PARENT SESSION
Oral Session #57: Plant Competition I.
Presiding: T. Seastedt
Wednesday, August 7. 8:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.

Sapling growth in relation to light, foliar nitrogen, and soil moisture across landscape variation in forest communities.

Kobe, Richard^*,1, ¹ Michigan State University, East Lansing

ABSTRACT- Variation in species-specific sapling radial growth was examined in relation to light availability and landscape-level variation in foliar nitrogen and soil moisture availability. Saplings of sugar maple (Acer saccharum), red maple (A. rubrum), American beech (Fagus grandifolia), and red oak (Quercus rubra) were located across a wide range of soil resource x light conditions in the glaciated landscape of Manistee National Forest in northwest lower Michigan. For each sapling, I measured light availability with hemispherical canopy photos (range: 1-88% full sun), foliar nitrogen concentrations averaged over two growing seasons (range: 1.03-3.3%), and soil moisture with time domain reflectometry averaged over repeated point samplings (range: 1 -15% volumetric water). Relative radial growth was regressed against light, soil moisture, and foliar nitrogen, which varied independently. Radial growth of all species was significantly related to light availability (p< 0.05). Red maple, sugar maple, and red oak showed significant growth increases with higher foliar nitrogen, with red maple displaying especially strong sensitivity to foliar nitrogen at higher light. Red maple and beech radial growth also increased significantly with soil moisture availability. Sugar maple's range of soil moistures was narrower and more mesic than other species and likely explains why soil moisture was not a significant predictor of its growth. In contrast, red oak was sampled from the full range of soil moistures and its insensitivity to soil moisture likely reflects morphological / physiological adaptations.

KEY WORDS: forest, landscape, nutrients, resources