Structural analysis of regeneration in tropical dense forest: combined effect of plot and spatial distribution patterns

Abstract This study assessed the combined effect of the size and shape of inventory plots on the analysis of the density and diameter structure of saplings and juvenile trees. Thirty square plots of 400 m² were randomly laid out and each one was divided into 400 quadrats of 1 m². Stem number of recruits was recorded for all tree species and their diameter at breast height was measured in the quadrats. Seven types of subplots with different shapes and sizes were considered by grouping adjacent quadrats of 1 m². The Green index was used to assess the spatial distribution of regeneration and Weibull distribution was applied to model stem diameter distributions. Box–Cox transformations and weighted regression were used to model the relationship between the Green index, the plot patterns and the standard error of the estimation of the regeneration density. The same analyses were applied to model the relationship between the Green index, the plot patterns and the mean absolute error of the shape parameter of the Weibull distribution. The Green index and the plot size had a significant impact on the error of the regeneration density estimation. For clumped distribution of individuals, the plot shape had a significant impact on the error of their density estimation. As for stem diameter distribution, only the plot size had a significant effect on the mean absolute error of the stem diameter structure. The rectangular plots and square plots of 100 m² (14 m × 7 m and 10 m × 10 m) appeared more suitable for an effective structural analysis of woody species regeneration in the tropical dense forest for an aggregated distribution and a random distribution, respectively.