Resource limitation in canopy versus understory trees.

Abstract

Because light intensity and need for water is likely to be greater in canopy trees than understory trees, we expect that the relative importance of light and water in limiting growth will differ between these two sizes of trees. We therefore hypothesize that understory tree growth should correlate more strongly with light intensity than canopy tree growth does, and canopy tree growth should correlate more strongly with water availability than understory trees. We predict the availability of the more limiting resource will correlate more strongly with growth than the availability of the less limiting resource. Similarly, in areas with less dense canopy where light is less limiting for understory trees, we would expect a weaker relationship between understory growth and light availability. We used white pine, Pinus strobus, a tall-growing tree found in the eastern temperature regions of North America, to test these predictions about differences between understory and canopy growth.