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a Pacific Forestry Centre, Natural Resources Canada, 506 West Burnside Road, Victoria, BC, Canada V8Z 1M5
b Forest Engineering Research Institute of Canada, 2601 East Mall, Vancouver, BC, Canada V6T 1Z4
* Corresponding author (cpreston{at}pfc.cfs.nrcan.gc.ca).
Received for publication May 14, 2003.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Abbreviations: C–DOC, combined colloidal and dissolved organic carbon fraction • CP, cross-polarization • CS, clean, sorted • CU, clean, unsorted • CT, condensed tannins • DD, dipolar-dephasing • DOC, dissolved organic carbon • DS, dirty, sorted • DU, dirty, unsorted • MAS, magic-angle spinning • NMR, nuclear magnetic resonance • POC, particulate organic carbon • TOSS, total suppression of sidebands
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Much of the residue generated in logyards is already reclaimed and used for wood chips, hog fuel (used for on-site power generation), and rock for surfacing, but the fines present a challenge (MacDonald, 2001; Forrester, 1999). This material, of approximately 5 cm or less, is often high in ash and moisture, and therefore not suitable as a fuel or as feedstock for pulp or fiberboard. Possible alternative uses include landscaping products, land rehabilitation, and composting with agricultural wastes and sewage sludge. However, utilization has been hindered both by economic considerations (e.g., high transport costs) and by environmental concerns, especially the potential for leachate production (Folk and Campbell, 1990).
Previous research specifically on logyard fines has been limited to a few studies on physical and chemical properties (Folk and Campbell, 1990), utilization as a soil amendment (Zeng et al., 1993), and options for marketing and utilization (Campbell and Tripepi, 1992; MacDonald, 2001). Our ability to predict the behavior of land-applied logyard fines requires more comprehensive information on their chemical composition, especially the carbon-containing building-blocks. Once material has been reduced to small particle sizes, mixed with mineral matter (many British Columbia logyards are unpaved), or stored for varying lengths of time, it is poorly served by traditional wet chemical methods such as proximate analysis (Preston, 1996; Preston et al., 1997).
The technique of nuclear magnetic resonance spectroscopy with cross-polarization and magic-angle spinning (13C CPMAS NMR) is well suited for characterizing directly the bulk organic composition of complex, insoluble samples as dry powders. It has been applied to many types of organic matter (Preston, 1996), including decomposing wood in forest ecosystems (McColl and Powers, 1998; Preston et al., 1990, 1998b), sewage sludge, and composts (Pichler et al., 2000; Preston et al., 1998a; Veeken et al., 2001).
In 1996, the Forest Engineering Research Institute of Canada (FERIC) and the Pacific Forestry Centre started a project to characterize logyard residues and test equipment to separate the organic and inorganic components under operational conditions. The original objective was to reduce the mineral content of fines to enhance their potential for production of energy. However, this remains largely uneconomic, while their potential as soil amendments is becomingly increasingly attractive. We present chemical and spectroscopic characterization of fines from British Columbia logyards, including results from a commercial composting operation, and water-extractable carbon. Our purpose is to provide information to assess the suitability of these materials as soil amendments, in particular for forestry applications.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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The main study was performed in summer 1996 during cleanup of a one-year accumulation of logyard residues by Tolko Industries Limited at its Lavington Planer Mill Division, east of Vernon, in the central-interior of British Columbia. A contractor was brought in with a separation system to reduce the residue flow to a landfill by reclaiming rock for logyard maintainance and wood and bark for burning, and also to find an alternate use for the fines component of the residue. The main species were lodgepole pine (Pinus contorta Douglas ex Loudon var. latifolia Engelm.) and Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco].
The objectives of the research project were threefold: (i) characterize residue types in the logyard, (ii) assess the costs and efficacy of the operational separation, and (iii) characterize the smallest size fractions before and after separation. For the first objective, five residue types were identified in this sortyard:
Examples of these residue types were manually sorted on site to determine their distribution in nine size classes (>100 cm, 60–100 cm, 30–60 cm, 15–30 cm, 7.5–15 cm, 3.2–7.5 cm, 13–32 mm, 3–13 mm, and <3 mm). Proportions of wood, slab, bark, branch, rock, and glass were determined for the four largest size classes. After completion of this preliminary survey, the accumulated residues were separated using a system based on a Powerscreen (Dungannon, Northern Ireland) 830 trommel (a cylindrical rotating screen) and a General Kinematics (Crystal Lake, IL) destoner. Recoveries were 10 to 15% by weight for reclaimed rock for logyard surfacing and 4 to 16% of wood and bark for burning, bringing the total residue utilized to 16 to 26%. The fines fraction from the separation was that retained by the 16-mm trommel screen. More detailed reports are available on the sorting and trommel screen separation, including weight and volume data, and economic analysis (Forrester, 1999; Forrester and Preston, 2002).
Vancouver Island Samples
Another sample of <16-mm fines was obtained from a similar trommel screen operation at Port Alberni on Vancouver Island and three compost samples from a commercial operation near Port McNeill on northern Vancouver Island. The main species were western hemlock [Tsuga heterophylla (Raf.) Sarg.] and western red cedar (Thuja plicata Donn ex D. Don). The compost process also used <16-mm trommel screen fines for composting with ensiled wastes (fish morts) from local fish farms. The three compost samples were taken from different positions in one pile (left, middle, right).
Reference samples of wood and bark were obtained from top, middle, and base sections along the stem of a 45-yr-old Douglas-fir. This tree was cut in a forest site near Victoria on southern Vancouver Island to provide baseline samples for studies of wood decomposition. Two other samples of thicker Douglas-fir bark were obtained from sites of logging debris on the western coast of Vancouver Island in May 1997. Heartwood of old-growth western hemlock was that used for the Canadian Intersite Decomposition Experiment (CIDET) (Preston et al., 2000).
Sample Processing and Leaching Study
Chemical characterization of the Lavington logyard wastes for this study was limited to the two smallest size classes, 3 to 13 mm and <3 mm. Of the five replicates from the site, two of each residue type were taken for analysis. The 3- to 13-mm fraction was obviously a mixture of woody fragments and small rocks, except for CU, which was essentially all organic. To facilitate chemical and NMR analyses, the organic fraction was separated by floatation and the rock fragments dried at 70°C, weighed, and discarded. The other samples (<3-mm fraction, <16-mm trommel screen fines, and composts) were used as received. Subsamples for analysis were dried at 70°C and ground through a Wiley mill to pass a 60-mesh (250-µm) screen (woody materials) or finely ground in a Siebtechnik (Mülheim an der Ruhr, Germany) mill (<3-mm fraction).
To give some indication of their possible leaching behavior, the <16-mm trommel screen fines were extracted with water. Two liters of distilled water were added to 1000 g (wet weight) of the fines in a large carboy that was shaken for 2 h. This resulted in a suspension that was poured through a 1-mm sieve. The residue was returned to the carboy and the process repeated. The resulting 4-L volume from the Alberni fines was run through a succession of filters down to a 2.7-µm glass-fiber filter. The retained material, designated as particulate organic carbon (POC; 2.7 µm–1 mm), was dried at 70°C. The 2.7-µm filter was used to define a combined colloidal and dissolved organic carbon fraction (C–DOC), as very little of the solution could be passed though a 1.0- or 0.45-µm filter. The aqueous phase (<2.7 µm) was reddish-amber in color, scattered light, and remained in suspension apparently indefinitely; a 2-L portion was freeze-dried for analysis.
Extraction of the Lavington <16-mm fines produced a very dark gray soupy mixture (<1 mm) that proved impossible to filter directly. Two liters were processed by centrifugation at 8000 rpm, and the resulting pale yellow solution was filtered to 2.7 µm. Although this solution did not scatter light and could pass through a smaller pore size, it was decided to use the same filter pore size for both extracts. As for the Alberni extraction, 2 L of the aqueous phase (C–DOC) was freeze-dried, and the 2.7 µm- to 1-mm material (POC) was dried at 70°C and a subsample finely ground for analysis. The extraction residue (>1 mm) was obviously high in rock fragments, which were separated, weighed, and discarded, as for the 3- to 13-mm logyard wastes. A subsample of the organic fraction was ground in a Wiley mill for analysis.
Chemical Analysis
Sample total C was analyzed by automatic combustion using a LECO (St. Joseph, MI) CR12 analyzer and total N by a Kjeldahl method (Preston et al., 1998b), due to the very low N concentration of many samples. Ash was determined by heating at 650°C for 16 h. The butanol–HCl (proanthocyanidin) assay was used to determine condensed tannin content of the samples, as the sum of extractable (70:30 acetone to water) and residual insoluble tannins as described in detail previously (Preston, 1999; Lorenz et al., 2000), with standardization against a purified condensed tannin from balsam fir [Abies balsamea (L.) Mill.].
Carbon-13 Cross Polarization Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy
Solid-state 13C CPMAS NMR spectra were run on a MSL 300 spectrometer (Bruker Instruments, Karlsruhe, Germany) operating at 75.47 MHz. To facilitate magic-angle spinning, subsamples of the 60-mesh materials were more finely ground using liquid nitrogen and a mortar and pestle. Samples were spun at 4.7 kHz in 7-mm-diameter zirconium oxide rotors. Spectra were acquired with a 1-ms contact time and 2-s recycle time, and up to 80000 scans for the samples lowest in C. Spectra were processed using 30- to 40-Hz line-broadening and baseline correction. Due to their low C content, spectra of the <3-mm fractions were distorted by a broad background signal from the probe and rotor cap. This was corrected by subtraction of the free induction decay obtained from an empty rotor, scaled to match the number of scans (Preston, 2001). Chemical shifts are reported relative to tetramethylsilane (TMS) at 0 ppm, with the reference frequency set using adamantane. Dipolar-dephased (DD) spectra were generated by inserting a 40- to 50-µs delay period without 1H decoupling between the cross-polarization and acquisition portions of the CPMAS pulse sequence. For most samples with >100 g kg–1 C, the DD spectra were obtained using the total suppression of sidebands (TOSS) sequence for total suppression of spinning sidebands.
Spectra were divided into chemical shift regions as follows: 0 to 45 ppm, alkyl C; 45 to 93 ppm, methoxyl and O-alkyl C; 93 to 112 ppm, di-O-alkyl C and some aromatics; 112 to 140 ppm, aromatic C; 140 to 165 ppm, phenolic C; and 165 to 190 ppm, carboxyl C. Areas of the chemical shift regions were determined after integration and expressed as percentages of total area ("relative intensity"). Areas were not corrected for spinning sidebands, as these were relatively small, and their effect would be similar among most of the samples. The low signal to noise ratio of many <3-mm samples also precluded accurate measurement of the spinning sideband integrals. There are other limitations in the quantitative reliability of CPMAS spectra, but it is appropriate to use them to compare intensity distributions among similar samples and to use DD spectra to point out general structural features (Preston, 2001). The TOSS spectra can suffer from additional distortions, but this technique was only used in combination with DD for qualitative interpretation.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Trommel Screen Fines and Wood-Fish Composts
The <16-mm trommel screen fines from Lavington (117 g kg–1 C, 1.5 g kg–1 N; Table 3) were obviously contaminated with soil and small rock fragments, with a black color mixed with gray particles. The Alberni sample, which came from a paved sortyard, was reddish-brown with very few rock fragments, consistent with its higher C, N, and tannin contents. To characterize the general nature of components that might be released under leaching conditions, we extracted the <16-mm fines with water and generated three fractions; insoluble residue of >1 mm in diameter, material 2.7 µm to 1 mm that remained in suspension (POC), and dissolved plus colloidal material of <2.7 µm (C–DOC). For both samples, no fraction showed unduly high tannin levels (maximum 5.3 g kg–1 in the Alberni insoluble residue). In particular, the C–DOC fractions accounted for less than 1% of total mass and carbon, and had the lowest tannin concentrations, with tannins in the Alberni C–DOC fraction below detection.
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Carbon-13 Cross Polarization Magic Angle Spinning Nuclear Magnetic Resonance— Bark and Wood
To facilitate interpretation of the residue spectra, we first show normal and DD 13C CPMAS NMR spectra of wood and bark (Fig. 1) , the main organic inputs to the logyard fines. Relative areas of all spectra are found in Table 4. The spectrum of fresh Douglas-fir wood (Fig. 1a) is typical of gymnosperms with guaiacyl lignin (Czimczik et al., 2002; McColl and Powers, 1998; Preston et al., 1998b), and dominated by strong signals from cellulose at 63 and 65 ppm (C6), 73 and 75 ppm (C2, C3, C5), 83 and 89 ppm (C4), and 105 ppm (C1). Guaiacyl lignin produces the sharp signal for methoxyl at 56 ppm and the broader peaks in the aromatic and phenolic region, and acetate the small peaks at 22 and 173 ppm. For guaiacyl lignin, the phenolic region typically has a peak at 147 to 148 ppm with a shoulder at 152 ppm. The DD–TOSS spectrum is also typical, with the main peaks due to methoxyl C, C- and O-substituted aromatic C, and carboxyl C. Spectra of heartwood from old-growth western hemlock (not shown) were very similar. The relative areas (Table 4) reflect the dominance of cellulose and hemicellulose structures, with highest intensity in the O-alkyl region and low alkyl to O-alkyl ratios.
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Similar contrasts between bark and wood spectra were found by McColl and Powers (1998) for red fir. We previously reported spectra run at lower magnetic fields of the three fresh Douglas-fir bark samples from the 45-yr-old tree (Preston, 1996). As shown there, spectra of the other two samples had similar features, and from the top to the bottom section, had decreasing O-alkyl intensity and increasing intensity in the alkyl, aromatic, and phenolic regions. Consistent with the chemical data for total C and condensed tannins, these trends indicate increasing proportions of suberin and tannins for older bark.
The thick bark from an old-growth Douglas-fir (Fig. 1c) has even lower O-alkyl intensity characteristic of carbohydrate, and higher alkyl, aromatic, and carboxy intensity. These indicate higher proportions of suberin and perhaps secondary compounds such as resin acids. There is a higher proportion of lignin to tannin, with greater methoxyl intensity and broadening and increased intensity of the peak at 145 ppm due to the overlap with the lignin peak at 148 ppm. For both bark samples, the broad peak at 105 ppm in the DD–TOSS spectra is a characteristic marker of tannins; by comparison the heartwood spectrum has a very weak signal in this region. Both NMR and chemical analysis indicate lower tannin contents for the older barks.
The DD–TOSS spectra of the bark samples also retain intensity for the methoxyl signal of lignin, and peaks at 30 and 33 ppm in the alkyl region for CH2 in long chains. Intensity is lost at a faster rate for the peak at 33 ppm, which represents components with lower molecular mobility than at 30 ppm (Pichler et al., 2000).
Carbon-13 Cross Polarization Magic Angle Spinning Nuclear Magnetic Resonance—Logyard Fines
Spectra of <3- and 3- to 13-mm fines (Fig. 2)
are represented by three of the five categories. The spectra can be interpreted by considering them as mainly wood mixed with some bark, and modified by leaching, decomposition, and incorporation of soil particles from manipulation and outdoor storage for up to one year. In most cases there was good agreement between the relative areas of the two replicates (Table 4), and in all cases, similarity in spectral features between the two. Especially for the <3-mm samples, the discrepancies in relative area between replicates may be related largely to paramagnetic effects of mineral soil components, and variations introduced by background correction, and difficulties of phasing and baseline correction of low-carbon samples.
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The CU samples have higher C, N, and CT contents, and their NMR spectra are much better resolved. In both CP and DD–TOSS spectra, the peaks at 145 and 154 ppm in the phenolic region are more characteristic of tannin than of lignin. The "sawtooth-like" pattern in the aromatic and di-O-alkyl regions is also characteristic of condensed tannins. The differences between the CU and the other 3- to 13-mm fractions do not extend to relative areas, illustrating the importance of also examining details of peak positions and linewidths.
The lower carbon contents of the <3-mm fractions result in lower signal to noise ratio and greater broadening (no useful spectrum could be acquired for DU 4), although the peak positions are similar to those of the 3- to 13-mm samples (Fig. 2b). The main features are found at 30 ppm (alkyl C), 73 ppm (O-alkyl C including carbohydrates), 105 ppm (di-O-alkyl C including anomeric C of carbohydrates), aromatic and phenolic (110–160 ppm), and a broad, weak region for carboxyl, amide, and ester C (170–190 ppm). The <3-mm CU samples again have the highest total C, resulting in the best spectral quality. Compared with the 3- to 13-mm samples, differences in relative intensity distributions are small, with the <3-mm samples tending to be slightly lower in O-alkyl C and higher in carboxyl C. However, the increasing dilution of C with mineral matter and probably direct effects of paramagnetic and ferromagnetic components, as well as the aforementioned difficulties with spectral processing, reduce the reliability of the area measurements.
No DD spectrum could be obtained for DS 28, and the DD spectra of DS 35 and DS 64 are of poor quality, probably due to background signal in the aromatic and phenolic region. However, the spectra of the other <3-mm fractions had features similar to the corresponding 3- to 13-mm spectra. In general, the <3-mm samples also gave spectra consistent with a composition mainly of wood mixed with some bark, but degraded by close association with mineral soil particles. There was no accumulation of aromatic, phenolic, or alkyl C, the former consistent with the low levels of condensed tannins found by chemical analysis.
Carbon-13 Cross Polarization Magic Angle Spinning Nuclear Magnetic Resonance—Trommel Screen Fines and Composts
Both CP and DD–TOSS spectra of the <16-mm trommel screen fines (Fig. 3a, 3c)
have characteristics similar to those of the Lavington 3- to 13-mm fractions. The Alberni sample (Fig. 3a), with sharper features and higher C concentration, is more like the CU samples, although not as high in tannins. Spectra of the insoluble residues (<1 mm, not shown) were well-resolved, and showed only small differences in relative areas from the intact material; the main difference being lower alkyl intensity for the Lavington sample. Spectra of the suspended POC fractions also showed only minor differences from the starting materials and are not shown. However, the C–DOC fractions (Fig. 3b, 3d) have higher relative intensity for alkyl and carboxyl C, and lower for O-alkyl C. The C–DOC fraction is slightly higher in aromatic + phenolic C for the Alberni sample, and slightly lower for the Lavington samples. The DD–TOSS and DD spectra differ from those of all other samples, being dominated by carboxyl C and a more mobile fraction of alkyl C, the latter especially prominent for the Lavington C–POC.
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Spectra of the fish waste–wood composts are not shown, as they were similar to those of the DS, DU, and CS 3- to 13-mm fines in Fig. 2. Relative areas of the three samples (Table 4) were essentially the same, except for slightly higher alkyl to O-alkyl intensity ratio for the right-side sample. There was thus little effect of the composting on the bulk organic composition of the Alberni fines, consistent with the small changes shown by chemical analysis.
Implications for Utilization
Chemical analysis and 13C CPMAS NMR spectra of the woody wastes in this study are consistent with a bulk organic composition due mainly to wood, mixed with varying amounts of bark and mineral soil, and further influenced by leaching and microbial decomposition during storage (Preston et al., 1990, 1998b, 2002; McColl and Powers, 1998). Our results for total C, N, and mineral content are similar to previous studies of logyard fine fractions (Zeng et al., 1993; Folk and Campbell, 1990). Neither NMR or tannin analysis indicate high phenolic content or accumulation of aromatic C, and the C–DOC fraction extracted by water was enriched mainly in alkyl C. The bulk properties of the larger fractions (3–13 and <16 mm) were also similar to those of woody forest floor, which is especially characteristic of British Columbia coastal forests (Preston, 1999; Preston et al., 2002), and it appears that most phenolics are present as structural polymers (lignins, tannins, suberins) of high molecular weight and low solubility. The incorporation of mineral soil into the <3-mm fractions mainly resulted in higher ash content, lower total C, C to N ratio, and tannins (either on a mass basis, or as g kg–1 of total C, not shown), and degradation of the quality of the NMR spectra.
Uncertainty concerning possible adverse environmental effects, especially due to leachates, is an important concern for the land application of logyard and harvesting residues to forest sites. Toxic effects have been demonstrated for bark wastewater tannins (Field et al., 1988), leachate from aspen chips (Taylor et al., 1996), and pulping effluents high in resin acids (Dorado et al., 2000), and leaching of both organic components and nutrients is exacerbated for residues or logs piled in heaps or windrows (Rosén and Lundmark-Thelin, 1987; Parfitt et al., 1998; Taylor et al., 1996). However, at least the resin acids and tannins in bark and heartwood are poorly soluble under conditions of rainwater leaching (Field et al., 1988; Dellus et al., 1997; Matthews et al., 1997), and such effects can be minimized under appropriate conditions of application. Due to accumulation and storage of logyard fines on site, leaching could be more of an issue at the origin than in a later application.
Wood and wood co-composts have long been used as soil amendments in both field and greenhouse applications (King, 1979; Martin et al., 1978; Salomon, 1953; Schuman and Belden, 1991; N'Dayegamiye and Angers, 1993; Tremblay and Beauchamp, 1998). Similar to the composting process of most organic residues, the phytotoxic effects of wood and bark wastes in the composting process are transient (Hardy and Sivasithamparam, 1989; Martin et al., 1978). In a pot and field trial, logyard fines contributed organic matter, nutrients, and improved soil physical properties, but reduced plant availability of N, typical of amendments with high C to N ratio (Zeng et al., 1993).
There are some reports on application, or retention of harvesting residues in forestry, although not specifically using logyard residues. Application of chipped aspen residue to an aspen regeneration site in northern Alberta showed little effect on a range of plant and soil properties, including mycorrhizal fungi (Corns and Maynard, 1998; Visser et al., 1998). Application or retention of residues with high C to N ratio may adversely affect tree growth (Bulmer, 2000; Zabowski et al., 2000), mainly due to immobilization of N. In other situations, however, this can provide longer-term benefits by reducing loss of nitrate in recently harvested systems (Vitousek and Matson, 1985; Piirainen et al., 2002). Studies of decomposition and nutrient release from logging residues have demonstrated the importance of the coarser materials for long-term nutrient release and maintenance of organic matter, especially in sites of low fertility (Barber and Van Lear, 1984; Hyvönen et al., 2000; Nzila et al., 2002; Parfitt et al., 1998, 2001; Smith et al., 2000).
Results from these many studies of soil amendment with woody materials, including logyard fines, indicate that logyard fines should be useful, or at least not detrimental as a soil amendment, although initial immobilization of N may be expected. In addition, applying or dumping these materials inappropriately so that leachate could enter streams would have a negative effect, due to BOD load, suspended fines, and components with direct toxicity (Field et al., 1988; Taylor et al., 1996). Under natural conditions, the large amounts of DOC with highly variable composition leached out of litter (needles, wood, cones, dead roots) and forest floor move into the mineral soil, where the competing processes of absorption and decomposition are a natural part of soil development (Jandl and Sollins, 1997; Kaiser et al., 2001; Kalbitz et al., 2000; Guggenberger et al., 1998).
This should also be the case with application of woody wastes under acceptable, appropriate practice for soil amendment, although few studies have been reported. Cronan et al. (1992) found that increases in O-horizon DOC after application of sawdust were within the range of natural variation for hardwood sites in the region (Maine). Increases in DOC from clearcutting slash also in a hardwood site (Appalachian Mountains, North Carolina) were balanced by absorption and decomposition in the C horizon of the mineral soil (Qualls et al., 2000). Their study also showed that leaching of DOC and DON could occur if hydrologic flowpaths near streams bypass the strongly adsorbing soil horizons, emphasizing the importance of appropriate site selection and application. In contrast to toxic effects, increases in soil microbial biomass and activity following retention or extra addition of blue gum (Eucalyptus globulus Labill.) harvesting residues were attributed to soluble C leaching from the residues to provide a readily available energy source (Mendham et al., 2002).
The samples in this study, while low in number, all represent materials produced under operational conditions in British Columbia. Extension to field application is now in progress in a related study, where a variety of woody residues including sortyard wastes have been applied for rehabilitation and reforestation of logging roads and areas disturbed by log handling and storage (preliminary results in Venner et al., 1999). Our studies indicate that the effects of fragmentation, leaching, microbial activity, and mixing with mineral soil on logyard wastes are similar to those that occur naturally in soil and forest floor. Decisions for management of logyard debris will inevitably be influenced by a mix of economic, societal, and environmental considerations (MacDonald, 2001), but incorporation into composting operations or returning the material to the forest ecosystem as a soil amendment or road cover should at least be compatible with its origin and chemical properties.
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ACKNOWLEDGMENTS |
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