A process-based approach to estimate lodgepole pine (Pinus contorta Dougl.) distribution in the Pacific Northwest under climate change

Coops, Nicholas; Waring, Richard

Lodgepole pine (Pinus contorta Dougl.) is a widely distributed species inthe Pacific Northwest of North America. The extent that the current distribution ofthis species may be altered under a changing climate is an important question formanagers of wood supply as well as those interested in conservation of subalpineecosystems. In this paper, we address the question, how much might the currentrange of the species shift under a changing climate? We first assessed the extent thatsuboptimal temperature, frost, drought, and humidity deficits affect photosynthesisand growth of the species across the Pacific Northwest with a process-based model(3-PG). We then entered the same set of climatic variables into a decision-treemodel, which creates a suite of rules that differentially rank the variables, to providea basis for predicting presence or absence of the species under current climaticconditions. The derived decision-tree model successfully predicted weighted presenceand absence recorded on 12,660 field survey plots with an accuracy of ∼70%.The analysis indicated that sites with significant spring frost, summer temperaturesaveraging <15◦C and soils that fully recharged from snowmelt were most likely tosupport lodgepole pine. Based on these criteria, we projected climatic conditionsthrough the twenty-first century as they might develop without additional efforts toreduce carbon emissions using the Canadian Climate Centremodel (CGCM2). In the30-year period centered around 2020, the area suitable for lodgepole pine in thePacific Northwest was projected to be reduced only slightly (8%). Thereafter, however,the projected climatic conditions appear to progressively favor other species, sothat by the last 30 years of twenty-first century, lodgepole pine could be nearly absentfrom much of its current range. We conclude that process-based models, because they are highly sensitive to seasonal variation in solar radiation, are well adapted toidentify the importance of different climatic variables on photosynthesis and growth.These same variables, once indentified, and run through a decision-tree model,provide a reasonable approach to predict current and future patterns in a species’distribution.

A process-based approach to estimate lodgepole pine (Pinus contorta Dougl.) distribution in the Pacific Northwest under climate change

Series

Collections