The frankincense tree Boswellia neglecta reveals high potential for restoration of woodlands in the Horn of Africa

Boswellia neglecta S. Moore is a frankincense-producing tree species dominantly found in the dry woodlands of southeastern Ethiopia. Currently, the population of this socio-economically and ecologically important species is threatened by complex anthropogenic and climate change related factors. Evaluation of tree age and its radial growth dynamics in relation to climate variables helps to understand the response of the species to climate change. It is also crucial for sustainable forest resource management and utilization. Dendrochronological and remote-sensing techniques were used to study periodicity of wood formation and leaf phenology and to assess the growth dynamics of B. neglecta. The results show that B. neglecta forms two growth rings per year in the study area. The growth ring structure is characterized by larger vessels at the beginning of each growing season and smaller vessels formed later in the growing season, suggesting adaptation to decreasing soil moisture deficits at the end of the growing season. Seasonality in cambial activity matches with a bimodal leaf phenological pattern. The mean annual radial growth rate of B. neglecta trees is 2.5 mm. Tree age varied between 16 and 28 years, with an average age of 22 years. The young age of these trees indicates recent colonization of B. neglecta in the study region. The growth rate and seasonal canopy greenness (expressed by Normalized Difference Vegetation Index – NDVI) were positively correlated with rainfall, suggesting that rainfall is the main climatic factor controlling growth of B. neglecta. The observed temporal changes in leaf phenology and vessel size across the growth rings indicate that the species is drought tolerant. Therefore, it can be regarded as a key tree species for restoration of moisture-related limited areas across the Horn of Africa