Abstract:

Abstract： Caloric value and nutrient characteristics of dominant plant species of six natural secondary plant communities of the Loess Plateau were investigated. The investigation showed that the gross caloric values of Hippophae rhamnoides, Populus davidiana, Betula platyphylla, Pinus tabulaeformis, P. tubuleformis f. shekansis and Quercus liaotungensis were 18972，19186，19227，19795，19735 and 18085 kJ·g-1, respectively and the ash free caloric values of the six species were 19590，20620，19824，20538，20168 and 18368 kJ·g-1, respectively. The weighted averages of either the gross caloric values or the ash free average caloric values of Quercus liaotungensis were the lowest. The caloric values of the dominant plant species first increased and then decrease with progressive successions of their communities, indicating that the energy utilization efficiencies of the dominant plant species tended to increase first and then decrease as the community successions were going on. The caloric value greatly varied in the different parts of the six dominant plant species. Foliage was the most active organ of the plant, and its gross caloric value and ash free caloric value were significantly higher than those of the other organs (P<005). The total phosphorous took an important
share in the caloric value compositions of the plant vegetations, and was significantly and positively correlated with the gross caloric values and the ash free caloric values in the different communities. The caloric values of the groundlitter were generally lower than of the standing trees and fresh litter falls. The groundlitters of Pinus tubuleformis f. shekansisas well as Pinus tabulaeformis and Quercus liaotungensis at the late succession stage decomposed rapily, and the higher groundlitter decomposition rates and higher light energy use efficiency of Pinus tubuleformisf. shekansis communities indicated that the Pinus tubuleformis f. shekansis community was probably the sub climax community at the middle or late succession stage.

Key words: Key words： dominant plant species, typical vegetation community, Loess Plateau