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Effects of Repeated-stand Entries on Terrestrial Salamanders and their Habitat
Jessica A. Homyack and Carola A. Haas

Southeastern Naturalist, Volume 12, Issue 2 (2013): 353–366

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2013 SOUTHEASTERN NATURALIST 12(2):353–366 Effects of Repeated-stand Entries on Terrestrial Salamanders and their Habitat Jessica A. Homyack1,2,* and Carola A. Haas1 Abstract - In recent years, silivicultural methods have shifted away from clearcut harvesting towards greater retention of overstory trees through part or all of a rotation. However, little is known about the effects of partial harvesting on wildlife populations. Thus, we examined effects of high-leave shelterwood management on terrestrial salamanders prior to and after an initial harvest and a subsequent overstory removal harvest (ORH) 13 years later. On an experimental research site in southwestern Virginia, we compared changes in salamander captures in this plot to a clearcut and control plot 1994–1996 and 2007–2009. Compared to contemporaneous estimates from an unharvested control, salamander captures were lower on shelterwood and clearcut plots 2-years after the initial harvest (1996) and lower on the shelterwood plot 1- and 2-years after the ORH (2008, 2009). Captures of the most common species, Plethodon cinereus (Eastern Red-backed Salamanders), followed similar trends with fewer captures in both harvested plots 2-years after the initial harvest (1996), but only the ORH differed from the control 2-years after the second partial harvest (2009). Abundance of woody debris was greater in the shelterwood following the ORH but was more decayed in the control plot. The regenerating clearcut (14 years post-harvest) had deeper leaf litter and denser understory vegetation than the ORH. These data are some of the first available describing effects of multiple harvest entries on terrestrial salamanders and suggest cumulative negative impacts on salamanders may occur from partial harvesting systems. More long-term monitoring of salamander populations is justified in silvicultural systems with multiple entries with in a rotation. Introduction Within many jurisdictions, forest harvesting has trended away from intensive management (e.g., clearcutting) and towards greater retention of overstory trees through all or part of the rotation (e.g., partial harvesting) (Fuller et al. 2004, McWilliams et al. 2005, Siry 2002). Partial harvesting is a general term that refers to forest stands in which multiple harvests are made during a single rotation and some canopy trees remain for at least a portion of the rotation. From the mid-1980s to the mid-1990s, clearcutting made up 45% and partial harvesting accounted for 55% of the average annual harvest in the southern US (US Department of Agriculture, Forest Servive 2010). The use of partial harvesting on such a significant land area may have occurred in part because of the emphasis for land managers to retain forest structure and biodiversity (Brunson and Shelby 1992, Gillis 1990) and the more positive public perception of multi-canopied forests compared to clearcuts (Bliss 2000, Brunson and Shelby 1992, Sedjo 1999). Thus, 1Department of Fish and Wildlife Conservation, Virginia Tech, Blacksburg, VA 24061. 2Current address - 1785 Weyerhaeuser Road, Vanceboro, NC 28586. *Corresponding author - jessica.homyack@weyerhaeuser.com. 354 Southeastern Naturalist Vol. 12, No. 2 silvicultural alternatives to clearcut harvesting are common across the southeastern United States, yet knowledge regarding the influence of partial cutting, and especially the cumulative effects of multiple stand-entries on wildlife populations and their habitats is limited (Fuller et al. 2004, Homyack and Haas 2009, McComb et al. 1993, Reichenbach and Sattler 2007). At a landscape scale, partial harvests must be extended over a larger area to produce the same amount of wood fiber per unit area as clearcut stands (Gillis 1990, Hagan 1996, Knapp et al. 2003), which may increase the effects of isolation and fragmentation on wildlife populations (Morrison et al. 1992, Saunders et al. 1991). At a stand scale, populations of species sensitive to disturbance may not have had adequate time to return to preharvest abundances prior to subsequent harvests in the rotation, and thus may face cumulative effects of multiple harvest events. Alternatively, by retaining some characteristics of more mature forest, partial harvests may have weaker effects on wildlife populations than clearcutting (Fuller et al. 2004, McComb et al.1993, Semlitsch et al. 2009), but these hypotheses have not been well studied. Finally, numerous structural habitat elements important for wildlife at a sub-stand scale, such as amounts of coarse woody debris and tree density and composition are altered by multiple stand entries (Barg and Edmonds 1999, Lilieholm et al. 1990). Terrestrial salamanders may be model organisms for examining effects of forest harvesting on wildlife occurring at the soil-litter interface because they are physiologically linked to microhabitat and microclimate features by their requirements of cool and moist conditions for cutaneous respiration (Welsh and Droege 2001). Additionally, terrestrial salamanders are long-lived, display low inter-annual variation in abundances, are an apex predator in the leaf litter, are one of the most abundant vertebrates in forested systems, and reach their highest levels of species diversity in the central and southern Appalachians (Burton and Likens 1975, Petranka 1998, Walton 2005, Walton and Steckler 2005, Welsh and Droege 2001, Wyman 1998). Thus, salamanders have ecological characteristics that make them useful for understanding broader effects of silvicultural practices on wildlife. Across forested systems in North America, research has consistently demonstrated that forest harvesting can have persistent negative effects on abundances of terrestrial salamanders (deMaynadier and Hunter 1995, Dupuis et al. 1995, Homyack and Haas 2009). In a meta-analysis of 14 studies, untreated control stands had 5 times greater abundances of plethodontid salamanders than clearcut forest stands (deMaynadier and Hunter 1995). Although a greater focus has been on short-term (≤2 years) effects of clearcut harvesting on salamanders, available information indicates that a wide range of forest practices that remove canopy trees can have negative and lasting effects on abundances (Ash 1997, deMaynadier and Hunter 1995, Homyack and Haas 2009, Petranka et al. 1993, Pough et al. 1987, Tilghman et al. 2012). Despite that multiple harvests in a stand during a single rotation are common for many silvicultural systems, effects from >1 harvest entry on terrestrial salamanders or their specific habitat components have not been well-documented. 2013 J.A. Homyack and C.A. Haas 355 The goal of this investigation was to evaluate whether multiple harvest entries in one type of partial harvest, a high-leave shelterwood system, had cumulative negative effects on terrestrial salamanders in a central Appalachian hardwood forest. We used a case-study approach to examine the effects both pre- and post-treatment at an experimental research site in southwestern Virginia. We predicted that captures of terrestrial salamanders would not have recovered to pre-harvest numbers prior to the second stand entry and would decline further after a second harvest. Specifically, we quantified (1) captures of terrestrial salamanders 1-year prior to and 2-years following an initial partial harvest and 1-year prior to and 2-years following a second overstory removal harvest and within a similar clearcut harvest and untreated control stand during the same time periods, and (2) within-stand habitat characteristics important for terrestrial salamanders after the second entry. Although inferences are limited by our case-study approach, this research expands the limited knowledge of cumulative effects of multiple shelterwood entries on terrestrial salamanders and their habitat. Field Site Description We compared the effects of several silvicultural treatments on terrestrial salamanders on the Jefferson National Forest, Montgomery County, VA. The study site (Blacksburg 1 [BB1]) is part of a long-term investigation of the effects of oak regeneration methods on biodiversity, the Southern Appalachian Silviculture and Biodiversity Project (SASAB), where terrestrial salamanders have been sampled yearly since 1994 (Atwood et al. 2009, Belote et al. 2008, Homyack and Haas 2009). The study site was south-facing (153°), had a moderate slope (16%), had no recent history of stand disturbance, and had uniform stocking of merchantable trees (Wender 2000). Dominant overstory trees included Quercus spp. (oaks), Liriodendron tulipifera L. (Yellow Poplar), Acer rubrum L. (Red Maple), and Oxydendron arboretum L. (Sourwood) as well as small components of other hardwoods and Pinus strobus L. (White Pine). Within the site, a single 2-ha plot of each silvicultural treatment (control, shelterwood, and silvicultural clearcut) were assigned randomly. The initial treatments occurred during winter 1994–1995. For the silvicultural clearcut (hereafter clearcut) plot, all stems >5 cm diameter at breast height (DBH) were cut (pre-treatment basal area = 24 m2/ha; 1-year post-treatment basal area = 4 m2/ha, 10-year post-treatment basal area = 7 m2/ha). Merchantable trees were skidded and removed from the site. In the shelterwood plot, the overstory was harvested in two entries to facilitate a cohort of advanced regeneration under the partial canopy (Smith et al. 1997). Following the first harvest in 1994–1995, 17 m2/ha of the pre-treatment basal area of 27 m2/ha was retained. Residual stems were dominant or co-dominant trees of preferred species (primarily oaks) with DBH of 25–40 cm. During winter 2007–2008, residual overstory stems were harvested with chainsaws and skidders, retaining 6 m2/ha of overstory basal area. No 356 Southeastern Naturalist Vol. 12, No. 2 treatments were applied to the control or clearcut plot during this time. During the pre-, 1-year post-, and 10-year post-treatment time periods, the control plot had 21, 21, and 22 m2/ha of overstory basal area, respectively. Methods We sampled terrestrial salamanders using night-time area-constrained searches on rainy nights April–early June and September–October during 1994–1996 and 2007–2009. For the first sampling years, 1994 was the pretreatment estimate and 1995 and 1996 were 1- and 2-years post-treatment. During the 2007–2009 sampling window, 2007 represented the pre-ORH sample and 2008 and 2009 were 1- and 2-years post-ORH, respectively. Prior to the initial harvest, we established a 3 × 3 grid of sampling transects (n = 9 transects/plot) in each 2-ha plot, with each transect measuring 2 m × 15 m. Transects were >30 m from plot edges and >30 m from each other. Each warm rainy night, we randomly selected one transect from each plot, and 2–3 observers hand-captured terrestrial salamanders active on the surface of transects. We standardized our sampling to only occur nights (>1 hour after sunset) during or after rain events when temperatures were >7 °C and the leaf litter was wet. We rotated the order that treatment plots were sampled among nights, and transects were only sampled once per sampling year. Salamanders were housed overnight in a laboratory environment, and the next morning we confirmed species identification and recorded morphological and reproductive data. We released all salamanders at the point of capture within 24 hours. We did not individually mark salamanders because toe-clipping may violate assumptions of tag loss from regeneration of digits (Heatwole 1961) and may decrease survival (Davis and Ovaska 2001, McCarthy and Paris 2004). Further, current marking technology (e.g., Visible Implant Elastomer, Northwest Technologies, Shaw Island, WA) was not readily available during the beginning of the study. We assumed that counts of individuals were positively and linearly related to the true population size and that detection did not differ across treatments, years, or species (Mazerolle et al. 2007, Pollock et al. 2002, Reichenbach and Sattler 2007, Welsh and Droege 2001). Knapp et al. (2003) and Homyack and Haas (2009) provide additional details on salamander sampling methods. Second, we a priori selected habitat characteristics that would be associated with mediating microclimate, providing foraging habitat, or providing habitat for brooding eggs for terrestrial salamanders. Habitat characteristics were measured on all salamander sampling transects on each of the three treatment plots in 2009, the second growing season after the ORH. To quantify coarse woody debris (CWD), we counted root masses (≥7.6 cm diameter at the base), stumps (<2 m height, ≥7.6 cm diameter), and logs (≥7.6 cm diameter, in contact with ground) within each transect. We measured log diameters at both ends and the length and converted it into a volume by using the formula for the volume of the frustum of a cone (Volume = [1/3]π[r2 + rR + R2]h), where r = small radius, 2013 J.A. Homyack and C.A. Haas 357 R = large radius, and h = height. We calculated stump and root mass volume as a cylinder with height and mid-point diameter. We evaluated decomposition class of each piece of CWD and assigned it a value from 1–5 based on Maser et al. (1979). We quantified density of trees (≥7.6 cm DBH, ≥1.5 m height, standing at >45º from the ground) that occurred within each transect and density of understory woody vegetation by counting the number of woody stems within a plot that were >0.5 m tall, but <7.6 cm DBH. We measured leaf-litter depth at six locations in a transect (centered at 2.0 m, 3.0 m, 7.0 m, 8.0 m, 12.0 m, 13.0 m) with a ruler held perpendicularly to the ground surface and averaged them into a single value. Statistical analyses We determined whether captures of all salamanders or just Plethodon cinereus Green (Eastern Red-backed Salamander) differed among treatments after both an initial and a second harvest in the shelterwood plot with separate Kruskal-Wallis tests comparing the control, shelterwood (or ORH), and clearcut treatment plot for each year of sampling (Conover 1999). When tests were significant (P < 0.05), we used a Bonferroni multiple comparison procedure to evaluate which treatments differed. Secondly, we evaluated whether six a priori selected habitat characteristics, including the volume, density, and decay class of CWD, density of overstory trees, density of understory trees, and leaf-litter depth differed among silvicultural treatments two-years after the ORH with Kruskal-Wallis tests (Conover 1999). We used SAS 9.3 (SAS Institute, Cary, NC) for analyses. Our analyses and thus the inferences made from our results are limited by our case-study approach without site replication and use of transects as the experimental unit. However, the random assignment of treatments and long-term collection of data in our study are improvements over the traditional before-after-control-impact (BACI) design, which often uses inferential statistics such as t-tests and analysis of variance to describe the effects of a stressor (Smith 2002). Results We recorded 672 total terrestrial salamander captures across 33 sampling nights. We sampled 4–7 sets of transects/year. Most (95%) salamanders were Plethodon cinereus, but captures also included P. cylindraceus Harlan (White-spotted Slimy Salamanders; 4% of captures) and <1% each of Desmognathus fuscus Rafinesque (Northern Dusky Salamander), Eurycea cirrigera Green (Southern Two-lined Salamander), and Gyrinophilus porphyriticus Green (Spring Salamander) (Table 1). Effects of shelterwood harvesting differed across years of post-harvest sampling for total salamander captures. Total captures of terrestrial salamanders in the control plot was similar to both the shelterwood and clearcut prior to the initial harvest (1994: χ2 = 1.10, df = 2, P = 0.58) and the growing season after 358 Southeastern Naturalist Vol. 12, No. 2 treatment (1995: χ2 = 2.24, df = 2, P = 0.33). However, 2 years after the initial harvest, there were 70–74% fewer salamander captures in the shelterwood and clearcut plots compared to the control (1996: χ2 = 11.60, df = 2, P = 0.004) Table 1. Number of salamander captures by species and year in a mature oak (control), silvicultural clearcut, and shelterwood-harvested forest in southwestern Virginia, 1994–1996 and 2007–2009. Plots were harvested in 1994–1995, and residual trees were removed in an overstory removal harvest (ORH) in the shelterwood plot during winter 2007–2008. Year Control Clearcut Shelterwood Plethodon cinereus Pre-treatment year 43 54 39 1-year post 59 52 45 2-years post 53 16 19 1-year pre-ORH 44 29 24 1-year post-ORH 55 21 13 2-years post-ORH 56 15 4 Total 310 187 144 Plethodon cylindraceus Pre-treatment year 1 1 5 1-year post 7 2 3 2-years post 1 0 0 1-year pre-ORH 4 0 0 1-year post-ORH 1 0 0 2-years post-ORH 0 0 0 Total 14 3 8 Desmognathus fuscus Pre-treatment year 1 0 0 1-year post 0 0 0 2-years post 1 0 0 1-year pre-ORH 0 0 0 1-year post-ORH 0 0 0 2-years post-ORH 0 0 0 Total 2 0 0 Eurycea cirrigera Pre-treatment year 0 0 0 1-year post 1 0 0 2-years post 0 0 0 1-year pre-ORH 1 0 0 1-year post-ORH 1 0 0 2-years post-ORH 0 0 0 Total 3 0 0 Gyrinophilus porphyriticus Pre-treatment year 0 0 0 1-year post 1 0 0 2-years post 0 0 0 1-year pre-ORH 0 0 0 1-year post-ORH 0 0 0 2-years post-ORH 0 0 0 Total 1 0 0 Grand total 330 190 152 2013 J.A. Homyack and C.A. Haas 359 (Fig. 1). During the second sampling period in 2007–2009, salamander captures did not differ significantly among treatments prior to the ORH (2007: χ2 = 2.86, df = 2, P = 0.24), but were different both 1 year (2008: χ2 = 7.185, df = 2, P = 0.03) and 2 years (2009: χ2 = 9.10, df = 2, P = 0.01) after the second harvest of the shelterwood plot (Fig. 1). The ORH had 58–76% fewer salamander captures than either clearcut or control plots 1 year after treatment (2008: P < 0.05), but at 2 years after treatment, was only significantly lower from the control (2009: P < 0.05). Mean captures of P. cinereus responded comparably, with similar number of mean captures across treatments in the pre-treatment year (1994: χ2 = 1.23, df = 2, P = 0.54) and 1 year after the initial harvest (1995: χ2 = 1.86, df = 2, P = 0.39). The second year after harvest, the control plot had 2.8 and 3.3 times more captures of P. cinereus than the shelterwood and clearcut plot, respectively (1996: χ2 = 11.07, df = 2, P = 0.004). During 2007–2009, captures of P. cinereus did not differ the year prior to (2007: χ2 = 1.73, df = 2, P = 0.42) or 1 year after the ORH (2008: χ2 = 5.31, df = 2, P = 0.07), but were different 2 years after the ORH (2009: χ2 = 9.10, df = 2, P = 0.01). In 2009, captures of P. cinereus in the control were greater than in the ORH (12.5 times greater, P < 0.05) but not the clearcut plot (3.3 times greater, P > 0.05). Structural habitat characteristics relevant to salamander life histories differed among treatments after the ORH. The density (χ2 = 8.50, df = 2, P = 0.01) and mean decay class (χ2 = 15.80, df = 2, P = 0.004), but not volume (χ2 = 4.73, df = 2, Figure 1. Mean (SE) number of terrestrial salamander captures/30-m2 transect during area-constrained night-time searches across three silvicultural treatments in southwestern Virginia, 1994–2009. Different letters indicate among-treatment differences (P < 0.05). 360 Southeastern Naturalist Vol. 12, No. 2 P = 0.09), of CWD differed among treatments (Fig. 2). Although CWD density in the control was only lower compared to the ORH, CWD in the control was significantly more decomposed than either of the harvested treatments (P < 0.05) (Fig. 2). Density of overstory trees was 1.5–2.8 times greater in the control than in the harvested treatments (Fig. 2), but understory trees (<7.6 cm DBH) were at a lower density (χ2 = 15.70, df = 2, P < 0.001; Fig. 2). Lastly, litter depth was lowest in the ORH, but differed significantly only from the clearcut (χ2 = 8.86, df = 2, P = 0.01; Fig. 2). Figure 2. Forest structural characteristics in an untreated control, shelterwood, and regenerating clearcut plot in southwestern Virginia. Forest structure was measured on nine 2- × 15-m transects/plot in summer 2009, the second growing season following an overstory removal harvest in the shelterwood plot and 14 years after the initial treatment to the clearcut and shelterwood. Different letters indicate among-treatment differences (P < 0.05). 2013 J.A. Homyack and C.A. Haas 361 Discussion In our study, both total captures of terrestrial salamanders and captures of the most commonly encountered species responded negatively to both the initial harvest and the ORH 13 years later. Salamander captures on the shelterwood plot relative to the control declined in the second year after the initial treatment, and declined again 1- and 2-years after the ORH. Other studies have reported that partial harvesting has either negative effects (Brooks 2001, Grialou et al. 2000, Homyack and Haas 2009, Knapp et al. 2003) or little effect (Brooks 1999, Duguay and Wood 2002, Mitchell et al. 1996, Pough et al. 1987, Reichenbach and Sattler 2007) on terrestrial salamanders. However, most prior research has focused only on effects to salamanders from initial harvest entries. In contrast, we quantified captures of salamanders through both the initial and second harvest, and provided evidence that repeated stand entries can negatively affect salamanders. At our experimentally manipulated study site, a second harvest caused an additional decline in the numbers of salamanders captured in the shelterwood as compared to the control and the 14–15 year-old clearcut. The result that salamander captures after the ORH declined to levels as low as those soon after the initial shelterwood is striking. Whether this negative effect will have cumulative long-term impacts to salamander populations is currently unknown as this study only examined salamander captures to two years after the ORH. Unless salamander populations can recover more quickly after the second harvest, partial harvest methods that require multiple stand entries within a rotation, such as a group selection regime, could possibly permanently depress salamander numbers (Homyack and Haas 2009). Discrepancies among studies on the effects of partial harvesting on salamander abundances may have resulted from variation in the type of partial harvest or in basal-area retention (but see Tilghman et al. 2012). For example, after the initial harvest in this study, the shelterwood plot retained 17 m2/ha of overstory basal area. Other investigations of effects of partial harvesting on terrestrial salamanders reported average residual basal areas of 9.1–18.3 m2/ha for a shelterwood harvest (Reichenbach and Sattler 2007), 4–15 m2/ha for a range of shelterwood management options (Harpole and Haas 1999), 6–14 m2/ha for a range of partial harvesting options (Knapp et al. 2003), and 48 m2/ha for a light thinning (Grialou et al. 2000), but many other researchers failed to report basal area or specific harvesting type, hindering the interpretation of results across investigations and ecosystems. Besides residual basal area of harvested stands, other aspects of forest structure likely influenced salamander numbers and communities after treatments. In our case study, a priori selected habitat characteristics associated with forestdwelling salamanders differed among an untreated control, regenerating clearcut, and a recently harvested shelterwood plot. Abundance of CWD and leaf-litter depth differed among control, clearcut, and post-ORH shelterwood plots. Not surprisingly, the ORH tended to have more abundant woody debris than control 362 Southeastern Naturalist Vol. 12, No. 2 plots, likely due to addition of logging residues (Fig. 2b). Coarse woody debris was decomposed further in the control compared to either harvesting treatment (Fig. 2c), further indicating that logging slash was a primary source of downed wood in treatment plots. Additionally, leaf-litter depth in the ORH was 55–68% of that in control or clearcut plots, but understory tree density was greatest on regenerating clearcut plots (Fig. 2e, 2f). Changing the structure of mature forest from harvesting generally is perceived to have negative effects on salamander populations. After harvesting, salamanders are hypothesized to emigrate from disturbed areas (evacuation hypothesis), retreat underground until conditions are more amenable (retreat hypothesis), or die, either directly from harvesting equipment or indirectly from changes to habitat (mortality hypothesis) (deMaynadier and Hunter 1995). Removal of overstory and understory trees leads to less leaf litter on the ground, thus reducing available foraging substrate and mediation of microclimate for salamanders. Further, opening of the canopy layer from harvesting can cause increased ground temperatures and decreased soil moisture, which may restrict movements, foraging opportunities, and cutaneous respiration of terrestrial salamanders (Chen et al. 1999, Harpole and Haas 1999, Jaeger 1980, Liechty et al. 1992) and increase energetic costs (Homyack et al. 2011). Lastly, terrestrial salamanders rely on CWD for several life-history requirements, including maintaining moisture and thermal balances, access to mates and foraging opportunities, and substrates for brooding eggs (de- Maynadier and Hunter 1995). Although harvesting produces large inputs of small diameter logging slash, this small woody debris often decomposes and does not persist through a rotation (Fraver et al. 2002, Spies et al. 1988). In our study, woody debris from the clearcut harvest persisted through 14 years, so that density of CWD was similar to the control during this period. The second growing season after the ORH, there were more individual pieces of CWD in the shelterwood plot. However, because this CWD was not welldecayed and total volumes were not increased significantly, slash may not have been used by salamanders for foraging or brooding eggs. Thus, the large inputs of logging slash after the shelterwood ORH may not have been sufficient to overcome negative changes to microclimate or other life-history requirements of terrestrial salamanders. Although conclusions drawn from this case-study approach are limited to our study area due to lack of replication, this experimental design included both pre-treatment estimates and randomly applied treatments, both of which are uncommon in investigations of forest harvesting on salamanders (deMaynadier and Hunter 1995, Perkins and Hunter 2006, Reichenbach and Sattler 2007). Our exploratory results indicate that silvicultural regimes that employ multiple entries within a rotation have the potential to negatively affect terrestrial salamanders, at least at our mixed hardwood sites and for the salamander community we examined. Given that >60 years is expected to be required for salamander populations in Appalachian oak forest to recover to pre-harvest levels of abundance from only one stand entry (Homyack and Haas 2009), it is likely that silvicultural regimes 2013 J.A. Homyack and C.A. Haas 363 such as shelterwood systems that repeatedly reduce salamander populations will require a longer period for population recovery, or may permanently suppress populations (see discussion in Knapp et al. 2003). Forest managers will need to weigh the consequences of partial harvests on biodiversity along with the higher costs of harvesting, potentially negative effects on soil erosion due to multiple stand entries within a rotation (Hood et al. 2002), and implications for landscapescale effects when applying forest plans. 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