Abstract:

[Objective]Larix gmelinii over cutting forest formed at the beginning of 1980s located at the chaocha forest farm, genhe forestry bureau, inner Mongolia, was selected as research object. The objective of this paper is to reveal the vertical structure characteristic of multi storied uneven-aged stand, and to provide some references for the further study on the succession trend and stand structure optimization.[Method]Based on the data of 10 sample plots in the larix gmelinii forest, the vertical stratification of stands of the over-cutting forest of Larix gmelinii was divided into main canopy layer, succession layer and regeneration layer, by using the principle of the canopies competition in height for light. The height, diameter distribution, species composition, forest stock volume and horizontal pattern of each layer were analyzed. [Result]1)The average height of the main canopy layer, succession layer and regeneration layer are 11.2 m, 6.8 m and 2.8 m, respectively. Through the variance analysis, the level was apparently difference at the level of 0.01. 2)With the increasing of vertical stratification of forest stands, the diameter distribution shifts from the reverse J-type distribution to the left-skewed unimodal-type distribution, and finally forms an irregular unimodal shape. The diameter distribution of main canopy layer was unimodal irregular, the peaks were found at 8~16 diameter. The highest peaks were found at 12 and 14 diameter. The succession layer level is left unimodal size distribution. The peak was mainly found at 8 diameter. The diameter class distribution of regeneration layer was reverse J type. The peak was found at 2 diameter. 3)The species composition in each layer varies apparently. The main canopy layer plays a vital role in the composition of the entire forest species, and the composition percentages of the two layers are closed to each other, which directly affects the composition of species in the regeneration layer. The species composition in the succession layer reveals three possibilities for the future forest stand succession trend: the Larix gmelinii percentage may increase; the white birch percentage may gradual increase; the species composition may be relatively stable. 4)With the increasing of forest layers, the forest stock volume increased. The average proportions of the main canopy layer, the succession layer and the regeneration layer in the total forest stock volume reached 67.3%, 28.6% and 4.1%, respectively. 5)The distribution pattern of each layer is of clustering type, which is not entirely consistent with the overall distribution pattern of stands. With the decline in the forest layer, the clustering coefficient increased gradually, and the degree of aggregation increased apparently. 6)Each layer has different effects on the forest structures and functions. With increasing the age of forest, trees in the regeneration layer will decrease. The regeneration layer will shift to the succession layer, and the diameter distribution in the succession layer will move to the right and gradually approach the diameter distribution in the main canopy layer. 7)The characteristics of different levels of the vertical structure of this study are based on the a (cut-off coefficient) value is 0.5. The results of each forest layer were quantitative analyzed. [Conclusion]We shall control the proportions and reasonable heights of trees for each diameter class of species and continuously ensure the existence of the regeneration layer, by starting with each layer of forest stand, optimizing the structure, regulating the succession of forest stand, and continuously managing the multiple-layer uneven-aged forest. Vertical structure is the characteristic of a particular stage of the forest. Along with the age growth, the vertical structure will be changed at different growth stages. How the expression of the vertical stand structure characteristics dynamically will be the focus of future research. In the stand, in-depth research is required for different species reach various forest layer heights and the time for the formation of the existing vertical hierarchy.

Key words: Larix gmelinii, over cutting forest, multi storied uneven-aged stand, vertical structure, succession trend