Seasonal and spatial variations in biogenic hydrocarbon emissions from southern African savannas and woodlands

Abstract

Biogenic volatile organic carbon (BVOC) emissions are an important component of the global BVOC budget, contributing more than 90%. Emissions vary with species and vegetation type; therefore to produce accurate global budgets data is required from different vegetation types. This study investigates BVOC emissions from savannas, Kalahari woodlands, Kalahari open shrublands and Mopane woodlands in southern Africa. BVOC emission samples from individual species were collected using leaf cuvettes and the BVOC concentrations were determined by GC-FID/MS. Ten of the 14 woodland species measured were high isoprene emitters, while two showed high monoterpene emission capacities. Landscape average isoprene emission capacities were estimated to be as high as 9, 8 and 1 mg C m −2 h −1 for savannas, woodlands and shrub lands, respectively. The monoterpene emission capacity for Mopane woodlands were estimated at almost 3 mg C m −2 h −1, while for other landscapes it varied between 0.04 and 3 mg C m −2 h −1. Isoprene and monoterpene emissions at a savanna site in South Africa showed a seasonal variation, which is more pronounced for isoprene. During the winter (June–September) estimated emissions were <10 mg C m −2 d −1, with peak emissions (ranging between 20 and 80 mg C m −2 d −1) occurring during the summer months (December–March) when foliar density peaked. The total BVOC emission from southern African (south of the Equator) savannas was estimated to be in the range of 18–74 Tg C yr −1.