SEED BANK OF A DRAINED PRAIRIE WETLAND 1

Thomas E. Dahi and David E. Nomsen'3

The abundance and diversity of ungerminated seeds were determined from ten (10) replicate soil cores (12x6.4 cm), taken from a prairie wetland basin which had been drained for 30 years. The seed bank density was estimated at 4,212 seeds/m2. Thirty six species of plants were represented.

part of which may remain dormant due to INTRODUCTION unfavorable environmental conditions. Recent studies have documented that the nationwide decline in wetlands has been STUDY SITE dramatic (Frayer et al. 1983; Tiner 1984). This has been particularly apparent in the The study was conducted in the north­ prairie pothole region of the United States central portion of section 17, T132N, R43W, where over half of the original wetland acres Buse Township, Ottertail County, Minnesota. have vanished (Redelfs 1980; Bishop 1981). The area is characterized by small, glacially formed depressions scattered over fairly flat The seed bank of these freshwater marsh terrain. The former vegetation was tallgrass systems is one factor which may provide clues and mixed prairie (Nat. Acad. Sci. 1970), now to the impact s of land use changes. Detailed work it is mainly small grains and forage crops·. with the seed banks of natural marshes has only recently been addressed (van der Valk and Davis The size of the study wetland was 1976; Smith and Kadlec 1983) and studies of 0.9 hectares. Historically, it has been wetland seed banks have dealt with actual a shallow emergent wetland, however, since germination results of collected seed and 1954 it has been drained by a 20 centimeter substrate from intact wetland habitats (8 inch) tile and used as farmland. Corn (Crail 1951; van der Valk and Davis 1975; (Zea mays) and soybeans (Glycina max) have 1978; Pederson 981; Smith and Kadlec 1983). been the dominant crops produced during most As a result, they have probably under estimated years since drainage. Residual soybean plants the size of the seed bank based on the total as well as barnyard grass (Echinochloa number of viable seeds (van der Valk and Davis crusgalli) and lamb's quarters (Chenopodium 1978). While these efforts have helped explain album), were found to be representative cover successional patterns in existing wetlands, type vegetation. they do not take into account the germination potential from a much larger seed reserve, METHODS

1 Paper presented at the Eighth Annual Techniques for assessing the seed bank Meeting of the Society of Wetland Scientists, in a drained we t land were modified from Seattle, Washington, May 26-29, 1987. previous studies of van der Valk and Davis (1976, 1978), which had incorporated 2 Thomas E. Dahl is the Assistant National germination results of seeds from substrate Coordinator, Wetlands Inventory , U.S. Fish samples. The abundance and diversity of and Wildlife Service, Washington, DC 20240 seeds were determined from soil cores. Ten (10) replicate s oil cores (12x6.4 cm) were ~ David E. Nomsen is a Resource Specialist taken at random sites along transects with the South Dakota Cooperative Wildlife systematically throughout the basin using Research Unit, South Dakota State Universit y, an aluminum corer. Soil samples were Brookings. South Dakota 57007 sieved through a 100/in.~ mesh screen. The remaining materials were dried and s earched as compared to other more natural wetlands. for seeds. The seeds in each core sample were Roberts (J958) reported finding from 19,000 separated to species and tallied. to 175,000 seeds/meter in agricultural soil. Thus t he information obtained on total seed Residual material which passed through numb ers in the farmed wetland basin in this the 100/in .~ screen was tested for seed study would seem to indicate a community content by simulating various soil moisture profile more closely resembling a natural levels similar to the procedures described prairie marsh than an agricultural field. by Pederson (1981). Samples were maintained This is remarkable considering agriculture under controlled conditions using a "grow-lux" has been the predominant land use for the light with a12 hour photo-period. Germination past 30 years and may atest to the conditions were maintained for periods of 196 resiliency of drained prairie wetlands. hours. No seeds germinated from the residual material. DISCUSSION

Little if any work has been done which RESULTS examined the seed banks of drained wetlands. Consequently, comparisons of the data to Seeds representing thirty-six species previous studies involving upland habitats, of plants were collected from ten soil cores. wetlands, or wetlands in drawndown phases may The seed bank density was estimated at 4,212 not be totally applicable. seeds/m~. Seed species found in each sample and their relative abundance are shown in -- -The floristic diversity of a wetland Table 1. seed bank may also be a accurate only to the depth sampled. While few researchers Although the basin studied has not have examined the number of seeds by soil functioned as an undisturbed wetland for depth (Moore and Wein 1977), several studies 30 years, it has retained wetland indicator have suggested that the majority of viable seed species as components of the seed bank. was found within the top five centimeters of Table 2 shows the diversity of the seed soil (Crail 1951 ; Moore and Wein 1977; bank and those species indicative of wetland Archibold 1978). It is reasonable to assume conditions. The potential for restoration that sedimentation, perhaps facilitated by of the wetland would appear to be enhanced agricultural activities, has accelerated by the persistance of a number of emergent sediment deposition burying remnant seeds hydrophytes which have remained as components at greater depths. While these seeds may of the seed bank. still persist, their role in the restoration of wetland vegetation is negligible if they Barnyard grass (Echinochloa~) was are buried below the maximum depth of present in all ten samples and made up emergence. 40 percent (1,365) of the total number of seeds. Alisma plantago aquatica was found The sedimentation process may also have in seven samples, totalling 474 individuals, influenced seed distribution within the representing 14 percent of the seed basin. Cultivation or sedimentation may composition. Polygonum lapathifolium was have buried a disproportionate number of the third most common species. It was seeds below the depth sampled. In such f ound in nine samples totalling 367 seeds circumstances, uneven sediment deposition and 11 percent of the seed bank. in certain parts of the basin may have Collectively, these three species formed also altered soil moisture regimes to the 65 percent of the total number of seeds extent that seed longev ity was affected. collected. Apparently this is not uncommon. Although hypothetical, this might help In Iowa marshes during drawndown, Scirpus account for the wide variation in the validus, Bidens cernua and Polygonum number of seeds collected f rom replicate lapathifolium collectively formed 69.4 samples. percent of the seed bank (van der Valk and Davis 1978). Not much can be surmised about the age and viability of buried seed when it has Initially total seed numbers found, been repeatedly disturbed by cultivation and appeared to be similar to the f indings subj ected to various agro-chemical applications. of other seed bank studies. However, The number and diversity of seeds found in the consideration must be given to the fact substrate is probably a major f actor in plant that total seed numbers used t o describe establishment in wetlands (Meeks 1969). the seed bank in this s tudy do not Species composition of seed banks result from reflect germination results. Since seed the accumulation of seeds over a period of many viability is some percentage of t ot al years (van der Valk and Davis 1976), and seed seed number and, germination is some banks often cont ain diverse concentrations of fraction of the viable population emergent, submergent and terrestrial plants with (Crail 1951) , t he seed bank examined actual floristic characterization being in this study may be somewhat deflated

305 Species A B C D E F G H I J TOTAL

Abronia fragrans 1 Agrostis sp . 1 1 Alisma plantago-aquatica 25 146 81 94 7 2 112 7 474 Amar anthus retroflexus 24 6 2 1 5 40 Ambrosia sp. 2 2 5

Bidens connota 8 8 Brassica kaber 33 1 1 1 1 3 40 Chenopdium album 10 11 2 3 5 11 42 Cirsium arvense 3 4 Cyperus esculentus 2 3 5

Cyperus schweinitizii 2 2 Echinochloa spp. 1 374 427 339 8 16 22 1 74 103 1365 Helianthus sp. 2 1 2 1 6 Lycopus americanus 4 7 1 12 Melilotus alba 2 2

Monarda punctata 2 3 6 Panicum capillare 98 11 1 4 214 Polygonum aviculare 1 1 Polygonum lapathifolium 15 9 10 290 7 3 24 8 367 Portulaca oleraccea 2 3 1 6 Ranunculus sceleratus 28 19 9 56 Rumex spp. 8 12 12 14 4 1 3 11 19 84 Scirpus spp./lva 67 29 10 86 24 17 11 25 36 305 xanthifolia Setaria sp. 2 16 2 20 3 21 64 Setaria lutescens 16 2 4 43 6 10 2 83

Silene noctiflora 1 1 Solanum nigrum 9 2 1 1 14 Sonchus sp. 1 1 Trifolium sp. 1 1 2 3 4 11 Unkown grass sp. 2 9 12

Vervena hastata 6 2 8 UnkOtfll miscellaneous 15 28 64 18 10 7 19 3 164

TOTALS: 250 733 585 1020 146 31 73 40 281 245 3404

Table 1. -- Number of individual seeds collected from ten samples taken in a drained prairie wetland basin following 30 years of cultivation. determined by soil moisture levels (National restoration efforts have been encouraging Research Council 1982). (National Research Council 1982) . This is probably du e largely to the abilit y of a seed bank to persist and remain viable even in times MANAGEMENT IMPLICATIONS of natural drought or induced drainage. Goss (1942) , recorded having found seeds of the genus Wetland restorations have been successful Polygum which successfully germination after where remant flora have persisted, but even in 16 years in the soil and, Moore and Wein (1977), areas where agricultural activities have been reported viable seed was found on study sites practiced for many years the response to following a period of 90 years.

306 Table 2. -- Seed bank species showing wetland be fairly resilient. indica t or status as assigned by the National List of Plant Species that Occur in Wetlands Seed bank information can be useful in ~ (1986) . Wetland status indicators are determining wetland restoration potential based I expressions of each species' f requency or on presence or absence of seed reserves. occurrence in wetland versus non-wetland Knowledge of the seed bank data can also govern habitats . We t land status coding was based we tland management options which might include on the following criteria: OBL-Obligate water l evel control or other more comprehensive hydrophyte - always found in wetlands; management options. FACW-Facultative - usually found in wetlandS; FAC-Facultative - sometimes found in wetlands; FACU-Facultative - LITERATURE CITED seldom found in wetlands; ND-Not designated; NW-non wetland species; DRA- Drawdown - Archibold, D.W. 1978. Buried viable propagules species which may pioneer into wetlands as a factor in postfire regeneration in during drawdown . northern Saskatchewan. Can. J. Bot. 57:54-58.

Bishop, R.A. 1981. Iowa's wetlands. Proc. Iowa Species Wetland Indicator Status Acad. Sci. 88:11-16.

Abronia fragrans FAC,-FACW Crail , L.R. 1951. Viability of smartweed and Agrostis sp. OBL millet seed in relation to marsh management Alisma plantago-aquatica FACU+, DRA in Missouri. Waterfowl management study, Amaranthus retroflexus FACU, DRA-FACW surveys and investigation projects, Missouri Ambrosia sp. FACU, DRA-FACW 13-R-S, Pittman-Robertson Program, Bidens connota OBL, DRA Conservation Commission.

Brassica kaber N.W. Frayer, W.E., T.J. Monahan, D.C. Bowden and F.A. Chenopodium album FAC, DRA Craybill. 1983. Status and trends of wetlands Cirisium arvense FACU and deepwater habitats in the conterminous Cyperus esculentus FACW United States 1950 ' s to 1970's. Colorado Cyperus schweinitizii FACU+ State Univ., Fort Collins, CO. Echinochloa spp. FACW, DRA-OBL, DRA Goss , W.L. 1924. The viability of buried seeds. Helianthus sp . UPL-FACW J. Argicultural Res., 29:349-362. Lycopus americanus OBL Melilotus alba FACU Meeks, R.L. 1969. The effect of drawdown data on Monarda punctata N.W. wetland plant succesion. J. Wildlife Manage, Panicum capillare FAC, DRA 33(4) :817-821. Polygonum aviculare FAC- Moore, J.M. and R.W. Wein. 1977. Viable seed Polygonum lapathifolium FAW+, DRA populations by soil depth and potential site Portulaca oleracea FAC- recolonization after disturbance. Can. J. Ranunculus sceleratus OBL, DRA Bot. 55:2408-2412. Rumex spp. FAC+, DRA-OBL Scirpus spp./Iva xanthifolia National Academy of Sciences. 1970. Land use and Setaria sp . FACU-FAC wildlife resources. Nat. Res. Council Committee on Agricultural Land Use and Setaria lutescens N.W. Wildlife Resources, Washington, D.C. Silene noctiflora N.W. Solanum nigrum NC FACU, FACU+ National Research Council. 1982. Impact s of Sonchus sp. FAC-FAC­ emerging agricultural trends on fish and Trifolium sp . FAC-,FACU+ wildlife habitat. National Acad . Press. Unkown grass sp. Washington, D.C.

Verbena hastata FACW+ Pederson, R.L. 1981. Seed bank characteristics Unknown Miscellaneous of the Delta Marsh, Manitoba; Applications for wetland management. I n selec ted proceedings of the midwest conference on Ove r all it would appear t hat the seed wetland values and management; 1981 J une bank of some pr airie wetlands have t he ability 17-19; St. Paul , Minnesota (B . Richar dson, to pers ist despite prolonged periods of drainage ed.) MN Water Planning Board. St. Paul, and intensive land use which may superficially Minnesota. alter the habitat . Although some segments of the seed bank may be susceptible to Redelfs , A.E . 1980. Wetland values and losses degration, at least some species of wetland in the United States. M.S. Thesis . Oklahoma emergent and mud - flat pioneer seeds appear to Stat es University , Stillwater.

30 7 Roberts, H.A. 1958. Studies on the seeds of v egetable crops. I. Initial effects of cropping on the seed in the soil. J. of Ecology 46:759-768.

Smith, L.M. and J . A. Kadlec. 1983. Seed banks and their role during drawdown of a North American marsh. J . Applied Ecol. 20:673-684 .

Tiner, R.W. 1984 . Wetlands of the United States: Current Status and Recent Trends. U. S. Fish and Wildlife Service.

U.S.D.I. Fish and Wildlife Service. 1986. Wetland Plant List - Minnesota, St. Petersburg, FL. van der Valk, A. G. and C. B. Davis. 1976. The seed banks of prairie glacicial marshes . Can . J. Bot. 54:1832-1838. van der Valk, A. G. and C.B. Davis. 1978. The role of seed banks in the vegeta t ion dynamics of prairie glacial marshes. Ecology 59(2):322-335.

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