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Harvard Forest Symposium Abstract 2016

• Title: Black birch dynamics following hemlock removal on Hemlock Hill at the Arnold Arboretum
• Primary Author: David Orwig (Harvard Forest)
• Additional Authors: Peter Del Tredici (100th EN Co)
• Abstract:

  Hemlock woolly adelgid (HWA; Adelges tsugae) was discovered on hemlock (Tsuga canadensis) trees growing on Hemlock Hill at the Arnold Arboretum after a significant winter storm in 1997. Because Hemlock Hill is well loved and frequently visited, as study was initiated to study vegetation and ecosystem responses to removal of adelgid-infested hemlocks in this urban park setting. In 2004, six 15 x 15 m plots were fenced off, and baseline data on soil nutrient cycling, microclimate, and vegetation composition was collected. Hemlocks were removed from four plots in February of 2005, while two remained uncut, as control plots. These unlogged plots continue to be infested with HWA and have thinning crowns, but survive due to continued chemical treatment by Arboretum staff. Slash was chipped and left on site in two chipped treatment plots, or removed from two logged (only) treatment plots. This series of treatments coincided in time with Harvard Forest’s Hemlock Removal Experiment at the Simes tract, in rural Petersham, where data continues to be collected. Results of ecosystem function and vegetation changes during the first 3 years following hemlock removal have previously been reported. A decade after cutting, we re-visited Hemlock Hill to conduct follow-up sapling counts. Black birch (Betula lenta) dominated the vegetation across all treatments, accounting for 75% of all stems > 1 cm dbh. Other common sapling species included black cherry (Prunus serotina) and glossy buckthorn (Frangula alnus). In only ten years since complete overstory removal of hemlock, mean sapling densities ranged from 2, 266 to 4,178 stems ha-1 and basal area has recovered to 8 – 12 m2ha-1 (Figure 1). Mean sapling diameters ranged from 5-5.45 cm in logged plots compared to 1.74 cm in unlogged plots. Median black birch heights in logged plots were 8.5 to 9 m, much taller than birch heights of identical age at the Simes logged plots (3-5m). Differences are likely attributed to higher nitrogen availability, warmer microclimate, and soil differences. We will continue to examine and compare long-term vegetation dynamics in these urban and rural hemlock removal plots.

• Research Category: Invasive Plants, Pests & Pathogens
  Large Experiments and Permanent Plot Studies


• Figures:
Hemlock Hill logging photos.docx