Seed Production Across a Soil Nitrogen Availability Gradient as a Model of N-Deposition

EPA Grant Number: FP917142
Title: Seed Production Across a Soil Nitrogen Availability Gradient as a Model of N-Deposition
Investigators: Minor, David Michael
Institution: Michigan State University
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: September 1, 2010 through August 31, 2012
Project Amount: $74,000
RFA: STAR Graduate Fellowships (2010) RFA Text |  Recipients Lists
Research Category: Fellowship - Ecosystem Services: Terrestrial Systems Soil and Plant Ecology , Academic Fellowships


Many factors may affect seed production in trees, including the size of an individual, interactions with neighboring trees, and the soil resources available. Because nitrogen deposition can alter the availability of this and other nutrients in the soil, it is important to understand how this changing chemical environment may alter fecundity of species differently, and subsequently alter the species composition of forest communities. This research will investigate the influence of tree size, local crowding, and nutrient availability on seed production in northern hardwood tree species.


Seed production is the fundamental process that determines the tree species present in a forest. Factors that may affect the chance of an individual producing seed include the size of the individual, crowding from neighboring trees, and the soil resources available, which are altered through nitrogen deposition. By measuring seed production in individual trees, this project will investigate the influence each of these factors has on seed production, and how nitrogen deposition may affect future production.


Seed production will be visually estimated in 11 northern hardwood species across a natural fertility gradient in northwest lower Michigan over the course of 3 years. Individual-based models will then be calibrated to test the influences of tree size, neighborhood crowding, and soil resource availability on seed production. In addition, the effect of specific nutrients, including nitrogen, will be assessed through measuring seed production in fertilized trees of four species.

Expected Results:

I expect that tree size will be the best predictor of seed production, but that additional variability will be explained by soil nutrient availability and neighborhood crowding. Because nitrogen is typically a limiting nutrient in temperate forests, I expect that it will have a greater positive effect on seed production than other nutrients, both along the natural gradient and in the fertilization experiment. Other nutrients, such as calcium, phosphorus, and potassium, may also affect seed production, and their effect may vary by species. Finally, I expect that size and proximity of neighbors will have a negative relationship with seed production.

Potential to Further Environmental/Human Health Protection:

Anthropogenic additions of nutrients, such as nitrogen deposition, may cause species-specific seed production responses. Because species differences in reproductive response may result in a change in the species composition of a community, understanding the response to changing soil nutrients is the first step to safeguarding future forests against diversity loss for the wide range of ecosystem services that they provide.

Supplemental Keywords:

seed production, soil nutrients, neighborhood crowding, nitrogen deposition,