Harvard Forest Research

Ants and ecosystem function in the Hemlock Removal Experiment

Principal Investigator: Aaron Ellison
Harvard Forest: Apr 01 2006 - Dec 31 2015:

Abstract:
Removal of hemlock by logging and infestation by the hemlock woolly adelgid results not only in a change in tree, shrub, and herb species composition, but also in a compositional shift in ant diversity. In particular, species in the genus Formica colonize large openings and are abundant in hardwood stands, whereas they are absent in hemlock stands. Aphaenogaster rudis dominates the ant fauna of hemlock stands but this competitively weak species is low in abundance in forest openings and in hardwood stands. The purpose of this project is to determine the effect of ants and different ant species composition on soil ecosystem processes in the context of hemlock decline. We propose to establish three treatments - ant exclosure (removal), exclosure (disturbance) control, and undisturbed control - in each of the 8 large plots of the Hemlock Removal Experiment at the Simes Tract. Treatment plots are based on an established design of David Wardle (diagram available on request), and will be 3 x 3 m; two replicates of each treatment will be established in each of the 8 large plots at Simes. Ant exclosures will be built as 2 x 2 m squares of 6" diameter PVC buried 1 cm into the soil, surrounded by a 3 x 3 m square of corrugated plastic roofing buried 5 cm into the soil. The top, outside edge of the outer (corrugated roofing) barrier will be coated with tanglefoot.

Disturbance controls will be flagged (2 x 2 m inner area and 3 x 3 m outer area), and soil will be dug as in the exclosures, but no pvc frame or corrugated roofing will be installed.

Installation of all plots and samplers will be done in April 2006.

Because of the disturbance to the soil, all exclosures and disturbance controls should be sited in the 30-m wide buffer area of each plot; we will avoid the salamander transects established by Brooks Mathewson. Note that the total area required for the exclosures and disturbance controls in each large plot is 36 m^2 (for 4 3x3 m plots) of the approximately 7200 m^2 of the buffer area. The control (undisturbed) plots will be established around soil respiration rings already installed by Kathleen Savage and Eric Davidson (WHRC).

Within the center 2 x 2 m of the exclosure and disturbance control plots, we will install permanent PVC rings for soil respiration (25 cm diameter; 10 cm high); permanent PVC tubes (3.5 cm diameter) for measuring soil N, and two 8 cm diameter pitfall traps to assess the effectiveness of ant exclosure. N-samplers and pitfall traps will also be installed near to the soil respiration rings in the control plots. I-buttons will be installed in all plots for continuous temperature monitoring. Soil respiration and soil moisture will be measured monthly during the summer. Soil N-availability will be measured quarterly using resin extractions. Ant community composition will be sampled twice/summer.

Summer REU students will work on this proposal.

A parallel experiment is being established in the hemlock stands at Coweeta by collaborators Aimee Classen (ORNL) and Nate Sanders (U. Tennessee).

Update 2007:

In 2007, we propose to add 14 additional 3x3 m subplots into the buffer areas of each of the 8 large (0.81 ha) plots at Simes. These new subplots include 2 each of the following 7 treatments: Ant addition (+A), Food addition (+F), Nitrogen addition (+N), and factorial combinations: +A+F; +A+N; +F+N; +A+F+N. Ant additions will be accomplished by placing 20 drilled dowels (10 cm long x 1.6 cm diameter) and 2 "Aphaenogaster houses" (25 x 12 x 4 cm hemlock "sandwiches" with a routed-out gallery) into each +A subplot. Subplots for food additions (+F) will have 250 g of finely ground tuna added once/week. Nitrogen additions will have slow-release urea fertilizer added once/week at levels equal to the tuna additions.

Plots will be established in April 2007 to allow dowels and Aphaenogaster houses time to "season" before spring ant recruitment.

In summer 2007, we will only monitor ant responses to these treatments. Should our NSF proposal for this work be funded (submitted January 2007), we will add resin samplers and soil respiration collars in summer 2008. Summer assistance for this project will include RET participant Katie Bennett.

Update 2008 In 2007 we added the additional subplots, but only actually implemented the ant nest additions. Food and Nitrogen additions were not done, and have been deleted from the design. An NSF proposal to fund this work was re-submitted in January 2008 (the 2007 proposal was declined).

Sampling will be done in May, July, and September for ant and spider colonization of artificial nests.

We will continue maintenance and monitoring of ant exclosure, disturbance control,and control plots in 2008.

Update 2009 No soil respiration measurements in 2009, pending results of HF Soil Respiration Synthesis activity. N availability (resins), and ant sampling will continue. I-buttons, which perform poorly in the field, have been removed from all plots. :