The performance of selected tree species in the rehabilitation of a limestone quarry at East African Portland Cement Company land Athi River, Kenya
Quarrying for limestone is an economic necessity that is not only hazardous to human but also one that invariably has deleterious effect on the environment. Information on the performance of trees species is important as plants are key in the revegetation of exhausted quarries. A comparison of field performance of Acacia xanthophloea, Schinus molle, Casuarina equisetifolia and Grevillea robusta was made in an exhausted limestone quarry, backfilled with limestone mine waste, in a semi-arid area, in Athi River, Kenya, between 2005 and 2008. The aim of the study was to assess the performance of the above tree species and to determine if these tree species had an influence on the soil physical and chemical properties. The seedlings were produced in a nursery and transplanted in plots established in the exhausted quarry site using randomised complete block design. Growth performances were estimated by measuring; tree height, diameter at the stem base (BD) , and diameter at breast height (DBH) from March 2006 to March 2008. The soils physical and chemical parameters measured were: moisture content; organic matter; pH; total Nitrogen; total Phosphorus and exchangeable cations. The study revealed that the time-species interaction was significant (p<0.001), indicating continuous tree growth for all the species. The trees species performance was varied. C. equisetifolia recorded the highest growth increments for the; height (525.3 em), BD (7.42 em) and DBH (4.94 em) and the highest growth rates for; tree height (14.24 cm/month), BD (0.23 em/month) and DBH (0.l4 em/month), indicating superior performance. This was followed by A. xanthophloea and S. molle. Grevillea robusta showed poor performance and recorded the lowest growth increments for; height (231.7 em), BD (4.41 ern) and BDH (2.0 ern) and growth rate for; tree height (5.04 em/month), BD (0.084 em/month) and DBH (0.023 em/month). These results indicate that there is species-specific response that may be due to different water- and nutrient-use strategies and growth patterns. The soil had low soil moisture content which ranged from 0.67% to 2.3%; alkaline pH, ranging from 8.0 to 8.98; low soil nitrogen content « 0.03%), related to the limited soil organic-matter content (ranging from 0.05% to 0.38%), and high to moderate exchangeable cations. All the tree species had a noticeable influence on soil chemical properties, by the end of the research period. The pH values and total Phosphorus were relatively lower in soils close to the tree row (0.5 m) and increased with distance from the trees, while the soil values for organic matter, total Nitrogen, and exchangeable cations were relatively higher close to the tree row and decreased with distance from the trees. From the study, C. equisetifolia has the best growth performance and also has a higher positive influence on the soil properties followed by A. xanthophloea. The two species are therefore recommended to be used in the rehabilitation of limestone quarries in similar semi-arid conditions.