Do species have the same regeneration niche? Assessing the role of the regeneration niche in differentiating high elevation deciduous and coniferous trees
Bond’s slow seedling hypothesis states that angiosperms should out-compete gymnosperms in the regeneration niche, which is the suite of site characteristics necessary for establishment and growth. For this question, species occurrence and environmental conditions (litter depth, canopy cover, and substrate) where seedlings grow will be used as measures of the regeneration niche. Species differences will be identified using niche overlap analysis. Parameterization of the regeneration niche for each species will be determined by identifying niche overlap. Niche overlap (NO) analysis provides a measure of species and species differences in niche space, as well as which environmental conditions (e.g. litter depth, canopy cover, and substrate) are primarily responsible in partitioning niche space. This study examines seedling establishment along five transects in the Northern Japanese Alps from the subalpine forest, through the birch treeline and into a pine mat above.
Preliminary results show that, overall, seedlings occupy similar niches. The lowest niche overplay occurs between Abies veitchii and Picea jezoensis, however both of these species have a low sample size (n=22, n=33, respectively). The highest niche overlap (0.87) occurs between Abies mariesii and Null sites, similarly, Betula ermanii has a niche overlap >0.8 with both A. mariensis and Null sites. Environmental conditions had a varying influence on overall niche overlap. For instance, there was no statistical difference in niche overlap based on the substrate for which seedlings established; however, if they were elevated on the surface B. ermanii, P. jezoensis and Pinus pumila all had NO <0.5. These three species are all shade intolerant species, which would have greater access to light being raised off the forest floor. These preliminary results imply that while there is clear division of forest types, the regeneration niche of seedlings throughout the subalpine forests of the Northern Japanese Alps do not significantly differ.