The effect of loggingand invasion of Acacia Mearnsii on regeneration of Ocotea Usambarensis in Chome Nature Reserve, Tanzania

Abstract

The East African Camphor (Ocotea), a canopy tree species and an important component of Chome Nature Reserve (CNR)which used to occupy more than 50% of the forest canopy is seriously declining in density. Although the species is illegally logged for timber, the main concern of ecologists is the declining regeneration and death of individuals in all age classes. Increasing selective logging and tree cutting for fuel wood are implicated to impair recovery of Camphor forests by changing suitable habitats for its growth and initiating severe heart wood decay through broken branches and injuries, thus creating entry points for the decay fungi. In addition, establishmentof Acacia mearnsii,an invasive tree in forest edges and its subsequent expansion in disturbed areas pose additional threats to the recovery and restoration of the Ocotea forests. Paucity of quantitative evidence of the influence of selective logging on regeneration and advance growth of Ocoteaand the spread of decay fungi from mature to young Ocotea individuals, poses significant gap in our understanding of the ecology of Ocotea and management of the problem. Similarly, lack of estimates of coverage and costs to control the invasive tree A. mearnsii retards conservation efforts that would have been taken to maintain and restore the forest with native tree species. Therefore, this study was carried out with the overall objective of assessing the effect of logging and invasion of A. mearnsii on regeneration of Ocotea usambarensis so as to generate knowledge that is needed for restoration and conservation of CNR. In this study, the influence of logging on regeneration and population structure of Ocotea was examined in 62 plots of 10 m wide by 100 m long. The spread of heart wood decay from mature individuals to root suckers were assessed from 31 pairs of parent - suckers of Ocotea. Also, the areainvaded byA. mearnsii in CNR wasmarked and tracked using the Global Positioning System device and estimated using the Quantum Global Information System. Control costs were estimated using established figures and rates from similar studies on management of A. mearnsiifromSouth Africa.Results indicated that the effect of selective logging was crucial in determining the regeneration and population structure of Ocotea. It is also noteworthy that Ocoteais rarely regenerating in disturbed areas below 1500m above sea level due to changes in their suitable habitat after severe logging. The study also indicated that, heart wood decay does not spread from parent individuals to suckers through the adjoining roots. With regard to coverage and cost to control A. mearnsii invasion which threatens restoration of Ocotea forest, it was found that the equivalent condensed area occupied by A. mearnsii is about 210 ha (i.e. 1.5% of the reserve area) and the total costs for mechanical clearing of the invaded area was estimated at TZS 164.64 million. It is recommended that, before embarking into mechanical control operations, experimental plots on clearing should be set to assess other externalities that may need management consideration during scaling up. To promoteregeneration, advance growth and hence recovery of Ocotea forest, ongoing conservation activities in CNR need to be supplemented with enrichment planting and slashing of brambles to free few regenerating sapling of Ocotea.