The overall objective of this thesis was to study the regeneration of Imperata grasslands in East Kalimantan, Indonesia, and to measure the effects of regeneration on soil properties, with emphasis on the organic fraction. The research strategy was to compare plots of different regeneration stages, characterized by the period elapsed since the vegetation was last burned. Chapter 1 presents as general introduction. Chapter 2 analyses the pathways of secondary succession after fire in Imperata grasslands of East Kalimantan, Indonesia. The relation between community structure, pattern and environmental gradients or soil properties is also discussed. Chapter 3 deals with the effect of forest regeneration after fire in Imperata grasslands on soil properties, with emphasis on soil carbon stocks. General chemical trends are explored by factor analysis and causes of change of carbon stocks are discussed. Chapter 4 uses stable C isotopes to measure the influence of C3 and C4 litter on soil organic matter (SOM). A relation between accumulation and replacement is explored and discussed. Chapter 5 explores changes in molecular chemistry of soil organic matter in relation to vegetation change, in order to decide whether changes in carbon stocks depend on chemical characteristics of litter. The used methodology, pyrolysis-gas chromatography/mass spectrometry allows a detailed interpretation of SOM chemistry. Chapter 6 deals with reliability of carbon stock estimate in Imperata grassland, using geo-referenced information. The chapter describes the spatial variability of soil carbon stocks using a sampling design consisting of transects, and resulting in geo-referenced information at various scales. Various carbon stock estimation procedures are discussed and recommendations for efficient sampling in similar areas to estimate carbon stocks are presented. Chapter 7 finally presents conclusions and recommendations: a synthesis of soil carbon stocks and changes upon forest regeneration.
