Influence of tree age on reproductive, seed, and seedling traits in three northern red oak stands at Black Rock Forest in Cornwall, NY: A preliminary study

Background/Question/Methods Northern Red Oak, Quercus rubra (Fagaceae), is a common and dominant species in the hardwood forest ecosystems in the Eastern United States. At Black Rock Forest in Cornwall, NY, where this species is currently showing limited recruitment, we have initiated a long-term study of reproductive traits (in parents) and seed and seedling traits (in offspring). Over the past two growing seasons we have quantified multiple reproductive and seed traits and examined their relationship to three age classes of the parent red oak trees: 35-40 years old, 90-95 years old, and 135-140 years old. Reproductive traits include abundance of male flowers produced in spring, abundance of mature acorns in fall, and acorn mass, viability, and germination. Seed and seedling traits include individual acorn mass, rate of germination, seedling growth rate, and a suite of above- and belowground seedling allocation traits. 

Results/Conclusions Flower and fruit production was significantly lower in trees of the young age class, but seed mass in the 35-40 age class was significantly larger than in the 90-95 and 135-140 age classes. When grown in uniform greenhouse conditions, seedlings from acorns produced by trees in the young age class were significantly smaller than seedlings from the 90-95 and 135-140 age class. This negative correlation between seed mass and seedling growth contradicts the accepted idea that larger seed mass leads to better seedling growth and performance. Soil nutrient composition at the three contiguous study site showed that the microsite of the 135-140 age class had twice as much carbon and nitrogen as the microsites of the young and middle age classes. We relate these results to recent studies of oak ecophysiology in these same stands. We anticipate collecting longer-term data to examine how age of the parent tree influences flower and fruit production, seed mass, and seedling quality, and whether factors other than seed mass, such as seed and seedling nitrogen content, also contribute to variation in seed size and seedling quality.