Wood ash and Biochar as soil amendments: To what extent can they help forests to adapt to climate change?

Abstract

Forest biomass is considered an alternative to fossil fuels in energy transformation, as part of global strategies for climate change mitigation. Application of by-products such as wood ash (WA) and biochar (BC) to soil could replace the nutrients removed by tree harvesting, increase soil carbon stocks, and therefore improve soil properties in order to face up to climate change. However, the extent to which these amendments can provide benefits depends on how the by-products interact with the system. We studied the short-term responses of WA and BC application in two different temperate forest plantations: A. Typic Udorthent (TU) with mature Pinus radiata; B. Typic Dystrudept (TD) with young Quercus pyrenaica, to test whether the addition of WA or BC to the forest floor could be a tool to adapt forest (by the forest soil) to Climate Change. In order to address the stated objectives, we established a field trial consisting of two experimental sites, and developed a laboratory trial based on incubations. In the field, BC was applied at rates of 3.5, 10 and 20 Mg ha-1 and WA at rates of 1.5, 4.5 and 9 Mg ha-1 (calcium equivalent). A nitrogen enriched treatment was applied with the intermediate doses. The incubations were only performed with the TU and the intermediate dosage of BC (with and without N). Our results were not conclusive to say whether BC or WA are good amendments to adapt Atlantic forests to climate change. Indeed, our findings confirm that the addition of biochar and wood ash to temperate humid forest soils affects different sites in different ways, depending on the soil type and system, as well as on application rates and whether nitrogen was also added.