Survival and Growth in a Moist-semi Deciduous Forest in Ghana: comparison of monoculture and mixed-species plantations

One major challenge of using indigenous species like Nauclea diderrichii and Pericopsis elata in plantations is the high incidences and damages from pests and pathogens. Nauclea diderrichii (De Wild.) and Pericopsis elata (Harms.) are adversely affected by damages from Orygmophora mediofoveata Hamps (Lepidoptera: Noctuidae) and Lamprosema lateritialis Hampson (Lepidoptera: Pyralidae), respectively when used in plantations. However no information exists in Ghana on alternative pest management options for these insect herbivores. The general recommendation which is gaining much attention is that planting these high-risk species in mixtures with companion species has the potential to reduce pest damages. This study which was part of a large scale restoration program in Ghana was therefore carried out to find out whether tree species diversity can reduce the susceptibility of N. diderrichii and P. elata to their respective primary pests, and also assess the growth performance of these species in monocultures and mixtures. N. diderrichii, P. elata and companion species (Albizia adianthifolia, Terminalia superba, and Tetrapleura tetraptera) were planted in various mixtures (0:100, 50:50, and 25:25:25:25%) in a replacement design in the Bia Tano Forest Reserve, near Goaso, Ghana. Survival rates and growth patterns (height, diameter and relative growth rate) were examined in plots composed of monocultures and mixed stands over 60 months. Overall survival for N. diderrichii and P. elata at stand age 60 months were 35.3% and 59.5% respectively. The overall survival rate, mean height and mean diameter for N. diderrichii in mixtures at stand age 60 months were highest in 50% mixture (50%Nauclea/50%Albizia), followed by 100% mixture (monoculture), and 25% mixture (25%Nauclea/25%Pericopsis/25%Terminalia/25%Tetrapleura). Mean relative growth rates in both diameter and height for N. diderrichii in mixtures were however highest in 100% mixture, followed by 50% mixture and 25% mixture.