PARENT SESSION
Poster Session 18: Paleoecology.

Wednesday, August 4 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.

Reconstructing recent defoliation of jack pine stands by jack pine budworm (Choristoneura pinus) and pine tussock moth (Dasychira plagiata) using larval head capsule remains in sedge peat deposits.

Tweiten, Michael^*,1, ¹ University of Wisconsin-Madison, Madison, Wisconsin, USA

ABSTRACT- In response to climate warming insect defoliators and fire could dramatically alter northern forests in ways that are difficult to anticipate. Analysis of sediment records holds the potential to elucidate the complex interaction of disturbance processes during periods of climate change. These records must be directly related to modern ecological systems to properly interpret their dynamics. This survey was conducted to assess the effectiveness of using larval head capsule remains in peat deposits to detect outbreaks of Lepidoptera species that defoliate stands of jack pine (Pinus banksiana) in the sand plain of northwestern Wisconsin, USA. Previous studies, using spectral mixture analysis of LANDSAT satellite imagery, documented areas of severe defoliation and subsequent salvage logging during the last major defoliator outbreak (1990-1995). Using the defoliation GIS map and aerial photography, four small forest hollow sites were located within the salvage areas and four paired sites were located in intact stands within 1-3 km. From the center of each hollow, five 10-cm-diameter, 25-cm-long peat cores were extracted. The cores were sliced in 1-cm increments and sieved into >700 u, >250 u and > 125 u fractions. Insect remains in the >250 u fraction were concentrated by kerosene floatation. The number of larval Lepidoptera head capsules in the >250 u fraction were recorded for each interval, as well as the total of all anatomically identifiable insect parts. Cores taken from the salvage sites show a distinct peak in the number of larval head capsules per interval in the upper part of the peat profile. Head capsules are rare or lacking at depth, rise to 3 or 4 capsules per interval for 2-3 intervals and are topped with peat deposition lacking head capsules. Head capsules remain rare or lacking in all intervals in peat cores taken from intact stands. These results support the contention that severe, localized defoliator outbreaks can be detected directly in forest hollow sediments using larval head capsule counts. Problems of interpretation and further studies will be discussed. This project is part of a larger investigation that seeks to examine the joint impacts of insect defoliators and fire on the vegetation of the sand plain during past periods of climate change and relate them to future global change.

Key words: climate change, insect defoliators, disturbance history, Jack pine budworm Choristoneura pinus