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Harvard Forest Symposium Abstract 2007
- Title: Ecosystem Responses to Forest Cutting After HWA Infestation: New insights from an urban site
- Primary Author: Heidi Lux (Harvard Forest)
- Additional Authors: Peter Del Tredici (100th EN Co); David Orwig (Harvard Forest)
- Abstract:
Our research on Hemlock Hill at the Arnold Arboretum continued into its 3rd year in 2006. High levels of nitrogen availability and dramatic growth of herbaceous and shrub vegetation were among the most remarkable findings.
In 2003, we began to study the effects of post-adelgid logging on ecosystem function at the urban Arnold Arboretum. Hemlock woolly adelgid (HWA) was discovered at the arboretum on blown down foliage in 1997, and had likely infested trees there for years before. Hemlock Hill is a heavily used portion of the Arboretum and many moribund hemlocks needed to be removed to address safety concerns. At this time a collaboration was initiated between the arboretum and Harvard Forest to study ecosystem responses to removal of adelgid infested hemlocks in this park-like setting. During 2004, six 15 x 15 m plots were fenced off, and baseline data on soil nutrient cycling, microclimate, and vegetation information was collected. Hemlocks were removed from 4 plots in February of 2005, while 2 remained untreated, as control plots. Slash was chipped and left on site in the Chipped treatment plots, or removed from the Logged (only) treatment. Minimal impact logging was conducted using a crane. This series of treatments coincided in time with Harvard Forest’s Hemlock Removal Experiment at the Simes Tract, where we are collecting analogous data and making comparisons.
To date we have completed one year of pre-treatment and two years of post-treatment measurements. Nitrogen availability, estimated with the use of resin bags, is very high at the arboretum in comparison to other, rural sites, but did not increase with tree removal (Fig. 1). In contrast, N availability at the Simes tract, initially 1/20th as high as the arboretum, doubled in the logged plots in the 2005 growing season. At the arboretum, herbaceous and shrub cover in both cut treatments has continued to increase dramatically (Fig 2), with Rubus overhead in some plots and herb cover, dominated by Aralia hispida, averaging 70% in the logged treatment. Total herb cover is lower, averaging around 50%, and less variable in the Logged + Chipped treatment. Seedling densities (fig. 2) declined in both cut treatments in 2006, further illustrating the dense cover of shrubs and herbs in these plots. Understory species richness has been largely unchanged. Vegetation continues to increase in the logged sites at the Simes tract, but the changes are slow in comparison.
Year 3 post-cut has shown significant pulses in nitrogen at logged sites in other studies. In 2007, continued investigation into nitrogen dynamics and vegetation changes, as well as collaborative work providing more insight into sources of nitrogen inputs at the arboretum will provide important data to help us better understand this different type of system.
- Research Category: Invasive Plants, Pests & Pathogens
- Figures: F:2007 LTER figsAA resins 2007 LTER.pdf
F:2007 LTER figsAA veg 2007 LTER.pdf
