Dendroecological analysis of frost ring occurrence in jack pine (Pinus banksiana) across northern lower Michigan

Background/Question/Methods

Frost rings are abnormal anatomical features in wood that result from abrupt sub-freezing temperatures subsequent to consecutive days of warm temperatures during the growing season.  Identification of factors influencing the frequency and spatial distribution of frost rings is essential to their use as a proxy in climate reconstructions.  This study was aimed to 1) quantify the frequency and timing of frost ring formation in jack pine; 2) verify that frost rings in the earlywood were in response to early growing season frost; and 3) contrast the influence of tree diameter, cambial age, and spatial location relative to temperature-moderating landforms such as Lake Michigan and Lake Huron on frost ring formation.  Two increment cores were extracted from a minimum of twenty-four trees at twelve sites.  Sites were selected to equally represent interior and exterior jack pine communities in the northern lower peninsula of Michigan.  Cores were visually cross-dated and measured using a LinTab™ 5 measuring system.  Visual cross-dating was validated using COFECHA software, and tree-ring chronologies were developed for each site in ARSTAN.  Frost ring features were located and dated.  Radial distance from pith and age at which each frost ring occurred was determined.

Results/Conclusions

Simple linear regression verified frost ring occurrence was highly correlated with abrupt sub-freezing temperatures during the early growing season (May) at each site.  Frost ring occurrence varied across radial distance and cambial age class for all sites combined.  Results indicate diameter and cambial age may significantly influence frost ring formation.  These results agree with previous research that indicates stems with a greater diameter are less likely to exhibit frost damage.  This may be attributed to increased bark thickness in older, large diameter stems.  Interior sites experienced a greater number of early growing season frosts and were marked with a later date in the growing season at which the last sub-freezing temperature occurred.  Thus, frequency of frost ring formation was greater for interior than exterior sites.  Lake Huron and Lake Michigan modified early growing season temperatures enough to reduce early growing season frost damage.  Frost rings may demonstrate the physiological consequences of premature bud burst and xylem formation in response to milder winters and warmer spring conditions associated with climate change.  This study illustrates the importance of considering biological factors along with spatial information relative to landforms when assessing the effects of climate change.