Moisture deficits limit growth of white spruce in the west-central boreal forest of North America.

• Climate change may cause reduced forest productivity and higher tree mortality. • We infer white spruce growth limitations from 9795 tree cores from 227 sample sites. • Water deficits make trees vulnerable to climate change in its west-central range. • Future climate projections imply water deficits in the southwest and central boreal. • The north-east may be a climate change refugium due to lack of water deficits. Climate change may cause reduced forest productivity and higher tree mortality due to water deficits that result from increased evapotranspiration. Such limitations may occur in some areas of the North American boreal forest where precipitation is low and warming trends are high. This paper analyzes climatic factors that limit the growth of a commercially important and widespread boreal tree species, white spruce (Picea glauca (Moench) Voss), based on a range-wide dendroclimatological analysis of 9795 trees from 227 sample sites across the North American boreal forest. A bootstrapped response function analysis was conducted for monthly temperature and precipitation variables, and a multivariate regression tree analysis was used to group white spruce populations with similar response coefficients where climatic factors explained 46% of the total variance in response coefficients. The results of this study show that white spruce populations in the west-central boreal forest of North America are the most precipitation-limited group and therefore likely to be most susceptible to climate change. Populations both to the north and south of this group appear less vulnerable, and eastern populations generally do not experience growth-limiting moisture deficits. Regional climate change projections suggest that moisture limitations will become more pronounced in the future, especially for southwest and west-central boreal tree populations. [ABSTRACT FROM AUTHOR]