= Solution
Assess the observation-error assumption with standardized residual plots and <quantile-quantile plots>, preferably comparing the same discrepancies with <posterior predictive> replicated data. Inspect tail behavior, asymmetry, variance versus fitted size and serial patterns within a tree; fitted residuals are dependent and do not behave exactly like independent errors.
\b[This does not test normality of the tree random effects.] For that, simulate new tree-specific log asymptotes from the population hierarchy and compare between-tree discrepancies or use leave-one-tree-out predictions. There are only five trees, so distributional checks on their population are intrinsically weak. Conditioning on the five fitted effects can hide misspecification of their normal population law.
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