Increased harvest of forest biomass has the potential for mitigating climate change as well as reducing dependency on fossil fuels across much of the boreal zone. For forestry to be sustainable in the long term, the supply of weathering (chemical dissolution of minerals) needs to be sufficient to compensate for what is harvested and washed out by acid deposition. There are indications that current levels of forest harvest in boreal regions are not sustainable because soils are already being depleted of key elements in large areas, and increased harvest rates will be even less sustainable. This weathering deficit threatens both trees and aquatic ecosystems. But there is also a concern that weathering estimates are uncertain relative to the accuracy needed to guide forest policy. This special issue brings together key results and syntheses from a 5-year research programme involving six universities and two research institutes to improve weathering estimates at the spatial and temporal scales relevant to sustainable forest management, including how climate and forest management can affect weathering rates.

The articles in this issue do the following:

• present improvements made in soil mineral weathering models via improved descriptions of tree physiology, forest ecology, and aqueous geochemistry;
• advance our understanding of the biological controls upon and responses to changes in soil mineral weathering rates;
• demonstrate the sensitivity of base cation weathering rates to small changes in mineralogy;
• use improved understanding to project weathering in the coming century across a broad section of the boreal region for multiple climate scenarios;
discuss weathering rates and their importance for sustainable forestry and aquatic ecosystems in the context of other nutrient pools in the soil.