Population Cycles of Poisonous Plants

Authors: Ralphs, Michael; JENSEN, D - USU

Submitted to: Poisonous Plant Global Research and Solutions
Publication Type: Book / Chapter
Publication Acceptance Date: 5/31/2006
Publication Date: 6/20/2007
Citation: Ralphs, M.H., Jensen, D.T. 2007. Population Cycles of Poisonous Plants. Poisonous Plant Global Research and Solutions. Ch 73. pp. 432-437.

Interpretive Summary: The abundance of poisonous plants in natural ecosystems is not constant, particularly in arid and semi-arid rangelands. Plant population cycle and are driven primarily by precipitation patterns and drought. Many species of locoweeds germinate following autumn rains, remain green over winter, flower in spring and may continue to grow for 1 or 2 years until the next drought occurs. White locoweed is more persistent, but many of its populations died out during droughts of the late 1990’s. Broom snakeweed’s populations also follow precipitation patterns. Low larkspur populations fluctuate greatly, but tall larkspur populations do no change because it is a long-lived perennial forb found in high mountain areas.

Technical Abstract: A poisonous plant is harmless until it is consumed. Once eaten the degree of damage depends on the amount of the plant consumed or more specifically the amount of toxin entering and absorbed by the body. Poisoning therefore, depends on two principal variables; the toxin level in the plant and the rate of ingestion by the animal. The rate of ingestion depends upon the availability or abundance of the plant in the ecosystem. Weed scientists have developed the concept of an economic threshold at which a weeds’ population increases to the point that it begins to suppress production of the crop. Poisonous plant populations are analogous, in that they are not a threat until their population reaches a density that an animal can consume enough of the plant, fast enough, that a sufficient amount of toxin is absorbed to cause harm. The presence or abundance of specific poisonous plants in natural ecosystems is not constant, particularly in arid or semi-arid rangelands. Plant population’s cycle and are driven primarily by precipitation patterns and drought. The objective of this paper is to present examples of population cycles of important poisonous plants in the western United States, relate them to precipitation patterns, and present management strategies to deal with fluctuating populations.