1. Changes in Insect Fauna Following Thinning and Clearcutting in an Oak-Pine Forest in the New Jersey Pine Barrens
Erin Pilkington, Ryan Pierson, Jennifer Gardener & Anthony Fetherman ADVISOR – Jamie Cromartie
ABSTRACT
Our goal is to determine whether thinning and clearcutting enhance the characteristic pinelands insect fauna of a fire-suppressed oak/pine forest.
Our objectives are to make collections of insect species present in thinned and clearcut sites and compare those collections to insects collected in the same area prior to forest management. The southeast forest management area at Stockton was initiated in the summer of 2015 with a combination of 50% thinning of the individual trees in 19 acres, a 2.6-acre clearcut and a 2.6-acre control area.
Strategies employed in the winter/spring of 2015/16 include: Lindgren bait traps for beetles, sugar bait for moths and bee cups for flower visitors. Preliminary results indicate that the moth fauna showed no large shifts, compared to previous years’ sampling of the same site and that traps and bee cups are catching different numbers of insects in the clearcut, thin and control areas, including many beetles associated with both live and dead oaks and pines. The winter of produced good numbers of winter moths in genera like Eupsilia and Lithophane. The very uncommon Lithophane lemmeri was collected for the first time at Stockton on March 8. The most abundant beetles, especially in the thin area, have been bark beetles (subfamily Scolytinae) and clerid beetles, which prey mainly on Scolytinae and other bark inhabiting insects.
We expect to see further differences between our treatments as we continue the surveys over the late spring and summer and as more methods, including light trapping are employed.
Lindgren funnel trap in the thinned area, 21 April 2016
Lindgren funnel trap, clearcut area 22 Mar 2016.
Alcohol baited bottle trap, NE forest management area, 1 May 2015
Beetles from the Lindgren funnel traps, March 2016: Clockwise from top left: Thanasimus dubius, Enoclarus nigripes, Pissodes strobi, Rhagium inquisitor.
Moths collected at bait in SE forest management area 8 March the moth in the center is Lithophane lemmeri.
RESULTS AND DISCUSSION, CONTINUED
We did not see any obvious changes in winter moth abundance during the winter baiting season of Bait catches, however, are highly dependent on weather events during the season, and it will take several years to detect any trends. At least the moths did not seem to avoid the thinned areas, as evidenced by the diversity and numbers seen, including the very rare Lithophane lemmeri, not previously found at Stockton.
Another species we plan to monitor closely is the uncommon tiger beetle, Cicindela unipunctata, which has been unusually abundant in the SE forest management area in some years since it was first detected in the late 1990s. We are particularly concerned to see whether this species, which seems to prefer shaded habitats, will be adversely affected by the thinning and clearcutting.
Cicindela unipunctata, an uncommon tiger beetle, which has had an unusually large population in the SE forest management area.
METHODS
Casual insect collecting has gone on in the areas designated for management at various times since The specimens from these early efforts will be included in our analysis
Since the late 1990s, insect trapping, using a variety of methods has been conducted on the site now designated the SE forest management area. This has included summer and winter bait trails, light traps, malaise traps, pitfall traps and ant baits. Alcohol baited plastic bottle traps have been used to monitor the SE site for beetles, beginning in early summer 2015, before cutting commenced. In the late winter and early spring of 2016 we began deploying Lindgren funnel traps, using alcohol and turpentine bait for beetles, two traps in each of the thin, clearcut and control areas. These are run for three days every two weeks. In the winter of we monitored a sugar bait trail through the SE forest management area for moths, whenever the weather was warm enough for the winter moths to be active. Since early March, we have set lines of thirty blue/white/yellow bee cups to trap bees and other flower visitors, every two weeks in thin, clearcut and control sites. We will also be conducting net surveys during the spring, summer and fall, targeting species not easily collected by other methods.
Captured insects are brought into the A&S insect lab to be sorted, preserved and identified. The catches from the Lindgren funnels provide the best material to directly compare species assemblages in the two treatments and the control site. We plan to use multivariate analysis of species numbers to look at treatment differences. We will also compare species lists from the other methods so far as sample sizes permit.
INTRODUCTION
The North American Coastal Plain, of which the NJ Pine Barrens is in the northernmost section, has recently been recognized as the world’s 36th global biodiversity hotspot (Noss 2016). One of the reasons that it had not been accorded this status earlier is that it has been mistakenly thought that this area was naturally vegetated by rather monotonous pine and oak-pine forests, with little variety of plant species. It is now understood that for hundreds of thousands of years, open savannas were the more dominant vegetation, created and maintained by natural fire (Noss, et al. 2015). Although much remains to be learned, it is clear that our current dense, low-diversity forests are a result of fire suppression in the past century (Forman and Boerner 1981).
In an attempt to begin the restoration of the natural biodiversity of the Pine Barrens, forest managers are using thinning, clear cutting, replanting of native species and controlled fire to recreate the open, park-like conditions that once prevailed over much of the region. Stockton has recently embarked on an ecological forest management program, designed to restore vigor and biodiversity while reducing the danger of catastrophic wildfire (Williams 2011).
This study is being done to see how these management efforts will affect the diversity of insects in the managed areas by monitoring the presence of a range of forest and savanna inhabiting species before and after the management plan is implemented.
Trapping methods employed in SE forest management area prior to cutting clockwise from top left, light trap sample, 2-3 Jun 2011, bait tree, 31 Jan 2012, Malaise trap, deployed fall 2010 through summer 2011, pitfall traps, same period
RESULTS AND DISCUSSION
We have just begin sorting and identifying the Lindgren funnel samples. The table below shows the numbers of the two commonest beetle species in the traps to date.
It is apparent that the numbers caught in the traps in each of the three areas is different and that the control area traps get the largest numbers of beetles, followed by the control and then the clearcut. Whether this parrern is consistent for all groups of beetles remains to be seen, as we sort and count the large numbers of small species of Scolytinae, the bark beetles, which play a key role in this ecosystem.
We expect bees to be more abundant as the clearcut and thinned area begin to develop more diverse understory vegetation, especially if native pinelands flowering herbs begin to grow: wild indigo, Maryland golden aster, blazing star, asters and goldenrods, etc. The same may apply to butterflies, skippers and moths whose caterpillars feed on grasses and forbs. We also plan to extend our analysis to ants, which we expect will form very different assemblages in the three different areas.
When control burns are undertaken in this area, it will give us a further variable to consider. In preliminary moth bait and Lindgren funnel studies in the control burned sections of the forest management area west of Lake Fred, we have not found any major differences in the insect fauna, but that may change if hotter fires can be used, as the long term management plans call for.
We will also continue studies using Lindgren traps in the NE forest management area, beginning this summer. These areas were sampled last year with alcohol baited bottle traps. Cutting is scheduled to begin in July 2016.
Bee cup lines in thin area and clearcut, March 2016.
LITERATURE CITED
Forman, R. and R. Boerner Fire frequency and the Pine Barrens of New Jersey. Bulletin of the Torrey Botanical Club 108:
Noss, R.F Announcing the World’s 36th Biodiversity Hotspot: The North American Coastal Plain. Critical Ecosystems Partnership Fund. Posted February 18, 2016 at:
Noss, R.F., W.J. Platt, B.A. Sorrie, A. S. Weakley, D.B. Means, J. Costanza, and R.K. Peet How global biodiversity hotspots may go unrecognized: Lessons from the North American Coastal Plain. Diversity and Distributions 21: Online version available November 2014: DOI: /ddi
Williams, R.R Richard Stockton College Forest Management Plan. Land Dimensions Engineering File No. F pp.