Growth of five species of trees on experimental plots on sand tailings left after mining for rutile in Sierra Leone
Dick, J., Garnett, T., Jones, S., Karim, A.B., Sundufu, A.J., Wadsworth, R.A., Okoni-Williams, A. (2015). Growth of five species of trees on experimental plots on sand tailings left after mining for rutile in Sierra Leone. NERC Environmental Information Data Centre. https://doi.org/10.5285/d4c6029a-464c-49d0-bcc7-75757cab2b3a
Data comprise measured heights of five species of trees after 2.5 years growth between June 2007 and November 2009 in plots reclaimed using a variety of planting techniques and surface applications following mining for rutile in Lanti South, Sierra Leone, West Africa. Eight 25 by 25 metres plots were divided into four squares and four rectangles and planted in June 2007. The five tree species included Gmelina (Gmelina arborea), mango (Mangifera indica), cashew (Anacardium occidentale), citrus (Citrus sinensis) and monkey apple (Anisophyllea laurina). Five rows of trees were planted at a spacing of 5 meters in each direction to minimize above and below ground competition. Four planting treatments were tested: 1 bucket of compost per planting hole, 1 bucket of topsoil, 1 bucket of a 50:50 mix of compost and topsoil and a control. Surface treatments included 2 cm of compost, 5 cm of mulch, 2 cm of top-soil and a control.
Trees were planted at a spacing of 5 meters (in each direction) to minimize the potential for above ground and below ground competition. The substrate (soil) that they are planted in is not very hospitable for plants as it consists of very coarse quartz sand the finer material (silts and clays) are removed as part of the initial processing of the rutile. The coarse nature of the sand and the high rainfall (~3 meters per year) means that leach rates are potentially high. Nutrient levels are low with an average concentration of Nitrogen of 0.0027% and an average soil Carbon of 0.073%; these values are barely 1% of the pre-disturbance conditions (typical undisturbed soils in the area have Nitrogen ~0.12% and Carbon ~4%). Eight (8) rehabilitation plots have been set out at Lanti South (7 deg 41' N, 12 deg 17' W). Each plot consists of four 25 by 25 meter compartments. Four plots (number 1 to 4) are square and four (5 to 8) are rectangular. Each compartment was planted in June 2007 with five rows of trees (one species per row) at a 5 meter by 5 meter spacing. Four planting treatments were tested: - 1 bucket of compost per planting hole, - 1 bucket of topsoil, - 1 bucket of a 50:50 mix of compost and topsoil - a control. The 'standard bucket' used is the local '34 centimeter' galvanized steel bucket and it contains 17 liters to brim full. The standard planting hole was 42 cm x 42 cm and 21 cm deep; the dimensions were chosen based on two spade blades wide and one deep when using the typical (standard) round mouth shovel sold in Sierra Leone. All trees in a compartment have the same planting treatment. Four surface treatments were applied; - 2 cm of compost, - 5 cm of mulch, - 2 cm of top-soil or - nothing (control) All four compartments in a plot have the same surface treatment. Planting and maintenance of the plots was carried out by the mining company (Sierra Rutile Ltd.) who hired labour and purchased compost from the local communities. Compost was produced by the local communities as part of a 'decentralized business model' (in essence this is a form of 'out-sourcing'). The compost contained many weed and vegetable seeds that resulted in very thick undergrowth on plots 3 and 7 that has overwhelmed the Monkey apple and citrus plants and may shortly do the same for the mangos. Dead or missing trees are recorded with a height of zero. No beating up or secondary planting was performed. Some trees were watered during the first dry season but we have no records of quantity or timing. Recording was done in two person teams, one measuring and the other recording. Measurements were made from the ground to the highest apical bud. It is the responsibility of the recorder to check that all measurements have been made. By 2009 there were some trees which were tall enough to be difficult to measure accurately with a simple tape measure, while the recorder can guide the measurer when they think the tape is properly vertical, making sure it is exactly level with the apical bud is error prone. In addition they help the person measuring for 'lost' trees (either dead, missing, or smothered). Although the plots and compartments were initially marked by sign boards several of these have disappeared and some have been (confusingly) relocated. The surface treatment is always obvious but the planting treatment is sometimes cross checked in the field against the plot location maps.
copyright UK Centre for Ecology & Hydrology
NERC Environmental Information Data Centre
Place, F.; Garrity, D. ; Mohan, S. ; Agostini, P. (2016). Tree-Based Production Systems for Africa’s Drylands. World Bank Studies;. © Washington, DC: World Bank.