Forest Ecology and Management 239 (2007) 159–168 www.elsevier.com/locate/foreco Distribution, composition, and orientation of down deadwood in riparian old-growth woodlands of Zoar Valley Canyon, western New York State, USA Erin K. Pfeil a, Nicole Casacchia b, G. Jay Kerns b, Thomas P. Diggins a,* b a Department of Biological Sciences, Youngstown State University, Youngstown, OH 44555, USA Department of Mathematics and Statistics, Youngstown State University, Youngstown, OH 44555, USA Received 24 August 2006; received in revised form 1 December 2006; accepted 1 December 2006 Abstract During 2005, we catalogued down deadwood (DDW) in forty-one 30-m  30-m quadrats on 10 riparian upper terraces within the minimally disturbed Zoar Valley Canyon of western New York State. Woodlands on these former floodplains represent late-successional stages of a diversity of broadleaf ecotypes, with increment core-based stand ages up to 351 years. Volume of DDW averaged 84.9  9.7 (S.E.) m3/ha among all quadrats, and ranged up to 145.3  43.2 m3/ha on individual terraces. Abundance of downed sugar maple reflected this species’ prevalence in the live overstory, but American beech deadwood was markedly overabundant due to beech bark disease mortality. Prevalence of very-shade-tolerant (sugar maple, American beech, eastern hemlock) DDW was modest for northern hardwood old growth (46.4  4.3% among all quadrats), and was not related to stand age. We speculate this may reflect the floodplain origin of these woodlands. Down deadwood volume was positively associated with stand age among terraces (R2 = 0.446, P = 0.035), but not at the neighborhood scale of 30-m quadrats (R2 = 0.027), where individual tree mortality may obscure broader patterns. Orientation of DDW was non-uniform (Kolmogorov–Smirnov goodness-of-fit, P < 0.05) on five of the ten study terraces, where statistical trends in treefall direction suggested the influence of prevailing westerly winds blowing through the east-west canyon (this DDW orientation was also opposite to stream flow). This was an unexpected result, however, as we otherwise found very limited evidence of episodic wind-throw within the study area. # 2006 Elsevier B.V. All rights reserved. Keywords: Down deadwood; Riparian forest; Orientation; Old growth; Zoar Valley 1. Introduction Ongoing processes of tree mortality and down deadwood (DDW) accumulation are integral to the development of nearly every forest. As suggested by Franklin et al. (1987), at death a tree ‘‘has only partially fulfilled its potential ecological function’’. It has long been recognized that fallen trees represent critical subunits of the forest ecosystem, complete with their own sets of physico-chemical and biological features (Graham, 1925). It is also recognized that the concurrent opening of light gaps often plays a defining role in canopy structure and composition (Runkle, 1982). Down deadwood may be generated by episodic disturbances such as wind (Lin et al., 2004), fire (Frelich and Reich, 1995), ice storm (Lemon, 1961), or disease (McGee, * Corresponding author. Tel.: +1 330 941 3605; fax: +1 330 941 1483. E-mail address: tpdiggins@ysu.edu (T.P. Diggins). 0378-1127/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2006.12.001 2000), or may accumulate more or less continuously through the aging and death of individual trees (Runkle, 2000). Varying combinations of any or all such factors may affect a woodland at any given point in time and space. Much attention has focused on the abundance, composition, state of decay, and habitat value of deadwood in stands of varying ages and disturbance histories (Bormann and Likens, 1979; Harmon et al., 1986; Goodburn and Lorimer, 1998; Idol et al., 2001). An abundance of downed and standing woody debris is widely regarded as a structural indicator of minimally disturbed old growth (Martin, 1992; Greenberg et al., 1997), although old forests are not necessarily the only type that may exhibit high deadwood loads (see McCarthy and Bailey, 1994; Hardt and Swank, 1997; Goodburn and Lorimer, 1998 for high DDW volumes immediately after harvest). Treefall and deadwood dynamics have been well described in central and eastern North American upland forests (Tyrell and Crow, 1994; Spetich et al., 1999; Ziegler, 2000; Webster 160 E.K. Pfeil et al. / Forest Ecology and Management 239 (2007) 159–168 and Jenkins, 2005), but less so in riparian ecosystems, where downed wood is often studied primarily in terms of its contribution to the stream channel (e.g., Bragg, 2000; Williams and Moriarity, 2000). The riparian ecosystem of Zoar Valley in western New York State contains pristine old-growth northern hardwood and mesophytic forest as well as a minimally regulated river (Hunt et al., 2002; Diggins and Kershner, 2005). The rugged isolation of this canyon system has left its forests unlogged and almost completely undisturbed by human activities. Sheer 100-m walls and deep meanders give an impression of substantial protection offered to the riverside terraces below. Impressive tree heights here of up to 47 m (Diggins and Kershner, 2005) are often casually attributed to protection from wind stress, although this premise has not been tested. Zoar Valley thus offers a rare opportunity to examine deadwood accumulation within a minimally disturbed eastern riparian zone that likely differs from a comparable upland site in at least two fundamental aspects: (1) successional dynamics will be predominantly primary, with riverside terrace woodlands ultimately having started on nascent floodplains; (2) physical protection may substantially influence the relative importance of episodic disturbance versus more continuous gap phase dynamics. The objectives of this study were to (1) quantify down deadwood distribution and composition on Zoar Valley’s riverside terraces in relation to stand age and live canopy characteristics and (2) quantify directional orientation of treefalls to assess the contribution of prevailing winds and/or episodic blowdowns. Because we surveyed DDW within discrete quadrats on spatially separated terrace landforms, we were able to examine woody debris across a gradient in stand age at multiple ecological scales. Survey quadrats corresponded to a 0.1-ha neighborhood scale, and terraces roughly corresponded to a 10-ha small stand scale (definitions of Frelich, 2002). To this end we likewise conducted a meta-analysis for eastern North America of DDW versus stand age using 22 published studies of hardwood and/or hemlock hardwood sites (100-ha large stand scale), including the present results from Zoar Valley. A number of authors (Bormann and Likens, 1979; Harmon et al., 1986; Hardt and Swank, 1997; Busing, 2005) have reported and compared woody debris data among independent studies, but none as extensively as in the present paper. 2. Methods 2.1. Study area The 60–130-m deep Zoar Valley Canyon (Fig. 1) in western New York State (N428260 , W788520 ) encompasses 11 km of the Main Branch and 8 km of the South Branch of Cattaraugus Creek, a 6th order tributary to Lake Erie. Hunt et al. (2002) qualitatively identified >300 ha of pre-settlement forest here, and 175 ha within the 1182-ha New York State Zoar Valley Multiple Use Area (Fig. 1B). The present study was conducted on 10 riparian upper terraces within the Multiple Use Area totaling 22.3 ha (Fig. 1C). These terraces represent former floodplains, but at present are likely no longer inundated. (A May 2004 flood of 1/2 the discharge of a 100-year event did not appear to reach any of the study terraces [pers. obs.].) Riverside vegetation in Zoar Valley likely represents a chronosequence of primary succession on various depositional fluvial landforms (Diggins, 2005). Aerial images (Fairchild Aerial Surveys, 1929; United States Geological Survey, 1962; Fig. 1. Zoar Valley study site details showing: (A) regional location, (B) Cattaraugus Creek Main and South Branches and New York State Multiple Use Area, and (C) canyon and river outlines with locations of study terraces. 161 E.K. Pfeil et al. / Forest Ecology and Management 239 (2007) 159–168 New York State Geographic Information Systems Clearinghouse, 2002 [high resolution satellite orthoimagery]) clearly show the sequential development of vegetation on present-day lower floodplain terraces, while qualitative evidence on upper terraces (e.g., riverbed cobbles at 0.5–2-m depths in treefall root pits and along erosional banks) suggests they too have followed a similar history, although farther in the past. Riparian woodlands on the study terraces include a diverse assemblage of mesic and riverfront ecotypes, with 24 tree species present. Sugar maple (Acer saccharum) dominates (30% of basal area), with American beech (Fagus grandifolia), tuliptree (Liriodendron tulipifera), white ash (Fraxinus americana), American basswood (Tilia americana), and eastern hemlock (Tsuga canadensis) also well represented (Diggins and Kershner, 2005). Much of the study area displays uneven multi-aged stand development, although some terrace woodlands are still in demographic transition, i.e., understory re-initiation (see Oliver and Larson, 1996; Frelich, 2002 for definitions). Core-dated eastern hemlock reach 385 years of age, while sugar maple, yellow birch (Betula allegheniensis), and American sycamore (Platanus occidentalis) exceed 250 years (present study). Canopy height is impressive for the northeastern United States, ranging between 33 and 43 m, with emergent tuliptree and sycamore to 47 m (Diggins and Kershner, 2005). Diggins and Kershner (2005) concluded that the lower five terraces along the Main Branch (Fig. 1C of present paper, terraces 4–8) had likely never been logged, even selectively. Particularly compelling was the presence of large and wellformed black walnut (Juglans nigra) up to 90 cm DBH and 38 m tall (Diggins and Kershner, 2005), and core-dated to 200 years (incomplete core of 181 years, J. Battaglia, NY Audubon, pers. commun., 2005). Previously undescribed terraces 9 and 10 are among the most remote in the entire canyon, and likewise support woodlands that are unmistakably primary old growth (Diggins, unpublished data, note also stand age ranges in Table 1 of present paper). In contrast, terraces 1–3 are located closer to the pre-1950 Valentine Flats farmstead (Fig. 1C) and to a small 19th century sawmill downstream of the Multiple Use Area, so if selective logging ever occurred within the study area it was most likely here. However, there is no present evidence of or specific historical reference to timber extraction. Therefore, we consider all 10 study terraces to be effectively free of direct human influence on forest dynamics, including DDW accumulation. 2.2. Down deadwood surveys During May–July of 2005, a quantitative survey of DDW was conducted in 41 previously established 30-m  30-m quadrats distributed among the terraces in a stratified design (Diggins and Kershner, 2005; Diggins, 2005). These quadrats had never been permanently marked, but were relocated within at most a few meters based on field notes, prominent trees, and other recognizable landmarks. All pieces of DDW >15 cm maximum diameter were identified to species where possible, measured for length, maximum and minimum diameter, and compass orientation, and assigned to one of five decay classes as defined by Pyle and Brown (1998). A fallen tree was included if >50% of its length was inside a quadrat, regardless of the location of its origin. Down deadwood displaying characteristics of multiple decay classes was assigned to the class representing the greatest amount of wood. Identity of DDW was determined using species specific characteristics including bark features, branching pattern, and sometimes even leaves (for decay class 1). Five species could be identified in advanced decay classes reliably enough that DDW quantification may have been relatively complete (identifying features in parentheses): (1) sugar maple (blackened and/or spalded [streaked] appearance of decayed wood), (2) American beech, (3) yellow birch (remnants of identifiable bark), (4) eastern hemlock (the only conifer, blocks of reddish wood, whorls of perpendicular branches/scars), and (5) American basswood (association with live trunks remaining in multi-stemmed clumps). We did not pursue identification of unknown DDW (1/3 of the total) based on wood anatomy (see Rubino and McCarthy, 2003) because multiple species of each major vascular type (ring porous versus diffuse porous) commonly occurred within the same stands, suggesting we might still have failed to identify much of this DDW. Table 1 Summary of overstory stand age and down deadwood (DDW) characteristics by terrace Terrace Stand age (years) DDW volume (m3/ha) Dead:live (ratio) % DDW shade tolerant Orientation (K–S P-value) 1 2 3 4 5 6 7 8 9 10 129–194 128–187 140–201 113–257 170–351 115–243 109–158 128–235 208–228 134–289 80.8  13.6 79.7  8.6 60.1  17.9 78.1  40.5 145.3  43.2 88.8  16.5 15.8  2.1 114.5  50.7 68.4  9.9 54.3  6.9 0.29  0.10 0.20  0.02 0.11  0.03 0.12  0.07 0.30  0.07 0.20  0.04 0.03  0.01 0.34  0.20 0.19  0.03 0.13  0.02 25.6  6.8 65.3  17.9 69.5  29.3 21.9  11.1 58.7  9.7 36.8  5.7 22.6  10.1 36.3  22.0 67.7  11.7 65.4  11.8 <0.001 0.092 0.079 <0.001 0.122 0.021 0.049 0.994 0.005 0.218 (n = 4) (n = 4) (n = 2) (n = 5) (n = 5) (n = 7) (n = 2) (n = 4) (n = 4) (n = 4) Notes: Number of survey quadrats (n) given for each terrace. Stand age presented as range of quadrat core-based estimates. Total DDW volume, dead:live volume ratio (for DDW and live trees >20 cm diameter), and % DDW volume shade tolerant presented as means (S.E.) among quadrats. Shade tolerant species constitute sugar maple, American beech, and eastern hemlock. Orientation vs. uniformity of DDW indicated by significance of Kolmogorov–Smirnov (K–S) goodness-of-fit test (P < 0.05 indicates non-uniform orientation). 162 E.K. Pfeil et al. / Forest Ecology and Management 239 (2007) 159–168 A Nikon 400 laser range finder was used to measure lengths of DDW pieces >10 m, whereas a tape measure was used for shorter pieces. For solid pieces of DDW, a tape measure was used to determine half-circumferences that were then converted to diameters. For substantially flattened DDW, diameter was measured directly. Volumes of down deadwood pieces were then calculated as cylinders having these measured lengths and average diameters. This approach likely overestimated the present volumes of highly decayed and flattened DDW pieces. Separate DDW pieces and/or large branches >10 cm diameter from the same fallen tree were measured individually in this fashion and summed to calculate volume. Orientation of DDW pieces was determined by a magnetic compass, starting from the origin of the fallen tree. If the origin of DDW was not apparent either from the presence of its stump, snag, or tip-up, or by a measurable taper, it was not included in assessment of DDW orientation. Additionally, DDW obviously generated by canopy branches was not assessed for orientation, as position on the ground might not indicate direction of fall. 2.3. Down deadwood characterization In addition to total volume, deadwood:live volume ratios and percentages of DDW volume identified as very-shade-tolerant species (sugar maple, American beech, eastern hemlock [Burns and Honkala, 1990]) were calculated for each quadrat. For deadwood:live ratios, live wood volumes were calculated using Zoar Valley overstory (>20 DBH) basal areas measured during 2002–2004 by Diggins and Kershner (2005) and Diggins (unpublished data). Deadwood:live ratios were calculated using only DDW >20 cm diameter to correspond to the size class of standing trees used. It is likely that some previously measured standing live wood now represents DDW, but only one large tree had come down within a quadrat (a 114 cm DBH American beech on Terrace #6), and was thus removed from live basal area for calculation. Average overstory height was estimated for each quadrat based on prior tree height measurements (Diggins and Kershner, 2005; Eastern Native Tree Society, 2004) throughout the study area using accurate laser range finder triangulation methods (Blozan, 2006). Because Zoar Valley’s terrace woodlands grow on level ground and are dominated by trees with single straight trunks and high first branches, tree volume was modeled as a simple cone (volume = 1/3 [height  basal area]). Wood volume below breast height was estimated by assuming DBH to represent 75% of tree diameter at the ground—a relationship based on trunk flare of numerous broadleaf trees in eastern old-growth woodlands (Rucker, 2003). We chose these somewhat cumbersome calculations rather than standard DBH:volume tables because we felt the former better represented the actual study area, and better estimated total wood volume rather than just merchantable volume. The methods outlined above were also used to calculate species deadwood:live volume ratios for sugar maple and American beech, the latter of which may be suffering excess mortality from beech bark disease (Cryptococcus fagisuga scale with associated Nectria spp. fungus). Because deadwood catalogued during the present study included only downed logs, volume ratios somewhat underestimate the contribution of all deadwood, including snags (e.g., see Goebel and Hix, 1996; Goodburn and Lorimer, 1998; Spetich et al., 1999). 2.4. Down deadwood orientation On each terrace, a Kolmogorov–Smirnov (K–S) goodness of fit test was performed to determine whether compass orientations of DDW pieces were uniformly distributed (DDW was uniformly distributed if P > 0.05, directionally oriented if P < 0.05). The K–S goodness-of-fit test is not affected by changes in scale, so the circular nature of orientation data was not a concern. The null distribution was continuous-uniform on the interval [08, 3608]. Because K–S requires that all data points be unique, matching DDW orientations were randomly perturbed by 0.018 increments to eliminate duplications in the data. Exact K–S P-values were obtained by the statistical package R 2.1.0 using the method of Marsalia et al. (2003). For DDW-oriented terraces, two-dimensional plots were generated on which locations along a unit circle with its center at the origin represented measured compass orientations of DDW pieces. Because compass orientations were thus converted to points in two-dimensional space, circularity of the data was again not a concern. The center of mass of points on the unit circle was then calculated for each terrace. Orientations of these centers of mass were taken as point estimates of the average orientation of DDW on each terrace. Due to the complicated nature of the sampling distributions of these centers of mass, their distributions were approximated using bootstrap resampling methods (B = 10,000 bootstrap iterations). Resulting distributions showed negligible bias, so 95% and 68% confidence intervals for terrace mean compass orientations were determined using adjusted bootstrap percentile (BCa) intervals (Venables and Ripley, 2003). Monte Carlo permutation tests (10,000 iterations) were used to compare mean maximum diameter between oriented DDW pieces (i.e., inside bootstrap confidence intervals) and non-oriented pieces, pooling data for all five terraces where Kolmogorov–Smirnov P < 0.05. This test was conducted for both 95% and 68% confidence intervals. 2.5. Stand age estimates Increment cores (obtained with Suunto 1000 and 1600 borers) of one or more of the suspected oldest trees in each quadrat were used to estimate minimum stand ages. Trees were cored perpendicular to any lean and at or near breast height (1.37 m), at which age estimates are presented. If a core missed the pith, a concentric circle overlay was used to estimate pith location. The innermost five rings (ten if tight) were then used to estimate the missing growth. Large and old sugar maple and American beech were often hollow, and it was decided to extrapolate the age of such individuals rather than summarily excluding them from stand age data. The potential length of missing core was calculated as the average radius minus the length of the core. 163 E.K. Pfeil et al. / Forest Ecology and Management 239 (2007) 159–168 Fig. 2. Species and decay class distribution of all down deadwood (DDW) by volume in study area. Missing growth was then estimated as the average growth over this increment (starting at pith) displayed by 3–5 conspecific trees for which the pith was reliably located. Some additional trees were cored solely for this purpose. To keep these estimates conservative, cores displaying periods of suppression were not used to estimate missing growth. A close agreement between extrapolated maximum ages and those obtained from complete cores (257 years versus 243 years, and 235 years versus 233 years, for sugar maple and American beech, respectively) suggested these hollow tree estimates were reasonable. 3. Results Mean (S.E.) DDW volumes on Zoar Valley terraces ranged from 15.8  2.1 m3/ha on terrace 7, to 145.3  43.2 m3/ha on terrace 5 (Table 1). Total study area mean among all 41 quadrats was 84.9  9.7 m3/ha. Mean deadwood to live wood ratios ranged from 0.03  0.01 on terrace 7, to 0.34  0.20 on terrace 8 (Table 1). Study area mean was 0.21  0.03. Among DDW identified to species, American beech and sugar maple contributed the greatest volumes (Fig. 2). Mean % DDW identified as very-shade-tolerant ranged from 21.9  11.1% on terrace 4, to greater than 60% on terraces 2, 3, 9, and 10 (Table 1). Shade tolerance averaged among all quadrats was 46.4  4.3%. Decay classes 2–4 were generally the most prevalent (Fig. 2). Where represented as both live trees and deadwood, American beech displayed high mean dead:live ratios (Table 2) ranging from 0.53 to a value greater than 2:1 (on terrace 5). In contrast, mean dead:live ratio for sugar maple was elevated only on terrace 3 (0.94  0.49), with values for all other terraces less than 0.3 (Table 2). Numerical distribution of all DDW (i.e., based on number of pieces) across 5-cm maximum diameter classes followed a distinctly negative exponential relationship (Fig. 3A, R2 = 0.920). Down deadwood diameter class distribution in terms of volume revealed a notable abundance between 30 and 60 cm, but also substantial volumes of large DDW up to 100 cm diameter (Fig. 3B). Comparison between numerical deadwood and live (Diggins and Kershner, 2005; Diggins, unpublished data) diameter distributions within 10-cm classes revealed no difference between DDW and the overstory (x2 = 12.431, P = 0.020). Regression of DDW volume on stand age for data collected during the present study indicated a significant positive relationship at the terrace scale (Fig. 4A, R2 = 0.446), but not at the quadrat scale (Fig. 4B, R2 = 0.027). A significant positive relationship (Fig. 5, R2 = 0.394) was also noted when DDW volume was regressed on stand age among 22 independent studies of eastern North American hardwood sites (listed in Table 3, including the present study), however, only if several reports of very high post-logging slash volumes were excluded (e.g., Hardt and Swank, 1997; Spetich et al., 1999; Idol et al., 2001). In Zoar Valley, percent DDW shade tolerance was not significantly related to stand age at either the terrace (R2 = 0.193) or quadrat scale (R2 = 0.035). Kolmogorov–Smirnov goodness-of-fit tests indicated that fallen trees in Zoar Valley were uniformly/randomly oriented on five terraces, but directionally oriented on five others Table 2 Down deadwood (DDW) of American beech and sugar maple by terrace Terrace American beech Sugar maple 3 DDW volume (m /ha) 1 2 3 4 5 6 7 8 9 10 a 0.0 16.5  9.5 0.4 a 13.2  11.5 33.1  15.2 16.3  10.7 0.0 a 65.5  61.5 29.0  9.6 16.7  8.9 Dead:live (ratio) a 0.00 0.59  0.51 <0.01a 0.53b 2.64  2.47 0.87b 0.00a 0.53  0.49 0.77b 0.86  0.24 DDW volume (m3/ha) Dead:live (ratio) 19.3  5.5 26.3  13.6 36.1  4.5 3.9  2.1 45.7  32.6 12.6  4.6 3.4  1.1 3.8  2.2 15.8  10.9 16.8  10.8 0.17  0.11 0.20  0.13 0.94  0.49 0.07  0.05 0.23  0.15 0.28  0.18 0.01  0.01 0.02  0.02 0.06  0.04 0.06  0.05 Notes: Data presented as means (S.E.) among quadrats except where noted. Dead:live wood volume calculations did not include quadrats that lacked a species entirely (both live and DDW). a Only one quadrat contained species; no standard error. b One or more quadrats contained only deadwood, so a dead:live ratio would require division by zero. Ratio was thus calculated for the terrace as a whole. 164 E.K. Pfeil et al. / Forest Ecology and Management 239 (2007) 159–168 Fig. 3. Maximum diameter distribution of all catalogued down deadwood (DDW) in study area: (A) by number of pieces and (B) by volume. Significant negative exponential curve shown in panel (A) (P < 0.05). Fig. 5. Down deadwood (DDW) volume vs. stand age as reported by 21 published studies indicated by lower case letters. Author(s) and geographic locales given in Table 3. Pooled Zoar Valley data indicated by open square symbol. Significant linear regression line and equation shown (P < 0.05). Figure includes only DDW catalogued in hardwood or hardwood/hemlock stands east of Mississippi River, and reported as volumes. Data reported by authors as representing residual logging slash were not included. Grouping of data by original authors into age classes and/or forest types was maintained here. Sampling effort varied among studies, but all data points represent multiple survey plots. (Table 1). Compass directions (designated clockwise from north at 08) of DDW where non-uniform ranged from 548 to 1518; i.e., in a predominantly eastward direction (Fig. 6). Monte Carlo permutation tests revealed no differences in mean maximum diameter between DDW pieces falling inside and those falling outside of bootstrap confidence intervals (P-values of 0.619 and 0.572 for 68% and 95% confidence intervals, respectively). Table 3 Data sources for Fig. 5 Fig. 4. Association of down deadwood (DDW) volume with stand age: (A) among terraces and (B) among quadrats (R2 for simple linear regression). Significant linear regression line and equation shown in panel (A) (P < 0.05). Code Citation Locale a b c d e f g I k m n o p r s u v w x y z & MacMillan (1981) Harmon et al. (1986) McCarthy and Bailey (1994) Tyrell and Crow (1994) Goebel and Hix (1996) Hardt and Swank (1997) Shifley et al. (1997) Goodburn and Lorimer (1998) Hale et al. (1999) McGee et al. (1999) Forrester and Runkle (2000) Ziegler (2000) Idol et al. (2001) McCarthy et al. (2001) Rubino and McCarthy (2003) Muller (2003) Stewart et al. (2003) Jenkins et al. (2004) Busing (2005) Wilson and McComb (2005) Webster and Jenkins (2005) Present study IN Eastern USA MD WI/MI OH So. Appalachians MO WI/MI MN Adirondacks NY OH Adirondacks NY IN OH OH KY Nova Scotia IN So. Appalachians New England So. Appalachians Zoar Valley NY E.K. Pfeil et al. / Forest Ecology and Management 239 (2007) 159–168 Fig. 6. Compass directions (solid arrows) and 68% bootstrap confidence intervals (dashed arrows) for down deadwood (DDW) orientation centers of mass where significantly different from uniform (Kolmogorov–Smirnov goodness-of-fit, P < 0.05). 4. Discussion Long-term series of quantitative stand data undoubtedly provide the clearest record of forest dynamics and disturbance history (e.g., Stearns, 1949; Whitney, 1984; Volk and Fahey, 1994; Ward et al., 1996). However, such data are available all too infrequently. Hence, we more often look to tree-ring chronologies (Nowacki and Abrams, 1994), or to current structural and compositional features such as canopy gaps (Runkle, 1982) or coarse woody debris (Harmon et al., 1986) as a surrogate for this information. In the Zoar Valley Canyon, historical quantitative data are entirely lacking, so this was the only option. Down deadwood on the Zoar Valley terraces (although far from uniform spatially) was generally consistent with expectations for hardwood and hemlock/hardwood old growth in terms of volume, size distribution, and state of decay (see references in Table 3 of present paper). This might not be surprising, though, because study area woodlands also meet broad quantitative and qualitative criteria for eastern old growth, and are dominated by later stand development stages. However, it should be realized that the Zoar Valley terrace woodlands have followed a distinctly different successional path from most other eastern woodlands where coarse woody debris has previously been quantified. Because they have developed on fluvial landforms deposited within Cattaraugus Creek’s dynamic river channel, they represent not a gradient in time since exogenous disturbance, but likely a chronosequence in primary succession. In upland forests, developmental age is effectively the time since stand-leveling disturbance, which in northern hardwoods may locally extend several thousand years absent logging (Frelich and Lorimer, 1991). In Zoar Valley, we suspect the developmental age of terrace woodlands more typically spans hundreds of years, although this has not yet been verified by dating fluvial landforms. Consequently, some, perhaps much, of the DDW beneath even the oldest living trees may represent earlier successional stages. This may have contributed to both the modest (for old growth) prevalence of very-shade-tolerant DDW and to a lack of association between DDW shade tolerance and overstory age. Of course, some shade-tolerant DDW may have been lost within the unidentified fraction of deadwood, although we had reasonable confidence in our visual identifications of downed sugar maple, hemlock, and beech. At the quadrat (neighborhood) scale, we documented a wide range in shade tolerance of DDW where the overstory was 165 predominantly late successional and shade tolerant (i.e., >60% of basal area). We speculate that under-representation of shadetolerant DDW compared to the overstory might suggest a more recent transition to the uneven-aged condition. In contrast, abundant shade-tolerant DDW could indicate a late-successional self-replacement stage. However, unlike spatial trends in stand development (e.g., demographic transition stands tended in Zoar Valley to be located away from the canyon slope and at the downstream ends of terraces where landforms are likely relatively young), DDW shade tolerance did not necessarily suggest such a connection to landform age. We thus conclude it may be difficult in late-successional riparian stands to discriminate the imprints of landform development from the concurrent effects of gap phase dynamics, especially at smaller spatial scales (i.e., neighborhood/study plot). Regardless of the proximate ecological influences on DDW generation, our study revealed that American beech has suffered disproportionate mortality from beech bark disease (see McGee, 2000; Griffin et al., 2003) that is visually apparent in Zoar Valley (Diggins and Kershner, 2005). Although beech mortality was highly variable among study terraces, DDW to live ratios averaged 3.2 times greater than those of sugar maple, curiously similar to the situation described by McGee (2000) in Adirondack northern hardwoods. Only one Zoar Valley quadrat (on terrace #3) supported a sizeable beech population free of recent mortality (25 m2/ha basal area [Diggins, unpublished data]). It should be noted that MacMillan (1988) found DDW decay rate for beech to be slower than for Acer spp., suggesting beech DDW might be more persistent. However, we feel the over-abundance of decay classes 1–3 beech DDW revealed by the present study was too dramatic to be explained only by differential decay rates. If terrace DDW totals in Zoar Valley were to be adjusted for excess beech bark mortality as suggested by McGee (2000), under-representation of shadetolerant species would be even more pronounced, supporting our speculation that some of these riparian woodlands may only recently have entered a climax stage. A positive association of DDW volume with maximum tree age among Zoar Valley’s streamside terraces was consistent with relationships previously reported by a number of studies of eastern hardwood forests (e.g., Tyrell and Crow, 1994; Hardt and Swank, 1997; Ziegler, 2000; Idol et al., 2001). This association was also consistent with the trend revealed by our meta-analysis of eastern North American DDW data from the peer-reviewed literature (Fig. 5, present study), although, we reiterate, only after the exclusion of high post-logging slash volumes. However, linear regression slopes of DDW volume to stand age where reported by individual studies varied considerably, from 0.43 (Tyrell and Crow, 1994) to 0.73 (Ziegler, 2000), suggesting they may be somewhat idiosyncratic. Likewise, the DDW to stand age regression line generated by the meta-analysis presented in Fig. 5 of this paper should be viewed as a trend, and not as a linear model, given the wide range of forest types and potentially variable study criteria included. Still, we were impressed by the degree to which these independently collected DDW data indicated woody debris accumulation with increasing stand maturity. We had initially 166 E.K. Pfeil et al. / Forest Ecology and Management 239 (2007) 159–168 suspected that perhaps differences in site conditions and forest types might obscure any such trend. In Zoar Valley, unlike the case for whole-terrace data (small stand scale), all relationships between DDW and stand age dissolved at the neighborhood/quadrat scale. We speculate that within 30-m quadrats individual tree mortality may override relationships apparent at larger scales (see also Frelich and Lorimer, 1991), such that the fall of one or two large and old trees could yield a high DDW load but a reduced maximum tree age. This clearly was the case for the two highest DDW volume quadrats in Zoar Valley, where it was obvious the oldest trees were on the ground at the time of surveying. We also suspect the riparian history of terrace woodlands has generated some large DDW loads associated with modest stand ages. American sycamore and eastern cottonwood are major components of the canyon’s emergent floodplain woodlands (Diggins, 2005), and persist on higher terraces to reach very large size (Diggins and Kershner, 2005). These trees are aging and contributing to DDW where terrace woodlands are in transition from riverfront to mesic ecotypes (see Meadows and Nowacki, 1996), e.g. the downstream end of terrace #6 where DDW volume ranged up to 118 m3/ha but maximum tree age was <130 years. In contrast, demographic transition stands that lacked sizeable bottomland species (e.g., terrace #7 and downstream quadrats on terrace #4) had only modest DDW accumulations (10–18 m3/ha) more suggestive of their <160-year stand ages. It would be very informative to study coarse woody debris dynamics within Zoar Valley’s early-successional floodplain woodlands, as the youngest overstory age in any quadrat during the present study was 109 years. However, two potentially confounding influences would need to be addressed on active floodplains: (1) some deadwood may have been deposited by floodwaters and would need to be distinguished from treefalls and (2) some Zoar Valley floodplains border recreationally popular stretches of Cattaraugus Creek where rafters, anglers, and day hikers collect downed wood for campfires. Neither of these factors precludes study of floodplain woody debris, although they may require a more restrictive sampling design. In terms of influence of prevailing winds on treefall, different lines of evidence produced by our study suggest an interesting paradox. The negative exponential diameter distribution of Zoar Valley’s DDW and the close agreement between downed wood and overstory size distributions are consistent with long-term gap phase mortality, rather than episodic disturbance (see also Spetich et al., 1999; McCarthy et al., 2001). Large-scale windthrow appears to be infrequent within our study area, and we encountered (not in a quadrat) only one modest example of what appeared to be a blowdown— a few dozen parallel fallen trees along the riverside margin of terrace #1, up to 50 cm diameter and in decay classes 3 or higher. An obvious wind event also struck the study area immediately after data collection in 2005 (at a narrow constriction of terrace #6 along a river meander), but this event brought down large crown branches rather than whole trees. Thus, we found it surprising that five of ten terraces revealed directional orientation in treefall, and that all five suggested prevailing westerly winds blowing up the length of the Main Branch Canyon. This orientation was exactly opposite to stream flow, and thus to any past hydrologic influence that may have repositioned DDW when the terraces were still active floodplains. The distinct qualitative impression of isolation and protection within this canyon may not reflect true meteorological and ecological conditions. Interestingly, though, the lack of a diameter difference between oriented and nonoriented fallen trees argued against the directional fall of canopy dominants that would be expected from storm events (Lin et al., 2004). Perhaps the most parsimonious explanation for these seemingly conflicting lines of evidence is that longterm mortality in the study woodlands has been dominated by gap phase dynamics, but that the action of prevailing winds may contribute to the actual fall of individual trees. It is often observed that trees growing in various topographic hollows surpass in height their more exposed conspecifics—a trend confirmed by accurate and systematic tree height surveys throughout the eastern hardwood region, including the present study area (Eastern Native Tree Society, 2004). However, given the evidence of wind effects even in Zoar Valley’s steep-walled canyon, it may be unwise to attribute such height potential exclusively to shelter. Other factors such as water availability, alluvial soil richness, and/or the interaction between tree architecture and sunlight interception could also play important roles. 5. Conclusions Volumes of DDW on riparian upper terraces in Zoar Valley varied spatially, but generally indicated the abundant accumulation typical of old growth. American beech was over-represented as deadwood, likely due to beech bark disease. Downed wood volume increased with stand age at the scale of separate terraces, but not at the neighborhood scale of individual survey quadrats. Fallen trees on five of the ten terraces were directionally oriented, apparently in line with prevailing westerly winds. However, there was no evidence that the study area has been regularly affected by episodic blowdowns. In the eastern United States and the Great Lakes Region, bottomland hardwoods are perhaps the rarest type of old growth (Hedman and Van Lear, 1995; Frelich, 1995; Cowell and Dyer, 2002), so there have been few opportunities here to study riparian forest dynamics within the ecologically mature stages that are too often altered by timber harvest and/or land clearing (see Wistendahl, 1958; Lindsey et al., 1961; Roberston et al., 1978; Hardin et al., 1989). The Zoar Valley Canyon represents one of the most significant intact riparian zones in the Northeast, although its woodlands have been the subject of concerted ecological investigation for barely 5 years (Hunt et al., 2002; Diggins and Kershner, 2005; Diggins, 2005). We anticipate that the present and subsequent studies in Zoar Valley on topics such as forest disturbance regime, ecological succession, fluvial geomorphology, and influences of watershed land uses will enhance the understanding of ecosystem function in eastern riparian zones, and aid in management and restoration decisions. E.K. Pfeil et al. / Forest Ecology and Management 239 (2007) 159–168 Acknowledgements Funding was provided by the National Science Foundation (NSF-DUE 0337558), and by URC (University Research Council) and PACER (Presidential Academic Centers for Excellence in Research) grants from Youngstown State University. Students A. Newman and B. Sinn aided in data collection. References Blozan, W., 2006. Tree measuring guidelines of the eastern native tree society. Bull. Eastern Native Tree Soc. 1, 3–10., http://www.uark.edu/misc/ents/ bulletin/index_bulletin.htm. Bormann, F.H., Likens, G.E., 1979. Pattern and Process in a Forested Ecosystem. Springer-Verlag, New York. Bragg, D.C., 2000. Simulating catastrophic and individualistic large woody debris recruitment for a small riparian system. Ecology 81, 1383–1394. Burns, R.M., Honkala, B.H. (Tech. Coord.), 1990. Silvics of North America: vol. 2. Hardwoods. Agriculture Handbook 654. U.S. Department of Agriculture, Forest Service, Washington, DC, 877 pp. Busing, R.T., 2005. Tree mortality, canopy turnover, and woody detritus in old cove forests of the southern Appalachians. Ecology 86, 73–84. Cowell, C.M., Dyer, J.M., 2002. Vegetation development in a modified riparian environment: human imprints on an Allegheny River wilderness. Ann. Assoc. Am. Geogr. 92, 189–202. Diggins, T.P., 2005. From gravel bars to old growth: primary succession in the Zoar Valley Canyon, NY. In: Proceedings of the Sixth Eastern Old-growth Forest Conference, Moultonboro, NH, pp. 55–56. Diggins, T.P., Kershner, B., 2005. Canopy and understory composition of oldgrowth riparian forest in Zoar Valley, New York, USA. Nat. Areas J. 25, 219–227. Eastern Native Tree Society, 2004. Tallest Examples of Eastern Native Tree Species. Eastern Native Tree Society, http://www.uark.edu/misc/ents/bigtree/webpage_tall_tree_list.htm. Fairchild Aerial Surveys Inc., 1929. Series 8326. Stereo Pairs 659–668. Available from the Map Collection, Samuel Capen Science and Engineering Library, State University of New York at Buffalo, Buffalo, NY. Forrester, J.A., Runkle, J.R., 2000. Mortality and replacement patterns of an old-growth Acer-Fagus woods in the Holden Arboretum, northeastern Ohio. Am. Midl. Nat. 144, 227–242. Franklin, J.F., Shugart, H.H., Harmon, M.E., 1987. Tree death as an ecological process. Bioscience 37, 550–556. Frelich, L.E., 1995. Old forest in the Lake States today and before European settlement. Nat. Areas J. 15, 157–167. Frelich, L.E., 2002. Forest Dynamics and Disturbance Regimes. Cambridge University Press. Frelich, L.E., Reich, P.B., 1995. Spatial patterns and succession in a Minnesota southern boreal forest. Ecol. Monogr. 65, 325–346. Frelich, L.E., Lorimer, C.G., 1991. Natural disturbance regimes in hemlockhardwood forests of the Upper Great Lakes Region. Ecol. Monogr. 61, 145– 164. Goebel, P.C., Hix, D.M., 1996. Development of mixed-oak forests in southeastern Ohio: a comparison of second-growth and old-growth forests. For. Ecol. Manage. 84, 1–21. Goodburn, J.M., Lorimer, C.G., 1998. Cavity trees and coarse woody debris in old-growth and managed northern hardwood forests in Wisconsin and Michigan. Can. J. For. Res. 28, 427–438. Graham, S.A., 1925. The felled tree trunk as an ecological unit. Ecology 6, 397–411. Greenberg, C.H., McLeod, D.E., Loftis, D.L., 1997. An old-growth definition for western and mixed mesophytic forests. Gen. Tech. Rep. SRS-16. U.S. Department of Agriculture, Forest Service, Southern Research Station, Asheville, NC, 14 pp. 167 Griffin, J.M., Lovett, G.M., Arthur, M.A., Weathers, K.C., 2003. The distribution and severity of beech bark disease in the Catskill Mountains, N.Y. Can. J. For. Res. 33, 1754–1760. Hale, C.M., Pastor, J., Rusterholz, K.A., 1999. Comparison of structural and compositional characteristics in old-growth and mature, managed hardwood forests of Minnesota, USA. Can. J. For. Res. 29, 1479–1489. Hardin, E.D., Lewis, K.P., Wistendahl, W.A., 1989. Gradient analysis of floodplain forests along three rivers in unglaciated Ohio. Bull. Torrey Bot. Club 116, 258–264. Hardt, R.A., Swank, W.T., 1997. A comparison of structural and compositional characteristics of southern Appalachian young second-growth, maturing second-growth, and old-growth stands. Nat. Areas J. 17, 42–52. Harmon, M.E., Franklin, J.F., Swanson, F.J., Sollins, P., Gregory, S.V., Lattin, J.D., Anderson, N.H., Cline, S.P., Aumen, N.G., Sedell, J.R., Lienkaemper, G.W., Cromack Jr., K., Cummins, K.W., 1986. Ecology of coarse woody debris in temperate ecosystems. Adv. Ecol. Res. 15, 133–302. Hedman, C.W., Van Lear, D.H., 1995. Vegetative structure and composition of southern Appalachian riparian forests. Bull. Torrey Bot. Club 122, 134–144. Hunt, D.M., Edinger, G.J., Schmid, J.J., Evans, D.J., Novak, P.G., Olivero, A.E., Young, S.M., 2002. Lake Erie Gorges Biodiversity Inventory and Landscape Integrity Analysis New York Natural Heritage Program, Albany, NY, 167 pp. Idol, T.W., Figler, R.A., Pope, P.E., Ponder Jr., F., 2001. Characterization of coarse woody debris across a 100 year chronosequence of upland oakhickory forests. For. Ecol. Manage. 149, 153–161. Jenkins, M.A., Webster, C.R., Parker, G.R., 2004. Coarse woody debris in managed central hardwood forests of Indiana, USA. For. Sci. 50, 781–792. Lemon, P.C., 1961. Forest ecology of ice storms. Bull. Torrey Bot. Club 88, 21– 29. Lin, Y., Hulting, M.L., Augspurger, C.K., 2004. Causes of spatial patterns of dead trees in forest fragments in Illinois. Plant Ecol. 170, 15–27. Lindsey, A.A., Petty, R.O., Sterling, D.K., Van Asdall, W., 1961. Vegetation and environment along the Wabash and Tippecanoe Rivers. Ecol. Monogr. 31, 105–156. MacMillan, P.C., 1981. Log decomposition in Donaldson’s Woods, Spring Mill State Park, Indiana. Am. Midl. Nat. 106, 335–344. MacMillan, P.C., 1988. Decomposition of coarse woody debris in an old-growth Indiana forest. Can. J. For. Res. 18, 1353–1362. Marsalia, G., Tsang, W.W., Wang, J., 2003. Evaluating Kolmogorov’s distribution. J. Stat. Software 8 (18), http://www.jstatsoft.org/v08/i18/kolmo.pdf. Martin, W.H., 1992. Characteristics of old-growth mixed mesophytic forests. Nat. Areas J. 12, 127–135. McCarthy, B.C., Bailey, R.R., 1994. Distribution and abundance of coarse woody debris in a managed forest landscape of the central Appalachians. Can. J. For. Res. 24, 1317–1329. McCarthy, B.C., Small, C.J., Rubino, D.L., 2001. Composition, structure, and dynamics of Dysart Woods, an old-growth mixed mesophytic forest of southeastern Ohio. For. Ecol. Manage. 140, 193–213. McGee, G., 2000. The contribution of beech bark disease-induced mortality to coarse woody debris loads in northern hardwood stands of Adirondack Park, New York, USA. Can. J. For. Res. 30, 1453–1462. McGee, G.G., Leopold, D.J., Nyland, R.D., 1999. Structural characteristics of old-growth, maturing, and partially cut northern hardwood forests. Ecol. Appl. 9, 1316–1329. Meadows, J.S., Nowacki, G.J., 1996. An old-growth definition for eastern riverfront forests. Gen. Tech. Rep. SRS-4. U.S. Department of Agriculture, Forest Service, Southern Research Station, Asheville, NC, 7 pp. Muller, R.N., 2003. Landscape patterns of change in coarse woody debris accumulation in an old-growth deciduous forest on the Cumberland Plateau, southeastern Kentucky. Can. J. For. Res. 33, 763–769. Nowacki, G.J., Abrams, M.D., 1994. Forest composition, structure, and disturbance history of the Alan Seeger Natural Area, Huntington County, Pennsylvania. Bull. Torrey Bot. Club 121, 277–291. New York State Geographic Information Systems Clearinghouse, 2002. Interactive Mapping Gateway. New York State Geographic Information Systems Clearinghouse, http://www.nysgis.state.ny.us/gateway/mg/. Oliver, C.D., Larson, B.C., 1996. Forest Stand Dynamics. Update edition. John Wiley and Sons, New York. 168 E.K. Pfeil et al. / Forest Ecology and Management 239 (2007) 159–168 Pyle, C., Brown, M.M., 1998. A rapid system of decay classification for hardwood logs of the eastern deciduous forest floor. J. Torrey Bot. Soc. 125, 237–245. Roberston, P.A., Weaver, G.T., Cavanaugh, J.A., 1978. Vegetation and tree species patterns near the northern terminus of the southern floodplain forest. Ecol. Monogr. 48, 249–267. Rubino, D.L., McCarthy, B.C., 2003. Evaluation of coarse woody debris and forest vegetation across topographic gradients in a southern Ohio forest. For. Ecol. Manage. 183, 221–238. Rucker, C.B., 2003. The Rule of 73. , http://www.uark.edu/misc/ents/measure/ rule_of_73.htm. Runkle, J.R., 1982. Patterns of disturbance in some old-growth mesic forests of eastern North America. Ecology 63, 1533–1546. Runkle, J.R., 2000. Canopy tree turnover in old-growth mesic forests of eastern North America. Ecology 81, 554–567. Shifley, S.R., Brookshire, B.L., Larsen, D.R., Herbeck, L.A., 1997. Snags and down wood in Missouri old-growth and mature second-growth forest. North. J. Appl. For. 14, 165–172. Spetich, M.A., Shifley, S.R., Parker, G.R., 1999. Regional distribution and dynamics of coarse woody debris in Midwestern old-growth forests. For. Sci. 45, 302–313. Stearns, F.W., 1949. Ninety years change in a northern hardwood forest in Wisconsin. Ecology 30, 350–358. Stewart, B.J., Neily, P.D., Quigley, E.J., Duke, A.P., Benjamin, L.K., 2003. Selected Nova Scotia old-growth forests: age, ecology, structure, scoring. For. Chron. 79, 632–644. Tyrell, L.E., Crow, T.R., 1994. Structural characteristics of old-growth hemlock-hardwood forests in relation to age. Ecology 75, 370–386. United States Geological Survey, 1962. Aerial Photos—Gowanda, NY and Collins, NY 1:24,000 Quadrangles. Available from the corresponding author. Venables, W.N., Ripley, B.D., 2003. Introductory Statistics with S, 4th ed. Springer, New York. Volk, T.A., Fahey, T.J., 1994. Fifty-three years of change in an upland forest in south-central New York: growth, mortality, and recruitment. Bull. Torrey Bot. Club 121, 140–147. Ward, J.S., Parker, G.R., Ferrandino, F.J., 1996. Long-term spatial dynamics in an old-growth deciduous forest. For. Ecol. Manage. 83, 189–202. Webster, C.R., Jenkins, M.A., 2005. Coarse woody debris dynamics in the southern Appalachians as affected by topographic position and anthropogenic disturbance history. For. Ecol. Manage. 217, 319–330. Whitney, G.G., 1984. Fifty years of change in the arboreal vegetation of Heart’s Content, an old-growth hemlock-white pine-northern hardwood stand. Ecology 65, 403–408. Williams, C.E., Moriarity, W.J., 2000. Composition and structure of hemlockdominated riparian forests of the northern Allegheny Plateau: a baseline assessment. In: Proceedings of the conference on sustainable management of hemlock ecosystems in eastern North America, USDA Forest Service Gen. Tech. Rep. Northeastern Research Station, pp. 210–218. Wilson, B.F., McComb, B.C., 2005. Dynamics of dead wood over 20 years in a New England oak forest. Can. J. For. Res. 35, 682–692. Wistendahl, W.A., 1958. The flood plain of the Raritan River, New Jersey. Ecol. Monogr. 28, 129–153. Ziegler, S.S., 2000. A comparison of structural characteristics between oldgrowth and postfire second-growth hemlock-hardwood forests in Adirondack Park, New York, USA. Global Ecol. Biogeog. 9, 373–389.