Science Inventory

The contribution of wildland fire emissions to deposition in the U S: implications for tree growth and survival in the Northwest

Citation:

Koplitz, S., Chris Nolte, R. Sabo, C. Clark, K. Horn, R. Thomas, AND T. Newcomer-Johnson. The contribution of wildland fire emissions to deposition in the U S: implications for tree growth and survival in the Northwest. Environmental Research Letters. IOP Publishing LIMITED, Bristol, Uk, 16(2):024028, (2021). https://doi.org/10.1088/1748-9326/abd26e

Impact/Purpose:

In addition to hazardous air pollutants, wildland fires also release nitrogen and sulfur into the atmosphere. These nutrients are subsequently deposited to land and water systems and can significantly affect ecosystem health. We find that wildland fire activity contributes up to 30% of total nutrient deposition in parts of the Northwest, where local fire activity is high and pollution from other sources is relatively low. Impacts on tree survival and growth rates are most severe in Oregon, northern California, and northeastern Idaho, regions where many areas already experience nitrogen deposition at or approaching critical load levels. These ecological impacts of wildland fires present a complex challenge for land managers trying to both avoid catastrophic wildfires through controlled burn practices and protect vulnerable ecosystems.

Description:

Ecosystems require access to key nutrients like nitrogen (N) and sulfur (S) to sustain growth and healthy function. However, excessive deposition can also damage ecosystems through nutrient imbalances, leading to changes in productivity and shifts in ecosystem structure. While wildland fires are a known source of atmospheric N and S, little has been done to examine the implications of wildland fire deposition for vulnerable ecosystems. We combine wildland fire emission estimates, atmospheric chemistry modeling, and forest inventory data to (a) quantify the contribution of wildland fire emissions to N and S deposition across the U S, and (b) assess the subsequent impacts on tree growth and survival rates in areas where impacts are likely meaningful based on the relative contribution of fire to total deposition. We estimate that wildland fires contributed 0.2 kg N ha−1 yr−1 and 0.04 kg S ha−1 yr−1 on average across the U S during 2008–2012, with maxima up to 1.4 kg N ha−1 yr−1 and 0.6 kg S ha−1 yr−1 in the Northwest representing over ~30% of total deposition in some areas. Based on these fluxes, exceedances of S critical loads as a result of wildland fires are minimal, but exceedances for N may affect the survival and growth rates of 16 tree species across 4.2 million hectares, with the most concentrated impacts occurring in Oregon, northern California, and Idaho. Understanding the broader environmental impacts of wildland fires in the U S will inform future decision making related to both fire management and ecosystem services conservation.