The status of soil organic carbon under indigenous forests, grasslands, wetlands and pine plantations in Woodbush, Limpopo Province, South Africa

[摘要] ENGLISH ABSTRACT: Storing soil organic carbon (SOC) is a possible way of reducing atmosphericCO2 and potentially mitigating the effects of global warming. This study looksat soil carbon stocks, the sampling methodology and modelling of soil organiccarbon in indigenous forests, wetlands, grasslands and pine plantations inWoodbush in the North-Eastern escarpment of Limpopo Province, SouthAfrica. Dominant Pine species planted in Woodbush are Pinus patula, Pinuselliotti and Pinus taeda. Woodbush plantation was selected as study areabecause it provided easy access to all the ecosystems that were to bestudied. All ecosystems in Woodbush are located in such a way that it waseasy to compare them, as they existed under similar environmental andclimatic conditions. The climatic conditions of Woodbush promoteaccumulation of SOC due to relatively higher precipitation and coolertemperatures than most parts of Limpopo Province.Five transects were made: two in indigenous forests and three in plantations.Only the surface (0-7 cm) layer was sampled with a distance of 20 m betweensampling points. Transects were not made in grasslands and wetlandsbecause of the patchy occurrence of these ecosystems. In addition totransects, eight 1ha plots, two in each ecosystem, were sampled. Surface (0-7 cm depth) samples were collected on a grid of 20 x 20 m in each samplingplot. Two soil profile pits were sampled in each sampling plot, with samplesbeing taken at 5, 10, 15, 20 30, 40, 50 60, 75 and 100 cm depth.The average carbon stocks per hectare of land to a soil depth of 100 cm wereas follows: 71 t.ha-1 in wetlands, 28 t.ha-1 in grasslands, 64 t.ha-1in indigenous forests, and 46 t.ha-1 in pine plantations. Although wetlands sequestered largeamounts of SOC per hectare, their relative contribution to carbonsequestration was low because of the relatively small area (87.2 ha) theyoccupy in the study area (and in South Africa).Prediction models for vertical distribution of SOC were developed usingSTATISTICA 6.0 for each ecosystem in order to estimate the carbon stocks toa depth of 100 cm based on SOC content and soil bulk density of the surfacesamples. These models were developed from observed values in soil profilesfor each ecosystem.SOC content and carbon stocks were analyzed using GIS (ARCVIEW). TheGIS analysis was aimed at assessing the effect of topography, elevation, soiltype, and vegetation on accumulation and distribution of SOC stocks. Mostshallow Inanda soils were distributed at elevations between 1545 m and1777 m, and on a gentle slope in the Northern aspect of the mountain. DeepInanda soils were found mostly in the lower elevation range of 967 m and1545 m on moderate slopes. Deep and shallow Inanda soils were found onthe southern aspect.Deep Kranskop soils are evenly distributed and mostly found at an elevationrange of between 1080 and 1430 m on gentle slopes, while at an elevationrange of between 1430 and 1780 m, they were found on moderate slopes.Deep soils had higher SOC stocks than shallow soils and soils in the southernaspects had higher SOC stocks than in the northern aspects.

[发布机构] Stellenbosch University