Community Structure And Natural Regeneration Of Natural Yunnan Pine Forest In Middle Yunnan, China

Based on pure Yunnan Pine (Pinus yunnanensis) forest (PPY)and mixed Ynanan Pine forest(MPY) after long enclosure for restoration, which distributed on dark-red soil(D), yellow-red soil(Y) and red soil(R) respectively with the same site conditions and located the south to west aspect at the elevation of 2200-2450m in Diaolinshan Natural Reserve, Middle Yunnan Plateau, Yunnan, China, as well as natural second-growth forests at different regeneration ages after selective logging, the characteristics of species composition, plant diversity, community structure and natural regeneration, together with dominant tree species'population dynamics, soil properties in PPY and MPY, growth rates and leaf stoichiometry of P. yunnanensis in different soils and communities were studied by representatively sampling. The main results indicate as follows:(1) The number of plant species in communities was in the order of D>R>Y. In dark-red soil, most of species were the family of Gramineae, Rosaceae, Compositae, Papilionaceae and Ericaceae, and the species of the family of Theaceae, Fagaceae and Aquifoliaceae increased in MPY apparently. Compared with dark-red soil, the number of species on yellow-red soil decreased by over 40%, but the species of Ericaceae and Fagaceae increased in MPY apparently. As for the red soil, the number of genus and species increased apparently in PPY, especially those of Gramineae and ferns increased apparently, but that of Compositae decreased relatively. P. yunnanensis was the dominant tree species in all communities with the highest important value. Other dominant tree and shrub species were partly attached to subtropical semi-humid evergreen broad-leaved forests to some extent, and the dominant species of Fagaceaea showed species replacement phenomena on different soils, namely Lithocarpus leucostachyus on dark-red soil, Quercus acutissima, Cyclobalanopsis delavayi on yellow-red soil, and Q. aliena on red soil. The harmful Eupatorium adenophorum invaded and occupied the herb layers in all communities and did little harm to forests on yellow-red soil.(2) Species richness in all layers showed significant difference among different communities. MPY on dark-red soil and PPY on yellow-red soil presented the highest values in tree layer, whearas MPY and PPY on dark-red soil were the highest in shrub and herb layers. Shannon-Wiener index of 3 layers showed significant difference with the same tendency of D>R>Y, but no constant order between MPY and PPY. Simpson index indicated the order of MPY>PPY in tree layer and D>R>Y in shrub layer, and Pielou index showed significant difference in tree and shrub layers.(3)Mean DBH of all trees was in the order of D>R>Y and PPY>MPY. Mean DBH of P. yunnanensis showed the tendency of D>Y>R in PPY, but indiceted the order of D>R>Y in MPY. The density of P. yunnanensis stumpage presented the tendency of PPY>MPY and R>Y>D, and total BA was in the order of MPY>PPY and D>Y>R. It was clear that soil total N changed along the gradients of MPY>PPY and D>R>Y. The ratio of C/N was changed as D>R>Y, and that of N/P as MPY>PY slightly, D>Y and R remarkably. Thus it was certain that PY and MPY changed with total N gradient on different soils. Soil total P, available N, available P changed remarkably and played an important role in the distribution of communities.(4) On dark-red soil, the forests were featured as uni-dominant tree of P. yunnanensis and divided into 4 layers. Community height was in the order of MPY>PY. As for yellow-red soil and red soil, the forests were divided into 3 layers, but MPY on yellow-red soil featured as co-dominant trees of P. yunnanensis and Cyclobalanopsis delavayi. DBH distribution types of all tree layer individuals in MPY showed a typical reverse"J"shape and in PY a similar reverse"S"shape. P. yunnanensis population structure in MPY on dark-red and red soils was characterized as constant type, in PPY on red soil as incremental type and others as recessionary type. Except that Keteleeria evelyniana, Cy. delavayi, Q. aliena, Castanopsis delavayi and L. dealbatus in MPY on red soil were featured as interim population type, others characterized as constant or incremental population types.(5) Leaf N of P. yunnanensis showed the same tendency along soil total N gradients. Over 90% individuals were N limited according to the threshold of limiting nutrients. The result of Nr>Pr tendency of leaf nutrient resorption efficiency was contrary to those in most study cases, thus it revealed that Yunnan Pine had higher ability of conserve N nutrient. Height and DBH growth rates showed the tendency of D>Y>R and PPY>MPY, but volume growth rate was in the order of MPY>PPY. There was positive correlation between leaf Nr and soil total N, total P, available N and available K. As for leaf Pr, there was positively remarkable correlation to available K, and positive correlation to soil total N, total P and available N. As far as the growth rates were concerned, HGR and DGR indicated remarkably positive correlation with available N, but VGR showed the same correlation with total N, total P and available N. As a whole, soil total N, available N, bulk density and natural water content affected HGR, DGR and VGR remarkably.(6)Regeneration density in natural forests after long enclosure for restoration revealed the tendency of MPY>PY and D>R>Y. In the meanwhile regeneration density and percentage of Fagaceae, Theaceae and Ericaceae differed significantly among different soils and communities, which may result in different succession tendency and species composition. It was indicated that regeneration density and frequency of P. yunnanensis in PPY and MPY on red soil were higher significantly than those in other communities, but was very poor in other communities. P. yunnanensis ranked the top tree species about regeneration frequency in sparse forest and logging areas, and its seedlings and saplings at different size classes may result in forests with hetero-aged structure. The densities ofâ…£small trees,â…¤small trees andâ… seedlings in second-growth forests after 20 years logging were higher significantly than that of forests after 10 years logging and in sparse P. yunnanensis forest. Understory substrates affected natural regeneration of P. yunnanensis. Over 60% of P. yunnanensis seedlings were found growing on the mineral soil, others were found on forest floor, rock, litter and CWD.From the results above, there are some implications for restoration. Soil total N increment or soil C/N ratio reduction may be proposed to enhance the growth of P. yunnanensis. Fire disturbance regimes may be introduced to create gaps and naked mineral soil in order to facilitate natural regeneration of P. yunnanensis. Thus P. yunnanensis will keep its dominance in communnities at lower costs so that community stability and landscape heterogeneity may be maintained regionally.