The aim of this investigation was to discover an effective index for salt-tolerant selection in plant tissue culture system and to assay the physiological responses in a salinity field trial. Netphotosynthetic rate (NPR) in salt-tolerant clones of Eucalyptus (Eucalyptus camaldulensis Dehnh.), Rain tree (Samanea saman Merr.) and Thai neem (Azadirachta siamensis Val.) was gradually reduced when exposed to 0.17, 0.34, 0.68 or 1.02 M NaCl salts contained in the culture media, while that in salt-sensitive clones was sharply decreased. The reduction percentage of NPR in salttolerant species grown under salt stress was lower than that in salt-sensitive species by a factor of 2-3 folds. The NPR reduction in plant species grown under salt-stress was evidently investigated as effective index for salt-tolerance. In addition, physiological characteristics, chlorophyll content and maximum quantum yield of PSII (Fv/Fm), in salt-tolerant clones were significantly adapted to salinity field trial at Mahasarakham province, Northeastern region of Thailand, leading to high survival percentage and grew well when compared to the salt-sensitive clones. The salt-tolerant clones of forest tree species can be further used for salinity phytoremediation and ecological succession.