Frost Upheaval of Overwintering Plants: A Quantitative Field Study of the Displacement Process^*

* Cornell University Department of Agronomy paper number 1583.

Abstract

Soil displacements caused by frost heave and thaw consolidation are an important deterrent to plant growth in northern temperate regions subject to seasonal freezing. They are a major cause of mortality among overwintering forage crops and influence vegetation succession in natural communities. Lack of quantitative data has limited our understanding of the upheaval process. Plant uplift is commonly ascribed to “jacking” by minor freeze-thaw cycles in the fall and spring, with no consideration of the major winter-long heave cycle. This scenario appears to be untenable because the forces involved are insufficient to uproot mature tap-rooted species. We monitored soil and plant displacements in established Medicago sativa (L.) stands throughout two winters at Ithaca, New York. Uplift of 2- and 3-yr-old plants occurred in conjunction with the major heave cycle, not during alternate freeze-thaw episodes. Consequently, we suggest the process of plant upheaval be divided into two modes corresponding to the type of frost action. While seedlings and transplants may be uprooted by surficial soil freezing in the fall and/or spring, well-anchored plants are displaced by deep frost penetration during midwinter.