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Harvard Forest Symposium Abstract 2007

  • Title: Community and Ecosystem effects of hemlock logging
  • Primary Author: David Orwig (Harvard Forest)
  • Additional Authors: Laura Barbash (Harvard Forest); David Foster (Harvard University); Heidi Lux (Harvard Forest)
  • Abstract:

    The recent unimpeded infestation of the hemlock woolly adelgid (HWA; Adelges tsugae Annand) across the northeastern U.S. has created a situation in which large-scale hemlock decline and mortality is occurring. HWA has already infested over 40% of the towns in Massachusetts and, as a result, many landowners are choosing to pre-emptively harvest their hemlock stands. Information from timber harvesters, state agencies, and studies of landscape patterns of hemlock decline in southern New England indicate that the recent broad scale increase in logging associated with HWA is occurring with little ecological assessment and in the absence of scientific background for conservationists, land managers, or policy makers.



    We are continuing our efforts to compare the impacts of hemlock logging with the impacts of HWA infestation on the magnitude and trajectory of community and ecosystem dynamics. Ten sites were selected for intensive study throughout central Massachusetts on public and private lands where hemlocks were harvested between 1 – 12 years ago. Forty-two to Ninety-seven percent of hemlock stems and basal area were removed from these sites. Sapling densities of 10,500 to 24,000 stems ha-1 dominated the vegetation at older cuts and consisted primarily of Betula lenta, Acer rubrum, and Pinus strobus. Seedling densities averaged 5 m-2 across sites, peaked at 20 m-2 at 6 to 9 year old sites, and consisted of Tsuga canadensis, B. lenta, and A. rubrum. Additional understory species that were common in cuts sites included various Rubus species, often averaging 30% cover, Dennstaedtia punctilobula, Aralia hispida, and Carex species.



    Harvesting resulted in soils that were 3 to 5 (oC) warmer and tended to be drier in recent vs. older cuts. Net nitrogen mineralization rates in organic soils averaged just over 10 kg N ha-1yr-1 in recent cuts and approx. 5 kg N ha-1yr-1 in older cuts. Mineral soil net mineralization rates were lower among all cuts, ranging from 2.1 to 3.5 ha-1yr-1. Nitrification rates were low in both soil horizons at all harvest ages. Recent cuts had much higher nitrogen capture (NH4 + NO3) on resin bags averaging around 1200 μg N g resin-1 vs. 300 to 600 μg N g resin-1 captured in older cuts.



    Findings from this study corroborate past work, as cutting resulted in high birch and maple establishment and higher N availability in recent cuts. In contrast to prior studies, cutting in Massachusetts sites also led to abundant conifer regeneration of P. strobus and T. canadensis, suggesting that seed tree availability, seedbed characteristics, and lack of HWA at most sites cut in MA contributed to the higher densities found in this study. In addition, nitrification rates and nitrate capture on resin bags were lower in Massachusetts sites than those reported on sites with a long history of HWA that were then subsequently logged. Findings have been incorporated into outreach pamphlets and scientific papers to help aid management decisions, and will continue to help shape decision-making in the larger framework of examining the various ecological consequences and changes in ecosystem services associated with a variety of press and pulse disturbances in forests, including introduced pests and pathogens.

  • Research Category: Invasive Plants, Pests & Pathogens