Forest composition influences how seasonal climate variables affect white spruce (Picea glauca (Moench) Voss) growth

Variation in annual white spruce growth (Picea glauca (Moench) Voss) has been shown to be dependent on weather conditions such as air temperature and moisture availability. However, questions remain about how intra-annual variation in climate variables influence annual growth, and whether stand composition and structure can influence climate conditions and the trees’ responses to weather stress. We evaluated the importance and influence of seasonal climate on growth (annual ring width increment) of 32-year-old white spruce trees in pure and mixedwood stands in northeastern British Columbia. The importance of climate variables, and their ranked order, differed between pure and mixedwood stands. Soil water potential (SWP) during spring and summer were the main factors influencing spruce growing in both pure and mixedwood stands. However, the relative importance of each variable, their direct effects, and their interactions differed between stand types. Warm springs increased spruce growth in both stands, while warm summers increased spruce growth in the pure spruce stand but decreased growth in the mixedwood stand. Spruce growth in the pure stand was positively correlated with soil water potential during spring and summer, while spruce growth in the mixedwood stand was negatively correlated. In both stand types, there was an interplay between the amount of water available in the soil and air temperature to influence annual growth. Our findings suggest stand composition influences the resilience of spruce to drought.