Plant functional traits have been important issues in ecological research in recent years. Leaf functional traits have close relationships with the biomass, resource acquisition and utilization, and resource-use efficiency of plants. Daqinggou forest plant communities are located in the Horqin Desert, where the habitat conditions are very distinctive. There is a dense forest in the sand ditch, which forms a sharp contrast with the surrounding dune landscape. Although the difference in elevation from the bottom to the top of the ditch is only 60-70 m, different forest communities have developed because of differences in soil conditions that have arisen at different distance from the water source in the bottom of the ditch. Ulmus macrocarpa, Quercus mongolica, and Fraxinus mandshurica communities are respectively located in the top, middle and bottom of the ditch in Daqinggou Nature Reserve. In order to study the different environmental conditions in the Daqinggou Nature Reserve, U. macrocarpa, Q. mongolica, and F. mandshurica communities were selected as the three main research objects. We measured five functional traits of dominant species in the main forest communities, namely, leaf thickness, specific leaf area, leaf dry matter content, leaf size, and leaf dry weight. The relationships between the different leaf functional traits were studied, and the leaf functional traits of different growth forms and different communities were compared. Correlation analysis showed that leaf thickness was significantly negatively correlated with specific leaf area and significantly positively correlated with leaf size and leaf dry weight. Specific leaf area was significantly negatively correlated with leaf dry matter content and leaf dry weight, and positively correlated with leaf size. Leaf dry matter content was significantly negatively correlated with leaf size and significantly positively correlated with leaf dry weight, whereas leaf size was significantly positively correlated with leaf dry weight. Analysis of the different growth forms showed that the leaf dry matter content of herbs was lower than that of trees and shrubs. However, the specific leaf area of herbs was higher than that of trees and shrubs. Comparison of the functional traits of different communities showed that in the U. macrocarpa and Q. mongolica communities, the leaf thickness and leaf dry matter content of trees and shrubs were significantly higher than those in the F. mandshurica community. In contrast, the specific leaf area of trees and shrubs in the U. macrocarpa and Q. mongolica communities were significantly lower than those in the F. mandshurica community. The higher leaf dry matter content and lower specific leaf area of trees and shrubs in the U. macrocarpa and Q. mongolica communities reflect their adaptation to a more arid environment. Similarly, the lower leaf dry matter content and higher specific leaf area of trees and shrubs in the F. mandshurica community reflect their adaptation to a moister environment. The species compositions in three main forest communities in the Daqinggou Nature Reserve have been regulated by the development of specific combinations of functional traits, which have enabled these species to adapt to the specific local environments.