Studies On The Distribution Pattern And Formation Mechanism Of Seed Plant Diversity In The Loess Plateau Based On Species Pool In Nature Reserves

The Loess Plateau is a typical ecologically fragile area,and the confluence zone of various flora in China.For a long time,due to the change of natural environment and human disturbance,serious soil erosion has occurred in the region,as well as the natural vegetation has been destroyed,which poses a serious challenge to biodiversity conservation.Nature reserves are a globally accepted strategy for addressing this crisis.Moreover,nature reserves have been protected for a long time,with less human interference,high biodiversity and complete ecosystems.They are also ideal natural experimental sites for studying the formation mechanism of species diversity.At present,scholars have studied the distribution pattern of plant diversity and its influencing factors on a small scale in the Loess Plateau.Plant species data acquisition is mainly through quadrat sampling or species distribution data.However,there are still few studies focusing on the regional scale of the Loess Plateau,which limits our understanding of the plant diversity pattern and formation mechanism of the Loess Plateau at the regional scale.Here,this study analyzes the basic construction of the Loess Plateau Nature Reserves.On the other hand,this study used single factor correlation analysis,multiple stepwise regression and variance decomposition to explore the distribution pattern of seed plant diversity and its main influencing environmental factors in the Loess Plateau based on species richness of seed plants in the nature reserves,as well as their corresponding climate,habitat heterogeneity and human factors.The results of this study provide a scientific basis for the protection of regional plant diversity.The results show as follows:(1)There are 148 nature reserves established on the Loess Plateau,covering an area of581.103×10~4km~2,account for 9.8%of the total land area of the plateau.However,the protected area in the region was still lower than that of China(14.86%by the end of 2017).These 148nature reserves include forest ecology,grassland meadow,desert ecology,inland wetland,wild animals,wild plants,geological relics and paleontological relics.The levels of protected areas are national,provincial,municipal and county reserves.Nature reserves in this region are mainly concentrated in the Qinling Mountains on the southern border of Shaanxi Province,while the overall density in the northwest is relatively low.Moreover,the NDVI value and stability of nature reserves in the southeastern part of the Loess Plateau are higher than those in the northwestern part.(2)The seed plant richness in 108 nature reserves of the Loess Plateau showed that the richness of seed plants decreases from southeast to northwest,and is higher in Qinling Mountains on the southern border of Shaanxi and Henan,and lower in Ningxia and northwest Inner Mongolia.The richness of seed plants ranged from 62 to 1997 species,with an average of642 species.The density per square kilometer was 7.53-207.43,with an average of 64.45.There are also 40 nature reserves without records of seed plant data.It shows that the investigation of species list of nature reserve the Loess Plateau needs to be strengthened.(3)Univariate correlation analysis and multiple stepwise regression analysis showed that hydrothermal and energy factors under climatic factors[precipitation in the driest month(PDM),annual mean temperature(AMT),minimum temperature in the coldest month(MTCM),normalized difference vegetation index(NDVI)],altitude range(Alt.R)and human footprint(HF)are important environmental factors that determine the distribution pattern of seed plant diversity in the Loess Plateau,which indicate that the diversity distribution pattern of seed plants in the Loess Plateau is affected by multiple factors,and they can explain 54%～55%of the variation in the diversity of seed plants in the Loess Plateau.Among them,habitat heterogeneity factors can explain 27%～46%of the variation;while the effect of climate explained about39%～43%.and human disturbance factors can explain 9%～12%.This paper describes the current construction achievements of the Loess Plateau Nature Reserve,and clarifies that habitat heterogeneity factors and climate factors are the main driving factors for the distribution pattern of seed plant diversity in the Loess Plateau.The impact of habitat heterogeneity on species diversity should be scientifically considered and included in the construction of nature reserves on the Loess Plateau and the conservation planning of species diversity.Furthermore,for the large areas in the northwest of the Loess Plateau that lack protected areas,the number of nature reserves can be increased reasonably according to the situation,and attention should be paid to the nature reserves with poor vegetation stability in the northwest to reduce negative human interference.