THESiS 300) 4“ LIBRARY Michigan State University This is to certify that the thesis entitled The Effects of Water Level Fluctuations on Two Coastal Emergent Wetland Plant Communities of Saginaw Bay, Lake Huron presented by Anne M. Vaara has been accepted towards fulfillment of the requirements for Master degree in WWW O / 0—7639 MSUiS ml I'm-mun"... A - Major professor Fish. & Wildl. ‘ , Institution PLACE iN RETURN Box to remove this checkout from your record. TO AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE | DATE DUE DATE DUE 111808 WOT c:/CIRC/DateDue.p65—p. 15 THE EFFECTS OF WATER LEVEL FLUCTUATIONS ON TWO COASTAL EMERGENT WETLAND PLANT COMMUNITIES OF SAGINAW BAY, LAKE HURON by Anne M. Vaara A THESIS Submitted to Michigan State University in partial fiilfillment of the requirements for the degree of MASTER OF SCIENCE Department of Fisheries and Wildlife 200 1 ABSTRACT THE EFFECTS OF WATER LEVEL FLUCTUATIONS ON TWO COASTAL EMERGENT WETLAND PLANT COMMUNITIES OF SAGINAW BAY, LAKE HURON by Anne M. Vaara Plant community composition was studied in two coastal wetland sites in Saginaw Bay, Michigan in 1994 and 1995. Plants were sampled along transects using circular plots with a 9.5 m radius from the shoreline to open water at two coastal sites, Cotter Road (T14N, R6E, section 14) and Vanderbilt Park (T14N, R7E) in July and early August during peak biomass. The Vanderbilt Park site was located along the windward side of a cove at Quanicassee, Michigan while the other was located in a more protected area along the leeward side of this cove. Mean annual lake levels decreased by 15 cm from 1994 to 1995. For both sites, species richness and stem density decreased with an increase in water depth and distance from shore with 80-85% of the plant species dropping out at depths greater than 55cm. Species richness increased two-fold for the strand and shallow areas (<25 cm deep) from 1994 to 1995 as water level dropped. Stem density also increased 2 to 5 fold for the strand communities. Few changes were evident at depths >25cm. Biomass weight differences were significant based on individual species type, however, biomass changed very little from year to year and from site to site, along the transects. ACKNOWLEDGMENTS Support for this project was firnded by the Michigan Department of Natural Resources. I would like to thank Dr. Thomas Burton, my patient advisor for his guidance, influence and insight into this project, and his helpfirl editing of the manuscript. Also, I would like to thank my committee members Dr. Harold Prince who was always encouraging and optimistic and Dr. Peter Murphy for his botany insight. Tom and Harold also provided me with an opportunity. Thank you to Joe Gathman for his advice and helping me organize my results. I am grateful for the help of student interns Holly Hinterman David Ford and Leslie Jagger and graduate students Robert Hollister and Kurt Stanley. Thank you to Pat Thomas for helping me keep things in perspective. My very special thanks are saved for my parents Mel and Josephine Vaara and my sisters Liisa, Ingrid and Tasha Because of their support and encouragement, I was able to accomplish this most dificult and important educational experience. TABLE OF CONTENTS Page LIST OF TABLES v LIST OF FIGURES vi INTRODUCTION 1 DESCRIPTION OF STUDY AREAS 4 METHODS 9 RESULTS 12 Description of Plant Community Response to Water Level Changes 12 Characterizing the Strand Community ..................................... 28 Plant Community Description and Water Level Zonation ...... 29 Species Area Curves '41 DISCUSSION 35 Plant Diversity '45 Effects of Wave Energy ’46 Site Geographical I nominn 17 Wetland Conservation '48 LITERAUTRE CITED 40 APPENDIX 44 LIST OF TABLES Table Page 1 Composition of the coastal plant community at Cotter Road in 1994 ...................................................... 13 2 Composition of the coastal plant community at Cotter Road in 1995 ...................................................... 15 3 Composition of the coastal plant community at Vanderbilt Park in 1994 ........................................ 18 4 Composition of the coastal plant community at Vanderbilt Park in 1995 ........................................ 20 5 Lake levels (m above sea level) for Saginaw Bay in 1994 and 1995 from the NOAA station in Essexville, Michigan ............................................. 23 6 Dominant assemblage using the top three species with the highest importance value using the four categories of water level zonation for both sites each year ........................ 30 A1 Plant species of the Saginaw Bay study areas at Cotter Road and Vanderbilt Park ........................................ 44 LIST OF FIGURES Page Saginaw Bay area map showing the study sites and the 585 ft. contour .......................................................... 5 Area maps showing the vegetation types and zones and the wetland and upland systems ............................. 6 Coastal wetland vegetation sampling techniques for Cotter Road and Vanderbilt Park from the shoreline to open water. In 1994 and 1995, three quadrats were taken from a point-centered circular plot with a 9.5 m radius by randomly selecting a distance (1-9 m) and direction (0-3600) from the center point. The center points for these plots were located at 50 m intervals in 1994 and at 20 m intervals in 1995. Transects were established each year using a set azimuth from a stake installed on the shore in 1994 and extended from the strand to open water ...................................................................... 7 Mean stem density (stems/m2) along a water level gradient for all points sampled for both sites in 1994 and 1995 ....................................................................... 24 Stem density using distance from shore to open water and comparing 1994 to 1995. 5a. Cotter Road ............................................................. 25 5b. Vanderbilt Park ....................................................... 26 Plant species richness for both sites in 1994 and 1995 ....................................................................... 27 Species Area curves for both sites in 1994 and 1995. 7a. Strand Community .................................................. 32 7b. 20-60 m distance .................................................... 33 7c. 80- 120 m distance ................................................... 34 vi INTRODUCTION Wetland loss and degradation in Saginaw Bay has been estimated at over 50% or roughly 8,097 hectares since early settlement times (J aworski and Raphael 1978). The Saginaw Bay coastal wetlands comprise 89% of Lake Huron coastal wetlands in Michigan and 33% of the total coastal wetlands for Michigan (Jaworski and Raphael 1978). Coastal wetlands are changing environments because both long-term and short- term changes occur with water level fluctuations (Batterson et al., 1991, Burton 1985, Enslin and McIntosh, 1978). Enslin and McIntosh (1982) suggested that changes in the amount and composition ofmacrophytes occur frequently in response to water level changes, longtermlakelevelandshorttermseicheandstormsurgerelatedchanges, site moisuuewndifionawaveaction, waterchemisuy, sedimentationandotherprocesses. WaterdepthisamajorfactorconfloflhrgthedisflibufionofaquaficpMsandis responsible for zonation in wetlands (Walker and Copeland, 1968; Stewart and Kantrud, 1972; Hroudova, 1980; Spence, 1982). Enslin and McIntosh (1978) mapped aquatic plant communities for several sites along the Saginaw Bay shoreline through interpretation of historical aerial photography for selected years from 1949 to 1978 and documented changesinplant zones inrelationto lake level changes. Theplant zonesintheirstudy were categorized into submergents, cattails, mixed emergents, sedges and grasses. Keddy and Remicek (1986) suggested that fluctuating water levels increase the area of shoreline vegetation, and the diversity of plant community types and species. Any stabilization of water levels would likely reduce marsh area, plant community zonation, and plant species diversity. Keddy and Reznicek (1986) observed that plants that were intolerant of drying died during low water‘periods and were replaced by species emerging from reserves of buried seeds. This phenomenon was also documented by van der Valk (1981), Keddy and Reznicek (1982), Smith and Kadlec (1983). The role of natural “disturbance” or stress in promoting species diversity has been discussed by Grubb (1977), Connell (1978), Huston (1979), White (1979), and Grime (1979). In Saginaw Bay, there is long term “disturbance” with year to year and seasonal water level fluctuations and short term *disturbance” in the form of seiche activity and storm surges. In 1994, Saginaw Bay experienced two large storm surges in May and June withwaterlevelsreachingapprordmately90anabovethemomhlymean(Whitt 1996) whichalteredtheplant and animal compositionforthat season The storm surge desuoyedvegetafionmnesdongpartsoftheshmemdthewmdsandwavesfippedthe tipsoftheflowersofl‘manyplantspecieswersonalobservation). Manyplantsgrew vegetativelybutneverflowered. Theefl‘ects ofthese storm surgesincluded changesin wildlife distributionandthegrowthand structure ofvariousplant species(personal observation). Long term efl‘ects fiom storm surges cannot be documented from this study. Giventheimportanceofwaterfluctuationsin structuring macrophytecomrmrnities in the literal zone of lakes (Keddy and Reznicek 1986, Enslin and McIntosh 1978), my hypothesis was that water level fluctuations and exposure to wave energy at bayward edge of the wetland were important abiotic factors structuring plant community composition along the Saginaw Bay shoreline. My objective was to document changes in plant community composition for the emergent macrophytes of the littoral zone of Saginaw Bay in relation to water depth and distance from the shoreline over two annual cycles. DESCRIPTION OF THE STUDY AREA Two sites were selected in two coastal wetlands sites in Bay and Tuscola Counties in Saginaw Bay (Figure l). The two study sites represented areas that had remained an emergent marsh since settlement by Europeans, although these sites are now partially or completely isolated fiom the wet meadow and lakeplain prairie because of agricultural drainage and/or levees. The two sites were: 1. Cotter Road: This site is located in Bay county (T14N, R6E, section 14), at the northern end of Cotter Road, approximately 7 miles east of Essexville (Figure 1) and 1.5 miles north oinghway 25. The area was classified in the 1978 National Wetlands Inventory Quanicassee, Michigan quadrangle as LZEM/ABH (lacusu'ine, littoral, emergent/aquaticbed, permanentwaterregime). Thissitewas separatedfrom adjacent uplands by a levee constructed in 1986 by the US. Army Corps of Engineers. Therewereagricultmal fields locatedjustsouthoftheleveeandasandyridgethat separated the levee from the emergent zone. The emergent vegetation extended approximately 800metersoutfromthe strand (anareathatis subjecttoroutine flooding and drying) to open water (Figure 2). Dominant wetland plants included Scirpus amen’cwms (three-square bulrush) and S. acums (hardstem bulrush), Dpha angumfolia (narrow-leaved cattail), Calmnagrostis canadensis (blue-joint reed grass), Lyrhrum salacarr’a (purple loosestrife), Eleochan’s mallii (Small’s spikerush), Eleocharis erythropoda (bald spikerush) and Carex spp. (sedge). .SoEoo .: mxm 2: can 3% 357. 2: 9:30.? ENE eons Imam BaEmam ._ ouzwi \ u ul Iu‘x : 9?. n : so 756 >5: 3a 5355 : mxm 2: ELF)» l «PE beam 0 H _ a la... E 237. .53— 33.5 >>» 32¢ 82: 8% 332. .2:vo of. .Emoa “8:3 2: 80¢ 003-8. :28on Ea E e- C cognac a meson—om bfiovefl .3 «.39.: 8 We a 5.3 SE 338.0 wcaoueooefiem a 89¢ :83 803 $833 ooh: .32 98 v3. 5 .583 some 8 0:222... 05 Set x8e “35.5.5 was used .5300 new weaving“ mam—gnaw 538%? wee—«03 .3800 .m 2:me T ...... , .,. , . .../ . .1... 9.80:. cc— l' ‘i =0~0E 06— Iv 220E own Q cow . m¢\vo¢~ 3.3m a__n..ouea> 220:. com - mQVoe. teem acteU faces— 88:95. 052.8 MEEEam 3.5.50 82:... I .5550»? E hi .333 :30 2. Vanderbilt Park: This site was located in Tuscola County, (T14N, R7E, section 21), on the north side of Gilmore Road, approximately 1.5 miles north of Highway 25 (Figure 1). The area had been identified by the 1978 National Wetlands Inventory Quarricassee, Michigan quadrangle as L2EM/ABH (lacustrine, littoral, emergent/aquatic bed, permanent water regime). The littoral wetland included in this study was bounded on the upland side by a sandy ridge that ran parallel to the shore. This sandy ridge was the first of two ridges in forested plant cover that paralleled the shore. A swale wetland between the two ridges was not included in this study. Agricultural fields were located inland of the second sandy ridge. The coastal marsh vegetation extended approximately 600 meters out from the shoreline to open water (Figure 2). Dominant vegetation included Scirpus mnericwms (three-square bulrush), Dpha mgurlifolia (narrow-leaved cattail), Calamagrostis canadensrls' (blue-joint reed grass), Lyrhrrmr salaam’a (purple loosestrife), Eleacharis smallii (small’s spikerush) and Eleochan‘s erythropoda (bald spikerush), Mmrphaea odorara (white water lily) and Carer: spp. (sedge). METHODS Plant Sampling Emergent plants were sampled from two coastal marsh sites (Figure 1 and 2) along three line transects/site (Figure 3). A total of 738 quadrats were sampled within 246 sampling points along the line transects for a total of 7, 420 meters (3,320 m at Vanderbilt Park and 4,100 m at Cotter'Road), (Figure 2). Site sampling was done in July and eariy August in 1994 and 1995 at or near peak biomass. Threetransects/site were set 100 m apart, parafldtoeachotherandperpentficrdartotheshorefromtheshorelmeoutto open water(F1gure2and3). 'I‘hefirstpointwassetinthestrand, atransitionzoneestablished usingthechangeinvegetationfi'omupland spedesalongtheridgetowetland species along the shoreline. Plants were sampled fi'om circular plots with a 9.5m radius (284m2) alongtransectsatSOmirrter'valsin l994andat20mintervalsin 1995. Ateachinter'val point,three0.25 mzquadratsweresampledatrandomlyselected 1 to9mdistancesfi‘om the center point of the circular plot using a randomly selected azimuth (0-360'). The (0.25 m") quadrat time was constructed of PVC pipe 0.5m long on each side. The quadrat wasplacedoverthesarnpledareasothathequadraterctendedfi’omthepointselectedto 0.5 m beyond the point. All stems were counted and identified to species. Any unknown species was collected and transported to the laboratory for identification using keys. Water depth was recorded for each sample point at the time of sampling. Above ground biomass was determined by randomly selecting 30 stems for each common species and cutting them at the base of the plant. The stems were dried in bags S. "i.. at 60° C to a constant weight. An average stem weight for each species was calculated as the mean of the 30 randomly collected stems. Average stern weight was multiplied by number of stems/quadrat to calculate biomass. Biomass was determined for rare species using weight classes of species with comparative phenology and biomass from other sites. Data Analysis Plant data were summarized for each circular plot using means ofthe three sampling quadrats. These data were summarized for the strand (shoreline) community and by depth fi'om the strand to the outer edge (open water) of the emergent zone using 25cm waterdepthintervalsinl994and10emwaterdepthintervalsinl995. mam (RD), rdafivefiequencyle)andrdafivebiomass(RB)waecalaflatedforthesfland andforeachdepthinterval. RD+RF+RBwerethenaddedtogethertoobtainan irnportancevahreranking. Cmtis(l947)usedanimportancevalueobtainedbyadding together relative frequency, relative density and relative dominance. For this study, we usedrdafivebiomassmhaflunrdafivedonnmncebemusedonnnanceornnponmceof any species can be expressed as the percentage oftotal biomass (Barbour et. al.). The importance values were divided by 300 (the highest possible score), (Barbour et. al.), to obtain a percent of total community importance for a particular water level gradient range category. Frequency=(nmnberofquadratsinwhichaspeciesoccurred+total number of plots sampled) * 100 Density = the mean number of individuals within each quadrat Biomass = weight of vegetation per m'2 - number of stems of each species 10 in a plot * mean weight per stern * 4 Importance Value (IV) = the relative contribution of a species to the entire community IV = relative fi'equency + relative density + relative biomass %IV = IV + 300 * 100 RF = number of quadrats sampled that contained the species 4- total number of quadrats sampled * 100 RD = number of stems per quadrat of each species -:- total of the average stems per sample plot " 100 RB = average biomass/sample plot + total biomass for all species in sample plots * 100 Average Stems/Sample Plot = total number of stem in three quadrats -z- 3 Importancevalueswereusedtodescribebothsites. Bycombiningtwoormoremeasures inasite,amomwmprehmsiveesfirnueoftheimponmceofspeciesinastmdcanbe obtainedthanispossibleusinganyonemeasm'eofabtmdance (Greig-Smith, 1964). Species area curves were prepared for each plant community following procedures outlined in Barbour (1987). 1] RESULTS Description of Plant Community Response to Water Level Changes Plant community composition and stem density changed rapidly as water depth increased from the shoreline strand community to the outer edge of the emergent plant zone about 500 m from shore (Tables 1-4). The strand community (area subjected to alternating wet and dry conditions as lake level rises and falls due to seiche activity) was the zone of highest species richness (Tables 1-4) and stem density (Figure 4). Species richness and stem density decreased as depth increased so that the outer emergent plant zone was characterized by scattered stems of only 3-5 species (Tables 1-4). In fact, the deepest, most exposed outer fringe of scattered stems was often made up of only one species, Scirpus americanus, in most places along the coast. The influence of water depth on plant community composition and stem density (Tables 1—4, Figure 4) was also illustrated by'changes that occm'red as mean lake levels dropped 15 cm from 1994 to 1995 (Table 5). Plants were sampled during July and August in 1994 and 1995. Mean lake levels during plant sampling in July and August, 1995, were 18.5 cm lower than they were during the same time period in 1994. Decreased lake levels in 1995 resulted in substantial increases in species richness for the strand community from 13-14 species in 1994 to 25-26 species in 1995 (Tables 1- 4, Figure 6) as new seedlings developed on the drying substrate. 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N N 235596 33 .NN NN NN N NN NN N NN N o\ N N.N ENNIN $N.NN NNN N.NN NN 8 NN NN NN N 3 Ne . NN. N38. 255 NNNN .6...» 85.59; Baa-.3..— N.aé a .33 2...: 2:238 .323 BEEN 25.3. .32 .NN N.NNN aegis» N. 5328 N.N-NNN N538 2.. s 52838 4.30 v 033—. 22 in 1995 at Cotter Road and from 534 stems/m'z in 1994 to 2576 stems/m'z in 1995 at the Vanderbilt Park site (Tables l-4, Figures 4 and 5). There were a total of 36 quadrats sampled in the strand community (1 8/year), 42 quadrats sampled within the 1-30 cm depth, 70 quadrats sampled within the 31-60 cm water depth and a total of 33 quadrats sampled within the 61-90 cm water depth (Figure 4). Major changes in stem density and species richness occurred in the strand and 0-30 cm depth zones, but few changes occurred at depths greater than 30 cm (Tables 1-4, Figures 4 and 6). Table 5. Lake levels (m above sea level) for Saginaw Bay in 1994 and 1995 from the NOAA station at Essexville, Michigan. Daily June July August DailL June July August Mean 176.76 176.81 176.82 Mean 176.66 176.61 176.65 Max. 177.63 177.1 1 177.19 Max. 177.16 176.95 176.92 Min. 176.55 176.44 176.27 Min. 176.47 176.32 176.35 1994 1995 Annual 176.68 176.53 Mean Stem density was also compared from site to site for 1994 and 1995 using distance from shore to open water (Figure 5a and 5b) instead of water depth. Total stem density decreased significantly from the strand (0 m) to 50 m and continued to decrease out to open water in both years. Total stem density increased in the strand and 50 m communities from 1994 to 1995 but few changes were documented at 100 m or greater distances from shore from 1994 to 1995 (Figures 5a and 5b). Thus, major changes occurred primarily in areas subjected to dryness during this study. 23 .32 v5 32 E 3:... 53 Now 825: #55 No.“ Nye—mes 382. EN Now .563 _o>o_ 5N3 a mac? AN.E\NEoNN.No £88 803 :82 .NN oNNNmE £954 .833 . Evan; 83- L... 5W. N.N-.. NNNN {N.N N.NNNNNEN >1... 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Plant species richness for both sites in 1994 and 1995. w. .J‘ 559%, '. \ Characterizing the Strand Community Plant species occurred in greater numbers and richness along the strand community in 1995 with conditions dry enough to stimulate germination (Tables 2 and 4). Since the lake level had dropped 15 cm from 1994 to 1995, the strand was less exposed to standing water over long periods of time in 1995 so the drier conditions allowed for a wet meadow type plant community to begin to develop. The plant species with the highest importance values at the Cotter Road site in 1994 included Lythrum salicaria, Calamagrostis canadensis, Scirpus americanus, Carex spp., Eleocharis spp., Juncus spp. and various grasses. In 1995, the plant species at Cotter Road included the same species as were found in 1994 but the species of plants counted and identified nearly doubled with several species of Carex, Juncus, and Eleocharis germinating in large numbers as well as a few woody plant species and herbaceous wetland perennial wildflowers (Tables 1 and 2). The plant species with the highest importance values at the Vanderbilt Park site in 1994 included Scirpus americanus, Juncus spp., Lythrum salicaria,, Typha angustifolia and various grasses. In 1995, the plant species at Vanderbilt Park included the same species as found in 1994, but the species of plants counted and identified nearly doubled and included additional species of Carex, Juncus, and Eleocharis as well as herbaceous wetland perennial wildflowers (Tables 3 and 4). Woody plant species were counted at Vanderbilt Park in 1994 and 1995. Plant biomass within the strand community was calculated in 1994 and 1995 based on weights of individual plant species. The larger the individual plant, the more it 28 weighed. However, the relative biomass of each species within the strand community from site to site and year to year did not change significantly (Tables l-4). Plant Community Description/Water Level Zonation Importance values were calculated for each plant species at every depth range (Tables 1-4). The plant species with the highest importance values for both sites in 1994 and in 1995 were Scirpus americanus, Lythrum salicaria, Typha angustifolia, Sagittaria latifolia, Scirpus acutus and Eleocharis pauciflora (Tables 1-4). Scirpus americanus was ranked the highest in importance at almost every sample point in 1994 and 1995 (Tables 1-4). Lythrum salicaria was ranked the highest at the strand at Cotter Road for both years (Tables 1,2). The dominant assemblages using the top three species and their importance values was broken into four categories: strand, shallow, mid and deep based on water depth from strand to open water (Table 6). Lythrum salicaria and Scirpus americanus were co- dominants in the strand community at each site during both years (Table 6). Eleocharis spp. was dominant at ‘both sites in 1995. Calamagrostis canadensis was dominant only at Cotter Road, and Juncus spp. was dominant at Vanderbilt. None of these species, except for Scirpus americanus, were among the top three dominants in shallow, mid or deep water habitats (Table 6). Scirpus americanus, Eleocharis smallii, E. erythropoda, Typha angustifolia, and Sagitaria Iatifolia were co-dominants in the shallow zone (Table 6). The mid zone dominant species were S. americanus, T. angustifolia, S. latifolia, E. smallii and 29 Nymphaea odorata. The dominant species in the deep zone were S. americanus, S. acutus, T. angustifolia and E. smallii. Table 6. Dominant assemblages using the top three species with the highest importance values for the four water level zones for each year. Strand Shallow Mid Deep Cotter '94 Cotter '95 Vanderbilt '94 Vanderbilt '95 L. salicaria C. canadensis S. americanus S. americanus E. smallii T. angustifolia S. americanus T angustifolia S. Iatifolia S. acutus T. angustifolia S. americanus L. salicaria E. erythropoda C. canadensis S. americanus E. erythropoda S. latifolia S. americanus T. angustifolia S. latifolia T. angustifolia S. acutus S. americanus S. americanus Juncus spp. L. Salicaria no sample taken no sample taken no sample taken S. americanus S. latifolia E. smallii S. americanus T. angustifolia E. smallii S. americanus L. salicaria T. angustifolia S. americanus T. angustifolia S. Iatifolia S. americanus N. odorata T. anguslifolia S. americanus E. smallii T. anguslifolia Zonation patterns in wetlands tend to be sharp and have abrupt boundaries that call attention to vegetation change and the uniqueness of each zone (Mitsch and Gosselink, 1993). This concept of zonation for this study has been applied to water level gradients and vegetation patchiness. In the shallow zone at Cotter road, S. americanus formed a monoculture with some open pockets of S. Iatifolia, E. smallii and T. angustifola in the more Open water areas. Patchincss was observed along each transect for both sites from the mid zone to open water. T. angustifola and Nymphaea odorata formed monocultures with minor species interspersed, while S. americanus, S. Iatifolia and E. smallii were usually found together. Species Area Curves Species area curves for both years and sites were similar within the strand community showing an increase in cumulative number of species as the number of quadrats sampled increased until the fifth and sixth quadrats (sampling area of 1.5 m ). There was little increase in cumulative number of species after six quadrats had been sampled (Figures 7a). In 1995, the water levels decreased and more plants germinated along the drier, exposed shore so the asymptote was higher for the strand community in 1995 than in 1994. Also, more plants were identified to species level in 1995 compared to 1994 which could partially account for the greater cumulative number of species in 1995 (Tables 2 and 4, Figure 7a). There was also a direct relationship between distance and depth. As distance increased from shore to open water, water depth increased gradually to 80-90 cm at the outer edge of the emergent zone. In 1994 samples were taken every 50 m and in 1995, samples were taken every 20 m so the sampling area increased in 1995 (Figure 7b and 7c). Although the number of quadrats sampled increased from 1994 to 1995, there is a resemblance in the shape of curve from year to year although the cumulative number of species sampled was greater within the 20-60 m sampling distance (Figure 7b). The increase in the cumulative number of species from quadrat twenty to twenty-one within the 80-120 m distance can be attributed to a shallow sand bar point along the transect where the water level decreased to 11 cm (Figure 7c). Other than that increase, the cumulative number of species for the 80-120 m distance was predictable given the relationship between distance and depth (Figure 7c). 31 533883 Baum N.NNN ENE? 32 Ba 33 NNN 3% 53 New 860% me 5:89: gnu—=83 05 39:8 023 8.8 860% .NN. 233m N.N..EN 2.. 55$ N.NNNENN 322.5 Na .2 a a N. e m v m N — c N N N N N N N N N e nae «tam u=€uvuu>+ .. t N mag 33% 3300+ 11 v vaa 3.3.— »:aaoefis lxl t e :3 33¢ 33:011. 1. a l 3 N1 Na x7 ix 1.. v— i w— t a— % ca 9 l «N i an 1 on I L ‘7 woods 10 '05} OAQIIIIIIIIIQ 32 .33 NNN N.NoNoE on boas N.NNN 39 E 8 cm bog :83 0.83 NNN—9:5 .227. Sou 853% mam: E co 3 E on Soc 32 v5 32 E 3%. 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L! _ m2: 23m 526 IT 32 .25. gigs; 1x1 -1 N 32 23. 5.5] x xl 1- n 1, v ,- m 1- e [I b -1 a ,1 a 1- S -- : l I N “ mazds JO 'oN upqnmng 34 DISCUSSION Plant Diversity The development of a plant community is characterized by many factors and conditions and include the seedbank viability and other propagules within the site, appropriate environmental conditions for germination and growth, and the replacement by plants of the same or different species as site conditions change in response to abiotic and biotic factors (Mitsch and Gosselink, 1993). This concept of succession dates back as early as 1917 when Gleason developed the hypothesis that individual species respond individualistically to changes along environmental gradients as an explanation for the distribution of plant species. From there, the continuum concept was developed (Whittaker, 1967) implying that the distribution of individual plant species directly responds to its environments, resulting in a continuum of overlapping species niches along environmental gradients. The emergent marsh community of the wetland fringe of Saginaw Bay changes along a depth gradient from the shoreline to the outer edge of the wetland. The highest diversity is at the shoreline in the strand community which is subject to alternate wetting and drying as lake levels rise and fall over short (seiche and storm surges) and long (seasonal and year to year) time periods. The diverse ecotonal community of the strand is comprised of a diverse mix of annuals and perennials with high stem density, and it is replaced by a community of perennials with fewer species present and with lower stem density as water depth increases until the emergent plant community is reduced to a few sparse, scattered stems of l-3 species at the outer edge of the marsh. Mine (1996) 35 described the general changes that occur along this gradient and divided the marsh into plant community zones that are projected to migrate shoreward or lakeward as lake levels rise or fall. Such general descriptions tend to mask the heterogeneity in the plant communities that exists within each plant community zone. I documented changes that occurred over a depth gradient that extended for 600- 800 m from the shoreline to the outer edge of the emergent zone at two sites from 1994 to 1995 when water level decreased by 15-20 cm. Over this short period of modest lake level changes, the plant communities did not migrate up or down slope as predicted. Instead, stem density and species richness increased dramatically for the strand and shallow water zones, perhaps from underground seed sources and/or from new shoots produced vegetatively, while plant communities that existed at depths of 25 cm or more in 1994 did not change much in 1995. Effects of Wave Energy Comparisons can be made between the Vanderbilt Park and Cotter Road sites with respect to wave energy and substrate. Keddy (1982), suggested that waves may affect shoreline plants directly by uprooting seedlings or indirectly by eroding fine sediments. Furthermore, exposure may be an important ecological factor affecting the within lake distribution of shoreline plants (Keddy, 1982). Keddy also believed that one of the most likely causes of variation in lakeshore vegetation aside from water depth is exposure to wave activity. Keddy hypothesized that this wave activity could have direct effects on plants by transporting seeds, uprooting seedlings and damaging mature plants. I observed this phenomenon at Vanderbilt Park in 1994 during large storm surges where 36 the vegetation was damaged and the tips or flowers were ripped off from the strong wave action. Wave activity also may indirectly have effects on erosion and deposition of sediments, nutrients and organic matter. I observed a difference in substrate between Cotter Road and Vanderbilt Park. At Cotter Road, the substrate was very sandy and firm with only small areas of organic deposits near the shore. At Vanderbilt Park, the substrate was very high in organic matter in protected areas shoreward of and in T ypha angustifolia stands and it was very difficult to walk the transects in these areas. The loose substrate was up to 60cm deep in places with high organic matter and detritus. In areas lakeward of the cattail stands, the substrate was also sandy and firm. Site Geographical Location The geographical location of the two sites may be important in determining substrate, patchiness and density and diversity along the shore. Cotter Road is located on the southwest shore of Saginaw Bay. The prevailing winds coming from the west tend to blow along the shore from west to cast into the southeast shore at Vanderbilt Park. Thus, Vanderbilt Park is in a much more exposed location than the Cotter Road site. ‘ I observed a large amount of detritus along the shore at Vanderbilt Park compared to Cotter Road. Most of the detritus was deposited along the strand and further inland by storm surges (personal observation). Cotter Road had a stable plant community along the shore and the Shallow zone consisting mainly of a dense stand of S. americanus. Vanderbilt park had less individual species within the shallow zone and tended to have more open water areas Within the patchy vegetation. Exposure to waves affects plant establishment, growth, 37 survival and dispersal directly as well as indirectly (Jupp and Spence, 1977; Keddy, 1982; Spence, 1982; Chambers, 1987). This may explain the absence of a large dense and stable shallow zone at Vanderbilt Park as compared to Cotter Road. Wetland Conservation Characterizing the plant community in Saginaw Bay is an essential component to the relevance of the environmental conservation for the site. Without a stable plant community, the entire wetland system is affected as evidenced by the effects of the storm surges in 1994 (Whitt, 1996). The coastal plant community acts as a buffer and protects the shoreline from long term erosion and instability. The importance of the coastal plant community is well documented as a staging, feeding and breeding area for waterfowl and other forms of aquatic life. Plans for successful wetland restoration for Great Lakes coastal wetlands need to be based on knowledge of how these coastal plant communities respond to water level changes and exposure to wave action and storm surges. The data collected for this thesis represent an essential first step in gaining the understanding of plant community dynamics in relation to water level changes and should be invaluable for restoration planning in the future. 38 - ll'lt-Kc "Int‘.V\¢. tyynuur'reaI'nfgg':c.1L-51..7.\.4_..‘.5.35..-.”cygaa.q.,k.g¢.fr. K"‘I!t'f\?“{""“ LITERATURE CITED 39 LITERATURE CITED Batterson, T.R., McNabb, CD. and EC Payne. 1991. Influence of water level changes on distribution of primary producers in emergent wetlands of Saginaw Bay. Michigan Academican 23:149-160. Barbour, M.G., Burke 1H. and W.D. Pitts. 1987. Terrestrial Plant Ecology. The Benjamin/Cummings Publishing Company, Inc. 634 pages. Burton, T.M. 1985. The effects of water level fluctuations on Great Lakes coastal marshes. Pages 3-13 in H.H. Prince and RM. D’Itri, editors. Coastal Wetlands. Lewis Publishers, Inc. Chelsea. Connell, J.H. 1978. Diversity in tropical rainforests and coral reefs. Science 199: 1302- 1310. Coops, H, Boeters, R, and H. Smit. 1991. Direct and indirect efl‘ects ofwave attack on helophytes. Aquatic Botany 41: 333-3 52. Curtis, IT, 1947. The palo verde forest type near Gonaives, Haiti, and its relation to the surrounding vegetation. Caribbean For., 8: 1-26. Enslin, B. and D. McIntosh.l982. Changes in aquatic vegetation in Quanicassee, Nayanquing Point and Widfowl Bay. Unpublished Report prepared for the East Central Michigan Planning and Development Region, October, 1982. Gleason, H. A, 1917. The structure and development ofthe plant association, Torrey Bat. Club Bull. 44: 463-481. Grieg-Smith, P. 1964. Quantitative Plant Ecology . Butterworth & Co. Publishers Ltd. 256 pages. Grime, J.P. 1979. Plant Strategies and Vegetation Processes. Chichester, UK: John Wiley and Sons. Grubb, PJ. 1977. The maintenance of species richness in plant communities: the importance of the regeneration niche. Biological reviews of the Cambridge Philosophical Society 52:107-145. PIroudova, Z. 1980. Occurrence of Sagitta'ia sagimfolia at difi‘erent depths of water. Folia Geobot. Phytotaxon. 15: 415-419. 40 Huston, M. 1979. A general hypothesis of species diversity. American Naturalist 113:8]- 101. Jaworski, E., and C.N. Raphael. 1978. Coastal wetlands value study in Michigan, phase 1: fish, wildlife, and recreational values of Michigan’s coastal wetlands. US. Fish Wild]. Serv., Twin Cities, MN. 209pp. Keddy, PA. 1982. Quarritfying within-lake gradients of wave energy: interrelationships of wave energy, substrate particle size and shoreline plants in Axe Lake, Ontario. Aquatic Botany 14:41-58. Keddy, PA and AA. Reznicek. 1982. The role of seed banks in the persistence of Ontario’s coastal plain flora. American Journal of Botany 67 2708-7 16. Keddy, RA and AA Reznicek. 1986. Great Lakes vegetation dynamics: the role of fluctuating water levels and buried seeds. Journal of Great Lakes Restoration 12(1);25-36. Minc, L.D. 1996. Michigan’s Great Lake Coastal Wetlands: Definition, Variability, and Classification. A report in 2 parts Submitted to Michigan Natural Features Inventory, October, 1996. Funded by EPA Great Lakes National Program Ofice (Federal Grant GL9 95810-02), through The Nature Conservancy’s Great Lakes Program Ofice. 143pp. Moore, D.RJ., and RA. Keddy 1989. The relationship between species richness and standing crop in wetlands: the importance of scale. Vegetatio 79:99-106. Shipley, B., Keddy, P.A, Gaudet, C. and D.RJ. Moore 1991. A model of species density in shoreline vegetation Ecology 72(5):]658-1667. Smith, L.M. and J.A Kadlec 1983. 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Plant species of the Saginaw Bay study areas at Cotter Road and Vanderbilt Park. Scientific Name Common Name status Acer rubrum red maple F AC Aster spp. aster OBL-FACW Calamagrostis canadensis blue-joint OBL Carex Iasiocarpa wooly-fi'uit sedge OBL Carex spp. sedge OBL-FACW Carex viridula little green sedge OBL Cirsium muficum swamp thistle OBL Cladium mariscoides smooth sawgrass OBL Convolulus arvense' field bindweed NI Camus stolomfera red-osier dogwood FACW Eleochan's calva spikerush OBL Eleochw'is erythropoda bald spikerush OBL Eleocharis obtusa blunt spikerush OBL Eleochw'is pauciflora few-flower spikerush OBL Eleochan’s anallii small's spikerush OBL Equisetwn sop. horsetail NI Eupatorium leucolepsis white-braced thorough NI Eupatorium perfoliatran common boneset FACW+ Erqxztoriran pilosum hairy thoroughwort F ACW+ Impatiens capensis touch-me-not FACW Juncus articukn‘us jointed rush OBL Juncus balticus baltic rush OBL Juncus eflilsus sofi msh OBL Juncus nodosus knotted rush OBL Leersia oryzoides rice cutgrass OBL Lobelia nuttaIIii nutall's lobelia NI Lycopus ameriamus arnerican bugleweed OBL Lysimachr'a quart-(flora prairie loosestrife OBL Lythrum salicaria purple loosestrife OBL Mentha arvensis field mint FACW Nymphaea odorata white water-lily OBL Panicum Iongrfolium panic grass OBL Potenfilla anserina silverweed FACW+ Sagittaria Iatrfolia arrowhead OBL Salix spp. willow OBL-FACW Scirpus acutus hardstern bulrush OBL Scirpus americanus three-square bulrush OBL Scirpus arrovirens green bulrush OBL Appendix 1. Can‘t. Scientific Name Common Name status Scutellaria galericulata marsh Skullcap OBL Solidago spp. goldenrod OBL-FACW Sparganium ewycarpum giant burreed OBL Spartina pectinata prairie cord grass FACW+ Stachys tennrfolia smooth hedgenettle OBL T eucrium canadense arnerican gerrnander FACW- T ”ha angusnfolia narrow-leaf cattail OBL unknown seedlings Obligate Wetland Occurs w/est. 99% probability in wetlands Facultative Wetland Occurs w/est. 679’r99% probability in wetlands Facultative Occurs w/est. 3496-6696 equal probability in wetlands and nonwetlands Facultative Upland 67%-99% probability in nonwetlands, l%-33% in wetlands ObligateUpland oocurs>99%innonwetlandsinthisregion No Indicator currently no indicator status 45 lulllililllllijlfllllllllll