Crown architecture of Larix laricina saplings: production and disposition of foliage and their simulation

Abstract

In saplings of Larix laricina (Du Roi) K. Koch (tamarack), correlations between projected leaf area (PLA) and architectural variables such as shoot length and shoot age were incorporated into existing simulation models to estimate the distribution of PLA in the crown according to several spatial, temporal, and morphological parameters. After five generations of simulated shoot growth, PLA values ranged from 8.2 m2 for trees with short height growth increments (HGIs) and no syllepsis to 25.5 m2 for those with long HGIs and heavy syllepsis. Although PLA increased, the rate of increase declined over time. In early simulated generations, long-shoot PLA predominated. In the fifth simulated generation, short shoots bore about 75% of the PLA. There was a basipetal increase in PLA by HGI, but the relationship was nonlinear. In trees with syllepsis, sylleptic origin branches on individual HGIs carried more PLA than concomitant proleptic branches for 1 year but thereafter the proportions were reversed. Over successive generations, the contribution of different branch orders to the total PLA shifted from mostly first-order long shoots (including PLA on daughter short-shoot axes) to second-order shoots carrying more than 50% by year 5. Because of the short-shoot contribution, there was considerable PLA in all regions of the crown, although the greatest concentration was in lower regions of midconic zones. Simulated PLA index increased substantially with crown development. Trees with short HGIs had the greatest PLA index and those with long HGIs had the least.