A field test of point relascope sampling of down coarse woody material in managed stands in the Acadian Forest1

Journal of the Torrey Botanical Society, Apr-Jun 2003 by Brissette, John C, Ducey, Mark J, Gove, Jeffrey H

BRISSETTE, J. C. (USDA Forest Service, Northeastern Research Station, Durham, NH 03824), M. J. DUCKY (University of New Hampshire, Durham, NC 03824), AND J. H. GOVE (USDA Forest Service, Northeastern Research Station, Durham, NFI 03824). A field test of point relascope sampling of down coarse woody material in managed stands in the Acadian Forest. J. Torrey Bot. Soc. 130: 79-88. 2003.-We field tested a new method for sampling down coarse woody material (CWM) using an angle gauge and compared it with the more traditional line intersect sampling (LIS) method. Permanent sample locations in stands managed with different silvicultural treatments within the Penobscot Experimental Forest (Maine, USA) were used as the sampling locations. Point relascope sampling (PRS) with three different angles spanning the practical range of angles for such stands was used along with 40 m of LIS sample per sample point. Compared to LIS, the three angles resulted in similar number of pieces and volume of CWM from stands with different histories of repeated partial harvests. In terms of sampling efficiency, PRS was up to 4 times more efficient than LIS. These results, while limited to only one forest type and a relatively small sample, are the first published results available on the field performance of PRS.

Key words: Angle gauge sampling, coarse woody debris, spruce-fir forests.

Dead wood on the forest floor, or down coarse woody material (CWM), is an important component of forest structure. It serves as wildlife habitat, as seedbed for many species, and has a role in nutrient cycling and soil formation (e.g., see: DeGraaf and Yamasaki 2000, Harmon et al. 1986, McGee 2001). Although the ecological importance of CWM is recognized, how much should be present and how should it be distributed in a stand to maintain ecosystem processes is largely unknown (Hagan and Grove 1999). This is especially true in regions like the Northeast where old growth forests, which can provide a benchmark, are rare. In managed forest ecosystems, CWM has become a premier conservation concern with respect to achieving balance between producing forest products and sustaining species that require dead wood (Hagan and Grove 1999). Consequently, sampling CWM is an important consideration for ecologists and managers alike.

One reason information about CWM is lacking is because traditional methods for measuring it, such as fixed area plots and line intersect sampling (LIS), are time consuming and laborious (Rubino and McCarthy 2000). Recently, point relascope sampling (PRS) for CWM has been introduced, which may provide an efficient alternative to traditional methods (Gove et al. 1999). A relascope is a simple angle gauge that can be fabricated with common materials (Gove et al. 2001). Using a relascope to assess whether a particular piece of CWM is "in", "out", or "borderline," PRS is analogous to inventorying standing trees in horizontal point sampling (HPS) with an angle gauge or prism (Grosenbaugh 1958).

While Gove et al. (1999) established the theoretical basis for PRS, they noted that field trials in different forest types were needed to determine the efficacy of the method. For example, in HPS using prisms, the appropriate prism factor varies depending on the range of diameter sizes and understory growth in the stands to be sampled (e.g. Wiant et al. 1984). Similarly, with PRS, the most efficient relascope angle is likely to vary with forest conditions.

The purpose of this study was to assess the field performance of PRS using three different relascope angles in differing stand conditions as compared with traditional LIS. LIS was chosen as the standard for comparison rather than fixed area plots because both theoretical considerations (Kaiser 1983) and simulation studies (Pickford and Hazard 1978) have shown LIS is more efficient than fixed area plots. The study was conducted in three stands of mixed northern conifers on the Penobscot Experimental Forest (PEF) in east-central Maine. The stands are part of a long-term silvicultural experiment and have marked differences in horizontal and vertical structure because of different harvest histories. Our goal is to encourage measurement of CWM by offering an innovative yet simple method for sampling this ecologically important component of forest structure.

Materials and Methods. STUDY SITE. The PEF is in the towns of Bradley and Eddington, in Penobscot County, Maine. Much of Atlantic Canada and adjacent Maine, including the area around the PEF, are in the Acadian Forest Region (Braun 1950, Rowe 1972). The PEF is 1540 ha and located at 44� 52' N, 68� 38' W. It was established in 1950 for conducting ecology and management research in the northeastern mixed conifer forest type. It is dominated by a diversity of conifers, including eastern hemlock (Tsuga canadensis (L.) Cam), balsam fir (Abies balsamea (L.) Mill.), red spruce (Picea rubens Sarg.), white spruce (P. glauca (Moench) Voss), eastern white pine (Pinus strobus L.), and northern white-cedar (Thuja occidentalis L.). Associated dominant hardwoods include red maple (Acer rubrum L.); paper birch (Betula papyrifera Marsh.); gray birch (B. populifolia Marsh.); and aspen, both quaking (Populus tremuloides Michx.) and bigtooth (P. grandidentata Michx.).