DROUGHT MORTALITY OF TREE SEEDLINGS IN AN ERODED TROPICAL PASTURE

Experimental restoration may both accelerate and elucidate natural processes of succession on degraded agricultural land by offering insight into factors that influence rates of succession and the composition of resulting communities. A novel study in restoration of degraded tropical agricultural land in coexistence with cattle ranching activities was established in southern Veracruz, Mexico. The experimental planting of 16 mixed‐species stands of 18 pioneer and late‐successional tree species was established from September to November 2006 on an eroded hillside pasture with an elevational gradient from 182 to 260 m and heterogeneous soil depths. An unusually severe dry season in 2007 killed 72 per cent of the seedlings: least squares regression suggested that survival of six pioneer and 12 late‐successional species was mainly explained by initial basal diameter at planting followed by soil depth for pioneers and by elevational position on the hillside for late‐successional species. Individuals with larger initial size at planting (>4 mm basal diameter), regardless of germination size in a growing house, survived better probably because larger seedlings developed deeper roots that found fissures in substrate underlying thin soils. Interestingly, seedlings small at planting (<4 mm basal diameter) survived as well as large seedlings in deeper (>19 cm) soils, but virtually, all small seedlings died on thin soils (<18·5 cm). Mortality in restoration plantings can be reduced by planting large seedlings of a mix of pioneer and late‐successional species, recognizing that soil depth is a key criterion for survival of the smallest seedlings in a cohort. Copyright © 2011 John Wiley & Sons, Ltd.     

An outbreak of avian malaria in captive yellowheads/mohua (Mohoua ochrocephala)

CASE HISTORY: Eight mohua, or yellowheads (Mohoua ochrocephala), were held in a large open aviary over the summer months of 2003–2004, following their capture for captivebreeding purposes. Two birds died of transportation trauma shortly after arrival, one became ill and died a month later, and another four died within a 2-week period in February 2004. The eighth bird also became ill at this time but survived for a year following treatment with chloroquine and doxycycline.

CLINICAL AND PATHOLOGICAL FINDINGS: The affected birds were depressed, lethargic and dyspnoeic. Necropsy of three birds showed a slightly pale and swollen liver and spleen. Impression smears of the liver of one bird revealed schizonts resembling Plasmodium spp. within the cytoplasm of many hepatocytes, which was confirmed histopathologically. Similar protozoal organisms were seen within splenic histiocytes and pulmonary endothelial cells of 5/6 birds. Electron microscopy identified these as protozoal schizonts containing merozoites of similar size and structure to those of Plasmodium spp.

DIAGNOSIS: The birds were infected with a protozoal haemoparasite resembling Plasmodium spp.; asexual stages within hepatocytes and endothelial cells of the lung and spleen were typical of this organism.

CONCLUSIONS AND CLINICAL RELEVANCE: The mohua captured from west Otago were highly susceptible to avian malaria as they came from an isolated population that was likely to be naïve and have had no previous contact with this organism. The birds were probably infected by bites from mosquitoes feeding off local populations of blackbirds subsequently found to be infected with Plasmodium spp.     

A qualitative approach to measure the effectiveness of active avian influenza virus surveillance with respect to its cost: a case study from Switzerland

The aim of the project was to apply cost-effectiveness analysis to the economic appraisal of avian influenza virus (AIV) surveillance, using the implemented surveillance programme in Switzerland as a case study. First a qualitative risk assessment approach was used to assess the expected impact of surveillance on the transmission and spread of AIV. The effectiveness of surveillance was expressed as the difference in defined probabilities between a scenario with surveillance and a scenario without surveillance. The following probabilities were modelled (i) transmission of highly pathogenic AIV (HPAIV) from wild birds to poultry, (ii) mutation from low pathogenic AIV (LPAIV) into HPAIV in poultry, and (iii) transmission of HPAIV to other poultry holdings given a primary outbreak. The cost-effectiveness ratio was defined conventionally as the difference in surveillance costs (ΔC) divided by the change in probability (ΔP), the technical objective, on the presumption that surveillance diminishes the respective probabilities. However, results indicated that surveillance in both wild birds and poultry was not expected to change the probabilities of primary and secondary AIV outbreaks in Switzerland. The overall surveillance costs incurred were estimated at 31,000 €/year, which, to be a rational investment of resources, must still reflect the value policy makers attribute to other benefits from having surveillance (e.g. peace of mind). The advantage of the approach adopted is that it is practical, transparent, and thus able to clarify for policy makers the key variables to be taken into account when evaluating the economic efficiency of resources invested in surveillance, prevention and intervention to exclude AIV.     

Impacts of summer versus winter logging on understory vegetation in the Chequamegon-Nicolet National Forest

In seasonal climates the timing of logging operations can be adjusted to avoid the major growing periods of understory plants and seedlings. We evaluated the understory vegetation at five pairs of hardwood-dominated sites in northern Wisconsin, U.S.A. where one site in each pair was logged during winter and the other during summer. All sites were dominated by sugar maple (Acer saccharum) and basswood (Tilia americana), with varying amounts of other native tree species. Most (84%) of the 247 vascular plant species recorded during the study are indigenous to the region. Winter-logged sites supported significantly higher numbers and percent cover of ecologically vulnerable native plant species as defined by independently established coefficients of conservatism. These differences between winter-logged and summer-logged sites suggest that winter logging may have fewer negative impacts than summer logging on vulnerable plant species and, in the long run, may help maintain plant biodiversity in managed forests of this region. In both types of sites, understory plant richness and diversity were significantly higher near logging roads, due largely to higher numbers of alien species and early successional native plants. Away from roads, neither species richness nor diversity differed between winter-logged and summer-logged sites. Studies that fail to account for differences in species composition and studies that fail to include samples of access roads or skid trails are likely to ignore important impacts of logging activities.     

Computed tomography diagnosis of eight dogs with brain infarction

Objective Medical records of eight dogs presenting with acute onset of neurological signs and a diagnosis of brain infarction as determined by computed tomography (CT) imaging were reviewed. Design Retrospective single-centre case review Results Ischaemic infarction in the territory of the rostral cerebellar artery was identified in three spaniel-breed dogs. All cerebellar infarcts were non-haemorrhagic. Telencephalic infarcts were identified in five dogs, in the territories of the middle cerebral artery (2/5) and rostral cerebral artery (3/5). One of these dogs had an ischaemic infarction, but all other infarctions appeared haemorrhagic. All dogs were geriatric (≥8 years old), with concurrent medical conditions identified in six dogs. One dog was euthanased after diagnosis because of the severity of its neurological signs and one dog was euthanased as a result of associated renal disease 2 months after diagnosis. Six dogs were alive at least 1 year after diagnosis. Conclusions CT is useful in the diagnosis of cerebrovascular accident in dogs, which can present as a spectrum of images with early changes in attenuation and subtle mass effects detected after infarction. CT is particularly sensitive for detecting haemorrhagic infarction, but under-represent ischaemic and lacunar infarctions when compared with MRI.     

A comparison of the dry matter yields of perennial legumes in the Dohne Sourveld

Abstract

Fifteen perennial legumes were compared, under dryland conditions on two sites, in the Dohne Sourveld. These sites were Dohne, which has a mild, but dry winter and an average of 743 mm of rainfall per year, and Grasslands, which is a colder site with an average rainfall of 866 mm per year. The legumes were compared in terms of their total dry matter production and the distribution of this production during the season.

At Grasslands, Coronilla varia produced more (10,6 t/ha/y) than Medicago sativa (7,1 t/ha/y). At Dohne, C. varia, M. sativa and Neonotonia wightii cv. Cooper all produced more than 6 t/ha/y. The high yields and persistence of C. varia, and N. wightii suggests that these two legumes can play a role in dryland pastures (as M. sativa should) in the Dohne Sourveld. C. varia could also have a role to play in replacing Stipa trichotoma. The monthly production of legumes at Dohne has been tabulated. Farm applications of the crops are postulated.     

On the sensitivity of seven legumes to the herbicide tetrapon

Abstract

A trial was conducted in a glasshouse to screen seven legumes for their sensitivity to tetrapion. The application rates were 0g, 750g, 1500g and 3000g a.i./ha. Lotus corniculatus and Vicia dasycarpa were not visibly affected even at the highest rates. L. pedunculatus was affected slightly and Coronilla varia was probably also affected slightly. Medicago sativa was affected moderately severely while Trifolium pratense and T. subterraneum were affected severely.

The legumes which were not severely affected by tetrapion show promise in the Dohne Sourveld and should be used in the nassella eradication campaign. The need for further screening and research is stressed.