Comparison of different competition indices in evaluating individual tree competition in farmer-managed plantations: a case study

The present research demonstrates the significance of competition indices (CIs) selection on evaluating individual tree competition in farmer-managed plantations, a widely established plantation type around the world. However, there is still a lack of understanding of the specific advantages of CIs in artificial forest management. The study utilised data from historical inventory records with detailed spatial information from farmer-managed plantations in China. The inter-tree competition was assessed by three CIs, including CI_Hegyi, CI_RK1 and CI_RK2. The primary objectives of this study were to analyse the performance of three CIs in detecting species-specific competition intensity and measure the contributions of microsite versus competition influence on tree growth. To achieve these objectives, the study carried out comparison of performance of three CIs and spatial dependence analysis. The study indicated that CI_Hegyi and CI_RK2 were likely to have similar patterns in evaluating individual tree competition of eight tree species, whereas CI_RK1 tended to show a different pattern. Tree species Camellia sp. (Cs), Ilex chinensis Sims (Ic) and Prunus subg. Cerasus sp. (PsC) exhibited consistent classifications based on the coefficient of variation (CV) of CI values across the three CI types, demonstrating their insensitivity to CI selection. Results also demonstrated microsite as the primary driver on tree growth, superseding competition effects in investigated plantations. These findings provide useful information on forest management practices. The conclusion emphasises the importance of CI selection and species' dependence on CIs in competitive interaction evaluation, as well as the importance of microsite effects on tree growth. This work delivers a framework for future research on competition evaluation in farmer-managed plantations.