Woody plants have expanded into many grasslands, in part due to anthropogenic suppression of natural fires. Restoring fire to grasslands is a shift in conservation strategy aimed to improve the health of these ecosystems, which depend on fire. However, fire exclusion changes ecosystem characteristics, and particularly in areas that have experienced extensive tree expansion, reintroducing fire can have important impacts on the carbon cycle, for example due to tree mortality, as well as on other nutrient cycles. Thus, it is critical to assess the biogeochemical impacts of prescribed fire.

Justin Gay from the University of Montana and colleagues do just this in experiments conducted in the northern Great Plains, USA. They assess changes in soil carbon, pyrogenic carbon and nitrogen concentrations over a gradient of wood cover and find an increase in soil carbon two years after fire. Furthermore, considering the two main types of conifer tree present, they find greater mortality for junipers than ponderosa pine. This led to larger relative nitrogen loss compared with carbon, as junipers had less carbon stored as aboveground biomass, but contained more nitrogen. These results indicate that the impact of fire on ecosystem carbon dynamics will be dependent on the types of tree present, an aspect that needs to be considered in fire management plans.

木本植物已经扩展到许多草原，部分原因是人为抑制了自然火灾。恢复草原的火是保护策略的转变，旨在改善这些依赖火的生态系统的健康状况。然而，防火会改变生态系统特征，特别是在树木广泛扩张的地区，重新引入火会对碳循环产生重要影响，例如由于树木死亡，以及其他营养循环。因此，评估计划烧毁的生物地球化学影响至关重要。

蒙大拿大学的 Justin Gay 及其同事在美国北部大平原进行的实验中就是这样做的。他们评估了土壤碳、热原碳和氮浓度在木材覆盖梯度上的变化，发现火灾后两年土壤碳有所增加。此外，考虑到存在的两种主要类型的针叶树，他们发现杜松的死亡率高于黄松。与碳相比，这导致更大的相对氮损失，因为杜松作为地上生物量储存的碳较少，但含有更多的氮。这些结果表明，火灾对生态系统碳动态的影响将取决于存在的树木类型，这是火灾管理计划中需要考虑的一个方面。