J. Range Manage. 57:300 -304 May 2004 Seed bank and community composition, Mixed of Saskatchewan

J.T. ROMO AND Y. BAI

Authors are Professor and Assistant Professor, Dept. of Plant Sciences, Univ. of Saskatchewan, 51 Campus Drive, Saskatoon, Saskatchewan S7N 5A8.

Abstract Resumen

Many range managers have suggested that clubmoss Muchos manejadores de pastizles han sugerido que el ( densa Rydb.) negatively alters the composition of "Clubmoss" (Selaginella densa Rydb.) altera negativamente la seed banks and inhibits the establishment of plant species thatcomposición de los bancos de semillas e inhibe el establecimento decrease under improper grazing management. Alternatively it isde especies de plantas que decrecen bajo un menejo inadecuado possible that soil seed banks contain few seeds of decreaser del apacentamiento. Alternativamente es posible que los bancos species and composition of the seed bank is independent of club- de semillas del suelo contengan pocas semillas de especies decre- moss. The purpose of this study was to determine the composi-cientes y que la composicion del banco de semillas de es indepen- tion and diversity of the soil seed bank in relation to the clubmoss diente del "Clubmoss ". El propósito de este estudio fue determi- cover and compositional characteristics of plant communities in nar la composición y diversidad del banco de semillas del suelo the Northern Mixed Prairie of southwestern Saskatchewan. en relación a la cobertura de "Clubmoss" y las características de Cover of vascular was determined and soil seed bank sam- composición de las comunidades vegetales de las Praderas ples were collected in 100 grazed plant communities. Soil seed Mixtas del Norte en el Sudoeste de Saskatchewan. Se determinó bank samples were incubated in the laboratory with emerging la cobertura de plantas vasculares y se colectaron muestras del seedlings being identified to species. Eight percent (SE ± 1.9) ofbanco de semilla en 100 comunidades de plantas apacentadas. emerging seedlings in the seed bank were decreasers, 73% (SE ± Las muestras del banco de semillas se incubaron en el laborato- 2.8) were increasers, and 19% (SE ± 2.3) were invaders, indicat- rio y las plantas emergidas fueron identificadas por especie. 8% ing regeneration of decreaser species might be limited by low (SE ± 1.9) de las plántulas emergidas del banco de semillas numbers of seeds in seed banks. Clubmoss cover was not corre- fueron especies decrecientes, 73% (SE ± 2.8) fueron espeies cre- lated (P = 0.32 to 0.98) with species richness, species diversity, cientes y 19% (SE ± 2.3) fueron invasoras, indicando que la density of decreasers, density of increasers, density of invaders,regeneración de especies decrecientes puede ser limitada por el and total seedling densities in the seed banks. Seed banks and bajo número de semillas en los bancos de semillas. La cobertura plant communities shared few species as indicated by a low simi- de "Clubmoss" no estuvo correlacionada (P = 0.32 to 0.98) con larity index (x = 0.31, SE ± 0.02). Species richness (i= 3.6 species la riqueza de especies, densidad de especies decrecientes, cre- per 102 cm2, SE ± 0.18) and diversity (x = 1.00, SE ± 0.05) of seed cientes e invasoras y las densidades totales de plántulas emergi- banks were poorly correlated with characteristics of the plant das en el banco de semillas. Los bancos de semillas y las comu- communities. Range condition score was positively correlated (r nidades de plantas comparten pocas especies tal como lo indica el = 0.17, P = 0.09) with total seedling densities in the soil seed bank, bajo indice de similaridad (x = 0.31, SE ± 0.02). La riqueza de indicating more seedlings can potentially develop from the seed especies (x = 3.6 species per 102 cm2, SE ± 0.18) y diversidad (x = bank with increasing range condition of plant communities. We=1.00, SE ± 0.05) de los bancos de semillas estuvieron pobre- reject the hypothesis that clubmoss negatively affects the compo- mente correlacionadas con las características de la comunidad sition of seed banks. Mechanically disturbing plant communities vegetal. La calificación de la condición de los pastizales estuvo to control clubmoss is predicted to lead to plant communities that positivamente correlacionado (r = 0.17, P = 0.09) con las densi- are dominated by increasers and/or invaders. Managing for pro- dades totales de plántulas en el banco de semillas del suelo, indi- duction of seeds by desired species should be a priority in pro-cando que más plántulas pueden potencialmente desarrollarse de moting establishment of desired species. un banco de semillas de las comunidades vegetales con una condición ascendente del pastizal. Rechazamos la hipótesis de que el "Clubmoss" afecte negativamente la composición de los Key Words: biodiversity, microbiotic crust, microphytic crust, bancos de semillas. Se predijo que el disturbio mecánico de las Northern Mixed Prairie, range condition, Selaginella densa comunidades de plantas para controlar el "Clubmoss" lleva a comunidades que son dominadas especies de plantas crecientes y/o invasoras. El manejo para la producción de semilla de Clubmoss (Selaginella densa Rydb.), a low- growing, vascular especies deseables debe ser una prioridad para promover el cryptogam, forms carpet -like mats on a wide range of sites in establecimiento de especies deseables. grasslands of the Northern (Coupland 1950, Van

Funding for this research was provided by a research grant to JTR from the Saskatchewan Agriculture Development Fund (Project - 9600054). Manuscript accepted 15 Jul. 03.

300 JOURNAL OF RANGE MANAGEMENT 57(3) May 2004 Dyne and Vogel 1967, Dolan and Taylor Methods in each quadrat was visually estimated to 1972). This spore- reproducing perennial, the nearest 5 %. Cover for each species generally increases with grazing or from the 2 quadrats was averaged and drought (Clarke et al. 1943, Heady 1952, This study was conducted in therangecondition was estimated Campbell et al. 1962, Smoliak 1965,Mixedgrass Ecoregion in the Prairie Ecozone (Padbury and Acton 1994) of(Abouguendia 1990). of plants Smoliak et al. 1972), but it also can follows Budd (1987). decrease with intense grazing and tram-southwestern Saskatchewan (49-51° N, Across all sites sampled, clubmoss pling (Coupland 1950, Van Dyne and 106 110 °W). This region was selected because it has the most native grasslandcover was between 3 and 63% (1 = 23, SE Vogel 1967). Extensive ground cover of ± 1.3) and range condition scores varied clubmoss in the Northern Mixed Prairieremaining in Saskatchewan, and it is inbetween 10 and 61 (x = 32, SE ± 1.0). has led some people to assume that thisthis area that many range managers per- ceive clubmoss as a management issue.Four percent of the plant communities plant alters composition of plant commu- were in good range condition, 69% were nities (Ryerson et al. 1970, Dolan andSoils of the study area are primarilyin fair range condition, and 27% were in Brown Chernozems (Ayres et al. 1985) Taylor 1972). poor range condition. Canopy cover Clubmoss is an important aspect ofderived from glacial and postglacial deposits (Christiansen 1979) and theyranged from 0 to 75% (x = 14, SE ± 1.4) seedbed ecology in the Northern Greatrange in texture from clay to sandyfor decreasers, 5 to 81% (x = 50, SE ± 1.6) Plains because it occupies a large amount for increasers, and 0 to 20% (x = 2.0, SE ± (Coupland 1950, 1961). Temperatures of of the soil surface (Bai and Romo 1995). 0.4) for invaders. Needle- and - thread, Heady (1952) concluded that clubmoss the area vary from a mean of about 17° C in January to 19° C in July, and averagenorthern wheatgrass and western wheat limits establishment of grasses, but grass were the most important decreasers Smoliak et al. (1976) believed that about 3° C annually (Environment Canadain the plant communities while blue seedling establishment is not affected by 1982). Annual precipitation averages about 300 to 400 mm of which most isgrama, Junegrass, fringed sagebrush, clubmoss in years of abundant precipita- sedges (Carex spp.) and native bluegrass tion. Mosses can reduce or have no effect receivedinMaythroughJuly (Environment Canada 1982). Plant com-(Poa secunda Presl.) were the most impor- on seedling emergence and survival tant increasers (Table 1). Invaders were munities in the Mixedgrass Ecoregion are (Rabotnov 1969). Substantial numbers of uncommon in plant communities. Cover seeds are generally present in soil ontypical of the Northern Mixed Prairieof clubmoss was negatively correlated Association (Stipa- Bouteloua) (Coupland rangeland (Archibold 1981, Grilz and with cover of decreasers (Y = 20.0 0.21X, Romo 1995), and the total number of 1950, 1961, 1992) and are characterized byr2 =0.04, P = 0.05 where Y is cover of perennial plants including needle -and- seeds and the proportion of early succes- decreasers and X is cover of clubmoss) sional species in the soil seed bank can thread (Stipa comata Trin. & Rupr.), west-and with cover of increasers (Y = 59.0- increase with grazing pressure (Johnston ern porcupine grass (Stipa spartea var. curtiseta Hitchc.), western wheatgrass0.40X, r2 = 0.11, P < 0.01 where Y is et al. 1969, Willms and Quinton 1995).(Agropyron smithii Rydb.), northern cover of increasers and X is cover of club- Species composition of soil seed banks moss). Cover of invaders was poorly cor- and plant communities can be similarwheatgrass (Agropyron dasytachyum [Hook.] Scribn.), Junegrass (Koeleriarelated with cover of clubmoss (P = 0.39). (Johnson and Anderson 1986, Henderson Species richness and the Shannon - Weiner et al. 1988), dissimilar (Coffin andcristata Pers.), blue grama (Bouteloua gra- cilis [HBK.] Lag.), sedge (Carex steno - diversity index for plant communities var- Lauenroth 1989, Peco et al. 1998, Lunt ied between 3 and 15 species per 0.5 m2 1990, Lopez- Marino et al. 2000, Tracyphylla Wahl. ssp. eleocharis [Bailey] Hulten), and fringed sagebrush (Artemisia= 6.4, SE ± 0.2) and 0.48 to 2.58 (x = and Sanderson 2000) and can vary with 1.57, SE ± 0.04), respectively. frigida [Willd.]). Annual plants are uncom- grazing pressure (Dutoit and Alard 1995) One soil core that was 5.7 cm in diame- mon in these grasslands (Coupland 1950, and successional stages (Tracy and ter and 7.5 cm long (volume of soil = 91 1961, 1992) except on disturbed sites. Sanderson 2000). cm3, area =25.5 cm2) was collected from 2 One hundred pastures supporting native In Saskatchewan many range managers random locations in each quadrat where have suggested that clubmoss inhibits plant communities were randomly selected to provide a variety of managerial activi-plant community cover was determined. establishment of desirable species, primar- The soil cores from the 2 quadrats were ties, range sites, range condition and club- ily species that decrease under improper combined in a plastic bag (volume of soil moss cover. Land that had been cultivated grazing management. This prediction pre- = 765 cm3, area =102 cm2) and air -dried in sumes that seeds of decreaser species are or was seeded to tame forages was not sampled. Sampling was completed inthe laboratory for about 3 months. We present in the seed bank and removal of combined seed bank samples at each site clubmoss will allow decreasers to estab-September because seed reserves in the soil were expected to be greatest at thisbecause of our interest in relationships lish from seeds. Alternatively, composi- among continuously distributed character- tion of seed banks may be unrelated totime of the year. After a site was selected, the soil taxonomic unit was determined istics of the seed bank and plant communi- clubmoss and few seeds of decreasers may ties. Furthermore variation among soil be present in seed banks. The purpose offrom soil surveys completed by the Saskatchewan Soil Survey (Ayres et al.seed banks at a particular site was not of this study was to determine the composi- interest and pastures could not be replicat- tion and diversity of the soil seed bank in1985), and the range site was determined (Abouguendia 1990). Of the 100 range ed. Soil samples for each site were mixed relation to the cover of clubmoss and com- thoroughly and placed in a 12.5 by 25 by 5 positional characteristics of grazed plant sites sampled, 7 were classified as clayey, 64 were loamy, 3 were sands, 7 werecm tray. Soil samples were about 2 to 3 communities in the Northern Mixed cm in thickness in the trays. The soil sam- sandy, and 17 were thin and 2 were bad Prairie in southwestern Saskatchewan. ples were watered and randomly placed in land. At each site, 2, 0.5 by 0.5 m quadrats a growth chamber with 12 hours of dark- were randomly established 5 m apart, and ness at 8° C and 12 hours light (220 µmol percent canopy cover of each plant species

JOURNAL OF RANGE MANAGEMENT 57(3) May 2004 301 Table 1. Relative importance ( %) of decreaser, increaser and invader species present in soil seed Data analysis banks and the relative importance of these same species in the plant communities in 94 grazed No seedlings emerged from 6 of the 100 pastures in southwestern Saskatchewan. Taxonomy is based on Budd (1987) while classification soil seed bank samples, thus they were not as decreasers, increasers, and invaders follows Abouguendia (1990). included in statistical analyses. Species richness and the Shannon diversity index Plant Seed Common name Latin name communities bank were determined for seedlings emerging ---- ( %) ( %) from each seed bank sample (Barbour et Decreasers al. 1999). Jaccards' similarity index of needle and thread Stipa comata Trin. &Rupr. 69 2 species composition in the plant communi- green needlegrass Stipa viridula Trin. <1 <1 ty and the soil seed bank was calculated western wheatgrass Agropyron smithii Rydb. 5 <1 for each site using the number of common indian ricegrass Oryzopsis hymenoides (Roem. &Schult.) Ricker 0 <1 species divided by the total number of northern wheatgrass Agropyron dasystachyum (Hook.) Scribn. 10 <1 species in both the plant community and 0 <1 western porcupine grass Stipa spartea var. curtiseta Hitchc. soil seed bank (Barbour et al. 1999). This sand dropseed Sporobolus cryptandrus (Torr.) A. Gray 0 <1 slender wheatgrass Agropyron trachycaulum (Link) Malte 0 <1 similarity index ranges from 0, or no simi- Increasers larity, to 1 or identical composition. Junegrass Koeleria cristata Pers. 87 100 Relative importance for each species was fringed sagebrush Artemisia frigida Willd. 73 25 determined in the plant communities and sedge Carex sp. 64 18 the seed banks by multiplying constancy native bluegrass Poa secunda Presl. 8 2 of each species among plant communities blue grama Bouteloua gracilis (HBK.) Lag. 100 <1 or seed banks by the proportion of the yellow umbrellaplant Eriogonum flavum Nutt. 0 <1 coneflower Ratibida columnifera (Nutt.) Woot. &Stanl.

302 JOURNAL OF RANGE MANAGEMENT 57(3) May 2004 Table 2. Correlations between the compositional characteristics of plant communities and soil seed seed bank composition agrees with Perez banks on 94 grazed pastures in southwestern Saskatchewan. Significant correlation coefficients et al. (1998) and contrasts with differences (P < 0.10) are bold and underlined. in seed bank species composition under different grazing intensities (Kinucan and Seedbank characteristic Smeins 1992, Willms and Quinton 1995) Plant Total in which early seral species tended to community Species Species Decreaser Increaser Invader seedling characteristic richness diversity density density density density increase with grazing while late seral (r) species decreased. Clubmoss cover 0.03 0.06 -0.01 0.01 -0.09 <0.01 Total seedling densities averaged 7.8 per Range condition score -0.04 0.05 0.11 -0.15 -0.11 0.17 102 cm2 (SE ± 0.62). These seedling den- Species richness 0.06 0.05 0.11 0.06 0.04 0.06 sities are within the range for soil seed Species diversity 0.08 0.06 0.08 0.10 0.09 0.10 banks in Mixed Prairie (Johnston et al. Decreaser cover -0.15 -0.08 <0.01 -0.20 -0.08 -0.22 1969) and Fescue Prairie in Alberta and Increaser cover 0.13 0.08 0.09 0.13 0.23 0.23 Invader cover -0.03 0.16 -0.07 0.30 -0.06 0.21 Saskatchewan (Archibold 1981, Willms and Quinton 1985, Grilz and Romo 1995). Total seedling density increased with Among emergent seedlings, 19% (SE ± Seven of 42 correlations between corn range condition score (P = 0.09), cover of 2.3) were invaders (1.7 seedlings per 102position of plant communities and seedincreasers (P = 0.03) and invaders (P < cm2, SE ± 0.30). Pygmyflower (Androsace banks were significant (P <0.10) (Table 2). 0.01) in plant communities. Increased seed septentrionalis L.), a native annual, was the Cover of clubmoss was poorly, and non -densities with increasing grazing intensity most important invader while flixweedsignificantly correlated (P = 0.32 to 0.98), were reported by Russi et al. (1992), (Descurainia sophia [L.] Webb.), a non-with all descriptors of composition of theWillms and Quinton (1995) and Marco native annual, was second in importance. soil seed banks. We therefore reject theand Paez (2000). The total density of Pygmyflower and fringed sagebrush were hypotheses that clubmoss has significant seedlings emerging from the seed banks the most common native forbs in the seedeffects on the composition of seed banks was negatively correlated (P =0.03) with banks, similar to reports from other grass- in the Northern Mixed Prairie of south-cover of decreasers in plant communities. lands in Saskatchewan and Alberta western Saskatchewan. Other factors must In summary, the fact that decreaser (Lagroix -McLean and King 1989, Grilz and therefore have greater influences on corn-species were a minor component of seed Romo 1995, Willms and Quinton 1995). position of seed banks than clubmoss. banks suggest that low seed numbers like- The density of increaser seedlingsly limit the potential for regeneration of Relationships between composition emerging from seed banks was negativelydecreaser species from seed banks. On the correlated with cover of decreasers (P = of seed banks and plant communities other hand, increaser and invader species 0.06) and positively correlated with coverwere most the most important species The seed banks and plant communitiesof invaders (P < 0.01) in the plant commu- shared few species as indicated by the low groups in seed banks and their regenera- nities. Densities of invader seedlingstion from seed may not be seed limited. similarity index (K = 0.31, SE ± 0.02,emerging from seed banks were positively range 0.00 to 0.60). Johnston et al. (1969),correlated with cover of increasers (P = Since invader and increaser species domi- Lunt (1990), Kinucan and Smeins (1992), 0.03). From an ecological perspective,nated the seed banks, mechanically dis- Bekker et al. (1997), Peco et al. (1998),these correlations are reasonable becauseturbing plant communities to control club- Perez et al. (1998), Lopez - Marino et al. abundance increasers and decreasers aremoss is predicted to lead to plant commu- (2000) and Tracy and Sanderson (2000) negatively correlated and the abundance ofnities that are dominated by increasers also reported little similarity between increasers and invaders are positively cor- and/or invaders as described by Ryerson et botanical composition of seedlings emerg- related in plant communities (seeal. (1970). It remains to be determined ing from seed banks and established plantAbouguendia 1990). whether clubmoss, other biotic factors, or communities. Lack of similarity between That species richness (K = 3.6 speciesfactors of the physical environment place seed banks and plant communities may be greater limitations on emergence and attributed to inputs of seeds from plant per 102 cm2, SE ± 0.18) and diversity (K = 1.00, SE ± 0.05) of seed banks were poor- establishment of decreasers when seed communities that have changed throughly correlated with characteristics of thenumbers are not limited. Seed production time and inputs from different communi- plant communities indicates that greatercan vary substantially from year -to -year ties in space. Predation, differential rates species richness and diversity in the vege- and relationships among compositional of loss of seed viability, and movement of tation is not necessarily associated withcharacteristics of plant communities and seeds from the sites may also reduce simi- seedbanks might therefore vary according- larity of seed banks and plant communi-higher species richness and diversity in the soil seed bank. Species richness of seedly. Although the economic feasibility of ties. In other studies (Johnson and mechanically disturbing range to reduce Anderson 1986, Henderson et al. 1988)banks was also similar among different range condition classes in Albertaclubmoss is questionable (Kulshreshtha et the abundance of species in the seed bank al. 2002) it may be useful to manage for was positively correlated with above- (Johnston et al. 1969) and grazing intensi- ties in (Kinucan and Smeins 1992). production of seeds by desired species or ground vegetation. Grazing management species groups and then, if necessary, to (Dutoit and Alard 1995, Bekker et al. The poor correlation between range con- dition score and seedling densities oftime control treatments with production of (1997), soil texture (Coffin and Lauenroth abundant amounts of viable seeds. (1989), and successional status of plantdecreasers, increasers and invaders agrees communities (Tracy and Sanderson 2000) with Kinucan and Smiens (1992) and all contribute to similarity of vegetationTracy and Sanders (2000). A poor correla- and soil seed banks. tion between range condition score and

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