• Premise of the Study: Differences in seed germination responses of trees in tropical forests to temperature and light quality may contribute to their coexistence. We investigated the effects of temperature and red:far-red light (R:FR ratio) on seed germination of two gap-demanding species (Ficus hispida and F. racemosa) and two shade-tolerant species (F. altissima and F. auriculata) in a tropical seasonal rainforest in southwest China.

• Methods: A R:FR ratio gradient was created by filtering fluorescent light through polyester filters. Four temperature treatments were used to test the effect of temperature on seed germination of the four Ficus tree species across the R:FR gradient.

• Key Results: Seeds of the four Ficus species were positively photoblastic. Seed germination of F. hispida and F. racemosa was not affected across the R:FR ratio gradient (0.25–1.19) at 25/35°C, but it was inhibited under low R:FR at 22/23°C. By contrast, germination percentages of F. altissima and F. auriculata were not inhibited along the entire light gradient in all temperature treatments.

• Conclusions: Differences in germination responses of Ficus species might contribute to differences in their habitat preferences. The inhibitory effect of understory temperatures in the forest might be a new mechanism that prevents positively photoblastic seeds of the gap-demanding species such as F. hispida and F. racemosa from germinating in the understory and in small canopy gaps.