Candidate perennial bioenergy grasses have a higher albedo than annual row crops

Abstract

The production of perennial cellulosic feedstocks for bioenergy presents the potential to diversify regional economies and the national energy supply, while also serving as climate 'regulators' due to a number of biogeochemical and biogeophysical differences relative to row crops. Numerous observational and model-based approaches have investigated biogeochemical trade-offs, such as increased carbon sequestration and increased water use, associated with growing cellulosic feedstocks. A less understood aspect is the biogeophysical changes associated with the difference in albedo (a), which could alter the local energy balance and cause local to regional cooling several times larger than that associated with offsetting carbon. Here, we established paired fields of Miscanthus 9 giganteus (miscanthus) and Panicum virgatum (switchgrass), two of the leading perennial cellulosic feedstock candidates, and traditional annual row crops in the highly productive 'Corn-belt'. Our results show that miscanthus did and switchgrass did not have an overall higher a than current row crops, but a strong seasonal pattern existed. Both perennials had consistently higher growing season a than row crops and winter a did not differ. The lack of observed differences in winter a, however, masked an interaction between snow cover and species differences, with the perennial species, compared with the row crops, having a higher a when snow was absent and a much lower a when snow was present. Overall, these changes resulted in an average net reduction in annual absorbed energy of about 5 W m À2 for switchgrass and about 8 W m À2 for miscanthus relative to annual crops. Therefore, the conversion from annual row to perennial crops alters the radiative balance of the surface via changes in a and could lead to regional cooling.

Importance of biophysical effects on climate warming mitigation potential of biofuel crops over the conterminous United States

“…Evaporative cooling of miscanthus and switchgrass, therefore, is augmented by higher albedo, consistent with previous results (Anderson‐Teixeira et al ., ). However, observed experiment data indicated that miscanthus and switchgrass have a higher albedo than corn during the growing season, thereby reducing Rn in bioenergy crops (Miller et al ., ). This discrepancy likely originates from the current model being unable to predict albedo of these perennial grasses through improper parameterization of leaf transmittance and reflectance, leaf angle, and canopy structure (Lawrence et al ., ).…”

On the Long-Term Hydroclimatic Sustainability of Perennial Bioenergy Crop Expansion over the United States

“…Albedo values were modified based on field site observation values obtained from Miller et al (2016). Seasonal profiles of albedo were determined by averaging daily albedo values across two perennial plant types (switchgrass and miscanthus) and across the observed years of 2010 and 2011.…”

“…In addition, the importance of field-scale studies has demonstrated the significance of appropriate biogeophysical representation in process-based models that can be used to examine scenario-based environmental implications. For example, Miller et al (2016), via a multiyear observational campaign, conducted field-scale measurements to determine that perennial bioenergy crops have consistently higher values of albedo than annual crops during the growing season. This higher albedo can reduce the amount of solar energy received at the surface, affecting the partitioning of sensible, latent, and ground heat fluxes (Georgescu et al 2011(Georgescu et al , 2013Anderson-Teixeira et al 2012;Anderson et al 2013;Bagley et al 2015;Miller et al 2016).…”

“…For example, Miller et al (2016), via a multiyear observational campaign, conducted field-scale measurements to determine that perennial bioenergy crops have consistently higher values of albedo than annual crops during the growing season. This higher albedo can reduce the amount of solar energy received at the surface, affecting the partitioning of sensible, latent, and ground heat fluxes (Georgescu et al 2011(Georgescu et al , 2013Anderson-Teixeira et al 2012;Anderson et al 2013;Bagley et al 2015;Miller et al 2016). Studies have noted regional cooling (Georgescu et al 2011;Le et al 2011;Khanal et al 2013;Goldstein et al 2014;Feng et al 2015) and the potential for increased precipitation (Georgescu et al 2011;Khanal et al 2013Khanal et al , 2014 associated with largescale deployment of perennial bioenergy crops.…”

Editorial: Optimizing the Delivery of Multiple Ecosystem Goods and Services in Agricultural Systems

“…The advantages of farmlands involving perennial crops and grasslands vs. annual crops is a topic of broad discussion and research over the past decade (e.g., Ferchaud et al, 2016;Miller et al, 2016;Vico et al, 2016). Several articles in this Research Topic focus on how different types of farmlands and other land uses are providing multiple long-term ecosystem services.…”