range. In the drought trial, measurement of photosynthetic capacity (Fv/Fm) as a stress metric, water potential, growth investments and survival show that S. sempervirens had similar or better drought response than native P. menziesii and consistently better than T. plicata. S. sempervirens cultivars showed similar levels of drought response, surviving almost 2 months of drought conditions, though a select few cultivars had early stress and mortality in the drought. In field conditions, S. sempervirens had a lower mortality rate (23% post establishment) than native, but nursery stock affected, P. menziesii (27.97% post establishment). A majority (10/16) of S. sempervirens cultivars also showed similar levels of vigor, while the remaining 6/16 demonstrated significantly lower vigor 10 months after planting. S. sempervirens cultivar performance in the greenhouse and field trial differ enough to suggest that greenhouse drought tolerance is not a predictor of successful S. sempervirens cultivar selection in Washington field conditions (p=0.342). While there is much left to understand about S. sempervirens ecophysiological limitations, assisted migration of S. sempervirens to western cascade region of Washington could be a feasible strategy to provide ecological and economic security to Washington forests.