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Harvard Forest Symposium Abstract 2006

• Title: Dynamics of coarse woody debris in the hemlock removal study
• Primary Author: Audrey Barker Plotkin (Harvard Forest)
• Additional Authors: David Foster (Harvard University); Natalie Levy (University of California - Berkeley)
• Abstract:

  Eastern hemlock (Tsuga canadensis), a foundation species of eastern forests (Ellison et al. 2005), is declining as the hemlock woolly adelgid (Adelges tsugae, HWA) invades the northeast. This exotic insect pest kills hemlock trees; in addition, many landowners are cutting hemlock forests in response to their impending decline, creating another disturbance type as an indirect effect of the pest. In 2003, we began a large-scale experiment to simulate the effects of hemlock removal from the forest ecosystem by adelgid and by logging. There are two replicates (0.8 ha plots) of the following treatments: hemlock girdling (to simulate many of the effects of HWA), hemlock commercial logging (to simulate the preemptive logging that is occurring in hemlock forests in our region), hemlock control (no treatment), and hardwood control (representing a possible future composition of post-hemlock forest). Logging and girdling treatments were completed in winter and spring 2005, and we are now tracking the response of vegetation, microclimate, nutrient cycling, salamanders and ants to these manipulations.
  
  
  
  
  
  One obvious response to the manipulations is a large input of coarse woody debris (CWD). Dead wood plays a key role in forest carbon dynamics and provides habitat to numerous species of fauna. We established a dead wood study in all plots in Summer 2005 just after the girdling and logging were completed, so logging debris was captured but girdled trees were still living. We surveyed coarse downed wood, fine woody debris, standing snags and stumps. We will track volumes, mass, species and decay class over time in response to the manipulations.
  
  
  
  
  
  This baseline survey reflected the immediate response to the logging manipulation, and provided some insight into the stand history of the plots. Logged plots had a larger volume of stumps and CWD and fewer snags than the other plots (Table 1). The species composition of CWD in the logged plots roughly reflected the tree species composition prior to the harvest. CWD volume in the girdled and hemlock control plots ranged from 11 – 32 m3/ha. Except for plot 3, CWD composition was more hardwood-dominated than the current species composition, implying that hemlock was less important in these sites in the past. One of the hardwood control plots (plot 8) had a large volume of very decayed conifer wood, suggesting a past disturbance that significantly shifted species composition. Across the study area (excluding the logged plots), the density of large snags (>25 cm diameter) ranged from 28 – 62 stems/ha.
  
  
  
  
  
  We expect that the girdled plots will soon show a major input of snags and eventually downed dead wood, as the girdled hemlocks die. The girdled hemlocks showed a major decline in vigor only 5 months after girdling (October 2005 vigor survey). Fifty percent or more foliage loss was observed for 20-45% of the girdled trees, compared with 3-11% percent in the hemlock control plots. Five to 12 percent of the girdled hemlocks were already dead, and a few had snapped at the girdle. Bark beetles activity was noted on some of the girdled trees in Winter 2005-2006.
  
  
  
  
  
  We will continue to monitor death and decay of trees in this study, comparing among treatments and between this manipulative study and long-term plots in forests affected by HWA.
  
  
  

  
  
  
  Ellison, A. M., M. S. Bank, B. D. Clinton, E. A. Colburn, K. Elliott, C. R. Ford, D. R. Foster, B. D. Kloeppel, J. D. Knoepp, G. M. Lovett, J. Mohan, D. A. Orwig, N. L. Rodenhouse, W. V. Sobczak, K. A. Stinson, J. K. Stone, C. M. Swan, J. Thompson, B. von Holle, and J. R. Webster. 2005. Loss of foundation species: consequences for the structure and dynamics of forested ecosystems. Frontiers in Ecology and the Environment 9: 479-486.
  
  
  

• Research Category: Large Experiments and Permanent Plot Studies