ASSESSING EQUALITY OF PRODUCTION AND INTERNAL STRUCTURE OF TWIN PLOTS IN CLONAL EUCALYPT PLANTATIONS: ANALYZING EARLY MEASUREMENTS

Abstract

Background: Extensive research seeks to improve forest management by understanding the effects of silvicultural treatments on productivity. Continuous forest inventory (CFI) plots offer valuable data for such studies. However, accuracy relies heavily on the twin plot concept, where two adjacent plots (twins) are established to isolate treatment effects from natural variation. This study explored the validity of the twin plot concept by analyzing data from 191 plot pairs in clonal eucalypt plantations. Specifically, it aimed to assess the equality of production volume and the internal structure between CFI plots and their twin plots.

Results: Normality assumptions for plot volume differences were not met, even after applying a transformation procedure. Paired t-tests couldn’t be performed, but the non-parametric Wilcoxon test indicated no statistical difference in plot volumes. However, a different procedure called the L&O test revealed significant statistical differences. Gini coefficients demonstrated variations in tree volume distribution between plot pairs. Limited tree numbers and varying diameter classes prevented the use of Chi-square tests for diameter distribution equality. The Kolmogorov-Smirnov test showed non adherence to estimated distributions using the Weibull distribution function. The L&O test identified significant differences in diameter distributions in 55 of the 191 plot pairs.

Conclusions: We have concluded that it is critical to determine the twin nature of plots during first tree measurement to properly analyze the effects of silvicultural treatments on forest productivity. This requires robust statistical tests, adherence to assumptions, examination of internal plot structures, and adequate plot sizes for modeling diameter distribution.