Process-Based Modeling to Assess the Effects of Recent Climatic Variation on Site Productivity and Forest Function across Western North America

This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by MDPI. The published article can be found at: http://www.mdpi.com/journal/forests.A process-based forest growth model, 3-PG (Physiological Principles Predicting\ud Growth), parameterized with values of soil properties constrained by satellite-derived\ud estimates of maximum leaf area index (LAI[subscript max]), was run for Douglas-fir (Pseudotsuga\ud menziesii) to contrast the extent to which site growth potential might vary across western\ud North America between a cool, wet period (1950–1975) and a more recent, generally\ud warmer and drier one (2000–2009). LAI[subscript max] represents a surrogate for overall site growth\ud potential, as demonstrated from a strong correlation between the two variables, with the\ud latter based on the culmination of mean annual increment estimates made at 3356\ud ground-based U.S. Forest Service survey plots across the states of Oregon and Washington.\ud Results indicate that since 2000, predicted LAI[subscript max] has decreased more than 20% in portions\ud of the Southwest USA and for much of the forested area in western Alberta. Similar\ud percentage increases in LAI[subscript max] were predicted for parts of British Columbia, Idaho and\ud Montana. The modeling analysis included an assessment of changes in seasonal constraints\ud on gross primary production (GPP). A general reduction in limitations caused by spring\ud frost occurred across the entire study area. This has led to a longer growing season, along\ud with notable increases in summer evaporative demand and soil drought for much of the\ud study area away from the maritime influence of the Pacific Ocean