Growth response of northern red-oak and yellow-poplar seedlings to light, soil moisture and nutrients in relation to ecological strategy

Northern red oak ( Quercus rubra L.) and yellow-poplar ( Liriodendron tulipifera L.) were grown from seed in containers for two seasons in six environments consisting of three levels of edaphic richness (high-moisture/high-fertility, high-moisture/low-fertility, low-moisture/high-fertility) and two light intensities (100%, 20% full sun). Seedling height, dry weights of leaves, stems, and roots, and projected leaf and root surface areas were measured at the end of the second growing season. Low levels of light, moisture, and fertility significantly reduced growth of both species, and effects of low moisture and low fertility were greater in full sun than in shade. Total dry-weight of yellow poplar was 36% greater than that of red oak under combined high levels of light, moisture, and nutrients, while total dry-weight of oak was 38–126% greater than that of poplar where at least one resource was at a suboptimal level. Reductions in growth for yellow-poplar due to low levels of all resources were greater than those for red oak, indicating greater stress tolerance for oak. Yellow-poplar had significantly greater shoot: root ratio and greater partitioning of leaf and root mass to absorbing surfaces compared to red oak. The relative tolerance of red oak to low resource levels and morphology suggests adaption to moderately unproductive environments (stress-tolerant strategy), while the characteristics of yellow-poplar (opportunistic capture of plentiful resources, maintenance of large absorbing surfaces) suggests adaptation to more productive environments (competitive strategy). The growth strategy of red oak is discussed in relation to ecological requirements for regeneration.