RESEARCH

The effects of climate change on tree phenology and competition dynamics
 
Adaptive carbon assimilation strategies in response to climate change
Relationship between drought- and shade-induced carbon starvation
Forest and climate change ecology

Canopy photo taken from one of my plots at the E.S. George Reserve near Pinckney, MI

Conducting a phenology census in Saginaw Forest

(Photo courtesy of Dave Brenner)

Shifts in foliar phenology of temperate tree seedlings in response to climate change
 

The relationship between climate change and northern temperate tree foliar phenology (i.e. the timing of leaf out) is well-established. As canopy trees track climate, the timing of light availability in the understory therefore also changes. Understory plants in these forests have been shown to heavily rely on early Spring light availability before canopy leaf out in order to assimilate the vast majority (> 80%!) of their annual carbon budget and their access to high light availability will depend on whether or not they are able to track climate at the same rate as the canopy.

To investigate this dynamic, I have transplanted over 1,000 tree seedlings and measured their foliar phenology (in both Spring and Fall), their photosynthetic rates, and their growth and survival for the past four years. Preliminary results suggest that tree seedlings are more responsive to climate change than canopy trees and therefor they may  actually increase their annual carbon budgets during climate warming.

Sugar maple (Acer saccharum) and northern red oak (Quercus rubra) seedlings in the greenhouse dry-down and shading experiment.

Shade-induced versus drought-induced tree seedling mortality

As described above, one of the main ways shifts in foliar phenology may affect tree seedlings is by limiting spring carbon assimilation for late-leafing seedlings causing them to deplete their carbon stores in a process known as carbon starvation. In extreme cases, carbon starvation causes plant death when the plant is no longer able to maintain basic metabolic rates and/or is no longer able to maintain turgor pressure.

 

However, carbon starvation can also occur during periods of extended drought when plants close their stomata (small pores located on leaves where plants lose oxygen and intake carbon dioxide) to limit the rate of water loss. Closing the stomata cuts the plants off from carbon dioxide which prevents them from assimilating carbon using photosynthesis, causing them to rely on their carbon stores. In my second project, I focus on teasing apart these two causes of mortality using a greenhouse dry-down and shading experiment.

 

© 2019 Ben Lee