Effects of season and frequency of burning on soils and landscape functioning in a moist montane grassland

Abstract

The effects of burning on soil properties and landscape function were investigated in a long-term experiment comparing different burning strategies in a moist montane grassland. Total C, total N, total S, bulk density, plant-available nutrients, and soil acidity were determined in the top 200mm of soil, together with vegetation basal cover at the soil surface. The no-burn treatment had the lowest basal cover (14.8%). Basal cover for the burnt treatments ranged from 19.0% (five-year spring burn) to 25.4% (alternate autumn/spring, burnt every 18 months). The organic matter content of these soils was very high with total carbon ranging from 114g kg -1 in the 0-50mm layer to 77g kg -1 in the 150-200mm layer. Bulk density was very low, being 0.57g ml -1 in the 0-50mm layer. There were no significant effects of burning on the quantity of soil organic matter. The C:N ratio was significantly affected throughout the top 200mm by burning treatments; in the 0-50mm layer it ranged from 14.43 in the no-burn treatment to 16.14 in the treatment burnt every 18 months. Higher C:N ratios in frequently burnt treatments suggests that grassland productivity is N-limited in these treatments. In the top 50mm, soil pH is lower in treatments burnt infrequently (5 year and no burn) than in those burnt frequently, whereas concentrations of basic exchangeable cations (K, Ca and Mg) were lower in treatments burnt infrequently (five-year and no burn) than in those burnt frequently. The higher pH and concentrations of basic cations in frequently burnt treatments wasprobably due to greater cycling of nutrients to the soil surface as a result of higher productivity and deposition of nutrients in ash, together with reduced leaching of cations with nitrate. Landscape Function Analysis was used to measure the functioning of the landscape in terms of scarce resources and the processes that maintain these resources. All sites were highly functional, irrespective of the burning treatment applied. The infrequently burned sites had significantly higher nutrient cycling and infiltration indices than frequently burnt sites and these indices were correlated well with soil chemical properties (acidity, acid saturation, Ca, Cu, K, Mg, P and pH). No significant differences were found between treatments for the stability index.

Short-Term Responses of Southern African Semi-Arid Rangelands to Fire: A Review of Impact on Plants

“…These slower recoveries in terms of basal cover can be explained by the low rainfall these arid and semi-arid areas received, as well as the intense damage to the grass tufts itself by fire. Just as the case with basal cover, plant density decreased due to fire (Emmerich and Cox, 1992;West and York, 2002) and possibly did not recover two seasons following the fire (Table 1; Manson et al, 2007). By contrast, in terms of individual grass species, Snyman (2014) reported from a semi-arid climate a density of the One of the reasons for this increase in density could be the fact that the extremely big unpalatable tufts of this grass species was saved from a self-shading=smothering effect, which caused active growth and establishment of many new plants.…”

“…Regardless of the rangeland type, most researchers reported a decrease in basal and canopy cover with burning of arid and semi-arid areas (Figure 1; Snyman, 2004c;Manson et al, 2007;Killgore et al, 2009). In these drier areas, with big tuft sizes (less dense plant cover) the fire is more intense on an individual tuft base, which leads to the die-off of partly or whole tufts, causing the decrease in basal cover.…”

Special Feature: Revisiting the Brotherton Burning Trial

“…The results were presented in a series of papers during a special session of the 40th Annual Congress of the Grassland Society of South Africa (18-22 July 2005). Two of those papers, on soil properties (Manson et al 2007) and invertebrate composition (Uys and Hamer 2007) are published in this volume of African Journal of Range & Forage Science. Each contribution was subjected to the normal peer-review process of the journal.…”

Restoring and managing natural capital towards fostering economic development: Evidence from the Drakensberg, South Africa

“…An "attainable" condition for the natural grasslands (i.e. those areas not yet degraded) in the Upper-Umzimvubu catchment would be a 100% veld condition (essentially no grazing) in the upper Quinaries, with a 70% condition (controlled rotational grazing) in the middle and lower Quinaries with spring burns every second year (Tainton, 1999;Tainton et al, 1999;Fynn et al, 2003;Uys, 2006;Reynolds et al, 2007;Manson et al, 2007). However, the already degraded natural grasslands in all bottom Quinaries are in such a poor state that it is considered neither financially feasible nor practical in the short term to restore the veld.…”

“…well managed) of the respective baseline grasslands in all Quinaries, with a spring burn only every second year, as recommended by ecologists and practiced as a general rule of thumb allowing for spatial variations by Ezemvelo KZN Wildlife. This practice is augmented by rotational grazing and reduced stocking rates to achieve the required outcome (Tainton, 1999;Tainton et al, 1999;Fynn et al, 2003;Uys, 2006;Reynolds et al, 2007, andManson et al, 2007).…”