Historical Tree Species Height Growth Pattern Associated With Climate Change in Western North America

BackgroundThe climate variables effect on tree growth in boreal and temperate forests has received increased interest in the global context of climate change. However, most studies are geographically limited and involved few tree species. Here, sixteen tree species across western North America were used to investigate tree response to climate change at the species range scale. MethodsForest inventory data from 36,944 stands established between 1600 and 1968 throughout western Canada and USA were summarized. Height growth (total height at breast-height age of 50 years) of healthy dominant and co-dominant trees were related to annual and summer temperatures, annual and summer Palmer Drought Severity Index (PDSI, and tree establishment date (ED). Climate-induced height growth patterns were then tested to determine links to spatial environment (soil conditions and geographic locations), species range (coastal, interior, and both ranges) and species traits (shade tolerance and leaf form), using linear mixed model for the global height growth and general linear model to test the height growth patterns for each species. ResultsIncrease of temperatures and PDSI had a positive effect on height growth for most of the study species, whereas Alaska yellow-cedar (Chamaecyparis nootkatensis, (D. Don) Spach) height growth declined with ED. All explaining variables and the interactions explained 59% of the total height growth variance. Although tree height growth response was species-specific, increased height growth during the 20th century was more pronounced for coastal ranged species, high shade tolerant species, and broadleaf species. Furthermore, height growth increase occurred mostly on rich soil, at the northernmost species range, and, unexpectedly, at lower elevations. A decline in height growth for some species further north and especially higher in elevation possibly related to increased cloudiness and precipitation. However, drought conditions remain in interior areas despite moving northward and upward that decrease height growth. ConclusionThese results highlight the general trend (species characteristics and range) and the species-specific height patterns, indicating the spatio-temporal complexity of the growth response to recent global climate change.