Database from forest inventory of the different states and provinces of western North America

The 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 often limited to local or regional
scales and involved a 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. Forest inventory databases from 36,944
stands established between1600 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 climate
variables (annual and summer temperature, annual and summer Palmer Drought
Severity Index) and tree establishment date (ED) using general linear
model. Climate-induced height growth patterns were then tested to
determine possible links to spatial environment (soil conditions and
geographic locations), species range (coastal, interior, and both ranges)
and species traits (shade tolerance and leaf form). Climate variables had
a positive effect on height growth for most of the study species, except
for a negative relationship of Alaska yellow-cedar height growth to ED.
All explaining variables and the interactions explained 57.2% of the total
species 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
higher in elevation possibly related to increased precipitation and
cloudiness, drought conditions in interior areas, or to the peculiarity of
western North America topography. These results highlight the spatial and
temporal complexity of the growth response patterns at the species range
to recent global climate change.