The Bryologist

THE BRYOLOGIST

AJOURNAL OF BRYOLOGY AND LICHENOLOGY

VOLUME 104 SUMMER 2001 NUMBER 2

The Bryologist 104(2), pp. 181 190 Copyright ᭧ 2001 by the American Bryological and Lichenological Society, Inc.

Harvestable Epiphytic Bryophytes and their Accumulation in Central Western Oregon

JERILYNN E. PECK1 AND PATRICIA S. MUIR Department of Botany & Plant Pathology, Cordley Hall 2082, Oregon State University, Corvallis, OR 97331-2902, U.S.A.

Abstract. Methods for characterizing the composition, biomass, and accumulation rates of harvestable epiphytic bryophytes in the understory of temperate forests have recently been developed, but have yet to be implemented in a much wider geographical area and adapted to provide estimates at the individual mat level. In response to regulatory need, we modi®ed and implemented these methods in 27 50ϩ yr-old upland and riparian forest stands below 915 m to: a) characterize the composition of harvestable epiphytic bryophytes in central western Oregon, b) evaluate the compositional changes immediately following harvest, and c) retrospectively estimate minimum simple accumulation rates for harvestable bryophyte mats. Twenty-two bryophyte species, two lichens, and one vascular plant were found in a total of 433 sampled mats, dominated by Isothe- cium myosuroides, Neckera douglasii, Antitrichia curtipendula, Frullania tamarisci subsp. nisquallensis, and Porella navicularis. Harvest brought on signi®cant shifts in the relative abundance of species primarily through the disproportionate removal of these species, which are commonly found in harvestable bryophyte mats throughout western Oregon. The minimum simple accumulation rate for bryophyte mats from 13 of these stands, calculated as the oven-dried mat mass per unit surface area divided by the stem age, was 22.4 (std 15.5) g/m2/yr and is approximately comparable to that previously observed in the Coast and Cascade Ranges of northwestern Oregon. This accumulation rate translates into a commercial harvest rotation period of at least 21 (std. 12) yr. This long rotation time, coupled with the scarcity of sites supporting harvestable mats, leads to our recommendation that commercial bryophyte harvest be prohibited in the study region.

In recent years, commercial ``moss'' harvest mits for 49,896 kg (10±30% moisture content; (typically a mixture of bryophytes; Peck 1997a) has 110,000 lbs) of epiphytic moss per year that may become a controversial issue in the Paci®c North- be harvested only outside of riparian areas, in the west. Federal land managers are increasingly faced lower canopy, and from ``every other stem'' in the with writing management guidelines that must bal- forest (USDA 1995). The Eugene District of the ance the demand for the resource, the multiple-use Bureau of Land Management (BLM) in western mandate on U.S. National Forest lands (Wilkinson Oregon also prohibits harvest in riparian areas, as & Anderson 1987), the need to protect species of well as in Late Successional Reserves (LSR). How- concern (ROD 1994), the sustainability of the in- ever, these harvest restrictions are based on almost ventory, and the ecosystem functions of epiphytic no solid information on four critical parameters: 1) bryophytes. For example, the Siuslaw National For- the long-term impacts of harvesting on species est (SNF) in western Oregon currently issues per- composition and the ecosystem functions associated with epiphytic moss, 2) the size of the moss 1 Current address: e-mail: jeri@strengthinperspective. resource (inventory) available for harvest, 3) the com actual amount of moss currently being removed

0007-2745/01/181±190$1.15/0 182 THE BRYOLOGIST [VOL. 104 from the forest, and 4) the rate at which mosses vestable epiphytic bryophyte mats in this area, the reaccumulate following harvesting (Peck & Mc- changes in these communities immediately follow- Cune 1998). Information on these parameters is vi- ing harvest, and our estimates of mat accumulation tally important to guide permitting decisions in the rates based on this modi®ed methodology. future (Liegel 1992). Recent work has begun to ®ll these gaps in our METHODS understanding. Firstly, estimates of the community composition of harvestable bryophytes now exist Of 100 randomly selected sites on the Eugene District for selected areas on the Hebo District, SNF and of the Bureau of Land Management in central western Oregon, only 27 had suf®cient quantities of harvestable the Salem District, BLM (Peck 1997a,b) and for bryophytes to enable sampling. All 100 sites were within various other areas around the state of Oregon the elevation and stand age ranges considered likely to (Vance & Kirkland 1997). Secondly, estimates of support harvestable epiphytic bryophytes in this region: the size of the moss resource are also available for Յ915 m and Ն50 yr (see Peck & Muir 2001 for site selection and stand characteristic details). Sites were located the Hebo and Salem Districts (Peck & McCune in the rain shadow of the Oregon Coast Mountain Range, 1998). Thirdly, although the illegal harvest is esti- between the eastern foothills of the Coast Range and the mated to remove between two and 30 times the western foothills of the Cascade Range in the Paci®c legal harvest quantity (USDA 1995), harvest permit Northwest of North America (43Њ30Ј±44Њ15Ј N, 122Њ30Ј± records provide some information on the rate of 123Њ50Ј W). Sites were located between 125 and 744 m in elevation with a basal area of conifers (primarily Pseu- removal of moss from the forest. Finally, some dotsuga menziesii) between zero and 46 m2/ha and were long-term studies of regrowth rates and the impacts in management units of greater than four ha (10 acres). of harvest on species composition are underway on Thirteen sites were in forests less than 150 yr in age (all the Hebo District (Peck 1999), on the Eugene Dis- over 50 yr) and 14 in forests over 150 yr in age. All sites were sampled using one 35 ϫ 35 m plot (1/8 ha ϭ 1/3 trict, BLM (Peck & Muir 1998), and in western acre), placed so as to be as internally consistent as pos- Washington (N. Nadkarni, pers. comm.; D. Shaw, sible with respect to slope, aspect, and forest composition. pers. comm.). These studies are based on harvest- Sampling occurred during the summers of 1997 and 1998. ing large bryophyte mats from permanently marked Harvestable bryophyte mats were de®ned, following shrub stems and periodically remeasuring reaccu- Peck (1997a), as loose clumps of green epiphytic bryophytes of at least 200 cm3 in volume. These harvestable mulation, and will require decades before reliable bryophytes mats were removed from approximately 10 reaccumulation rates can be obtained. However, shrub stems or shrub boles (95% vine-maple, Acer circin- managers are faced with resource utilization issues atum, 5% huckleberry, Vaccinium parvifolium) per plot, right now. which had been randomly selected from among those bearing harvestable bryophyte mats (in most plots this The current project, generated by the recognized was the entire population). From each of these stems a need for inventory, monitoring, and research in single continuous harvestable bryophyte mat (of variable nontimber product programs (USDI 1993), was de- length and volume) was harvested by lifting and peeling signed to characterize the impacted bryophyte com- away from the stem in one motion. All taxa were identi- munities, and estimate rates of mat accumulation, ®ed and their relative abundances estimated, after McCune (1990). The total volume of each mat, as well as the length in sites where harvestable bryophytes occur on the and diameter of the section of stem from which it was Eugene District, BLM in central western Oregon. removed, was also measured. In 13 sites (the ``rate'' sites), Traditional estimates of bryophyte growth, such as an increment core was taken from the center of the har- measuring shoot-tip growth or the length of annual vested section of the stem to provide the retrospective estimation of accumulation rates (see below). Increment growth segments (see discussion in Russell 1988) cores were sanded and annual growth rings counted uti- are inadequate to estimate biomass accumulation in lizing a dissecting microscope. In the other 14 sites (the situ at large spatial scales. A methodology has been `ìmpact'' sites), all bryophytes remaining on the stem in developed and employed in the Coast Range of the section from which the mat was harvested were also northwestern Oregon that provides stand-level es- recorded and their relative abundances estimated. These stems were not cored and are intended to be remeasured timates through retrospective means (Peck & ®ve years following harvest to facilitate regrowth-based McCune 1998). We chose to employ a modi®ed estimates of accumulation rates (to be remeasured in 2002; version of this procedure in central western Oregon, Peck & Muir 1998). Harvested mats were weighed after where harvestable biomass, and presumably accu- oven drying (24 hr at 60 C). Nomenclature follows An- derson et al. (1990) for mosses, Stotler and Crandall-Sto- mulation rates, are relatively low (Peck & Muir tler (1977) for hepatics, Esslinger and Egan (1995) for 2001). Our goal was to determine the minimum ac- lichens, and Hitchcock and Cronquist (1973) for vascular cumulation rate of individual harvestable bryophyte plants. mats, rather than stand-level estimates, to enable The frequency of occurrence was calculated for each more direct comparisons with the results of prom- species for all sites combined and separately for the impact and the rate datasets. The quantitative data in all sub- ising new transplant methods for estimating epi- sequent analyses were relative proportions of each species phytic bryophyte growth rates (e.g., Rosso 2000). out of the total volume of each mat. Comparisons of har- We report here on the species composition of harvested mat species compositions (``pre'') and post-harvest 2001] PECK & MUIR: HARVESTABLE BRYOPHYTES 183 residual species compositions (``post'') for the impact sites calculated a second set of accumulation values in a way were conducted using the Mantel test, a nonparametric test that approximates theirs as closely as possible. They sam- that evaluates the similarity between two distance matrices pled mat growth per unit stem (i.e., grams per one m of (PCORD, McCune & Mefford 1997; Sokal & Rohlf stem length, regardless of whether or not a mat was pres- 1995). Comparisons of species composition among sites ent on the entire segment, as g/m(stem)/yr), whereas the were conducted using multi-response permutation proce- length of our stem segments depended upon the length of dures (Mielke 1984; 1,000 permutations with procedure the mat itself (m(mat)) and thus varied, rarely reaching MRPP in PCORD, McCune & Mefford 1997), a non-para- one m in length (average 0.6 m). In comparison to our metric group comparison statistic, with site as the group methods, their methods would lead to an underestimation membership variable. The Sùrensen coef®cient (also of accumulation for an individual bryophyte mat. Because known as the Czekanowski coef®cient) was chosen as the Peck and McCune (1998) did not measure the actual distance measure in all cases. The relative abundance and length of their epiphyte mats, it is impossible to convert frequency of species among groups was calculated and their g/m(stem)/yr values to g/m2(mat)/yr values that are compared using `ìndicator species analysis'' with a Monte comparable with ours. We therefore converted our g/ Carlo randomization test (DufreÁne & Legendre 1997; m2(mat)/yr values to g/m(stem)/yr by: a) ignoring surface 1,000 permutations in PCORD, McCune & Mefford area (i.e., the circumference of the stem; our averages are 1997), with site or pre- versus post-harvest as the group comparable to those of Peck and McCune, unpubl. data), membership variables. We also evaluated the change in and b) assuming the absence of other mats within the 1- species composition immediately following harvest by or- m stem segment centered on our mat (which was the case dinating the pre-harvest mat compositions and the post- at least 90% of the time). harvest residual compositions using nonmetric multidi- Finally, we estimated compound accumulation rates mensional scaling (procedure NMS in PCORD, McCune based on different initial weights using the following con- & Mefford 1997) for a two-dimensional solution. An ap- tinuously compounding interest formula (Edwards & Pen- rt proximate oven-dried biomass (in kg/ha) was estimated ney 1990, p. 373): A(t) ϭ A0e where A(t) is the ®nal for each species by multiplying the average proportion of weight (our mat mass), A0 is the initial weight (we used that species in each harvestable mat by the total biomass two values; see Discussion), r is the rate, and t is time of harvestable bryophytes in each plot (from Peck & Muir (our stem ages, in yrs). 2001). In addition, species composition was compared (using RESULTS MRPP) across three land management classi®cations (ROD 1994) in which our sites occurred: matrix forest, Community description. Twenty-two bryo- Adaptive Management Areas (AMA), and Late Succes- sional Reserves (LSR). Species composition was further phytes, two lichens, and one fern were found in the contrasted between sites classi®ed as ``riparian'' or `ùp- 433 sampled bryophyte mats from all 27 sites (Ta- land'' on the basis of their location within, or outside for ble 1). The most frequent, and most abundant, spe- the latter, a 61 m buffer on either side of perennial cies were: Isothecium myosuroides, Neckera doug- streams. The chi-squared test for homogeneity (Ramsey & Schafer 1997) was also used to evaluate whether har- lasii, Porella navicularis, Frullania tamarisci vestable moss occurrence (presence/absence) was inde- subsp. nisquallensis, and Antitrichia curtipendula. pendent of the riparian and upland land classi®cations. The typical bryophyte mat had four (standard de- We estimated a minimum simple accumulation rate (in viation (std) 1) taxa (mean alpha diversity). No dif- 2 g/m /yr; masses are for oven-dried material) for the 218 ference was seen in species composition among the mats sampled across the rate sites by assuming that the bryophyte mat could not have taken longer to accumulate three land management classi®cations or the ripar- than the stem was old, following Peck and McCune ian/upland land classi®cations (MRPP, all p Ͼ 0.1). (1998). Hence the mass of the mat per unit surface area Community change following harvest. Group- of stem segment under the mat (e.g., 500 g/m2) divided ing all 215 mats in the 14 impact sites together, by the age of the stem at that segment (e.g., 25 yr) pro- there was more correspondence between pre- and vided a minimum simple accumulation rate (e.g., of 20 g/ m2/yr). We present the data using a cumulative distribution post-harvest relative species composition than function (program CDF, Binns 1994), which ranked sam- would have been expected by chance (Mantel test, ples by their accumulation rate and then plotted the cu- r ϭ 0.37, p Ͻ 0.001). However, this result varied mulative probability of occurrence for each observed rate among sites as species composition varied (MRPP, against that rate. We report, in addition to the arithmetic p Ͻ 0.001), re¯ected particularly in the patchy dis- mean, the accumulation rate at the 50th percentile. Ap- proximate reaccumulation rotation times, in years, were tribution of Antitrichia curtipendula, Dicranum calculated by dividing the average mass per unit area (in scoparium, Eurhynchium oreganum, Homalothe- g/m2) by these estimated accumulation rates (in g/m2/yr). cium fuscescens, Plagiomnium venustum, and Po- Three mats with masses more than two standard devia- rella cordaeana among sites (indicator species tions from the mean of the population were considered re¯ective of a different population and deleted from the analysis, all p Ͻ 0.01). Each of the 14 plots was analyses (see litterfall discussion of Peck & McCune then considered separately, and we found that pre- 1998). We then tested for correlations between the esti- and post-harvest relative species compositions were mated accumulation rates for each site and site character- less similar for seven plots than would have been istics (PROC COR, SAS 1996). expected by chance (Mantel test, all r Ͼ 0.24, p Ͻ Because a direct comparison with the only other published estimates of harvestable moss accumulation rates 0.05). Although A. curtipendula, Hypnum subim- (Peck & McCune 1998) is impossible due to differences ponens, and P. cordaeana generally became signif- in both sampling methods and sampled populations, we icantly less frequent and abundant relative to other 184 THE BRYOLOGIST [VOL. 104

TABLE 1. Epiphytes found in harvestable bryophyte mats in central western Oregon, U.S.A. Species in bold are species commonly targeted for commercial harvest; the rest are incidental and non-target species (Peck 1979a). Pre ϭ harvested bryophyte mats; post ϭ residual on stem following harvest; ␯ϭfrequency of occurrence (%); g/m2(mat) ϭ average oven-dried mass per square meter stem surface area for only the area directly under the sampled mat. An approximate oven-dried biomass (in kg/ha) is estimated for each species for comparison with Peck (1997a). L indicates lichen taxa, F indicates the species of fern, and * indicates species for which there is a chance that they were inadver- tently combined with their congener in the ®eld.

14 impact sites 13 rate sites 27 sites pre n ϭ 215 pre n ϭ 218 n ϭ 433 % ␯ % ␯ g/m2 (mat) kg/ha post % ␯ % ␯ g/m2 (mat) kg/ha Antitrichia curtipendula 29 31 90.1 4.1 2 27 32.5 1.0 Cladonia sp.L 1 1 0.1 Ͻ 0.1 Ð 2 0.1 Ͻ 0.1 Claopodium crispifolium 7 7 3.7 0.7 7 10 6.0 0.1 Dendroalsia abietina 2 3 0.4 Ͻ 0.1 4 Ð Ð Ð Dicranum fuscescens 8 3 7.8 0.7 Ͻ 1 14 4.0 0.2 Dicranum scoparium * 3 1.2 0.1 Ð * Ð Ð Eurhynchium oreganum 20 23 39.1 4.8 9 20 29.8 0.8 Eurhynchium praelongum * Ͻ 1 Ͻ 0.0 Ͻ 0.1 Ͻ 1 * Ð Ð Frullania tamarisci subsp. nisquallensis 33 33 11.3 0.9 7 31 4.5 0.2 Homalothecium fulgescens 4 10 2.4 0.1 3 Ð Ð Ð Homalothecium nuttallii 2 3 0.5 Ͻ 0.1 1 3 0.6 Ͻ 0.1 Hypnum subimponens 15 10 4.6 0.5 1 20 13.5 0.2 Isothecium myosuroides 92 91 503.4 33.6 82 88 310.1 10.7 Leptogium polycarpumL Ͻ 1 Ͻ 1 1.0 0.2 Ð Ð Ð Ͻ 0.1 Leucolepis acanthoneuron 3 2 2.3 0.1 Ð 4 4.2 Ð Metaneckera menziesii 1 3 3.6 2.1 2 Ð Ð Ð Neckera douglasii 64 72 180.2 12.9 53 55 58.9 1.9 Orthotrichum lyellii 2 3 2.3 0.1 2 Ð Ð Ð Plagiomnium venustum 2 4 1.4 0.1 1 Ð Ð Ð Polypodium glycyrrhizaF 4 1 0.5 0.3 2 Ð Ð Ð Porella cordaeana * 11 3.7 Ͻ 0.1 Ͻ 1 * Ð Ð Porella navicularis 62 65 71.3 7.4 26 56 39.5 1.5 Rhizomnium glabrescens 9 7 0.6 0.3 1 13 3.4 0.1 Rhytidiadelphus loreus * 7 8.4 1.4 2 * Ð Ð Rhytidiadelphus triquetrus 4 3 9.1 1.1 Ͻ 1 4 2.4 Ͻ 0.1 species in the seven sites where signi®cant changes (std 15.5). At this rate, to reaccumulate the mats of occurred, and most other species retained their pre- an equivalent mass to those removed from these vious positions, Claopodium crispifolium, Isothe- stems would require at least 21 yr (std 12). At the cium myosuroides, Neckera douglasii, and Porella 50th percentile of the cumulative frequency distri- navicularis always took on more dominant posi- bution, the simple accumulation rate was estimated tions in the community immediately following har- to be 20.8 g/m2/yr (90th percentile from 15.1 to vest (indicator species analysis, p Ͻ 0.05). Figure 23.5; Fig. 2). At this somewhat reduced rate, future 1 shows the typical pattern of compositional change mats equivalent in mass to those we harvested as exempli®ed by one of these seven sites, from would require 23 yr (std 13) to accumulate. No sig- more similar compositions prior to harvest, with ni®cant association was found between these rates one- to two-species dominance (open circles, to- and the measured site characteristics, which includ- ward the top and middle) to more variable relative ed elevation, conifer and hardwood basal area, and compositions following harvest (®lled circles, dis- distance to water (all p Ͼ 0.1). tributed variously relative to pre-harvest open cir- Converting our values to values comparable to cles). Peck and McCune (1998), we obtain a mean min- Accumulation rates. The 218 stems from the 13 imum simple accumulation rate of 1.2 g/m/yr (std rate sites ranged from 8 to 83 yr (average 29 yr, 0.7; Fig. 3). Although we are not able to estimate S.D. 13) and harbored mats ranging from 60 to 931 compound accumulation rates directly, with an as- g/m2 (average 475 g/m2, S.D. 198; all masses are sumed initial weight we can estimate these rates for oven-dried material). The average mat of 29 g using a compound interest formula (see Eq. 1 from (std 12) measured 0.6 m (std 0.2) in length on a methods) and our estimated accumulation rates in stem with a circumference of just over 0.2 m (std g/m2/yr or g/m/yr. If we presume that early mat 0.2). On average, these highly variable mats accu- growth rates are relatively low (e.g., 0.8 g/m/yr in mulated at a minimum simple rate of 22.4 g/m2/yr the ®rst four years, from Peck 1999) but increase 2001] PECK & MUIR: HARVESTABLE BRYOPHYTES 185

FIGURE 1. NMS ordination of a single site, showing the typical pattern for the 50% of impact sites that had signi®cantly altered species composition immediately following harvest. The direction of the arrows indicates the shift in relative species' frequencies and abundances from mature harvestable bryophyte mats (open circles) to the residue left on the host stem immediately following harvest (®lled circles). Harvestable bryophyte mats, which tend to be dominated by one or two species although several may be present, cluster toward the top and center of this ordination. Following harvest, most species remain, but with substantially altered relative abundances such that stems may be dominated by a variety of species, which is re¯ected here by the variety in directions of change. at some point in time to produce an average of 22.4 species Rhytidiadelphus triquetrus, but lacks sev- g/m2/yr over a 29 yr period, we can use both of eral species of lichen and a number of species oc- these rates to bound an approximate range for min- casionally found as large mat epiphytes in relatively imum percent growth rates. Taking our initial moist stands (e.g., Hypnum circinale, Metzgeria weight to be the weight at year one from these temperata, and Plagiothecium undulatum). A sim- mean estimated accumulation rates (e.g., 0.8 g/m/ ilar situation is found in the contrast between our yr for young mats and 22.4 g/m2 for older mats), list and that provided by Vance and Kirkland our average mat mass per unit stem area as the ®nal (1997), who, in harvestable bryophyte mats on weight (29.5 g/m/yr here ϭ 475 g/m2), and our av- vine-maple from eight sites of very high epiphyte erage stem age (29 yr) for time, we calculate com- biomass distributed throughout western Oregon, pound growth rates of roughly 13% and 11% for found one more species of moss, four more hepat- young and older mats, respectively. ics, ten more lichens, and an additional vascular plant. The seemingly low gamma diversity for non- DISCUSSION vascular species in our study may re¯ect the ho- Community description. The epiphytes found mogeneity of our sites and the drier conditions of in this study are similar to those found in previous our study area. studies of harvestable epiphytes in Oregon, al- The low frequency of vascular species in our though our list of 25 taxa is considerably shorter sites may also be a function of the relative dryness than the 34 and 39 found previously on the Hebo of our study area. Wetter sites often have thicker and Salem Districts, respectively (Peck 1997a). By mats with more accumulated organic matter (Ken- comparison, our list adds the forest ¯oor and log kel & Brad®eld 1986). While Peck and McCune 186 THE BRYOLOGIST [VOL. 104

FIGURE 2. Frequency histogram and cumulative frequency distribution of the minimum simple accumulation rate (g/m2/yr; masses are for oven-dried material) for mats harvested from the 13 rate sites. The rate at the 50th percentile (20.8 g/m2/yr) is shown (solid lines), along with the 90th percentile con®dence interval (dotted lines). Note that rates Ͼ50 g/m2/yr are relatively rare and may represent mats impacted by the addition of canopy litterfall.

(1998) sampled deep mats averaging 44 g/m, the among studies and regions is not surprising. A con- average mat in our study was thinner, with only 30 sistent pattern is beginning to form in which the g/m. The drier conditions in our area, and hence same species, the ``target'' species of Peck (1997a) more desiccating canopy conditions, may explain occur again and again in harvestable epiphyte mats the lower frequency of Antitrichia curtipendula, a throughout the Paci®c Northwest (Table 1). The species most commonly found in the canopy that composition of harvestable bryophyte mats on Acer appears to establish fairly frequently in the under- circinatum did not vary between the Coast and Cas- story through litterfall from the canopy. cade Ranges of Oregon in a previous comparison The lack of differences in species composition (Peck 1997b). The less dominant ``incidental'' and among the three types of management areas and ``non-target'' (Peck 1997a) species tend to be very between the riparian/upland areas merely re¯ects responsive to local variations in microclimate and that these management classi®cations span across hence their occurrence varies considerably from the environmental gradients that affect abundant site to site and even stem to stem. By contrast, the bryophyte growth. In the case of the riparian and dominant target species vary in relative abundance upland designations, the 61 m buffer used by the but are consistently present across substantial light Eugene District to protect riparian communities is and moisture gradients. In our sites, over 90% of simply too broad to capture a moisture gradient that the harvested biomass was contributed by the target probably extends no more than 30±50 m from a species (Table 1), the same ®gure as found by Peck riparian corridor in this region. Most harvestable (1997a) for the Hebo and Salem Districts. bryophytes in this study were found less than 50 m However, it is important to note that in the past in horizontal and 30 m in vertical distance from a ®ve years it has become more common to ®nd in- perennial source of water (Peck & Muir 2001). cidental and non-target species in commercially The large overlap of the bryophyte community sold moss in the Paci®c Northwest (J. Peck, pers. 2001] PECK & MUIR: HARVESTABLE BRYOPHYTES 187

pear to be much different from natural disturbances resulting from downed trees or wildlife, where large epiphyte mats are often brushed off host stems onto the forest ¯oor. However, differences among species in growth strategies and rates imply that the species composition at early stages of mat maturation, which is in¯uenced by the manner in which bryophyte mats are removed, probably great- ly in¯uences the community that later develops. Thus the selective harvest of particular (e.g., target) species of epiphytic bryophytes over others may, in addition to immediately changing the community, lead to the development of altered future communities. For instance, A. curtipendula, mats of which are a prime target for harvest because of their ®rm texture, full volume, and ease of harvest, has relatively few rhizoidal connections to the host shrub compared to Isothecium myosuroides, mats of which must be relatively large and old before they build up enough epiphytic soil to separate the rhi- zoids from the host shrub and hence become easy to harvest (note the difference between these species in residual frequencies, Table 1). This would lead one to believe that, because A. curtipendula mats are more often targeted for harvest and leave less residue behind, future mats on such harvested stems would develop with relatively more I. myosuroides. However, the substantially higher growth rate of A. curtipendula relative to I. myosuroides FIGURE 3. Frequency histogram of harvestable bryo- (P. Muir, unpub. data) suggests that what little of phyte mat mass (oven-dried) and plot of host stem (Acer A. curtipendula does remain following harvest circinatum) age against mat mass, measured as grams on a one-meter section of stem and scaled to be comparable could possibly grow back fast enough to overcome with Figure 3 of Peck and McCune (1998). Although quite the setback caused by its disproportionate removal variable, mat masses (both total and per m biomass val- during harvest. Results from a reaccumulation ues) are generally smaller than those reported by Peck and study in the Oregon Coast Range (Peck 1999) sug- McCune (1998), re¯ective of the much lower harvestable biomass in our region. gest that, in the ®rst few years following harvest, developing mats are dominated by precisely the incidental and non-target species that were left behind obs.). This shift in harvest practices is likely in re- immediately following harvest. At ®ve years after sponse to a tightening of harvest regulations, which harvest, there is suggestive evidence that factors has restricted the land base available for legal com- such as differences in growth rates, growth form, mercial moss harvest in Oregon and presumably led and encroachment from neighboring mature mats to an increase in illegal harvest as well. Commer- may ultimately lead to the development of mature cial moss buyers report that, because demand has mats with different compositions from those now remained constant while supply has dwindled, they observed in the recovering mats. However, in the are now willing to buy ``moss'' of much lower current study, no correlation was found between the quality than beforeÐi.e., with more incidental and proportion of an epiphyte mat composed by an in- non-target species (various buyers, pers. comm. to dividual target species and the accumulation rate J. Peck, 1998). It would thus appear that tighter for that mat (all p Ͼ 0.1; i.e., A. curtipendula-dom- regulations of moss harvest on publicly owned inated mats did not have higher accumulation rates lands has, although protecting communities in some than mats dominated by I. myosuroides). Long term areas, opened the communities in the remaining ar- monitoring will be necessary to resolve whether the eas to a much greater threat of uncommon and rare future mats will resemble the pre-harvest mats, the species extirpation than before, an outcome that recovering mats, or will establish an entirely new was obviously not anticipated. pattern. Community change following harvest. Com- Accumulation rates. Unfortunately, at this early mercial bryophyte harvest sometimes does not ap- stage in the inventory of harvestable bryophytes, 188 THE BRYOLOGIST [VOL. 104 very few accounts of understory bryophyte mat rates re¯ect conditions of little, if any, disturbance, growth rates exist for comparison. The one previ- they are expected to be substantially higher than ously published in situ study that does exist (Peck our observed rates. Isothecium myosuroides, one of & McCune 1998) requires a certain amount of cre- the primary constituents of our harvestable bryo- ativity to extrapolate across differences in climate phyte mats, has been recorded to increase in mass and methods from the present study and thereby at simple rate of 28% over a 15 month period as enable comparisons. Climatically, the geographic mat transplants onto wooden dowels in forests in area of our inferences is located in a segment that western Oregon, and Antitrichia curtipendula at lies in the rain shadow of the Oregon Coast Range, 44% over the same period (P. Muir, unpubl. data). whereas the previous study was conducted half in A simple accumulation rate for mixed species mats the fog-belt on the coastal side of this mountain based on remeasurements of harvested stems on the range (the Hebo District) and half in a region just Hebo District ranged from seven to 20%/yr (Peck north of our study area (the Salem District). The 1999), closer to the simple rate of 4%/yr for our total biomass of harvestable bryophytes in our area sites (both estimated as the ratio of the estimated is much less than in the coastal zone (Peck & Muir accumulation rate (g/m/yr) to actual mat masses (g/ 2001) and accumulation rates were expected to be m)). Comparable rates are 4%/yr for the Salem Dis- lower as well. trict and 3%/yr for the Hebo District (Peck & The methodological leap between Peck and McCune, unpub. data). McCune (1998) and the current study is unfortu- As a rate for ``mature'' mats of more than 200 nately larger. Although both of our rates represent cm3, our rate (22 g/m2/yr) is much higher than the minimum simple accumulation rates (not to be con- ®rst estimates from reaccumulation following har- fused with rates that compound over time), our vest in northwestern Oregon, which at four years sampled populations are slightly different. Because after harvest (i.e., very small ``mats'') was esti- our intention was to characterize the accumulation mated at 0.8 g/m/yr (Peck 1999; n ϭ 8). Although of bryophyte mats, treating them as individuals further biomass estimates will not be available from within the population of harvestable bryophytes, that study for several more years, there is sugges- we sampled individual bryophyte mats and based tive evidence already of a strong non-linear, nearly the length of our sampled stem segment on the exponentially increasing pattern in accumulation at lengths of the mats. By contrast, to estimate stand- those sites, which was only in the early stages at level harvestable bryophyte accumulation, Peck the time the aforementioned estimates were calcu- and McCune (1998) sampled a pre-determined lated. Future epiphytic bryophyte growth studies length of stem segment (1 m) to facilitate extrap- are also likely to span more than one year, thus olation to the stand level on the basis of stem enabling the calculation of compound rather than lengths and densities. Although our converted g/ simple growth rates. Our calculated compound m(stem)/yr values represent the closest possible ap- growth rates of roughly 11±13% are comparable to proximation to the rates of Peck and McCune those found for both the Salem (12±14%) and Hebo (1998), they may be underestimates. Our value (1.2 (11±13%) Districts (Peck & McCune, unpubl. g/m/yr) is somewhat lower than the means of 1.4 data). The similarity of estimated accumulation g/m/yr for an area just north of ours in the Salem rates among these regions was not anticipated. The District and 1.6 g/m/yr for the coastal Hebo District substantially lower frequency and biomass of har- of Peck and McCune (1998). Our estimated rotation vestable bryophytes in our study (Peck & Muir period is also in keeping with other preliminary es- 2001), the more than 40 yr history of commercial timates, which ranged from 10 to 15 yr for the harvest on the Hebo District, as compared to only Hebo District based on the retrospective method scattered reports of harvest in our area, and the no- used in this study (Peck & McCune 1998), to 10 to tably drier climate of our area would suggest lower 30 yr based on post-harvest reaccumulation mea- accumulation rates. sures on the Hebo District in their fourth year (Peck We can only speculate why our accumulation 1999). rates would be comparable to those of other, wetter Our estimated simple accumulation rate sets the areas. Firstly, in order for harvestable mats of the minimum boundary for our expectations of reac- size we sought to develop in relatively dry regions, cumulation of individual mats in moist, moss-con- pockets of forest with unique microclimatic condi- ducive sites in our area. Under ideal settings, with tions may be required. These unique pockets may no disturbance, one would expect potentially higher not only facilitate the transition from a small mat rates. Because we measured individual mat accu- to a large, harvestable mat, but may also maintain mulation, our estimates can be compared to results the growth of that mat at a rate comparable to from growth experiments using transplanted epi- moss-conducive sites throughout the Paci®c North- phytic bryophyte mats. However, because the latter west. One hypothesis suggests that, because the 2001] PECK & MUIR: HARVESTABLE BRYOPHYTES 189 moisture-retaining capacity of an epiphytic bryo- mulation rates for those sites. If their sites had been phyte mat is inversely related to its surface area to harvested 15 yr prior to sampling, and 15 yr was volume ratio (Hosokawa et al. 1964), a mat of larg- thus used as the time for accumulation in the cal- er volume should be better able to conserve water culations, then their average rate for the coastal and would therefore be expected to have a higher Hebo District would have been 3.0 g/m(stem)/yr growth rate than a smaller mat (D. Norris, 1995, (Peck & McCune, unpubl. data), with a rotation unpublished report to the Siuslaw National Forest, period of 15 yr; considerably faster accumulation Oregon). In drier climates such as ours, mats would than we documented here. have to achieve larger sizes to obtain this bene®t Although all of these rate estimates remain to be than in wetter climates, and moisture conditions validated by long-term regrowth studies, they do would be suf®cient to enable the development of enable the prediction that, under similar conditions, mats from small to such large volumes only in cer- comparably sized mats would require over two de- tain areas. Those same areas of presumably higher cades to accumulate at these sites. A myriad of eco- moisture would then also facilitate rapid growth logical issues remain to be considered with respect rates through high moisture availability to the large to commercial moss harvest. For example, it is gen- mats. We, therefore, would have found mats large erally recognized that epiphytic bryophytes contrib- enough for harvesting only in areas where moisture ute to biodiversity (e.g., hundreds of taxa of inver- conditions are conducive to both the development tebrates per mat, J. Peck & A. Moldenke, unpubl. of the mats and to relatively high growth rates (e.g., data), nutrient cycling (Brown & Bates 1990), and true riparian areas and higher humidity draws in our hydrological bufferingÐperhaps substantially (D. region). If harvestable mats only occur in areas Norris, 1995, unpublished report to the Siuslaw Na- with fairly similar microclimatic conditions tional Forest, Oregon). However, we continue to throughout the Paci®c Northwest, then growth rates lack quantitative data on these ecosystem roles and in these areas would also be expected to be similar, on the impact of moss harvesting on them for the given the same species composition, which we have areas most affected by commercial moss harvest in already established. This hypothesis is supported by the Paci®c Northwest. We feel that the relatively the fact that, out of 100 randomly selected sites low biomass of commercially harvestable bryo- (within the stand age and elevation ranges likely to phytes in our study area (Peck & Muir 2001), the support harvestable bryophytes), only 27 supported patchy distribution of those bryophytes, the rela- any harvestable mats at all, and each of these con- tively low accumulation rates, and the unknown im- tained at least 10 large-volume mats (Peck & Muir pacts of bryophyte harvest on ecosystem functions 2001). That is, harvestable mats were absent from dictate that moss harvest be completely prohibited most sites, but when present they tended to be large in this and similar, relatively dry portions of west- and vigorous. Indeed, although no difference in es- ern central Oregon. timated accumulation rates was observed between riparian and upland sites as de®ned by the 61 m ACKNOWLEDGMENTS buffer criterion (ANOVA, p Ͼ 0.1), harvestable epiphytes were 3.6 times more likely to be found We would like to thank Nancy Wogen of the Eugene District, BLM and Jenny Lippert of the Willamette Na- in riparian than upland sites (95% con®dence in- tional Forest for facilitating this project and providing as- terval, 1.3±9.5; the chi-squared odds ratio test, p Ͻ sistance with the design and logistics. We also owe thanks 0.001). The lack of association between accumu- to Rob Stein for site selection assistance and Dylan Keon, lation rates and measured site characteristics sug- Ray Fiori, and Cy Berryman for help in the ®eld. Emma gests that standard variables such as conifer and Pharo and Wilfred Scho®eld made helpful comments on the manuscript. Support was provided by a cost-share hardwood basal area, elevation, and aspect are in- agreement between the Eugene District, Bureau of Land suf®cient to capture this microclimatic gradient. Management and Oregon State University (Agreement Given the rarity of such mossy sites in our study numbers H952AL010131 and 1422H090P970076). area, our estimated accumulation rates should only be applied to comparably mossy sites rather than LITERATURE CITED taken as an average for the entire study area. Secondly, the mats in our area may have expe- ANDERSON, L., H. CRUM,&W.BUCK. 1990. List of the mosses of North America north of Mexico. THE BRY- rienced less disturbance than those in the previous OLOGIST 93: 448±499. study. Although no obvious signs of disturbance BINNS, R. 1994. Cumulative distribution frequency gen- were noted by Peck and McCune (1998) at their erator. 3041 Cornvallis Rd., Durham, NC. sites, they did suspect that their coastal sites may BROWN,D.&J.BATES. 1990. Bryophytes and nutrient cycling. Botanical Journal of the Linnean Society 104: have been subject to partial commercial moss har- 129±147. vest roughly 15 yr prior to measurement, which DUFREÁ NE,M.&P.LEGENDRE. 1997. Species assemblages would result in substantial underestimates of accu- and indicator species: The need for a ¯exible asym- 190 THE BRYOLOGIST [VOL. 104

metrical approach. Ecological Monographs 67: 345± ÐÐÐ&P.S.MUIR. 2001. Estimating the biomass of 366. harvestable epiphytic moss in central western Oregon. EDWARDS,JR.C.,&D.PENNEY. 1990. Calculus and An- Northwest Science (in press). alytic Geometry, 3rd ed. Prentice Hall, NJ. RAMSEY,F.&D.SCHAFER. 1997. The Statistical Sleuth. ESSLINGER,T.&R.EGAN. 1995. A sixth checklist of the Duxbury Press, Belmont, CA. lichen-forming, lichenicolous, and allied fungi of the ROD. 1994. Record of Decision for Amendments to For- continental United States and Canada. THE BRYOLO- est Service and Bureau of Land Management Planning GIST 98: 467±549. Documents and Standards and Guidelines for Man- HITCHCOCK, C. & A. CRONQUIST. 1973. Flora of the Paci®c agement of Habitat for Late-Successional and Old- Northwest. University of Washington Press, Seattle, growth Forest Related Species within the Range of the WA. Northern Spotted Owl. U.S. Government Printing Of- HOSOKAWA T.,N.ODANA &H.TAGAWA. 1964. Causality ®ce 1994-589-111/0001. Region No. 10, Washington, of the distribution of corticolous species in forests with D.C. special reference to the phyto-sociological approach. ROSSO, A. L. 2000. Shrub Epiphyte Communities in Re- THE BRYOLOGIST 67: 396±411. lation to Stand Management in Forests of Western KENKEL,N.&G.BRADFIELD. 1986. Ordination of epi- Oregon. Ph.D. Dissertation, Oregon State University, phytic bryophyte communities in a wet-temperate co- Corvallis, OR. niferous forest, South-Coastal British Columbia. Ve- RUSSELL, S. 1988. Measurement of bryophyte growth I. getatio 45: 147±154. Biomass (harvest) techniques, pp. 249±257. In J. Gli- LIEGEL, L. 1992. Concerns and issues for special forest me (ed.), Methods in Bryology. Hattori Botanical Lab- product research in the Northwest. Paci®c Northwest oratory, Nichinan, Japan. Research Station, Forestry Sciences Laboratory, 3200 SAS. 1996. SAS v. 6.12. SAS Institute, Inc., SAS Campus SW Jefferson Way, Corvallis, OR. Drive, Cary, NC. MCCUNE, B. 1990. Rapid estimation of abundance of epi- SOKAL,R.&F.ROHLF. 1995. Biometry, third edition. W.H. phytes on branches. THE BRYOLOGIST 93: 39±43. Freeman & Co., NY. ÐÐÐ&M.MEFFORD. 1997. Multivariate analysis of STOTLER, R. & B. CRANDALL-STOTLER. 1977. A checklist ecological data, ver. 3.20. MjM Software, Gleneden of the liverworts and hornworts of North America. Beach, OR. THE BRYOLOGIST 80: 405±428. MIELKE,JR. P. 1984. Meteorological applications of per- USDI. 1993. Bureau of Land Management Task Force: mutation techniques based on distance functions, Pp. Managing special forest products in Oregon and 813±830. In P. Krishnaiah & P. Sens (eds.), Handbook Washington: A Final Report. Portland, OR. of Statistics, Vol. 4. Elsevier Science Publishers, NY. USDA. 1995. Special Forest Product Program Environ- PECK, J. 1997a. Commercial moss harvest in Northwest- mental Assessment. Siuslaw National Forest, Corval- ern Oregon: Describing the epiphyte communities. lis, OR. Northwest Science. 71: 186±195. VANCE,N.&M.KIRKLAND. 1997. Bryophytes associated ÐÐÐ. 1997b. The association of commercially harvest- with Acer circinatum: Recovery and growth following able bryophytes and their host species in northwestern harvest, pp. 267±271. In T. Kaye, A. Liston, R. Love, Oregon. THE BRYOLOGIST 100: 383±393. D. Luoma, R. Meinke & M. Wilson (eds.), Conser- ÐÐÐ. 1999. Moss Recovery Report, Hebo Ranger Dis- vation and Management of Native Plants and Fungi. trict, Siuslaw National Forest. Corvallis, OR. Native Plant Society of Oregon, Corvallis, OR. ÐÐÐ&B.MCCUNE. 1998. Commercial moss harvest WILKINSON,C.&H.ANDERSON. 1987. Land and Resource in northwestern Oregon: biomass and accumulation. Planning in the National Forests. Island Press, Wash- Biological Conservation 86: 299±305. ington, D.C. ÐÐÐ&P.S.MUIR. 1998. Towards sustainable commercial ``moss'' harvest. Final report to the Eugene District, BLM. Eugene, OR. ms. received May 26, 2000; accepted Dec. 20, 2000.