Crude protein changes on grassland along a degradation gradient in a semi-arid climate

The aim with this investigation was to quantify the impact of different veld condition classes, viz. poor, moderate and good on soil-water utilization (SWU: crude protein produced per unit of evapotranspiration), during four growing seasons (2000/01 – 2003/2004). Evapotranspiration was determined by quantifying the soil-water balance equation with the aid of runoff plots and soil-water content measurements. Crude protein (CP) content was calculated from measured nitrogen content (Kjeldahl method) of the leaves, stems and seed. Although the monthly CP concentration (g/kg) of grassland in poor condition was generally higher than that of grassland in good condition, CP production decreased significantly with veld degradation when expressed as total quantity (kg/ha) of dry matter produced. Grassland in good, moderate and poor condition produced on average over the season 141, 97 and 32 kg CP/ha, respectively. Both monthly and seasonal SWU declined significantly with grassland degradation. Grassland in good condition averaged a SWU of 0.32 kg CP/ha/mm during the four growing seasons, compared to the only 0.09 kg CP/ha/mm produced from veld in poor condition. The study shows that it is important to keep grassland in optimal condition to utilize limited soil water for sustainable plant and therefore animal production. Keywords: Crude protein; evapotranspiration; soil-water content; soil-water utilization; veld condition South African Journal of Animal Science Vol. 36 (5) 2006: pp.34-3

Estimating grassland production loss due to fire for a semi-arid climate

Accidental, runaway veld fires cause enormous fodder flow problems in dry regions. It was the objective of this study to estimate the short-term (one year) impact of fire over 10 growing seasons (1995/96 – 2004/05) on the productivity (aboveground phytomass and litter) of a semi-arid grassland ecosystem. Fire caused a 41% decrease in basal cover over the first season following burning. On average over the study period the seasonal aboveground phytomass and litter production were decreased significantly, from 1 536 to 1 150 kg/ha and 111 - 42 kg/ha, respectively by fire. Seasonal production losses due to fire varied between 238 and 444 kg/ha. The relationship between aboveground phytomass production loss due to fire and two independent variables, namely seasonal rainfall and fuel load (aboveground phytomass plus litter) before burning, was investigated. One year after an accidental fire the production losses can be accurately (79%) estimated if the fuel load before burning is known. In general, the higher the fuel load before burning, the greater the production loss due to fire. The relationships can also serve as a simple empirical model for managers to determine short-term production loss due to unplanned fires in a semi-arid grassland. This information can serve as a scientific guideline in court cases in estimating production losses in claims for damages caused by fires. Keywords: Aboveground phytomass production; basal cover, fuel load; litter South African Journal of Animal Science Vol. 36 (5) 2006: pp.38-4

Degradation of communal rangelands in South Africa: towards an improved understanding to inform policy

In South Africa, the relative extent of range degradation under freehold compared to communal tenure has been strongly debated. We present a perspective on the processes that drive rangeland degradation on land under communal tenure. Our findings are based on literature as well as extensive field work on both old communal lands and ‘released’ areas, where freehold farms have been transferred to communal ownership. We discuss the patterns of degradation that have accompanied communal stewardship and make recommendations on the direction policy should follow to prevent further degradation and mediate rehabilitation of existing degraded land.Keywords: communal rangelands, land degradation, rehabilitation, social systemsAfrican Journal of Range & Forage Science 2013, 30(1&2): 57–6

More Stable Productivity of Semi Natural Grasslands than Sown Pastures in a Seasonally Dry Climate

In the Neotropics the predominant pathway to intensify productivity is generally thought to be to convert grasslands to sown pastures, mostly in monoculture. This article examines how above-ground net primary productivity (ANPP) in semi-natural grasslands and sown pastures in Central America respond to rainfall by: (i) assessing the relationships between ANPP and accumulated rainfall and indices of rainfall distribution, (ii) evaluating the variability of ANPP between and within seasons, and (iii) estimating the temporal stability of ANPP. We conducted sequential biomass harvests during 12 periods of 22 days and related those to rainfall. There were significant relationships between ANPP and cumulative rainfall in 22-day periods for both vegetation types and a model including a linear and quadratic term explained 74% of the variation in the data. There was also a significant correlation between ANPP and the number of rainfall events for both vegetation types. Sown pastures had higher ANPP increments per unit rainfall and higher ANPP at the peak of the rainy season than semi-natural grasslands. In contrast, semi-natural grasslands showed higher ANPP early in the dry season. The temporal stability of ANPP was higher in semi-natural grasslands than in the sown pastures in the dry season and over a whole annual cycle. Our results reveal that, contrary to conventional thinking amongst pasture scientists, there appears to be no increase in ANPP arising from replacing semi-natural grasslands with sown pastures under prevailing pasture management practices in seasonally dry climates, while the temporal distribution of ANPP is more even in semi-natural grasslands. Neither sown pastures nor semi-natural grasslands are productive towards the end of the dry season, indicating the potential importance of the widespread practice of retaining tree cover in pastures

Allelopathic potential, seed ecology and germination of the encroacher shrub Seriphium plumosum

Seriphium plumosum encroachment in South Africa has converted extensive areas of grassland into less productive shrubland-grassland. In addition to its competitive ability, it is hypothesised that the encroachment of S. plumosum is linked to the allelopathic potential of the plant. Interference between S. plumosum and four plant species (Eragrostis curvula, Festuca arundinacea, Solanum lycopersicum and Lactuca sativa), and between mature shrubs and seedlings of S. plumosum, was investigated in the field and greenhouse. The germination of all species was suppressed (P 15 weeks when dead plant material remained on the soil. These findings indicate that S. plumosum can inhibit the recruitment of other plant species under natural conditions.Keywords: bankrupt bush; slangbos; toxin; Stoebe vulgaris; vaalbosAfrican Journal of Range & Forage Science 2010, 27(1): 29–3

Soil seed bank evaluation and seedling establishment along a degradation gradient in a semi-arid rangeland

The effects of rangeland degradation on the size and species composition of the seed bank and seedling establishment in the field were quantified over a two year period (2000–2001 and 2001–2002 growing seasons). Soil seed bank sampling was carried out at three-monthly intervals from 0.25m2 blocks 50mm deep. Sampling was from rangeland artificially maintained in three different rangeland conditions viz. good, moderate and poor. The total seedling establishment in the field for every species was obtained at the end of the growing season. Soil temperatures at 100mm depth and soil-water content at 50mm depth intervals were recorded once a week. Due to the lower basal cover with rangeland degradation, soil temperatures increased significantly both daily and seasonally, while soil-water content also decreased. Rangeland in poor condition was characterised by a significantly higher seed density in the seed bank and more seedling establishment than grassland in good condition. No climax seedlings were present in rangeland in poor condition, while very few survived in rangeland in good condition at the end of the season. A mean seasonal seed bank density of rangeland in good, moderate and poor condition was respectively: 48, 74 and 98 seedlings m–2 for October; 28, 32 and 40 seedlings m–2 for January; and 58, 172 and 128 seedlings m–2 for April. Rangeland degradation showed a decrease in species richness in both the seed bank and seedling establishment in the field. A mean number of 1.67, 2.27 and 2.83 seedlings m–2 established in rangeland in good, moderate and poor conditions respectively at the end of the growing season.Keywords: germination, grassland degradation, seedling emergence, seed longevity, seed recruitment, soil temperature, soil-water contentAfrican Journal of Range & Forage Science 2004, 21(1): 37–4

Short-term response of the encroacher shrub Seriphium plumosum to fire

Quantification of the short-term impact of burning in terms of the encroacher shrub Seriphium plumosum and grass tuft mortality, seed germination of the shrub (field and seed bank), aboveground phytomass production, plant density and basal cover of the grass sward was conducted in semiarid grassland following an accidental fire. These variables were determined along a terrain morphological unit where S. plumosum density increased with altitude. On average 57% of S. plumosum seedlings were killed by fire, but fire had no significant (P > 0.05) influence on the mortality of mature shrubs. Fire significantly (P . 0.01) stimulated seedling emergence of S. plumosum, to such an extent that an average of 510 seedlings ha-1 occurred on the foot slope, while only 9.14 seedlings ha-1 emerged in the unburnt treatment. Seedling emergence showed greater association with protection from direct sunlight and seedlings emerged not closer than 281 mm from the nearest leaves (canopy) of a mature S. plumosum shrub. The aboveground phytomass production of the unburnt grass sward was nearly double that of the burnt areas over the first season following the fire. Fire as a control measure should be carefully handled because it can lead to increased encroachment of S. plumosum.Keywords: bankrupt bush, mortality, seed germination, slangbos, Stoebe vulgarisAfrican Journal of Range & Forage Science 2011, 28(2): 65–7

Fire and the dynamics of a semi-arid grassland: influence on soil characteristics

The short-term impact of fire burning with the wind (head fire) and against the wind (back fire) on soil characteristics (soil-water content, soil compaction, soil temperature, organic matter, pH, exchangeable Ca, Mg, K, Na and extractable P) were determined in a semi-arid grassland. This study was conducted over two growing seasons (2000/01 and 2001/02) after only one burning treatment in August 2000. The back fire moved approximately 7.5 times slower than the head fire, leading to the greatest change in hydrological characteristics. The decline in plant cover due to the fire resulted in a considerable increase in soil compaction, soil temperature and a decrease in organic material in turn leading to a lowered soil-water content. Much of the influence of these variables had not been completely reduced two growing seasons after the fire. Burning reduced the soil-water content (0mm to 300mm soil depth) after one month and one year by 13.4% and 31% respectively. Temporary wilting for all grass species occurred more rapidly with burning. During March of the first year, the greatest soil temperature difference (50mm depth) occurred between burnt and unburnt grassland, with the highest soil temperatures recorded in January. The highest temperature on the surface of the soil for each year after burning also occurred during January. Over the first growing season burning significantly reduced organic carbon (C) and total nitrogen (N) content and extractable phosphate, but increased the pH and concentration of exchangeable Ca, Mg, Na and K in the soil, over the first 0–50mm layer. There were no differences in the soil properties of head and back fires, except for organic material that was further lowered by the back fire. With depth, organic matter and K decreased significantly and Ca increased between surface (0mm to 50mm) and lower (50mm to 100mm) layers due to burning. Thus, an unplanned event can increase the intensity and frequency of seasonal droughts in the ecologically sensitive semi-arid grassland areas leading to increase risk management in the short-term. Keywords: back and head fires; organic matter content; soil compaction; soil-water content; soil temperature; soil properties; temporary wilting African Journal of Range & Forage Science 2002, 19(3): 137-14

Fire and the dynamics of semi-arid grassland: influence on plant survival, productivity and water-use efficiency

There is a lack of knowledge concerning the effect of fire behaviour on the vegetation dynamics of semi-arid climates. Arising from this, an investigation was initiated to characterise the behaviour of fires burning with the wind (head fire) and against the wind (back fire). The behaviour of these fires was related to the response of the vegetation by monitoring the recovery and productivity of the grass sward after only one burn over a two year period (2000/01 to 2001/02 seasons). The results showed that head fires had significantly greater flame height and rate of spread than back fires. However, at ground level back fires were more intense and had a negative effect on recovery of the grasses, resulting in lower litter, yield and water-use efficiency (aboveground phytomass or crude protein produced per unit of evapotranspiration). Fire had a significant effect on plant density and cover, with basal cover 68% lower than that of unburnt grassland two months after the fire. Cymbopogon plurinodis with large tufts had the most die-back of all the species. With the exception of plant cover and density, which takes longer to recover, it takes approximately two complete growing seasons to recover from most of the detrimental effects of fire. The initial increased crude protein content of the plant material caused by fire did not off set the approximately 50% reduction in plant production the first growing season after the fire. Fire significantly decreased WUE (water-use efficiency), with an average over the two growing seasons of 3.06kg ha-1 mm-1 and 2.45kg ha-1 mm-1 for unburnt and burnt grassland respectively. In various semi-arid grassland areas, the use of fire as a management tool is questionable if there is no specific purpose for it.Keywords: back and head fires; basal cover; crude protein content; grass sward recovery; tuft mortalityAfrican Journal of Range & Forage Science 2003, 20(1): 29–3