PARENT SESSION
Poster Session 37: Forest Ecology.
Thursday, August 5 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.
Soil moisture affects conifer shade tolerance.
Bigelow, Seth*,1, North, Malcolm1, 2, Horwath, William3, 1 Sierra Nevada Research Center, Davis, CA, USA2 Department of Environmental Horticulture, Davis, CA, USA3 Department of Land, Air and Water Resources, Davis, CA, USA
ABSTRACT- Availability of soil-based resources can affect performance of juvenile trees and hence have long-term effects on patterns of species composition in forests. We examined stem diameter growth with respect to light and soil resource availability for six conifer species (40 saplings each) in northern California. Saplings were located along an east-west transect that straddled the crest of the Sierra Nevada mountain range providing a gradient in precipitation and a variety of soil conditions. Soil factors measured were mass wetness at the beginning and end of the growing season, depth to impermeable layer, pH, mineralizable nitrogen, and exchangeable base cations (Ca, Mg, and K). Plant moisture stress was assayed from carbon isotopic composition and light availability was estimated from canopy hemispherical photographs. The growth-light relationship was modeled with the Michaelis-Menten equation and the capacity of soil variables to influence this relationship was evaluated with the Akaike information criterion. Early-season soil mass wetness influenced the growth-light relationship of several species. Shade-tolerance (i.e., rate of growth at low light) of Pinus ponderosa was increased on wetter soils, and maximum growth rate of Pseudotsuga menziesii was positively correlated with soil wetness. Surprisingly, shade-tolerance of Calocedrus decurrens decreased on wetter soils. Our findings support the concept of shade-tolerance as a malleable attribute that responds to soil-resource availability and the results suggest that regeneration patterns of Pinus ponderosa, an important commercial species, will be affected by changes in soil moisture that are likely to accompany predicted global changes.
Key words: soil moisture, relative growth rate, shade tolerance, Pinus ponderosa