| The Baili Rhododendron has the most concentrated wild Rhododendron community in the world,but the natural regeneration of the rhododendron community is very difficult.Forest gap disturbance is an important type of disturbance in the process of forest renewal and succession.To understand the impact of forest gap disturbance on the natural regeneration barrier of natural rhododendron forest in Baili Rhododendron National Forest Park,Guizhou Province.In this study,the forest gaps of wild Rhododendron community of Pudi and Jinpo scenic spots in Baili Rhododendron were the main research object,and the forest was the main control group.Based on the field investigation and plant resource survey and sample collection and analysis,the multivariate statistical analysis was used to analyze and compare the plant species diversity and environmental factors between the forest gap and closed canopy.The effects of environmental factors on the diversity of forest plants in natural Rhododendron forest were also analyzed.Through the field artificial assisted natural regeneration under the closed canopy and forest gap,the seeds of the orychophragmusviolaceus seeds were planted,the seedings in the forest were analyed,and the influence of environmental factors on the growth process of the orychophragmusviolaceus was analyed.Meanwhile,the distribution characteristic of wild Rhododendron seedings under the different forest gaps and closed canopy were investigated.The main results of this study are as follows:(1)There are a large number of forest gaps in the natural rhododendron forest of study area,and the number of forest gaps with an area of less than 50m~2is the largest,their main reason for the forest gap is artificial.The light intensity of natural rhododendron forest was as follows:forest gap>forest gap edge>closed canopy,and the soil surface temperature of forest gap was forest gap>forest gap edge>closed canopy.The litter thickness showed the variation characteristics of the closed canopy>forest gap>forest gap edge.The rhododendron seedlings formed by fruit germination in the forest gap were mainly germinated and updated,followed by the germination renewal of the stump.The Margalef index and Simpson index of plants in different size scale gaps were significantly larger than those closed canopy.The Margalef index,Simpson index,Shannon-Weiner index and Pielou evenness index of the gap plants with an area of more than 300 m~2were the largest,and both significantly larger than the forest gap edge and closed canopy.Soil p H value,forest gap size,soil moisture content,and forest gap topsoil slope were significantly correlated with the Shannon-Weiner index and the Pielou evenness index.(2)The contents of soil TP,TK and AK in different gaps with slope position and slopes were increased in the natural rhododendron forest;the soil AK content in the small forest gap increased significantly,and the soil C/P ratio in the closed canopy decreased significantly.The soil AK content was significantly higher in the mid-slope position forest gap,but the soil C/P ratio was lower.The contents of soil TP and AK in the surface soil of the mid-slope forest gap increased significantly,and the soil C/P ratio decreased.Soil p H and AK are the most important variables affecting the spatial distribution of soil properties,followed by TP.Soil p H,Ca and altitude are important environmental factors that determine the spatial distribution of small forest gap species.Soil Na,TK,TP,Mg and p H have a greater impact on the closed canopy.(3)Compared with the national soil environmental quality(GB 15618-2018)screening value,The average content of Cd in the soil of small gap is 1.53 times of the screening value of soil environmental quality,and the closed canopy is 1.47 times of the screening value.The content of Cd in the soil of small forest gap samples exceeded the rate of 27%closed canopy.Forest gap interference promoted the enrichment of Hg and Cd in the surface soil of the forest area,and the ecological risk is high.The comprehensive potential ecological risk of forest gaps is higher than that of closed canopy.(4)The investigation found that the rhododendron seedlings formed by seed germination in the forest gap accounted for 97.65%of the total number of seedlings of rhododendron,and the artificially sown orychophragmusviolaceus germination seedlings accounted for 72%of the total.The number and distribution of seedlings in the gap are affected by the size of the gap and the slope of the surface soil.The number of seedlings of Rhododendron and Orychophragmusviolaceus in the forest gap with an area of less than 50m~2is relatively large,which is 56.34%and 62.83%of the total,respectively.The surface soil temperature and light intensity in the area of less than 50m~2forest gap are smaller than the area more than 50 m~2.The p H,water content and slope of the surface soil in the area more than 300 m~2forest gaps were significantly larger than those of closed canopy.The number of rhododendron seedlings formed by fruit germination in the forest gap was medium grade>steep slope>gentle slope,and the number of steep slopes in the forest gap was the highest,accounting for 56.31%of the total number of seedlings of gap and closed canopy.The surface soil temperature and the light intensity of the forest gap of different slope forests were significantly higher than that of the closed canopy,and the surface litter in the gentle slope and steep slope was significantly lower than that of closed canopy.(5)The slope aspect and slope position of the forest gap also affect the number and distribution of the seedlings of the forest gap.The number of seedlings of the wild rhododendron forest in the sunny slope aspect is 13.33 times that of the shady forest gap,and the number of the orychophragmusviolaceus seedlings in the sunny slope aspect is 7.93 times that of the shady slope gap.The soil temperature,p H value,surface litter thickness,light intensity,surface soil temperature difference and light intensity difference of the sunny slope aspect forest gap were lower than those of the shady slope aspect forest gap.The light intensity and soil temperature of the forest gap surface soil were significantly higher than those of closed canopy.The number of rhododendron seedlings in the forest gap was the highest in the mid-slope position,while the number of orychophragmusviolaceus seedlings in the forest gap was the highest in the downhill,which was 60.86%of the total number of orychophragmusviolaceus seedlings.The p H value of the surface soil of the downhill forest gap is significantly higher than that of the uphill and downhill gap.The surface soil temperature of the mid-slope position forest gap is significantly higher than that of the upper slope and the lower slope position gaps.The surface soil temperature and light intensity of the upslope and mid-slope forest gaps were significantly higher than those closed canopy.The thickness of litter in different sizes,forest soil surface slope and slope aspect of gap is significantly lower than that of closed canopy.The formation of forest gaps promoted the germination and seedling growth of Rhododendrons and orychophragmusviolaceus seedlings in the gaps,indicating that the experiment of simulating the rhododendron buds through the orychophragmusviolaceus orchid has achieved good results. |
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