A sub-continental scale living laboratory: Spatial patterns of savanna vegetation over a rainfall gradient in northern Australia

Savanna landscapes across north Australia are characterised by limited topographic variation, and in the Northern Territory, by a relatively constant decline in rainfall with distance inland. The North Australian Tropical Transect (NATT) traverses this 1000 km gradient of largely intact vegetation which provides an ideal ‘living laboratory’ and framework to investigate the influence of vegetation structural and floristic change and climate drivers on land-atmosphere exchange at a regional scale. We conducted a multidisciplinary program examining carbon, water and energy fluxes as a function of climate and vegetation change along a sub-continental environmental gradient. Initial findings are reported in this Special Issue. During the program, an intensive field campaign was undertaken during the dry season to characterise vegetation and soil properties of eight flux tower sites used to describe spatial and temporal dynamics of fluxes across this gradient. This paper provides an overview of the savanna landscapes of north Australia detailing vegetation structural and physiological change along this gradient. Above-ground woody biomass, stem density, overstorey LAI and canopy height declined along sites that spanned an 1100 mm annual rainfall gradient. Biomass ranged from 35 to 5 t C ha⁻¹ with dry season LAI ranging from ∼1 to 0.05 across savanna sites both intact and cleared for grazing. Across open-forest and woodland savanna, basal area ranged from 9.7 to 5.3 m² ha⁻¹. While structural change was significant and correlated with rainfall, leaf scale physiological properties (maximal photosynthesis, V_cmax, c_i/c_a, light use efficiency) of the dominant woody species showed little variation, despite the significant environmental gradient. It is likely that changes in structural properties dominate spatial patterns of flux as opposed to physiological plasticity or species differences along this gradient.     

Prevalence of agglutinating antibodies to Sarcocystis neurona in raccoons, Procyon lotor, from the United States.

Equine protozoal myeloencephalitis (EPM) is the most important protozoal disease of horses in North America and it is caused by Sarcocystis neurona. Natural cases of encephalitis due to S. neurona have been reported in raccoons, Procyon lotor. We examined 99 raccoons for agglutinating antibodies to S. neurona using the S. neurona agglutination test (SAT) employing formalin-fixed merozoites as antigen. Raccoons originated in Florida (N=24, collected in 1996), New Jersey (N=25, collected in 1993), Pennsylvania (N=25, collected in 1999), and Massachusetts (N=25, collected in 1993 and 1994). We found that 58 (58.6%) of the 99 raccoons were positive for antibodies to S. neurona using the SAT; 44 of 99 raccoons (44%) had titers of ≥1:500. This prevalence is similar to the reported seroprevalence of 33–60% for S. neurona antibodies in horses from the United States using the Western blot test.     

Chemoprophylaxis of cryptosporidiosis in chickens, using halofuginone, salinomycin, lasalocid, or monensin

Chemoprophylaxis of Cryptosporidium baileyi infections was attempted by feeding 4 groups of chicks diets containing 3 mg of halofuginone/kg of feed, 60 mg of salinomycin/kg, 75 mg of lasalocid/kg, or 110 mg of monensin/kg. Rations were fed 5 days before oral or intratracheal inoculation with oocysts and were continued for 20 days. None of the drugs prevented C baileyi infections. Clinical signs of respiratory tract disease and gross lesions of airsacculitis were observed in intratracheally inoculated birds in all treatment groups and nonmedicated controls. Orally inoculated birds did not develop clinical signs of infection. Pathogenic bacteria were not isolated from the respiratory tract systems of any chicks. Halofuginone delayed the establishment of infections of the bursa of Fabricius and cloaca, but not of the trachea.     

Neosporosis in dogs

A bitch was inoculated subcutaneously and intramuscularly with Neospora caninum tachyzoites on Day 35 of pregnancy. Eight pups were born 28 days later. Five pups became ill and necropsies were performed before 20 days of age. Three pups and the bitch remained clinically normal for 7 weeks after parturition when they were intramuscularly injected with 40 mg kg-1 methylprednisolone acetate weekly to activate chronic N. caninum infection. Necropsies were performed 48, 17, 18, and 18 days respectively after administration of corticosteroids. Hepatic necrosis, pneumonia, encephalomyelitis, and myonecrosis were the main changes seen in these dogs.