Do shade tolerant species out-grow intolerant trees in low light? Dr. MB Walters Michigan State University

Do shade tolerant species out-grow intolerant trees in low light? n Assume to be to true... –but is it? n Published studies show mixed results... – but compared few species.

Numbers of species with growth data Temperate Tropical Intolerant Tolerant Temperate Tropical Intolerant Tolerant 80130

Growth rates for shade tolerance groups by forest type Shade tolerance group Growth rate (mg/g -1 day -1 ) Error bars are  one SE.

Something to take home….. n Growth did not differ significantly. n Other factors?

Abstract: Foresters have long assumed that, compared to shade intolerant tree species, shade tolerant species grow faster in shade. Several studies have tested this question, but results have been mixed, perhaps because most have included only small numbers of species, thus preventing general conclusions. In this study, I analyze data from 104 published studies to seek a general answer to the question: do shade tolerant species outgrow intolerant trees in low light environments? The data I used were restricted to seedlings grown in <4% light (forest understory conditions) and were divided into tropical evergreen broad-leaved species and temperate broad-leaved species. The final data set included 372 species. For both temperate and tropical species groups we found no significant difference in growth between tolerant and intolerant species. My results suggest that other characteristics, such as low-light survival are more important than low light growth rates in determining shade tolerance.