Machine for Row-Mulching Logging Slash to Enhance Site,A Concept

Peter Koch, Dan W. McKenzieMEMBER

ASAE

ABSTRACTP ROPOSES that stumps, tops,

and branches residual after log-ging pine plantations be hogged tobuild mulch beds spaced on about2.S-m centers, thereby eliminatingpile and bum operations. Growth ofseedlings planted through mulchbeds should be accelerated becauseof moisture conservation, weedsuppression, and minimum disturb-ance of topsoil.

Information contained in thisreport has been developed for theguidance of employees of the U.S.Department of Agriculture-ForestService, its contractors, and its co-operating Federal and State agencies.The Department of Agriculture as-sumes no responsibility for the inter-pretation or use of this informationby other than its own employees.

The use of trade, firm, or corpor-ation names is for the informationand convenience of the reader. Suchuse does not constitute an officialevaluation, conclusion, recommenda-tion, endorsement, or approval of anyproduct or service to the exclusion ofothers which may be suitable.

INTRODUCTION

In pine plantations throughoutthe world it is usual, after clear fellingthe final crop trees, to windrow andburn residual tops and branches,thereby diminishing the hazard fromwildfire. Frequently the burning oper-ation is followed by strip plowing toform beds and to control weed compe-tition in rows that are to be bare-rootplanted. Although this procedure isin wide use, it has several disadvan-tages. First, burning of slash causes

FIG. 1 High-lite lobloU, pi- plantadon In South-t after pile and bumoperations. [Trees show good growth rate when topeoU was aDdI8tarbed;reduced growth rate Is evident In blade-scalped area In center.]

air pollution and diminishes nutri- return logging slash nutrients to theents - principally nitrogen - re- soil, and to conserve soil moistureturning to the soil (Jorgensen et al. while suppressing weed growth in1975). Second, fertility on some sites planting beds, we propose a simplemay be significantly reduced if bull- site preparation technique that obvi-dozer operators inadvertently blade ates the necessity for burning andoff topsoil during piling operations strip plowing on some sites. The con-(Figs. 1 and 2). Third, burning of the cept calls for tops, branches, stumps,slash removes material that could underbrush, and small trees residualact as a mulch to slow moisture loss after harvest (in short, all loggingin rain-deficient areas. Finally, after slash) to be hogged by a long cylindri-piling.and burning, weed control must cal cutterhead horizontally mountedbe achieved by strip plowing or the use across the front of a prime mover. Asof weedicides. this mobile mulching machine slowly

To reduce the hazard from fire, to traverses the acreage, hogged material

Article was submitted for publication inApril 1976; reviewed and approved for publi-cation by the Power and Machinery Division ofASAE in September 1976. Presented as ASAEPaper No. 75-1529.

The authors are: PETER KOCH. ChiefWOtXl Scientist. Southern Forest ExperimentStation. USDA Forest Service. Pineville, LA;DAN W. McKENZIE, Mechanical Engineer.Equipment Development Center. USDA ForestService. San Dimas. CA.

FIG. 2 Significant reductions in growth rate, caused by blading off top-soil during pUe and bum operatiom, are evident in this aerial view of alobloUy pine plantation in the Southeast. [Trea show good growth rateIn rows where slash was plJed and burned, and where bladed top..U wuconcentrated. ]

This article is reprinted from the TRANSACTIONS of the ASAE (Vol. 20, No. I, pp. 13, 14, IS, 16, 17,1977)Published by the American Society of Agricultural Ensineers. St. Joseph, Michigan

would be collected from the cutter-head and delivered via belt to spacedplanting beds about 60 cm in widthand perhaps 5 to 7 cm in depth; cen-terline distance between beds mightrange from 2 to 3 m. Using averagebed dimensions and spacing, thiswould call for 144 m3 of mulched ma-terial per hectare; at 320 kg per m3,about 46 <XX> kg of green mulchedchips would be required per hectare.

In attempting to evaluate the meritof the concept, it is pertinent to notethat two k:nowledgeable silviculturistsin the South (E. Shoulders and J.Burton) have voiced some reservationsabout the idea. They comment that,while nitrogen is released to the atmo-sphere by burning of slash, mostother nutrients remain in the ash andare quickly returned to the soil -much more rapidly than if the slashwere allowed to decompose naturally,and that the loss of nitrogen poses noserious problem in site deterioration(Boyle et al. 1973; Shoulders andMcKee 1973). They further observethat chips mulched in beds immedi-ately under planted trees may consti-tute more of a fire hazard that theslash in situ. Also, there is somequestion whether a mulch bed of thethickness contemplated will controlcompetitive sprouts from hardwoodroot -stocks.

Another reviewer questions whethersouthern pine plantations yield suffi-cient logging slash to form the pro-posed mulch beds. Indeed, the wholeissue of the merit of complete-treeharvest of southern pines (e.g., asproposed by Koch and Coughran1975) versus less intensive harvest,as here described, has yet to be eluci-dated.

In spite of these reservations, theconcept appears to the authors to havesufficient advantages to merit a trial.To promote such a trial, additionaldata follow on quantity of slashavailable, experience with mulchedpine, and progress on machine design.

QUANnTYOFAVAILABLE SLASH

If the concept is to be workable,sufficient wood, bark, and foliagemust be residual on the site to buildthe mulch beds to the required widthand depth. Quantities available willvary greatly - depending on species,nature of preceding and final har-vests, density of stand, site, and firehistory on the acreage. Some dataare available indicating that for

certain species and logging regimesthe quantity of slash is sufficient.Simonsson (1974) reported on fourstands of Norway spruce (Picia abies(L.) Karst.) and Scotch pine (Pinussylvestris L.) logged by various mech-anized methods, all of which includedbranch-trimming equipment; hefound that the quantity of slash variedfrom 41 000 to 57 000 kg per ha.He noted that the slash accumulatedin heaps or swaths, covering 20 to 45percent of the felling area to a depthgreater than 10 cm; the rest of thearea remained virtually clear.

Clark and Taras (1974) used regres-sion equations to estimate the dryweight and composition of loggingresidue remaining after harvestinga natural unevenage loblolly (Pinustaeda L) stand to various merchant-able tops. Results indicated that, ifthe sale trees were harvested to a 15.2-cm top, 263 kg of dry logging residuewould remain for every 1<XX> kg (dry)of wood and bark removed. Loggingthe sale to a 10.2-cm top would reducelogging residue to 196 kg per 1<XX> kgof wood and bark logged, and loggingto a 5.1-cm top (plus utilizing limbslarger than 5 cm in diameter) wouldleave only 100 kg of residue per 1<XX>kg of wood and bark logged.

Chappel and Beltz (1973) evaluatedclearcut southern pine acreage inAlabama and observed that about46 <XX> kg (green basis) per ha wereleft in residual trees, tops of cut trees,unused bole sections, and above-ground portions of stumps.

C. J. Storch (1975), in an evaluationof hogged slash residual from clear-felled Monterey pine (Pinus radiata D.Don) in South Australia, found thatit yielded a mulch about 2-cm thickover the entire felling area. If thisamount was concentrated in therows described, mulch depth wouldlikely have averaged about 7 cm.

From these limited data, and fromobservations in the field, it wouldseem that many logging sites wouldhave residues sufficient to build theproposed mulch beds. However, whereintensive utilization of tops, or whole-tree or complete-tree harvesting ispracticed, the concept would not beapplicable.

EXPERIENCE WITHMULCHED PINE

As noted previously, a major ob-jective of the concept is to eliminatewindrowing and burning because offertility diminution from the loss of

topsoil during bulldozing and theloss of nutrients during burning.What about other effects?

Loblolly Pine in East TexasBilon (1960), in a study of the

effects of root development in mod-ified environments - i.e., naturallysodded ground, a 5.1-cm mulch ofpine needles (both unshaded and SOpercent shaded), bare ground (bothunshaded and SO percent shaded),and bare sand - examined the rootsof loblolly pine seedlings that hadbeen bar-planted at age 1 on 61-cmspacing in east Texas during February1957 and then allowed to grow anadditional year before excavation. Hisconclusions follow.

On plots protected by mulch,shade, or sod, more than half theroot growth was in the uppermost 7.6cm of soil, and over 70 percent of theroot weight was in the top 15.2-cmlayer. On an ovendry basis, the rootsystems weighed about as much asstems and needles combined; rootweight was generally less than 90 gper seedling.

Scalping sites before seedlings wereplanted increased the total dry weightof the roots by more than four times,increased the temperature at the soilsurface, and caused a general down-ward shift of the entire root system.Mulching of scalped soil favored rootdevelopment very close to the soilsurface, probably by improving mois-ture conditions and mitigating tem-perature extremes. About 70 percentof ovendry root weight on mulchedplots was in the uppermost 7.6 cmof soil. Mulching increased the lengthof lateral roots, but decreased rootbranching and lignification; the totalbiomass on scalped and mulchedplots was somewhat less than onscalped plots with no mulch.

Monterery Pine in South AustraliaIn 1974, while traveling near

Tarpeena, South Australia, it wasthe senior author's privilege to see animpressive response in Montereypine that had been mulched. C. G.Stephens and C. J. Storch (1975),foresters responsible for the experi-ment, have provided some responsedata. The experiment consists of 14rows of 25 trees each. Planting with1-year-old nursery stock took placein August and September 1969, atwhich time the mulch was also ap-plied. Rows 1, 6, 10, and 14 are con-trols and received a "normal" fer-

TABLE 1. TREATMENT OF FOUR ROWS OF MONTEREYPINE IN MULCHING EXPERIMENT.

Row Treatment

u

11

113 & of superphosphate plus 711 of potassium sulphate pertree; no mulch.

Fertilizer as in row 11 (above), plus a mulch of pine bark forhalf the row lenatb and pine chips for the balance.

113 & of superphosphate per tree, plus mulches of bark andchips as in row 12 (above).

113 I of superphosphate per tree; no mulch.

tilizer treatment of 113 g of super-phoshate per tree. Rows 2, 3, 4, 5, 7,8, and 9 received a variety of othertreatments. Rows II, 12, 13, and 14were involved in the mulching experi.ment and received the treatments indi-cated in Table 1.

A basal dressing of 82 kg of groundrock phosphate was spread uniformlyover the whole area of the 14 rows.The other fertilizers were spread overthe space around each tree within acircle 0.9 m in diameter. The bark andchip mulches were applied to a depthof about 10 cm after planting andapplication of fertilizer; the mulchcompletely covered the ground be-tween trees in rows 12 and 13 andextended halfway towards rows 11 and14 (Fig. 3). The bark mulch camefrom the sawmill log skids and wasquite variable in size, with largerpieces measuring about 10-cm squareby 2-cm thick. The chips came fromthe sawmill hog and were somewhatless variable in size, with the largestpieces measuring about 15 by 5 by1 1/4 cm (Fig. 4).

In the experimental area, ground-water lies in polyzoal Miocene lime-stone about 9.1 m below ground level.Observations repeated in dry weathereach summer show dry soil in thecontrol plots and moist soil belowbark and chip mulches, with lowerlevels of the mulches also moist.Annual rainfall in the area averagesabout 84 cm.

Wood chips provided almost com-

TABLE 2. MEAN DIMENSIONS OF MONTEREY PINE IN MULCHING EXPERIMENT.

Yearmeasured

Row 11.no mulch

Row 12 Row 13with mulch

Row 14no mulch

Dimensionsmeasured

197019711972

Height. emHeight. emHeight, emDiameter,t emVolume, em3Height, emDiameter, emVolume, em3Heigbt, emDiameter, emVolume, em3

53103

1403.6

721268

6.03097

4708.2

10688

78168260

7.86130

42910.9

16097634

13.536962

741M245

7.34163

40510.1

12 394619

13.232 132

551041&5

3.9983274

6.03978

4708.7

127ZZ

19'"

1974

FIG. 4 Typical Monterey pine, about 15 mont"after plantfn&.

.See Table 1 for details on fertilizer and mulch (if any) used on each row.tDiameters measured 15 cm above ground level.

plete weed control (Figs. 3 and 4);bark was slightly less effective; butwith early canopy closure, weeds inthe bark mulch were much reduced byJuly 1975. Unmulched control plotshad a full covering of weeds soon afterplanting.

Data taken 1 through 5 years afterplanting indicate that the mulchedtrees responded immediately to exceedthe unmulched trees in height anddiameter (Table 2). To determine ifthe rapidly growing mulched treesmight become nitrogen deficient, P.DeVries of the Australian Common-wealth Scientific and Industrial Re-search Organization, sampled andanalyzed the needles from trees inrows 10, 11, 12, 13, and 14. He foundthat needles from the mulched treeshad greater content of nitrogen thanthe unmulched trees. In short, underconditions of the experiment, mulch-ing accelerated growth. Because thisexploratory study did not includereplication, a follow-up experimentof more rigorous design and largersize is now underway in Australia(Stephens and Storch 1975). In areasof water surplus, it is doubtful thatmulched trees would differ so mark-edly from unmulched trees.

EVOLUTION OFROW -MULCHING MACHINE

In response to a need for equip-ment to hog logging slash and broad-cast it more or less uniformly over an

FIG. 3 Virtually weed-free rom of wood-chipmulched moDteft.J pine, about 15 mODal. 8fterplaDtIn&.

area, a number of commercialmachines have been manufactured.The literature contains evaluation ofsome of these machines (e.g., USDAForest Service 1970; Lambert 1974;and Harrison 1975). For one reasonor another none of these commerciallyavailable machines appear capableof row mulching in the manner wevisualize.

Development of CutterheadTo evaluate cutter head designs

for brush and slash disposal, theForest Service's San Dimas Equip-ment Center constructed a test standfor both horizontal- and vertical-axishogging cutterheads (Fig. 5). Aftertesting commercially available heads,a development effort on a horizontal-axis cutter head began. This evolvedinto a configuration of two individualcutters, mounted at opposite ends ofa support member (Fig. 6), whichpivot about hinge bars. Each stirrup-l~e cutter is about 26-cm long fromits pivot point to cutting edge and thecutting circle diameter is 119.4 cm.

Guided by data obtained from aseries of test runs using various woodtypes and cutter design concepts theengineers and technicians at the

~ ~

FIG. 7 Prototype cuttedtead mounted OR aHydro-Ax modeI1CMM).

a hydraulic motor, will demand about260 hp and will rotate at ~ rpm.The conveyor belt will catch the chips

FIG 6 M Hftft f tha __I. oL- as they are formed and will deposit. oun 0 cutters t waae up -- th . 60 .d 5 7 dtest bed cutterb_d. em In -cm WI e, - to -cm eep

beds, spaced as desired alongside thecutters are always available to engage prime mover as it moves slowly alongthe wood being hogged. its traverse path. In addition to the

When driven at ~ rpm, about slash on the ground, the machine will150 hp is required to chip wood up be able to chip standing softwoodto 20 cm in diameter; chips and trees up to 20 cm in diameter andchunks produced measure up to 15 cm residual hardwoods up to 15 cm inin the largest dimension (Fig. 10). diameter.Specific cutting energy expended On level terrain, under conditionswhen the cutterhead produces such typical after final felling of a southernsoftwood chips is about 3.0 x 10-4kw- pine plantation, travel speed willhr per kg (i.e., 0.36 hp-hr per ton). likely be in the range of from 1 to 5By varying the rake and clearance km per hr. Spacing of mulch bedsangles, etc. of the cutters, the aver- will be determined by the spacing ofage size of the chips can also be varied the traverse lines of the prime mover;(Fig. 11). The chips shown in Fig. 11 if the traverse lines are spaced inwould be more acceptable for use as excess of 2.6 m, some residual willsite enhancement planting mulch. escape mulching.Specific cutting energy for such chips The concept appears promising andis about 8.2 x 10-4 kw-hr per kg (or development work is continuing.1 hp-hr per ton).

FIG. 5 Tat stand for evaluating cutters de-signed for IIaIh treatmentjutUlzation equip-meat.

Equipment Development Center builta prototype cutterhead that wasmounted on a Hydro-Ax model 1<XX>prime mover (Fig. 7). The 15.9-cmwide cutters (Fig. 8) with relativelyblunt cutting edges were assembledin a 9-stirrup-wide arrangement of18 cutters having a total length ofabout 1.5 m and a cutting circle di-ameter of 121.3 cm. Steel discs wereplaced after every third stirrup as-sembly to support these assembliesand limit the depth of the cutter'sbite. Each individual cutter can swingthrough a limited arc of 232 deg. Thegeometry and dynamics of the cuttersare such that, after being folded backduring a cut, they return to their cut-ting position by the time the cutter-head has made a revolution. Thus the

ReferencesProduction Machine Concept 1 BiIan, M. V. 1960. Root development

.. of loblolly pine seedlings in mooified enYiron-The success obtaIned WIth the 1.S-m ments. Stephen F. Austin Coll. Forest. Dep.

prototype has encouraged us to pro- Bull. 4.reed with concept drawings for a 2 Boyle, J. R., J. J. Phillips, and A. R. Ek.commercial machine. The cutterhead 1973. "~ole tree" harvesting: Nutrient budget

ill tt f th d . h evaluation. J. For. 71(12):760-762.~ ~arry cu ers 0 e eslgn.S o,,!n 3 Chappel. T. W. and R. C. Beltz. 1973.m Fig. 8. arranged as shown 1D Fig. Southern logging residues: an opportunity.9; its length will be 2.6 m. The cutter- J. For. 71:688-691.head, together with a chip hood and 4 Clark, A.. .111, and ~. A. Taras. 1974.an integral conveyor belt (Fig. 12). ~ffect of harveSUng. to vanous m~hantable

.11 be .ed h fr d f limits on loblolly pme logging residue. For.WI carn on t e ont en 0 an Prod. J. 24(6):45-48.

articulated wheeled prime mover. 5 Harrison, R. T. 1975. Slash: equipmentThis longer cutterhead powered by and methoos for treatment and utilization., Equip. Dev. and Test Rep. 7120-7, USDA For-

est Serv., San Dimas, Calif.6 Jorgensen, J. R., C. G. Wells, aoo L. J.

~

"

~

FIG. 10 Chipped wood produced by prototypecutterbead.FIG. 9 Prototype catterbead.FIG. 8 Sdrnlp.type cutter.

~

r?-'::~1~':::;"-1"--. "IIU.~~.~

~...FIG. 11 Chipped wood produced with sharpercutteR haviDg greater rake and less negativeclearance angles.

Mm. 1975. The nutrient cycle: key to continu-ous forest production. J. For. 73(7):400-403.

7 Koch. P. and S. J. Coughran. 1975. De-velopment of a puner-buncher for harvestingsouthern pines with taproot attached. For.Prod. J. 25(4):23-30.

8 Lambert, M. B. 1974. Evaluation ofpower requirements and blade design for slashcutting machinery. ASAE Paper No. 74-1570.USDA Forest Serv. Equip. Dev. Ctr., SanDimas, Calif. d in9 Shoulders, E. and W. H. McKee. Jr. FIG. 12 Concept of commercial row-muichiDI machine for hogging logging ,Iuh an convey g1973. Pine nutrition in the West Gulf Coastal resultiDg chip' to mulch beds.Plain: a status report. Gen. Tech. Rep. SO-2.USDA Forest Serv., South. For. Exp. Stn., New Forskningsstiftelsen Skogssarbeten. No.5.Orleans. La. II Stephens, C. G. and C. J. Storch. 1975.

10 Simonsson, N. 1974. The distribution of Private communication, Southern Australiaslash after mechanized final felling. Ekonomi, Perpetual Forests Limited. (18 July)

12 USDA Forest Service. 1970. Results offield trials of the tree eater: a tree and brushmasticator. Equip. De¥. and Test Rep. 7120-1.USDA Forest Serv.. San Dimas. Calif.