PS 51-47 - A point pattern analysis of trees by age class, mycorrhizal type, and phylogeny in a temperate hardwood forest

Thursday, August 10, 2017
Exhibit Hall, Oregon Convention Center
Andrew C. Eagar, Colleen Cosgrove, Mark W. Kershner and Christopher B. Blackwood, Department of Biological Sciences, Kent State University, Kent, OH

Examining spatial distributions of individual trees can provide important information regarding ecosystem processes and future changes to community composition in temperate hardwood forests. However, the longevity of adult trees and the amount of attrition that occurs between each life stage can make long-term studies challenging. Frameworks of plant-soil feedback and nutrient cycling are beginning to consider mycorrhizal associations as useful predictors of community dynamics, with arbuscular mycorrhizal (AM)-associated trees exhibiting greater negative plant-soil feedback effects and ectomycorrhizal (ECM)-associated tree communities having decreased or patchy nutrient availabilities. Additionally, the phylogenetic relatedness of tree community members may exacerbate these effects, with closely related species utilizing similar resources or being susceptible to similar enemies. To better understand these mycorrhizal and phylogenetic effects on tree recruitment and community assembly, we performed point pattern analyses on trees in three distinct age classes along a mycorrhizal gradient in a diverse hardwood forest located in northeastern Ohio. Working within this framework, AM-associated tree communities should have lower seedling and juvenile recruitment, with seedling and juvenile trees aggregating away from adults. Conversely, ECM-associated seedlings and juveniles should cluster around nutrient patches regardless of the relative position of adult trees, with individuals being over dispersed because of competition.


Our results indicate no changes in total seedling or juvenile densities across the mycorrhizal gradient. Quadrat tests suggest that adult tree distributions are random whereas juvenile and seedling trees are non-random, regardless of the dominant mycorrhizal association of the tree stand. Preliminary results from the point pattern analyses indicate that juvenile trees appear to cluster within 2m of each other in ECM-dominated stands and within 1m of each other in AM-dominated stands, with a secondary level of clustering occurring at 4m in AM-dominated stands. Additionally, juvenile trees appear more likely to aggregate with other juveniles rather than adult trees, regardless of the dominant mycorrhizal association of the stand. This suggests that juvenile trees of both mycorrhizal associations are negatively affected by the presence of adult trees. Seedlings in plots dominated by both mycorrhizal types appear to cluster within 1m of other seedlings, with no pattern in relation to juvenile or adult trees. These patterns suggest that seedling communities are structured primarily by dispersal mechanisms. Future point pattern analyses will be performed to see if the phylogenetic relationship between an individual and its neighbors influences patterns of assembly, and if the phylogenetic interactions are dependent on mycorrhizal association.