Commercial moss harvest in northwestern Oregon: biomass and accumulation of epiphytes

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  • Commercial moss harvest in northwestern Oregon: biomass andaccumulation of epiphytes

    JeriLynn E. Peck *, Bruce McCuneDepartment of Botany and Plant Pathology, Cordley 2082, Oregon State University, Corvallis, OR 97331-2902, USA

    Received 1 February 1997; received in revised form 10 February 1998; accepted 11 February 1998

    Abstract

    As concern over the sustainability of commercial moss harvest in the Pacific Northwest has grown, so too has the need to developmethods for estimating the rate of harvest, the biomass inventory, and the rate of accumulation of commercially harvestable epi-phytes. We estimated biomass and net moss accumulation in 10 sites in both the historically heavily moss-harvested Coast Range

    and the historically relatively unharvested Cascade Range of northwestern Oregon. Harvestable epiphyte biomass in the lowercanopy (226 800 kg year1 (500 000 lb year1; 1030%water content; unpublished data). Althoughmost moss isharvested from publicly owned land, some agencies do

    not issue formal permits, and those that do are awarethat most moss is harvested illegally (F. Duran, SiuslawNational Forest, personal communication, 1996).Concern over the impact of commercial moss har-

    vesting is particularly acute now that data exist todocument the removal of a number of species associatedwith old-growth forests (Peck, 1997a) that may be listedfor greater protection in the future (ROD, 1994). Thereis also concern over the impact on the ecological role ofepiphytic bryophytes and the likelihood that commu-nities may require decades to recover (Peck, 1996). Inresponse to these concerns, some agencies have begun totighten regulations on moss harvesting. One NationalForest district in northwestern Oregon (56 660 ha) hasset a ceiling of 49 896 kg year1 (110 000 lb year1),which has been the average legal harvest for the past10 years, but is generally considered to be less than halfthe actual annual harvest from this district (USDAForest Service, 1995).Public lands managers realize that moss harvesting

    will continue whether or not it is legal as long as thedemand exists for fresh green moss. The immediateeect of prohibiting harvest on one National Forest dis-trict was a 20-fold increase in harvest on a neighboring

    BIOLOGICAL

    CONSERVATION

    Biological Conservation 86 (1998) 299305

    0006-3207/98/$19.00 # 1998 Elsevier Science Ltd. All rights reservedPII: S0006-3207(98)00033-0

    * Corresponding author. e-mail: jeri@strengthinperspective.com

  • district and an unknown increase in illegal harvest(F. Duran, Siuslaw National Forest, personal commu-nication, 1996). The goal of conservation eorts, there-fore, is to propose management practices that willprotect the epiphytic bryophyte community whileserving the multiple-use mandate of US National For-ests. To manage commercial moss harvest for sustain-ability, we must know the rate of harvest, the rate ofaccumulation, and the biomass inventory of availableharvestable moss. The rate of illegal harvest is ambig-uous at best (Peck, 1990), requiring detailed economicand anthropological studies beyond the scope of thecurrent paper. Managers are, however, able to controlthe rate of legal harvest by setting harvest limits. Someestimates of accumulation rates based on post-harvestrecovery (e.g. Peck, 1997c) are available, but requiremany more years of data collection to provide reliableestimates of growth trends. The objectives of this paper,therefore, were to report estimates of the available bio-mass of harvestable epiphytes, describe a retrospectivemethod for estimating accumulation of harvestablemoss, consider some of the factors influencing thisaccumulation, and demonstrate how managers can usethis information to manage commercial moss harvestsustainably.

    2. Methods

    2.1. Sites

    We focused on two areas in the northwestern cornerof Oregon, as commercial moss harvesters indicate thisas the region of primary harvest activity in the state: (1)the Coast Range, which historically and currently pro-duces the vast majority of commercial moss; and (2) theCascade Range, which is closer to the population cen-ters of the Willamette Valley, but has only recentlyproduced commercial moss. Although there were nosigns of recent disturbance at any of the sites, we suspectthat the Coast Range sites may have been partially har-vested for moss c. 15 years ago.In the Coast Range, 10 sites were sampled within the

    Hebo District of the Siuslaw National Forest, Oregon(452045130N, 12350123550W). These sites werechosen specifically to represent suitable sites for com-mercial moss harvest and typically supported mixedconiferhardwood stands of c. 100 years (natural post-fire regeneration) between 120 and 410m in elevation.The basal area of conifers, estimated using a wedgeprism (basal area factor=2.3m2 ha1=10 ft2 acre1) atfive points, was between 2.5 and 46.5m2 ha1 (Peck,1997a).In the Cascade Range, nine sites were sampled on

    Bureau of Land Management land and one on the San-tiam State Forest (4430045200N, 122120122350W).

    These sites were chosen to span a broad range of standages, including unmanaged old growth and plantationsecond growth and included mixed coniferhardwoodstands of c. 50290 years between 75 and 780m in ele-vation. The basal area of conifers was between 12.5 and40m2 ha1 (Peck, 1997a).

    2.2. Moss mat sampling

    Epiphyte abundance has typically been evaluatedusing percent cover (e.g. Homan and Kazmierski,1969; Pike et al., 1977) rather than destructive biomasssampling (Russell, 1988). Exceptions include Wolf(1993), who directly sampled epiphyte biomass on tro-pical trees, McCune (1993) and Nadkarni (1984), whosampled biomass of canopy epiphytes from temperatetrees, and the current study, which mimics commercialepiphyte harvest. Most studies concerned with theaccumulation of epiphytic bryophytes have only focusedon the growth component, reporting increases over timein length or cushion area (Tallis, 1959; Pitkin, 1975),cover (Vance and Kirkland, 1997), or CO2 assimilation(Green and Sneglar, 1982; Aro et al., 1984). Our esti-mates of harvestable moss accumulation are netestimates for 1m long contiguous segments of epi-phytes, dominated by live, green brophytes, whichincorporate processes such as growth, mortality, her-bivory, litterfall and stochastic disturbance events.The objective of the moss mat sampling was to

    approximate the methods used by commercial mossharvesters in this area. These include partial removal ofcontiguous epiphyte mats in the lower canopy that aredominated by fresh, green bryophytes that are easy toremove, but often include a variety of epiphytic taxathat are taken incidentally (Peck, 1997a). Only har-vestable quantities of moss were sampled, defined asquantities of non-adherent species (i.e. no tiny appres-sed liverworts, e.g. Radula, firmly attached species, e.g.Dendroalsia, or individual tufts, e.g. Ulota) that a har-vester would consider worth removing. Generally, matsof at least 100 cm3 were considered harvestable quan-tities. Harvestable moss mats were typically composedof the mosses Isothecium myosuroides and Neckera dou-glasii, with varying amounts of the mosses Antitrichiacurtipendula, Eurhynchium oreganum, and Rhytidiadel-phus loreus and the liverworts Frullania and Porella,with a dozen other bryophytes, half a dozen lichens(especially Parmelia sulcata and Lobaria oregana), and acouple of vascular plants (Montia sibirica and Poly-podium glycyrrhiza) (Peck, 1997a). Nomenclature fol-lows Anderson et al. (1990) for mosses, Stotler andCrandall-Stotler (1977) for liverworts, and Hitchcockand Cronquist (1973) for vascular plants.Within each site, a 200m (seven sites) or 300m (13

    sites) transect was established, 50m from the nearestroad. Every 50m along each transect a sampling point

    300 J.E. Peck, B. McCune/Biological Conservation 86 (1998) 299305

  • was established, such that there were five samplingpoints on the 200m transects and seven on the 300mtransects. At each sampling point, four quadrants wereestablished, using the transect line and a line perpendi-cular to it as boundaries (Cottam et al., 1953). Withineach quadrant we sampled harvestable quantities ofmoss below a 2m vertical height cut-o on the stems ofshrubs such as vine maple Acer circinatum and huckle-berry Vaccinium parvifolium, and on the trunks ofhardwood trees such as red alder Alnus rubra and big-leaf maple Acer macrophyllum. Because most sampleswere taken from shrubs, we refer to all hosts hereafteras stems. Although the upper canopies of conifer treesoften support harvestable quantities of epiphytes, wedid not sample conifers, because harvestable quantitiesof moss are rare on conifer boles and live conifer bran-ches are rare below 2m.For each selected stem, the distance to the transect

    point and the total length of the stem up to the 2mheight cut-o were recorded (Fig. 1). Many shrub stemsgrow at an angle and, thus, never reach this verticalheight. All harvestable epiphytes (the moss mat) werethen removed from a 1m length of stem (the micro-plot) randomly selected between the ground and the2m height cut-o, and the stem diameter measuredfrom the center of the microplot. An increment core orcross-section was taken from the center of the microploton all vine maples to determine stem age. Most stemswere permanently tagged to enable future regrowthmeasurements (e.g. Peck, 1997c). In the laboratory, themoss mats were sorted by species, their abundance esti-mated visually as a percentage of the total volume ofmaterial in a given mat (after McCune, 1990), then ovendried (60C for 24 h) and weighed. All epiphytes weregrouped together for biomass estimates, to bestapproximate the harvest techniques of commercial mossharvesters. The biomass of individual species, their

    relative abundances, their relationship to site character-istics (Peck, 1997a) and their relationship to the hostspecies (Peck, 1997b) are presented elsewhere.

    2.3. Calculations

    The density of harvestable stems at each site per unitarea was estimated using the point-centered quartermethod. If the mean value of the distances to the fournearest stems d1d4 is m, then 1/

    2 gives an estimateof the density of stems per m2. Thus, the density ofstems per ha is given by 10 000/2. Although the point-centered quarter method is known to underestimatedensity in aggregated populations, this bias is con-sidered marginal unless stems grow in tight clusters(Persson, 1971), a condition we did not observe at thesesites. The point-centered quarter method was chosen asa fast and ecient means of selecting samples to esti-mate harvestable epiphyte biomass given the time con-straint of 1 day per stand, which was desirable to makethe method practical for use by public land managerswith limited budgets. In our sites, the densities of vinemaple, which was the host for 60% of our samples,averaged 3053 stems ha1 in the Cascade Range and3940 stems ha1 in the Coast Range. This falls withinthe range of values for previous estimates of 1044144 stems ha1 for vine maple alone (ODea et al.,1995).The total biomass of harvestable epiphytes per site

    was estimated from the 20 or 28 samples and thesedensity calculations. To describe the accumulation ofthe moss mats, we plotted the mass of each microplotsample against the age of the stem from which it washarvested.

    3. Results

    3.1. Biomass estimates

    Moss mat biomass was highly variable among allsites, ranging from 24 to 1068 kg ha1 in the CascadeRange, with an average of 358 [standard error (SE) 99],and from 119 to 1469 kg ha1 in the Coast Range, withan average of 550 (SE 130) (Table 1). This variabilitycan be considered a function of variability in (1) sitequality for growing harvestable moss and (2) theamount of suitable substrate among sites. Thus, the matmass was positively correlated with host surface area(Pearson correlation coecient r=0.74), such that siteswith more large surface area hosts had higher averagemat masses.Average mat mass is our most direct indicator of site

    quality, with the best site having 81 gm1 and theworst site, still with harvestable quantities of moss,having only 19 gm1 on average. Sites in both the

    Fig. 1. Harvestable moss mat sampling schematic. Microplots (1m

    long) were randomly centered between 0.5m above the ground and

    0.5m below the 2m height cut-o.

    J.E. Peck, B. McCune/Biological Conservation 86 (1998) 299305 301

  • Cascade and Coast Ranges averaged 44 gm1 (SE 6.3and 5, respectively). Stem density, however, was higherin the Coast Range sites (Table 1). The variability in sitequality and substrate availability results in variability inthe stand-level biomass estimates; Fig. 2 models theharvestable moss biomass (kg ha1 oven-dry weight) asa function of average biomass per stem and stem den-sity. The position of sites on the mat biomass axisdepends on site quality and the relative influence ofcommercial moss harvest and mat development. A sitethat is harvested for moss would shift down the bio-mass axis, but if allowed to accumulate moss, it would

    gradually move up the axis. The position of sites on thestem density axis depends on host availability. Man-agement to reduce shrub density would decrease mossbiomass and shift a site to the left, while management toincrease shrub density would shift a site to the right.

    3.2. Mat mass accumulation estimates

    Harvested vine maple stems ranged from 4 to 83 yearsin age in the Cascade Range, and from 7 to 76 years inthe Coast Range. Moss mats on these stems rangedfrom 1 to 222 gm1 in the Cascade Range, and from 1to 191 gm1 in the Coast Range. Averaging over theperiod from 10 to 60 years of stem age (Fig. 3), the meanaccumulation rate was, therefore, 1.4 (standard devia-tion (SD) 1.3) gm1 year1 for the Cascades, and 1.6

    Table 1

    Mean values for mat mass, stem length, stem density, and stand-level oven-dry biomass estimates of harvestable epiphytes in the Cascade (letters) and

    Coast (numbers) Ranges, northwestern Oregon. Values in parentheses are standard errors

    Site Mat mass

    (gm1)Stem length

    (m stem1)Stem density

    (stems ha1)Biomass

    (kg ha1)Site Mat mass

    (gm1)Stem length

    (m stem1)Stem density

    (stems ha1)Biomass

    (kg ha1)

    Ca 19 2.6 6090 (870) 288 (40) 1 38 2.6 3140 (290) 329 (30)

    Da 37 3.6 2920 (425) 1068 (200) 2 30 3.1 4620 (480) 339 (35)

    Ea 29 2.9 3220 (325) 612 (113) 5 41 2.2 2710 (95) 210 (10)

    Ga 81 2.3 1010 (65) 195 (22) 8 50 2.5 2790 (250) 597 (87)

    L 64 2.2 340 (20) 37 (2) 9 78 2.7 4440 (415) 712 (50)

    Oa 55 3.5 5030 (465) 379 (29) 10 40 3.0 7300 (565) 1469 (194)

    Pa 51 2.3 4130 (435) 519 (44) 11 38 2.7 1260 (60) 119 (6)

    Q 22 2.4 610 (20) 24 (1) 13 65 2.7 3040 (260) 558 (54)

    Sa 54 2.6 1710 (75) 211 (16) 14 23 2.9 3210 (115) 227 (21)

    T 27 2.8 4630 (275) 501 (56) 15 38 3.4 7450 (380) 947 (53)

    Mean 44 (6.3) 2.8 (0.2) 3050 (633) 385 (99) Mean 44 (5) 2.8 (0.1) 4000 (635) 550 (130)

    a Sites with 20, rather than 28, samples per site.

    Fig. 2. Harvestable moss biomass (kg ha1) as a function of moss matmass per stem (kg stem1) and stem density (stems ha1). Triangles areCascade Range sites; dots are Coast Rang...

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