Showing papers on "Growing season published in 1989"

The Continuum of Plant Responses to Herbivory: The Influence of Plant Association, Nutrient Availability, and Timing

Abstract: In a single population of Ipomopsis arizonica (Polemoniaceae), we show a continuum of compensatory responses to vertebrate herbivory. We demonstrate experimentally that the degree of herbivore impact depends on plant association, nutrient availability, and timing of grazing. From 1985 to 1987, the most common response to vertebrate herbivory was equal compensation, whereby grazed plants set numbers of fruits and seeds equal to controls within the same growing season. However, we also observed cases of significant overcompensation and undercompensation. In 1985 and 1987, overcompensation occurred in vertebrate-grazed plants that were supplemented with nutrients and growing free of competition. These plants produced 33% to 120% more fruit than control, ungrazed plants. Cases of undercompensation occurred in groups where I. arizonica grew in association with grasses or where nutrients were not supplemented. Grazed and clipped plants in these groups produced from 28% to 82% as many fruits as did ungrazed cont...

Woody plant invasion of grasslands: establishment of honey mesquite (Prosopis glandulosa var.glandulosa) on sites differing in herbaceous biomass and grazing history

Abstract: Emergence and survival of honey mesquite (Prosopis glandulosa var.glandulosa Torr.) seedlings was quantified on sites with contrasting grazing histories: long-term continuous grazing (LTG) and long-term protection (LTP) from grazing by cattle. On each site, different levels of heroaceous defoliation were imposed at monthly intervals (no defoliation=ND, moderate=MD and heavy=HD). The two weeks following seed dissemination appeared to be the most critical toProsopis establishment on LTP-ND plots. Openings in the herbaceous layer created by moderate defoliation of grasses on the LTP site increased germination and/or survival 7-to 8-fold during this period. However, increasing the degree of defoliation from moderate to heavy did not stimulate additional emergence on either the LTP or LTG site. Emergence from scarified seed placed in cattle dung (17 to 30%) was lower than that of bare seed placements in various microhabitats (43–60%). However, deposition of scarifiedProsopis seed in dung in conjunction with graminoid defoliation may be the most likely combination of events when livestock are present. Emergence from seeds transported into grasslands by other fauna likely would be low, unless seeds were deposited in areas where grasses had been defoliated.Prosopis survival was comparably high in dung and bare seed placements after one growing season. survival of seedlings present two weeks after seed dissemination ranged from 74 to 97% at the end of the second growing season. Seedling survival and shoot development (biomass, leaf area and height) were similar on LTP and LTG sites, regardless of the level of herbaceous defoliation or seed placement. In addition, the magnitude and patterns of net photosynthesis, stomatal conductance and xylem water potential were comparable among one-year-old seedtings on ND, MD and HD plots, even though differences in herbaceous species composition and above- and below-ground biomass between these treatments were substantial. Such data suggest competition for soil resources between grasses andProsopis may be minimal early in the life cycle ofProsopis. High rates ofProsopis emergence and establishment on LTP-MD plots are counter to the widespread assumption that long-term and/or heavy grazing is requisite forProsopis encroachment into grasslands. Results are discussed with regard to factors contributing to the recent, widespread invasion of this woody legume into grasslands of southwestern North America.

Growth and senescence in plant communities exposed to elevated CO2 concentrations on an estuarine marsh.

Abstract: Three high marsh communities on the Chesapeake Bay were exposed to a doubling in ambient CO2 concentration for one growing season Open-top chambers were used to raise CO2 concentrations ca 340 ppm above ambient over monospecific communities of Scirpus olneyi (C3) and Spartina patens (C4), and a mixed community of S olneyi, S patens, and Distichlis spicata (C4) Plant growth and senescence were monitored by serial, nondestructive censuses Elevated CO2 resulted in increased shoot densities and delayed sensecence in the C3 species This resulted in an increase in primary productivity in S olneyi growing in both the pure and mixed communities There was no effect of CO2 on growth in the C4 species These results demonstrate that elevated atmospheric CO2 can cause increased aboveground production in a mature, unmanaged ecosystem

Optimal Growth Schedule of a Perennial Plant

Abstract: The optimal growth schedule of a deciduous perennial plant is studied theoretically. We make three basic assumptions. First, the daily net photosynthetic rate of a plant increases but saturates with the size of the production part (vegetative organs working for photosynthesis). Second, the production part is discarded at the end of a growing season, but it may be rebuilt at the beginning of the next season using stored material. And finally, the plant maximizes the lifetime reproductive investment by choosing both the growth schedule within each season and the resource allocation between reproduction for the year and storage for the next season. The model is analyzed by the combination of maximum principle and dynamic programming. Our analysis showed three basic results. First, the annual life cycle is optimal under low storage efficiency, low habitat reliability, low growth rate, and a short growing season. Second, under any other conditions, perennial growth is optimal. During years in which the final a...

Plant dispersal by motor cars

Abstract: Mud from a car driving more than 15 000 km in the growing season of 1986 in the area surrounding Gottingen (FRG) was sampled systematically to assess the size and nature of the car-borne flora. The sludge from front and back mudguards, wheels and other lower parts of the car was set out for germination in a greenhouse. Until the end of 1987, 124 plant species with a total of 3926 seedlings were identified and counted. Germination success was significantly related to the sampling date, the front or back position of the car and the influence of low temperature during exposure. The nature of this potentially car-dispersed flora was compared with the local flora as a whole as well as the flora and plant communities of road verges in the studied area. It can be supposed that almost all plant species growing in plant communities along roadsides can be carried by cars and therefore belong to the car-dispersed flora.

Effects of cropping on carbohydrate content and water-stable aggregation of a clay soil

Abstract: In a previous study, the mean weight diameter of water-stable aggregates of a clay soil was increased by up to 50% after two growing seasons under barley and alfalfa compared to fallow or corn. The...

Nutritional ecology of a browsing ruminant, the kudu (Tragelaphus strepsiceros), through the seasonal cycle

Abstract: The activities and food selection of four hand-reared kudus were recorded in a large fenced enclosure containing natural savanna vegetation in the Nylsvley Nature Reserve, South Africa. Leaves of selected species were analysed chemically for crude protein, fibre constituents, phosphorus, condensed tannin and total polyphenols. Available protein and metabolizable energy were estimated allowing for potential antinutritional effects of tannins. Leaves of palatable deciduous woody plants and herbaceous forbs formed the main dietary constituents during the late wet season. Foliage from palatable evergreens and robust forbs were added to the diet during the dry season. Towards the end of the dry season unpalatable species of evergreens were eaten. At the start of the growing season new leaves of otherwise unpalatable woody species formed the staple food source, together with fruits of Strychnos spp. Correspondingly, protein and digestible dry matter concentrations in the diet declined to reach a low at the end of the dry season. Total daily food intake increased to compensate for reduced dietary quality during the dry season, until little edible foliage remained. While the estimated daily intake of protein remained well above maintenance requirements, the estimated metabolizable energy intake fell below requirements during the late dry season. Phosphorus intake may have been submaintenance in the dry season. Nutritional balance was dependent on the availability of particular vegetation components to serve as nutritional stepping stones during crucial times of the year. These included forbs during the late wet season, palatable evergreens in the dry season, and Strychnos fruits plus early-flushing woody plants during the dry season-wet season transition.

Geostatistical description of the spatial distribution of Lygus hesperus (Heteroptera: Miridae) in lentils

Abstract: The spatial distribution of Lygus Hesperus Knight (Heteroptera: Miridae) in lentils was evaluated at five locations over two years using geostatistical methods. Geostatistics uses temporal or spatial variation to determine the degree of association and dependence of temporally or spatially related data. These analyses revealed unique spatial distributions for adults and nymphs, which varied as the growing season progressed and population densities changed. After immigrating into lentil fields, adults were aggregated. During the middle of the growing season, adult distributions were clumped at low densities and were uniform or random at higher densities. At the end of the growing season, newly emerged adults again had a clumped distribution. Nymphs showed random to uniform distributional patterns until late in the growing season when, as population densities increased, their spatial distribution became clumped.

Large niche overlaps among coexisting plant species in a limestone grassland community

Abstract: In the present study measurements were made on six niche axes, including phenology of above-ground growth over a five-month growing season, together with sol depth, pH, and the levels of available nitrogen, phosphorus and potassium in soil samples taken at the end of the growing season. Analysis of separation in this niche space indicates that it is insufficient to account for the coexistence of all eight species. The possibility that inappropriate or insufficient niche axes may have been chosen is recognized and discussed

Experimental analysis of patch dynamics and community heterogeneity in tallgrass prairie

Abstract: Effects of fire and small-scale soil disturbances on species richness, community heterogeneity, and microsuccession were investigated in a central Oklahoma tallgrass prairie. In the fall of 1985, 0.2 m2 soil disturbances were created on burned and unburned tallgrass prairie. Vegetation on and off disturbances was sampled at monthly intervals over two growing seasons. During the first growing season, the cover of forbs and annuals, and species richness were significantly greater on versus off disturbances, but these differences did not persist through the second year. The variation in species composition among disturbed plots (heterogeneity) was significantly greater compared to undisturbed areas throughout the study. Fire had no consistent effect on richness and heterogeneity of vegetation on soil disturbances but fire reduced heterogeneity on undisturbed vegetation. Rate of succession, based on an increase in cumulative cover of perennial grasses over time, did not differ among treatments during the first growing season. During the second year, rate of succession was significantly greater on burned soil disturbances compared to unburned soil disturbances. These results suggest that while small-scale soil disturbances have primarily short-lived effects on grassland community structure, disturbances do help to maintain spatial and temporal variation in tallgrass prairie communities. Unlike in undisturbed vegetation, however, species richness and heterogeneity on soil disturbances were little effected by fire, but the rate of colonization onto disturbances appeared to be enhanced by fire.

The effect of increased nutrient availability on leaf turnover and aboveground productivity of two evergreen ericaceous shrubs

Abstract: Leaf turnover and aboveground productivity in relation to nutrient availability were studied in the evergreen shrubs Erica tetralix and Calluna vulgaris. In monospecific stands of these species four levels of nutrient (NPK) availability were created during three growing seasons. Percentage survival and life expectancy of Erica leaves decreased with increasing nutrient availability. For Calluna there was no effect. Winter mortality of Erica leaves was smaller than growing season mortality. These was no difference for Calluna. The timing of leaf mortality of both species was not affected by nutrient treatment. At the end of the experimental period current year leaf biomass, total biomass and current year second year and third year biomass of both species showed a significant increase with increasing nutrient availability. The relative increase was greater for Calluna, except for second and third year biomass. Stem production and stem mortality of both species increased with increasing nutrient availability. The increased stem mortality resulted also for Calluna in an increased leaf turnover (per unit ground area) with increasing nutrient availability. Nutrient cycling in ecosystems dominated by these species will increase with increasing nutrient availability, because of increased leaf and stem turnover and productivity. This phenotypic effect is similar to the effect of the shift in dominance between different species which occurs along natural gradients of nutrient availability.

Plant biomass, species diversity and net primary production in a central himalayan high altitude grassland

Abstract: SUMMARY (1) Plant biomass, species diversity and net primary production are presented for a high altitude grassland of Central Himalaya, India. (2) The time-series of live shoot biomass exhibited a unimodal growth pattern during each of the two years of study. The peak live shoot biomass, which was attained in August, ranged between 382 and 409 g m-2. (3) The relative growth rate of live shoots ranged between 8 and 42 mg g- day-', the maximum rate occurring during the early part of the growing season. Rise in temperature which caused the snow-melt in mid-April was followed by vegetation growth. Snow-melt provided the plant-available moisture as well and shoot growth began at a rapid rate during April-May. Biomass accumulation was sustained by monsoon rainfall in JuneAugust. (4) Species diversity declined from a maximum in June to a minimum in October. Danthonia cachemyriana showed increasing dominance with advancement of the growing season. (5) The minimum annual net shoot production ranged between 453 and 527 g m-2 and the minimum total below-ground net production between 284 and 449 g m-2. (6) The total dry matter disappearance almost balanced the total net organic matter input within the annual cycle indicating that the system is in equilibrium.

Optimizing Soil and Fertilizer Nitrogen Use by Intensively Managed Winter Wheat. I. Crop Nitrogen Uptake

Abstract: The treatments in these experiments consisted of single or split N applications at Zadoks growth stages 25 (GS 25) and 30 (GS 30) totaling 0, 90, or 135 kg N/ha Crop N uptake at GS 30 also appeared as a potentially good indicator of the plant N requirement Total amounts of N found in leaves and stems decreased with time during the spring, while spike N increased from the early stages of head development until harvest Climatic conditions in the different growing seasons affected plant N uptake Variations in residual soil N and temperatures in early spring probably determined the differences in amounts and patterns of N uptake by whole plants and by the various plant fractions

Biomass, and nitrogen, phosphorus and heavy metal content of Phragmites australis during the third growing season in a root zone waste water treatment

Abstract: This study includes extensive investigations of the underground plant part biomass as well as element concentrations of the three fractions, green shoots, rhizomes, and roots

Measurements of the quantum yield of carbon assimilation and chlorophyll fluorescence for assessment of photosynthetic performance of crops in the field

Abstract: An apparatus is described for the rapid measurement in the field of the quantum yield of CO 2 assimilation, o, and chlorophyll fluorescence kinetics from attached leaves exposed to ambient CO 2 concentrations. This apparatus was used to measure o and the ratio of variable to maximal fluorescence, F v /F M , of fully expanded leaves of a maize crop in northeast Essex at monthly intervals throughout the growing season. The quantum yield of CO 2 assimilation and F v /F M increased from May to August and then decreased in September. A linear correlation between o and F v /F M was observed for the leaves. The relations between light, temperature, the quantum yield of CO 2 assimilation and fluorescence emission kinetics of leaves of a maize crop during the early growing season were also examined. Decreases in o associated with chilling temperatures and high light were observed and identified from analyses of fluorescence kinetics as being attributable to photoinhibitory damage of the photosynthetic apparatus. The possibility of using measurements of o and fluorescence kinetics for screening the photosynthetic performance of crops is considered. Studies with winter rape demonstrated that changes in o during the growing season were correlated with changes in the efficiency of light-energy conversion to dry matter by the crop.

Dynamics of Mononychellus tanajoa (Acari: Tetranychidae) in Africa: Seasonal factors affecting phenology and abundance.

Abstract: Populations of Mononychellus tanajoa (Bondar) increased on new leaf growth of cassava, Manihot esculenta Crantz, during the early dry season, averaging 20–200 active mites per leaf depending on plant age, leaf age, and cultivar. Mite populations declined later in the dry season, when severe defoliation and reduced leaf production followed prolonged drought. Early rains resulted in a flush of new foliage that supported an increase in mite numbers, but rainfall drove mite populations to less than one individual per leaf several months into the wet season. Throughout the growing season, mite age structure was relatively constant within, but varied between, strata of the canopy. Differences between strata were related to the age of the foliage. These results suggest that the availability of new foliage and the presence of rainfall are the primary factors limiting M. tanajoa populations in Africa.

Dendroclimatological Study of Pinus Sylvestris L. in Southern Catalonia (Spain)

Abstract: Two modem tree -ring width chronologies of Pinus sylvestris L. have been established in an area near the southern limit of the species' distribution. Trees were sampled in the South of Catalonia in northeastern Spain where Mediterranean climatic conditions are of primary influence. To better understand climate ring -width relationships, tree -ring index series have been studied in relation to local climate. Ring -widths are strongly related to low precipitation at the beginning of the growing season in March, in June of the current growth year, and in September prior to tree -ring growth. High temperatures mainly affect growth in summer during the growing season and in autumn of the year prior to growth. During the winter, mainly in December, mean monthly temperatures show a significant positive correlation with growth. Major factors controlling the southern distribution of P. sylvestris may be related not only to water stress in summer but also to the amount of precipitation at the beginning of the growing season and in autumn, even in mild winters.

Fire studies in mallee (Eucalyptus spp.) communities of western New South Wales: The effects of fires applied in different seasons on herbage productivity and their implications for management

Abstract: The post-fire development of herbaceous understoreys of Tnodia/mallee burnt in different seasons was studied over a 3 year period in south-western New South Wales, Australia. Near Pooncarie, NSW, a 3 year sequence of above-average rainfall immediately following burning in either the spring, autumn or winter resulted in a substantial increase in species richness and herbage dry matter production. Plots burnt in the spring produced significantly more dry matter than either the autumn or the winter-burnt plots but only in the first growing season after burning. Some species such as Haloragis odontocarpa behaved as ephemerals, being abundant in the first post-fire season, particularly after spring fire, before becoming inconspicuous. Short-lived grasses, such as Stipa species, then became relatively abundant except during drought. Other experiments confirmed the potential of fire to increase herbage diversity and productivity when there was adequate rainfall. During drought, post-fire herbage production was low and the dominant perennials, viz. mallee Eucalyptus and Triodia irritans, regenerated at the expense of the herbs. There was a strong negative correlation between combined mallee and Triodia cover and total herbage cover over time. Seedling recruitment of Triodia irritans was significantly higher on plots burnt in the spring at Pooncarie.

Time-course of N2-fixation (15N) in the field by clover growing alone or in mixture with ryegrass to improve pasture productivity, and inoculated with vesicular-arbuscular mycorrhizal fungi

Abstract: SUMMARY The isotope 15N was used to estimate N2-fixation by white clover, and N-transfer from clover to perennial ryegrass. Pure stands of each of these pasture plants and a mixed sward of both were established in a field soil in which it had been demonstrated that vesicular-arbuscular mycorrhizal inoculation was necessary for suitable development of the clover. All plants, whether clover or ryegrass, received the same amount of a selected mycorrhizal inoculum. The 15N/14N ratio of the grass in pure stands was used to evaluate N2,-fixation by clover growing alone, and that of the grass in the mixture to estimate that by the companion clover. Tentative evidence of N-transfer was obtained by comparing the 15N/11N ratio in the grass growing alone with that when mixed with the legume. In spite of a decline with time in 15N enrichment, the N2-fixation rates were about the same throughout the growing season and for the two cropping systems. The total N, P and dry matter yields in the grass/clover mixture were greater than in monocultures. A lower 15N enrichment of the grass growing mixed compared to that growing alone, suggesting N-transfer, was only obtained at the second harvest. The mycorrhizal colonization of the grass in the mixed grass/closer sward was significantly enhanced, as compared with that of the grass in pure stands. Mycorrhizal hyphae are known to be involved in NH4+ uptake, translocation and transfer to the host plants, and this may partly explain the improvement of pasture productivity when grass and mycotropic legumes are grown together.

Comparative effects of downslope water and nutrient movement on plant nutrition, photosynthesis, and growth in Alaskan tundra

Abstract: Changes in water and nutrient movement are common disturbances resulting from human activities in arctic regions. To assess the influence of water and nutrient movement on different plant growth forms, we added water and NPK fertilizer along 10 to 20 m linear transects across small natural drainages on an Alaskan tundra slope. Water was added by continuous-flow emitters from a drip irrigation system at a rate of 450 L m−1 d−1 during the 1986 growing season and 110 L m−1 d−1 in the 1987 growing season. NPK in the form of Osmocote, a slow release fertilizer, was applied at 0.5 kg per linear meter in early and mid-season of the 1985 growing season. Tissue N and P contents, light-saturated photosynthetic rates, and aboveground biomass production were measured at peak season for key species 2 m above and 2 and 6 m below the water and nutrient applications in 1986 and 1987. Mean leaf N and P of the species tested increased slightly 2 m below the water addition sites and dramatically below the fertilizer addition sites. Increases in tissue N and P were also found 6 m below the fertilizer addition points. Leaf photosynthesis tended to increase 2 m below the water and nutrient additions for the species tested. Six meters below the treatment application points, photosynthesis was minimally affected in 1986 but increased in 1987. Increases in leaf area on the irrigation treatments were found only for the evergreen species, Ledum palustre and Vaccinium vitis-idaea, 2 m below the site of addition. In contrast, fertilizer addition caused large increases in leaf area production for all species tested at 2 m below the treatment, and for some species at 6 m below treatment. The overall effects of the two treatments were similar, but were greater for the fertilizer addition.

The phosphorus budget of a field-grown strawberry (Fragaria x ananassa cv. Hapil) crop: evidence for a mycorrhizal contribution

Abstract: Summary The phosphorus content of a field-grown strawberry crop was monitored over one growing season and the allocation of P to different plant parts determined. In the early part of the season, leaves were the major sink for P and this was partly supplied by redistribution from rhizomes. Once flowers were initiated, these became the major sink and their P requirement was satisfied by new uptake. The calculated rates of P inflow to the roots in this phase of growth were so large that it was necessary to postulate not only that P uptake was assisted by mycorrhizas, but that the whole root system, including the old, brown roots, was active. The implications of this conclusion for concepts of vesicular-arbuscular mycorrhizal function under field conditions are discussed.

Midrib nitrate concentration as a means for determining nitrogen needs of cauliflower

Abstract: Plant analysis has been used to evaluate the nutritional status of many crops for diagnostic and corrective purposes. This study was initiated to establish critical nitrogen (N) plant tissue levels using midrib NO3‐N concentration for cabbage (Brassica oleracea L., capitata group) during the growing season. Tissue samples for nitrate analysis were taken from cabbage plants over a period of four growing seasons beginning at the 4 to 6 leaf stage of growth and biweekly through pre‐harvest. The midrib from the most recently full sized leaf was sampled for NO3‐N concentration determination. A high degree of correlation existed between NO3‐N concentration in cabbage midribs at various sampling dates and yield as determined by stepwise regression analysis. Nitrate‐N concentration in cabbage midribs indicated the N status of the plant. Minimum or critical levels of NO3‐N in cabbage midribs for sampling dates throughout the growing season were established for conditions such as are found in the desert re...

Seasonal Leaf Area-Leaf Weight Relationships in the Cotton Canopy

Abstract: Specific leaf area (SLA), the ratio of leaf area to leaf dry weight, is used in crop simulation models to estimate total leaf area or dry weight. This experiment was designed to study changes in SLA in various parts of a cotton (Gossypium hirsutum L.) canopy throughout the growing season. The main stem of the cotton plant was divided into five-node segments. Leaf area and leaf dry weight were measured for each segment throughout the growing season

Animal performance and diet quality as influenced by burning on tallgrass prairie

Abstract: Burning on good to excellent condition tallgrass prairie in central Oklahoma yielded results which visually appeared much greater than would be expected from previous burning research. Therefore, a study was designed to quantify the effect of burning on plant and livestock responses. During 1984-1986, average daily gains of stocker cattle were monitored from late May to midOctober in replicated burned and unburned pastures. Stocking rates varied from 0.8 to 1.5 ha per animal depending on initial animal weights. Fistulated cattle were used to monitor diet quality on the pastures. Standing crops were measured at the end of the growing season (early October) in exclosures, and at the end of the grazing period (late October) in the pastures. Animal performance was improved by burning during the early part of the grazing season, and over the season animal production per ha averaged 11.2 kg higher on burned compared to unburned pastures. Dietary crude protein tended to be higher on unburned compared to burned pastures, but the opposite was true for in vitro organic matter digestibility. Standing crop remaining after the grazing period averaged 4,304 and 2,539 kg/ha for burned and unburned pastures, respectively. Standing crop was 57% higher in burned compared to unburned exclosures. Burning caused a shift in species composition to favor tallgrass species and lower production of weedy forbs in both exclosures and grazed pastures. Key Wom: pruadu fonequfy,m The use of prescribed burning for manipulation of range vegetation has gained wider acceptance in recent years. Vegetation changes associated with burning have been documented in a number of ecosystems (Wright and Bailey 1982). Responses tend to be ecosystem-specific and are further influenced by timing of the burn, nature of the fire, environmental conditions (especially precipitation) during the year of burning, management after burning, site, and species composition. Considerably less information exists on the influence of burning on livestock performance. However, research from the Flint Hills of Kansas (Launchbaugh and Owensby 1978), timbered range in the southeastern U.S. (Hilman and Hughes 1965), the Edwards Plateau in Texas (McGinty et al. 1983), and the Texas Coastal Prairie (Angell et al. 1986) all show that burning can improve livestock performance. The majority of research on burning response of tallgrass prairie has been conducted in Kansas. Generally, late spring (about 1 May) burning has yielded the most desirable results compared to other burn dates in terms of forage production and species composition. However, late spring burning has been shown to decrease (Aldous 1934), have no effect on (Launchbaugh and Owensby 1978), or increase (Towne and Owensby 1984; Knapp 1984, 1985) production of tallgrass prairie species. Burning has been studied in Oklahoma; however, the burns were generally not timed to obtain Author is range scientist, USDA/ ARS, 920 Valley Road, Reno, Nevada 89512. At the time of the research, he was research agronomist, USDA/ ARS, Forage and Livestock Research Laboratory, El Reno, Oklahoma 73036. The author thanks Jim Browning, Bobby Handke, Wes Jackson, Jim Trent, and Dr. Michael Zavy for assistance during the study. Drs. Robert Gillen, Wayne Leininger, and an anonymous reviewer provided constructive comments on earlier versions of the manuscript. Manuscript accepted 24 August 1988. maximum forage production (e.g., Adams et al. 1982, Rice and Parenti 1978, Kelting 1957), or burning was intended to improve poor to fair condition tallgrass prairie (Graves and McMurphy 1969). Results from management burns conducted on good to excellent condition tallgrass prairie in central Oklahoma suggested that positive response to fire was greater than might be expected. Burning of tallgrass prairie is used as a management tool in some parts of Oklahoma, especially the northcentral portion of the state, but data detailing the response of livestock to these prescribed burns are not available in the literature. This study was conducted to assess the impact of burning on seasonal trends in diet quality and livestock performance on native tallgrass prairie in central Oklahoma. Study Site The study was conducted from 1984 to 1986 at the USDA/ARS Forage and Livestock Research Laboratory near El Reno, Oklahoma. Vegetation on the study site was typical of good condition tallgrass prairie, with big bluestem (Andropogon gerardii Vitman var. gerardii), Indiangrass (Sorghastrum nutans L.), and little bluestem (Schizachyrium scoparium [Michx.] Nash) as dominants. Soils were silt loams classified as either Udic Paleustolls or Pachic Arguistolls, tended to be well drained, relatively deep (150 cm), and had high available water capacity (Fisher and Swafford 1976). Mean annual precipitation is 762 mm, of which 68% (520 mm) occurs during the April through September growing season. Precipitation was below average during 1984, when yearly and growing season totals were 724 and 349 mm, respectively. Precipitation was above average in 1985 (annual = 969 mm, growing season = 602 mm) and 1986 (annual = 1,108 mm, growing season = 817 mm). Mean annual temperature is 15.60 C. The site has had a history of moderate grazing, but had not been burned for at least 15 years prior to the initiation of the study. Materials and Methods Two adjacent pastures, 37 and 53 ha in size, were used in the study. Each pasture was split, and at random half was assigned to either burning or control treatments. Pastures were treated as blocks, and treatment/block combinations will subsequently be referred to as paddocks. Burning was conducted on 23 April 1984; 10 April 1985; and 7 April 1986. Paddocks were burned when big bluestem had 2 to 4 cm of leaf growth. This criteria was selected because it ensured that ambient conditions would support growth of tallgrass species immediately following burning. At the beginning of the grazing period sward height was about 15 to 22 cm. Each paddock was stocked at 1.5 ha/animal from 13 June to 11 October 1984 and 19 May to 16 October 1985. Heifers with initial average weights of 425 and 460 kg were used in 1984 and 1985, respectively. Steers averaging 190 kg were stocked at 1.2 ha/ animal from 19 May to 1 July, and 0.8 ha/animal from 2 July to 18 September 1986. Average daily gain (ADG) was calculated on the steers initially placed in the paddocks; the additional animals were used to adjust the stocking rate to more nearly match available forage. Animals were penned during late afternoon and weighed JOURNAL OF RANGE MANAGEMENT 42(1), January 1989 11 This content downloaded from 207.46.13.129 on Sat, 25 Jun 2016 06:56:02 UTC All use subject to http://about.jstor.org/terms

Comparative analysis of temporal and spatial variability in above-ground production in a deciduous forest and prairie

Abstract: Production patterns of tallgrass prairie and adjacent eastern deciduous forest were summarized for a five to seven year period. Each system responded differentially to annual or growing season rainfall and solar energy (measured by pan water evaporation). Overall, forest productivity was negatively correlated with annual precipitation; the prairie exhibited no relationship with precipitation. These differences probably reflect the lack of water limitation of the forest and the “downstream” position of the forest. Wood and seed production in the forest were the most variable components measured in our study. Neither variable was related to forest foliage production. Seed production in the prairie was also variable within and between years but was related to prairie foliage production. Prairie seed production was not correlated with seed production of the forest. The two ecosystems respond differentially and independently of each other within the range of climatic variation observed here. Such differences have potential significance to consumers who use both systems for habitat or resources.