An evaluation of veld condition assessment techniques in Highland Sourveld

An evaluation of six methods used to index veld condition showed that the majority provided indices that were insensitive to long‐term grazing impact. However, certain species were found to either increase or decrease in relative abundance with an increase in grazing intensity. A key species method is therefore suggested to be a potentially sensitive approach for indexing veld condition in relation to grazing management in the Highland Sourveld.     

The effect of stocking rate and lick supplementation on the performance of lactating beef cows and its impact on Highland Sourveld

Abstract

The Highland Sourveld of Natal is an important beef producing area. Although it covers only 13% of the total area of the province, it supports 18% of the beef cattle population.

The performance of cows and their calves stocked at four stocking rates on Highland Sourveld was studied. Two stocking rates were duplicated to test the benefit of an energy lick against a mineral lick. The effect of stocking rate on the veld was monitored in terms of compositional change.

Stocking rate significantly affected cow performance and consequently calf performance. An energy lick supplement, as opposed to a mineral lick supplement, was beneficial at the 1,0 LSU/ha stocking rate, but not at the 1,67 LSU/ha stocking rate.

The composition of the veld in the low to moderately stocked treatments changed relatively little, over the recording period, whilst the very high stocking rate treatments showed a rapid delcine in veld composition score.     

Annual and herbaceous perennial native Australian plant species are symptomless hosts of Phytophthora cinnamomi in the Eucalyptus marginata (jarrah) forest of Western Australia

Resistant annual and herbaceous perennial plant species were identified as key hosts which allow Phytophthora cinnamomi to persist on severely impacted black gravel sites within the Eucalyptus marginata (jarrah) forest of southwest Western Australia. Of the annual and herbaceous perennial plant species present on black gravel sites, 15 out of 19 species were found to be hosts of P. cinnamomi, and 10 of these were symptomless hosts. In particular, the native annual Trachymene pilosa and the two native herbaceous perennials Stylidium diuroides and Chamaescilla corymbosa were commonly found to be hosts of the pathogen. Species from 12 new genera including three from new families (Crassulaceae, Droseraceae and Primulaceae) are reported for the first time to be hosts of P. cinnamomi. The species from which P. cinnamomi was recovered were the native species: Chamaescilla corymbosa, Crassula closiana, Drosera erythrorhiza, Hydrocotyle callicarpa, Levenhookia pusilla, Paracaleana nigrita, Podotheca angustifolia, Pterochaeta paniculata, Rytidosperma caespitosum, Siloxerus multiflorus, Stylidium diuroides and Trachymene pilosa, and the introduced annual weeds Hypochaeris glabra, Lysimachia arvensis and Pentameris airoides.     

The effect of pre‐industrial charcoal kilns on chemical properties of forest soil of Wallonia,Belgium

In Wallonia, Belgium, intensive in situ charcoal production that was linked closely to pre‐industrial smelting and steel‐making affected a large part of the forested area in the late eighteenth century. Charcoal kiln relics can be detected under forest as domes of about 10 m in diameter, with the topsoil greatly enriched with charcoal residues. We sampled 19 charcoal kiln sites and the adjacent reference soil by soil horizon on four different soil types (Arenosols, Luvisols, Cambisols and Podzols). Data were analysed with linear mixed models to assess the effect of the charcoal kiln site on soil properties in relation to depth and soil conditions. We also addressed the evolution of soil properties over time by a comparison of the soil characteristics at a currently active kiln site. The charcoal‐rich topsoil has a larger C:N ratio and cation exchange capacity (CEC) per unit of organic carbon than the reference soil. The largest CECs per unit of carbon were observed on soil with coarser textures. On acidic soil, the increase in base saturation in the subsoil reflects the past liming effect of ash produced by wood charring, whereas the topsoil is re‐acidified. The acidity of carbonate‐rich Cambisols, however, is not reduced. Regardless of soil type, the kiln topsoil is greatly depleted in exchangeable K⁺ and available P, which may be attributed to the small affinity of the exchange complex of charcoal for K⁺ and a decrease in P availability with time. Therefore, we recommend further research on the long‐term effects of biochar on the dynamics of plant nutrients.     

Fungi and oomycetes in open irrigation systems: knowledge gaps and biosecurity implications

Water used for the irrigation of plants has the potential to harbour and spread plant pathogens yet little research is conducted within this field. This review was undertaken to critically review current understanding of waterborne fungal and oomycete plant pathogens in open irrigation systems, particularly in the context of plant biosecurity. It was determined that very limited data exists on these plant pathogens, with the majority of previous studies only recording pathogen presence. There are significant gaps in current knowledge of pathogen survival and spread, and very limited information on their ability to cause disease when contaminated irrigation water is applied to crops. This review highlights the need for new research on the epidemiology and pathogenicity of putative plant pathogens isolated from water, in order to determine their risk to crops. The importance of regular monitoring of irrigation systems for the early detection of plant pathogens is also discussed.     

A thirteen‐year study on the impact of a severe canker disease of Corymbia calophylla,a keystone tree in Mediterranean‐type forests

Worldwide, forests and woodlands have shown progressive declines in health as a result of global environmental changes in combination with local anthropogenic drivers. This study examined the incidence and progression of a canker disease of marri (Corymbia calophylla) caused by the endemic fungal pathogen Quambalaria coyrecup at three paired forest and anthropogenically disturbed sites in the southwest of Western Australia over 13 years. At the time of plot establishment in 2001, cankers were present on trees at all six sites with 22.7% of the assessed trees cankered. By 2014, cankers had led to the death of 6.7% of the trees, and an additional 10.0% of the trees developed cankers during this time. A further 2.3% of trees died due to causes other than canker, resulting in a final figure of 65.0% of trees remaining alive and free of cankers for the duration of the survey period. Canker incidence was significantly greater on trees present at anthropogenically disturbed sites (along roadsides and in paddocks) than forest trees (35.3% increasing to 50.7%, 10.0% increasing to 14.7%, respectively). Trunk diameter at breast height, tree height and crown ratings were not correlated with canker presence. This long‐term study provides evidence of the increasing severity of this canker pathogen and the impact it is having on the survival of marri.     

Growth responses of three coexisting conifer species to climate across wide geographic and climate ranges in Yukon and British Columbia

This work aimed to compare radial growth–climate relationships among three coexisting coniferous tree species across a wide geographic and climate range from southern British Columbia (BC) to central Yukon, Canada. Tree-ring data were collected from 20 mature stands of white spruce (Picea glauca), lodgepole pine (Pinus contorta var. latifolia), and subalpine fir (Abies lasiocarpa). Linear relationships between annual growth variation and monthly and seasonal climate were quantified with correlation and regression analyses, and variation in climate–growth responses over a climatic gradient were quantified by regressing growth responses against local mean climatic conditions. Temperatures had more consistent and stronger correlations with growth for all three species than precipitation, but growth–climate responses varied among species and among sites. In particular, pine and fir populations showed different responses between BC and Yukon, whereas spruce showed a more consistent response across the study domain. Results indicate that (1) the response and sensitivity of trees to seasonal climate variables vary among species and sites and (2) winter temperatures prior to growth may have significant impacts on pine and fir growth at some sites. The capacity to adapt to climate change will likely vary among the study species and across climatic gradients, which will have implications for the future management of mixed-species forests in Yukon and BC.     

Alternative protein blends as a replacement for fish meal in diets for white seabass,Atractoscion nobilis

An 8‐week feeding trial was conducted to determine the effectiveness of replacing fish meal (FM) with blends of alternative proteins in diets for white seabass (WSB, Atractoscion nobilis) at a starting weight of 5.6 g. Five diets were formulated with 400–440g kg^?1 crude protein (380g kg^?1 digestible). These included a high 520g kg^?1 FM control diet, a series of three diets with a sequential replacement of FM containing 410g kg^?1, 510g kg^?1 and 630g kg^?1 of a soy‐based protein blend (SPC) and 200g kg^?1, 100g kg^?1 and 0g kg^?1 FM, respectively and a fifth diet containing 550g kg^?1 of a corn‐based protein blend (CGM) and 100g kg^?1 FM. Survival was highest in the FM control group at 99% but all other performance measures (weight gain, feed conversion ratio, specific growth rate and protein retention efficiency) were worse than the other treatment groups. Weight gain reached a maximum of 595% in the SPC 200g kg^?1 FM treatment group. Performance decreased as inclusion of the soy‐based protein blend increased. The CGM treatment performed comparably to the SPC 100g kg^?1 FM treatment among all measures, except for survival, which was higher in the CGM 100g kg^?1 FM treatment. With nutrient levels and alternative protein blends used in this study, FM can be reduced to 100g kg^?1 of the diet for WSB without reductions in performance.