Increasing tropical cyclone (TC) pressure on temperate forests is inevitable under the recent global increase of the intensity and poleward migration of TCs. However, the long-term effects of TCs on large-scale structure and diversity of temperate forests remain unclear. Here, we aim to ascertain the legacy of TCs on forest structure and tree species richness by using structural equation models that consider several environmental gradients and use an extensive dataset containing >140,000 plots with >3 million trees from natural temperate forests across eastern United States impacted by TCs. We found that high TC activity (a combination of TC frequency and intensity) leads to a decrease in maximum tree sizes (height and diameter), an increase in tree density and basal area, and a decline in the number of tree species and recruits. We identified TC activity as the strongest predictor of forest structure and species richness in xeric (dry) forests, while it had a weaker impact on hydric (wet) forests. We highlight the sensitivity of forest structure and tree species richness to impacts of likely further increase of TC activity in interaction with climate extremes, especially drought. Our results show that increased TC activity leads to the homogenization of forest structure and reduced tree species richness in U.S. temperate forests. These findings suggest that further declines in tree species richness may be expected because of the projected increase of future levels of TC activity.

Department of Earth and Spatial Sciences University of Idaho Moscow ID 83843 USA

Department of Geography Indiana University Bloomington IN 47408 USA

Institute of Botany of the Czech Academy of Sciences 25243 Průhonice Czech Republic; Department of Botany Faculty of Science University of South Bohemia České Budějovice Czech Republic

Institute of Botany of the Czech Academy of Sciences 25243 Průhonice Czech Republic; Faculty of Forestry and Wood Sciences Czech University of Life Sciences Prague Kamýcká 129 165 21 Prague 6 Suchdol Czech Republic

Laboratory of Tree Ring Research University of Arizona Tucson AZ 85721 USA

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