Species-specific water-use characteristics of trees in old-growth and secondary tropical forests of Thailand

Tree water use is a critical component of the forest water cycle and is influenced by global climate changes, such as shifts in precipitation patterns. These changes may disproportionately affect forest runoff depending on how sensitive tree water use is to environmental conditions. Therefore, understanding the water-use strategies of different tree species is essential for predicting how forests will respond to environmental changes. This study investigated how daily sap flux density (Js), representing water flow per a unit of sapwood area, varies with environmental factors in eight common tree species in successional tropical forests in Thailand. Using thermal dissipation probes, we measured Js in an old-growth (OF) and a young forest (YF). When averaging across all species, trees in OF were highly sensitive to rising vapor pressure deficit (VPD) under low soil moisture, responding to high atmospheric demand, while those in YF maintained their water use rate regardless of changing VPD..., The tree species were selected based on their relative basal area abundance and number of trees within each plot, using inventory data from the sites (W. Chanthorn, pers. comm, 2018). This was determined by calculating each species' basal area as a proportion of the total basal area across all species in each site. We focused on common tree species, i.e., those in the top 20 tree species with high relative basal area ranking and more than 100 trees. However, our choice of species selection was limited to the requirement that the sampled trees for sap flux measurement had to be within 25 m radius from the data logger. This requirement resulted in 21 trees of eight evergreen species in total, with one species existing in both sites (Syzygium antisepticum). Sap flux density (g cm-2 s-1) was measured using self-constructed thermal dissipation probes (Granier, 1985). Details about sap flux density measurement and its estimation are described in Ampornpitak et al. (2023).
Our monitoring perio..., , # Species-specific water-use characteristics of trees in old-growth and secondary tropical forests of Thailand

[https://doi.org/10.5061/dryad.51c59zwj8](https://doi.org/10.5061/dryad.51c59zwj8)

## Description of the data and file structure

This study investigates the variation of tree water use with environmental factors in two successional forests in Khao Yai National Park, Thailand. Sap flux density (Js), expressed as the rates of water flow per unit sapwood area, was used in the analyses. The Js data were monitored from January 2021 to April 2022 in the old-growth forest, and September 2020 to June 2023 in the young forest. We used daily sum values in all analyses presented in the corresponding paper. The descriptions of labels in the data set are as follows.

**Site:**

·       OF = the old-growth forest (>200 years old)

·       YF = the young forest (<10 years old)

**REW (Relative extractable water) class:**

·       low = low soil moisture (REW < 0.2 for OF and < 0.1 for YF)
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