Vegetation and soils are compared on two forested, lower north-facing slopes over marble and schist parent materials in northern Georgia. Moisture and parent material are probably the most important factors determining differences in soils and vegetation. Soils over marble have a mean pH of 6.1, ranging from 5.3 to 6.6. These soils.have a relatively high moisture, particle density, pore space, clay, stones and litter, total N and extractable, K, Ca, Mn, B, Cu and Zn; in contrast, soils over schist have a lower mean pH of 5.3, ranging from 4.6 to 6.0, relatively less of the above factors and higher sand, silt and extractable P, Fe, Na, Al, Si and Mo.
The number of species per 100 m2 is greater over marble (36 vs 20). Herb species (31 vs 15) make up the largest part of the difference. Herbs crowd the forest floor over marble (111% cover) while a sclerophyllous shrub (<em>Rhododendron maximum</em>) dominates most positions over schist (14% herb cover). Ground basal area of shrubs is much larger over schist due to <em>Rhododendron</em> (1.1 vs. 2.9 m2ha-1). Tree basal areas are not significantly different.
Samples are also treated as points on a continuum of soil variability. Trends in vegetation and species distributions are correlated with soil variability. Whereas herb cover increases with greater soil pH (range up 6.6), the number of herb species increases with pH up to a peak near pH 6 above which numbers drop. This may be due to micronutrient deficiencies and/or intense competition from dominant herbs. Groups of species are distributed in similar ways with respect to soil variability, but groups are somewhat artificial and evidence for niche separation and habitat heterogeneity indicate that each species is unique.
The trend from an herbaceous to woody and sclerophyllous understory with lower pH is discussed. In this study apparency (sensu Feeny 1976) in forest understory plants responds to soil nutrient status. Herbs succeed on less acid macronutrient-rich soils with fewer large or permanent C-based structures and so have a less apparent life form. Sclerophyllous shrubs such as <em>Rhododendron maximum</em> succeed on most acid soils by efficient nutrient uptake and conservation. They use C-based adaptations that are larger and more permanent, and therefore more apparent.