A Cost-Benefit Analysis of Leaf Habit and Leaf Longevity of Trees and Their Geographical Pattern

TLDR

The study aims to maximize a tree’s net gain by replacing leaves when the leaf’s net gain per unit time over its lifespan is highest. The authors construct a model that maximizes leaf net gain per unit time, linking leaf longevity to leaf habit and simulating how favorable photosynthetic periods shape leaf habit distribution across latitudes. The model predicts that leaf longevity is inversely related to initial photosynthetic rate and rate decline, directly related to construction cost, and that evergreenness percentages decline with shorter favorable periods, dip at intermediate lengths, and rise again, producing a bimodal latitudinal pattern, while deciduousness follows a unimodal distribution peaking at midlatitudes.

Abstract

To maximize net gain of a tree, leaves must be replaced when net gain of a leaf per unit time over the leaf's life span is maximum. A model in which leaf longevity is determined to maximize the net gain of a leaf per unit time is constructed. The model predicts that leaf longevity is short when initial net photosynthetic rate of the leaf is large, long when the construction cost of the leaf is large, and short when the decrease in net photosynthetic rate with time is large. The model describes leaf habit (deciduousness and evergreenness) with the length of the favorable period for photosynthesis within a year and simulates distributional pattern of leaf habit along latitudes. The percentages of evergreenness decrease with decreasing favorable-period length and reach the minimum at an intermediate length of the favorable period but increase again with a decrease in the length of the favorable period. A bimodal distributional pattern with two peaks, one at lower and the other at higher latitudes, is observed for the percentages of evergreenness. Percentages of deciduousness show a unimodal distribution pattern with a peak at midlatitude.