ISOTOPE DENDROCHRONOLOGY OF AFRICAN MAHOGANY FROM THE NGOTTO FOREST, CENTRAL AFRICAN REPUBLIC

Tropical dendroclimatology data are frequently lacking because distinct anatomical growth rings in many tropical species are absent, or if growth rings are present, they are not necessarily annual. However, tropical regions are frequently affected by climate change the most, indicating the need for paleoclimate data to assess current and future changes. This study analyzes δ¹⁸O values of cellulose from the tree species Entandrophragma macrophyllum that was cored and collected from the Ngotto Forest, Central African Republic in 2012. Entandrophragma macrophyllum is classified under the Meliaceae family, the most abundant family of trees in the Ngotto Forest. Entandrophragma macrophyllum is one of the “African Mahoganies” and is an important species for the local and global economy. Although this species displays anatomical parenchyma bands, earlier studies reported one to two rings being formed per year. A micro-milling approach was used to collect samples at an average resolution of three samples per growth ring. Alpha cellulose was extracted, and samples were analyzed on a continuous flow isotope ratio mass spectrometer. Based on former dendroclimatology studies, it is expected that the δ¹⁸O cellulose values of tropical trees should be predominately affected by the δ¹⁸O value of the source water (precipitation in our case). Since the δ¹⁸O values of precipitation are tied to the ratio between evaporation and precipitation, and therefore precipitation volume, it is expected that there will be a correlation between precipitation and the oxygen isotopic composition of the cellulose. The δ¹⁸O cellulose values from this study will be compared to precipitation data both collected in the field at the study site, as well as data collected by regional precipitation monitoring stations.