Role of Canopy Gaps and Downed Woody Material in Maintaining Biodiversity in the Acadian Forest of Maine
Robert G. Wagner1, Malcolm L. Hunter2, and Stephen A.Woods3
1 Department of Forest Ecosystem Science
2 Department of Wildlife Ecology
3 Department of Biological Sciences University of Maine Orono, ME
Funding Agency: USDA National Research Initiative Competitive Grants Program (NRICGP)
Amount: $260,000
Duration: 3 years (2000-2003)PROJECT OVERVIEW
Current recommendations for maintaining biodiversity in managed forests include 1) designing harvest treatments that mimic natural disturbances and 2) retaining biological legacies in the form of deadwood after harvesting. Two components of forest structural diversity -- canopy gaps and downed woody material (DWM) -- are thought to be particularly important for maintaining biodiversity and long-term productivity of forest ecosystems. When managing canopy gaps and DWM, it is currently assumed that an increase in structural complexity leads to an increase in species richness, however these assumptions have not been tested together in a well-designed experiment. To test these assumptions, we are examining the influence of canopy gaps and DWM on understory vegetation, insects, and amphibians. We are testing three specific hypotheses as part of the Forest Ecosystem Research Program on the Penobscot Experimental Forest in southeastern Maine: 1) characteristics of canopy gaps [gap size, gap origin (harvest or natural), and location within gap] influence the diversity of understory vegetation and insect communities, as well as the numbers and attributes of amphibians; 2) characteristics of DWM (decay class, species, and structural complexity) influence the diversity of insect communities, and the numbers and attributes of amphibians; and 3) predation by amphibians influences the abundance and composition of insect communities, and these interactions are affected by the characteristics of DWM. Understanding these relationships will promote the development of forest management approaches that can maintain biodiversity while satisfying society's increasing demand for wood production.
PROGRESS (as of Nov 2002)
Four graduate (2 MS, 2 PhD) students completed the second field season of their thesis research addressing the above objectives. In addition, a new PhD student was brought into the project this year.
EXPERIMENT #1: Modeling the effects of harvesting on the vertical and horizontal forest structure (M.R. Saunders and R.G. Wagner) - From June-August 2002, a total of 33 plots from the long-term USFS silvicultural experiment on the Penobscot Experimental Forest were stem-mapped. This complimented the 17 plots measured in Summer 2001. Ten plots in each of the clearcut, 5-year selection, 3-stage shelterwood, fixed-diameter limit, and control treatments were measured. Height, lowest live crown, crown radius, diameter, and species were recorded for over 7000 trees across the 50 plots. Additionally, all dead stems that could be positively identified were mapped. From these data, simulation of structural development over time for the 5 silvicultural treatments were begun. These simulations will compliment over 30000 mathematical simulations that have been conducted to test the Stand Complexity Index (SCI; Zenner 2000, Ecol. Appl. 10: 800-810) and other structural models. Early results indicate that the SCI is inadequate in its current form to separate low-density, uneven-aged stands with "high" amounts of observed forest structure from high-density, even-aged stands with "low" amounts of observed forest structure.
EXPERIMENT #2: Vegetation diversity in natural and artificial gaps of the Acadian forest (D.A. Schofield and R.G. Wagner) - We have evaluated 42 artificial gaps, 23 natural gaps, and 23 non-gaps. All vegetation data was collected 4 growing seasons after harvest and completed in August 2001. Vegetation, including trees, shrubs, herbs, and ferns, was identified to the species and measured by percent cover within 4m2 quadrats located every 2 m along a North/South transect within each gap. Gap basal area was also measured with 5 and 10 factor prisms, and canopy gap fraction was measured with Licor LAI 2000 within each quadrat. Furthermore, in the artificial gaps of RA 1-2, the 4 most common species of overstory gap edge trees within the northern half of the gap and the 2 most common conifer understory saplings within the gap were evaluated to determine radial growth response to known canopy disturbance. Data collection was completed in October 2001. Preliminary results indicate that abundance (p<0.001) and diversity (p<0.0001) are greater in gaps than under closed canopy. Overall, Abies balsamea, Acer rubrum, Tsuga canadensis, and Aralia nudicaulis are the four most important species in harvested gaps, natural gaps, and closed canopy. Harvested gaps had the greatest number of regenerating tree stems for all height classes, and closed canopy transects had the least number of tree stems for all height classes, but the average number of stems per hectare was independent of gap origin or closed canopy (p=0.1516). This study is also testing the response of canopy disturbance on tree growth patterns using harvested gaps with a known formation date. We are testing several methods to determine the best species and the best canopy strata for identifying canopy disturbance dates in the Acadian forest, Maine. Sixty understory sapling cookies and 240 overstory gap edge trees cores were collected and are currently being analyzed for their response.
EXPERIMENT #3: Influence of Gaps and DWD on Insects (S. Thomas and S.A. Woods) - Samples from 2001 were sorted over the winter of 2001/2002. There were 854 total click beetles (Family Elateridae) specimens, 587 from soil emergence traps and 267 from log emergence traps. These included 42 species of Elateridae: 32 species were collected from log traps, and 33 species were collected from soil traps, with 23 species found in both log and soil traps. Nine species were found in logs but not in soil traps. Size of log, decay class, gap vs. nongap, and softwood vs. hardwood were found to be significant factors for some species found in the log emergence traps. Emergence traps were deployed again in 2002 inside and outside harvest gaps in each of the replicate harvested treatments. Ninety six traps were deployed examining log decay class, location relative to gap, tree species class, and size. Thirty six emergence traps were deployed over the root systems of six different tree species. Yelloe bowl traps and malaise traps were used to examine the influence of gaps on parasitic Hymenoptera. Microclimate changes (temperature and relative humidity) measurements were taken in the gaps, at the edge of the gaps, and in the woods surrounding the gaps. Flower surveys were conducted within a 10m radius of selected traps. Preliminary results indicate that parasitic wasps avoided the harvest gaps.
EXPERIMENT #4: Influence of Natural and Artificial Gaps on Amphibians (C. Strojny and M.L. Hunter) - The objectives are 1) to compare relative abundance of forest amphibians among harvested and natural canopy gaps and contiguous, closed-canopy forest, 2) to compare relative abundance of forest amphibians within artificial and natural canopy gaps, and 3) to determine how redback salamander (Plethodon cinereus) distribution and body size are affected by DWM size under both open and closed canopy conditions. To address objectives 1 and 2, we are sampling forest amphibians in 53 harvested gaps, 19 natural gaps, and 36 full-canopy plots using 3-m straight-fence pitfall arrays. These plots were identified and set with pitfall arrays during 2001, and results from a fall pilot study were used to refine the sampling design and techniques for 2002. Each sample plot (harvested gap, natural gap, full-canopy) has a pitfall array located 5 m south of the plot center, at center, and 5 m north of the center. Captures from these pitfall arrays were pooled to compare relative amphibian abundance among treatments. Seven natural gaps and 23 harvested gaps have pitfall arrays positioned every 5 m along the entire north-south transect of the gap to study gap aspect. Between 10 May and 26 July 2002, we captured 950 frogs and salamanders representing 10 species. Initial results indicate that amphibians in gaps are active in numbers similar to those of nearby full-canopy sites. There also appears to be no distinct pattern in amphibian captures between the north and south aspects within gaps. Further sampling during the fall of 2002 and spring and fall of 2003 may clarify possible underlying trends that were not detected thus far. During summer 2002, we searched for redback salamanders under logs (decay class II and III) in gaps and under closed canopy. We searched 131 logs in gaps and detected 11 redback salamanders. Under closed canopies, we searched 124 logs and detected 22 redback salamanders. We plan to adjust our sampling protocol during 2003 in order to increase our sample size of logs with salamanders.
EXPERIMENT #5: Role of DWM in redback salamander habitat selection (D. Queheillalt and M.L. Hunter) - The objective for this new study component (begun July 2002) is to examine how predation on invertebrates by redback salamanders affects the invertebrate community in the presence of DWM compared to the forest floor. A literature review was completed to determine current knowledge about relationships between redback salamanders and their prey, as well as the importance of DWM as a component of redback salamander habitat. A prototype experimental enclosure, after Wyman (1998), was assembled to determine feasibility. Final experimental design details are being determined for implementation during the 2003 field season.
PUBLICATIONS
Journal papers and other peer-reviewed publications:
Fraver, S., Wagner, R.G., and Day, M. 2002. Dynamics of down woody debris following gap harvesting in the Acadian forest of central Maine, USA. Canadian Journal of Forest Research 32: 2094-2105.
Conference proceedings:
Saunders, M.R. 2002. Overview of the Forest Ecosystem Research Program (FERP). "Silviculture of Hardwood Forests workshop", Orono, ME, August 20-21.
Saunders, M.R. R.G. Wagner, and J. Brissette. 2002. Developing metrics for 3-dimensional forest stand structure: A test of the stand complexity index hypothesis. pp. 63. In R.G. Wagner (Comp.) Proc. Eastern CANUSA Forest Science Conference, October 19-20, 2002, University of Maine, Orono, Maine. 122 p.
Schofield, D.A. and R.G. Wagner. 2002. Vegetation diversity in natural gaps, harvested gaps, and closed canopy in the Acadian forest, Maine. pp. 65. In R.G. Wagner (Comp.) Proc. Eastern CANUSA Forest Science Conference, October 19-20, 2002, University of Maine, Orono, Maine. 122 p.
Saunders, M.R., R.G. Wagner, M. Hunter, S. Woods, D. Schofield, C. Strojny, S. Thomas, S. Fraver, and L. Case. 2002. FERP: Designing and understanding silvicultural systems for the future. pp. 116. In R.G. Wagner (Comp.) Proc. Eastern CANUSA Forest Science Conference, October 19-20, 2002, University of Maine, Orono, Maine. 122 p.
Strojny, C.A. and M.L. Hunter, Jr. 2002. Effects of harvested canopy gaps on forest amphibians. pp. 68. In R.G. Wagner (Comp.) Proc. Eastern CANUSA Forest Science Conference, October 19-20, 2002, University of Maine, Orono, Maine. 122 p.
Saunders, M.R., Wagner, R.G., Hunter, M., Woods, S., Schofield, D., Strojny, C. Thomas, S., Fraver, S., and Case, L. 2001. FERP: Designing and understanding silvicultural systems for the future. Forest Structure: A Multilayered Perspective, Forest Ecosystem Information Exchange Fall Meeting, Orono, ME.
In preparation:
Calhoun, A. and M.L. Hunter, Jr. IN PRESS. Managing ecosystems for amphibian conservation. In R. Semlitsch. Amphibian conservation. Smithsonian Institution Press, Washington DC.
Saunders, M., R.G. Wagner, L. Rustad, and S. Fraver. IN PREPARATION. Nutrient content of down woody material in the Acadian Forest. Canadian Journal of Forest Research.
FOR MORE INFORMATION
- Bob Wagner
- Dept. of Forest Ecosystem Science
- 5755 Nutting Hall
- University of Maine
- Orono, ME 04469-5755
- Phone: (207) 581-2903
- Fax: (207) 581-2833
- Email: bob_wagner@umenfa.maine.edu
