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Published online 31 January 2005
Published in Crop Sci 45:494-502 (2005)
© 2005 Crop Science Society of America
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Release of Seed Dormancy in Field Plantings of Eastern Gamagrass

Lance R. Gibson*, Ezra Z. Aberle, Allen D. Knapp, Kenneth J. Moore and Roger Hintz

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011

* Corresponding author (lgibson{at}iastate.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Seed dormancy is a main factor limiting the use of eastern gamagrass (Tripsacum dactyloides L.) for forage and conservation purposes; however, there is little available information on the seed bank dynamics of eastern gamagrass plantings. Knowledge of the degree and rate of seed dormancy loss would improve decisions concerning eastern gamagrass plantings and provide a better understanding of the seed bank longevity for this species. In this study, cold, moist stratified seed or unstratified seed was planted at 2.5- and 5.0-cm depths on 16 Aug. 1999, 1 Nov. 1999, 14 April 2000, 15 May 2000, and 16 June 2000 for the first year of the study and 15 Aug. 2000, 31 Oct. 2000, 17 April 2001, 15 May 2001, and 15 June 2001 in the second year. Plants and seeds were retrieved at 3, 6, 9, and 12 mo after planting of 50 seeds for each seed treatment and planting depth combination. Intact seeds were germinated for 28 d and the viability of ungerminated seeds was determined with a tetrazolium test. Seed dormancy of both stratified and unstratified eastern gamagrass seed was lost mostly between mid-September and mid-November. No more than 12% dormant seed remained after mid-December and dormancy was completely lost by April and May. Seed dormancy in eastern gamagrass was substantially reduced with several weeks of soil temperatures below 15°C and adequate soil moisture.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
EASTERN GAMAGRASS is a warm-season, perennial, bunch grass found growing naturally from the northeastern and north central USA and south into Mexico, Central America, the Caribbean, and into Bolivia and Paraguay in South America (Newell and de Wet, 1974). It has agronomic (Brejda et al., 1994; Dickerson and Van Der Grinten, 1990; Fine et al., 1990; Joost and Roberts, 1996) and quality characteristics (Burns et al., 1992; Fine et al., 1990; Horner et al., 1985) that make it excellent forage. It also has a number of conservation uses including grass hedges for reducing runoff and erosion in row-crop fields, use in riparian zones, buffer strips, and conservation reserve program (CRP) acres in low-lying or wetter locations (Dewald et al., 1996).

Poor stand establishment remains one of the greatest factors inhibiting more widespread use of eastern gamagrass for forage and conservation purposes. Viability between 75 and 95% has been reported for commercially available seed, but laboratory germination of the seed was generally less than 15% (Aberle et al., 2003; Ahring and Frank, 1968; Tian et al., 2002). Planting eastern gamagrass seed in the late summer, fall, or winter months has resulted in acceptable stands (Aberle et al., 2003; Mueller et al., 2000). Planting untreated seed in the spring and early summer resulted in very poor stands (Aberle et al., 2003; Ahring and Frank, 1968; Mueller et al., 2000). Cold, moist stratification has been recommended and adopted as a practice for breaking eastern gamagrass seed dormancy (Ahring and Frank, 1968) in spring plantings, but stand establishment with this practice was not as successful as planting dry seed in the fall (Aberle et al., 2003). Fall and winter plantings may be some of the more successful practices for establishing eastern gamagrass because winter conditions trigger natural processes that break its seed dormancy (Ahring and Frank, 1968; Anderson, 1985).

The seed dormancy mechanisms for eastern gamagrass have not been fully determined. Stratification of hydrated seed at 4°C for at least 6 wk has been the most practical method of breaking the dormancy (Ahring and Frank, 1968; Anderson, 1985). The caryopsis of eastern gamagrass is encased in a cupule, a hard fruit case comprised of a modified rachis and hard glumes that surrounds the lemma and palea. Springer et al. (2001) hypothesized that the cupule restricts germination and its integrity must be reduced before germination will occur. Some dormancy has been eliminated by cupule removal (Anderson, 1985; Tian et al., 2003), but further treatment is needed to more fully break dormancy. Dehulled seed germination was increased 40 to 45.5% by 300 g kg–1 hydrogen peroxide solution (Kindiger, 1994). Removing the cupule and scarifying the pericarp over the embryo resulted in germination of all dormant seeds (Tian et al., 2003). Cupule removal followed by gibberellic acid application resulted in germination within 10% of all viable caryopses (Tian et al., 2003). However, gibberellic acid application to seeds contained in the cupule was only marginally effective at breaking seed dormancy (Tian et al., 2003). Tian et al. (2002)(2003) concluded that the cupule contributes to dormancy, but the pericarp and/or testa are the main factors restricting the germination of this species. Salt solutions of KNO3, sodium hypochlorite, and ethylene chlorohydrin, and 50 mL L–1 CO2 did not stimulate germination (Ahring and Frank, 1968; Anderson, 1985)

Several methods for breaking seed dormancy of eastern gamagrass have been identified and field studies confirm that dormancy is broken by winter climatic conditions. However, there is little knowledge of the seed bank dynamics for eastern gamagrass plantings. The objectives of our study were to determine the rate of dormancy loss and survivability of field planted eastern gamagrass seed. An advanced understanding of the sequence of events between seeding and plant establishment would allow land managers to make informed decisions about the timing and success of eastern gamagrass plantings. This information can also provide insights into seed bank longevity and dormancy mechanisms for this species.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
A 2-yr field experiment was conducted beginning in August 1999 at the Iowa State University, Sorenson Farm near Ames, IA (41°59' N, 93°55' W), on a Canisteo silty clay loam [fine-loamy, mixed (calcareous), mesic Typic Haplaquoll]. Eastern gamagrass was seeded in a randomized complete block design with four replications and factorial combinations of five planting dates, two planting depths, and two seed treatments. The planting dates were 16 Aug 1999, 1 Nov. 1999, 14 April 2000, 15 May 2000, and 16 June 2000 for the first year and 15 Aug. 2000, 31 Oct. 2000, 17 April 2001, 15 May 2001, and 15 June 2001 in the second year of the study. The two planting depths were 2.5 and 5.0 cm and the two seed treatments included cold-moist stratification and no stratification. Precipitation (Fig. 1) and temperature (Fig. 2) was monitored at the Iowa State University Agronomy/Agricultural and Biosystems Engineering Farm approximately 2 km northwest of the experiment site.


Figure 1
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  		Fig. 1. Monthly average precipitation from August 1999 to June 2002 for the Iowa State University Agronomy/Agricultural and Biosystems Engineering Farm near Ames, IA.

 

Figure 2
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  		Fig. 2. Monthly mean temperature from August 1999 to June 2002 for the Iowa State University Agronomy/Agricultural and Biosystems Engineering Farm near Ames, IA.

 
Seed of ‘Pete’ eastern gamagrass used for this experiment was purchased from Gamagrass Seed Company, Falls City, NE. Seed planted in Year 1 was harvested in 1998 and seed planted in year two was harvested in 1999. Seed (0.7 kg) for the cold, moist stratification treatment was soaked in 1 L of 2.5 g kg–1 thiram (tetramethylthiuram disulfide) solution, drained after 24 h, and placed in cold storage for 6 wk at 4°C and 40% relative humidity (RH). Unstratified seed was continuously stored dry in 4°C and 40% RH until planting.

A standard germination test, with three replications, was performed on both stratified and unstratified seed at each planting date. Fifty seeds were placed in 13- x 13- x 3.5-cm, covered containers containing two layers of Anchor Steel Blue seed germination paper (Anchor Paper Co., St. Paul, MN) moistened with distilled water. The tests were performed in a Conviron (Pembina, ND) model G30 germinator at 20/30°C alternating temperature (Ahring and Frank, 1968) with light (four 40-W cool-white fluorescent lights vertically oriented on each the left and right sides of the germinator) and 30°C for 8 h daily. Germination counts were made every 7 d for 28 d. Seeds were considered germinated if the coleoptile exceeded the seed in length and the seedling was normal according to the seedling evaluation criteria of AOSA for comparable grasses (AOSA, 1992). Normal seedlings were removed as they were counted. Water was added to each germination box as needed to maintain optimum moisture levels. After 28 d of incubation, ungerminated seeds were examined by tetrazolium (TZ) tests (AOSA, 1998) and classified as dormant or dead.

Seed bank dynamics and the rate of dormancy release for eastern gamagrass were determined through burial and retrieval of seeds in conjunction with a companion study assessing stand establishment of eastern gamagrass (Aberle et al., 2003). Four-row wide and 6.1-m-long plots were planted in 76.2-cm rows with a row crop planter. Fifty eastern gamagrass seeds were buried in 15-cm-long cylinders made from 30.5-cm diam, white PVC pipe placed within each row for retrieval later. The cylinders were positioned on alternate ends of each row and 1.5 m from the plot edge. Twelve centimeters of the cylinder was placed below the soil surface and it was filled with soil to within 2.5 or 5.0 cm of the soil surface depending on the planting depth treatment. Seeds were randomly scattered on the soil within each cylinder, additional soil was used to bury the seed to the appropriate planting depth, and the soil was firmed by hand. Seed was retrieved from one randomly selected cylinder in each plot at 3, 6, 9, and 12 mo after planting for a total of four retrievals per planting date, depth, and stratification treatment combination.

There were five possible fates for the 50 seeds retrieved at each date: (i) germination, emergence, and development into a live plant; (ii) viable, not dormant, and not yet germinated; (iii) viable and dormant; (iv) not viable; and (v) lost to predation or plant death after emergence. These fates were determined by washing soil retrieved from each cylinder through a screen to recover plants and seeds. The amount of nondormant seed was determined by germinating intact seeds for 28 d by the procedures described earlier. Seed that germinated on retrieval had experienced dormancy-breaking conditions, but had not experienced conditions suitable for germination in the field. The number of dormant and nonviable seeds remaining after the 28-d germination period was determined by a tetrazolium test (AOSA, 1998). Dormant seed did not germinate, but remained viable after the 28-d controlled germination test.

Statistical Analysis
The statistical design for the study was a split-plot randomized complete block design with replications being assigned within years. Planting date, planting depth, and seed treatment were randomly assigned to 18.6-m2 plots within each of four replicated blocks. Effects of these treatments were tested by the plot mean squares. The four retrieval times were randomly assigned to cylinders within each plot. Effects of retrieval times were tested using the residual mean squares. Analysis of variance for the effects of planting year, planting date, seed stratification, planting depth, and retrieval time on the number of plants, germinating seed, and dormant seed was performed by Proc Mixed of SAS (SAS Institute Inc, 1999). All treatment variables were analyzed as fixed effects. Because an F test indicated highly significant effects of planting year, planting date, and the interaction of these two factors, further Proc Mixed analysis was performed on the effects of seed stratification, planting depth, and retrieval time for each individual planting date. Tukey's test (Steele and Torrie, 1980, p. 185) was used to do statistical comparisons between means for seed stratification and planting depth treatments at each retrieval date. The significance level for all statistical comparisons was P < 0.05 and only significant differences are mentioned in the results and discussion text.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Since year x planting date interactions were significant for plant emergence, germinating seeds, and dormant seeds, the data were presented by planting date. Planting depth data are not presented in the figures because it had little influence on the fate of the seed. Seed stratification influenced the amount of plant emergence (Fig. 3) and germinating seed (Fig. 4) in six of the 10 plantings and dormant seed (Fig. 5) in four of the 10 plantings. A single line for each planting date in the figures was used to indicate that stratification treatment and interactions of stratification treatment with retrieval date were not significant. Separate lines for stratified and unstratified seed with no denotation of significance for individual retrieval dates were used to represent significant main effects of seed stratification treatment. When interactions of stratification treatment with retrieval date were significant, significance of stratification treatment was indicated for each retrieval date.


Figure 3
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  		Fig. 3. Plant emergence from 50 seeds of eastern gamagrass planted at various dates and retrieved 3, 6, 9, and 12 mo after planting. Seed was either wet stratified at 4°C for 6 wk or unstratified before planting. Letters indicate statistical significance for the main effects of retrieval date. Plant emergence from retrieval dates with the same letter did not differ at P ≤ 0.05 according to Tukey's test. When interactions of stratification treatment with retrieval date were significant, significance of stratification treatment at each retrieval date was determined with Tukey's test. *, **, *** indicate differences between stratification treatments for a retrieval date at P ≤ 0.05, 0.01, and 0.001 levels, respectively. Separate lines for stratified and unstratified seed with no denotation of significance for individual retrieval dates represents significant (P ≥ 0.05) main effects of stratification treatment. A single line for a planting date indicates that stratification treatment and interactions of stratification with retrieval date were not significant.

 

Figure 4
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  		Fig. 4. Germinating seeds retrieved at 3, 6, 9, and 12 mo after planting 50 eastern gamagrass seeds at various dates. Seed was either wet stratified at 4°C for 6 wk or unstratified before planting. Letters indicate statistical significance for the main effects of retrieval date. Seed germination from retrieval dates with the same letter did not differ at P ≤ 0.05 according to Tukey's test. When interactions of stratification treatment with retrieval date were significant, significance of stratification treatment at each retrieval date was determined with Tukey's test. *, **, *** indicate differences between stratification treatments for a retrieval date at P ≤ 0.05, 0.01, and 0.001 levels, respectively. Separate lines for stratified and unstratified seed with no denotation of significance for individual retrieval dates represents significant (P ≥ 0.05) main effects of stratification treatment. A single line for a planting date indicates that stratification treatment and interactions of stratification with retrieval date were not significant.

 

Figure 5
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  		Fig. 5. Dormant seeds remaining after a 28 d germination test for seed retrieved at 3, 6, 9, and 12 mo after planting of 50 eastern gamagrass seeds at various dates. Seed was either wet stratified at 4°C for 6 wk or unstratified before planting. Letters indicate statistical significance for the main effects of retrieval date. The number of viable seeds from retrieval dates with the same letter did not differ at P ≤ 0.05 according to Tukey's test. When interactions of stratification treatment with retrieval date were significant, significance of stratification treatment at each retrieval date was determined with Tukey's test. *, **, *** indicate differences between stratification treatments for a retrieval date at P ≤ 0.05, 0.01, and 0.001 levels, respectively. Separate lines for stratified and unstratified seed with no denotation of significance for individual retrieval dates represents significant (P ≥ 0.05) main effects of stratification treatment. A single line for a planting date indicates that stratification treatment and interactions of stratification with retrieval date were not significant.

 
Seed Dormancy and Plant Production
Laboratory germination and tetrazolium tests on dry seed indicated that the percentage of inherent dormancy was 83 to 85% of the viable seed used in this study (Table 1). Seed dormancy was lost in all plantings within the first year after planting. Only April plantings had seed that germinated after being retrieved from the soil at 12 mo after planting. The greatest number of plants produced from 50 seeds was 35 indicating that about 70% of the seeds were capable of producing a plant under the field conditions of this study. This was greater than the 37 to 50% germination for stratified seed of the two lots used. However, it was less than the 78 to 95% viability of the seed lots.


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  		Table 1. Seed quality of the lots used in the study.

 
The number of emerged plants had reached a maximum at three months after planting for both stratified and unstratified seed planted on 16 Aug. 1999, 14 April 2000, and 17 April 2001. Plant emergence reached its peak in the spring following the 15 Aug. 2000, 1 Nov. 1999, 31 Oct. 2000, 15 May 2000, 15 May 2001, 16 June 2000, and 15 June 2001 plantings.

Mid-August Plantings
In the August plantings from either year, there were less than five dormant seeds remaining by mid-November and nearly all dormancy was lost by mid-February. There was never more than one germinating seed retrieved in mid-May from the August plantings. In 1999, 50% of the seed had produced plants and another 40% of the seed germinated when retrieved three months after planting. Plant number did not increase in the mid-May retrieval suggesting that the 40% of seed that germinated at 3 mo after planting contributed little to final plant number. However, it was more likely that some plants were lost from fall to spring and seed that remained until spring provided replacement plants. Divergent plant emergence patterns between August plantings in the 2 yr may have resulted from precipitation differences. August and September rainfall was 15% above the 50-yr average in 1999, but 68% below average in 2000 (Fig. 1).

Late-October–Early-November Plantings
For the 1 Nov 1999 planting, nearly all the seed dormancy was gone by February. However, dormancy of seed planted on 31 Oct. 2000 was not completely lost until the May retrieval. Stratification increased the amount of germinating seed in the February retrieval by seven to eight seeds, but had no affect on the amount of dormant seed in any of the retrievals. Plant emergence for the October-November plantings was completed by mid-May. Some plant death occurred between mid-May and mid-August for the 31 Oct. 2000 planting.

Mid-April Plantings
Seed stratification had its greatest effect on April plantings. Interactions of seed stratification treatment with retrieval date were significant for April plantings in both years. By mid-July, the stratified seed produced as many as 27 plants compared with 11 or less for the unstratified seed. The unstratified seed mostly remained dormant in the summer following planting and dormancy in the mid-July retrieval was at least double that of stratified seed. By mid-October the dormancy was almost completely gone from both stratified and unstratified seed. However, the seed had not experienced climatic conditions suitable for field emergence by mid-April of the year following planting. At 12 mo after planting, there were 19 to 23 seeds in the unstratified treatment capable of germination. Between five and 12 germinating seeds were retrieved from the stratification treatment in the winter indicating that the cold, moist pretreatment did not completely break dormancy before planting.

Mid-May Plantings
Seed dormancy played a significant role in the emergence patterns for May plantings. At 3 mo after planting, there were 10 plants emerged in both 2000 and 2001 and 10 to 15 dormant seed. Stratification treatment had no effect on dormant seeds in either year. By mid-November, there were only five dormant seeds remaining in the 15 May 2000 planting and no dormant seeds in the 15 May 2001 planting. Seed dormancy in the 15 May 2000 planting was mostly gone by mid-February, but not completely lost until the 12-mo retrieval in mid-May. Stratification treatment influenced plant emergence and seed germination in 2000, but not in 2001. The responses to stratification in 2000 were not significant until the 15 November retrieval when stratification resulted in greater emergence and germination. More than half the emerged plants from the unstratified seed planted in May 2000 and both the stratified and unstratified seed planted in May 2001 were counted at the 12-mo retrieval. Most of the plants emerging from stratified seed planted on 15 May 2000 appeared in the summer of the planting year. However, there was an increase in the number of plants from 17 at the 6- and 9-mo retrievals to 23 at the 12-mo retrieval. Two to five seeds retrieved in mid-August germinated in the controlled germination test indicating that some of the nondormant seed did not germinate in the field because summer conditions were unfavorable.

Mid-June Plantings
Seed stratification effects were significant for the June planting in 2000, but not in 2001. The interactions between retrieval date and stratification treatment in 2000 most likely resulted because the stratification treatment released dormancy within much of the seed, while substantial amounts of dormancy remained in the unstratified seed until the winter and spring retrievals. Much of the emergence from the stratified seed planted on 16 June 2000 occurred in the first three months. However, there were 10 dormant seeds in the stratified seed at the mid-September retrieval and an additional eight plants were counted at the 12-mo retrieval. Emergence from the unstratified seed planted on 16 June 2000 mostly occurred in the spring following planting and were counted in the 12-mo retrieval. Precipitation was well below normal in June, July, and August of 2001, so that few plants emerged from the stratified or unstratified seed treatments in the summer immediately following the 15 June 2001 planting. Seed dormancy was broken during the winter months; so most of the emergence occurred in the spring following planting. When viewed over both study years, two to six dormant seeds remained at the mid-December retrieval, but the seed dormancy was mostly lost by the mid-March retrieval.

Planting Depth
There were only small differences in response to planting depths of 2.5 and 5.0 cm. Planting depth influenced plant production in only three of the 10 planting dates and there were no consistent trends among relatively minor differences (data not shown). Planting depth had no significant affect on the number of germinating seeds retrieved. The interaction of planting depth and retrieval date was significant for the number of viable seeds retrieved from the 16 June and 15 Aug. 2000 plantings. These interactions occurred because there were three to five fewer dormant seeds at 2.5 than 5.0 cm when seeds were retrieved 3 and 6 mo after planting and no viable seed remaining at 9 and 12 mo after planting.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Dormancy levels in the unstratified seed used in this study were representative of the high dormancy levels of newly harvested seed of eastern gamagrass (Ahring and Frank, 1968; Anderson, 1985). Dormant seeds were viable but did not germinate in the laboratory germination test. Using these criteria, 63 and 81% of the seed was dormant in the lots used for 1999–2000 and 2000–2001 plantings, respectively. While cold, wet stratification of seed before planting released some of the seed dormancy, 30 and 58% of the seed remained dormant after the stratification of seed used in 1999–2000 and 2000–2001, respectively.

The results from the five planting dates used in this study suggest that seed dormancy of both stratified and unstratified eastern gamagrass seed was lost mostly between mid-September and mid-November. There was a small amount of dormancy that lingered into mid-December, mid-January, and mid-February. But dormancy levels in these retrievals remained at or below 12% of the planted seed. Seed dormancy was completely lost from all plantings by April and May of the year following planting. Although the amount of dormant seed retrieved in the summer months immediately after the mid-April, mid-May, and mid-June plantings was often less than half the amount of dormancy measured in the laboratory tests, the amount of plant emergence was similar to or less than the laboratory germination rates. This suggests that seeds dormant at planting either remained dormant until the fall or died shortly after planting.

Seed dormancy in eastern gamagrass can be broken with cold, wet prechilling (Ahring and Frank, 1968; Anderson, 1985). Previously reported temperatures for wet, prechilling of seed were 4.4°C for 60 d (Anderson, 1985) and 5 to 10°C for 6 to 8 wk (Ahring and Frank, 1968). Field conditions needed to release dormancy from most of the seeds were experienced between mid-September and mid-November in the location used in our study. The average mean temperature for mid-September to mid-October was 13°C (Fig. 2) with an average low of 6°C and an average high of 20°C. Seed dormancy was lost during this period even though precipitation for these months was below normal for this location in both years (Fig. 1). While the seed dormancy mechanisms in eastern gamagrass have yet to be fully determined, the current study indicates that the dormancy was quickly and almost completely released in a field setting with several weeks of soil temperatures below 15°C and adequate soil moisture.

Dormant seed remained through the first summer in the stratified seed planted in mid-April, mid-May, and mid-June as indicated by the amount of viable seed retrieved in the summer, germinating seed retrieved in the winter, and plant emergence in the spring. The dormancy levels remaining through the summer were below the levels in the stratified seed before it was planted. This, as well as no viable seed remaining at 1 yr after any planting date, indicates that secondary dormancy, defined as the reintroduction of a state of dormancy after primary dormancy has been completely, or almost completely terminated (Simpson, 1990, p. 50), did not occur.

The rapid, complete, and irreversible loss of dormancy that occurred when eastern gamagrass seed experienced fall and winter climatic conditions has implications for the management of field plantings of this species as well as its survival in managed and natural settings. As a bunchgrass, eastern gamagrass does not possess the ability to rapidly spread via vegetative propagation. This, coupled with a short-lived seed bank, suggest that rapid and uniform establishment may be more critical for this species than ones that can spread by creeping rhizomes and stolons or possess a persistent seed bank because of prolonged seed dormancy. Poor establishment would result in within-row gaps devoid of eastern gamagrass plants. If these gaps exist at 1 yr after planting, they are likely to remain for several years.

It is generally accepted that eastern gamagrass is one of the first species to be eliminated from range and pasture sites by overgrazing (Roberts and Kallenbach, 1999; Stubbendieck et al., 1992, p. 45; Wright et al., 1983) and the loss of natural stands in North America has been attributed to overgrazing shortly after European settlement of rangelands (Polk and Adcock, 1964; Roberts and Kallenbach, 1999). The need for stored carbohydrates in the leaf bases for regrowth has been recognized as a primary factor in the survivability of eastern gamagrass. Grazing to a minimum height of 30 to 38 cm or a rest period after grazing is critical to its productivity and survival (Aiken and Springer, 1998; Brejda et al., 1997; Aiken and Springer, 1998). While a lack of regrowth potential under frequent and close defoliation limited the survival of eastern gamagrass on settled range lands, low seed production (Polk and Adcock, 1964; Lemke et al., 2003) and lack of long-term seed dormancy probably limited its ability to repopulate range lands and pastures if and when intense grazing pressures were removed.

Received for publication July 28, 2003.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 





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