Tree water use for the dominant tree species at Mt. Kilimanjaro

Thomas Leipold1, Dennis Otieno1, Eun-Young Jung1, John Tenhunen1
1 Department of Plant Ecology, University of Bayreuth

P 3.9 in Fluxes between the atmosphere and ecosystems

Poster Session 2 on Tuesday, 16:30-18:00

Tropical mountains are very important but vulnerable ecosystems. World wide, they are subject to different kinds of human induced changes in climate and land use. In Africa, mountains play a critical role in water supply. They act as water storage pools and are the main sources of major rivers and streams. The ongoing degradation of mountain ecosystems is, therefore, a serious threat to communities, hydrology and climate on local and even large scale. Altered environmental conditions due to deforestation, expansion and intensification of agriculture and a growing population are shifting local and regional water balances. Water availability has already become a source of conflict for most African communities who depend on these mountains. To quantify the role and contribution of trees in mountain water balance, transpiration of single trees was determined with sap flux measurements on Mt. Kilimanjaro, one of the most important Africa Mountains. The measurements were structured in order to capture the effects of elevation and land use. Four of the most dominant ecosystem types were considered: Savannah, coffee plantation, homegarden and lower montane forest. We conducted measurements for the dominant tree species, using Granier type thermal dissipation probes (TDP), micro climate and ecophysiological parameters. Altogether we observed 13 different species with 73 individuals between 2011 and 2013. The aims were to: 1) measure single tree water use and identify the key controlling mechanisms, 2) develop upscaling approaches from tree to whole stand transpiration and 3) quantify the impact of land use and elevation on forest water use. First correlation analysis of the measured sap flux density (SFD) for a dry period showed large data scatter between the different ecosystems with no clear tendencies regarding species or ecosystems. The gained SFD values are ranging from half hourly means of 0.16±0.05 kg*cm-2 to 0.02±0.01 kg*cm-2, measured for Cordia abyssinica (homegarden) and Agauria salicifolia (lower montane forest), respectively. Depending on water availability vapour pressure deficit (VPD), radiation or stand structure are the main controlling factors of SFD. Future analysis will focus on tree and stand transpiration and their regulation. In prospective studies the result of this work may be used for further analysis of tree and stand transpiration in East Africa as well as input parameter for local climate models.

Letzte Änderung 19.06.2014