Probabilities of small-gap capture by sugar maple saplings based on height and crown growth data from felled trees

We simulated the probability that Acer saccharum Marsh. saplings in single-tree gaps would reach the overstory before lateral gap closure. The model was calibrated with height and crown growth data from destructively sampled trees that ranged from 1 to 27 m tall. Each of the major initial conditions and growth processes was evaluated separately to determine its effect on gap-capture probabilities. Factors such as sapling height at the time of gap formation, continued height growth of border trees, and stochastic growth variation had pronounced effects on the outcome. Stochastic variation generally increased chances of sapling success by delaying closure times in some of the gaps and allowing some saplings to grow at above-average rates. In stochastic simulations with continued (asymptotic) border-tree height growth, probabilities of successful gap capture ranged from <20% of saplings 1-2 m tall to 35%-86% for saplings 7-8 m tall. The results suggest that some saplings may be able to capture gaps after one gap event, but probabilities are low for small saplings and for all saplings in small and medium gaps. Based on the mechanisms simulated here, most of the larger single-tree gaps (78 m^2) are captured by advance regeneration more than 4 m tall.