Implications of Future Climate Extremes for Red Spruce

This study aimed to better understand the impact of extreme weather on red spruce, a crucial species in northern forests. Researchers conducted two experiments to assess red spruce's responses to water stress and thinning, and to explore the implications in the context of climate change.

Key Findings 

• Red spruce exhibits initial resistance to extreme water stress, but sustained drought conditions lead to long-term tree declines.
• Thinning, a common forestry practice, results in abrupt changes in microclimate that can temporarily negatively affect the remaining trees. Climate change may amplify these effects.
• Adaptive management practices should consider both soil and atmospheric conditions to minimize overall climate stress on red spruce trees.
• Targeted thinning strategies, emphasizing the retention of healthy upper canopy trees, can contribute to reducing the impact of thinning on forest ecosystems and promote climate resilience. 

Photo Credit

Maddie Eberly

Student Kelly French downloading red spruce sap flow data from a data logger.

In the first experiment, taking place within a red spruce stand of the University of Maine’s Dwight B. Demeritt Forest, scientists simulated drought conditions by girdling live red spruce trees, essentially blocking the transport of water. The girdled trees initially resisted water stress, but as the stress continued, it led to a decline in the trees’ health. This finding indicates that persistent drought conditions that may occur with climate change could result in long-term declines for red spruce trees.

The second experiment focused on thinning, a common forestry practice aimed at reducing tree density and enhancing resilience by making more resources like light and water available to the remaining trees. However, thinning also leads to changes in the immediate microclimate and can induce a phenomenon known as thinning shock. Thinning shock occurs when trees have a negative response to abrupt changes caused by thinning activities. 

To investigate thinning's effects on tree function, researchers attached sensors to trees and monitored them before and after thinning. They discovered that shade-grown red spruce trees experienced hotter and drier microclimatic conditions after thinning, which temporarily reduced their ability to photosynthesize and acquire carbon. While this effect was temporary, it highlights the potential significance of thinning shock in hotter and drier climates.

These findings underscore the need to retain vigorous, upper-canopy trees when conducting thinnings, rather than suppressed lower-canopy trees for which microclimate will change more after release.