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.
Factors shown to influence wetland species composition and relative abundance include flooding regime, plant life history requirements, water and soil chemistry, species interactions and disturbance by physical processes or animals [
There are plant nutrients that have positive bearing on plant growth. Chemical analysis of plants shows that carbon, hydrogen, oxygen and nitrogen are the major constituents, with potassium, calcium, magnesium, phosphorus and sulphur also present in appreciable quantities [
At the moment several species are considered to be endangered around the world. An endangered species is a population of an organism which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters [
Humans induce pressure and variation in natural environments and can threaten the integrity of certain plant species. The best strategy for conservation of endemic species is to keep them in their natural habitat as free as possible from any form of abnormal (human related) disturbance, such as grazing by livestock, suppression of wildfires, tourism, water extraction, atmospheric deposition of nitrogen and perhaps the most importantly the invasion of exotic species [
The Okavango Delta in Northern Botswana is one of the natural ecosystems which house several rare, threatened and endangered species. In a recent study by [
The study was conducted some kilometers from Xakanaka in Moremi Game Reserve, Okavango Delta (
The GPS coordinates from the Peter Smith maps and Department of Water Affairs in Maun, Botswana were used to help locate E. angolensis in the Okavango Delta. A survey of the area where the plant was sighted in 2004 was carried out to locate the species habitat. Observations were also made for potential identification of new sites for the species, which were recorded and stored using a GPS.
Line transects were used for vegetation survey of the area covering recorded GPS points. Once the place was found, two line transects of 15 m each from the center of a GPS point were laid out pointing at different directions and a search for the plant was carried out. After the E. angolensis species was identified, other species that coexist with it were also identified. The number of E. angolensis plants were counted and recorded. Thereafter, the density of E. angolensis was calculated using the formula according to [
where D = density, n = number of species, A = area sampled.
Soil samples were collected along transects where the E. angolensis species occurred. The samples were collected at 10 cm depth immediately around the plant and at 5 m, 10 m, 15 m away from it. The samples were kept in plastic bags and transported to Okavango Research Institute for laboratory analysis.
Soil samples were allowed to air dry for 5 days and finally for 24 hours in an oven at a temperature of 60 degrees Celsius. The samples were cleaned for stones and plant residues, grinded with a pestle and mortar, and then passed through a 2 mm sieve.
The sieved soils were then digested using the sulphuric acid digestion method, 1 g of soil was digested using 6 mL sulphuric acid, one kjedehl catalyst tablet and 2 g sodium sulphate. The samples were placed in a Block Digester heater at a temperature of 450 degrees Celsius for an hour to boil. After an hour the samples were removed from the heater and put aside to cool for 15 mins, however, still in the fume hood. Distilled water was added. The samples were given a further 30 mins to cool then taken out the fume hood, topped with more distilled water, closed with rubber stoppers and left over night. The digested soils were filtered and analyzed accordingly: Potassium (K) was analyzed using Flame Photometer, nitrogen (N) and phosphorus (P) using a Segmented Flow Analyzer.
Spatial analysis and mapping was carried out using ArcGIS software to map areas where E. angolensis was found.
A t-test was used to determine if the macronutrients and SOC concentrations were significantly different directly around the plant compared to its environment.
E. angolensis was not located within all the areas that it was once sighted in the south of the Okavango Delta and quite notably wildfires were reported in the very same areas 6 months before this study quest for the species. However, E. angolensis was found in two new sites along the Gadikwe channel. Both sites contained only three species each. The species were very close to the water channel, approximately 40 cm away from the water channel, with only one plant about 60 cm away, and this one species appeared to be unhealthy and dying.
The average macronutrients concentrations in the site that contained E. angolensis as shown in
A t-test was conducted to compare soil macronutirents and SOC contents using samples within E. angolensis habitat, i.e. soil samples directly around the E. angolensis plants species against soil samples collected from the line transects at 5, 10, 15 meters away from the plant species. Of all the four nutrients tested, there was only a significant difference in K (
Coordinates of previous sightings of E. angolensis and locations where it was not sighted were placed on a map. Of all the 11 coordinates of previous sightings, E. angolensis was not found by this study (
Parameter | Nitrogen (mg/L) | SOC (mg/L) | Potassium (mg/L) | Phosphorus (mg/L) |
---|---|---|---|---|
N | 25 | 25 | 25 | 25 |
Mean | 2.61 | 40.1 | 14.41 | 7.02 |
Median | 2.49 | 39.87 | 12.70 | 7 |
Std. Deviation | 0.61 | 10.28 | 4.28 | 0.80 |
Levene’s Test for Equality of Variances | t-Test for Equality of Means | |||||
---|---|---|---|---|---|---|
t | df | Sig. (p = 0.05) | Mean Difference | Std. Error Difference | ||
Lower | Upper | Lower | Upper | Lower | ||
Soil organic carbon | Equal variances assumed | −0.204 | 23 | 0.840 | −0.85641 | 4.20116 |
Equal variances not assumed | −0.208 | 19.991 | 0.837 | −0.85641 | 4.12080 | |
Nitrogen | Equal variances assumed | 0.012 | 23 | 0.991 | 0.00295 | 0.24740 |
Equal variances not assumed | 0.012 | 17.342 | 0.990 | 0.00295 | 0.24090 | |
Potassium | Equal variances assumed | 2.999 | 23 | 0.006 | 4.45385 | 1.48495 |
Equal variances not assumed | 3.057 | 20.108 | 0.006 | 4.45385 | 1.45705 | |
Phosphorus | Equal variances assumed | −1.533 | 23 | 0.139 | −0.47545 | 0.31005 |
Equal variances not assumed | −1.541 | 22.975 | 0.137 | −0.47545 | 0.30855 |
According to [
In general, the high nutrient content in sites where E. angolensis occur can be attributed to high levels of organic matter, higher vegetation density, moisture and microbial activity. Organic matter is a reservoir for soil nutrients [
The wild fires that were reported in the areas where previous E. angolensis species were sighted could be the main reason why this report did not find the species there. The fires could have burnt away the species; [
According to [
E. angolensis requires critical concentrations of soil organic carbon, nitrogen, phosphorus and potassium. Potassium and water are the main limiting factors for the species. Frequent monitoring of threatened and endangered plant species is critical for their conservation status. Therefore, monitoring of threatened and endangered plant species in the Okavango Delta should be carried out. General census of the plant population density should be conducted regularly. Furthermore, ex-situ conservation of the species in the country in the form of a botanical garden should be established for future generations.