Neighborhood models were adapted to examine the influence of plant community assemblage and spatial distribution on soil mycorrhizal inoculum potential and eastern hemlock seedling success. The objective of the study was to quantify the role of mycorrhizal plant communities on emergence, survival, growth and the ectomycorrhizal (EM) colonization of establishing hemlock seedlings. Contrasting EM hemlock and arbuscular mycorrhizal (AM) sugar maple dominated communities were used as an in situ setting for developing and testing the model. Hemlock seeds were sown into three treatments at 120 plots in order to alter mycorrhizal inoculum potential: (i) an undisturbed control with limited soil mixing, (ii) a disturbed soil treatment with extraction, homogenization and replacement, and (iii) a swapped soil treatment from the alternate community type. 

Results/Conclusions

The mycorrhizal model performed the best in explaining seedling biomass in control treatments. The null model based on edaphic factors performed the best for all other response variables in all treatments with the disturbed and swapped soil treatments effectively removing belowground interactions between surrounding neighbors and establishing seedlings. EM Pinaceae had an approximately neutral effect, AM species had a positive effect up to 10 m, and EM hardwoods had a strongly negative effect up to 12 m. Belowground interactions negatively affect hemlock seedling growth in sugar maple dominated communities while EM confamilial communities have a neutral or facilitative belowground affect on hemlock seedlings. This research provides quantification of the relative effect of mycorrhizal plant distribution on seedling establishment in mature mixed-species forests.