Studies On The Regeneration Of Forest Communities In Malan Forest Region On The Loess Plateau

Abstract: 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, 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 prorooting 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, the study on the regenerative characteristics of main canopy tree junior, for example, Quercus liaotungensis and Pinus tabulaeformis etc., the effect of environment on the regeneration of main canopy tree junior, the population dynamics of the dominant species were carried on and got the results as follow:1. Q. liaotungensis seedlings widely distributed at seven typical vegetation types in Malan forest region on the Loess Plateau. The density of Q. liaotungensis seedlings: Q. liaotungensis forest＞P. tabulaeformis+Q. liaotungensis mixed forest＞P. tabulaeformis forest＞P, tabulaeformis+B. platyphylla mixed forest＞B, platyphylla forest＞B. platyphylla+P. davidian mixed forest＞P. davidiana forest; Q. liaotungensis were composed of both individuals from seedling and sprout. It formed the strategy of double regeneration. The densities of seedling crops were higher than that of sprout crops in all vegetation types. Its regeneration would rely mainly on seedling crops. The quantity of P. tabulaeformis seedlings was lower than that of Q. liaotungensis seedlings, but relatively abundant in the P. tabulaeformis+B, pIatyphylla mixed forest, P. tabulaeformis forest and P. tabulaeformis+Q. liaotungensis mixed forest. The spatial distribution patterns of Q. liaotungensis and P. tabulaeformis junior were all clump distribution. There were different extents of clump with different species and life stages. The seedlings of B. platyphylla and P. davidiana were lack. They had no the ability of normal regeneration. Because of widely distribution and strongly adaptation, It refer to Acer ginnala as main accompany canopy tree of artificial reforestation.2. The abiotic and biotic factors including light, water and shrub and herbaceous cover influenced the scope and richness of dominant species juniors in Malan forest region. The canopy gaps played an important role in the regeneration of plant community. But there were the difference on gap regeneration of different species. Q. liaotungensis seedlings occurred more likely in the gaps, suggesting that gaps might be contribute to the regeneration of this species. Therefore, it seemed that the regeneration of seedling bank under the canopy was as important as the gap regeneration as a strategy to maintain the stability of Q. liaotungensis population. P. tabulaeformis renewal was inferior. A. ginnala and A. grosseri juniors were more inclined to occupy the forest floor under the canopy, due to their strong shade tolerance and/or shade avoidance. Juniors bank was a main strategy for regeneration of A. ginnala and A. grosseri. In terms of regeneration strategies, the key to understanding the coexistence of the principle co-occurred species were different regeneration niches including other factors such as the different ecological properties of the juniors.3. The densities of Q. liaotungensis juniors were higher that of P tabulaeformis juniors on all slop aspect. The densities of Q. liaotungensis and P. tabulaeformis adults were close. Q. liaotungensis mainly distributed on northeast and northwest slope aspect. P. tabulaeformis mainly distributed on northeast slope aspect. Slope direction, the density of tree, litter thickness and the fertility of soil were the relative dominant factors to influence the distribution and regeneration of Q. liaotungensis and P. tabulaeformis. These factors had different effect on the different species and life history stage. On the one hand, we must pay attention to the slope aspect in the restoration of vegetation on the Malan forest region. On the other hand, we must notice the density of reforestation.4. The size structure of Q. liaotungensis population was clear difference among different vegetation types. In the P. tabulaeformis+Q, liaotungensis mixed forest and the Q. liaotungensis forest, the size structure of Q. liaotungensis population was characterized by a stationary type. Whereas, the size structure of population tended to be a growing type in the P. tabulaeformis forest, P. tabulaeformis+B, platyphylla mixed forest, B. platyphylla forest, P. davidiana forest and P. davidiana+B. platyphylla mixed forest. The size structure of P. tabulaeformis population was characterized by a stationary type in these vegetation types. The size structure of P. davidiana and B. platyphylla population tended to be declining type. The vegetation type of dominating B. platyphylla and P. davidiana would be displaced with that of dominating P. tabulaeformis and Q. liaotungensis. In Malan forest region on the Loess Plateau, these indicated that Q. liaotungensis have an important effect on the restoration of natural vegetation in this region; P. tabulaeformis population would play an important role in the restoration of vegetation from the past to the future in this region.5. The static life table analysis showed that the peak mortality appeared in the stage of juniors. It became stability in the stage of middle and end. Due to all kinds of causes (human disturbance), there had higher vanishing rate. The mortality and survival rate was the reciprocity result of interior change of population and exterior environment. So, we should protect not only biology but living space. The theory of survival analysis indicated that the survival curves of Q. liaotungensis and P. tabulaeformis all tended to be the type DeeveyⅡ. The spectral analysis showed that the regeneration of Q. liaotungensis and P. tabulaeformis population was slow. As a whole, forest cover in Malan forest region was the stage of restoration after longer disturbing and destroying. The dominant species of the end stage of succession had good regenerative potential.In our study, Q. liaotungensis community was the climatic climax in Malan forest region. This conclusion might have been decided by the seedling stage of Q. liaotungensis. P. tabulaeformis could regenerate well, had good population structure and could reach the stability. P. tabulaeformis forest and P. tabuIaeformis+Q. liaotungensis mixed forest had the biological and environmental condition of longer existence in Malan forest region. P. tabulaeformis plantation or artificial P. tabulaeformis in Q. liaotungensis forest could accelerate the restoration of vegetation. The key problems of vegetation restoration were to choose the appropriate plantation density.