Estimating Forage Production Following Pinyon-Juniper Control: A Probabilistic Approach
An important management practice within the 60-80 million acres of Pinyon-Juniper woodlands is to convert these woodlands to open rangelands. The success or failure of seedling adapted grasses in place of trees is contingent upon the revegetation techniques employed and upon fortuitous weather patte...
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| Format: | Others |
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DigitalCommons@USU
1966
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| Online Access: | https://digitalcommons.usu.edu/etd/4292 https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=5346&context=etd |
| Summary: | An important management practice within the 60-80 million acres of Pinyon-Juniper woodlands is to convert these woodlands to open rangelands. The success or failure of seedling adapted grasses in place of trees is contingent upon the revegetation techniques employed and upon fortuitous weather patterns. In order to formulate policy for Pinyon-Juniper control decisions, persons responsible for such policies need to know the risks of introducing range grasses into given areas. This thesis is essentially a hypothesis concerning the magnitude of such risks.
Pinyon-Juniper control has been practiced widely in the five state areas of Arizona, Colorado, Nevada, New Mexico, and Utah. Justification for control and conversion of the woodlands to open grazing areas rests on the assumption that the trees have little apparent utility and, therefore they should be replaced by a grass resource which has relatively greater value. In its extreme form the assumption involves the notion that the trees are actually detrimental to the productivity of the land. they become a hindrance to the growth of various forms of plant life considered desirable.
Considerable investment, primarily at the expense of society, has been incurred in the transformation process. Until recent years control projects have been limited to the most accessible sites and areas "invaded" by Pinyon-Juniper trees. At present the conversion place has slackened due to the limited number of remaining accessible sites in some areas, but more importantly to the fact that the projects have had a history of mixed success. While certain rules of thumb have been put forth to explain the nature of the factors influencing seedling emergence and increased forage production, these are so volatile that an apprehension of failure exists among land managers.
The intensity of investment can only be balanced against risk levels if there is basic understanding of the roles played by the variables influencing seedling establishment and forage increase. Both policy and nonpolicy (not subject to human manipulation) variables must be identified and their influences upon success measured.
The analysis that follows begins by setting forth the objectives to be achieved in evaluating the tree conversion process and its associated risk. Next a theory of range grass seedling establishment is presented. The appropriate variables are identified and an "establishment" model is applied to the empirical data. A third section specifically treats weather as a major influence upon seedling emergence and forage production. A model expressed in probabilistic terms, employing the Markov property is applied to available data to evaluate weather index movements. Finally having dealt with emergence, a theory is developed to explain expected forage production in the period following emergence. The parameters of the associated model are obtained from empirical data. |
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