Patterns of Bryophyte Richness in a Complex Boreal ... - BioOne

The Bryologist 106(3), pp. 372 382 Copyright q 2003 by the American Bryological and Lichenological Society, Inc.

Patterns of Bryophyte Richness in a Complex Boreal Landscape: Identifying Key Habitats at McClelland Lake Wetland DALE H. VITT Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901-6509, U.S.A. e-mail: dvitt@ plant.siu.edu

LINDA A. HALSEY Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9 Canada

JAMES BRAY Department of Biology, Blackburn College, Carlinville, IL 62626-1498, U.S.A.

ABEL KINSER Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901-6509, U.S.A.

Abstract. The McClelland Lake Wetland Complex is a large (3,481 ha), boreal, wetland complex dominated by peatlands located in northeastern Alberta, Canada. We intensively sampled the bryophyte flora in 44 sites chosen to capture all landscape features of the wetland. We furthermore partitioned these 44 sites into 67, structurally defined stands. One hundred and fourteen species of bryophytes (91 mosses and 23 hepatics) were found. Mean stand species richness is 16.6, with a range of 2–41 species. Thirty-nine species were recorded only 1–2 times in the 67 stands and these are defined as locally rare species. Additionally, 18 species were recorded that are currently on the Alberta Rare Species Tracking List (ANHIC), although commonness of some within the complex suggests regional under-collection. A strong relationship was found between species richness and locally rare species occurrence at both the site and stand levels. Neither species richness nor locally rare species occurrence is related to landscape position within the wetland complex nor to internal wetland chemical gradients. Both species richness and local species rarity are influenced by stand type and structure. Shrubby, wooded, or forested stands contain 70% of the locally rare species occurrences, and swamps and wooded fens are species rich habitats. Stands with high numbers of locally rare species also tend to be stands that have high species richness; however, not all stands with high species richness have high numbers of locally rare bryophytes. Indicators and assessment protocols based on rare species and richness are developed to define Key Habitats for this wetland complex. Criteria for Key Habitats are stands with both high species richness and high numbers of locally rare species—‘Category 6’ stands, and these are identified as significant features in developing management protocols for bryophyte species and wetland function. Six ‘Category 6’ stands capture 58% of the locally rare species and 90% of the total wetland species richness. All six Key Habitats are wooded or forested.

Boreal landscapes are mosaics of seemingly uniform stands of trees over a broad, undulating, rather flat landscape. Superficially, they appear to be mosaics of sites dominated by one or two tree species. In western Canada, the landscape mosaic consists of upland stands of Populus tremuloides, Pinus banksiana, mixed wood of Picea glauca and Populus tremuloides, and peatlands. Organic soils compose about 31.4% of the landscape of western Canada’s Boreal Forest (Vitt et al. 2000) and often occur on the landscape as mosaics of intermixed peatland types. These peatland mosaics have been termed peatland complexes and in western Canada generally consist of wooded rich fens dominated by Larix laricina in which are positioned ombrogen-

ous bog islands and peninsulas dominated by stunted Picea mariana, patterned and/or non-patterned open fens, densely wooded (forested) swamps of Picea mariana, and permafrost mounds some of which are melting with the subsequent formation of collapsed poor fen internal lawns. Marginal to these peatland complexes, are non-peat accumulating wetlands that include shrubby, wooded, and forested swamps as well as marshes along lake margins. Thus, wetland complexes have surprising diversity that includes not only site specific landform types (e.g., islands, pools, internal lawns) but also a number of stand-types with different structure [closed canopy (forested), open canopy (wooded), shrubby, open].

0007-2745/03/$1.25/0

2003]

VITT ET AL.: BRYOPHYTE RICHNESS

Patterns of species richness and species rarity have been related to key habitats (McCune et al. 2002). These key habitats in upland forests often differ in stand age, structure, and landscape position, all seemingly important factors for species occurrence. Although studied in upland forests, key habitats have not been examined in peatlands. Peatlands are ideal ecosystems for such studies as they form complex landscape units, with individual peatland (site) types having unique landscape positions within the peatland complex. Furthermore, individual peatland types contain well-defined physiognomic features, and there is considerable literature of bryophyte species responses to both chemical and hydrological gradients (Belland & Vitt 1995; Gignac et al. 1991). Stand structure is relatively simple, with the one or two tree or shrub species developing simple, low canopies. Bryophytes dominate the ground layer in many boreal ecosystems, especially in conifer-dominated sites, where leaf-fall is limited. Conifer-dominated inorganic soils are characterized by species of feather-mosses covering the forest floor (Frego & Carleton 1995; LaRoi & Stringer 1976), while organic soils are dominated by either Sphagnum in bogs and poor fens or an assemblage of true mosses that are reddish brown in color and termed ‘brown mosses’ in rich fens (Vitt & Belland 1995). This assemblage of rich fen species is taxonomically diverse, but many of the species belong to the Amblystegiaceae. Peatlands, especially bogs, have long been considered communities poor in species, however bryophytes are surprisingly diverse in many peatland types and keystone species for ecosystem function are found among these moss species. Keystone species include Sphagnum fuscum in continental bogs (Vitt et al. 2003); Sphagnum riparium in internal lawns melting from boreal permafrost (Beilman 2001); Scorpidium scorpioides in extreme-rich fen carpets (Slack et al. 1980); and Tomenthypnum nitens in rich fen hummocks and strings (Li & Vitt 1997). When geographically separated peatland sites are compared, alpha (site) diversity is variable, with no significant differences between peatland types (bogs, poor fens, rich fens) when examined along a chemical (acidity/alkalinity) gradient. However, again at the site level, species turnover (beta diversity) among extreme-rich fens is markedly higher than in the remaining peatland types, and locally rare species are much more frequent in extreme-rich fens than in other rich fens, poor fens, and bogs (Vitt et al. 1995). These few studies in western Canada have so far investigated bryophyte species richness using only geographically isolated sites, each of these sites influenced by differing climatic and local hydrogeo-

373

morphic regimes. However, much of the peatland cover of the boreal forest is comprised of complex peatland systems that contain many individual peatland types in one integrated landscape unit. Horton et al. (1977), Nicholson (1987), and Nicholson and Vitt (1990) have studied the development and physical-chemical environments of these peatland complexes. Much attention has been given to identifying hotspots (Myers 1988, 1990)—areas with exceptional concentrations of species richness and areas high in narrow endemics. These studies have mostly concentrated on high profile organisms—organisms with range size rarity (narrow endemics—Williams et al. 1996). With some noted exceptions found in the work of Bruce McCune and students mostly working with lichen rarity (McCune et al. 2002), few studies in North America have examined patterns of bryophyte rarity. Bryophytes have long been known to contain fewer narrow endemics than flowering plants and in the northern hemisphere, many if not most species have widespread and often disjunct ranges between here and Europe and/ or Asia (Frahm & Vitt 1993). However, this is not to say that bryophytes do not contain regionally rare species that are often confined to specific, narrowly defined habitats. These widespread, regionally distributed species are sometimes quite scattered at the local scale and many species are infrequent or rare locally and dependent on habitat availability (Heinlen & Vitt 2003; Vitt & Belland 1997). Thus understanding and managing (at the correct scale) for bryophytes is extremely relevant, even for species that are locally rare but regionally widespread. Vitt and Belland (1997) used the term mesohabitat to describe non-randomly occurring landscape features that they considered important in determining patterns of species richness on the regional landscape. Here we explore the patterns of bryophyte species richness and rarity within one wetland complex (a single mesohabitat) examining the influence of both landscape position and stand structure on species patterning. In particular we address the following questions: 1) Are patterns of species richness related to patterns in local species rarity and is rare species aggregation apparent? 2) Are these patterns associated with site characteristics—that is to internal chemical gradients and to landscape position? and/or to 3) stand characteristics—that is to structure and complexity of individual habitats? 4) Using these attributes, we then propose criteria, indicators, and assessment protocols for the Key Habitats at the McClelland Lake wetland complex.

374

THE BRYOLOGIST

FIGURE 1. Location of McClelland Lake Wetland in western Canada and the location of the 44 sites examined in the McClelland Lake Wetland.

[VOL. 106

north of the town of Fort McMurray, Alberta at 57.48 N. Latitude and 111.38 W. Longitude (Fig. 1). The wetland complex is located in the Central Mixedwood Subregion of the Boreal Forest Natural Region of Alberta (Achuff 1994). This subregion is the largest in spatial extent in the province. It is characterized by a cool, moist climate regime characterized by short, cool summers and long, cold winters. The climate is conducive to the growth of mixed Populus tremuloides-Picea glauca forests in upland areas and to bogs and fens in poorly drained, depressional areas. Soils consist of Gray Luvisols in well-drained upland sites, Eutric Brunisols on sandy uplands, and Organics and Gleysols in wet depressional areas (Achuff 1994). The wetland complex itself is composed of a variety of wetland types that include a strongly patterned rich fen; nonpatterned wooded, shrubby, and open fens; marsh; and forested and shrubby swamps. In addition, isolated pockets of bogs with or without permafrost and wooded fen with internal lawns and local forested peat plateaux are present along the margins of the wetland complex as defined by the Alberta Wetland Inventory Standards (Table 1, Halsey & Vitt 1997). Westworth et al. (1990) identified the patterned fen element of the wetland complex as a significant provincial feature for preservation.

METHODS STUDY AREA The McClelland Lake Wetland Complex is a large boreal peatland complex with marginal non-peat accumulating components typical of boreal wetland complexes associated with patterned fens in western Canada (Halsey et al. 2001). The complex is 3,481 ha in area and located on the west side of McClelland Lake, approximately 85 km

Field sampling. Using 1:20,000 air photographs and a polygon base established for the Alberta Vegetation Inventory, the wetland was defined and all landscape-scale features were delineated. Using criteria in the Alberta Wetland Inventory (Halsey & Vitt 1997), 14 site types were identified based on wetland type (Bog, Fen, Marsh, Swamp, Ice-Push Ridge); site physiognomy [non-wooded (5 open), wooded (open canopy), forested (closed cano-

TABLE 1. Wetland site types as defined by Alberta Wetland Inventory (AWI) with their area, stand type, and species occurrence in the stand types. Abbreviations of sites are first letters: B-bog, F-fen, I-ice, M-marsh, S-swamp; second letters: F-forested, O-open, P-pushed, T-treed; third letters: N-no pattern, P-patterned, R-ridge, X-permafrost; and fourth letters: C-collapse scar, G-graminoid, N-no collapse scar, internal lawns, or frost mounds, R-internal lawns and frost mounds, S-shrubby. Areas identified as ** were not mapped as unique polygons in the wetland inventory due to their limited extent.

Site type

AWI abbreviation

Wooded nonpermafrost bog Wooded permafrost bog with collapse scars

BTNN BTXC

14.97 33.93 —

BTXN FONG FONS FOPN FTNN

4.50 333.41 211.86 ** 866.84

Wooded permafrost bog without collapse scars Open nonpatterned graminoid fen Open nonpatterned shrubby fen Open patterned fen Wooded nonpatterned fen Wooded nonpatterned fen with internal lawns and frost mounds Wooded patterned fen Ice push ridge Marsh Forested swamp (not sampled) Shrubby swamp Wooded swamp Total

FTNR — FTPN — IPR MONG SFNN SONS STNN 14

Area (ha)

183.72 — 898.83 — ** 7.54 24.77 95.22 809.98 3,481.10

Stand type

No. of stands

Mean stand richness

Number of rare species occurrences

— Lawn Frost

2 2 4

14.5 15.5 19.8

1 5 3

— — — — —

1 7 3 1 10

16.0 11.0 11.7 10.0 24.4

2 1 2 0 5

Lawn Frost Flark String — — — — —

1 1 10 10 2 3 0 3 7 67

13.0 12.0 8.9 16.6 8.0 4.0 — 29.3 24.6 15.1

1 0 5 9 3 1 — 10 12 60

2003]


py)]; site landform modifier [patterned, non-patterned, permafrost)]; and stand landform [graminoid, shrub, lawn (permafrost collapse), and frost mound permafrost)]. Areas for these 14 site types were calculated in ARC/INFO (Table 1). Forty-four sites were selected throughout the peatland complex using two criteria: 1) site types were sampled at an intensity approximating their area of cover within the peatland and 2) all site types were sampled at least once. [Note: one uncommon wetland type was not sampled (SFNN—Table 1) due to access difficulties.] The 44 sites were used to examine questions related to chemical gradients and landscape position. In order to examine our questions related to structure, the sites with complex morphology, that is, having either pattern or collapse were further divided into stands, each stand with an area of uniform structure. Thus the patterned fen sites (FTPN) were divided into wet, open flarks and drier, wooded strings; the permafrost bogs (BTXC) were divided into areas with permafrost (frost mounds) and areas of internal collapse (internal lawns); while wooded fens with internal lawns have areas without permafrost (fens), areas with permafrost (frost mounds), and areas of external collapse (marginal lawns). In addition, lake edge sites with marshes (MONG) separated from drier ice-push ridges (IPR) were sampled. These 67 stands represent what we term ‘habitats’ and were used in analyses of stand structure. Wetland site types and areas covered, stands (5habitat) types, and number of stands sampled are given in Table 1. At each of the 67 stands, we searched all microhabitats thoroughly for species of bryophytes. At each stand, sampling began at a randomly located central point and two persons searched an approximately 50-meter radius for a period of about one hour. In general, no new species were found after the first 30–45 minutes. Presence was recorded. Voucher specimens are deposited in ALTA and SIU. In all 1,112 species occurrences were recorded. Water samples for electrical conductivity and pH were collected from standing surface water where present, placed on ice, and analyzed electronically within six hours of collection. All field data were collected on May 19–21, 2002 during dry, sunny conditions just after spring snow melt. Specific site and stand locations, list of all species, and pH and conductivity data are available from the first author. Data analysis. Nomenclature and authorities in abbreviated form follow Anderson et al. (1990) for true mosses and Sphagnum and Grolle (1976) for hepatics. Exceptions are Orthotrichum elegans and Drepanocladus polycarpus, both recognized at the species rank. Alpha (site or stand) and gamma (overall species richness) diversity follow definitions of Whittaker (1972). Species are defined as locally rare in the complex when there are two or less stand occurrences. ANHIC rare species were identified via the ANHIC rare species list for bryophytes (ANHC 2001). We examined spatial patterns of richness and rarity at the site level for landscape position (location within the wetland complex) as well as for stand type and structure. If locally rare species are distributed randomly with respect to each other, then the frequency distribution of these species observed in a stand should follow a Poisson distribution. We tested our locally rare species distribution using a Chi-square text. With a Poisson distribution the variance in the number of species equals the mean number of these species. Significant deviation of the variance-tomean ratio (V/M) from the number one determines the aggregation of the species. Greater than one indicates a clumped dispersion; one indicates a spatially random dispersion; and less than one indicates a regular dispersion. The more that rare species are aggregated in particular

375

TABLE 2. List of locally rare bryophyte species at McClelland Lake Peatland. Species listed here were recorded two or less times in the 67 stands sampled. Hepatics are denoted by *. Rare species as recognized by their status (ANHIC SU, S1, S2, S3 status [see ANHIC 2001 for definitions]). 1 denotes widespread species of upland habitats that are rare in wetlands. Species name

Number of occurrences

Amblyodon dealbatus S2 Brachythecium turgidum Bryum argenteum1 Bryum lisae var. cuspidatum1 Calliergon richardsonii *Cephalozia pleniceps S2, S3 Dicranum fuscescens1 Dicranum groenlandicum Dicranum scoparium1 Distichium inclinatum Distichium capillaceum Drepanocladus aduncus Eurhynchium pulchellum1 Funaria hygrometrica1 Hypnum lindbergii Limprichtia cossonii SU *Lophozia incisa S2 *Lophozia laxa S1 Meesia longiseta S1 Orthotrichum elegans1 Paludella squarrosa Plagiomnium drummondii Plagiothecium laetum Platydictya jungermannioides Platygyrium repens1 Polytrichum commune1 Polytrichum juniperinum1 *Scapania irrigua S2 Sphagnum centrale Sphagnum fimbriatum S2, S3 Sphagnum obtusum Sphagnum riparium Splachnum sphaericum S2 Tetraplodon angustatus Thuidium recognitum1 Timmia megapolitana Warnstorfia tundrae S2 Warnstorfia exannulata Warnstorfia fluitans

1 1 1 2 1 2 2 1 1 1 2 2 2 2 2 1 2 1 1 2 2 1 2 2 2 2 1 1 1 1 2 1 2 2 2 2 1 2 1

ANHIC tracked species found more than two times (actual number of occurrences) are: Calypogeia sphagnicola (19), Calpogeia suecica (9), Campylium polygamum (18), Cephaloziella rubella (13), Conardia compacta (4), Drepanocladus sendtneri (10), Lophozia longidens (3), and Riccardia latifrons (5).

stands, the more readily they can be managed (McCune et al. 2002). Assessment protocols. We ranked the stands from those with the least to those with the greatest number of species and number of locally rare species. Using median rank and and percentile cut-offs for stand species richness and greater than expected percentages based on Chisquare percentiles for stand local rarity, we propose categories of 1 (least) to 3 (most) for stand species richness (SR) and stand local rarity (LRS). Stands having category 3 standing for both rare species and species richness

376

THE BRYOLOGIST

[VOL. 106

FIGURE 2. Number of occurrences of the 114 bryophyte species at McClelland Lake Peatland. Rare species are to the left and frequent species to the right. Sixty-seven stands were sampled. achieve category 6 status and define Key Habitats for the wetland complex. Ecological and biological indicators were examined through assessment of a DCA ordination and TWINSPAN output as carried out by Belland and Vitt (1995). Outputs from these analyses are not shown, but were used to determine how Key Habitats relate to potential indicators.

RESULTS

AND

DISCUSSION

Species richness and rarity. One hundred and fourteen species of bryophytes, including 91 moss species (80%) and 23 hepatic species (20%) were found. The second order jack knife estimate of total diversity is 129 (PC-ORD—McCune & Mefford 1999). Mean stand species richness (alpha) at McClelland Lake Peatland is 16.6, with stand richness varying from a low of two species to a high of 41 species. There is no significant relationship

between the number of stands sampled from the 16 stand types and species richness (r2 5 0.06). Eighteen (16%) of the species were collected only one time and 21 species (18%) were collected only twice; these 39 species occurred a total of 60 times and are considered to be locally rare species for this wetland complex (Table 2). Four (10%) of these locally rare species are hepatics and ten (26%) are present on the ANHIC rare species list (ANHIC 2001). Thirty-seven species (32%) were recorded more than three times and less than eleven times, and are considered infrequent species of the peatland. Additionally, another 38 species were collected between 11 and 44 times; these are frequent species of the area. However, only five species occurred in more than 50% of the stands, and no species is common throughout all stands in the peat-

FIGURE 3. Regression using a second order polynomial of species richness against locally rare species occurrence at — A. 44 sites and B. — 67 stands in McClelland Lake Wetland.

2003]


FIGURE 4. Number of species found at each of the 44 sites. Sites with 30 or more species have open circles and sites with less than 20 species have shaded circles.

land (Fig. 2). Aulacomnium palustre, Tomenthypnum nitens, Dicranum undulatum, and Bryum pseudotriquetrum are the most common species. Richness and rarity at the site level. At the level of site, species richness is significantly correlated to rare species occurrence [r2 5 0.23 (second order polynomial regression)—Fig. 3A]. Of the 44 sites sampled, 12 (27%) have greater than 30 species, whereas 11 (25%) have less than 15 species (Fig. 4). Eight (18%) of the 44 sites have three or more rare species, whereas 15 sites (34%) contain no rare species and 11 sites (25%) have only one (Fig. 5). Thus a relatively few sites (8 sites—18%) contain over 50% of the rare occurrences, and many sites (26 sites—59%) have one or no rare species. Clearly there are sites that are related to rare species. Of the 12 species rich sites, only six have high numbers of rare species, whereas six of the eight sites with high rarity also contain high numbers of species. Thus sites with rare species usually have high overall species richness, but the reverse is not true: species rich sites may not contain locally rare species. When species poor sites are examined for rare species, none contain more than two rare species and sites with high numbers of rare species never occur with sites having low richness. Thus locally rare species are not frequent in sites with low species richness. In conclusion, locally rare species are clearly associated with species rich sites, however species rich sites can occur without having rare species. Species poor sites have few rare species occurrences. No apparent relationship is present between lo-

377

FIGURE 5. Number of locally rare bryophytes found at each of the 44 sites. Sites with three or more locally rare species have open circles, sites with one or two species have open squares, and those sites with no locally rare species have shaded circles.

cation of the site within the peatland complex (landscape position) and site diversity (Fig. 5). Sites with high alpha diversity are located at the perimeter in the SE (site 44), SW (sites 24, 33), west (site 13), north (site 10), and in the center of the peatland at the east end (site 2) and west end (site 16). Likewise, rarity is not related to landscape position (Fig. 5). We found no significant relationship between species richness and either conductivity (r2 5 0.004) or pH (r2 5 0.003) nor between rarity and conductivity (r2 5 0.0013) or pH (r2 5 0.012; all n 5 42) even though there is a strong conductivity gradient in the peatland complex, with high values along the southern boundary (300–700 mS/cm), lower, yet still high values in the center and west central patterned portion (240–400 mS/cm) to low values at the northwestern and northern boundaries (50–200 mS/cm—Fig. 6). In conclusion, no apparent relationship exists between landscape position of the site or site chemistry (as measured by pH and conductivity) and either rarity or species richness. Richness and rarity at the stand level. Since neither site position nor chemistry appear to influence species richness and rarity, yet sites display strong differences in these attributes, we examined the influences of structure by partitioning sites into stands based on vegetation characteristics. Species richness is significantly correlated to number of locally rare species in the 67 stands [r2 5 0.42 (second order polynomial regression)—Fig. 3B]. When

378

THE BRYOLOGIST

FIGURE 6. Electrical conductivity measured at 44 sites at McClelland Lake Peatland. Hatched areas with less than 200 mS, shaded areas with less than 100 mS.

stands are grouped into habitat categories (Table 1), mean alpha richness varies from 4 to 29 and rare occurrences from zero to 12 (Fig. 7). When wooded string stands are compared to their open flark counterparts, the string stands have significantly more species than the open flarks—[mean 18.6 (range 12–39) species on strings versus mean 8.9 (range 2–13) in flarks]. Likewise, when wooded permafrost bogs are compared to their open internal lawn

[VOL. 106

collapse features, the bogs have higher species richness (19.8 versus 15.5 for lawns). In these two cases, rarity is not so clear, with both the open flarks and the internal lawns both having five rare occurrences, compared to the strings with nine and the permafrost bog with three. Species richness also varies with structural type. Open marsh mean richness is 4.0; open fen mean richness is 11.1, while wooded fens have a mean richness of 24.4. Wooded bogs have mean richness of 17.7 whereas the open lawns have a richness of 15.5. Finally, swamps (by definition with woody vegetation) have mean richness of 26.0. Overall, the stands dominated by shrubs or trees have 70% of the rare species occurrences. Epiphytes above tree bases are few due to the continental climatic conditions and dominance of conifers, and epiphytes do not contribute appreciably to species richness patterns. Marsh sites have the least number of locally rare species, while swamps with 25 occurrences contain the most. In conclusion, complexity at the stand level appears to be the most influential factor in controlling both species richness and rare species occurrence. Stands with woody vegetation always have greater species richness and usually have greater rare species occurrences than open stands. Marshes and open fens (including flarks) have less species richness and fewer rare species occurrences, even though in the case of the flarks, they occur in the same landscape position and under the same chemistry conditions as do their wooded string counter-

FIGURE 7. Mean stand richness and number of locally rare species occurrences for the 16 stand types at McClelland Lake Peatland. Means stand richness values are given in Table 1. S—swamp, F—fen, B—bog, M—marsh, I—ice-push ridge.

2003]


TABLE 3. Godness of fit to a Poisson distribution for locally rare species. No. of LRS

Expected (%)

Actual (%)

Deviation

0 1 2 3 4 5 6

41.50 36.50 16.10 4.70 1.00 0.20 0.03

52.2 26.9 10.4 6.0 1.5 1.5 1.5

110.70 29.60 25.70 11.30 10.50 11.30 11.47

parts. Thus stand level factors appear to be more influential than site level factors when species richness and rarity are examined within this complex landscape area. Stands, (not sites), become the ‘key habitats’ for which management needs to focus. Key habitats. Criteria for selection of key habitats should strive to identify stands that possess high numbers of species and that serve as habitat for rare species—here we treat rarity at the local level and define locally rare species as those found in two or less of the 67 stands sampled. This coarse filter approach strives to identify key areas that will capture both the highest number of total species and the highest number of rare species. Stand assessment. SPECIES RICHNESS: Species richness of individual stands is extremely variable and does not follow a Poisson distribution (Fig. 8a). We divided the ranked stands into three categories: 14 stands (21%) each contained greater than 20% of the total flora, 19 stands (28%) contained greater than 15% of the total flora and fell above the ranked stand median, and 34 stands (51%) individually contain less than 15% of the flora and fall below the ranked median (Fig. 8a). We labeled these three species richness (SP) categories as SR1, (fewest species), SR2 (intermediate), and SR3 (most species). The SR3 category stands, in total, capture 90% of the species richness of the site (Fig. 8b). LOCAL SPECIES RARITY: Stands also vary in the number of locally rare species (LRS). Seven stands have between 3 and 6 rare species, 26 stands have 1 or 2 rare species, and 34 stands have no rare species (Fig. 8c). Locally rare species do not follow a Poisson distribution (p , 0.01—Chi square, Table 3). Moreover, the V/M ratio is 1.84 indicating that the locally rare species are strongly aggregated (ttest p , 0.001). Stands having between 3–6 LRS have greater than expected Poisson distributions, while stands with 1–2 LRS have less than expected distributions. Thus LRS species are aggregated in stands having between 3–6 LRS species. We labeled three locally rare species categories as LRS1 (no rare species), LRS2 (1–2 rare species), and LRS3 (3–6 rare species), based on these having

379

a significantly greater aggregation. The LRS3 category stands capture 60% of the rare species, while a combination of the LRS Category 3 stands plus about half of the LRS 2 stands (30% of all stands in total) captures 100% of the LRS (Fig. 8d). Identification of key habitats. We composed a category index that combines the 1–3 categories for SR and for LRS (Fig. 9). Stands with Category 3 status for both attributes account for 90% of the species richness and 58% of the locally rare species. These Category 6 stands we believe are worthy of ‘Key Habitat’ status. At the McClelland Lake Wetland Complex six stands have Category 6 status. Indicators of Category 3 and Category 6 stands. All stands of Category 3 (either SR3 or LRS3) are shrubby, wooded, or forested. No open stands are Category 3 habitats. Of the 14 SR3 stands, six are swamps, seven wooded rich fens, and two are wooded bogs with permafrost, while of the seven LRS3 stands, four are swamps and two are wooded fens, and one is a wooded bog. The Category 6 stands are either forested swamps (4) or wooded fens (2). Additionally, examination of the TWINSPAN analysis (not shown) reveals that Plagiomnium ellipticum occurs in 33% of the 67 stands; it occurs in all but one of the 14 SR3 stands and all but one of the LRS3 stands. As well, it occurs in all six Category 6 stands. In summary, non-exclusive indicators of Category 3 as well as Category 6 (Key Habitats) stands are 1) structurally complex woody vegetation and 2) presence of the moss Plagiomnium ellipticum. Forested and wooded habitats have significantly more species and significantly more locally rare species (Student’s t-tests, p , 0.05) then open stands. These highly structured, wooded habitats appear to be more species rich and contain species rare in the wetland complex for three reasons: 1) they contain their own unique wetland flora (e.g., Amblyodon dealbatus, Plagiomnium ellipticum), 2) they contain widespread upland species that are rare within wetlands (Eurhynchium pulchellum), and 3) they contain sufficient wet depressional habitats at tree bases and open lawns for the open fen species to occur (i.e., Paludella squarrosa). Thus the presence of trees may create additional habitat diversity allowing greater species richness along with aggregations of species rare within the wetland complex. Wetland locally rare species include species that also occur in upland habitats [11 of the 39 species (28%) listed in Table 2]. We argue here that land use changes in the boreal region of Canada, especially through agriculture and forestry, have been and will continue to be concentrated on upland sites; wetland refugia for these upland species may

380

THE BRYOLOGIST

[VOL. 106

FIGURE 8. Ranked stand richness and species capture at McClelland Lake Peatland. — A. Total number of species found in the 67 stands. Stands with .20% of the total flora are Category 3 (SR); stands with .15% of flora and falling above the median are Category 2 (SR); stands having ,15% pf the flora and falling below the median are Category 1(SR). Black dots indicate stands in which Plagiomnium ellipticum occurs. — B. Maximum number of species captured through addition of stands left to right. Stands with black bars accomplish 90% of species capture (SR3 stands), black bars and gray bars together (SR2 stands) 5 100% species capture. — C. Number of locally rare species (LRS) found in the 67 stands. Stands with three or more LRS are Category 3, stands with 1–2 LRS are Category 2 stands, stands

2003]


FIGURE 9. Categories 1–3 (horizontal) give species richness (SR) and Categories 1–3 (vertical) give locally rare species (LRS) categories. Numbers in center of boxes are number of stands, numbers in top row and right column are total number of stands in each SR or LRS category—total 67. Small numbers in bottom right of each box is the combined category index value; thus these are six Category 6 stands (shaded) 5 Key Habitats.

become increasingly important as development of the Canadian boreal forests proceeds over the next century. Key Habitats at McClelland Lake Wetland complex. Six Key Habitats (or 9% of the stands sampled) at this boreal wetland complex capture 58% of the locally rare species and 90% of the total species richness. They are found scattered throughout the wetland complex (Fig. 10). Key sites are swamps and wooded fens, both habitats with considerable structural diversity that yields numerous microhabitats for bryophyte occupation. The assessment protocol proposed here suggests that hot spots for locally rare species and overall species richness do exist in boreal wetland complexes and that these can be identified using a mixture of structural and biological indicators. At this wetland complex, all species were captured in 34% of the stands, however only six Category 6 stands were needed to capture 90% of the richness and 58% of the rare species. Thus much of the diversity of an area can be accounted for by a relatively small number of carefully selected stands. Future studies and management protocols for complex boreal peatlands must take stand level dynamics into consideration. Species rich stands that correlate with high local rare species occurrences should be considered ‘Key Habitats’ and it is these to which man-

381

FIGURE 10. Location of the six Category 6 stands (5 Key Habitats) from among the 67 stands at McClelland lake Wetland. S—swamp; W—wooded fen.

agement efforts should be directed. The lack of range restricted (narrow endemics) species in boreal wetland floras and the strong aggregation of locally rare species within this large wetland complex, species that include those from uplands, open wetland areas, and species unique to wooded habitats indicates that a coarse filter approach to habitat recognition and preservation will achieve protection of nearly all of the species of this wetland. In most cases for McClelland Lake Wetland, most species do not need to be tracked individually. Protecting Identified Key Habitats from development and anthropogenic disturbance should perpetuate almost all of the species of the Wetland. Outside of the boreal region, forested wetlands may also play significant roles in preserving rare species (Kuusinen 1996; McCune et al. 2002; Ohlson et al. 1997). ACKNOWLEDGMENTS This study was carried through funding from TrueNorth Energy L.P. via funds managed by AXYS Environmental Consulting, Limited, for which we are grateful. Geoff Chow, Director of Environmental Affairs, TrueNorth Energy L.P has continued to enthusiastically support this and other research related to our understanding of these northern wetland systems. We would like to thank Kim Ottenbreit for peer review and Lindsay Giles for GIS support. Sandi Vitt designed and produced the graphics for this paper and Tiffany Bone carried out the statistical and mul-

← with no LSR are Category 1 stands. — D. Maximum number of locally rare species captured through addition of stands left to right. Stands with black bars accomplish 58% rare species capture (LRS 3 stands), black together with gray bars (LRS2 stands) 5 100% species capture.

382

THE BRYOLOGIST

ti-variate analyses, for which we are appreciative. Bruce McCune and Emma Pharo provided important suggestions for the improvement of this paper.

LITERATURE CITED ACHUFF, P. 1994. Natural Regions, Subregions and Natural History Themes of Alberta (Revised). Alberta Environmental Protection, Parks Service. Edmonton, AB. ANHIC (ALBERTA NATURAL HERITAGE INFORMATION CENTRE). 2001. Mosses, Liverworts & Hornworts Tracking List. Online: http://www3.gov.ab.ca/env/narks/anhic/ nonvastk.html. ANDERSON, L. E., H. A. CRUM & W. R. BUCK. 1990. List of the mosses of North America north of Mexico. THE BRYOLOGIST 93: 448–499. BEILMAN, D. 2001. Plant community and diversity change due to localized permafrost dynamics in bogs of western Canada. Canadian Journal of Botany 79: 983–993. BELLAND, R. & D. H. VITT. 1995. Bryophyte vegetation patterns along environmental gradients in continental bogs. Ecoscience 2: 395–407. FRAHM, J. P. & D. H. VITT. 1993. Comparisons between the moss floras of North America and Europe. Nova Hedwigia 56: 307–333. FREGO, K. A. & T. J. CARLETON. 1995. Microsite conditions and spatial pattern in a bryophyte community under mature black spruce. Canadian Journal of Botany 73: 544–551. GIGNAC, L. D., D. H. VITT, S. C. ZOLTAI & S. E. BAYLEY. 1991. Bryophyte response surfaces along climatic, chemical, and physical gradients in peatlands of western Canada. Nova Hedwigia 53: 27–71. GROLLE, R. 1976. Verzeichnis der lebermoose Europas und benachbarter gebiete. Feddes Repertorium 171– 279. HALSEY, L. A., B. J. NICHOLSON, K. DEVITO & D. H. VITT. 2001. Landscape and landform variation in patterned fens within Alberta, Canada. Report prepared for True North Energy, Calgary, AB. ——— & D. H. VITT. 1997. Alberta Wetland Inventory Standards. In Alberta Vegetation Inventory Standards. Resource Data Division, Alberta Environmental Protection, Edmonton, AB. HEINLEN, E. R. & D. H. VITT. 2003. Patterns of rarity in mosses of the Okanogan Highlands of Washington state: An emerging coarse filter approach to rare moss conservation. THE BRYOLOGIST 106: 34–52. HORTON, D. G., D. H. VITT & N. G. SLACK. 1977. Habitats of circumboreal-subarctic Sphagna: 1. Quantitative analysis and review of species in the Caribou Mountains, northern Alberta. Canadian Journal of Botany 57: 2283–2317. KUUSINEN, M. 1996. Cyanobacterial macrolichens on Populus tremula as indicators of forest continuity in Finland. Biological Conservation 75: 42–49. LAROI, G. H. & M. H. STRINGER. 1976. Ecological studies in the boreal spruce-fir forests of the North American

[VOL. 106

taiga. II. Analysis of the bryophyte flora. Canadian Journal of Botany 54: 619–643. LI, Y. & D. H. VITT. 1997. Patterns of retention and utilization of aerially deposited nitrogen in boreal peatlands. Ecoscience 4: 106–116. MCCUNE, B. & M. MEFFORD. 1999. Multivariate Analysis of Ecological Data, Version 4.0. MjM Software. Gleneden Beach, OR. ———, J. HUTCHINSON & S. BERRYMAN. 2002. Concentration of rare lichens along large streams in a mountainous watershed. THE BRYOLOGIST 105: 439–450. MEYERS, N. 1988. Threatened biotas: ‘‘hot spots’’ in tropical forests. The Environmentalist 8: 187–208. ———. 1990. The biodiversity challenge: expanded hotspots analysis. The Environmentalist 10: 243–256. NICHOLSON, B. J. 1987. Peatland paleoecology and peat chemistry at Mariana Lakes, Alberta. M.Sc. thesis, University of Alberta, Edmonton, AB. ——— & D. H. VITT. 1990. The paleoecology of a peatland complex in continental western Canada. Canadian Journal of Botany 68: 121–138. OHLSON, M., L. SO¨DERSTRO¨M, G. HORGNBERG, O. ZACKRISSON & J. HERMANSSON. 1997. Habitat qualitities versus long-term continuity as determinants of biodiversity in boreal old-growth swamp forests. Biological Conservation 81: 221–231. SLACK, N. G., D. H. VITT & D. G. HORTON. 1980. Vegetation gradients of minerotrophically rich fens in western Alberta. Canadian Journal of Botany 58: 330–350. VITT, D. H. & R. J. BELLAND. 1995. The bryophytes of peatlands in continental western Canada. Fragmenta Floristica et Geobotanica 40 (1): 339–348. ——— & ———. 1997. Attributes of rarity among Alberta mosses: patterns and predictions of species diversity. THE BRYOLOGIST 100: 1–12. ———, L. A. HALSEY, I. E. BAUER & C. CAMPBELL. 2000. Spatial and temporal trends of carbon sequestration in peatlands of continental western Canada through the Holocene. Canadian Journal of Earth Sciences 37: 683–693. ———, Y. LI & R. J. BELLAND. 1995. Patterns of bryophyte diversity in peatlands of continental western Canada. THE BRYOLOGIST 98: 218–227. ———, K. WIEDER, L. A. HALSEY & M. TURETSKY. 2003. Response of Sphagnum fuscum to nitrogen deposition: a case study of ombrogenous peatlands in Alberta, Canada. THE BRYOLOGIST 106: 235–245. WESTWORTH, D. A. & Associates Ltd. 1990. Significant Natural Features of the Eastern Boreal Forest Region of Alberta. Alberta Forestry, Lands, and Wildlife Technical Report. Edmonton, AB. WHITTAKER, R. H. 1972. Evolution and measurement of species diversity. Taxon 21: 213–251. WILLIAMS, P., D. GIBBONS, C. MARGULES, A. RBELO, C. HUMPHRIES & R. PRESSEY. 1996. A comparison of richness hotspots, rarity hotspots, and complementary areas for conserving diversity of British birds. Conservation Biology 10: 155–174. ms. received Feb. 7, 2003; accepted May 1, 2003.