A shade tolerance index for common understory species of northeastern North America

Since Baker’s [Baker, F.S., 1949. A revised tolerance table. J. For. 47, 179–181] classic contribution, shade tolerance indices have not been much modified for North American plant species. While many common tree and shrub species are included in the shade tolerance index, much less is known about this characteristic for the abundant and rich understory vascular and nonvascular plant layers. The classification of the shade tolerance is widely used to compare relative growth and survival among plant species under closed canopies and is also fundamental to an understanding of stand development following small and large scale disturbances. Although qualitative, it is frequently used both in research and management implications. Here we provide a significant revision to Baker’s shade tolerance table to include the most common forest understory plant species found in northeastern North America forests. Our index is based on: (1) the compilation of the opinions of five experts, (2) a comparison with Ellenberg’s index from Europe as well as, (3) information from current literature. For most of the 347 plant species investigated, a consistent and robust shade tolerance index, ranging between 1 (very tolerant) and 9 (very intolerant), was found. Here we present revised shade indices for 71 tree and shrub species, 185 herbaceous species, and 91 bryophyte and lichen species.