An Assessment of the Impact of Fire on Rare Lepidoptera in the Ossipee Pine Barrens Preserve
Updated: Dec 18, 2020
Title: An Assessment of the Impact of Fire on Rare Lepidoptera in the Ossipee Pine Barrens Preserve (2013)
Author: Carly Brown
Abstract: The Ossipee Pine Barrens Preserve, managed by The Nature Conservancy (TNC), was once part of a much larger pine barrens ecosystem. Currently, the pine barrens stretch across the towns of Madison, Freedom, Ossipee, and Tamworth in Carroll County, New Hampshire. The pine barrens ecosystem is an imperiled rare natural community that was historically maintained by fire. Pitch pine, the dominant tree in the pine barrens, is well adapted to a fire regime. Scrub oak and blueberry, the dominant shrub and ground cover, can also flourish post-fire.
The Ossipee Pine Barrens host a suite of rare species, including Lepidoptera, i.e. moths and butterflies. The Nature Conservancy has identified 18 conservation target Lepidoptera that are expected to be present in the Preserve, though some have not been verified on the landscape for several decades. There have been multiple surveys of the Ossipee Pine Barrens moths, the most recent intensive survey having occurred in the summer of 2002. The goal of the 2002 survey was to identify rare and non-rare moths, and to provide management and monitoring recommendations that will most benefit these pine barrens specialists.
Prescribed fire is just one management technique for returning historically fire-adapted ecosystems to a desired condition. The Nature Conservancy first began burning the pine barrens in 2007, and as of the summer of 2011 had burned just under 400 acres. TNC also mows and harvests parts of the landscape as a way to remove unwanted encroaching vegetation. The goals of these management techniques are not only to favor the desired vegetation (pitch pine, blueberry, and scrub oak), but also to provide habitat for the fauna that rely on pine barrens conditions.
The goal of this project was to assess the impact that prescribed fire has had on rare moths, as well as to provide additional records of moth presence. We collected moths using black light bucket traps, black light sheet traps, and sugar baiting. I chose four land management units to sample intensively: two that have been managed by fire within the past four to five years, and two that have not burned for several decades. Three sample points were randomly selected in each management unit. I sampled from each of these sample points once a month from May to September in the summer of 2012. I also sampled for moth species presence in several other management units of interest to TNC. Furthermore, TNC sampled spring flying moths in March in five management units, generally using sugar bait.
During the course of the study, I collected 5,846 moths representing 290 species. Between June and September I collected six of the TNC defined conservation target Lepidoptera species in the four intensively sampled management units. I collected three additional species that I included in my analyses since they are described as pine barrens specialists and potentially rare (Wagner et al. 2003, Kart 2003). Using a chi-square analysis, I found that three Lepidoptera species (Nepytia pellucidaria, 2 Zanclognatha martha, and Euretegrotis attentus) were significantly higher in abundance in the unburned management units as compared to the burned. Six Lepidoptera showed no significant difference between burned and unburned units. I used a t-test to compare the abundance, richness, Shannon-Weiner Diversity Index, and Simpson Index of all moth species in the burned and unburned units and did not find a significant difference in these factors.
When I included the early spring collections, and those from the less intensively sampled management units, I identified a total of ten target Lepidoptera species: Lithophane lepida lepida, Lycia rachelae, Nepytia pellucidaria, Sympistis dentata, Xestia elimata, Xylena thoracica, Zale lunifera, Zale obliqua, Zale submediana, and Zanclognatha martha. I collected five additional pine barrens specialist species: Abagrotis brunneipennis, Eueretagrotis attentus, Sideridis maryx, Xestia youngii, and Xylena cineritia (Wagner et al. 2003, Kart 2003).
Based on the chi-square evaluation of target moth abundance between burned and unburned units, I do not recommend any drastic changes in the current prescribed fire management regime. While there were significant differences in three species, with the numbers being lower in the burned units, the majority of moth species showed no difference in abundance between burned and unburned units. Thus, after just a one-year monitoring effort, it is premature to alter the current prescribed fire practice. I do highly recommend that the conservation target Lepidoptera continue to be monitored. I also highly recommend following conservative guidelines on the length of burn intervals, in order to ensure that the moths have regained healthy populations prior to more burning.
Summary of the management recommendations based on my findings:
Continue managing for pitch-pine scrub oak habitat, but pay particular attention to moth life histories as outlined in Kart 2003.
Maintain corridors of unburned vegetation to provide a refuge and source population when burning larger management units.
Coordinate the current post-burn vegetation surveys carried out by TNC with moth collections, as a way to evaluate the habitat moths are collected from.
Monitor target moths more frequently using a less intensive sampling design that allows the target moths to be the focus in collections. Instead of collecting all moths in black light bucket traps, black light sheet traps will allow for target moths to be captured and released.
Continue doing intensive monitoring every ten years or so, and include microlepidoptera in the collection data.
Explore the possibility of monitoring other well-known taxa in addition to the moths to track multiple responses to prescribed fire.