Effects of adaptive multiple paddock and continuous grazing on fine-scale spatial patterns of vegetation species and biomass in commercial ranches

Landscape Ecology - In rangelands, alterations to vegetation from grazing have potentially significant consequences for a wide variety of ecosystem structure and function. This study measured the...     

Bistatic-radar observation of long-period, directional ocean-wave spectra with loran a

Bistatic-radar scattering from medium- to long-wavelength (80 to 200 meters) ocean waves has been observed with the use of loran A (1.85 megahertz) transmissions and a receiver located 280 kilometers away. The received echoes have been converted into a time-delay, Doppler-frequency map in which the effects of anisotropies in the ocean-wave spectra are clearly shown. The distribution of the echoes in delay-Doppler space is consistent with Bragg scattering from trains of dispersed ocean waves.     

Growth patterns and annual growth cycle of Acacia karroo Hayne in relation to water stress I. Leaf and shoot growth

Abstract

A field study was conducted to describe the growth patterns of A. karroo at different levels of water stress in different edaphic situations.

Shoots are heterophyllous and are formed by free growth. The degree of development of a shoot, relative to others in the canopy, is governed by branch and position in the canopy. At least six phenological phases were identified in the annual growth cycle.

The pattern of growth and the phenological cycle are not changed by water stress. Initiation, emergence and development of shoots and leaves are governed by how favourable environmental conditions are. If there is little shoot growth early in the season, these plants can partially compensate by producing more leaf per unit of shoot if environmental conditions improve.

Leaf and shoot growth at the beginning of the season took place only if there was sufficient moisture available, and if the minimum temperature had risen above a threshold amount. Where there was insufficient soil moisture, no growth was observed before rains had fallen. The growth strategy of A. karroo differs markedly from that of broadleaved African savanna tree species. Growth in A. karroo is dominated by current growing conditions, rather than those of the previous season. They are able to make opportunistic growth at any time.

Soil depth had a marked influence on plant growth, presumably due to a larger available nutrient and moisture pool.     

The application of various picloram formulations to cut stumps of Brachystegia spiciformis Benth., Julbernardia globiflora (Benth.) Troupin,Terminalia sericea Burch. ex DC. and Acacia karroo Hayne trees

Trees were felled 150 mm above ground level and various mixtures of picloram with 2,4‐D araine, 2,4,5‐T amine in water solution or 2,4,5‐T ester in diesel oil were applied to the freshly‐cut surfaces. Mixtures of picloram/2,4‐D amine and picloram/2,4,5‐T amine, both water soluble, gave the highest kill rates when applied to trees in the growing season (October and May). The oil emulsifiable picloram/2,4,5‐T ester formulation tended to be effective throughout the year and high kill rates were frequently obtained with applications made in June or July. Application rates of picloram/2,4‐D amine or picloram/2,4,5‐T amine (expressed as g a.e. picloram per mm girth) required to kill 80% of the trees were 0,012–0,016 for A. karroo; 0,016–0,037 for T. sericea and 0,037 for J. globiflora. Few of the treatments applied to B. spiciformis trees resulted in kill rates of more than 65%.     

The effect of ringbarking Brachystegia spiciformis Benth., Julbernardia globiflora (Benth.) Troupin and Terminaliasericea Burch. ex DC. trees at different heights with or without the addition of a pidoram/2,4‐D mixture

Trees were ringbarked at three different heights relative to ground level (1 000 mm above the ground, at ground level and 100 mm below ground level). In a separate trial, arboricide was applied at four different rates to the lower lip of the ringbarked trees either 1 000 mm above the ground or at ground level. Ringbarking without the arboricide was most effective when carried out in February and at a height of 1 000 mm above the ground. Application of a picloram/2,4‐D mixture to the lower lip of ringbarked trees in January or April resulted in higher kill rates than applications made in June or October. Using this method, somewhat less picloram was necessary than was required to effect the same kill rate to these tree species by applying the arboricide to cuts in their stem bases. In both trials, the kill rate was positively related to the amount of coppice removed.     

Herbaceous diversity and composition in mixed Juniperus Pinchotii-Prosopis Glandulosa communities in Southern mixed-grass prairie

Herbaceous biomass and composition were measured across a continuum of increasing cover of mixed Prosopis glandulosa and Juniperus pinchotii woody plant from 1996 to 2003. The study site in northwest Texas had no history of woody plants treatment and comprised trees up to 6 m tall with cover averaging 65%. A strong, negative, linear relationship between woody plant cover and herbaceous biomass was measured (p = 0.0001). Precipitation differences resulted in 2.7 fold variation in herbaceous biomass between years (p = 0.003) and affected the slope of the decline of herbaceous biomass associated with increasing woody plant cover (p = 0.034). Within any year the slope of decline of herb biomass was parallel for Prosopis and Juniperus cover (p = 0.843). Relative to zero woody cover, 100% Prosopis cover reduced herbaceous biomass by 56% (p = 0.0001) while 100% Juniperus cover reduced herbaceous biomass 73% (p = 0.0001). At 100% cover Prosopis had twice the herbaceous biomass compared to Juniperus (p = 0.0021) but both species reduced herbaceous biomass by ± 1300 kg ha^?1. Warm season herb biomass decreased with increasing Prosopis or Juniperus cover while cool season herbaceous biomass was minimally influenced by increases of either species. Multivariate analysis indicated vegetation associations differed between tree species. Vegetation differed (p = 0.001) between low (<25%) and high (>75%) Prosopis cover (dissimilarity R = 0.98), between low and high Juniperus cover (R = 0.81). Ten herbaceous species consistently decreased and 2 consistently increased with increasing woody plant cover.     

Competition between palatable and unpalatable prairie grasses under selective and non-selective herbivory in semi-arid grassland

In a small plot study we used a systematic additive design to evaluate at what severity and frequency of defoliation sideoats grama (Bouteloua curtipendula) would remain competitive and recover from defoliation while growing with meadow dropseed (Sporobolus compositus). In the 3-year study plants were transplanted from pots into the experimental design when equal in size. When B. curtipendula was selectively defoliated moderately or severely, at both 30- and 60-day intervals, it still produced as much as when undefoliated growing with undefoliated S. compositus. Moderately defoliated B. curtipendula did not reduce biomass yield of S. compositus growing with it compared to when S. compositus was growing alone. When both plants were non-selectively defoliated severely, S. compositus responded very weakly and B. curtipendula recovered at the same rate as it had under the other defoliation treatments. The total biomass produced by both species growing together was highest when B. curtipendula was moderately defoliated. As soil moisture was not limited in this experiment we do not believe our results refute the hypothesis that selective grazing by livestock in these ecosystems has contributed to a reduction of B. curtipendula relative to S. compositus. Although S. compositus was reduced more than B. curtipendula by heavy nonselective defoliation this treatment is unlikely to produce desirable results in the long term as the highest total vegetation production occurred when B. curtipendula was moderately defoliated.     

A longitudinal study of Neospora caninum infection on a dairy farm in New Zealand

A 600-cow New Zealand dairy herd experienced an abortion storm in 1997 and was monitored (blood sampling at about 3-month intervals) from May 1997 until January 1999. Abortion risk reached 9% in 1997 and was highest in heifers at 19%. The abortion risk decreased in 1998 to 3.2% (still somewhat higher than during the years prior to the outbreak). The serological reaction pattern for Neospora caninum showed an association with abortion risk only around the time of the 1997 outbreak when seropositive cows were 4.2 times more likely to abort than negative ones. Over the whole study period, only 27% of cows that were sampled on all nine visits always tested negative. Offspring from dams which had positive tests for Neospora caninum were 2.4 times more likely to abort than those from dams testing consistently negative. Controlling for age and breed, seropositive cows produced more milk than those that were consistently negative. Infection might have been present endemically within this herd prior to the epidemic, but in 1997 an additional factor appeared to have triggered the outbreak.     

An aerosolized fluorescent microsphere technique for evaluating particle deposition in the avian respiratory tract

The objective of this study was to examine the feasibility of using aerosolized fluorescent microspheres to examine particle distribution in the respiratory tract of birds following aerosol exposure. Adult domestic pigeons (Columbia livia domestica; n = 5 birds per microsphere size) were exposed to aerosolized monodispersed populations of various sized carboxylate microspheres (0.5, 1.0, 2.0, 3.0, 6.0, and 10.0 microm) for 30 min. For aerosol-exposure purposes, the birds were anesthetized with injectable anesthetics, intubated, and placed on positive-pressure ventilation using a mechanical ventilator. Immediately following aerosol exposure, the birds were euthanatized, and carcasses were preserved via intravenous infusion of modified paraformaldehyde/gluteraldehyde fixative (pH = 7.2 and 340 mOsm). Initial evaluation of microsphere distribution in air sacs (cranial and caudal thoracic and abdominal) and at the level of the ostia was performed using a stereoscopic microscope with an epifluorescent module. More detailed examination of the distribution of microspheres within the respiratory tract was achieved using a confocal scanning laser microscope with a krypton argon laser and a scanning electron microscope. The results from this study revealed that positive-pressure ventilation resulted in distribution of smaller sized fluorescent microspheres (sizes 1.0, 2.0, and 3.0 microm) throughout the pigeon's respiratory tracts, and these microspheres were in highest concentration in the secondary bronchi and ostia for all of the examined air sacs. The larger sized beads (6.0 and 10.0) were confined to the upper airway (trachea and primary bronchi). The results from this study allow for a better understanding of particle deposition following positive-pressure ventilation and aerosol exposure in birds.