Application of self-organizing neural networks to classification of plant communities in Pangquangou Nature Reserve, North China Application of Self-Organizing Feature Map to Classification and Ordination of Picea wilsonii Forest in Luya Mountain Nature Reserve SOFM-based nutrient cycling classification of forest ecosystems in the Loess Plateau Self-organizing feature map classification and ordination of Larix principis- rupprechtii forest in Pangquangou Nature Reserve