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Recently, Stovall et al. 1 showed that during an extreme drought, remotely sensed mortality of tall trees was more than double that of short trees. They interpreted this to be a consequence of inherently greater hydraulic vulnerability of tall trees, and suggested that tall-tree vulnerability should generalize more broadly. Here we reassess their conclusions using contemporaneous, ground-based data from near their study sites. We find that 90% of trees belong to taxonomic groups showing declining, not increasing, mortality with height, and that the overall increase in mortality with height is instead a consequence of height-related changes in forest composition, not intrinsically greater vulnerability of tall trees. Similar mechanisms likely explain mortality patterns at Stovall et al.’s sites, and, regardless, we show that their conclusions should not be accepted in the absence of robust tests of alternative mechanisms. Because Stovall et al.’s remote-sensing approach did not distinguish among tree taxonomic groups, they could not test plausible alternative mechanisms. For example, consider the following two scenarios, each of a drought-stricken forest comprising two species. In the first scenario, mortality of both species declines with increasing tree height. However, at any given height, species B has substantially higher mortality than species A. In addition, the relative abundance of species B increases markedly with height. The net effect is that mortality in the forest as a whole increases with height (Supplementary Table 1). But because mortality declines with height for each species individually, we must reject explanations invoking intrinsically greater drought vulnerability of tall trees. In the second scenario, species C’s mortality declines gradually with height, but species D’s mortality increases sharply with height. Even without height-related changes in relative species abundances, mortality in the forest as a whole can increase with height, even if species D is the minority species (Supplementary Table 2). But in this scenario, we must seek mortality mechanisms that can explain opposite height-related drought responses of cooccurring tree species. To explore whether one or both of these scenarios could explain Stovall et al.’s results, we analyzed data from 89 randomly located forest plots distributed across a 1705-ha mixed-species, old-growth forest landscape, roughly 45–65 km southeast of Stovall et al.’s study areas in California’s Sierra Nevada2,3. During the last year of the drought (2016, also Stovall et al.’s last year of analysis), we recorded 5855 living and dead trees ≥5 m tall belonging to 15 species, which we assigned to three groups of species (hereafter: taxonomic groups) according to magnitude of mortality during the drought2,4–6 (Supplementary Table 3). Height classes of individual trees (5–15 m, 15–30 m, and >30 m, following Stovall et al.) were estimated from trunk diameter using species-specific allometric equations (Supplementary Table 3). Numbers of trees alive in 2013, and 2014–2016 mortality, were calculated as described in ref. 2 and as summarized in “Methods” section. When all trees were considered together, our results were similar to Stovall et al.’s: mortality of the tallest trees was ~2-fold greater than that of the shortest trees (Fig. 1a). But this simple analysis masked profound—and consequential—differences among taxonomic groups in both the magnitude of mortality and its relationship to tree height. For example, across the three height classes, mortality was low (<0.09) in angiosperms, intermediate (0.17–0.26) in non-Pinus conifers, and high (0.17–0.56) in Pinus (Fig. 1b). Within each taxonomic group, individual species had magnitudes and patterns of mortality that were largely similar to one another (Supplementary Fig. 1). Notably, variation in mortality was greater within height classes (among taxonomic groups) than among height classes (within taxonomic groups). In addition, only 10% of trees belonged to a taxonomic group (Pinus) in which mortality increased with tree height. The remaining 90% belonged to groups (angiosperms and non-Pinus conifers) in which mortality declined slightly with height. With increasing height, angiosperms, with their low mortality in all height classes, declined in relative abundance, whereas the intermediate-mortality non-Pinus conifers and high-mortality Pinus increased (Fig. 1c). To explore the effects of these changing relative abundances, we calculated hypothetical mortality for all https://doi.org/10.1038/s41467-020-17213-5 OPEN