| A plant community is an assemblage of plant populations that live in certain area, and interact with and adapt to one another in the context of long-term environmental changes. Plant communities play a critical role in regulating terrestrial ecosystem functions. It provides the main physical resources for human beings to survive and develop, and provides food and habitat for wildlife. At present, vegetation resources and biodiversity are under great threat from the rapidly expanding population and the development of economy, and the excess exploitation and unreasonable utilization of vegatation resources. Therefore, conducting systematic plant community inventories to understand current conditions of vegetations, predicting the responses of vegetations to global climate changes and developing sound conservation and management strategies have become imperative.Shandong Province has a long history of vegetation exploitation and suffers from serious natural or man-made disturbances. There are many questions need to be answered. For instance, what kind of plant community types in Shandong Province? what is species composition of these plant communities and where are they distribution? What are the spatial patterns of plant diversity? How to protect plant communities, and so on. We conducted systematic field investigation using unified method in Shandong Province. In this study, we conducted systematic field investigation using unified method and technical specification. A total of 1107 plots were sampled, including 245 plant community types. This paper studied the species composition, species diversity and community structure of main plant communities in Shandong Province. We explored the vertical and horizontal patterns of plant diversity and its potential causes, offering comprehensive information as scientific basis for the conservation and utilization of vegetation resources in Shandong Province. The main conclusions in this paper are as follows:In Shandong Province, the flora is complex in geographical elements, having 15 areal types. It is obvious that temperate elements play important roles in ShandongProvince and the proportion of tropical elements is high. By comparing the geographical elements of the flora in hilly areas of central south of Shandong Province, hilly areas of eastern of Shandong Province and plain areas of west and north of Shandong Province, we found that the proportion of tropical elements is higher in plain areas of west and north of Shandong Province than in other two areas. The reason caused this phenomenon may be that the heat conditions in plain areas of west and north of Shandong Province is better than other two areas. In addition, the number of Chinese endemic species is higher in hilly areas of eastern of Shandong Province than other two areas. This phenomenon is due to the special geographic position and historical forming process in hilly areas of eastern of Shandong Province.The forest communities of Shandong Province were distributed mainly in hilly areas of central south and eastern of Shandong Province. The common coniferous forests of Shandong Province were Pinus densiflora community, Pinus tabuliformis community, Platycladus orientalis community, Pinus thunbergii community and so on. The common broad-leaved forests of Shandong Province were Quercus acutissima community, Quercus variabilis community, Robinia pseudoacacia community etc. The shrub communities were scattered across Shandong Province. The common shrub communities in hilly areas of Shandong Province were Vitex negundo var heterophylla community, Lespedeza bicolor community, Ziziphus jujube community, Indigofera kirilowii community etc. Native Tamarix chinensis community was mainly distributed in Yellow River Delta. The meadow type of Shandong Province can be classified into three types, mountain meadow, plain meadow and salt meadow. The common mountain meadow are Imperata cylindrica community, Zoysia japonica community, Themeda japonica community etc, often distributed in mountaintop and open area of forest edge. The common plain meadow were Cynodon dactylon community, Phragmites australis community, Paspalum paspaloidesn community etc, often distributed in flood land and lakeshore. The common salt meadow were Aeluropus sinensis community, Suaeda salsa community, Limonium bicolor community etc, often distributed in coastal saline areas. Comparing species diversity of major forest communities in Shandong Province, found that herb richness under Quercus acutissima and Quercus variabilis forests was significantly lower than other forest communities. Quercus acutissima and Quercus variabilis were broadleaf deciduous trees, with higher canopy density and insufficient light in the understory. In addition, the thicker ground litter in Quercus acutissima community and Quercus variabilis community was unfavorable for herb plants update and growth, which results in lower herbs richness. Comparing species diversity of major shrub and meadow communities in Shandong Province, found that species diversity was low in Tamarix chinensis and Suaeda salsa communities. Tamarix chinensis and Suaeda salsa communities were mostly found in saline and alkaline land. Habitat conditions are relatively poor, only salt-tolerant plants can survive in this habitat. We compared the structures of diameter class of major tree populations in Shandong Province. The diameter class distribution of Quercus acutissima, Quercus variabilis, Robinia pseudoacacia and Pinus thunbergii communities showed the "L" form, indicating good community regeneration. The diameter class distribution of Platycladus orientalis and Larix kaempferi showed unimodal pattern, indicating bad community regeneration. The plant communities of Shandong Province are in a steady positive succession and developing to deciduous broadleaf forests. We analyzed the relationships between species composition and environmental variables found that temperature and precipitation are main environmental factors affecting species distributions.We explored the altitudinal patterns of plant species by using phylogenetic and traditional diversity analyses in combination. We found that total species richness had a monotonically decreasing pattern and tree richness had a unimodal pattern along the elevation gradients in the two study areas. However, altitudinal patterns in shrub richness and herbs richness were not consistent on the two mountains. Plant communities in high elevation locations above 1250 m exhibited significant phylogenetic clustering, which demonstrates that environmental filtering is the main driver of plant community assembly at high elevations. At low elevations, plant communities may have been affected by multiple factors simultaneously and did not display a uniform phylogenetic structure. Shrubs and herbs in understory layers were more sensitive to changes in microenvironment, such as human disturbance and canopy density. Phylogenetic beta diversity and species beta diversity consistently increased with increasing altitudinal divergence for different plant groups in the two study areas. However, the altitudinal patterns of species richness did not completely mirror phylogenetic diversity patterns. Conservation areas should be selected taking into consideration the preservation of high species richness, while maximizing phylogenetic diversity to improve the potential for diversification in the future.We examined the variation in alien and native plant richness and composition along the elevation gradient to explore the invasion mechanisms of alien species in mountain forests. In contrast to native plants, which presented two different richness patterns along the elevation gradient on Mount Tai and Mount Lao, alien species richness presented a consistent decreasing tendency with increasing elevation, suggesting that mechanisms driving native and alien species richness may be different. While native plants had many specialists at high altitudes and presented an obvious change of chorological groups along the elevation gradient, most alien species distributed in high altitude areas also occurred at lower elevations. All findings indicated that the invasion process in mountain forests is from great majority of alien species that are introduced at low altitude, successively filtered out by worsening climatic conditions and decreasing anthropogenic propagule pressures along the elevation gradient, and a subset of this community spreads upward to high altitude areas. We conclude that approaches of monitoring and managing alien plant species should focus on low elevation areas of mountain forests to prevent invasions of high elevation areas.Total species richness exhibited an inverted unimodal pattern along the latitude in mountain forests of Shandong Province. Minimum species richness occurred at 36.5° north latitude. This phenomenon is due to special geographic position of Shandong Province. The majority of mountains above 36.5° north latitude located at the eastern of Shandong Province. The eastern of Shandong Province is surrounded by the sea on two sides. The weather is often mild and moist, which is in favor for the survival of plants. Total species richness presented monotonically decreasing pattern from low to high longitude. These results proved that the hilly areas of eastern ofShandong Province with high biodiversity. We found that species composition similarity decayed with environmental divergence and geographic distance increased. However, the effects of environmental divergence on species turnover were more significant than geographic distance. The results suggested that the combined impact of environmental filtering and spatial processes influenced community assembly in Shandong Province. But, environmental filtering is a dominant factor. |
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