Life Cycle Assessment Used to Determine Potential Midpoint Environment Impact Factors and Water Footprint of Field-grown Tree Production Inputs and Processes

Abstract

Previously published life cycle assessment (LCA) studies regarding the global warming potential (GWP) of tree production have shown that the carbon footprint during the cradle-to-grave life cycle of a tree can reduce atmospheric CO2. This study provides another unique contribution to the literature by considering other potential midpoint environmental impacts such as ozone depletion, smog, acidification, eutrophication, carcinogenic or non-carcinogenic human toxicity, respiratory effects, ecotoxicity, and fossil fuel depletion for 5-cm-caliper, field-grown, spade-dug trees. Findings from this study validate using data from various literature sources with a single-impact focus on GWP and compiled and calculated in a spreadsheet or using a LCA software package with embedded databases (SimaPro) to generate comparable GWP estimates. Therefore, it is appropriate to use SimaPro to generate midpoint environmental impact estimates in LCA studies of field-grown trees. The authors also compared the midpoint environmental impacts with other agricultural commodities [corn (Zea mays), soybean (Glycine max), potato (Solanum tuberosum), and wool] and determined that trees compare favorably, with the exception that fossil fuel depletion for the trees was greater than the other products as a result of the high equipment use in harvesting and handling trees. In addition, the water footprint (WF) associated with tree production is also determined through LCA using the Hoekstra water scarcity method in SimaPro. The propagation-to-gate WF for the three tree production systems ranged from 0.09 to 0.64 m3 per tree and was highly influenced by irrigation water, which was the major contributor to WF for each production system. As expected, the propagation stage of each tree represented significantly less WF than the field production phase with larger plants and lower planting densities, even with more frequent irrigation/misting in liner production.