Ziwuling Forest Communities In Forest Gap Characteristics Of Species Updated

It is imperative under the situation to accelerate the recovery and restoration of degenerative ecosystem on the Loess Plateau, because the ecosystem is seriously degraded due to soil and groundwater depletion. Malan forest region, which is located at the south tip of Ziwuling Mountain, a relative intact natural secondary forest on the Loess Plateau, is important water conversation and ecological availability forest for loess plateau central area. Malan forest region has crucial effect on adjusting regional climate, maintaining ecological balance and promoting ecologically sustainable economic development on the Loess Plateau. So the research of forest community regeneration has significant ecological meaning for recovery and restoration of degenerative ecosystem.In this paper, through investigation on forest gaps on the Loess Plateau, the study on the forest gap of five main forest community types were studied and analysis, to overall understanding the manner of gap formation, the size of gap, the age structure of gap, and so on .Through further analyzes and contrasts the seedlings and saplings, which are the dominant species Quercus liaotungensis and Pinus tabulaeformis, in response to the canopy characteristic. Thus the mechanisms forest gap disturbance to the regeneration strategies and species diversity dominant species tree can be revealed. And the theory basis of tending, recovery and rational protection also can be offered. The results as follow:1 Through investigation on forest gaps on the Loess Plateau, the size of forest gaps are mainly 20～40m~2 and 40～60m~2 and the quantity and size proportion of 40～60 m~2 are the most. The quantities of forest gaps' age structure are most of prometaphase and after-metaphase, which respectively account for the total number of forest gaps 42.31% and 38.46%. The fell stub account for quite large proportion in the manners of forest gaps formation, which shows the forest gaps are mainly formed by human disturbance in this area. The numbers of forest gaps maker mostly are Quercus liaotungensis and Pinus tabulaeformis, which are mainly made by middle and small diameter.2 The rational forest gap disturbance promote the nature regeneration of dominant species in the area and the two dominant species Q. liaotungensis and P. tabulaeformis have different regeneration strategies and gap promote mechanisms. Q. liaotungensis depend on the high germination rate to guarantee the regeneration number, while P. tabulaeformis depend on the low mortality rate to guarantee the regeneration number. The relation of the seedlings of P. tabulaeformis to forest gap size was expressed in a single peak curve with a peak. And when the gap area is 20～40 m~2, P. tabulaeformis has best nature regeneration. But the nature regeneration of Q. liaotungensis has a more complex condition in different size gap, and with the forest gap size increasing the Q. liaotungensis seedling' promotes will be inhibited and promoted the sapling's growth. But the final of forest gap effect still promotes the nature regeneration of Q. liaotungensis. Although forest gap promote the nature regeneration of dominant species, but this cannot change the dominant status of the Q. liaotungensis and P. tabulaeformis in the Q. liaotungensis forest and P. tabulaeformis forest in a short period. So the Q. liaotungensis and P. tabulaeformis in the Q. liaotungensis forest and P. tabulaeformis forest will exist as the succession climax and subclimax in this area.3 The response of three vegetation's species diversity indices to the forest gap size and development stage were single peak type. When the area are 40～60 m~2, the arbor layer species diversity of forest gaps is higher. While when the area are 20～40 m~2, the shrub layer and herb layer species diversity of forest gaps is higher. In different development stage of forest gaps, the herb layer species diversity of forest gaps is higher when the gap stage is prometaphase, while the arbor layer and shrub layer species diversity of forest gaps is higher when gap stage is after-metaphase. This show that the species diversity index peak values often appear in critical or transition state, and the regeneration level's response was often more sensitive than the upper plant.After the implementation of the Natural Forest Protection Project the recent years in Ziwuling mountain area on the Loess Highlands, the human factor were expressed in a heavy frequency influence on the forest gap and a light intension. This directly caused this area the forest gap disturbance intensity to be small, and this disturbance intensity promote the nature regeneration of two dominant species Q. liaotungensis and P. tabulaeformis at the same time. And it also advantage vegetation's species diversity maintenances. Thus the Q. liaotungensis and P. tabulaeformis in the Q. liaotungensis forest and P. tabulaeformis forest will exist for a long period as the succession climax and subclimax in this area. The P. tabulaeformis best regeneration forest gap area can provided a certain theory basis of reasonable chopping and the artificial afforestation.