Plant functional traits can be used to reflect the responses of plants to environmental changes. In order to understand how plant functional traits change along the environmental gradients and to find the factors driving such changes, especially in the islands of eastern China, six plant functional traits, including diameter at breast height (DBH), tree height (H), mean leaf area (MLA), specific leaf area (SLA), twig wood density (TWD), and twig water content (TWC), were measured in typical plant communities in seven islands. One-way analysis of variance was used to compare the variations in traits among different climatic zones. Stepwise regression analysis was used for quantifying relationships between traits and seven environmental factors (soil total carbon, soil total nitrogen, soil total phosphorus, soil water content, mean annual temperature, mean annual precipitation, and mean annual wind speed). The results showed that:(1) Significant differences exist in most plant functional traits among different climatic zones except SLA, but the functional traits of evergreen and deciduous plants differ among climatic zones, which indicated that plants of different life forms have different reaction and adaptation to the environment. (2) Climatic factors, rather than soil factors, are the main controllers of trait differences along the gradient. Plants in the southern islands have higher DBH and TWC, lower MLA and TWD. The results in northern islands are opposite. Moreover, twig wood traits (TWD and TWC) are significantly influenced by mean annual wind speed in the islands. These results may offer a reference for selecting suitable species for afforestation and reforestation programs in the islands.