Reconstructing sapling diameter and height growth history for four tree species in the northeastern United States

In mesic forests, light availability is usually the most important factor limiting understory sapling growth. Growth of individual trees includes both radial and length (height) increments. While a lot of wisdom has been invested on radial increment, height growth receives little attention. Temporal variation in light regimes is often seen during the course of canopy recruitment, which shapes historical growth patterns of individual saplings. In this study, we reconstruct complete diameter and height growth histories for saplings of four temperate tree species (white pine (Pinus strobus), eastern hemlock (Tsuga canadensis), white ash (Fraxinus americana), and sugar maple (Acer saccharum)) in a New Jersey state forest with stem cookies taken from different tree heights. And recent light availability for each sapling is measured with a fisheye camera. Our goals include: 1. developing a three dimensional sapling growth model; 2. detecting the effect of light availability on both radial and length growth for saplings of different life history strategies; 3. testing the hypothesis that the diameter – height allometric relationship is invariable under different light regimes. Our preliminary analysis shows that shade intolerant species are usually more sensitive to the variation of light availability than shade tolerant species. While the diameter growth – height growth allometric relationship does not vary much with different growth rates, shade intolerant species tend to invest more in height growth than shade tolerant species under growth suppression.