Stomata in leaves of trees can change in response to factors like humidity and plant hormones. Researchers studied how three tree species in China reacted to different levels of humidity and three plant hormones in June, August, and October. They found that the trees' stomata responded differently to humidity changes in each season, unlike what most studies have shown. The amount of a plant hormone called ABA was linked to how sensitive the stomata were to humidity changes. Traditional models used to predict stomatal behavior didn't work well for these trees. The temperature in the area also affected how wide the stomata opened.