Vegetation response to climate change and human impacts in the Usambara Mountains

Abstract

East and West Usambara Mountain blocks are unique based on three characteristics. Firstly, they are connected blocks; secondly, they have an oceanic-influenced climate; and thirdly, the rain seasons are not easily discernible due to their close proximity to the Indian Ocean and Equator. Sediment cores were collected from peat bogs in Derema (DRM) and Mbomole (MBML) in East Usambara and from Madumu (DUMU) in West Usambara. The multiproxy record provides an understanding on climate and vegetation changes during the last 5000 years.DRMandMBMLcores result in radiocarbon ages and age-depth curvewhich showed hiatus at 20 cm and 61 cm and huge inversion for DUMU core at 57 cm. Period 5000–4000 14C yr BP for DUMU core revealed increased Montane forest indicative of relatively moist conditions. Periods 3000–2000 and 2000–1000 14C yr BP, DUMU core demonstrated increased submontane and lowland forests. Period 1000–200 14C yr BP,DUMUcore signified increased coprophilous fungi while DRM and MBML cores signified fluctuating herbaceous pollen spectra (wet-dry episodes). Period 200 14C yr BP to present, all cores demonstrated stable recovery of forest types especially dominance of submontane forests. Abundant coprophilous fungi indicated increased human impacts including forest fires, cultivation, and grazing.