A recent paper in this journal has criticized our previous study, in which we identified an adaptive significance of trunk inclination on slopes. Our main argument was that a tree on a slope may gain some benefit by leaning, which provides the tree with shorter access to the canopy light, and thus a better chance for survival, and that if this benefit outweighs the cost involved in leaning, trunk inclination will be favoured by selection. Although the criticisms are based on some misunderstandings, the situations considered in the critique, which are different from ours, have inspired us into an extension of our previous study. In the course of a reply to the criticisms, we present a further thought on the adaptive significance of trunk inclination in a broader scope. Specifically, we show that our model, with its modified formulation of the benefit component of tree leaning, may evaluate the fitness of a tree with its trunk inclined. It can also be used to examine the conditions for tree leaning, and make predictions on the optimal tree leaning in any situations, including canopy gaps and permanent openings, which the critique is mainly concerned with.