Soil Factors That Influence the Abundance and Distribution of Threatened and Endangered Species in the Okavango Delta; with Particular Emphasis on <i>Eulophia angolensis</i>

Abstract

Eulophia angolensis is an endangered plant species found in the Okavango Delta. Generally, there is lack of botanical information on this species in Botswana, which is necessary for its in-situ and ex-situ conservation. The objectives of this research are to map areas where E. angolensis occurs, determine the species that co-exist with it, and establish soil factors that influence its abundance and distribution in the Okavango Delta. A survey of the area where the plant was sighted in 2004 was carried out using recorded GPS points. Soil samples were collected at 0 - 20 cm depth from the floodplain where the species occurred to determine the macronutrients: total nitrogen, phosphorus, potassium (N, P, and K) and soil organic carbon (SOC) contents. The researchers could not find the plant at all GPS locations where the plant was sighted in 2004, but discovered a new unrecorded site for the species. The species was very close to the water channel; approximately 40 cm away, with only one plant about 60 cm away. The mean macronutrients concentrations in the site that contained E. angolensis were total N = 2.61 ± 0.61 mg/L, P = 7.02 ± 0.8 mg/L and K = 14.41 ± 4.28 mg/L. SOC concentration was 40.1 ± 10.28 mg/L. Furthermore, there was K biogeochemical gradient within the E. angolensis habitat, with more concentrations directly around the plant. Therefore, E. angolensis needs critical amounts of N, P, K and SOC, with K, SOC and water requirement being the crucial factors. Frequent monitoring of the endangered species found in the Okavango Delta is required, and ex-situ conservation of the species in the country in the form of a botanical garden should be established for future generations.