Coffee Agroforests Can Store Significant Levels of Carbon

by Stephen Johnson

Over 40% of the world’s terrestrial surface is covered by agricultural activities, and approximately half of that area is agroforestry. Agroforests, agricultural areas that are at least 10% covered by tree shade, run the gamut from areas with a few exotic species to structurally complex, highly diverse ecosystems that mimic natural forests. Woody vegetation biomass is approximately 50% carbon, so incorporating trees into agricultural areas significantly improves the ability of these systems to sequester and store carbon. Given that agroforests cover almost half a billion hectares, they may represent a significant and underestimated carbon sink. The amount of carbon that can be stored is determined by a variety of factors, including the number of trees and the density of their wood. The type of and number of the trees present in turn depends on the individual management of the farm. In Ethiopia, Tadesse et al. (2014) investigated how different management regimes affected the species of trees present and the amount of carbon stored, compared to natural forests. They measured the density and species of trees in smallholder coffee farms, state-owned plantations, and forest fragments, and used these measurements to determine the carbon storage capacity of each forest. They also interviewed farmers to see how and why species are selected for inclusion in plantations. Tadesse et al. found that agroforests can store 50-62% of the carbon that natural forests can store. They also found that farmers tended to prefer and harvest denser-wooded species, though less dense species were used for some limited purposes. Continue reading

Self-Biased Solar-Microbial Device for Sustainable Hydrogen Generation

by Allison Kerley (Photo above of Hanyu Wang, first author of this paper at the University of California, Santa Cruz.)

Most hydrogen generating devices require an external addition of a 0.2 to 1.0 V electric potential in order to sustain the hydrogen generation. Wang et al. (2013) explored the feasibility of a self-powering photoelectrochemical-microbial fuel cell (PEC-MFC) hybrid device to generate hydrogen. The PEC-MFC was a combination of a photoelectrochemical fuel cell and a microbial fuel cell. The Hydrogen production of the device was tested when powered by a ferricyanide solution inoculated with a pure strain of Shewanellla oneidensis MR-1 and when powered by microorganisms found naturally occurring in the municipal wastewater. In both scenarios, given replenishments of fuel, the device produced enough voltage to be self-sustaining. However, when the device was powered by wastewater it produced both a lower current and a smaller hydrogen production than when powered by ferricyanide solution. Continue reading