Agronomy Journal Grow Your Career With ASA
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (4)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by McFarland, J.B.
Right arrow Articles by Mitchell, R.
Right arrow Search for Related Content
PubMed
Right arrow Articles by McFarland, J.B.
Right arrow Articles by Mitchell, R.
Agricola
Right arrow Articles by McFarland, J.B.
Right arrow Articles by Mitchell, R.
Related Collections
Right arrow Forage Management
Right arrow Other Forage Crops
Right arrow Nutrient Cycling
Agronomy Journal 92:42-47 (2000)
© 2000 American Society of Agronomy

FORAGES

Fire Effects on Weeping Lovegrass Tiller Density and Demographics

J.Brent McFarlanda and Rob Mitchella

a Dep. of Range, Wildlife, and Fisheries Management, Texas Tech Univ., Lubbock, TX 79409-2125 USA

c7mrb{at}ttacs.ttu.edu


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
Prescribed burning is a common management practice applied to weeping lovegrass [Eragrostis curvula (Schrad.) Nees], but little is known about tiller density and demographic response to burning. Our objectives were to determine fire effects on weeping lovegrass tiller density and demographics on a site, seeded in 1989, in western Texas. Tillers were sampled at 14-d intervals in 1996 and 1997 to determine tiller density and demographics. Tiller density response to burning differed between years. Burning increased tiller density 61% compared with no burning in 1996, but did not affect tiller density in 1997. In 1996, tiller density ranged from 1068 to 2052 and 1623 to 2617 tillers m-2 in nonburned and burned areas, respectively. In 1997, tiller density ranged from 1337 to 2398 and 1313 to 2027 tillers m-2 in nonburned and burned areas, respectively. Tillers in nonburned and burned areas remained primarily vegetative throughout each growing season with few tillers advancing to reproductive and seed-ripening stages, likely a response to poor fertility on the site. Burning increased reproductive tiller numbers by 238% compared with no burning in 1996, but few advanced to the seed-ripening stage. In 1997, most reproductive tillers advanced to the seed-ripening stage, likely responding to precipitation. Burning apparently altered the light environment and increased nutrient availability to weeping lovegrass. Yearly variation in the response to burning of weeping lovegrass tiller density and tiller demographics demonstrates that management must be based on current tiller populations.

Abbreviations: CRP, Conservation Reserve Program • DOY, day of the year


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
WEEPING lovegrass is a perennial, warm-season bunchgrass introduced from central and southern Africa in the 1930s (Crider, 1945; Masters and Britton, 1990). Weeping lovegrass is productive on a wide variety of soils, but is best suited to sandy and sandy loam soils (Dahl and Cotter, 1984). Consequently, weeping lovegrass monocultures were seeded on more than 400000 ha of highly erodible sandy soils in a seven-county region on the southern High Plains of Texas during the Conservation Reserve Program (CRP) from 1987 through 1990.

Weeping lovegrass produces more forage than native rangeland (Staten and Elwell, 1944) and has produced more than 700 kg of beef ha-1 during a 6-mo grazing season in western Texas (Dahl and Cotter, 1984). Consequently, large quantities of plant detritus may accumulate annually, which affects many ecological processes (Knapp, 1984) and may significantly lower weeping lovegrass productivity. Excessive accumulations of litter in weeping lovegrass tend to lower dry matter production and forage quality (McIlvain and Shoop, 1970). Like other cespitose species, weeping lovegrass grows from the center outward and tillers in the middle of the clump die, preventing new tillers and roots from growing on the inner portion of the plant. As a result, a few weak tillers form on the perimeter of the decadent clump, and unused weeping lovegrass stands may eventually die (Dahl and Cotter, 1984). Proper management is the key to maintaining weeping lovegrass production (McIlvain and Shoop, 1970).

Prescribed burning is a practical and efficient management tool for maintaining weeping lovegrass stands (Dahl and Cotter, 1984; McIlvain and Shoop, 1970). Klett et al. (1971) noted that burning increased weeping lovegrass herbage production by 14% compared with no burning. Along with increased herbage production, burning influenced cattle (Bos sp.) grazing preference. Due to reduced amounts of rank old growth and increased protein content, cattle were observed grazing 52% of the burned area and only 8% of the nonburned area. Dalrymple (1968) found that burned plots had 50% more grazable forage early in the growing season compared with nonburned plots. Early spring forage after burning was darker green and had higher moisture content, increasing weeping lovegrass palatability. Burned areas had a greater density and uniformity of leaves compared with nonburned areas.

Asexual reproduction of new tillers is the primary mechanism for perennation of established grass swards (Waller et al., 1985). Tillering allows young seedlings to become established and to regenerate a sward following the flowering stage of a plant (Jewiss, 1972). In perennial grasses, there is often a high tiller natality and high tiller mortality associated with flowering (Matthew et al., 1993). Grass leaves that have been removed are subsequently replaced by new leaves from apical meristems, or from axillary buds if the growing points have been removed (Sims et al., 1972). Grasses that can produce numerous tillers, therefore, have the ability to persist under severe conditions, such as heavy grazing or frequent fire.

Reduced tiller density does not necessarily result from plant stress, but may be a consequence of the developmental morphology of the grass (Gatsuk et al., 1980). Few tillers are formed after reproduction in warm-season grasses native to North America, causing tiller density to decline (Mitchell et al., 1998). Additionally, vegetative tiller mortality usually occurs during the flowering stage due to the increased demand for nutrients of the reproductive tillers (Ong, 1978). Tiller mortality causes the centers of cespitose grasses to die, resulting in lower overall productivity. Perennial grasses depend on successive development of axillary buds to initiate new tiller formation, which allows for the continued existence of the plant (Briske, 1991). Plants lose all growth potential and will die if tiller recruitment is suspended for a time equivalent to the maximum longevity of the most recently formed tillers.

Shade from excessive litter can inhibit tiller growth and, thereby, seedhead production. Removal of old, decadent material by burning may stimulate reproductive and seed-ripening tiller development (Field-Dogdson, 1976). Burning increased seed production in weeping lovegrass (Kruger, 1984) and stimulated weeping lovegrass to flower in the immediate post-burn stage (Field-Dogdson, 1976). Weeping lovegrass seed production increased from 187 kg ha-1 on nonburned areas to 532 kg ha-1 on burned areas following early spring burning.

Little is known about weeping lovegrass tiller density and tiller demographics, or the effect of prescribed burning on weeping lovegrass tiller density and tiller demographics. Our objectives were to determine the influence of fire on weeping lovegrass tiller density and tiller demographics throughout the growing season in the Southern High Plains of Texas.


   Materials and methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
Results and discussion
 Conclusions
 REFERENCES
 
This study was conducted in 1996 and 1997 in Lynn County, Texas (33°10' N, 101°49' W; 951 m above mean sea level) on an Amarillo loam soil (fine-loamy, mixed thermic Aridic Paleustalf). The area was seeded to `Ermelo' weeping lovegrass in 1989 as part of the CRP. Management practices including fertilization, grazing, and harvesting were excluded as required by the CRP contract. Prior to enrollment in the CRP, the site produced continuous dryland cotton (Gossypium hirsutum L.). Average annual precipitation is 508 mm with 85% occurring from 1 April through 31 October (NOAA, 1995).

The experiment was a completely random split-plot design with three replicates. Whole plots were burning treatment (30 by 30 m) and split plots were sampling date. Three randomly selected plots were burned with headfires on 8 Apr. 1996 and three previously nonburned areas were burned on 4 Apr. 1997. Nonburned areas were not disturbed prior to sampling in either year. No clipping or grazing occurred on these sites except for sampling. Although weeping lovegrass is commonly fertilized, no fertilizer was applied during this study. Sampling areas were based on site characteristics, including areas burned with a headfire and areas away from terrace tops, terrace bottoms, and water collection sites. Estimated fine fuel load on plots burned in 1996 and 1997 was 6780 and 8520 kg ha-1, respectively. During burning in 1996, maximum air temperature was 23°C, minimum relative humidity was 24%, and average wind speed was 16 km h-1. During burning in 1997, maximum air temperature was 17°C, minimum relative humidity was 36%, and average wind speed was 14 km h-1.

First growth of weeping lovegrass was harvested at crown level from two randomly selected sites per plot using 0.1 m2-frames. Samples were collected 10 times during the growing season at 14-d intervals from 28 May to 1 October in 1996 and 1997. Weeping lovegrass tillers were separated and morphologically classified by vegetative, elongation, reproductive, and seed-ripening stages in the nonburned and burned areas using the system described by Moore et al. (1991). Tillers from each sampling date were counted to determine changes in tiller density in both the nonburned and burned areas throughout the growing season. Tillers from each developmental stage were counted to determine tiller demography throughout the growing season.


   Results and discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
Conclusions
 REFERENCES
 
Total precipitation from burning to completion of sampling was 523 mm and 493 mm in 1996 and 1997, respectively. The primary difference between years was in precipitation pattern (Fig. 1) . The majority of the precipitation (81%) occurred between 1 June and 30 September in the 1996 growing season. No precipitation occurred from the burn date [8 April; Day of Year (DOY) 99] to the first sampling date (28 May; DOY 149) in 1996. Cumulative precipitation from 9 July (DOY 191) to 3 September (DOY 247) 1996 was 372 mm. Precipitation pattern in 1997 was the inverse of 1996. The majority of the precipitation (58%) occurred between the burn date (4 April; DOY 94) and 30 June (DOY 181) in 1997, with 385 mm occurring during this period. Average high temperature during the 1996 and 1997 sampling period was 31°C. The highest average temperature in 1996 occurred from 26 June (DOY 178) to 9 July (DOY 191) and 24 July (DOY 206) to 6 August (DOY 219). Average high temperature in 1997 fluctuated between only 31 and 33°C from 12 June (DOY 163) to 17 September (DOY 260). Average low temperature in 1996 and 1997 was 17°C.



View larger version (34K):
[in this window]
[in a new window]
  		Fig. 1 Precipitation occurrence and average high and low temperatures at approximately 14-d intervals from burn date to final sampling in Lynn County, Texas, during the 1996 and 1997 growing seasons

 
Tiller Density
Weeping lovegrass tiller density response to burning was different in 1996 and 1997. Burning increased weeping lovegrass tiller density by an average of 61% compared with no burning in 1996 (Table 1) . Tiller density in nonburned areas was higher in 1997 than in 1996, probably because of higher precipitation in 1997, but burning did not increase weeping lovegrass tiller density in 1997 (Table 1). In 1996, tiller density ranged from 1068 to 2052 tillers m-2 in nonburned areas, and from 1623 to 2617 tillers m-2 in burned areas. In 1997, tiller density ranged from 1337 to 2398 tillers m-2 in nonburned areas, and 1313 to 2027 tillers m-2 in burned areas.


View this table:
[in this window]
[in a new window]
  		Table 1 Weeping lovegrass tiller density on nonburned and burned areas in Lynn County, Texas during the 1996 and 1997 growing seasons. Values are means ± 1 standard error

 
Tiller density was probably correlated to precipitation events in 1996 and 1997. The majority of the 1996 summer rainfall occurred after 9 July (DOY 191). Tiller density increases occurred later in the growing season on nonburned and burned areas in 1996. Additionally, more tillers were found in nonburned areas at the first sampling date in 1997 than in 1996 and more precipitation occurred prior to the first sampling. Tiller density on nonburned and burned areas was erratic in 1997. The unpredictable tiller density pattern on nonburned and burned areas in 1997 may have resulted from little late-season precipitation.

Late-season increases in weeping lovegrass tiller density differ from other warm-season grasses native to North America. Big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) tiller densities decreased with plant maturity (Mitchell et al., 1998). Like big bluestem and switchgrass, weeping lovegrass develops a closed canopy, reducing light quantity and modifying light quality. On burned areas, weeping lovegrass maintained a relatively open canopy throughout the growing season. Removing excessive, decadent plant material probably increased the amount of light available for activating axillary buds and producing new shoots (Knapp, 1984). Burning to remove plant debris stimulates plant growth by improving light availability to the plant.

Tiller Demographics
Tiller demographics varied throughout the growing season in 1996 and 1997. Tillers in nonburned and burned areas remained primarily vegetative throughout the 1996 and 1997 growing seasons with few tillers advancing to the reproductive and seed ripening stages (Fig. 2 and 3) . Weeping lovegrass vegetative tiller trends were similar to tiller density trends throughout the 1996 and 1997 growing seasons, which indicates vegetative tillering controls total tiller density. Burning increased weeping lovegrass vegetative tillers by 36% compared with no burning in 1996. The effect of burning on vegetative tillering was less predictable in 1997. Vegetative tillers comprised at least 99 and 96% of the tillers in nonburned areas and 96 and 92% of the tillers in burned areas in 1996 and 1997, respectively (Fig. 2 and 3). Similar results were reported for nonburned big bluestem (Mitchell et al., 1998). However, big bluestem vegetative tillers declined as the season progressed, whereas vegetative tillers in weeping lovegrass increased from initial sampling to the end of sampling. Switchgrass, on the other hand, exhibited decreased vegetative tillering as the growing season progressed with no vegetative tillers present at the end of the growing season.



View larger version (48K):
[in this window]
[in a new window]
  		Fig. 2 Tiller density (no. m-2) in vegetative, reproductive, and seed-ripening developmental stages as a function of day of the year on nonburned and burned areas of weeping lovegrass in Lynn County, Texas, during the 1996 growing season

 


View larger version (47K):
[in this window]
[in a new window]
  		Fig. 3 Tiller density (no. m-2) in vegetative, reproductive, and seed-ripening developmental stages as a function of day of the year on nonburned and burned areas of weeping lovegrass in Lynn County, Texas, during the 1997 growing season

 
Few weeping lovegrass tillers were found in the elongation stage in 1996 and 1997. Of the approximately 40000 tillers staged in 1996 and 1997, only 5 tillers in the elongation stage were detected. Although differentiation occurred, the nodes of elongating weeping lovegrass tillers may be too small to be visible or palpable during staging, making identification of the elongation stage difficult. However, the few elongating tillers identified during staging were readily identifiable. An equally plausible explanation for the lack of identification of elongating tillers could be the rapid occurrence of elongation in perennial grasses. It is likely that elongation occurred rapidly during the 14-d interval between sampling dates, so elongation was not observed.

Reproductive tillering was influenced by burning and sampling date in 1996 and by sampling date in 1997. Burning increased reproductive tiller numbers by 238% compared with no burning in 1996. However, few vegetative tillers advanced to the reproductive stage on nonburned and burned areas in 1996 and 1997. In 1996, only 3 and 4% of the tillers on nonburned and burned areas, respectively, advanced to the reproductive stage. In 1997, 10 and 14% of the tillers on nonburned and burned areas, respectively, advanced to the reproductive stage. More reproductive tillers were found during the middle of the growing season in 1996 compared with the beginning and end, whereas a majority of reproductive tillers were found early in the 1997 growing season. Nonburned weeping lovegrass reproductive tillers increased little during the 1996 growing season, and were not present until the final sampling. Nonburned reproductive tillering peaked on 6 August (DOY 219) at 53 tillers m-2 in 1996 and on 11 June (DOY 162) at 107 tillers m-2 in 1997. After 9 July (DOY 190) 1997, no reproductive tillers were found on nonburned areas. Reproductive tillers on burned areas peaked on 6 August (DOY 219) at 148 tillers m-2 in 1996 and on 11 June (DOY 162) at 290 tillers m-2 in 1997. This is consistent with other studies reporting that burning stimulates weeping lovegrass reproductive tillering (Field-Dogdson, 1976; Kruger, 1984). Field-Dogdson (1976) reported 370 seedheads m-2 on nonburned areas and 1203 seedheads m-2 on burned areas in South Africa. Removal of decadent material increases light penetration in grasslands by removing sources of absorption and reflection of incoming radiation (Knapp, 1984), which may result in increased reproductive tillering. In North American tallgrass prairie, burning increased big bluestem ramet density by 52% and flowering stem density by 87% (Knapp, 1984). Other warm-season grasses have shown similar trends. Kucera and Ehrenreich (1962) reported that burning increased reproductive tillers in big bluestem, little bluestem [Schizachyrium scoparium (Michx.) Nash], and indiangrass [Sorghastrum nutans (L.) Nash] by at least 270%.

Increased reproductive tillering on burned sites followed the first significant precipitation event in 1996 and 1997. Therefore, weeping lovegrass appears to initiate reproductive tillering in response to precipitation events, especially in burned areas. Accumulation of litter in grasslands inhibits grass growth, primarily by maintaining low soil temperatures and reducing soil bacterial activity (Sharrow and Wright, 1977). Burning grasslands increases soil temperature through increased insolation, which increases nitrification of organic matter when soil water is adequate, resulting in increased nutrient availability. The combined effect of precipitation and increased nutrient availability on burned areas probably promoted reproductive tiller development.

Burning increased seed ripening tiller density in 1996 and 1997 . However, relatively few reproductive tillers advanced to the seed ripening stage in 1996, whereas a majority of reproductive tillers advanced to the seed ripening stage in 1997, probably the result of increased late season precipitation in 1997. In 1996, less than 1% of reproductive tillers advanced to the seed ripening stage on nonburned areas and at least 3% of reproductive tillers advanced to the seed ripening stage on burned areas. In 1997, at least 4% of reproductive tillers advanced to the seed ripening stage on nonburned areas and at least 16% of reproductive tillers advanced to the seed ripening stage on burned areas. Burning increased seed ripening tiller density later in the growing season during 1996. Many of the reproductive tillers found early in 1996 failed to produce seed, preventing advancement into the seed-ripening stage. The failure to produce seed was probably due to the adverse effect of precipitation deficit during critical seed-filling periods (Masters et al., 1993). Seed-ripening tillers in both nonburned and burned areas did not appear until 20 August (DOY 233) in 1996. Seed-ripening tillers peaked on both nonburned and burned areas on 17 September (DOY 261) at 15 and 80 tillers m-2, respectively in 1996. In 1997, burning increased seed ripening tillers by 385% compared with no burning. Seed-ripening tillers were present on nonburned and burned areas as early as 25 June (DOY 176) and peaked at 97 tillers m-2 on 9 July (DOY 190) in nonburned areas and at 320 tillers m-2 on 20 August (DOY 232) in burned areas in 1997. The morphological classification system used assesses different stages of development for each seed-ripening tiller, which accounts for the presence of seed-ripening tillers throughout the 1997 growing season in spite of the decline in reproductive tillers.


   Conclusions
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
REFERENCES
 
Burning is imperative for reducing litter in decadent weeping lovegrass stands. Burning will increase light quantity, improve light quality, increase nutrient availability to the plant, and optimize availability of green forage to livestock. Climatic conditions appear to be the primary factor determining the response of weeping lovegrass tiller density and demographics to prescribed burning. Only a small portion of the tillers advanced to reproductive and seed ripening stages, which makes management of the vegetative tillers in first growth critical. Both nonburned and burned weeping lovegrass maintains vegetative tillers throughout the growing season, but burning increases reproductive and seed-ripening tiller density compared with no burning. The high density of vegetative tillers in nonburned and burned areas supports the typical recommendation to rotationally graze weeping lovegrass stands heavily from early spring through early summer, rest pastures through the fall, and use summer and fall regrowth for winter grazing with protein supplementation. Ecologically, the high concentration of vegetative tillers provides a mechanism for reducing plant damage from herbivory by exposing few growing points to grazing throughout the growing season. Since weeping lovegrass stands are typically fertilized, additional research evaluating the effects of burning, fertilization, and possibly the alleviation of moisture deficits on tiller density and demographics would help determine maximum weeping lovegrass tiller density in this region.National Oceanic and Atmospheric Administration 1995


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
Contribution no. T-9-891 of the College of Agric. Sciences and Natural Resources, and Fire Ecology Center Tech. Pap. 3, Texas Tech Univ.

Received for publication October 14, 1998.
   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 




This article has been cited by other articles:


Home page
 Agron. J.Home page
R. Mitchell, J. Fritz, K. Moore, L. Moser, K. Vogel, D. Redfearn, and D. Wester
Predicting Forage Quality in Switchgrass and Big Bluestem
Agron. J., January 1, 2001; 93(1): 118 - 124.
[Abstract] [Full Text]

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (4)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by McFarland, J.B.
Right arrow Articles by Mitchell, R.
Right arrow Search for Related Content
PubMed
Right arrow Articles by McFarland, J.B.
Right arrow Articles by Mitchell, R.
Agricola
Right arrow Articles by McFarland, J.B.
Right arrow Articles by Mitchell, R.
Related Collections
Right arrow Forage Management
Right arrow Other Forage Crops
Right arrow Nutrient Cycling

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Crop Science Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome