Do Forests Burn Alone? The Role of Wildfire on Fertility in the United States

Fertility is a complex amalgamation of human choice, economic conditions, and environmental factors. While the biological toxicity of wildfire-induced air pollution is well-documented to have severe detrimental effects on human health and the reproductive system, reproductive outcomes are not dictated by biology alone. They are profoundly shaped by human behavioral responses. This study analyzes the net effect of wildfire exposure, alongside economic shocks and non-parametric temperature extremes, on fertility in the United States. Utilizing a comprehensive county-monthyear panel dataset from 2010 to 2023, the analysis employs a Poisson Pseudo-Maximum Likelihood (PPML) regression incorporating high-dimensional county and year-month fixed effects. The primary findings reveal a statistically significant positive relationship between wildfire exposure and fertility. Utilizing SafeGraph mobility data, this study empirically isolates the behavioral mechanism driving this result: wildfires cause a highly significant increase in the proportion of the population sheltering completely at home, altering daily routines in a manner that overrides the biological detriments of smoke exposure. Furthermore, a continuous interaction analysis reveals a stark environmental justice divide: while the shelter-in-place "baby bump" occurs universally across income groups, economically vulnerable counties suffer severe fertility depressions from the economic anxiety accompanying disasters, significantly muting the behavioral bump. A 500iteration randomization inference (placebo) test confirms the causal robustness of these findings, yielding an empirical p-value of < 0.01.