Seedling abundance, composition and growth forecast under two logging intensities in a moist tropical forest in Ghana

2015

English

Timber species differ in their response to logging disturbance. Knowledge about the impacts of different logging intensities is necessary to determine levels of timber extraction compatible with species responses in order to refine management interventions. We examined the effects of two logging intensities on the abundance and composition of tree seedlings in gaps in Pra Anum Forest Reserve within a Moist Semi-deciduous forest in Ghana. In addition, we assessed seedling growth by forecasting the probability of locating a seedling (≥ 55 cm) in the two logging intensities compared to controls. Logging was carried out experimentally at two intensities, 26 m3/ha (1 AAC) and 52 m3/ha (2 AAC) of extracted timber, in a 128 ha compartment. Twenty plots each of 60 m2 were randomly established in gaps in each of the logging treatments and in the unlogged forest. These plots were monitored for number of seedlings and height growth of timber tree species for 33 months in four different enumerations. We used mixed effect models to assess the abundance of seedlings over time. A non-metric multidimensional scaling (NMDS) was used to determine the shifts in species composition. Seedling abundance was significantly different in gaps for both high and low logging intensities, however, a significant interaction effect between abundance and time was found only in the low intensity treatment. There was a significant difference in the rate of change in species composition between the high intensity and unlogged forest (P = 0.03) but the rate of change between the low intensity and unlogged forest was not significant (P = 0.27). After 3 years, we predicted that it was approximately three and two times more likely to locate a seedling (≥ 55 cm) in the low and high intensity treatments, respectively compared to controls. This could be attributable to enhanced competition from herbaceous weeds in the high intensity treatment, which affected the survival and growth of tree seedlings. Based on this result, we recommend enforcement of silvicultural prescriptions to the management of logged forests in order to achieve the level of forest manipulation needed to ensure productivity.

Duah-Gyamfi, A.; Kyereh, B.; Agyeman, V. K.; Adam, K. A.; Swaine, K. A. M.