The nursery industry is often referred to as part of the green industry. However, research to understand how system components of the production and use of landscape plants contribute to environmental impacts such as global warming potential is lacking and will determine the relative sustainability of nursery crop production (Marble et al., 2011; Prior et al., 2011). Therefore, system-level research is needed to provide reliable, reproducible information for scientists, the industry, and the general public.
Greenhouse gases (GHGs), primarily CO2, N2O, and CH4, are increasing in the atmosphere and human activity is contributing to that, primarily through the use of fossil fuels [BSI British Standards, 2011; International Panel on Climate Change (IPCC), 2007]. The GWP of those gases in a standard 100-year assessment period are expressed in relation to the GWP of CO2, which is set as 1. Although present in the atmosphere at much smaller concentrations, the GWPs of N2O and CH4 are 298 and 23, respectively (BSI British Standards, 2011). The production, distribution, and use of products and services result in emission of GHG and thus a carbon footprint, expressed as the GWP of that product or service in kilograms CO2 equivalent.
Life cycle assessment (LCA) is a tool used to quantify the environmental impact of products or services. LCA is a systematic process accounting for environmental impacts of interrelated input components and processes of a product or practice during its complete life cycle, cradle to grave (Baumann and Tillman, 2004). LCA usually includes information on the three primary life phases of a product or service: production phase, use phase, and post-life phase. However, boundaries for a LCA may be referred to as cradle to grave or even cradle to gate, but defining what is the cradle and what is the grave or gate of a product or practice is an important issue. Cradle to grave refers to the impacts of a product during manufacturing, transport, and use but ends with the impact of that product at the end of its useful life through recycling or disposal. Most published LCAs have focused on carbon footprint, but the tool can be used to assess other environmental impacts such as water footprint, toxicity potential, acidification potential, and resource depletion. International standards govern LCA protocols [BSI British Standards, 2011; International Organization for Standardization (ISO), 2006].
LCA has been used to study agriculture and biofuel production systems and their individual components (Debolt et al., 2009; Hayashi et al., 2006; Liebig et al., 2008; Nemecek et al., 2005, 2006; Williams et al., 2006). Nitrogen fertilizers have been identified as an important component of GHG emissions in agriculture as well as stimulating yield increases (Brentrup and Palliere, 2008; Hillier et al., 2009). Plastic greenhouse covers and containers represented a significant portion of the carbon footprint for floral crops in European LCA studies (Russo et al., 2008; Russo and Mugnozza, 2005; Russo and Zeller, 2008). LCA studies in Europe with forest tree seedling production have shown greenhouse heating and seedling transportation (Aldentun, 2002) and production and disposal of plastics (Cambria and Pierangeli, 2011) to be major GHG emission sources in those systems.
The cutting-to-landscape carbon footprint of a 5-cm-caliper, field-grown, spade-dug Acer rubrum (red maple) was calculated to be 8.2 kg CO2e (Ingram, 2012). Unlike most products, plants take CO2 from the atmosphere and sequester C to varying degrees in wood (U.S. Department of Energy, 1998). Trees sequester more C than shrubs and large trees sequester more C than small trees. Residential trees also provide other environmental services (McPherson and Simpson, 1999). Kendall and McPherson (2012) reported that 4.6 and 15.3 kg CO2e were emitted in the production and distribution of trees grown in #5 and #9 containers, respectively. Their work modeled an intensive container nursery in California and did not include the impact of sequestered C during production.
Individual components of production systems result in GHG emissions to varying degrees. Ingram (2012) reported that a significant contributor to GHG emissions in the field production of red maple was fuel consumption by farm machinery and truck transport of the finished product. That report also estimated the impact of altering certain production system protocols to reduce GHG emissions. GHG emissions have been estimated for various other agricultural production systems (Lal, 2004; West and Marland, 2002a, 2002b).
The purpose of this study was to use LCA to determine the carbon footprint of a 2-m-tall, field-grown, spade-dug Picea pungens (colorado blue spruce) in the lower midwestern and upper midwestern United States (hardiness zones 6a to 7a) and to analyze the contributions of system components. The scope included the production system from seed to the farm gate and from the farm gate to transplanting in a landscape site. The impact of the use phase and end-of-life phase was also assessed.
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