These include climate, soil depth,
droughtiness, rock outcrops, wind exposure and top soil stone.
Matthews, "Long-term
droughtiness and drought tolerance of eastern US forests over five decades," Forest Ecology and Management, vol.
Ruling out a topsoil thickness effect on vegetation degradation, isolates soil by way of its influence on
droughtiness, leaching potential, organic matter accumulation, nutrient retention and natural plant-species distribution (Schmidt et al.
For example, between 6,000 and 3,000 ybp, northern Minnesota underwent a reversal of the prairie period
droughtiness, while the area south of the Great Lakes underwent a slight increase in
droughtiness.