Ecosystem Studies and Management
Understanding the Forest Carbon Cycle in Harvard Forest: Hemlock Removal Experiment
To explore the contribution of the components of soil respiration (root and microbial respiration), Center scientists participated in a girdling and logging experiment at the Harvard forest. By measuring soil respiration in controlled plots, along with treatments plots, more will be learned about the relative contribution of root and microbial respiration from the difference in measurements between control and treatments.
Methods and Measurements
Two treatments, girdled and logged, were applied to two hemlock stands at the Harvard forest. The first treatment was a girdling treatment. All hemlock trees with dbh>5cm where girdled by cutting into the tree trunk through to the xylem (at breast height). This prevented the flow of substrate to roots. The second treatment was a logged treatment. All trees of economically usable size were harvested from the location. Slash piles were left in place. Both the girdled and logged treatments were conducted during the winter of 2004. Six soil respiration collars were randomly placed at each of the treatments (n=36). Soil respiration was measured, using the manual method, on a weekly to bi monthly basis from early spring to early fall between the hours of 9am to 3pm. Soil temperature (Type T thermocouple) at 10cm depth and soil moisture (Campbell Scientific Hydrosense moisture sensor) was measured concurrently to Sr measurements.
On left - Logged plot, on right - A girdled hemlock tree. Girdling effectively cuts the supply of carbohydrates between the tree roots and aboveground.
Results:
• The seasonal total soil respiration in the girdled and logged plots declined after treatment, likely a result of loss of the root respiration component of soil respiration.
• Four years after logging, soil respiration increased in the logged plots to levels similar to that observed in the control plots, this is likely due to the increase in shrubs in the logged plots reading as root respiration component to the measured soil respiration rates
• Soil respiration rates from the girdled plot did not appear to show significant decline in rates until 3 years after girdling.
