Vegetation Response to the 1995 Drawdown of the 

Navigation Pool at Felsenthal National Wildlife 

Refuge, Crossett, Arkansas 

By Rebecca J. Howard and Christopher J. Wells 

Open-File Report 2007–1379 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2007 

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Suggested citation: 

Howard, R.J., and Wells, C.J., 2007, Vegetation response to the 1995 drawdown of the 

navigation pool at Felsenthal National Wildife Refuge, Crossett, Arkansas: U.S. Geological 

Survey Open-File Report 2007-1379, 52 p.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
iii 

Contents 

Abstract ...................................................................................................................... 1 

Introduction ............................................................................................................... 2

Methods ..................................................................................................................... 3 

Study Area and Experimental Design ............................................................ 3 

Data Collection .............................................................................................. 6 

Statistical Analysis ........................................................................................ 7 

Results ........................................................................................................................ 8 

 Transects and Plant Community Descriptions ............................................... 8 

 Transect and Elevation Effects ...................................................................... 19 

 Disturbance and Elevation Effects ................................................................. 23 

 Base Pool Stage Vegetation ........................................................................... 29 

 Seed Bank ...................................................................................................... 30 

 Soil Characteristics ........................................................................................ 33 

Discussion .................................................................................................................. 37 

Conclusions and Management Implications .............................................................. 41 

Acknowledgments ......................................................................................... ............ 41 

References Cited ........................................................................................................ 42 

Appendix 1. Description of 19 transects monitored at Felsenthal National Wildlife 

 Refuge from June 1995 to June 1996, indicating quadrat distance from base 

 marker and relative elevation ............................................................................... 45 

Appendix 2. Plant species percentage of frequency of occurrence at five sampling 

 times at Felsenthal National Wildlife Refuge ...................................................... 49 

Appendix 3. Plant species total cover summed over transects at five sampling times 

 at Felsenthal National Wildlife Refuge ............................................................... 51 
iv 

Figures 

1. Mean daily water levels recorded at Felsenthal lock and dam ............................. 4 

2. Map of Felsenthal National Wildlife Refuge showing approximate 

locations of transects ............................................................................................ 5 

3. View of transect 8 ................................................................................................ 9 

4. View of transect 10 .............................................................................................. 10 

5. Growth of Cyperus erythrorhizos at transect 6 .................................................... 15 

6. Total species richness by transect ........................................................................ 16 

7. Total vegetation cover by transect ....................................................................... 17 

8. Total Cyperus cover (includes C. erythrorhizos, C. iria, and Cyperaceae) 

by transect ............................................................................................................ 18 

9. Duncan’s multiple range test from an ANOVA of the effect of transects on 

 vegetation response .............................................................................................. 22 

10. View of transect 4b .............................................................................................. 24 

11. Species richness by elevation class on undisturbed and disturbed transects ....... 26 

12. Total vegetation cover by elevation class on undisturbed and 

disturbed transects ................................................................................................ 27 

13. Cyperus cover by elevation class on undisturbed and disturbed transects .......... 28 
v 

Tables 

1. Modified Daubenmire cover scale used to estimate species cover ...................... 6 

2. Location and description of permanent vegetation transects ............................... 11 

3. Plant species identified at 19 transects at Felsenthal Navigation Pool, 

 Felsenthal National Wildlife Refuge ................................................................... 12 

4. Five most frequently-occurring species and five species with the highest 

 total cover at five sampling times ........................................................................ 14 

5. Overall vegetation response at five sampling times on undisturbed transects 

and four sampling times on disturbed transects ................................................... 19 

6. Results of an ANOVA of undisturbed and disturbed transects during base 

pool water stage ................................................................................................... 20 

7. Results of repeated measures MANOVA of undisturbed and disturbed 

 transects during pool drawdown .......................................................................... 21 

8. Results of a repeated measures ANOVA of elevation effects on vegetation at 

 undisturbed transects ............................................................................................ 23 

9. Results of a paired t-test analysis of disturbance effect on vegetation 

 during pool drawdown at five paired transects .................................................... 25 

10. Vegetation response at five undisturbed and five disturbed transects ................. 25 

11 Count of species present in 20 or more quadrats summed across all 

 undisturbed transects in June 1995 or June 1996, plus the introduced 

 species Bacopa egensis ........................................................................................ 29 

12. Total cover at transects in June 1995 and June 1996 of species with 

 cover that exceeded 400 percent summed across all transects at either time, 

 plus the introduced species Bacopa egensis ........................................................ 30 

13. Species that germinated in soil collected at Felsenthal National Wildlife Refuge 

 in June and October 1995, and the presence of those species in the standing 

 vegetation during field sampling ........................................................................ 31 

14. The ten most-frequently germinating species in soil samples collected in June 

 and October 1995 at Felsenthal National Wildlife Refuge .................................. 32 
vi 

15. Species richness of seed bank samples and of standing vegetation in high 

 and low elevation quadrats ................................................................................... 33 

16. Soil characteristics at 14 transect locations at Felsenthal National Wildlife 

 Refuge, June 2005 ................................................................................................ 34 

17. Concentration of eight essential plant nutrients in soil collected in June 1995 

 at 14 transects at Felsenthal National Wildlife Refuge ........................................ 35 

18. Results of an ANOVA of the effects of transect and elevation on the content 

 of eight plant nutrients in soil at Felsenthal National Wildlife Refuge ............... 36 

19. Representation of Duncan’s multiple range test means comparisons by nutrient 

 from an ANOVA of transect effect on soil nutrient concentration at Felsenthal 

 National Wildife Refuge in June 1995 ................................................................ 36 

20. Precipitation by month in 1995 and 30 year (1961-1990) mean monthly 

precipitation in Crossett, Ark. ................................................................................ 39 

Conversion Factors 

SI to Inch/Pound

Multiply By To obtain 

Length 

centimeter (cm) 0.3937 inch (in.) 

millimeter (mm) 0.03937 inch (in.) 

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi) 

Area 

hectare (ha) 2.471 acre 

Horizontal coordinate information is referenced to the North American Datum of 

1983 (NAD 83) 
1

Vegetation Response to the 1995 Drawdown of the Navigation Pool at 

Felsenthal National Wildlife Refuge, Crossett, Arkansas

 

By Rebecca J. Howard and Christopher J. Wells 

Abstract 

 Felsenthal Navigation Pool (“the pool”) at Felsenthal National Wildlife Refuge near Crossett, 

Ark., was continuously flooded to a baseline elevation of 19.8 m (65.0 ft) mean sea level (m.s.l.) 

from late fall 1985, when the final in a series of locks and dams was constructed, until the 

summer of 1995. Water level within the pool was reduced by 0.3 m (1.0 ft) beginning July 5, 

1995, exposing about 1,591 ha (3,931 acres) of sediment; the reduced water level was 

maintained until October 25 of that year. A total of 15 transects was established along the pool 

margin before the drawdown, extending perpendicular from the pool edge to 19.5 m (64.0 ft) in 

elevation. Plant species composition and cover were recorded at six to seven quadrats on each 

transect; 14 of the transects were also monitored three times during the drawdown and in June 

1996. Soil near five of the original transects was disturbed two weeks into the drawdown by 

scraping the soil surface with a bulldozer. Soil cores were collected to characterize soil organic 

matter, texture class, carbon and nitrogen content, and plant nutrient concentrations; soil samples 

were also collected to identify species present in the seed bank prior to and during the 

drawdown. 

 Plant species, several of which were high quality food sources for waterfowl, colonized the 

drawdown zone within four weeks. Vegetation response, measured by species richness, total 

cover, and cover of Cyperus species, was often greater at low compared to high elevations in the 

drawdown zone; this effect was probably intensified by low rainfall during the summer of 1995. 

Vegetation response on the disturbed transects was reduced compared to that on the undisturbed 

transects. This effect was attributed to two factors: (1) removal of the existing seed bank by the 

disturbance technique applied and (2) reduced incorporation of seeds recruited during the 

drawdown because of unusually low summer rainfall. Seed bank studies demonstrated that 

several species persisted despite nearly 10 years of continual flooding, and that seed bank 

species richness increased during the drawdown. Analyses indicated that predominantly clay 

soils containing relatively low organic matter were present along the pool margin. Levels of the 

plant nutrients measured were consistent with normal values reported for soils. Although 

conclusions from this study are limited by its one-year time frame, it is unlikely that permanent 

change to plant community function in the drawdown zone resulted from the lowered water 

levels during the summer of 1995. While species composition in the summer following the 

drawdown differed from that prior to the drawdown, the plant community remained dominated 

by annual floating-leaved or submersed species. It is probable that any future decrease in 

summer water levels in the pool will result in increased growth of desirable waterfowl food 

plants, such as Cyperus erythrorhizos (red-root flat sedge) and Leptochloa fascicularis var. 

fascicularis (bearded sprangletop), in the drawdown zone. 
2

Introduction 

 Felsenthal National Wildife Refuge (NWR), near Crossett, Ark., was established with a 

primary objective of providing high quality habitat for wintering and resident waterfowl species. 

 Effective waterfowl habitat management requires ensuring that adequate food is present, 

including both macroinvertebrate (for example, insects, mollusks, isopods) and plant food 

sources. Plant food quality and quantity are influenced by seed bank composition, plant 

germination conditions, and plant growth and survival. Land managers within the lower 

Mississippi River Valley ecosystem use various methods to influence plant succession and 

composition in wetlands with the intent to increase habitat quality for various invertebrate and 

vertebrate species; methods include water level manipulation, prescribed fire, soil treatments 

such as disking, and vegetation plantings. These actions demonstrate recognition of the 

importance of disturbance regimes in affecting wetland plant community structure and function 

and in influencing biodiversity in wetland systems. Two management techniques widely used by 

land managers to improve wetland habitat quality for waterfowl include constructing greentree 

reservoirs in forested areas to manipulate water levels and seasonally flooding herbaceous 

habitats, a practice called moist-soil management. 

Greentree reservoirs (GTRs) are created by impounding bottomland forest habitat during the 

dormant season to increase food availability for migrating and wintering waterfowl (Fredrickson 

and Batema, 1992). Early reports on the effects of GTRs indicated either no impacts or positive 

impacts of the flooding regime on tree health and mast production (Broadfoot, 1958; Merz and 

Brakhage, 1964; Broadfoot, 1967). Later studies, however, demonstrated long-term negative 

impacts of GTR management on forest composition and structure (Malecki and others, 1983; 

Wigley and Filer, 1989; Young and others, 1995; King and Allen, 1996; King and others, 1998; 

Fredrickson, 2005; Gray and Kaminski, 2005; Ervin and others, 2006), including a shift to more 

flood-tolerant species and reduced woody species regeneration. Moist-soil management 

practices involve manipulating water depth within impoundments to stimulate growth of 

herbaceous plants from seeds or tubers present in the soil, thereby maximizing food production 

(Reineke and others, 1989). Several factors may influence the resulting vegetation community 

on moist-soil management units, including timing of the drawdown, seed or propagule 

availability, soil type, soil temperature, soil salinity, litter, and soil moisture level (Fredrickson, 

1991; Brock and others, 1994). Direct soil manipulation such as disking and tilling have also 

been used in moist-soil management to influence plant community composition and structure 

(Fredrickson and Taylor, 1982; Fredrickson and Reid, 1988; Gray and others, 1999). 

Nevertheless, a host of abiotic and biotic factors that affect seed germination and propagule 

success make it difficult to predict the outcome of moist-soil management practices. The 

correlation between composition of seed banks and standing vegetation often varies among sites 

within a wetland (Leck, 1989; Rossell and Wells, 1999) and over time (Leck and Simpson, 

1995). Predictions may be further complicated by hydrologic history that can also influence the 

composition of the seed bank and seed viability. Species richness (number of species) of 

freshwater marsh seed banks was found to decrease with increasing water depth (Wilson and 

others, 1993). Few viable seeds of emergent plants were found in sediments from a Texas 

reservoir following several years of inundation (van der Valk and Pederson, 1989). Schneider 

and Sharitz (1986) also noted that continuous flooding decreased incorporation of tree seeds in 

forested wetland seed banks. 
3

 Management actions in 1995 at Felsenthal NWR included an experimental drawdown of a 

large reservoir associated with the refuge GTR. This action represented implementation of 

moist-soil management practices. Several agencies were involved in assessing drawdown effects 

on navigation, habitat, water quality, recreation, cultural resources, and fish and wildlife 

resources. The objectives of this study were to (1) describe vegetation succession and soil 

characteristics within the zone exposed by the reduced water level, (2) determine the influence of 

soil elevation on plant species composition, (3) compare postdrawdown vegetation to the species 

composition of the available seed bank, and (4) quantify the effect of soil disturbance on plant 

community composition and structure. 

Methods 

Study Area and Experimental Design 

 Felsenthal NWR was established in 1975 to partially mitigate impacts of the U.S. Army 

Corps of Engineers’ (USACE) Ouachita-Black Rivers Navigation Project on bottomland forest 

habitat. The navigation project included construction of Felsenthal lock and dam in 1985, 

which, in combination with an earlier-constructed dam, resulted in flooding of refuge lands 

below 19.8 m (65.0 ft) m.s.l. Approximately 6,450 ha (15,938 acres) of bottomland forest 

habitat were permanently flooded by the resulting reservoir (King and others, 1998). The 

reservoir, Felsenthal Navigation Pool (hereafter referred to as “the pool”), is managed by the 

USACE Vicksburg District. Under the routine GTR management schedule, pool water level is 

held at 19.8 m through the spring, summer, and early fall each year. In early November, the 

water level is gradually raised to a maximum of 21.3 m (70.0 ft), held at this level for a few 

weeks, and then gradually lowered to reach base pool level in early March. As noted by King 

and others (1998), however, this schedule has been altered to allow extended flooding into spring 

during some years, and heavy rainfall events have prevented lowering water levels during other 

years. Under the GTR management schedule, the pool was continuously flooded to at least 19.8 

m from November 1985 until the summer of 1995 (fig. 1). On July 5, 1995, the USACE 

initiated a partial drawdown of the pool to reduce the water level by 0.3 m (1.0 ft). The target 

drawdown level was realized on July 15, 1995, and exposed about 1,591 ha (3,931 acres) of 

previously flooded soil (geographic information system [GIS] analysis conducted by the U.S. 

Geological Survey National Wetlands Research Center, Lafayette, La.). Water levels in the 

pool were raised beginning October 25, 1995, and the base water level of 19.8 m was reached on 

November 5; the pool was retained at this level until December 1, when water was gradually 

raised to reach a winter water level of 21.0 m (69.0 ft) in the GTR by January 1, 1996 (Felsenthal 

NWR Annual Narrative Report - Calendar Year 1995). 
Year

1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996

Pool Stage (m)

19

20

21

22

23

24

25

26

27

28

Pool Stage (ft)

65

70

75

80

85

90

Figure 1. Mean daily water levels recorded at Felsenthal lock and dam from 1985 to 1996. Major 

tic marks on the x axis indicate January 1, and minor tic marks indicate July 1 of each year. 

 Plant community composition and structure as well as environmental characteristics were 

monitored prior to the drawdown along 15 permanent transects (fig. 2) that were selected by 

refuge staff as characteristic of the pool margin. The base of each transect was located at the 

pool edge prior to the drawdown event (reference elevation 19.8 m), and transects extended 

perpendicular from the pool margin into the pool to end at 19.5 m (64.0 ft) in elevation. Global 

Positioning System (GPS) locations (NAD83) were determined for the transect bases; the 

readings were corrected by using real-time differential with the Vicksburg, Miss., broadcast site 

and were accurate within 1-5 m. Permanent 1-m2 sampling quadrats were located at the pool 

margin (base station or quadrat 0) for each transect and at decreasing elevation intervals of 

approximately 6.1 cm (0.2 ft). Elevation at each quadrat was measured with a laser level. Six 

quadrats, with the final quadrat located at about 19.5 m elevation, were initially established for 

each transect. The lower left corner of each quadrat was marked with a pin-flag, and the 

horizontal distance between quadrats was recorded. Quadrat elevation was measured again 

following drawdown; there was a liquid soil slurry at the sediment surface that consolidated 

upon drying, and postdrawdown elevations were often higher than those obtained prior to 

drawdown (that is, the soil slurry did not support the weight of the survey rod). For several 

transects, a seventh quadrat was added to sample the true lower extent of the drawdown. 

Considering the original pool edge as a reference elevation level of 30.5 cm (1.0 ft), 

postdrawdown quadrat elevations were classified into two categories: high (≥ 15.0 cm [0.5 ft]) 

and low (< 15.0 cm). 

4
Figure 2. Map of Felsenthal National Wildlife Refuge showing approximate locations of 

transects along the perimeter of Felsenthal Navigation Pool. Transect 13 was dropped from the 

study after initial measurements in June 1995 . 

5
6

 Two weeks following the drawdown, soil disturbance treatments were established for five 

transects that were accessible to heavy equipment. The disturbance consisted of scraping the soil 

surface with a bulldozer to create a strip about 10-m wide parallel to, and about 20 m to the right 

of, the original transect. The five paired transects were identified by following the transect 

number designation with the letter “a” for undisturbed transects and the letter “b” for disturbed 

transects. Vegetation at one of the original transects (transect 13) was heavily impacted by rice 

(Oryza sativa) planting and the construction of a waterfowl trapping station immediately 

following the drawdown and consequently was dropped from the study. As a result, 19 transects 

were monitored following the drawdown. 

Data Collection 

 A vegetation survey was conducted on the original 15 transects prior to the initiation of the 

pool drawdown, beginning June 26, 1995. Species composition was recorded, and cover class of 

all species was estimated in each quadrat by using a modified Daubenmire cover scale (Bonham, 

1989) (table 1). Cover classes for exposed soil, standing water, and dead vegetation were also 

recorded. In June 1995, a soil core (9-cm diameter by 15-cm deep) was collected outside each 

quadrat to determine soil organic matter, and carbon and nitrogen content. This core was also 

used to measure the concentration of the plant nutrients Cu, Zn, Mn, Fe, P, Mg, Ca, and K (listed 

in order of increasing concentration required by plants for growth and metabolism). An 

additional core was collected outside quadrat 1 (high elevation, about 24 cm) and quadrat 4 (low 

elevation, about 6 cm) at each transect for seed bank analysis. A final soil core was collected 

midtransect, outside quadrat 2 (about 18 cm elevation), for analysis of particle size distribution 

of the soil mineral fraction (that is, sand, silt and clay content). All soil samples were stored on 

ice in the field and refrigerated upon return to the laboratory until analysis. No initial data were 

collected for the areas designated as soil disturbance treatments. 

Table 1. Modified Daubenmire cover scale used to 

estimate species cover. Classes may sum to greater than 

100 percent cover because different height strata may 

overlap. 

Cover Class Percent Cover 

Class Midpoint 

Percent 

P <1 0.5 

1 1 - 10 4.5 

2 11 - 25 18 

3 26 - 50 38 

4 51 - 75 63 

5 > 75 88 

 
7

 Subsequent to pool drawdown, transects with soil disturbance were established near five of 

the original transects and all 19 transects were sampled at approximately 6-week intervals 

beginning August 1 (time 2), September 12 (time 3), and October 23 (time 4). Plant species 

composition and cover were measured during all sampling events. In October, soil core samples 

were collected outside quadrat 0 (30.5 cm elevation) and quadrat 5 (about 0 cm elevation) for 

seed bank analysis, and outside quadrat 4 (about 6 cm elevation) for determination of organic 

matter and carbon and nitrogen content. The soil core used for sample collection was 2 cm in 

diameter and 15 cm deep; to compensate for the smaller sample size compared to the June soil 

samples, three cores were taken at each location and combined prior to analyses. Species 

composition and cover were sampled a final time in June 1996 (time 5) at base pool water level. 

 Species composition of the seed bank was determined by using the seedling emergence 

method (Poiani and Johnson, 1988). Soil cores were stored about 3 months at 7 °C; following 

cold storage, the samples were mixed with tap water, and large plant tissues were removed to 

prevent regeneration from remnant rhizomes. The resulting slurry was evenly spread over 

potting soil in standard plastic flats (25.4-cm by 25.4-cm by 5.1-cm deep). The flats were 

randomly arranged in a greenhouse in Lafayette, La. on a plastic-lined table, and water on the 

table was maintained at a constant depth of 2 cm by adding tap water. A water-cooling system in 

the greenhouse kept the maximum temperature below 35 °C. Cover class of all seedlings was 

estimated after 6 weeks; all seedlings were then removed from the trays. Cover was estimated a 

second time after an additional 8 weeks of growth. The two seed bank experiments were 

initiated on September 22, 1995 (June samples) and April 8, 1996 (October samples). 

 Soil cores for physical and chemical analyses were dried at 55 °C to a constant weight. The 

dried samples from all quadrats were homogenized by mixing and then were divided into two 

subsamples. Organic matter of one subsample was determined by applying loss upon ignition 

techniques (Soil and Plant Analysis Council, 1992). The second soil subsample was sieved 

through a 2-mm mesh screen and then further divided into two subsamples. Total soil nitrogen 

and carbon content was obtained for one subsample by using a CE 440 Elemental Analyzer 

(Leeman Labs, Inc., Lowell, Mass.). Micronutrients were extracted from the second by using 

nitric acid and microwave digestion (Nieuwenhuize and others, 1991), and nutrient 

concentrations in the extractions were evaluated with an inductively-coupled argon plasma 

spectrometer (ICP) (Optima 3000, PerkinElmer, Inc., Waltham, Mass.). Organic matter in the 

samples collected for particle size distribution was removed by digestion in household bleach. 

The sand fraction was then separated with wet sieving, and the remaining clay and silt fractions 

were determined by using the pipette method (Schumacher and others, 1995). 

Statistical Analysis 

 All analyses were conducted by using SAS/STAT® software, Version 6 (SAS Institute, Inc., 

 Cary, N.C.). A multivariate two-way nested analysis of variance (ANOVA) model was used to 

analyze vegetation prior to (June 1995, time 1) and following (June 1996, time 5) the drawdown, 

with transect and elevation class (low or high) within transect as independent variables. The 

analyses were conducted by using the general linear model procedure (Proc GLM) of SAS 

software. A significance level of α = 0.05 was used for these and all subsequent analyses; the 

significance level was adjusted for the number of comparisons when appropriate. When 

required, appropriate variable transformations were made to conform to model assumptions. To 
8

determine how vegetation responded during the drawdown (times 2-4), a repeated-measure 

multivariate ANOVA (MANOVA) model was applied. Disturbed and undisturbed transects 

were analyzed separately. In all vegetation analyses, the cover class variable for each species 

was converted to the percentage of cover represented by the midpoint of the class range (for 

example, class 2 was converted to 18 percent); Class P was assigned a cover value of 0.5 percent 

(table 1). The dependent variables for vegetation analyses were species richness, percentage of 

total vegetation cover, and percentage of Cyperus cover, defined as the sum of Cyperus iria, 

Cyperus erythrorhizos, and Cyperaceae (plants identified to family level only) cover values. To 

further investigate the effect of soil elevation, transects were pooled, and a one-way ANOVA 

was performed by using elevation class as an independent variable. Disturbed and undisturbed 

transects were again analyzed separately, and repeated measures techniques were applied for 

times 2-4. The effect of soil disturbance and disturbance by elevation on vegetation for the five 

transects that included a parallel transect impacted by soil scraping were examined with paired ttests. 

 The impact of the 1995 drawdown on pool vegetation in 1996 was examined by 

characterizing the plant community at two times during normal pool stage (times 1 and 5 [June 

1995 and 1996]). Data from disturbed transects were not included in these analyses. The 

community was characterized two ways: as species present in 20 or more quadrats summed 

across all transects at either time, and as species with total cover greater than 400 percent 

summed across all transects at either time. The nonnative species Bacopa egensis was also 

included, regardless of its frequency or cover value. The quadrat count data were adjusted to 

equal sample sizes and analyzed as a categorical two-way ANOVA by using a chi-square test, 

and the cover data were analyzed by using paired t-tests. 

 The effect of elevation on seed bank species richness was examined by using a one-way 

ANOVA with elevation class as the independent variable. Seed bank species richness was 

compared to that of the standing crop in both June and October by using paired t-tests; paired ttests were also conducted to describe the effect of disturbance on seed bank species richness 

(October samples). 

 Two-way ANOVA was used to examine the effect of transect and elevation (nested within 

quadrat) on soil variables, with dependent variables of soil percentage of carbon, percentage of 

nitrogen, nutrient concentration (P, K, Ca, Mg, Na, Cu, Fe, Mn, and Zn), and organic matter; no 

analyses of soil percentage of sand, silt, and clay were performed because only a single data 

point per transect was obtained for each variable. Paired t-tests were used to examine the effect 

of disturbance on soil percent carbon and nitrogen content and percent organic matter. 

Results 

Transect and Plant Community Descriptions 

 Plants quickly colonized undisturbed areas of the drawdown zone (figs. 3 and 4). The GPS 

location of the base quadrat for the 19 transects and length of each transect are listed in table 2. 

Relative elevation of the quadrat locations in reference to the transect base station ranged from 

30.48 cm (1 ft) to -5.49 cm (-0.18 ft) (appendix 1). We identified 63 vascular plants and 2 

bryophytes within quadrats (table 3); 13 of the vascular plants were identified only to genera or 
family level, and one species was unknown. Species frequency, defined as the percentage of 

total quadrats (all transects) in which a species was found, ranged from 0 to 89.6 percent (Wolffia

sp., June 1996) during the study (appendix 2); total cover by species summed across all transects 

ranged from 0 to 3,324 percent (Ludwigia peploides, August 1995) (appendix 3). While flooded 

in June 1995 and 1996, the most frequent species and species with the highest cover were 

primarily submersed or floating; during the drawdown, emergent species became common (table 

4 and fig. 5). 

Figure 3. View of transect 8 (specific location on the transect varied with each 

photograph). A, June 1995. B, August 1995. C, October 1995. D, June 1996. 

9
Figure 4. View of transect 10 (specific location on the transect varied with each 

photograph). A, June 1995. B, August 1995. C, September 1995. D, October 1995. E, 

June 1996. 

10
11

Table 2. Location and description of permanent vegetation transects. 

[Paired transects that included a soil disturbance treatment are indicated by letters next to the 

transect number; a = undisturbed, b = disturbed. Abbreviations are: Trans = transect number, 

Quads = number of quadrats located on transect, Northing and Easting are UTM coordinates, 

Bearing is compass bearing, and Length is distance from base marker to final quadrat] 

Trans Quad Northing Easting Bearing 

Length 

(m) 

1 7 578980 3659052 20 29.4 

2a 7 577580 3660694 60 51.1 

2b 7 -- -- 60 64.9 

3a 7 576991 3661631 90 111.0 

3b 6 -- -- 90 96.0 

4a 7 578053 3663084 105 26.9 

4b 7 -- -- 105 19.6 

5 7 578910 3663903 179 51.5 

6 6 580431 3665170 167 77.9 

7 6 579314 3661738 208 82.3 

8 7 581031 3662675 55 223.6 

9 7 582413 3662114 348 134.3 

10 7 582620 3661534 194 22.0 

11 7 582333 3660180 96 36.7 

12 6 584843 3666320 0 19.4 

14a 7 585851 3666656 270 69.0 

14b 7 -- -- 270 46.4 

15a 7 585845 3664597 280 32.0 

 15b 7 -- -- 280 29.6 
12

Table 3. Plant species identified at 19 transects at Felsenthal Navigation Pool, Felsenthal 

National Wildlife Refuge, Crossett, Ark. 

[Plant names according to Integrated Taxonomic Information System (2007). Some plants were 

identified to family or genus only. Life form designations are: E = emergent herbaceous, F = 

floating-leaved, S = submersed aquatic, W = woody] 

 

Species 

Life 

Form Common Name Code 

Vascular: 

Ammannia coccinea Rottb. E purple ammannia Amco

Azolla caroliniana Willd. F Carolina mosquitofern Azca 

Bacopa egensis (Poepp.) Pennell E Brazilian waterhyssop Baeg 

Bacopa rotundifolia (Michx.) Wettst. E disk waterhyssop Baro 

Bidens aristosa (Michx.) Britt. E bearded beggarticks Biar 

Brunnichia ovata (Walt.) Shinners W redvine Brov 

Cabomba caroliniana Gray S Carolina fanwort Caca 

Carex sp. E sedge Casp 

Cephalanthus occidentalis L. W common buttonbush Ceoc 

Ceratophyllum demersum L. S common hornwort Cede 

Cyperaceae E sedge Cy 

Cyperus erythrorhizos Muhl. E redroot flatsedge Cyer 

Cyperus iria L. E ricefield flatsedge Cyir 

Diodia teres Walt. E rough buttonweed Dite 

Diospyros virginiana L. W common persimmon Divi 

Echinochloa crus-galli (L.) Beauv. E barnyard grass Eccr 

Echinodorus cordifolius (L.) Griseb. E creeping burhead Ecco 

Eclipta prostrata (L.) L. E yerba de tajo Ecpr 

Eleocharis microcarpa Torr. E smallfruit spikerush Elmi 

Eleocharis obtusa (Willd.) J.A. Schultes E blunt spikerush Elob 

Fimbristylis miliacea (L.) Vahl E grasslike fimbry Fimi 

Gleditsia aquatica Marsh. W water locust Glaq 

Heteranthera reniformis Ruiz & Pavon E kidneyleaf mudplantain Here 

Hibiscus sp. E rosemallow Hisp 

Hydrolea quadrivalvis Walt. E waterpod Hyqu 

Ipomoea sp. E morning-glory Ipsp 

Juncus sp. E rush Jusp 

Leersia oryzoides (L.) Sw. E rice cutgrass Leor 

Leptochloa fascicularis var. fascicularis 

 (Lam.) Gray 

E bearded sprangletop Lefa 

Limnobium spongia (Bosc) L.C. Rich. ex Steud. F frogbite Lisp 

Lindernia dubia (L.) Pennell E yellowseed false pimpernel Lidu 

Ludwigia decurrens Walt. E wingleaf waterprimrose Lude 

Ludwigia leptocarpa (Nutt.) Hara E anglestem waterprimrose Lule 

Table 3. Continued. 
13

Species 

Life 

Form Common Name Code 

Ludwigia palustris (L.) Ell. E marsh seedbox Lupa 

Ludwigia peploides (Kunth) Raven E creeping waterprimrose Lupe

Ludwigia sphaerocarpa Ell. E globefruit primrose-

 willow

Lusp

Ludwigia uruguayensis (Camb.) Hara E Uruguay waterprimrose Luur

Mikania scandens (L.) Willd. E climbing hempweed Misc

Mimosa strigillosa Torr. & Gray E herbaceous mimosa Mist

Myriophyllum sp. S watermilfoil Mysp

Najas sp. S water nymph Nasp

Panicum sp. E panicgrass Pasp

Planera aquatica J. F. Gmel. W planertree Plaq

Pluchea foetida (L.) DC E stinking camphorweed Plfo

Poa annua L. E annual bluegrass Poan

Poa autumnalis Muhl. ex. Ell. E autumn bluegrass Poau

Poaceae E grasses Po

Potamogeton sp. S pondweed Posp 

Rhynchospora sp. E beaksedge Rhsp

Sagittaria graminea Michx. E grass-leaf arrowhead Sagr

Sagittaria latifolia Willd. E broadleaf arrowhead Sala

Sagittaria sp. E arrowhead Sasp

Sesbania exaltata (Raf.) Rydb. ex A.W. Hill E hemp sesbania Seex

Sphenoclea zeylanica Gaertn. E chickenspike Spze

Spirodela polyrrhiza (L.) Schleid. F greater duckweed Sppo

Taxodium distichum (L.) L.C. Rich. W bald cypress Tadi

Triadenum walteri (J.G. Gmel.) Gleason E greater marsh St. 

 Johnswort

Trwa

Utricularia gibba L. S humped bladderwort Utgi

Utricularia inflata Walt. S swollen bladderwort Utin

Vitis rotundifolia Michx. W muscadine grape Viro

Wolffia sp. F watermeal Wosp

Xanthium strumarium L. E rough cocklebur Xast

---- unknown dicot Uk

Bryophytes: 

Riccia sp. riccia Rici

Ricciocarpos sp. ricciocarpus Rico
14

Table 4. Five most frequently-occurring species and five species with the highest total cover at 

five sampling times, listed in decreasing order. 

[Some plants were identified to family or genus only. A slash indicates species with equal 

frequency or total cover measures] 

 

Month Frequency Total Cover

June 1995 Spirodela polyrrhiza Spirodela polyrrhiza

Ludwigia palustris Eleocharis microcarpa

Limnobium spongia Najas sp.

Utricularia gibba Ludwigia palustris

Wolffia sp. / Eleocharis microcarpa Limnobium spongia

August 1995 Ludwigia peploides Ludwigia peploides 

Eleocharis microcarpa Eleocharis microcarpa 

Cyperaceae Ludwigia palustris 

Spirodela polyrrhiza / Ludwigia palustris Sagittaria latifolia

Bidens aristosa Spirodela polyrrhiza

September 1995 Ludwigia peploides Ludwigia peploides 

Cephalanthus occidentalis Cyperus iria 

Cyperus iria Eleocharis microcarpa 

Bidens aristosa Cephalanthus occidentalis 

Eleocharis microcarpa Sphenoclea zeylanica 

October 1995 Cyperus erythrorhizos Cyperus erythrorhizos 

Cephalanthus occidentalis Cephalanthus occidentalis 

Triadenum walteri Eleocharis microcarpa

Eleocharis microcarpa / Eclipta prostata Fimbristylus miliaceae / 

Triadenum walteri 

Bidens aristosa Leptochloa fascicularis v. 

fascicularis 

June 1996 Wolffia sp. Utricularia inflata 

Spirodela polyrrhiza Wolffia sp.

Utricularia inflata Spirodela polyrrhiza 

Ludwigia peploides Ludwigia peploides 

Limnobium spongia / Azolla caroliniana Potomogeton sp.
Figure 5. Growth of Cyperus erythrorhizos at transect 6 in October 1995. 

 Species richness within quadrats ranged from 0 to a maximum of 14 (June 1995), 10 (August 

1995), 13 (September 1995), 9 (October 1995), and 10 (June 1996); mean species richness was 

higher during flooded conditions compared to the drawdown at several transects (fig. 6). 

Patterns in total cover by transect (fig. 7) resembled those of species richness. Cyperus species 

cover was very sparse prior to the drawdown, but composed more than 50 percent of total cover 

in some transects in September and October (fig. 8); Cyperus was absent during sampling in 

June 1996. Overall means for the three vegetation response measures in the 14 undisturbed 

transects exceeded those in disturbed transects at all measurement times (table 5). 

15
June 1995

2

4

6

8

10

September 1995

Species Richness

2

4

6

8

10

June 1996

Transect

1 2a 2b 3a 3b 4a 4b 5 6 7 8 9 10 11 12 14a 14b 15a 15b

2

4

6

8

10

October 1995

2

4

6

8

10

August 1995

2

4

6

8

10

Figure 6. Total species richness (mean ± 1 SE) by transect at five times. The letter “a” indicates 

the undisturbed transect for the five paired transects; disturbed transects are indicated by the 

letter “b” and by hatching. 

16
October 1995

40

80

120

160

200

August 1995

40

80

120

160

200

September 1995

Total Cover (percent)

40

80

120

160

200

June 1996

Transect

1 2a 2b 3a 3b 4a 4b 5 6 7 8 9 10 11 12 14a 14b 15a 15b

40

80

120

160

200

June 1995

40

80

120

160

200

Figure 7. Total vegetation cover (mean ± 1 SE) by transect at five times. The letter “a” 

indicates the undisturbed transect for the five paired transects; disturbed transects are indicated 

by the letter “b” and by hatching. Cover can exceed 100 percent because various species may be 

present in different strata. 

17
June 1995

1

2

August 1995

8

16

24

32

40

September 1995

Cyperus Cover (percent)

20

40

60

80

October 1995

Transect

1 2a 2b 3a 3b 4a 4b 5 6 7 8 9 10 11 12 14a 14b 15a 15b

20

40

60

80

Figure 8. Total Cyperus cover (mean ± 1 SE; includes Cyperus erythrorhizos, Cyperus iria, and 

Cyperaceae) by transect at five times. The letter “a” indicates the undisturbed transect for the 

five paired transects; disturbed transects are indicated by the letter “b” and by hatching. Note 

different scales on y axis. 

18
19

Table 5. Overall vegetation response (mean ± 1 SE) at five sampling times on undisturbed (n = 

84 in June 1995; n = 95 at all other times) and four sampling times on disturbed (n = 31) 

sampling quadrats. 

[Abbreviations are: Rich = species richness, Cov = total vegetation cover (percent), and CyCov 

= Cyperus cover (percent)] 

Time Rich Cov CyCov 

Undisturbed Transects 

June 1995 5.7 ± 0.2 106.4 ± 5.8 0.2 ± 0.1

August 1995 3.8 ± 0.2 89.0 ± 4.8 2.9 ± 1.0

September 1995 4.8 ± 0.3 97.5 ± 4.8 24.5 ± 3.5

October 1995 2.8 ± 0.3 53.6 ± 4.8 22.5 ± 3.5

June 1996 5.6 ± 0.2 110.6 ± 7.0 0.0 ± 0.0

Disturbed Transects 

August 1995 0.8 ± 0.2 4.8 ± 3.0 0.0 ± 0.0

September 1995 1.8 ± 0.4 11.1 ± 4.5 1.2 ± 0.6

October 1995 0.7 ± 0.3 7.8 ± 4.3 1.7 ± 1.2

June 1996 5.0 ± 0.3 81.9 ± 10.5 0.0 ± 0.0

Transect and Elevation Effects 

 In June 1995, when the pool was at base level, vegetation response varied by elevation (table 

6). Significant responses consisted of greater total cover (percentage) at low elevation (217.3 ± 

39.8; mean ± 1 SE) compared to high elevation (65.5 ± 22.5) in transect 11, and greater total 

cover at high elevation (139.8 ± 28.8) compared to low elevation (25.5 ± 10.5) in transect 4a. In 

June 1996, when the pool again was flooded to base level, vegetation response (richness and 

total cover) varied by transect location for undisturbed transects (table 6). Mean species richness 

in undisturbed transects ranged from 3.2 ± 0.4 (transect 7) to 7.4 ± 0.6 (transect 1), with overlap 

among transects with intermediate values (fig. 6). Although there was a significant overall 

elevation effect for disturbed transects (table 6), when the alpha level was adjusted by the 

number of pairwise comparisons (five comparisons, α = 0.01), no transects were significantly 

different from the others. 
20

Table 6. Results of an analysis of variance (F values) of 

undisturbed and disturbed transects during base pool water stage in 

June 1995 and 1996. 

[Abbreviations are: Trans = transect and Elev = elevation class. 

The significance value is P < 0.05*] 

Source June 1995 June 1996

Undisturbed Transects 

Trans 1.32 3.46*

Elev(Trans) 1.64* 1.51

Disturbed Transects 

Trans -- 2.51

Elev(Trans) -- 3.15*1

1

Pairwise comparisons not significant. 

 During the drawdown, transect and the time and elevation interaction significantly affected 

vegetation response on undisturbed transects; vegetation on the disturbed transects was not 

affected (table 7). For the undisturbed transects, there were often overlapping groups of 

transects with similar mean values for each of the vegetation variables (fig. 9), and no consistent 

patterns in groupings across time were apparent. Significant elevation effects at a particular time 

were found in undisturbed transects for total cover in August and for Cyperus cover in August 

and September. In August, total cover (percentage) was greater in the high (98.2 ± 23.8) 

compared to low (5.3 ± 4.8) elevation class in transect 9; no other significant responses were 

identified for this variable. Elevation affected Cyperus cover in three transects, 5, 7, and 12, in 

August and September; in all cases, cover was lesser at high compared to low elevation. 

Looking at response over time, elevation significantly affected vegetation response for seven 

time intervals (table 8). While the results are difficult to present in detail, general patterns were 

evident. Richness increased from August to September at both elevation classes, but the 

magnitude of the increase was greater at low compared to high elevations. From September to 

October, richness decreased at high elevation at all four transects, while at low elevation it 

decreased at three transects and remained steady at the fourth. At two of the transects where 

richness decreased over time at both elevations, the magnitude of change was greater at low 

compared to high elevation. Total cover from August to September increased or remained 

relatively constant at low elevations, but decreased at high elevations; this pattern was also 

evident from September to October with the exception of transect 1, where cover decreased at 

both elevations. Cyperus cover increased at both time intervals, to a greater magnitude at low 

compared to high elevations. 
21

Table 7. Results of repeated measures multiple analysis of variance (F values) 

of undisturbed and disturbed transects during pool drawdown, in August, 

September, and October 1995. 

[Abbreviations are: Trans = transect and Elev = elevation class. Significance 

values are P < 0.05* and P < 0.0001**] 

 

Source Undisturbed Transects Disturbed Transects

Trans 1.94* 0.73

Elev(Trans) 2.44** 1.33

Time1 -- --

Time*Trans 1.03 -- 

Time*Elev(Trans) 2.67** 0.74

1

 Insufficient degrees of freedom to estimate effect. 
A. August 1995

B. September 1995

C. October 1995

2a 15a 14a 4a 8 1 3a 10 7 9 12 5 11 6

Total Cover

4a 6 7 5 12 8 11 1 15a 10 2a 3a 14a 9

Cyperus Cover

12 5 1 10 4a 11 7 15a 2a 8 9 14a 6 3a

Species Richness

5 4a 10 1 6 12 11 7 9 8 15a 2a 14a 3a

Total Cover

6 5 4a 7 12 11 1 10 15a 9 8 3a 14a 2a

Cyperus Cover

12 1 5 11 10 4a 8 7 2a 15a 9 6 3a 14a

Species Richness

5 12 4a 1 6 11 7 15a 2a 9 10 8 14a 3a

Total Cover

6 5 4a 7 12 11 9 1 15a 8 10 2a 14a 3a

Cyperus Cover

12 7 5 4a 15a 6 8 11 1 3a 2a 9 14a 10

Species Richness

Figure 9. Duncan’s multiple range comparisons from an analysis of variance of vegetation 

response at undisturbed transects (noted by an “a” in paired transects) along the edge of 

Felsenthal Navigation Pool. Lines connect transects with similar means for the three variables—

species richness, total cover, and Cyperus cover—at three times during the pool drawdown. 

Transects are ordered from highest to lowest value. 

22
23

Table 8. Results of repeated measures analysis of variance of elevation 

effect on vegetation at undisturbed transects (noted by an “a” in paired 

transects) at Felsenthal Navigation Pool. Transects listed are those that 

had a significant effect on the response over the time interval indicated. 

[Times are: 2 = August 1995; 3 = September 1995; and 4 = October 1995] 

 

Response Time Interval Transect

Species richness 2 - 3 1, 9, 11 

3 - 4 1, 5, 7, 10 

Total cover 2 - 3 2a, 7, 14a, 15a 

2 - 4 7, 8, 9 

3 - 4 1, 6, 9 

Cyperus cover 2 - 3 5, 7, 12 

2 - 4 5, 7, 9, 12 

 When undisturbed transects were pooled, elevation did not affect vegetation response in June 

1995 (P = 0.2869) or June 1996 (P = 0.3595). Repeated measures analysis of data collected 

during the drawdown indicated a significant elevation effect (P = 0.0225) across time for the 

undisturbed transects. These results were consistent with those from the earlier analyses, 

indicating that species richness and total cover increased from August to September, to a greater 

extent in low compared to high elevations. Cyperus cover increased from August to September at 

low elevation but decreased at high elevation. Elevation did not affect vegetation response when 

disturbed transects were pooled, either during the drawdown (P = 0.3573) or in June 1996 (P = 

0.5620). 

 

Disturbance and Elevation Effects 

 Disturbance, which consisted of scraping the soil surface with a bulldozer, significantly 

affected vegetation response during the pool drawdown on the five paired transects (fig. 10 and 

table 9). Soil disturbance decreased species richness at all three times and decreased total cover 

in August and September (table 10). Examining disturbance by elevation class, species richness 

was greater in undisturbed compared to disturbed transects at high elevation all three times 

during the drawdown and in August and October at low elevations (fig. 11). Total cover was 

greater at undisturbed transects in both elevation classes in August and September; in October, 

however, cover was greater in undisturbed transects only at low elevations (fig. 12). Disturbance 

did not significantly affect Cyperus species cover in either elevation class (fig. 13). In June 

1996, no effect of disturbance on species richness (P = 0.4658) or total cover (P = 0.2874) was 

identified. 
Figure 10. View of transect 4b (specific location on the transect varied with each 

photograph). A, August 1995. B, October 1995. 

24
25

Table 9. Results of a paired t-test analysis (t values) of disturbance effect on vegetation during 

pool drawdown, in August, September, and October 1995, at five paired transects. Significance 

value is P < 0.05*. 

 

Month Species Richness Total Cover Cyperus Cover

August 5.47* 10.56* 1.00 

September 2.76* 3.72* 1.14 

October 4.41* 2.43 1.09 

Table 10. Vegetation response (mean ± 1 SE) at five undisturbed (“undisturb”) and five 

disturbed (“disturb”) transects. Data were collected in August, September, and October 1995, 

and June 1996. Significant differences between undisturbed and disturbed transects from paired 

t-test analysis are indicated by dissimilar letters. 

 

Species Richness Total Cover (percent) Cyperus Cover (percent)

Month Undisturb Disturb Undisturb Disturb Undisturb Disturb

Aug. 3.5 ± 0.3 a 0.8 ± 0.2b 112.1 ± 6.8a 4.8 ± 3.0b 4.8 ± 2.6 0.0 ± 0.0 

Sept. 3.7 ± 0.3a 1.8 ± 0.4b 79.0 ± 8.9a 11.1 ± 4.5b 15.0 ± 5.2 1.2 ± 0.6 

Oct. 1.8 ± 0.3a 0.7 ± 0.3b 39.9 ± 7.6 7.8 ± 4.3 12.3 ± 4.7 1.7 ± 1.2 

June 5.4 ± 0.3 5.1 ± 0.3 101.7 ± 11.1 84.6 ± 10.4 0.0 ± 0.0 0.0 ± 0.0 
Disturbed

August 1995

2

4

6

8

September 1995

Species Richness 2

4

6

8

October 1995

2

4

6

8

June 1996

H L

2

4

6

8

Elevation Class

H L

a

b

a

b

June 1995

2

4

6

8

Undisturbed

a a

b

b

b

a

Figure 11. Species richness (mean ± 1 SE) by elevation class on undisturbed (n = 5) and 

disturbed (n = 5) transects at five times (disturbed transects not sampled in June 1995). 

Elevation classes are: H (high) > 15 cm [0.5 ft] and L (low) < 15 cm. Significant differences 

between undisturbed and disturbed transects by elevation class are indicated by dissimilar letters. 

26
August 1995

8

16

24

32

Disturbed

June 1995

40

80

120

160

200

Undisturbed

August 1995

40

80

120

160

September 1995

Total Cover (percent)

40

80

120

160

October 1995

40

80

120

160

June 1996

Elevation Class

H L

40

80

120

160

September 1995

8

16

24

32

October 1995

8

16

24

32

June 1996

Elevation Class

H L

40

80

120

160

a

a

b

a

b

b

b

b

a

a

Figure 12. Total vegetation cover (mean ± 1 SE) by elevation class on undisturbed (n = 5) and 

disturbed (n = 5) transects at five sampling times (disturbed transects not sampled in June 1995). 

 Elevation classes are: H (high) > 15 cm [0.5 ft] and L (low) < 15 cm. Note different y-axis 

scales for undisturbed versus disturbed transects. Significant differences between undisturbed 

and disturbed transects by elevation class are indicated by dissimilar letters. 

27
Disturbed

0.5

1.0

1.5 Undisturbed

August 1995

4

8

12

September 1995

Cyperus Cover (percent)

8

16

24

32

October 1995

H L

8

16

24

32

H L

Elevation Class

June 1995

Figure 13. Cyperus cover by elevation class (mean ± 1 SE) on undisturbed (n = 5) and disturbed 

(n = 5) transects at five sampling times (disturbed transects not sampled in June 1995; no 

Cyperus was present on disturbed transects in August 1995). Elevation classes are: H (high) >

15 cm [0.5 ft] and L (low) < 15 cm. Note variation in scale for the y-axis. 

28
29

Base Pool Stage Vegetation 

 To compare plant community composition prior to and following the drawdown, 11 species 

with quadrat count total equal to or greater than 20 (that is, those species that appeared in 20 or 

more quadrats summed across all undisturbed transects) in either June 1995 or 1996 were 

analyzed (table 11). Categorical analysis of variance indicated significant differences in the 

species and time interaction (P < 0.001), so only the responses in terms of this interaction were 

examined. Pairwise comparisons identified frequency differences for nine species; only 

Spirodela polyrrhiza and Bacopa. egensis had similar frequencies at both times. A total of 12 

species had greater than 400 percent cover at either time when summed across all undisturbed 

transects; the cover of six of these species varied significantly between times (table 12). 

Table 11. Count of species present in 20 or more quadrats summed across all undisturbed 

transects in June 1995 or June 1996, plus the introduced species Bacopa egensis. 

[Significant differences between times from categorical analysis of variance are indicated by 

dissimilar letters. Some plants were identified to genus only. Life form designations are: E = 

emergent herbaceous, F = floating-leaved, S = submersed aquatic, W = woody] 

Species Life Form June 1995 June 1996 

Azolla caroliniana F 5a 40b

Bacopa egensis E 6 2 

Eleocharis microcarpa E 32a 11b

Limnobium spongia F 59a 40b

Ludwigia palustris E 63a 5b

Ludwigia peploides E 0a 54b

Najas sp. S 25a 9b

Spirodela polyrrhiza F 72 76 

Utricularia gibba S 41a 3b

Utricularia inflata S 8a 50b

Wolffia sp. F 32a 77b
30

Table 12. Total cover (mean ± 1 SE, n = 14) at transects in June 1995 and 1996 of species with 

cover that exceeded 400 percent summed across all undisturbed transects at either time, plus the 

introduced species Bacopa egensis. 

[Significant difference from paired t-tests are indicated by dissimilar letters. Some plants were 

identified to genus only. Life form designations are: E = emergent herbaceous, F = floatingleaved, S = submersed aquatic, W = woody] 

 

Species Life Form June 1995 June 1996

Bacopa egensis E 9.7 ± 6.1 0.1 ± 0.1

Cabomba caroliniana S 35.3 ± 17.1 11.7 ± 10.7 

Ceratophyllum demersum S 34.2 ± 14.6 2.3 ± 1.7 

Cephalanthus occidentalis W 12.1 ± 4.7 28.6 ± 10.2 

Eleocharis microcarpa E 101.2 ± 43.4a 19.3 ± 14.8b

Limnobium spongia F 39.5 ± 7.8 30.0 ± 17.4 

Ludwigia palustris E 93.4 ± 18.6a 6.4 ± 6.3b

Ludwigia peploides E 0.0 ± 0.0a 117.9 ± 28.0b

Najas sp. S 95.1 ± 28.5a 9.0 ± 6.4b

Spirodela polyrrhiza F 133.2 ± 39.0 100.5 ± 39.4 

Utricularia inflata S 18.7 ± 13.0a 132.0 ± 45.1b

Wolffia sp. F 4.6 ± 2.0a 127.4 ± 44.3b

Seed Bank 

 A total of 39 species that germinated in the two seed bank studies were identified (table 13), 

17 in the June samples and 33 in the October samples; one species remained unidentified in both 

studies. Thirteen species that germinated from the seed bank were not present in standing 

vegetation in the quadrats any time during the study. The species that germinated in the most 

quadrats at both sampling times was Cyperus erythrorhizos (table 14). Mean species richness 

was 4.6 ± 0.4 (n = 28) in June and 5.5 ± 0.3 (n= 38) in October. Analysis of variance indicated 

that elevation did not have an effect on seed bank species richness at either time (P = 0.2092 in 

June, P = 0.2284 in October). Considering undisturbed transects only, a two sample t-test 

indicated no difference (P = 0.083) in mean species richness in June compared to October. 

Comparison of the five paired transects with soil disturbance indicated no effect (P = 0.5763) of 

the disturbance on mean species richness (5.8 ± 0.6 in disturbed transects, 5.5 ± 0.4 in 

undisturbed transects; n = 10). Disturbance within elevation also did not affect species richness 

(P = 0.6213 at low elevation, P = 0.4557 at high elevation; n = 5). Comparisons between 

standing vegetation and germinating seeds indicated that standing vegetation richness exceeded 

that of the seed bank in June at low elevation only, but that seed bank richness exceeded standing 

vegetation at both elevations in October (table 15). 
31

Table 13. Plant species that germinated in soil collected at Felsenthal National Wildlife Refuge 

in June and October 1995 and the presence of those species in the standing vegetation at any of 

the five sampling events. Some plants were identified to family or genus only. 

 

Species June 1995 October 1995 Standing Vegetation 

Ammannia coccinea Rottb. x x x 

Bacopa egensis (Poepp.) Pennell x x 

Bacopa rotundifolia (Michx.) Wettst. x x 

Bidens aristosa (Michx.) Britt. x x 

Cephalanthus occidentalis L. x x 

Chamaesyce humistrata (Englem.) Small x 

Coreopsis sp. x 

Cyperus erythrorhizos Muhl. x x x 

Cyperus esculentus L. x 

Cyperus iria L. x x 

Cyperus sp. x 

Echinochloa crus-galli (L.) Beauv. x x 

Eclipta prostata (L.) L. x x 

Eleocharis microcarpa Torr. x x x 

Eleocharis obtusa (Willd.) J.A. Schultes x x 

Eupatorium capillifolium (Lam.) Small x 

Fimbristylis autumnalis (L.) Roemer & 

 J.A. Shultes. 

x 

Fimbristylus miliacea (L.) Vahl x x x 

Gratiola virginiana L. x 

Heteranthera reniformis Ruiz & Pavon x x 

Leersia virginica Willd. x 

Lindernia dubia v. anagallidea (Michx) 

 Cooperrider 

x 

Lindernia dubia (L.) Pennell x x 

Limnobium spongia (Bosc) L.C. Rich. ex 

 Steud. 

x x x 

Ludwigia decurrens Walt. x x x 

Ludwigia leptocarpa (Nutt.) Hara x x 

Ludwigia palustris (L.) Ell. x x x 

Ludwigia peploides (Kunth) Raven x x x 

Ludwigia sphaerocarpa Ell. x x 

Panicum virgatum L. x 

Poaceae x x x 

Ptilimnium capillaceum (Michx) Raf. x 

Sagittaria latifolia Willd. x x 

Salix nigra Marsh. x 
32

Table 13. Continued. 

 

Species June 1995 October 1995 Standing Vegetation 

Solidago sp. x

Spirodela polyrrhiza (L.) Schleid. x x x

Sphenoclea zeylanica Gaertn. x x

Bryophytes: 

Riccia sp. x x x 

Ricciocarpos sp. x x

Table 14. The ten most-frequently germinating plant species in soil samples 

collected in June and October 1995 at Felsenthal National Wildlife Refuge. Total 

quadrat indicates the total number of quadrat samples (n =28) within which the 

species germinated, summed across all undisturbed transects. Some plants were 

identified to family or genus only. 

 

Month Species Total Quadrat 

June 1995 Cyperus erythrorhizos 23

Ludwigia peploides 14

Lindernia dubia 13

Poaceae 12

Spirodela polyrrhiza 12

Bacopa egensis 10

Ricciocarpus sp. 10

Riccia sp. 7

Limnobium spongia 6

Ludwigia decurrens 4

October 1995 Cyperus erythrorhizos 28

Lindernia dubia v. anagallidea 14

Ludwigia peploides 13

Ludwigia palustris 8

Ammania coccinea 7

Ludwigia leptocarpa 7

Eleocharis obtusa 6

Poaceae 6

Eleocharis microcarpa 5

Bidens aristosa 4
33

Table 15. Species richness (mean ± 1 SE, n = 14) of seed bank samples and of standing 

vegetation in high and low elevation quadrats; soil for seed bank studies was collected outside 

the quadrats where vegetation was measured. Significant differences within elevation class by 

month are indicated by dissimilar letters. 

 

Low Elevation High Elevation

Month Vegetation Seed Bank Vegetation Seed Bank

June 6.1 ± 0.4a 4.1 ± 0.4b 5.2 ± 0.5 5.1 ± 0.6 

October 3.5 ± 0.8a 5.1 ± 0.5b 3.2 ± 0.6a 6.0 ± 0.5b

Soil Characteristics 

 Analyses indicated the presence of predominantly mineral soils along the margin of the pool 

in the transects. Organic matter content in June 1995 was low, ranging from 3.57 ± 0.48 percent 

to 6.32 ± 0.65 percent (table 16). In June 1995, organic matter varied by transect (P < 0.001) 

and elevation class (P < 0.001). For transects with a significant elevation effect (transects 5, 8, 

11, 12, 14a, and 15a), organic matter at high elevation was greater than that at low elevation. In 

October, when just a single quadrat was sampled, organic matter did not differ among transects 

(P = 0.07 ). Soil disturbance significantly (P = 0.0397; n = 5) affected organic matter content, 

which was greater at the undisturbed (7.57 ± 1.04) compared to the disturbed (4.44 ± 0.76) soil 

treatments. Examining data from quadrat 4 for undisturbed transects, organic matter content in 

October (7.28 ± 0.60) was greater than that in June (4.30 ± 0.30; n = 14; P = 0.0014). 

 Percent carbon and nitrogen were also very low in June 1995 (table 16). At this time, the 

variables differed significantly by transect (P < 0.001, both elements) and elevation (P < 0.001, 

both elements). The effect of elevation was not consistent across transects. Percentage of 

carbon was greater at high compared to low elevation in transects 3a, 12, and 14a, but the 

opposite effect was found in transects 4a and 9. Percent nitrogen at high elevation was greater 

than that at low elevation in transects 11 and 12 but was less compared to low elevation at 

transects 7, 9 and 10. October samples included only one quadrat per transect, so elevation 

effect was not analyzed. Percent carbon and nitrogen varied among transects in October (P < 

0.001, both elements). The soil disturbance treatment affected (P = 0.0342, n = 5) both 

elements; carbon content was higher at the undisturbed (3.59 ± 0.56) compared to disturbed 

(1.92 ± 0.40) transects. Nitrogen content was also higher (P = 0.0467; n = 5) at the undisturbed 

(0.27 ± 0.05) compared to undisturbed (0.16 ± 0.04) transects. 
34

Table 16. Soil characteristics, expressed as percent (mean ± 1 SE), at 14 transect locations at 

Felsenthal National Wildlife Refuge, June 2005. The number of subsamples per transect varied 

from two to six. 

[The abbreviation “OM” indicates organic matter] 

 

Transect OM Carbon Nitrogen Sand Silt Clay

1 4.76 ± 0.40 1.90 ± 0.21 0.18 ± 0.01 22.89 ± 0.12 12.64 ± 0.85 64.47 ± 0.97 

2a 6.32 ± 0.65 3.08 ± 0.19 0.27 ± 0.02 2.87 ± 0.01 13.17 ± 3.11 83.96 ± 3.10 

3a 5.34 ± 0.41 2.73 ± 0.35 0.22 ± 0.02 2.55 ± 0.09 20.31 ± 0.47 77.13 ± 0.55 

4a 5.56 ± 0.46 2.51 ± 0.03 0.22 ± 0.02 5.83 ± 0.33 16.34 ± 3.94 77.83 ± 3.62 

5 4.40 ± 1.34 2.20 ± 0.75 0.14 ± 0.04 53.56 ± 5.27 15.90 ± 9.09 30.53 ± 4.60 

6 5.50 ± 0.32 2.07 ± 0.28 0.21 ± 0.02 2.51 ± 0.74 32.41 ± 18.99 65.08 ± 18.31 

7 3.75 ± 0.38 1.66 ± 0.21 0.19 ± 0.02 -- -- -- 

8 4.43 ± 0.69 2.00 ± 0.42 0.22 ± 0.01 1.17 ± 0.22 24.15 ± 3.67 74.67 ± 3.86 

9 3.57 ± 0.48 1.75 ± 0.22 0.28 ± 0.04 32.19 ± 1.05 8.25 ± 0.61 59.56 ± 1.66 

10 4.49 ± 0.28 2.02 ± 0.19 0.05 ± 0.09 19.51 ± 4.68 22.72 ± 10.18 57.77 ± 14.83 

11 4.67 ± 1.22 1.63 ± 0.19 0.32 ± 0.17 0.29 ± 0.08 41.43 ± 14.51 58.28 ± 14.45 

12 5.25 ± 2.04 2.79 ± 1.16 0.19 ± 0.07 32.68 ± 1.23 16.91 ± 0.89 50.41 ± 1.98 

14a 4.51 ± 0.54 2.25 ± 0.25 0.19 ± 0.02 10.56 ± 0.82 15.64 ± 1.46 73.80 ± 2.14 

15a 6.26 ± 0.80 2.36 ± 0.40 0.23 ± 0.03 9.72 ± 0.19 41.49 ± 19.87 48.78 ± 19.81 

 Texture analyses indicated a predominance of clay particles in the upper 15-cm layer of soil 

(table 16). Because soil from a single quadrat was collected, elevation effect on soil particle size 

was not determined. Both percentage of sand (P < 0.001) and clay (P = 0.0289) varied by 

transect. Five groups were identified by sand content; excluding transects 10, 14a, and 15a, 

where percentage of sand was similar to that at several other transects, three distinct groups were 

apparent. Transect 5 had the highest sand content; transects 1, 9, and 12 were intermediate, and 

the remaining transects had low sand. Clay content at transects 2a, 3a, 4a, 8, and 14a was greater 

than that at transect 5; percentage of clay at the remaining transects was not different from the 

high or low groups. Mean (n = 14) values in pool soils were 14.04 ± 0.23 for sand, 25.01 ± 4.34 

for silt, and 60.94 ± 4.43 for clay. 

 With the exception of manganese and iron, soil nutrients (table 17) varied with either 

transect or elevation class (table 18). The elevation effect consisted of lower Cu content at high 

(1.96 ± 1.19) compared to low (9.89 ± 3.81) elevation at transect 12. Mean comparisons 

indicated that the transects separated into five to seven groups for each element, with a great deal 

of overlap within the groups (table 19). 
35

Table 17. Concentration (mg/kg dry weight, mean ± 1 SE) of eight essential plant nutrients in soil collected in Jutransects (Trans) at Felsenthal National Wildlife Refuge. [The number of observations per transect varied because of sample loss and instrument malfunction, ranging from error indicated) to six; for transects combined (indicated by “all”), observations per element varied from 54 to 67

transect 15a were lost. Data from transect 13, which was dropped from the study because of the later constructiocapture station, are presented here] 

Trans Cu Zn Mn Fe P Mg C

1 17.78 ± 2.71 38.25 ± 4.39 21.97 ± 7.18 3158.21 ± 772.32 75.71 ± 18.42 268.67 ± 75.39 389.98 ± 2 14.99 ± 1.13 49.40 ± 4.28 31.99 ± 2.69 5109.69 ± 403.69 108.58 ± 11.57 351.15 ± 35.65 587.55 ± 

3a 5.13 ± 0.31 9.61 ± 9.61 14.57 ± 1.16 3215.95 ± -- 54.86 ± 4.36 154.61 ± 7.89 338.05 ± 4a 3.44 ± 1.07 -- 31.96 ± 12.08 2381.28 ± -- 36.93 ± 17.25 193.06 ± 30.39 386.15 ± 

5a 4.58 ± 1.67 6.32 ± 6.21 45.84 ± 15.28 1796.76 ± 431.29 9.96 ± 7.99 124.43 ± 35.70 136.01 ± 

6 8.70 ± 0.98 38.77 ± 1.45 46.66 ± 7.68 5090.58 ± 80.07 69.78 ± 4.65 391.39 ± 34.42 320.82 ± 7 7.07 ± 0.45 35.10 ± 1.26 30.17 ± 3.73 4748.46 ± -- 65.90 ± 7.79 321.62 ± 14.04 495.98 ± 

8 7.91 ± 0.90 32.52 ± 2.02 35.51 ± 9.93 4460.54 ± 279.35 67.37 ± 10.98 372.51 ± 21.34 584.62 ± 9 6.57 ± 0.71 22.84 ± 4.88 23.86 ± 4.07 3108.54 ± 220.95 34.49 ± 4.11 224.82 ± 24.42 518.69 ± 

10 5.52 ± 0.52 13.48 ± 1.30 34.57 ± 3.29 3719.48 ± 231.22 51.02 ± 6.64 225.43 ± 25.90 572.97 ± 

11 4.62 ± 0.49 17.40 ± 1.37 34.99 ± 3.10 4144.05 ± 112.00 68.65 ± 2.60 380.53 ± 20.04 465.41 ± 

12 5.13 ± 2.38 15.70 ± 4.38 62.23 ± 28.11 3486.06 ± 414.94 70.67 ± 16.73 165.93 ± 25.15 469.29 ± 

13 4.31 ± 0.62 14.46 ± 0.62 20.48 ± 4.34 1774.03 ± 108.79 36.61 ± 2.36 145.72 ± 9.17 384.72 ± 

14a 3.82 ± 0.50 17.13 ± 3.61 13.05 ± 4.38 2559.37 ± 261.99 35.12 ± 2.63 184.63 ± 14.42 -

All 6.88 ± 0.51 23.08 ± 1.82 32.59 ± 2.95 3458.21 ± 195.74 56.18 ± 3.66 261.41 ± 12.95 454.70 ± 
36

Table 18. Results (F value) of an analysis of variance of the 

effects of transect and elevation on the content of eight plant 

nutrients in soil at Felsenthal National Wildlife Refuge. 

Significance levels are P < 0.05* and P < 0.001**. 

 

Element Transect Elevation

Cu 19.71** 4.04*

Zn 12.64** 1.81

Mn 2.00 1.74

Fe 1.98 1.23

P 6.29** 1.02

Mg 11.88** 2.37*1

Ca 6.83** 1.21

K 7.61** 0.94

1

Comparisons not significant. 

Table 19. Representation of Duncan’s multiple range test means comparisons by nutrient from 

an analysis of variance of transect effect on soil nutrient concentration. Soils were collected at 

Felsenthal National Wildife Refuge in June 1995. Transect did not affect soil Mn or Fe content. 

 

[Letters indicate transects with indistinguishable means; the number of observations varied from 

two to six. Letters are ordered in decreasing concentration (that is, for each nutrient, group “a” 

has the highest concentration] 

 

Trans Cu Zn P Ca Mg K

 1 a ab b abc bcd abc

 2 b a a a ab ab

 3 defg efg bcd cb ef defg

 4 g g cde abc def cdef

 5 efg fg e d f g

 6 c ab bc c a abc

 7 cde bc bcd ab ab abcde

 8 cd bc bcd a a abcd

 9 cdef cde ed a cde defg

10 defg efg bcd a cde bcdef

11 efg def bc abc a ab

12 defg def b abc ef efg

14 fg def ed -- def fg 

 

 
37

Discussion 

 The 0.3 m (1 ft) drawdown of the pool exposed sediment that had been continuously flooded 

for almost 10 years. Total vegetation cover at transect locations was relatively high 4 weeks 

following the initiation of the drawdown (on Aug. 1, 1995) (fig. 7). Plant species dominance in 

the drawdown zone shifted from the submersed and floating-leaved species that were present at 

normal pool stage to herbaceous emergent species; a woody species, Cephalanthus occidentalis, 

was also dominant during the drawdown. Several of the plant species that colonized the 

drawdown zone are considered good seed producers and are valuable food sources for waterfowl 

(Fredrickson and Taylor, 1982). Desirable waterfowl food species that were relatively abundant 

within the drawdown zone included Cyperus erythrorhizos, Cyperus iria, Echinocloa grus-galli, 

Fimbristylus miliacea, Leptochloa fascicularis, Bidens aristosa, and Panicum sp. In addition to 

the benefits to waterfowl species, Twedt and others (1998) described the value of habitat created 

by reservoir drawdowns in the Mississippi Alluvial Valley to shorebirds and recommended 

drawing down public reservoirs from July through October to provide foraging habitat during 

southward migration. 

 The relatively abundant vegetative cover found in the drawdown zone is characteristic of 

vegetation succession following a decrease in water levels in wetlands (Smith and Kadlec, 1983; 

Welling and others, 1988). DeBerry and Perry (2005) have identified a regional drawdown flora 

in Virginia. The flora consists of species that form persistent seed banks in the substrate of 

reservoirs and characteristically produce small seeds on dense inflorescences; these species 

therefore are capable of producing viable seeds in large quantities. Cyperus erythrorhizos, 

which was dominant in the pool drawdown zone, was part of the drawdown flora described by 

DeBerry and Perry (2005). Seeds of Cyperus erythrorhizos have been shown to be persistent 

under flooded conditions and are able to germinate quickly when water recedes (Baskin and 

others, 1993). 

 The number of woody plant species, including vines, increased as a result of the pool 

drawdown. Woody species were absent from the list of five most frequently-occurring species in 

June and August 1995, but Cephalanthus occidentalis was the second most frequently-occurring 

species in both September and October 1995. Two woody species (Cephalanthus occidentalis

and Taxodium distichum) occurred in 16 quadrats (frequency = 19.0 percent) in June 1995. 

During the drawdown, woody species richness increased to three and seven in August and 

September, respectively, then dropped to four in October. The number of quadrats that 

contained woody species was 21 (frequency = 16.9 percent), 70 (frequency = 55.6 percent), and 

49 (frequency = 39.2 percent) in August, September, and October, respectively. Most of the 

woody plants identified in September and October were small seedlings of Cephalanthus 

occidentalis, Planera aquatica and Taxodium distichum. The drop in woody species richness 

and occurrence in October was probably due to grazing by small mammals, including nutria 

(Myocastor coypus), which were abundant in the study area. In June 1996, four woody species 

were found in 25 quadrats (frequency = 20.0 percent). The frequency of Cephalanthus 

occidentalis dropped from a high of 38.1 in September to 16.0 in June 1996 (appendix 2), and 

total cover of this species dropped from a high of 731.5 percent to 438.0 percent for those two 

times. In comparison, cover of this species before the drawdown in June 1995 was 169.5 percent 

(appendix 3). Because only one measurement was made at base pool stage following the 

drawdown, it is not known if the increase in woody species cover persisted. It is probable, 
38

however, that continued flooding was stressful to young seedlings and may have led to their 

death. Short periods of total submergence kills seedlings of most bottomland tree species 

(Hosner, 1958), and even the very flood-tolerant species Taxodium distichum is only able to 

persist as long as some leaves remain above water during most of the growing season (Demaree, 

1932). In an early study on vegetation succession in Ohio, woody plant encroachment was not a 

problem after seven consecutive years of July to September drawdowns in marsh habitat 

(Meeks, 1969). In warmer climates, however, more rapid growth of woody species may become 

important if the spread of these species is not desired. At Catahoula Lake in central Louisiana, 

annual summer drawdowns have resulted in the encroachment of Cephalanthus occidentalis and 

Forestiera acuminata (swamp privit) over the past several years (T. Michot, oral commun.); 

apparently, some seedlings were able to grow tall enough to remain above water level during 

normal lake levels. At Lake Chicot, also in central Louisiana, Taxodium distichum seedlings 

were able to establish on exposed sediments when the drawdown extended over 18 months and 

included two consecutive growing seasons (Keeland and Conner, 1999). 

 The effect of transect and elevation on vegetation response was complex. Although response 

varied with transect among those transects that were not subjected to soil disturbance (fig. 9), 

there is no consistent pattern in groupings related to direction of location along the pool margin 

(north, south, east, or west) or to soil characteristics. Elevation significantly affected vegetation 

at some transects during the drawdown, and those affects were somewhat consistent. Values 

reflecting vegetation response were often greater at low elevation than those at high elevation. 

When a response varied over time and increased at both elevations, the magnitude of the increase 

was greater at low compared to high elevation. When a variable decreased over time at both 

elevations, as did species richness from September to October on three transects, the relationship 

between elevations was variable. These responses may be related to species phenology and/or 

weather conditions during the study. The decrease in total cover on undisturbed transects in 

October probably reflects seasonal senescence of some species. In contrast, cover of annual 

Cyperus species, which can flower late in the growing season, remained fairly constant in 

September and October. The summer of 1995 was unusually dry in southern Arkansas (table 

20), and soil moisture has been found to influence recruitment of species from the seed bank 

(Welling and others, 1988). It is likely that low elevation locations at the pool had sufficient 

moisture for seed germination and vigorous plant growth for the first several weeks of 

drawdown. During late summer to fall, however, the cumulative effect of the drought may have 

led to a dieback in vegetation. A possible explanation for the greater decrease in species 

richness observed at low compared to high elevation is that some species present at low 

elevation were more susceptible to reduced soil moisture in late summer than species at high 

elevations, so the decrease in richness would be more dramatic at the low elevation sites. We 

also noted heavy insect (beetle) herbivory in September 1995; Ludwigia peploides was the 

species affected to the greatest degree and was often grazed to the extent where only stems 

remained. 
39

Table 20. Precipitation by month in 1995, 30 year (1961-

1990) mean monthly precipitation, and annual precipitation in 

Crossett, Ark. Data for 1995 are from Felsenthal National 

Wildlife Refuge records and mean data are from the Crossett 

Water Commission, Crossett, Ark. 

 

Precipitation (cm)

Month 1995 Mean

January 15.82 12.29

February 8.15 13.34

March 14.33 14.40

April 16.66 12.19

May 8.03 14.43

June 6.93 11.61

July 10.92 11.23

August 0.99 9.04

September 2.69 8.79

October 2.16 9.68

November 4.70 12.80

December 20.39 13.36

Annual 111.77 143.16

 

 Soil disturbance decreased species richness and total vegetation cover during the drawdown. 

 Although soil disking and tilling are recommended as a management technique to facilitate seed 

germination (Fredrickson and Reid, 1988; Gray and others,1999), disking at the pool margin was 

logistically difficult due to the abundant woody debris. The use of a bulldozer to remove the 

woody debris scraped away some of the topsoil, thereby removing much of the available seed 

bank. It is likely that low summer rainfall levels contributed to low germination of seeds that 

were recruited onto disturbed transects. 

 Comparison of predrawdown and postdrawdown vegetation communities at base pool level 

indicated a significant shift in cover and frequency of some species. While submersed and 

floating-leaved species dominated in both June 1995 and June 1996, the frequency of the 

floating-leaved species Azolla caroliniana and Wolffia sp. was higher following the drawdown, 

while Limnobium spongia decreased (table 11). The frequency and cover of the emergent 

species Ludwigia palustris and Ludwigia peploides displayed opposite trends; Ludwigia 

palustris decreased following the drawdown while Ludwigia peploides increased (tables 11 and 

12). This trend was also apparent for frequency of the submersed species Utricularia gibba and 

Utricularia inflata. Because of structural similarity of the species that varied between times, 

however, it is unlikely that the shifts affected plant community function. 

 Analyses of the seed bank data were problematic because different soil volumes were 

collected in June and October, which likely affected the total number of seeds present. Although 

data on species abundance (that is, cover class at two time intervals) were collected for each seed 

bank study, only data on species richness were analyzed; we do not believe that the sample size 
40

difference invalidated analyses that included this variable. Species richness per quadrat was not 

different between the two times, but species composition did vary. There were 22 species that 

germinated in October samples that were not present in June samples, and six that germinated in 

June but not October samples (table 13). This variation may be related to three factors: (1) 

species variation in timing of flowering and seed maturation, (2) inherent variability in seed 

longevity, and (3) the effect of prolonged flooding on seed recruitment. 

 Our seed bank results are consistent with those of Leeds and others (2002), who found that 

more species germinated in Florida Everglades soils collected in October than in soils collected 

in May. This variation was attributed to a July peak in seed maturity and dispersal (Leeds and 

others, 2002). Seed longevity varies widely among plants, ranging from less than a year to 

several decades (Baskin and Baskin, 1998). Many of the woody species present in bottomland 

hardwood forests produce short-lived seeds that are dispersed by water (Schneider and Sharitz, 

1986; Middleton, 2000). Herbaceous species are well represented in the seed banks of forested 

systems (Leck, 1989; Middleton, 2003); in general, the mean longevity of seeds of wetland 

species exceeds that of woody species by about three times (Thompson and others, 1998). 

Results from our seed emergence studies indicate the predominance of herbaceous species in the 

seed bank at the pool. While seed persistence is primarily a species trait, it can be modified by 

environmental conditions (Fenner and Thompson, 2005). A reduction in seed species richness in 

wetland seed banks under prolonged flooding has been noted in several studies (for example, 

Keddy and Reznicek, 1982; Smith and Kadlec, 1983; Schneider and Sharitz, 1986; Poiani and 

Johnson, 1989). This reduction may be due to lower incorporation of seeds in standing water 

(Schneider and Sharitz, 1986); however, the anoxic conditions found in flooded soils reduces 

seed deterioration (Leck, 1989) and therefore can increase seed longevity. Because the area of 

our study was limited (that is, restricted to the area exposed by the 0.30-m drawdown), it is not 

surprising that 13 species identified in the seed bank studies were not represented in the standing 

vegetation. The higher species richness in standing vegetation versus that of germinating seeds 

that we observed in June is consistent with a study by Bossuyt and others (2007), who examined 

a drained lake bed in Belgium. We can not be confident that this difference is real; as noted by 

Bossuyt and others (2007), it may be an artifact of the difference in sample size (that is, quadrat 

size was several times larger than the soil core). Higher species richness in the seed bank 

compared to standing vegetation, which we identified in October, is the more common 

relationship reported for wetlands (Smith and Kadlec, 1983; Schneider and Sharitz, 1986; 

Wilson and others, 1993). 

 The soils of the pool margin were predominantly clay with low organic matter content; some 

transects revealed relatively high sand content. Texture analysis results were similar to those 

determined for low elevation soils (19.8-20.7 m) within the greentree reservoir, where mean 

values were 7.33 ± 1.49 (mean ± 1 SE) for sand, 16.28 ± 2.54 for silt, and 76.41 ± 2.98 for clay 

(J. McCoy, unpub. data from 15-cm deep core samples collected July 1995; n = 16). Although 

there was no consistent trend by elevation class in June 1995, the higher organic matter content 

found for some transects at high compared to low elevation may be related to greater production 

by plants across the growing season at high elevation (that is, water less than 15-cm deep) over 

the 10-year flooding period. Organic matter content at the water edge may also be influenced by 

the tendency for floating debris to accumulate along the shoreline. The increase in organic 

matter from June to October is counterintuitive. Although the aerobic conditions and higher soil 

temperatures during the drawdown would be expected to increase decomposition and therefore 
41

reduce organic matter content, the low rainfall and extremely dry conditions during the study 

would act to impede decomposition. In addition, difference in litter quality exists between the 

two times. The submersed and floating-leaved species of June are more easily consumed by 

microbial decomposers than the sedge and woody species that dominated in October, which have 

higher concentrations of recalcitrant materials such as lignin and cellulose (Lockaby and others, 

1996). The lower organic matter and percentages of carbon and nitrogen content on disturbed 

compared to undisturbed sites was due to the fact that application of the soil disturbance 

removed the top several centimeters of soil. The plant nutrient concentrations in soils of the pool 

margin were well within the average content reported for soils worldwide and below toxic levels 

for plants (Market, 1992; Sparling and Lowe, 1998). It is interesting to note that transects 1 and 

2 consistently had the highest nutrient concentrations, while transect 5 and often transect 4 had 

the lowest concentrations. All four transects are located on the western side of the pool, with 

transects 1 and 2 located further south towards the lock and dam. Higher nutrient concentration 

in the southwestern corner of the pool may be related to past land-use patterns. 

 

Conclusions and Management Implications 

 The 0.3-m drawdown at the pool resulted in an increase in both emergent and woody 

vegetation cover within the area of exposed soil and was accompanied by an increase in cover of 

waterfowl food species. Total vegetation cover was generally high in undisturbed transects 

during the drawdown, and vegetation response was often greater at low compared to high 

elevation. The application of soil disturbance, which removed the upper layers of soil, decreased 

species richness and cover by removing the existing seed bank; these negative effects were 

probably intensified by the extremely dry weather conditions during the study. Seed bank 

studies indicated that seeds of some species, including valuable waterfowl food species, persisted 

during the 10-year period the pool was flooded and that the diversity of the seed bank increased 

during the drawdown. No distinct patterns in soil characteristics or nutrient content in the 

drawdown zone were identified. Pool vegetation in early summer following the drawdown was 

not structurally different from that prior to the drawdown, indicating no permanent impacts on 

vegetation. Future drawdown events are likely to follow the same trajectory, and will increase 

food quality and quantity for waterfowl species. Encroachment of woody vegetation into the 

drawdown zone is unlikely if drawdowns are scheduled on cycles that subject young seedlings to 

flooding stress in the subsequent growing season. 

Acknowledgments 

 We appreciate the assistance provided by the staff at Felsenthal NWR throughout the study. 

Most notably, the logistical support and help provided by Robert Ellis in locating sampling sites, 

collecting data, and identifying plant species were essential to the completion of the study. We 

thank Darren Johnson for completing statistical analyses, Janelda Biagas for help with field data 

collection and graphics preparation, Christina Boudreaux for preparing the study area map, and 

Connie Herndon for editorial review. Bob Keeland provided historical data on water levels at 

Felsenthal lock and dam. Review comments from Bob Keeland, Rassa Dale, Beth Middleton, 

and Jack Waide are greatly appreciated. 
42

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531. 
45

Appendix 1. Description of 19 transects monitored at Felsenthal National 

Wildlife Refuge from June 1995 to June 1996, indicating quadrat distance 

from base marker and relative elevation. Paired transects that included a 

soil disturbance treatment are indicated by letters next to the transect 

number, a = undisturbed, b = disturbed. 

[The total number of quadrats sampled for vegetation at each time were as 

follows: n = 84 in June 1995 (quadrat 6 was not established), n = 124 in 

August 1995, n = 126 in September 1995, and n = 125 in October 1995 

and June 1996] 

 

Transect Quadrat

Distance from 

Base (m)

Relative 

Elevation (ft)

Relative 

Elevation (cm)

1 0 0.0 1.00 30.48

1 7.2 0.86 26.21

2 9.2 0.68 20.73

3 10.3 0.68 20.73

4 24.3 0.62 18.90

5 23.2 0.27 8.23

6 29.4 -0.03 -0.91 

2a 0 0.0 1.00 30.48

1 12.0 0.70 21.34

2 14.5 0.62 18.90

3 19.1 0.55 16.76

4 26.0 0.52 15.85

5 38.0 0.26 7.92

6 51.1 0.17 5.18

2b 0 0.0 1.00 30.48

1 1.3 0.79 24.08

2 3.6 0.63 19.20

3 8.0 0.45 13.72

4 40.5 0.29 8.84

5 48.5 0.18 5.49

6 64.9 -0.07 -2.13 

3a 0 0.0 1.00 30.48

1 15.4 0.90 27.43

2 27.9 0.81 24.69

3 58.8 0.54 16.46

4 100.8 0.40 12.19

5 111.0 0.27 8.23

6 . 0.18 5.49 
46

Appendix 1. Continued. 

 

Transect Quadrat

Distance 

from Base (m)

Relative 

Elevation (ft)

Relative 

Elevation (cm)

3b 0 0.0 1.00 30.48

1 6.5 0.82 24.99

2 9.7 0.63 19.20

3 25.6 0.48 14.63

4 53.5 0.29 8.84

5 96.0 0.07 2.13

4a 0 0.0 1.00 30.48

1 7.9 0.90 27.43

2 12.2 0.76 23.16

3 13.6 0.58 17.68

4 17.6 0.50 15.24

5 21.7 0.29 8.84

6 26.9 -0.03 -0.91 

4b 0 0.0 1.00 30.48

1 2.0 0.78 23.77

2 3.1 0.60 18.29

3 5.5 0.42 12.80

4 17.5 0.23 7.01

5 19.6 0.17 5.18

5 0 0.0 1.00 30.48

1 2.1 0.66 20.12

2 4.3 0.32 9.75

3 7.1 0.27 8.23

4 9.0 0.22 6.71

5 10.8 0.12 3.66

6 51.5 0.06 1.83

6 0 0.0 1.00 30.48

1 4.0 0.80 24.38

2 19.4 0.57 17.37

3 22.7 0.52 15.85

4 75.4 0.41 12.50

5 77.9 0.02 0.61

7 0 0.0 1.00 30.48

1 6.7 0.68 20.73

2 36.4 0.62 18.90

3 71.7 0.58 17.68

4 79.7 0.23 7.01

5 82.3 -0.05 -1.52 
47

Appendix 1. Continued. 

 

Transect Quadrat

Distance 

from Base (m)

Relative 

Elevation (ft)

Relative 

Elevation (cm)

8 0 0.0 1.00 30.48

1 20.7 0.70 21.34

2 53.6 0.69 21.03

3 58.4 0.60 18.29

4 96.8 0.55 16.76

5 143.1 0.36 10.97

6 223.6 0.02 0.61

9 0 0.0 1.00 30.48

1 6.2 0.78 23.77

2 8.9 0.76 23.16

3 13.5 0.68 20.73

4 87.7 0.57 17.37

5 99.0 0.29 8.84

6 134.4 -0.11 -3.35 

10 0 0.0 1.00 30.48

1 6.0 0.75 22.86

2 9.2 0.62 18.90

3 13.7 0.49 14.94

4 15.2 0.30 9.14

5 17.5 0.09 2.74

6 22.0 -0.03 -0.91 

11 0 0.0 1.00 30.48

1 1.9 0.90 27.43

2 4.3 0.86 26.21

3 14.6 0.52 15.85

4 18.7 0.34 10.36

5 21.1 0.30 9.14

6 36.7 -0.18 -5.49 

12 0 0.0 1.00 30.48

1 1.9 0.94 28.65

2 2.5 0.87 26.52

3 5.3 0.84 25.60

4 17.0 0.44 13.41

5 19.4 0.07 2.13
48

Appendix 1. Continued. 

 

Transect Quadrat

Distance 

from Base (m)

Relative 

Elevation (ft)

Relative 

Elevation (cm)

14a 0 0.0 1.00 30.48

1 3.7 0.90 27.43

2 13.6 0.63 19.20

3 15.5 0.68 20.73

4 18.3 0.49 14.94

5 45.0 0.38 11.58

6 69.0 -0.02 -0.61 

14b 0 0.0 1.00 30.48

1 3.0 0.72 21.95

2 5.7 0.59 17.98

3 18.2 0.45 13.72

4 28.1 0.24 7.32

5 46.4 0.25 7.62

15a 0 0.0 1.00 30.48

1 10.9 0.72 21.95

2 13.3 0.66 20.12

3 15.5 0.60 18.29

4 17.0 0.40 12.19

5 24.0 0.13 3.96

6 32.0 -0.12 -3.66

15b 0 0.0 1.00 30.48

1 3.2 0.85 25.91

2 8.5 0.63 19.20

3 18.5 0.45 13.72

4 22.5 0.20 6.10

5 29.6 0.06 1.83
49

Appendix 2. Frequency of occurrence (percentage) of plant species at five sampling times at 

Felsenthal National Wildlife Refuge. See table 3 of the report for species codes. 

 

Species June 1995 Aug. 1995

Month

Sept. 1995 Oct. 1995 June 1996

Amco 1.2 5.6 7.1 4.0 0.0

Azca 6.0 0.0 0.8 0.8 41.6

Baeg 7.1 2.4 5.6 1.6 1.6

Baro 4.8 1.6 0.0 0.0 0.8

Biar 10.7 17.7 22.2 13.6 12.8

Brov 0.0 0.0 3.2 3.2 0.8

Caca 17.9 0.0 0.8 0.0 10.4

Casp 0.0 0.8 0.0 0.8 0.0

Cede 21.4 0.8 2.4 0.0 4.8

Ceoc 17.9 12.9 38.1 28.8 16.0

Cy 4.8 20.2 13.5 0.0 0.0

Cyer 0.0 0.8 1.6 44.0 0.0

Cyir 0.0 3.2 35.7 1.6 0.0

Dite 0.0 0.8 3.2 2.4 0.0

Divi 0.0 0.0 1.6 0.0 0.0

Ecco 9.5 8.9 7.9 5.6 8.0

Eccr 0.0 0.8 10.3 4.0 0.0

Ecpr 0.0 0.0 16.7 10.4 0.0

Elmi 38.1 42.7 19.0 13.6 11.2

Elob 1.2 2.4 2.4 1.6 0.0

Fimi 0.0 1.6 13.5 4.8 0.0

Glaq 0.0 0.0 0.8 0.0 0.0

Here 3.6 10.5 1.6 0.8 0.8

Hisp 0.0 0.0 0.8 1.6 0.0

Hyqu 0.0 3.2 1.6 3.2 4.0

Ipsp 0.0 1.6 0.0 0.0 0.0

Jusp 0.0 0.0 0.8 0.0 0.0

Lefa 0.0 0.0 0.8 7.2 0.0

Leor 1.2 5.6 1.6 0.8 1.6

Lidu 0.0 2.4 7.1 3.2 0.0

Lisp 70.2 14.5 12.7 8.0 41.6

Lude 6.0 3.2 7.1 4.0 0.0

Lule 0.0 0.0 7.9 0.0 0.0
50

Appendix 2. Continued. 

Species June 1995 Aug. 1995

Month

Sept. 1995 Oct. 1995 June 1996

Lupa 75.0 19.4 2.4 0.0 19.6

Lupe 0.0 54.0 53.2 4.0 57.6

Lusp 1.2 1.6 2.4 0.0 0.0

Luur 0.0 0.8 0.0 0.0 0.0

Misc 0.0 0.8 3.2 4.0 0.0

Mist 0.0 0.0 1.6 0.8 0.0

Mysp 1.2 0.8 0.0 0.8 0.8

Nasp 29.8 0.0 0.0 0.0 18.4

Pasp 3.6 0.0 2.4 0.0 0.0

Plaq 0.0 3.2 4.8 5.6 1.6

Plfo 0.0 0.0 1.6 1.6 0.0

Po 0.0 0.8 1.6 0.0 2.4

Poan 0.0 0.0 1.6 0.0 0.0

Poau 0.0 0.0 0.0 3.2 0.0

Posp 15.5 0.0 0.0 0.0 18.4

Rhsp 0.0 0.8 0.0 0.0 0.0

Rici 2.4 0.0 1.6 1.6 1.6

Rico 0.0 0.0 0.0 3.2 0.8

Sagr 2.2 0.0 0.0 0.0 0.0

Sala 10.7 12.9 11.1 4.8 1.6

Sasp 0.0 0.0 0.0 0.0 0.8

Seex 0.0 3.2 5.6 1.6 0.8

Sppo 85.7 19.4 11.9 4.0 87.2

Spze 4.8 10.5 15.1 3.2 0.8

Tadi 1.2 0.8 6.3 1.6 1.6

Trwa 17.9 13.7 16.7 16.8 12.8

Uk 1.2 0.8 6.6 0.0 14.4

Utgi 48.8 3.2 3.2 2.4 7.2

Utin 9.5 0.0 0.0 0.0 60.8

Viro 0.0 0.0 0.8 0.0 0.0

Wosp 38.0 1.6 4.8 1.6 89.6

Xast 0.0 0.0 0.8 0.8 0.0
51

Appendix 3. Plant species total cover summed over transects at five sampling times at 

Felsenthal National Wildlife Refuge. See table 3 of the report for species codes. 

 

Species June 1995 Aug. 1995

Month

Sept. 1995 Oct. 1995 June 1996

Amco 0.5 74.5 24.5 14.5 0.0

Azca 10.5 0.0 0.5 0.5 209.5

Baeg 136.0 5.5 80.0 9.0 1.0

Baro 14.0 5.0 0.0 0.0 4.5

Biar 12.5 63.0 254.0 202.5 8.0

Brov 0.0 0.0 2.0 23.5 0.5

Caca 494.0 0.0 0.5 0.0 308.5

Casp 0.0 0.5 0.0 0.5 0.0

Cede 479.0 4.5 1.5 0.0 120.5

Ceoc 169.5 253.0 731.5 663.0 438.0

Cy 14.0 110.5 116.5 0.0 0.0

Cyer 0.0 63.0 67.5 2,172.5 0.0

Cyir 0.0 103.5 2,185.0 18.5 0.0

Dite 0.0 0.5 18.0 5.5 0.0

Divi 0.0 0.0 5.0 0.0 0.0

Ecco 92.0 144.5 135.0 27.5 217.5

Eccr 0.0 18.0 233.5 119.5 0.0

Ecpr 0.0 0.0 72.0 50.5 0.0

Elmi 1,417.0 2,017.0 779.0 642.5 275.0

Elob 88.0 5.5 9.0 22.5 0.0

Fimi 0.0 88.5 237.0 250.5 0.0

Glaq 0.0 0.0 0.5 0.0 0.0

Here 23.0 219.0 1.0 18.0 4.5

Hisp 0.0 0.0 4.5 5.0 0.0

Hyqu 0.0 37.0 151.0 111.0 116.5

Ipsp 0.0 5.0 0.0 0.0 0.0

Jusp 0.0 0.0 0.5 0.0 0.0

Lefa 0.0 0.0 4.5 248.5 0.0

Leor 4.5 15.5 1.0 4.5 5.0

Lidu 0.0 1.5 34.0 18.0 0.0

Lisp 553.0 73.5 252.0 142.5 453.5

Lude 24.0 18.0 55.5 55.0 0.0

Lule 0.0 0.0 125.5 0.0 0.0

 
52

Appendix 3. Continued. 

 

Species June 1995 Aug. 1995

Month

Sept. 1995 Oct. 1995 June 1996

Lupa 1,307.0 796.5 23.0 0.0 123.0

Lupe 0.0 3,324.0 2,337.0 18.5 1,712.5

Lusp 4.4 5.0 1.5 0.0 0.0

Luur 0.0 38.0 0.0 0.0 0.0

Misc 0.0 0.5 6.0 22.5 0.0

Mist 0.0 0.0 9.0 0.5 0.0

Mysp 0.5 4.5 0.0 4.5 18.0

Nasp 1,331.0 0.0 0.0 0.0 515.5

Pasp 5.5 0.0 5.5 0.0 0.0

Plaq 0.0 14.0 19.0 15.5 5.0

Plfo 0.0 0.0 5.0 9.0 0.0

Po 0.0 0.5 5.0 0.0 1.5

Poan 0.0 0.0 1.0 0.0 0.0

Poau 0.0 0.0 0.0 14.0 0.0

Posp 107.0 0.0 0.0 0.0 588.5

Rhsp 0.0 4.5 0.0 0.0 0.0

Rici 1.0 0.0 1.0 1.0 1.0

Rico 0.0 0.0 0.0 6.0 0.5

Sagr 1.0 0.0 0.0 0.0 0.0

Sala 217.0 469.0 304.0 23.0 42.5

Sasp 0.0 0.0 0.0 0.0 0.5

Seex 0.0 6.0 166.5 9.0 0.5

Sppo 1,864.5 278.0 179.5 28.0 2,185.5

Spze 10.0 228.5 441.0 19.5 0.5

Tadi 0.5 0.5 16.0 5.0 1.0

Trwa 51.5 105.0 237.0 250.0 41.5

Uk 0.5 0.5 4.0 0.0 9.0

Utgi 178.5 2.0 39.5 72.0 30.0

Utin 262.0 0.0 0.0 0.0 2,930.0

Viro 0.0 0.0 0.5 0.0 0.0

Wosp 64.0 5.0 215.5 1.0 2,675.0

Xast 0.0 0.0 4.5 4.5 0.0