A Field Test of Point Relascope Sampling of Down Coarse Woody Material in Managed Stands in the Acadian Forest1 John C

Journal of the Torrey Botanical Societ?; 130(2), 2003, pp. 79-88

A field test of point relascope sampling of down coarse woody material in managed stands in the Acadian Forest1 John C. Bris~ette*.~ Northeastern Research Station, USDA Forest Service, Durham, NH 03824 Mark J. Ducey University of New Hampshire, Durham, NH 03824 Jeffrey H. Gove Northeastern Research Station, USDA Forest Service, Durham, NH 03824

BRISSETTE,J. C. (USDA Forest Service, Northeastern Research Station, Durham, NH 03824), M. J. DUCEY (University of New Hampshire, Durham, NC 03824), AND J. H. GOVE(USDA Forest Service, Northeastern Research Station, Durham, NH 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 ance between producing forest products and sus- woody material (CWM). is an important com- taining species that require dead wood (Hagan ponent of forest structure. It serves as wildlife and Grove 1999). Consequently, sampling habitat, as seedbed for many species, and has a CWM is an important consideration for ecolo- role in nutrient cycling and soil formation (e.g., gists and managers alike. see: DeGraaf and Yamasaki 2000, Harmon et al. One reason information about CWM is lack- 1986, McGee 2001). Although the ecological ing is because traditional methods for measuring importance of CWM is recognized, how much it, such as fixed area plots and line intersect sam- should be present and how should it be distrib- pling (LIS), are time consuming and laborious uted in a stand to maintain ecosystem processes (Rubino and McCarthy 2000). Recently, point is largely unknown (Hagan and Grove 1999). relascope sampling (PRS) for CWM has been This is especially true in regions like the North- introduced, which may provide an efficient al- east where old growth forests, which can pro- ternative to traditional methods (Gove et al. vide a benchmark, are rare. In managed forest 1999). A relascope is a simple angle gauge that ecosystems, CWM has become a premier con- can be fabricated with common materials (Gove servation concern with respect to achieving bal- et al. 2001). Using a relascope to assess whether a particular piece of CWM is "in", "out", or "borderline," PRS is analogous to inventorying ' Work on this project was funded by U.S.D.A. Na- tional Research Initiative Grant #00-35 101-935 1. "Ef- standing trees in horizontal point sampling ficient Methods of Sampling Coarse Woody Material (HPS) with an angle gauge or prism (Grosen- in Forest Ecosystems." baugh 1958). Author for correspondence. While Gove et al. (1999) established the the- We thank the following for their help in field sampling: Alison Dibble, Rick Dionne, Charlie Koch, Al oretical basis for PRS, they noted that field trials Meister, Tom Skratt, Heather Smith, Tim Stone, and in different forest types were needed to deter- Bob Wagner. We thank Ken Deamarais and John Ha- mine the efficacy of the method. For example, gan for helpful comments on an earlier draft of this in HPS using prisms, the appropriate prism fac- manuscript and two anonymous referees for insightful reviews. tor varies depending on the range of diameter Received for publication February l I, 2002, and in sizes and understory growth in the stands to be revised form November 27, 2002. sampled (e.g. Wiant et al. 1984). Similarly, with 80 JOURNAL OF THE TORREY BOTANICAL SOCIETY [VOL.130

PRS, the most efficient relascope angle is likely cutting is considered exploitative and perhaps to vary with forest conditions. dysgenic (Nyland 1996). The treatment was in- The purpose of this study was to assess the cluded in the experiment as an example of poor field performance of PRS using three different forestry practice. We chose those compartments relascope angles in differing stand conditions as for this study because they have been treated the compared with traditional LIS. LIS was chosen same except in one the most recent harvest was as the standard for comparison rather than fixed 5 years before we sampled while in the other it area plots because both theoretical consider- had been 22 years since it was last cut (Fig. 1). ations (Kaiser 1983) and simulation studies Compartment 16 is one of the replicates of se- (Pickford and Hazard 1978) have shown LIS is lection management with a five-year cutting cy- more efficient than fixed area plots. The study cle. The goal of selection silviculture is to re- was conducted in three stands of mixed northern generate and maintain a multi-aged structure, conifers on the Penobscot Experimental Forest and in this case, a defined species composition. (PEF) in east-central Maine. The stands are part Compartment 16 was chosen because, of all the of a long-term silvicultural experiment and have treatments, it is the one most frequently entered marked differences in horizontal and vertical for harvests (Fig. 1). structure because of different harvest histories. Detailed descriptions of these treatments are in Our goal is to encourage measurement of CWM Brissette (1996) and briefly summarized here: by offering an innovative yet simple method for In the diameter-limit treatment, harvests occur sampling this ecologically important component periodically when stand volume reaches roughly of forest structure. the average volume of the two replicates prior to the first harvests in the 1950s. The diameter Materials and Methods. STUDYSITE. The at breast height (dbh) that determines whether a PEF is in the towns of Bradley and Eddington, tree is cut depends on species; in general, more in Penobscot County, Maine. Much of Atlantic commercially valuable species have higher di- Canada and adjacent Maine, including the area ameter limits than less valuable species. Com- around the PEE are in the Acadian Forest Re- partment 4 has had three harvests: June 1952, gion (Braun 1950, Rowe 1972). The PEF is May 1973, and January 1994 (Fig. 1). Com- 1540 ha and located at 44" 52' N, 68" 38' W. It partment 15 has had two harvests: September was established in 1950 for conducting ecology 1956 and August 1977 (Fig. 1). The heavy cuts and management research in the northeastern in these stands have created a range of opening mixed conifer forest type. It is dominated by a sizes, resulting in prolific regeneration of woody diversity of conifers, including eastern hemlock and herbaceous vegetation. (Tsuga canadensis (L.) Cam.), balsam fir (Abies Selection silviculture is practiced by cutting balsamea (L.) Mill.), red spruce (Picea ruhens at regular intervals with a set of objectives to Sarg.), white spruce (P. glaz~ca(Moench) Voss), achieve a sustainable, multi-aged stand with de- eastern white pine (Pinus strobus L.), and north- sired structure and attributes. In the long-term ern white-cedar (Th~tjaoccidentalis L.). Asso- experiment, there are objectives for residual ciated dominant hardwoods include red maple stand basal area, maximum tree diameter, di- (Acer rubrunz L.); paper birch (Betula papyrijera ameter distribution, species composition and tree Marsh.); gray birch (B. populijolia Marsh.); and quality. Every five years, trees of all sizes and aspen, both quaking (Populus trenzuloides species are selected for harvest to meet the stat- Michx.) and bigtooth (P. grandidentata Michx.). ed objectives. Compartment 16 has had nine har- Three stands were used in this comparison in vests since the start of the experiment: March order to evaluate PRS in a variety of forest struc- 1957, June 1963, October 1966, April 1972, Jan- tures. The stands (experimental units, called uary 1977, September 1982, August 1987, Sep- compartments) are part of a replicated, long- tember 1991, and March 1997 (Fig. 1). The se- term experiment designed to evaluate individual ries of light harvests has resulted in only small tree and stand responses to a range of silvicul- openings and maintained a nearly continuous tural treatments. The treatments were devised to overstory canopy. create and maintain an array of single- and mul- Each compartment in the silvicultural experi- ti-aged or cohort structures with varying control ment has a network of permanent, fixed radius of tree species composition. plots located systematically after a random start Compartments 4 and 15 are replicates of a from which stand inventory data are collected diameter-limit cutting treatment. Diameter-limit periodically. The center of each plot is monu- BRISSETTE ET AL.: SAMPLING COARSE WOODY DEBRIS

Compartment 4

200 Compartment 15

200 Compartment 16

1950 1960 1970 1980 1990 2000 Year Fig. 1. Harvest histories of three compartments sampled for downed coarse woody material on the Penobscot Experimental Forest in Maine. JOURNAL OF THE TORREY BOTANICAL SOCIETY

Fig. 2. Inclusion areas (partial circular regions) for point relascope sampling with three different angles (dashed lines) listed in Table 2 for a log (solid heavy line) of given length. IS the sample point falls inside the inclusion area for a log, the log will be tallied with the relascope. mented with a metal stake and the sampling de- there are no agreed upon standards for CWM, sign for CWM was superimposed over the per- they are arbitrary. Nevertheless, the same stan- manent plot system. Compartment 4 has 13 per- dards were used for all sampling methods. The manent plots and Compartments 15 and 16 each volume of each piece of CWM was calculated have 12 plots. using Smalian's formula (Avery and Burkhart 1983). CWM SAMPLINGMETHODS.Four methods Because of the novelty of the PRS technique, were used for sampling the CWM component of we describe the sampling process in more detail. the stands. First, a LIS scheme (Kaiser 1983, With PRS, an angle of fixed width is projected Warren and Olsen 1964) was used to provide a using the relascope from a sample point. The standard for comparison with the PRS. The LIS relascope angle can be determined in degrees (0 design consisted of four 10 m segments radiat-

Fig. 3. Sample design for the Penobscot Experimental Forest survey with arbitrary pieces of downed coarse woody material (numbered). Line intersect sampling (LIS) design is oriented in the cardinal directions with 10m lines; two projections of relascope angles v, and v2 are also shown. Projection of u, corresponds to any two perpendicular legs of the LIS sample lines in those given directions, though in practice, a continuous 360 degree swing about the point is done for each angle. gle, any sample point falling inside a log's in- would have encountered logs in the sampling clusion area would select that log into the tally procedure for two different angles v, and v, (Ta- record for that point. Because the surveyor must ble 1). The third relascope angle, v, = 90°, can be able to view the length of a log through the also be imagined as being coincident with any angle gauge, it should be observed that as one two of the LIS line segments connecting at right views the log more end-on instead of broadside, angles (e.g., the north and east sections). It is the likelihood of sampling the log vanishes. As clear from the illustration that logs 1, 2, 4 and mentioned earlier, this procedure is completely 5 would be sampled once each on the LIS in- analogous to the circular inclusion areas formed ventory phase. In addition, log 2 is longer than by a wedge prism or angle gauge in HPS for the width of the projected angle from v, and standing trees and snags. therefore is clearly "in", while log 3 is "bor- The sampling design used in this study is il- derline;" in which case, measurements from the lustrated in Figure 3. The four 10 m LIS seg- point center to the ends of the log would be re- ments are shown centered on the permanent quired to ascertain whether it is indeed in the sample point. The dashed-line circle represents sample (Gove et al. 1999, 2001). Similarly, log the smaller of two fixed-area plots used on the 6 is clearly a sample log for v, and therefore PEF (0.02 ha or 8 m radius). Ten pieces of would also be sampled with v,. There are other downed CWM are arbitrarily scattered about. logs, such as log 5, that could also be tallied Also shown are two positions where the 360" with one or more of these three relascope angles; swing of the relascope about the point center however, log 10 would be clearly be "out" for 84 JOURNAL OF THE TORREY BOTANICAL SOCIETY [VOL.130 any chosen angle on this sample point since the construction of confidence intervals, exactly as combination of its orientation and distance make is done when estimates are taken from multiple it impossible to be sampled (refer to Fig. 2). In point samples of overstory or multiple fixed-area addition, there may be other logs that are longer plots (Gove et al. 1999, 2001). than those illustrated that could be significantly It should be noted that while LIS was chosen farther from the point center, falling outside the as a convenient method for comparison against area shown, and still be sampled with PRS; this the field test of PRS, it only provides an estimate is especially true for the smaller angle. and does not represent the "truth." Therefore, A relascope is simple to construct using com- we used a measure of relative efficiency that in- mon materials (Gove et al. 2001). There are corporates the sampling error in all methods for three pairs of pins on top of the wooden support, comparison rather than some measure of abso- one pair for each of the three angles or ratios in lute accuracy. The same considerations would Table 1. The strapping attached to the relascope, apply if fixed-area plots had been used as the which, in conjunction with the pairs of pins, de- basis for comparison. Short of conducting de- fines the angles, is held next to the surveyor's tailed simulations on the efficiency of PRS, this eye and directly over the sample point location. is perhaps the best approach available for field The gage is always held in the horizontal plane studies. when used and should never be tilted towards Much of the time spent on a sampling method the log or along the slope. An easy way to en- is taken up with measurement of individual tal- sure accuracy, especially for "borderline" logs, lied pieces. This impacts the efficiency of dif- is for other crew members to hold poles verti- ferent sampling methods. For example, a method cally at each end of the log being sampled, al- with high variability between points may still be lowing the surveyor to look horizontally. On more efficient than one with low variability, if sloping ground, simple conversions detailed in the method with high variability requires tally- Stghl et al. (2002) may be applicable. In addi- ing and measuring fewer pieces per point. We tion, both LIS and PRS require corrections when calculated efficiency of a method (the three re- sampling close to the forest edge. The reflection lascope angles in this case), relative to LIS, as: or "mirage" method may be applied to both LIS and PRS to provide the requisite corrections. Gregoire and Monkevich (1994) discuss the ap- plication of the reflection correction method to where fi is the average number of pieces tallied LIS, while Gove et al. (1999) detail its use with on a point, and s2is the sample variance between PRS. points. An efficiency of 200% for an angle in- The expansion of sample quantities to per unit dicates that to obtain equal confidence limits, area means and totals in PRS is straightforward. twice as many logs would have to be tallied us- For each relascope angle there is a correspond- ing LIS as using the angle in question. The rel- ing squared length factor, L, that plays the same ative efficiency measure E can be derived in a role as the basal area factor in HPS. With PRS, straightforward manner by setting the confi- however, L connotes the amount of squared dence limits to be obtained under LIS and an length (e.g., m2/ha) represented by each sampled alternative method equal, and solving for the log and is a constant for a given relascope angle number of sample points needed under each (Table 1). Therefore, for any variable, J,, (e.g., method. Measuring the total inventory cost for volume) associated with the ith log, the estimate a given method as some constant times the num- for a given sample point is determined as: ber of points required, times the mean number of pieces tallied at each point, the relative efficiency measure is simply the ratio of the costs for the two methods. where rn is the number of logs tallied about the An assumption of the efficiency measure used point and I, is the length of the ith log. PRS here is that number of pieces tallied per point is would typically be applied using multiple sam- a reasonable proxy for time required per point, ple points in the area being inventoried. In this and that the time cost per piece is similar for case, each sample point provides a value of 9. LIS and PRS. This assumption may not hold The uwal mean and variance formulas can be when volume is the only variable of interest as applied to the individual point estimates for the LIS requires only one measurement (diameter at 20031 BRISSETTE ET AL.: SAMPLING COARSE WOODY DEBRIS 85

Compartment 4 Compartment 15 Compartment I6

LIS Vl v2 v3 LIS Vl v2 v3 4:l 2:l 1:l 4:l 2:l 1:l

LIS Vl v2 v3 LIS Vl v2 v3 LIS Vl v2 v3 4:l 2:l 1:l 4:l 2:l 1:l 4:l 2:l I:?

Fig. 4. Comparison of line intersect sampling (LIS) and point relascope sampling inclusion angles (v,, q, v,) for all compartments with number of logs and volumelha; in addition average number of logs tallied per point for each technique is given. Confidence intervals at the 95% level are shown about the histogram bars.

the intersection with the sample line to obtain will be more efficient than LIS unless measure- unbiased estimates of volume per unit area). ment time per piece is more than twice as long. However, LIS requires set-up time to lay out a line, or to follow carefully a line that has not Results and Discussion. In the Acadian For- been laid out. Furthermore, when variables other est, PRS compared favorably with LIS for mea- than volume, such as number of logs, are of in- suring CWM. Each of the relascope angles gave terest, LIS requires measurement of length for results comparable to LIS for the number of each log, so that time spent measuring each log pieces of CWM, or "logs", per unit area and for becomes virtually identical. An alternative inter- volume of CWM per unit area (Fig. 4). How- pretation of the efficiency measure views the ever, in this forest the average number of logs number of pieces tallied as similar but varies the tallied per sample point using angle v, was the relative measurement time. If PRS with a certain most comparable to LIS. angle has a relative efficiency of 200%, then it When using LIS, it is commonly assumed that JOURNAL OF THE TORREY BOTANICAL SOCIETY

Volume, m3/ha 450 1

LIS Vl v2 v3 LIS Vl V2 V3 LIS v1 v2 v3 4:l 2:l 1:l 41 211 1:l 4:l 2:l 1:l Comp. 4 Comp. 15 Comp. 16 Fig. 5. Relative efficiencies of point relascope sampling inclusion angles (v,, y, v,) compared to line intersect sampling (LIS) for density and volume of coarse woody material: no logs should be missed; however, Ringvall and The relative sampling efficiency of PRS in Stihl (1999) have documented that surveyors do each stand is shown in Figure 5. The results for miss logs, either intentionally or unintentionally, log density are highly variable. There is always especially in stands with dense amounts of at least one relascope angle that is substantially CWM, leading to an underestimation bias with more efficient than LIS. However, this angle LIS. The fixed diameter limit stands (compart- varies among stands. Relascope angle v, is al- ments 4 and 15) had dense understory vegeta- ways at least competitive with LIS. The results tion resulting in poor visibility and mobility. for volume are more consistent across methods. Consequently, we were concerned that PRS, es- PRS was more efficient than LIS across all pecially with v,, might not work as well as LIS stands and using all angles, except for v, in in those stands. This challenge was largely al- Compartment 16. Even there, however, the ef- leviated by using range poles placed at the ends ficiencies of PRS and LIS are similar. Wider an- of candidate logs for determining their sample gles were also generally more efficient. Given status with the angle gauge (Gove et al. 1999, the clumped distribution of downed CWM in 2001). The results suggest that no logs were these stands, it makes more sense to tally a few missed. Because the understory in Compartment pieces on average at many sample locations, 16 was quite open, finding all the CWM asso- than to tally many pieces on a few sample lo- ciated with a plot was not difficult with any of cations; the estimate is strongly influenced by the PRS angles. how many points land in clumps or between 20031 BRISSETTE ET AL.: SAMPLING COARSE WOODY DEBRIS 87 clumps. Although the ability to move through with v, also requires sampling at a large number the forest may influence sampling design (e.g., of points. The efficiency calculations presented following a severe wind throw disturbance), in here do not consider the fixed costs of setting general sampling at more locations is a more up a new sample location. Operationally, v, pre- efficient way of improving estimates, than sam- sents some practical advantages as well. Using pling intensively at fewer locations in stands like that angle, a log cannot be tallied unless it is at those we studied. least as close to the sample point as it is long The agreement between the average number (and may not be tallied even then depending on of logs sampled per point with v, and LIS is its orientation). If the downed CWM in a forest purely serendipitous. The choice of four, 10m comes predominantly from trees of the current LIS line segments per point, was completely ar- dominant cohort, using the v, angle gauge sets bitrary and was not determined with any fore- an effective maximum search radius of approx- thought to "matching" the tally of a given PRS imately one dominant tree height. From a prac- angle tally. In fact, this would be a difficult task tical standpoint. this allows field crews to avoid even with prior knowledge of CWM size and excess search time in areas far from the point, spatial distributions. while at the same time helping crews to under- In all cases, while not recorded, PRS took no stand how far from the point they should travel more time to conduct on a sample point than in order to ensure no downed logs are missed. LIS, even at the smallest angle (v,).Indeed, us- It should be remembered that the results of ing the medium and large angles (v, and v,) was this study are dependent on the specifications for much faster than LIS. If we assume that the time the minimum dimensions of CWM to be sam- it takes to measure any given log is proportional pled. That is, it must be expected that results, to its length because of travel time between even within the same stands, would vary from ends, then the above conclusion can be logically those found in this study if, for example, the defended, especially for v, and v,, since the av- smallest log sampled was required to have a erage number of logs tallied per point is low small-end diameter of 10 cm and minimum of 2 (Fig. 4) and the effective search radius for these m in total length. Guidelines for defining and logs is small (Fig. 2). For v,, larger logs can be measuring CWM have been presented by Har- some distance from the sample point; but these mon and Sexton (1996).Inventory specifications occur infrequently. Because there is no setup for CWM are analogous to merchantability stan- time with PRS as there is laying out lines in LIS, dards in typical forest inventories but, in the ab- the only extra time associated with this tech- sence of a specific rationale such as the habitat nique beyond the actual measurement time is the requirements of a particular species of wildlife, time spent locating candidate logs and determin- are more arbitrary. Nevertheless, it remains an ing whether "borderline" logs are "in" or important point for consideration when design- "out". ing inventories for down CWM and subsequent comparison with other studies. Conclusions. For even the most basic ecological investigations, field effort is often a lim- Literature Cited iting factor. In the Acadian Forest, PRS has po- AVERY,T. E., AND H. E. BURKHART.1983. Forest mea- tential to provide an accurate, relatively fast surements, third edition. McGraw-Hill, New York. method of measuring downed CWM, making it 331 p. easier to include this important structural ele- BRAUN,E. L. 1950. Deciduous forests of eastern North America. Hafner Press, New York. 596 p. ment in ecological assessments. Compared to BRISSETTE,J. C. 1996. Effects of intensity and fre- LIS, PRS provides similar estimates of CWM quency of harvesting on abundance, stocking and density and volume, but with greater sampling composition of natural regeneration in the Acadian efficiency and without the need to layout sample Forest of eastern North America. Silva. Fennica 30: transects or other plot boundaries. The results 301-314. DEGRAAF,R. M., AND M. YAMASAKI.2000. New Eng- shown in Figures 4 and 5 suggest that for all- land wildlife: habitat, natural history, and distri- around use in stands similar to the PEE whether bution. University Press of New England,- Hanover, managed or unmanaged, a relascope angle be- NH. 482 p. tween v, and v, may be appropriate, ~h~ GREGOIRE,T. G., AND N. S. MONKEVICH.1994. The reflection method of line intercept sampling to smallest was more efficient for eliminate boundary bias, En", Ecol, Stat, 1: 219- volume, but was not always efficient for deter- 226, mining log density. Obtaining reliable estimates GROSENBAUGH,L. R. 1958. Point-sampling and line- 88 JOURNAL OF THE TORREY BOTANICAL SOCIETY [VOL.130

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