Natvik and Henry_Differential effects of the grasses Festuca rubra, Andropogon gerardii, and Elymus virginicus on the growth of Eurasian versus North American oak seedlings

OVERVIEW OF RESEARCH: Research was conducted to compare how the origin of grass cover effects the growth of oak seedlings. Our hypothesis was that that grass species origin may influence oak recruitment. The experiment included 3 grasses species consisting of 2 species native to North America (Andropogon gerardii and Elymus virginicus) and 1 species native to Eurasia (Festuca rubra var. rubra). Comparisons were made between 6 oak species consisting of 3 species native to North America (Quercus alba, Q. macrocarpa, and Q. rubra) and 3 species native to Eurasia (Quercus acutissima, Q. cerris, and Q. robur). We predicted that oak seedlings would demonstrate greater growth when growing in grasses that they share a co-evolutionary history with.

EXPERIMENTAL DESIGN: The 3 grass species were seeded into single-species plots measuring 6 x 7 metres. There were 8 plots seeded for each of the grass species (for a total of 24 grass plots). All 6 oak species were seeded into the plots as acorns. Each of the 24 plots contained 1 oak seedling of each species, with a total of 144 oak seedlings in the entire experiment (6 seedlings x 24 plots).

DESCRIPTION OF DATA:

1. OAK SEEDLING MEASURMENTS: After 2 growing seasons, all oak seedlings were harvested. Measurements of each oak seedling were taken including stem height, stem diameter, total biomass (separated into stem biomass and root biomass), and root-to-shoot ratios. This data was analysed to compare the growth of all 6 oak species between the 3 species of grasses.

2. LIGHT READINGS: Photosynthetically Active Radiation (PAR) was measured from all of the grass plots at 15 cm above the soil surface during spring summer, and fall. These measurements indicate how much exposure to light the oak seedlings received across the growing season within the 3 different species of grasses.

3. SOIL TESTS: A range of soil parameters were measured from all grass plots at the end of the experiment (3 years after the grass plots were established). The purpose of the soil tests was to see if soil parameters were impacted in any way by the 3 different species of grasses.

SUMMARY OF RESULTS: Our results demonstrate that grass cover has a significant but species-specific impact on the growth of two-year-old native and non-native oak seedlings. The variation in seedling growth in response to variation in grass cover was, in part, consistent with the hypothesis that grass species origin may influence oak recruitment, but there were nevertheless exceptions that could be explained in part by shading effects.