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Harvard Forest Symposium Abstract 2008
- Title: Biology of the hemlock borer, Melanophila fulvoguttata
- Primary Author: Xiujun Wen (Hebei Academy of Forestry Science)
- Additional Authors: Aaron Ellison (Harvard University)
- Abstract:
Following the initiation of treatments in the hemlock removal experiment at Harvard Forest's Simes Tract, we observed high levels of infestation of the hemlock borer Melanophila fulvoguttata (Coleoptera: Buprestidae) in the trees that were killed by girdling. Little is known of the biology of this borer, and we undertook to survey levels of infestation of the borer at the Simes Tract and in other hemlock stands in Massachusetts. Because borer larvae are fed on by woodpeckers, large amounts of bark accumulate at the base of borer-infested hemlocks. Bark has a very high C:N ratio, and so it will decompose at a much slower rate than hemlock needles or other litter. Thus, as borer infestations can have strong local effects on soil ecosystem processes, we set up an experiment to examine decomposition rates of hemlock bark versus hemlock needles in the Simes plots.
Methods
All hemlocks in the Simes Tract were examined using two methods in May 17th and June 20th, 2007. One was by observing the sign of woodpeckers: the grade of the infected hemlock was divided into six classes (0-5) according to the reddish area in the hemlock trunk made by woodpeckers. 0 (none); 1 (< 5% of the total surface of the trunk); 2 (6-20% of the total surface of the trunk); 3 (21-40%); 4 (41-60%); 5 (> 61%). The second was by counting the emergence holes in the first two meters of the trunk. We then felled three hemlocks in our test girdled plot (Simes plot 9), and cut the boles into 1-m sections. We stripped the bark off of each section and then counted the number of hemlock borer larvae and measuring the area of beetle galleries in the wood. In addition, we caged several sections of the boles in window screening to capture emerging beetles and parasitoids. Finally, to examine decomposition rate of bark and needles, we set out replicate decomposition bags in Simes plots 1 and 5 on June 21, 2007. The first subsamples was collected in September 2007, and the remaining subsamples will be collected in April and September 2008.
Initial results
The borer infests only dead trees, so there is no evidence of synergistic impacts of the borer and the adelgid (or other agents) in causing hemlock mortality. Similar results were found in plots infested by the adelgid at Mount Tom and in Connecticut. In Simes plot 1, 45% of dead trees were infested by the borer, and in Simes plot 5, 33% of dead trees were infested by the borer. Visual assessment of borer infestation by woodpecker sign was not as accurate as counting exit holes; only about one-third of infested trees were detected by the woodpecker method. Infestation appeared to be randomly distributed within the plots. In the felled trees, 3-22% of the wood surface had borer galleries; densities ranged from 0.6 - 4 larvae per m2. Borers were evenly distributed through the entire bole.
C:N ratio of hemlock bark is >200, a strong contrast with needles (C:N = 51), twigs (C:N = 89), and buds and cones (C:N = 21). After three months, only about 1% of bark mass had been lost in decomposition bags, compared with over 20% of needle mass lost.
Future work
In 2008 we will finish the bark and needle decomposition work, and collect additional data on infestation rates and population biology of the borer at Simes.
- Research Category: Biodiversity Studies
Large Experiments and Permanent Plot Studies - Figures: DSCF0973.jpg
