Dominant Perennial Grass Research Articles

Perennial Grass Response to Seasonal Rests in Naturalised Pastures of Central New South Wales.

The influence of grazing management, herbicide and fertiliser on botanical change in two perennial grass based pastures was assessed over six years at two sites in central New South Wales. Ten treatments at both sites compared continuous grazing, three seasonal rests from grazing (autumn, winter, summer), and herbicide application for seedling grass control, each at two levels of fertiliser addition (nil, recommended). These treatments were designed to screen options for management rather than devise complete systems. In a degraded perennial pasture dominated by annual grasses, the proportion of perennial grasses and forbs increased with summer rests, especially at the recommended fertiliser level. Legumes increased with herbicide application, and annual grasses remained high in the continuously grazed control and other treatments. There were no significant effects on composition from autumn or winter rests. On the summer rest treatment at the recommended fertiliser level, perennial grasses (mostly cocksfoot) increased from 11% to 30% compared with the control where perennial grass declined below 5%. The increase was due to both recruitment and increase in size of existing plants, as a consequence of resting the perennial grasses when actively growing, flowering and setting seed, in favourable seasons. In contrast, on the better quality perennial pasture dominated by phalaris, there were limited management effects and perennial grasses increased on all treatments over time. The absence of a response at this site was attributed to a lenient stocking rate, dominant perennial grasses and limited rainfall during periods when active growth might be expected. Summer rests in this case also led to a small increase in forbs. The data suggest that perennial grasses can be encouraged with a conservative stocking policy that maintains the available feed-on-offer above 1 t DM/ha through seasons of active growth.

Herbage Dynamics on 2 Northern Great Plains Range Sites

Quantity and quality of forage produced are primary determinants of level of livestock production derived from grazing lands. Moreover, species composition of herbage is often considered a primary determinant of the ecological condition of rangelands. The broad objective of this study was to quantify the productivity, growth dynamics, and quality of herbage growing on 2 Northern Great Plains range sites and to concurrently relate magnitude and composition of production to the ecological condition of the sites. Using frequent harvest techniques, the 2-year study showed herbage production on the highly productive silty range site averaged 219 g m-2 as compared to 218 g m-2 on the supposedly less productive clay pan range site. The primary reason the clay pan site proved to be as productive as the silty site was attributed to the greater amounts of introduced annual grasses on the clay pan (148 g m-2) than the silty site (104 g m-2). The annual grass component on the clay pan was a near equal mix (71 vs 51 g m-2) of Japanese brome (Bromus japonicus Thunb.) and cheatgrass (B. tectorum L.) whereas the overwhelming dominant on the silty site was cheatgrass (73 g m-2). Western wheatgrass [Pascopyrum smithii Rydh. (Love)] was the dominant perennial grass on both sites averaging 49 g m-2 on the clay pan site and 57 g m-2 on the silty site. There were minimal differences between sites in terms of nutrient quality values (i.e., crude protein, acid detergent fiber, neutral detergent fiber) with results showing clearly that age of tissue was the major factor altering seasonal forage quality values. Range condition analyses revealed the clay pan site was in fair ecological condition and the silty site was in good condition. Study results demonstrate the need for land management agencies to continue to refine productivity estimates as well as adopt new techniques for assessing the ecological condition of rangelands.

Composition and Population Responses of an African Savanna Grassland to Rainfall and Grazing

Summary 1. The influence of inter-annual rainfall variability and cattle grazing on the abundance (density, basal area), population dynamics (recruitment, growth, survival) and population structure of the dominant perennial grasses of an African savanna was investigated from 1984 to 1989. The unpalatable Aristida bipartite and the palatable Heteropogon contortus and Themeda triandra reproduce by seed; Bothriochloa insculpta reproduces mainly by seed, but sometimes by stolons; Digitaria eriantha can be stoloniferous; Setaria incrassata has rhizomatous growth. 2. Species abundance was more responsive to rainfall variability than to grazing. Density increased in all species in response to several successive dry years because of recruitment and tuft fragmentation, but eventually decreased in a severe final drought year because of plant mortality. The response of basal cover differed between species and sites, although all species (except Digitaria) declined in the final drought year. 3. Seedling recruitment, plant basal area, and mortality were likewise more strongly influenced by rainfall variability than by grazing. Differences in the population dynamics of species were related to their life history attributes. Aristida, a prolific seed producer, was favoured by grazing because high levels of seedling recruitment could be maintained. Seedling recruitment of palatable species (Heteropogon, Themeda) and of Bothriochloa was initially increased under heavy grazing because openings were produced within the vegetation, but this was reversed by the end of the study because of a decline in available seed. There was limited seedling recruitment of Digitaria and Setaria, but recruitment of Digitaria from stoloniferous growth increased population size, although there was no expansion of Setaria clones under the conditions of this study. Themeda and Aristida seedlings attained greater size under heavy than under light grazing.

Effects of Fire in Tallgrass Prairie on Growth and Reproduction of Prairie Coneflower (Ratibida columnifera: Asteraceae)

Effects of fire on growth and reproduction of the perennial forb Ratibida columnifera were studied on the Konza Prairie Research Natural Area in northeastern Kansas, USA. Populations were sampled in seven different tallgrass prairie watersheds that varied in fire frequency and in the number of years elapsed since the last fire. Plants from sites not burned for many years were 2.6 times larger and produced 50% more stems than plants from recently burned sites. Number of seeds per plant was also higher in long-unburned sites due to greater numbers of flower heads per plant and greater numbers of achenes produced per head. Reproductive effort (ratio of inflorescence biomass to total vegetative biomass) was 33% lower in annually burned prairie than in any of the other sites. Significant differences in the relationships of inflorescence biomass to vegetative plant biomass in burned vs. unburned sites indicated that burning causes direct changes in plant reproductive effort independent from its effects on plant size. There was no clear relationship between patterns of seed production among sites and patterns of R. columnifera abundance. Ratibida columnifera responses to fire are most likely a result of changes in the relative competitive abilities of forbs and the dominant perennial grasses due to post-fire changes in abiotic conditions rather than a result of direct effects of fire on the fate of buds and subsequent vegetative and floral development.

EFFECTS OF FIRE IN TALLGRASS PRAIRIE ON GROWTH AND REPRODUCTION OF PRAIRIE CONEFLOWER (RATIBIDA COLUMNIFERA: ASTERACEAE)

Effects of fire on growth and reproduction of the perennial forb Ratibida columnifera were studied on the Konza Prairie Research Natural Area in northeastern Kansas, USA. Populations were sampled in seven different tallgrass prairie watersheds that varied in fire frequency and in the number of years elapsed since the last fire. Plants from sites not burned for many years were 2.6 times larger and produced 50% more stems than plants from recently burned sites. Number of seeds per plant was also higher in long‐unburned sites due to greater numbers of flower heads per plant and greater numbers of achenes produced per head. Reproductive effort (ratio of inflorescence biomass to total vegetative biomass) was 33% lower in annually burned prairie than in any of the other sites. Significant differences in the relationships of inflorescence biomass to vegetative plant biomass in burned vs. unburned sites indicated that burning causes direct changes in plant reproductive effort independent from its effects on plant size. There was no clear relationship between patterns of seed production among sites and patterns of R. columnifera abundance. Ratibida columnifera responses to fire are most likely a result of changes in the relative competitive abilities of forbs and the dominant perennial grasses due to post‐fire changes in abiotic conditions rather than a result of direct effects of fire on the fate of buds and subsequent vegetative and floral development.

Distribution of Microlaena stipoides and Its Association With Introduced Perennial Grasses in a Permanent Pasture on the Northern Tablelands of New South Wales

The distribution of Microlaena stipoides (Labill.) R.Br. and its association with introduced perennial grasses was studied in a 10.2-ha permanent pasture on the Northern Tablelands of New South Wales. There were 105 systematically arranged plots (2m × 2m quadrats) located in the field, and at each sampling location composition by basal cover of the perennial herbaceous species encountered was recorded using 100 points. Dominant perennial grasses identified in the field were the native M. stipoides and the introduced Lolium perenne L., Dactylis glomerata L. and Poa pratensis L. Trifolium repens L., sown in the field in 1961, was also widespread. M. stipoides was abundant throughout the paddock, although higher composition by basal cover was observed under tree canopies. Discriminant function analysis and hierarchical classification showed a tendency towards aggregation of plots dominated by M. stipoides, L. perenne and T. repens, which may indicate the stability of this combination of species. T. repens was present in almost all plots and had a similar distribution to M. stipoides; both species were quite close in the species ordination analysis and were found associated with other perennial grasses at different locations in the paddock. These species associations are probably stable and appear to be common in permanent pastures in the eastern parts of the Northern Tablelands.

Succession in Old‐Field Plant Communities: Effects of Contrasting Types of Nutrient Enrichment

We investigated the effects of monthly nutrient applications on succession in two old—field plant communities. Succession was monitored for 3 yr in 1—yr (younger) and 4—yr (older) experimental plots. Three 0.1—ha plots in each old field were treated with sludge, three with fertilizer, and two were left as untreated controls. In the younger community, herbaceous perennials and winter annuals replaced summer annuals by the 3rd yr of succession in control plots. Summer annuals, however, dominated enriched plots throughout the study. Species richness was significantly higher in enriched plots than in control plots during the 1st yr, but was significantly lower than control plots thereafter. Annual aboveground net primary productivity (ANPP) was significantly greater in enriched plots than in controls in the 1st yr, but the converse occurred in the 3rd yr. The type of nutrient enrichment affected ANPP; sludge plots had significantly lower ANPP than fertilizer plots in the 1st and 3rd yr. In the older community, two summer annuals and a biennial displaced dominant perennial grasses in enriched plots. In contrast to the younger community, ANPP was consistently greater in nutrient—enriched plots than in controls, and nutrient enrichment did not alter species richness. The type of nutrient enrichment affected the older community in an opposite manner from the younger community; sludge plots had significantly greater ANPP than fertilizer plots in the 3rd yr. We concluded that the age and physiognomy of the old—field community, the type of nutrients applied, and the duration of enrichment, each influenced the course of succession; responses observed in the 1st yr of enrichment were not indicative of later trends.

The Relationship of Sheep Grazing and Soil Heterogeneity to Plant Spatial Patterns in Dune Grassland

(1) Plant spatial patterns and their relationship with sheep grazing and the underlying soil patterns were examined in a dune grassland at Newborough Warren, Anglesey, Wales. (2) In the absence of grazing a hummock-hollow system in the vegetation was evident. The hummocks were 10-40 cm diameter units formed from tussocks of the dominant perennial grasses in the grassland, Arrhenatherum elatius, Poapratensis and Festuca rubra ssp. rubra. The majority of other species co-occurred on the hummocks, which represented high diversity, high density patches. In contrast, the hollows had few species present and a low plant density. (3) Grazing led to the break up of the hummock-hollow system, with A. elatius, in particular, declining in vigour. Other species such as Holcus lanatus and Anthoxanthum odoratum invaded the hollows and spread throughout the grassland. A. elatius, P. pratensis and F. rubra maintained a concentration of dominance on the hummocks, but the latter two species were spreading into the hollows. (4) The underlying soil showed a strong heterogeneity that was related to the hummockhollow microtopography. Soil under the hummocks had higher percentage roots and percentage organic carbon, was moister, more acidic, had higher conductivity and had higher levels of Ca, K, Mn, Mg, Na and P04 than the soil under the hollows. After three years of grazing, this pattern of soil heterogeneity had not changed. (5) The heterogeneity that existed in the vegetation reflected the level of sheep grazing. Grazing led to rapid changes in the plant patterns, whereas soil patterns were more stable and hence less dynamic.

Seed Production and Germination Response of Four Louisiana Populations of Uniola paniculata (Gramineae)

Sea oats, Uniola paniculata, is a characteristic and often dominant perennial dune grass of the southeastern Atlantic and Gulf coasts of the United States. However, U. paniculata loses its dominance and becomes almost nonexistent along a relatively narrow portion of its range, from west of the Mississippi River delta, Louisiana, through northeastern Texas. In Louisiana, U. paniculata is abundant on the Chandeleur Islands east of the delta, but along the barrier island chain west of the delta only three sizable populations have been identified, all on the Caminada-Moreau coast. We measured seed production and germination response to various moisture and temperature combinations in these populations. Seed production was found to range from one to three orders of magnitude less than what has been reported in areas where U. paniculata is dominant. Rates ranged from 0.091 seeds/spikelet on the Chandeleur Islands to only 0.002 seeds/spikelet on the Caminada-Moreau coast; one population failed to produce any seeds at all. Seed germination in an 18.3–35.0 C alternating thermoperiod was high (65–88%) after exposure of the seeds to a variety of pregermination moisture and temperature conditions. Exposure to 4.4 C during imbibition did not increase percentage germination, but did significantly increase the rate of germination over the pregermination treatments that did not include moisture. The very low seed production rates of these populations could explain the limited distribution of this species along the Louisiana coast, where overwash events are frequent, and rates of coastline retreat often exceed the highest measured rates of vegetative lateral spread.

SEED PRODUCTION AND GERMINATION RESPONSE OF FOUR LOUISIANA POPULATIONS OF UNIOLA PANICULATA (GRAMINEAE)

Sea oats, Uniola paniculata, is a characteristic and often dominant perennial dune grass of the southeastern Atlantic and Gulf coasts of the United States. However, U. paniculata loses its dominance and becomes almost nonexistent along a relatively narrow portion of its range, from west of the Mississippi River delta, Louisiana, through northeastern Texas. In Louisiana, U. paniculata is abundant on the Chandeleur Islands east of the delta, but along the barrier island chain west of the delta only three sizable populations have been identified, all on the Caminada‐Moreau coast. We measured seed production and germination response to various moisture and temperature combinations in these populations. Seed production was found to range from one to three orders of magnitude less than what has been reported in areas where U. paniculata is dominant. Rates ranged from 0.091 seeds/spikelet on the Chandeleur Islands to only 0.002 seeds/spikelet on the Caminada‐Moreau coast; one population failed to produce any seeds at all. Seed germination in an 18.3–35.0 C alternating thermoperiod was high (65–88%) after exposure of the seeds to a variety of pregermination moisture and temperature conditions. Exposure to 4.4 C during imbibition did not increase percentage germination, but did significantly increase the rate of germination over the pregermination treatments that did not include moisture. The very low seed production rates of these populations could explain the limited distribution of this species along the Louisiana coast, where overwash events are frequent, and rates of coastline retreat often exceed the highest measured rates of vegetative lateral spread.

Effects of Drought on a Grassland in the Northern Rolling Plains of Texas

A 2-year study was conducted in the northern rolling plains of Texas to evaluate the effects of brush management on above-ground biomass dynamics and net primary production. The study was completed in 1980 in the midst of a severe 10-month drought. Post-drought observations in 1981 indicated that both foliage and ground cover of the dominant perennial grasses were reduced. Buffalograss production declined because the drought interrupted its normal growth pattern. In contrast, Texas wintergrass production increased, in part because the drought did not begin until after it had completed most of its annual growth. The cumulative effect on all species was a 143 G/M/sup 2/ reduction in total annual net primary production. Differences in response between native and seeded areas may be related to differences in amount of herbaceous litter.

Germination of Seeds of 'Paloma' and 'Nezpar' Indian Ricegrass

Seedlots of the cultivars ‘Paloma’and ‘Nezpar’ Indian ricegrass [Oryzopsis hymenoides (R. & S). Ricker] were classified as to seed type, germination, and germination in response to the additive enhancement treatments of removing the lemma and palea by dissection, enriching the germination substrate with gibberellin (G&), and cool-moist stratification at 2’C for 2 weeks. The seedlots contained different proportions of polymorphic seed size, color, and covering types. Seedlots of ‘Paloma’were dominated by big black seeds while lots of ‘Nezpar’ contained roughly equal propertions of big and small black seeds. The various seed types had different germination characteristics both under control and enhancement treatments. The initial germination of untreated seeds of either cultivar was very low; however, maximum germination with enhancement did not exceed 5%. Indian ricegrass [Oryzopsis hymenoides (R. & S.) Ricker] is the dominant perennial grass species of salt desert ranges occurring at lower elevations within the sagebrush (Artemisiu) vegetation zone of western North America. On sand dunes Indian ricegrass may form relatively pure stands, sometimes several thousand hectares in extent. Being a widely occurring valuable forage species and a monospecific dominant of harsh, arid environments, Indian ricegrass has received considerable attention from agronomists and range managers as a potential revegetation species (Robertson 1976). Recently, interest in this species has increased because of the importance of revegetating sandy-textured spoils from mining operations. Indian ricegrass seeds (caryopses) are highly polymorphic, but all forms are generally dormant (Huntamer 1934). The nature of the dormancy has been attributed to the persistent lemma and palea and pericarp that probably inhibit oxygen transfer to the embryo (Huntamer 1934, Fendal 1964, Clark and Bass 1970, Shaw 1976, McDonald and Kahn 1977, Zemetra 1979). The lemma and palea have to be removed and the pericarp pricked in order for the seeds to germinate. A form of embryo dormancy that gradually breaks down over time, but can be overcome by cool-moist stratification, has also been documented for Indian ricegrass seeds (Tooele 1940, Clark and Bass 1970). The cool-moist stratification requirement of some lots of Indian ricegrass seeds can be partially or totally substituted by adding gibberellic acid to the germination substrate (McDonald and Kahn 1977). Our purposes were to determine whether different seed types could be identified in seedlots of ‘Paloma’ and ‘Nezpar’ Indian ricegrass and whether these seed types have different germination with and without enhancement treatments.

Response of Western North Dakota Mixed Prairie to Intensive Clipping and Five Stages of Development

Response of Western North Dakota Mixed Prairie to Intensive Clipping and Five Stages of Development

Intraspecific competition in grassland species I. Dichanthium annulatum (forsk) stapf

Intraspecific competition in a dominant perennial grass, Dichanthium annulatum (Forsk) Stapf., of the grasslands at Varanasi has been studied at four different densities during 1970–1971 under pot culture conditions. Effect of competition, both on the individual plant as well as on the population, has been discussed in the light of certain ecophysiological parameters. Keenness of competition varies with density and age of the plant. Increase in density is detrimental to the individual's growth behaviour, particularly at the peak period of vegetative growth (210 days), while functioning of the population as a whole increases with enhancing density up to 135 plants/m 2.

Growth and Development of Arizona Cottontop (Trichachne Californica [Benth.] Chase)

Arizona cottontop is a productive, palatable, dominant perennial grass on many southwestern semidesert ranges. Although cottontop is a warm-season grass and grows mostly during the summer, new basal shoots normally start their development in the spring growing period, go dormant during the May-June drought, resume growth with the onset of summer rains, and produce an inflorescence. Most culms produce branch shoots from axillary buds, primarily on the upper part of the culm. These axillary shoots may mature during the same summer or go dormant over winter and mature the following spring or summer. Cottontop culms live more than 1 year, some 3 or more. Numbers of internodes on mature reproductive culms vary from three to 21. Generally, the shortest internodes are at the base of the culm, internode lengths increase gradually toward the top; the top two, and especially the topmost (panicle internode), are greatly elongated. An axillary bud generally is present on each internode of the culm except the panicle internode. Axillary buds at the base of the culm sprout primarily in the spring, producing the year's crop of basal culms. Axillary buds above ground sprout throughout both the spring and summer growing periods, depending on the availability of soil moisture. The first structure to elongate in a newly developing shoot is a leaf blade. The youngest six leaves of a vegetative shoot are in the process of elongating at any one time, of which only the oldest two or three exceed 1 mm in length and are elongating rapidly. In the field, new leaves are initiated at the rate of one about every 4 days. The lengths of leaf sheaths and leaf blades vary with position on the culm, but in different ways. The top, or flag-leaf sheath, is always the longest (to 202 mm), twice as long as the second sheath and three times as long as the third. The longest blade (to 173 mm long), however, is generally on one of the leaves between the third and the sixth from the top, inclusive, and blade length decreases toward both the top and bottom of the culm. Most florets that reach anthesis flower during the first 3 hr after sunrise on the part of the panicle that has emerged from the sheath during the previous 24 hr. Inflorescences begin emerging from the boot 2-3 weeks after growth starts in the summer. The first panicles to emerge are always on culms that started their development the previous fall or spring. New panicles continue to be produced as late in the fall as soil moisture is available. Individual basal culms, during their 3-4-year life, produce up to nine panicles. Perennial culms, long-lived roots, and the ability to produce new shoots quickly and to flower seasonlong make Arizona cottontop an exceptionally valuable forage grass for the semidesert.

Changes in pattern and density of perennial grasses in an intensively grazed sown pasture influenced by drought in southern NSW

Significant changes in the pattern of distribution and density of perennial ryegrass were recorded in an intensively grazed pasture at 'Wollogorang' near Breadalbane, New South Wales, between March 1963 and May 1965. This period was marked by relatively low rainfall and droughts of moderate and severe intensity. A regular pattern of ryegrass plant distribution characterized the pasture in March 1963. This pattern was modified in subsequent years as the ryegrass cover deteriorated under stress conditions. Phalaris, originally an insignificant component in the pasture, persisted and eventually became the dominant perennial grass. These changes are discussed in relation to rainfall, soil moisture status and the contrasting characteristics of root distribution developed by perennial ryegrass and Phalaris on the 'Wollogorang' site.

Competition in the Semidesert Grass‐shrub Type as Influneced by Root Systems, Growth Habits, and Soil Moisture Extraction

Measurements of phenological development, herbage production, basal area, and density of annual and perennial grasses and of the half—shrub burroweed (Aplopappus tenuisectus (Greene) Blake), over a 4—year period show that production of each class of plant was affected to some extent by each of the others, except that annual grasses had no effect on burroweed crown area. Production of Arizona cottontop (Trichachne californica (Benth.) Chase), the dominant perennial grass, was restricted about 25% on plots with annual grass or burroweed competition and 46% by both together. Annual grass production averaged 18% lower with burroweed competition and 44—54% lower with perennial grass competition. Burroweed crown area increased 220% on plots with no perennial grass, but only 111% on plots with perennial grass competition. Presence of burrowed reduced perennial grass yield only moderately, because the root systems of burroweed and grass do not overlap greatly, and their main growth periods are at different seasons. High evaporation rates during the summer growing season masked most differences in moisture extraction between species. During the winter—spring growing period, on the other hand, burroweed depleted the available soil water rapidly, while water loss on perennial grass plots was little more than from bare soil.

The short term effects of time and frequency of burning on native pastures at Katherine, N.T

A report is given of the first five years of an experiment at Katherine, N.T., concerned with the effects of time and frequency of burning on the dry matter yield, nitrogen yield and botanical composition of native pasture on Tippera clay loam. Sampling in 1961-62 showed that all burning treatments reduced dry matter yield in comparison with unburned pasture Pasture burned biennially in the late dry season (September) showed the least reduction in yield. Biennial burning was less detrimental than annual burning ; burning in late dry season was less detrimental than burning in early dry season. Burning in late dry season increased the proportion of annuals in the pasture. All treatments other than biennial burning in late dry season reduced the proportion of Themeda australis (R. Br.) Stapf., the dominant perennial grass. Burning biennially in January or in April increased the proportion of Chrysopogon fallax, S. T. Blake. The provisional recommendation for Themeda-Sorghum pastures in the Katherine area is to bum in late dry season at intervals of not less than two years.