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Climate change reduces the growth of the Mukusi trees (also known as Zambezi teak), which are Zambia’s main hardwood-timber source. The threat is caused by increasing temperatures and less rainfall. New research by Justine Ngoma, PhD student at Wageningen University, and colleagues on annual growth rings shows a clear relationship between climate and the annual growth of these important Zambian trees. The research is published in the scientific journal Dendrochronologia.
In Zambia increasing temperatures and declining rainfall are being observed. This is also reported by the Inter-governmental Panel on Climate Change (IPCC). Temperature and rainfall are important factors in the trees’ photosynthesis that drives growth. Photosynthesis is the process by which plants absorb sun light to convert carbon dioxide and water to sugars. These sugars are the building blocks of plants. When the temperature increases and rainfall is reduced, most sugars are respired and thus not available to create new wood or leaves. Plant growth therefore slows down
A new study led by Justine Ngoma and colleagues, conducted in the Sesheke, Namwala and Kabompo districts by researchers of the Zambian Copperbelt University, the Dutch Wageningen and VU Universities, and the USA Indiana State University, found that climate change is already limiting the annual growth of the Mukusi tree (scientifically known as Baikiaea plurijuga). In Sesheke district, the researchers conducted their study in Masese forest reserves, while in Namwala district, the study was conducted in Ila forest reserve. In Kabompo district, researchers conducted their study in Kabompo and Zambezi forest reserves.
Zambezi teak forests are found in flat areas with seasonally high water tables. Most of the area is covered with a thick layer of so-called ‘Kalahari sand’. The Mukusi trees are found in southern, western and north-western Zambia. These trees, being half of all the tree types in the studied reserves, have always been a source of hardwood timber. The timber has been supplied to local, national and international markets and strongly contributes to Zambia’s national economy. The timber has been used for railway sleepers and making furniture. “Unfortunately, little research was done to understand how the Mukusi trees respond to climate change,” Justine Ngoma says. “Thus, in our research we addressed this gap and showed the clear relationship between climate and the annual growth of these important Mukusi trees.”
The researchers examined annual growth rings from felled trees and correlated the width of individual growth rings with annual rainfall and mean annual temperature over a longer period. Their established relationships between rainfall, temperature and ring width allowed them to show that in a warmer and dryer climate, trees grow more slowly. Justine Ngoma: “We therefore conclude that the likely future temperature increase and rainfall decrease that are projected by IPCC for southern Africa, are likely to adversely affect Mukusi trees and thus negatively affect the Zambian timber industry.”