Increased climate variability is expected to intensify short-term drought events. Plants have evolved stress tolerance strategies involving trade-offs in resource conservation, mycorrhizal collaboration and plant size, yet how these strategies promote drought resistance across different herbaceous plant groups remains unknown. Leveraging 63 globally distributed grassland and shrubland sites from the International Drought Experiment, we identified plant traits linked to drought resistance in 661 populations of 421 species after 1 year of extreme drought. We assessed how traits, site precipitation and drought severity affected cover change across growth forms and lifespans, and how trait-environment interactions influenced drought resistance. Across all species, leaf N (an acquisitive trait) was associated with drought resistance, whereas in forbs, drought resistance was also associated with a conservative root trait and plant size. In addition, interactions among traits mediated drought resistance; root traits predicted performance only in concert with other traits. Environmental variables influenced trait effects on drought resistance, notably for annuals in wetter sites, suggesting that drought-escape strategies in annuals may be advantageous only under mild stress. Our study highlights variability in traits that predict drought resistance across herbaceous plant groups, emphasizing the importance of species context, environmental stress and the selection of traits in research and management.

Predicted increases in extreme droughts will likely cause major shifts in carbon sequestration and forest composition. Although growth declines during drought are widely documented, an increasing number of studies have reported both positive and negative responses to the same drought. These divergent growth patterns may reflect thresholds (i.e., nonlinear responses) promoted by changes in the dominant climatic constraints on tree growth. Here we tested whether stemwood growth exhibited linear or nonlinear responses to temperature and precipitation and whether stemwood growth thresholds co-occurred with multiple thresholds in source and sink processes that limit tree growth. We extracted 772 tree cores, 1398 needle length records, and 1075 stable isotope samples from 27 sites across whitebark pine's (Pinus albicaulis Engelm.) climatic niche in the Sierra Nevada. Our results indicated that a temperature threshold in stemwood growth occurred at 8.4°C (7.12-9.51°C; estimated using fall-spring maximum temperature). This threshold was significantly correlated with thresholds in foliar growth, as well as carbon (δ13 C) and nitrogen (δ15 N) stable isotope ratios, that emerged during drought. These co-occurring thresholds reflected the transition between energy- and water-limited tree growth (i.e., the E-W limitation threshold). This transition likely mediated carbon and nutrient cycling, as well as important differences in growth-defense trade-offs and drought adaptations. Furthermore, whitebark pine growing in energy-limited regions may continue to experience elevated growth in response to climate change. The positive effect of warming, however, may be offset by growth declines in water-limited regions, threatening the long-term sustainability of the recently listed whitebark pine species in the Sierra Nevada.

Millions of seahorses a year are traded internationally, with many eventually sold at retail shops as curios, as aquarium pets, and especially for use in traditional medicine. The entire genus is now protected by CITES, but conservation measures have been limited in part by difficulties with species identification and incomplete understanding of trade patterns. In this study, we use molecular techniques to make species- and population-level identifications of 56 seahorses sampled from both traditional medicine and curio shops in San Francisco and central California. Seahorses from medicinal sources included unexpectedly large numbers of the eastern Pacific Hippocampus ingens, a species poorly protected by current CITES export recommendations. Curio shops were dominated by H. barbouri, a spiny species that has been reportedly confused in trading records as H. histrix. Specific populations of origin could be inferred for several species through comparison with publicly available phylogeographic data. Our results underscore the strengths and weaknesses of current recommended export regulations, and we suggest that molecular forensics can help in verifying trade documentation and developing more effective conservation measures.