1. In seasonally dry tropical forests, plant functional type can be classified as deciduous low wood density, deciduous high wood density, or evergreen high wood density species. While deciduousness is often associated with drought-avoidance and low wood density is often associated with tissue water storage, the degree to which these functional types may correspond to diverging and unique water use strategies has not been extensively tested. 
2. We examined (1) tolerance to water stress, measured by pre-dawn and mid-day leaf water potential; (2) water use efficiency, measured via foliar δ¹³C; and (3) access to soil water, measured via stem water δ¹⁸O.
3. We found that deciduous low wood density species maintain high leaf water potential and low water use efficiency. Deciduous high wood density species have lower leaf water potential and variable water use efficiency. Both groups rely on shallow soil water. Evergreen high wood density species have low leaf water potential, higher water use efficiency, and access alternative water sources. These findings indicate that deciduous low wood density species are drought avoiders, with a specialized strategy for storing root and stem water. Deciduous high wood density species are moderately drought tolerant, and evergreen high wood density species are the most drought tolerant group. 
4. Synthesis. Our results broadly support the plant functional type framework as a way to understand water use strategies, but also highlight species-level differences. 

Leaf water potential was measured using a Scholander pressure chamber (1505D, PMS Instrument Company, Albany, OR) for leaves collected at pre-dawn (4:30–6:00 AM) and at mid-day (11:30–1:00 PM). The leaves were bagged and kept in cooler with ice, then immediately measured in-situ.  For foliar δ¹³C analysis, the additional leaves collected at pre-dawn  were oven-dried in the lab at 75°C to 80°C for at least 48 hours, then transported to the Stable Isotopes for Biosphere Science (SIBS) Laboratory at Texas A&M University, College Station, for grinding, weighing, and packing. These samples were analyzed for δ¹³C with an Elemental Analyzer (Costech Analytical Technologies, Valencia, CA) coupled to a Thermo Scientific Delta V Isotope Ratio Mass Spectrometer (EA-IRMS; Thermo Fisher Scientific, Waltham, MA). Soil and stem samples representing wet conditions were collected on April 10, 2018, and those representing dry conditions were collected on June 12, 2018. Samples for the evergreen species group were collected separately on September 19, 2018. The soil samples from seven pits at three integrated depths: 5–15 cm, 20–30 cm, and 40–50 cm. Soil and stem water was extracted via cryogenic vacuum distillation at 100°C. Rainwater and throughfall samples were collected approximately bi-weekly from January 18, 2018 until June 9, 2018 (Fig. 1) in collectors wrapped with aluminum foil filled with a thin layer of paraffin oil to reduce evaporation (IAEA, 2014). Groundwater and surface water samples were also collected from the surrounding area. Water samples containing debris were filtered (0.2 μm) to remove particles. All water samples were analyzed using a High Temperature Conversion/Elemental Analyzer coupled to a Delta V Advantage Isotope Ratio Mass Spectrometer (TC/EA-IRMS). Please see corresponding publication for more details. 

Missing data is marked as NA. Data has been summarized (mean and standard deviation) by date and tree species or sample ID.