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Other Forestry and Forest Sciences | Plant Biology


Stephen Saupe


Wood density and wood volume determine the amount of carbon fixed by trees; however, while we are beginning to understand normal seasonal variation in wood density, anomalies are common, and their drivers are poorly understood. In conifers, wood density normally increases continuously throughout the season, but intra-annual fluctuations in wood density can occur and have been linked to climatic events. The causes of these fluctuations in density at the micro-scale (hereafter micro-density anomalies) are still debated.

Mesic regions are experiencing more droughts, but micro-density anomalies are rarely studied in these ecosystems. This study examined micro-density anomaly distribution within the boles of white pines (Pinus strobus) in central Massachusetts and its relationship with climate. We cored 41 white pines at (i) breast height (1.5m), (ii) near branches, (iii) and from the 2010 growth section. To determine if the timing of climatic variables impacted anomaly formation, we broke the growing season apart into early, mid, and late growing season. All of the trees had at least two micro-density anomalies. There was not a higher occurrence of micro-density anomalies near branches or in the 2010 growth section. Even in this temperate mesic ecosystem, anomaly formation was related to particular drought events. Micro-density anomalies coincided with low soil moisture in the early, mid, and late growing season as well as higher mid-season air temperature. It is unclear why the anomalies are uniformly distributed throughout the bole. Micro-density anomalies may be a physiological response to drought and may prevent embolisms from forming. Thus, with a better understanding of micro-density anomaly drivers we can anticipate how trees in mesic areas may react to drought.