Abstract: The community structure and species diversity of Pinus tabuliformis natural forest were studied by using quadrat investigation in the Liaoheyuan Nature Reserve, Hebei Province. The results showed that 146 vascular species existed in the sampling plots, belonging to 92 genera and 42 families. The four aged P. tabuliformis natural forest stands exhibited obvious vertical structures. The dominant species in arbor layer, shrub layer, and herb layer were P. tabuliformis, Spiraea pubescens + Quercus mongolica, Carex tristachya, respectively. The richness and diversity indexes were higher in herb layer than in shrub layer. The evenness index was higher in shrub layer than in herb layer in young stands, while the opposite was true for the other stands. The richness and Shannon diversity indexes in shrub layer of the four stands ranked as follows: young forest > mature forest > middle-aged forest > pre-mature forest, Simpson diversity index ranked from high to low as mature forest > young forest > middleaged forest > pre-mature forest, while evenness index had the order of pre-mature forest > middle-aged forest > mature forest > young forest. In herb layer, the richness index followed an order of young forest > pre-mature forest > mature forest > middle-aged forest, while the Shannon diversity index, Simpson diversity index and evenness index showed the order of pre-mature forest > mature forest > middle-aged forest > young forest.

Key words: reduced N application, fertilizing distance, maize/soybean intercropping system, N use efficiency