Changes in albedo (∝) can alter ecosystem energy balance and potentially mitigate climate warming. Understanding albedo change upon conversion to perennial biofuel cropping systems is important as albedo may be an important component of a system’s total global warming potential. Here, we examine temporal changes of albedo in managed biofuel systems by measuring albedo-induced radiative forcing (RFΔα). Direct field measurements of albedo at high temporal resolution (5 min) were used to quantify the magnitudes and temporal (i.e., intra- and inter-annual) changes of albedo and RFΔα in bioenergy crops of maize, sorghum, switchgrass, miscanthus, native grasses, restored prairie, and early successional bioenergy systems in southwest Michigan from May 2018 to December 2019; a nearby forest was used as a historical reference.
Results/Conclusions
During the growing season, albedo was stable in perennial croplands, averaging 0.22 ± 0.06 (SD), significantly higher than that of annual no-till maize (0.17 ± 0.06). However, the albedo of sorghum (0.22 ± 0.04) was similar to that of the perennial crops, reflecting sorghum’s planting density, plant morphology, and canopy architecture. Throughout winter, the average albedo of miscanthus, early successional, and restored prairie systems was similar in both years (0.48 ± 0.08), while switchgrass had a lower albedo in winter 2018 (0.29 ± 0.07) and 2019 (0.48 ± 0.11). Sorghum and maize had lower winter albedo compared to perennials (0.30 ± 0.10 and 0.43 ± 0.09, respectively). The albedo of our reference forest was consistently lower than all biofuel systems during the growing season (0.12 ± 0.07), winter (0.15 ± 0.08), as well as annually (0.14 ± 0.07). Differences among crops during the growing season and annually were statistically significant (p ≤0.05). These results show that perennial biofuel systems are more reflective of radiant fluxes and suggest that conversion from annual to perennial crops lowers the amount of annual absorbed energy and leads to an overall cooling effect.