Hemlock Removal Experiment - Community and Ecosystem Impacts

• Investigators: David Foster, Heidi Lux, David Orwig
• Contact: David Orwig
• Start date: 2003-08-05
• End date: ongoing
• Location: Simes Tract (Harvard Forest)
• Latitude: +42.47 to +42.48
• Longitude: -72.22 to -72.21
• Elevation: 200 to 240 meters
• Taxa: Adelgis tsugae (hemlock woolly adelgid), Betula lenta (black birch), Tsuga canadensis (eastern hemlock)
• Keywords: pest infestation, salvage logging, successional dynamics, tree mortality, Tsuga canadensis
• Abstract:

  Hemlock decline in New England is caused by direct and indirect effects of invasion of the hemlock woolly adelgid. Direct damage from the insect is causing gradual mortality of hemlock, and widespread harvesting of hemlock in advance of mortality creates a contrasting disturbance. Although both processes affect thousands of acres of forest annually, we have only a limited understanding of their effects on forest ecosystem function and productivity and the nature of the subsequent forest community. We anticipate that harvesting will yield different consequences than gradual mortality from the insect. Therefore we have designed an experiment to simulate the impact of both in order to contrast them. To simulate some of the effects of the adelgid (e.g., progressive mortality, retention of the wood on the site) we are girdling all hemlocks in a hemlock-dominated stand. In the adjacent area we are conducting a commercial harvesting of hemlock. Results from both experimental treatments will be compared to the changes observed in forests that are being infested by the adelgid, and can also be included in integrated analyses of a suite of large experiments that form a core component of the Harvard Forest LTER program.

• Methods:

  Nitrogen mineralization was measured using 4 closed-topped cores at each of eight 30 x 30 m plots. Sampling occurred at 5-week intervals during each growing season with one set of cores left over winter. An additional assessment of forest floor N availability and mobility was determined from mixed-bed cation + anion resin bags that were buried for 6-month intervals at the organic layer-mineral layer interface (ca. 5 cm) in each sampling plot. Soil temperature at 1 and 5 cm depths were measured at each soil sampling plot every 30 minutes throughout the growing season using iButton temperature data loggers.

  Soil samples were returned to the laboratory on ice and processed the next day. Organic and mineral soils were passed through a 5.0 mm mesh screen, weighed for total mass, and subsampled for gravimetric moisture and inorganic N. NH4-N and NO3-N were extracted from all soils using 1M KCl and from resin bags using 2M KCl and concentrations were determined colorimetrically with a Lachat flow-injection 8500 autoanalyzer.

  We determined the following properties of soils collected during our initial sampling at each site: organic matter by loss on ignition (5.5 hrs at 550 oC), pH in a soil and CaCl2 slurry (1:10 organic soil:solution; 1:4 mineral soil:solution), and total C and N content by dry combustion with our Fisons CHN autoanalyzer. Remaining organic and mineral soils were air-dried and stored in our sample archive.

• Related datasets: HF061