Seth W. Bigelow, Charles D. Canham
Rhodora 112 (949), 1-21, (1 January 2010) https://doi.org/10.3119/08-32.1
KEYWORDS: northern hardwood forest, calcicole, calcifuge, Seedling survival, canopy tree, exchangeable calcium, exchangeable aluminum, site fidelity, Plant-soil relationship
Tree species composition of hardwood forests of the northeastern United States corresponds with soil chemistry, and differential performance along soil calcium (Ca) gradients has been proposed as a mechanism for enforcing this fidelity of species to site. We conducted studies in a southern New England forest to test if surface-soil Ca is more important than other factors in determining survival of seedlings of six common canopy tree species. Our hypothesis was that the calcicole species Acer saccharum and Fraxinus americana would show elevated survival rates at higher Ca levels, and that the calcifuge species A. rubrum, Fagus grandifolia, Quercus rubra, and Tsuga canadensis would show lower survival at high Ca. Other factors examined were 1) exchangeable magnesium (Mg), potassium (K), and aluminum (Al); 2) understory light availability; and 3) identity of overstory tree species. In one study, seedlings were transplanted into plots fertilized with Ca or Mg sulfate and survival was measured over 2 years. In the other study, 1-year or 2-year survival of naturally established seedlings in stands dominated by mature trees of one of the six study species was followed. Fertilization with Ca or Mg did not affect survival of planted seedlings, but ambient exchangeable Al was strongly negatively correlated with survival of F. americana. Of the three species with sufficient naturally established seedlings, exchangeable Al plus a proxy for light (overstory tree identity) were the most important determinants of survival. Survival of A. saccharum declined and A. rubrum and F. grandifolia increased at higher levels of exchangeable Al. This pattern is consistent with the positions of these species along the soil gradient. We conclude that soil chemistry effects on seedling survival play a role in establishing the soil relationships characteristic of these species as adults, but that Al is more important than Ca in establishing these effects during the seedling stage.