To replant or to irrigate: A silvicultural decision model for afforestation projects

This article develops an economic model that compares the option of replacement planting to maintain target density with the option of enhancing seedling survival from the beginning by applying irrigation. The model we develop uses variables common in forestry practice and yields the threshold value of seedling failure at which both alternatives offer the same economic result based on a comparative analysis of costs and benefits. By comparing this threshold with the level of seedling failure expected for an afforestation in the absence of irrigation, the planner can make an informed decision between both alternatives. The model has been applied to thirteen practical cases covering a wide range of plantations with different density, purpose and average annual net income. Based on the results obtained, a k-means clustering is carried out to identify five groups according to their suitability for irrigation. The sensitivity of the model's input variables in respect to the threshold of seedling failure is also analized. Irrigation is profitable when the expected level of seedling failure is high and/or the value of the threshold decision is low. The latter is usually the case at afforestations that require a low acceptable level of seedling failure and/or in productive plantation forestry.