Assistant Professor Ohio University, Ohio, United States
Abstract: Masting is a plant reproductive strategy defined by large variation in seed production between years and high levels of reproductive synchrony within a population. Annual variation in seed production and the occurrence of years with high seed production are thought to be influenced by factors such as weather and resource availability. In oaks, significant variation in seed production has also been observed within populations as certain individuals will consistently have larger seed crops or reproduce more frequently than others. The goal of this study is to examine possible explanations for individual level variation by (1) quantifying differences in topography and their influence on microclimate between individuals of the same population, (2) identifying if differences in microclimate affect phenological synchrony and conspecific density, and (3) examining the relationship between these factors and seed production. Microclimate was quantified by collecting data on spring temperature, humidity, slope, elevation and aspect of 36 chestnut oak (Quercus montana) individuals from populations found in two forest stands in southeast Ohio. For each individual, observations on flower development were made from March through May of 2022 and 2023. The number of nearby conspecifics was recorded using eight 50 meter transects radiating outward from each individual in the cardinal and ordinal directions. Data on seed production was from acorns collected in seed traps from August to December of 2022, in addition to data collected from a long-term seed study started in 2001 that used the same trees.
Our results show that elevation and north/south aspect significantly affected mean microclimate temperature during spring flowering, which ranged from 13.86°C to 19.87°C, with individuals at higher elevation and on south facing slopes experiencing warmer temperatures. There was a significant positive relationship between mean microclimate temperature and the mean number of days flowering shared with other individuals (synchrony) in the Vinton Furnace population (t = 2.375, df = 16, P = 0.03). There was also a significant positive relationship between the number of flowers produced (based on the weight of spent catkins collected under each tree), and elevation and diameter at breast height. Preliminary analysis showed that there was no significant correlation between synchrony in flowering and seed production, however individuals that had higher seed production tended to be located on ridge tops at higher elevations between 267 and 286 m, also with a higher conspecific density. Taken together, the results suggest that pollen availability can influence individual variation in reproduction.