Large-scale patterns of species diversity are one of the most important and attractive issues of ecology and biogeography. Using the investigation data of tree layers in 13 typical forest ecosystems in China, we explored the geographical patterns and main influencing factors of species diversity in the forest community. Our results indicated that four species diversity indices decreased with an increase in latitude and longitude in the 13 typical forest ecosystems. Species richness, in particular, showed a significant variation along both latitude and longitude gradients, while the other indices showed a significant change only with an increase in latitude. A regression analysis showed that the species diversity indices were not consistent in correlation with a single factor, i.e., plant traits, energy, and moisture factor. The indices such as, species richness, Shannon-Wiener index, and Simpson index, showed the most remarkable correlation with the annual average temperature, coldest month average temperature, annual temperature difference, and potential evapotranspiration (P < 0.01). The Pielou index showed a significant correlation with the annual mean temperature, mean temperature of the coldest month, actual evapotranspiration, potential evapotranspiration, and crown density (P < 0.05). A variation partitioning analysis demonstrated that the synergy of energy and moisture had the highest explanation rate for the spatial distribution of species diversity index, reaching 15%-42%, and the interactions among plant traits, energy, and moisture factors had a secondary effect on the geographic distribution patterns of species diversity, with an explanation rate of 14%-27%. Furthermore, the shared effects of the other combinations of plant traits and energy factors were insignificant. The effect of energy factors on the distribution of species diversity indices was higher than the effect of plant traits or moisture in determining the species diversity in 13 typical forest ecosystems. Our results revealed that the shared effects of energy and moisture were the most crucial factors impacting the development of large-scale species diversity in the studied forest tree layer. Meanwhile, the effects of plant traits should not be ignored.