The effects of spruce decline and meteorology on radial growth within and beyond the native range of Picea pungens and P. glauca

Background/Question/Methods

Tree growth is closely tied to climate, and many species are now grown outside their native ranges in novel climates. How does living outside of the native range affect growth, and how does it interact with meteorology and disease to affect growth? Our objective was to assess the impact of spruce decline on radial growth and to correlate radial growth with monthly precipitation and temperature for two species in Michigan: Picea pungens, a landscape tree native to the Western United States, and P. glauca, a tree native to northern North America, including northern Michigan. For each species we looked at healthy trees, and trees exhibiting spruce decline. We studied one population of P. pungens in northern Michigan, and two populations of P. glauca, one in its native range in northern Michigan, and one outside of its native range in southern Michigan.

Results/Conclusions

We did not find significant differences in growth between disease classes. This could be due to low sample size or due to insufficient time for spruce decline to affect radial growth. However, we found significant differences in correlations with meteorology between disease classes and between sites, allowing us to generate hypotheses about the life cycle of the fungal pathogen that has been associated with spruce decline. For example, we found significantly negative correlations with spring precipitation for diseased P. glauca in southern Michigan, but significantly positive correlations with spring precipitation for healthy P. glauca in southern Michigan, suggesting that the pathogen benefits from spring precipitation in southern Michigan. However, in northern Michigan, we found positive correlations with spring precipitation for both species of diseased trees, but no correlations with spring precipitation for either species of healthy trees. In northern Michigan, we found significant negative correlations with January precipitation in diseased trees of both species, but no correlations with January precipitation in healthy trees of either species, suggesting that the pathogen may benefit from snow insulation-induced growth in northern Michigan. Our results suggest that trees respond differently to meteorology depending on disease status and their location relative to the native range. Disease may exacerbate abiotic stress induced by novel climates, or climate-related stress may increase the likelihood of disease.