Mast reproduction is a population-level phenomenon, characterized by highly variable seed production between years. However, there is also a considerable degree of variation between individuals within a population. The goal of this study was to identify what causes this individual variation in reproductive effort, by examining microclimate and individual tree characteristics of black oak (Quercus velutina) and chestnut oak (Q. montana) in southeast Ohio. Annual acorn production data came from 144 seed fall traps from 2000 – 2018, located in Vinton Furnace Experimental State Forest and Zaleski State Forest. For each tree, we measured tree height, canopy height, crown size, DBH, distance and DBH of neighborhood species. We also took tree cores to estimate age, basal area increment, and determine if there is a trade-off between annual reproduction and growth for these two species. Microclimate measurements included elevation, slope, aspect, and soil cores. Soil was analyzed to determine pH, texture, phosphorous content, and carbon to nitrogen (C:N) ratio. Generalized linear models were then used to predict individual reproductive effort from microclimate and tree characteristics.
Results/Conclusions
Access to resources at the individual level (e.g. light and essential nutrients) was critical for increasing reproductive effort in both black oak and chestnut oak. For black oak, basal area increment and soil phosphorous content had significant negative relationships with increased acorn production, while slope and soil pH had significant positive relationships. Black oak also showed a slight positive relationship between seed production and basal area increment from 2000-2017, indicating the trade-off between growth and reproduction for these individuals was minor over time. For chestnut oak, slope and average DBH of neighboring trees had a significant negative relationship with acorn production, while DBH, soil clay content, and average distance of neighboring trees had a significant positive relationship. Chestnut oak showed a slight positive relationship between seed production and basal area increment over the 17 years analyzed. Reproduction dynamics of individuals determines the overall fitness of a population. Identifying characteristics that increase reproductive effort for individuals can allow us to make predictions for how population-level phenomena (e.g., relationship between masting events and wildlife food resources) may be altered.