| Robinia pseudoacacia is a deciduous tree of the genus Robinia in the leguminous family.It was widely introduced and planted in the Taishan area in the 1950s and 1960s,and is one of the main tree species in the Yaoxiang Forest Farm of Shandong Province.R.pseudoacacia is a kind of light-loving,fast-growing,and strong ability of root tillering regeneration tree species.Due to the strong wind caused a large number of locust collapsed in the Yaoxiang forest farm,forming a large number of different areas of the gap.How will the microhabitat change after the gap is formed?What is the effect of this micro-habitat change on the regeneration of R.pseudoacacia?In order to solve this problem,this study in different size,different years of acacia wind fallen tree gap as the research object,the adjacent self-cultivating forest was divided into control,investigation of soil nutrients and micro climate,were locust seedling and update distribution,the purpose is to investigate the gap size,the influence of the formation time of microenvironment were,revealed the main influencing factors of acacia update,To provide basic data and theoretical basis for reasonable vegetation protection and restoration.The main research results are as follows:1.R.pseudoacacia regeneration in different canopy gapsWith the increase of gap area,the height(18.83cm,7.3cm)and density(5297 plants/hm~2and 3523 plants/hm~2)of black locust sprouts and seedlings in gaps increased significantly(p<0.05),and the regeneration of large gaps was significantly better than that of medium and small gaps and closed stands.With the increase of gap formation age,the regeneration of R.pseudoacacia seedlings in gaps became significantly worse.In gaps formed in 2019,the height(19.2cm,8.1cm)and density(4851 plants/hm~2,3817 plants/hm~2)of R.pseudoacacia seedlings and seedlings were the highest,which were significantly higher than those formed in gaps in 2000 and 1980.In different gaps,R.pseudoacacia seedlings were concentrated in the pits formed by uprooting and falling trees(83%),and R.pseudoacacia seedlings were concentrated in the middle of the gap(45%)and half of the gap(53%),and mainly located in the front of the area where R.pseudoacacia wind fell trees.Based on SSR molecular markers and root digging method,it was found that the regeneration of bud seedlings was mainly due to the sprout regeneration of wind-blown trees.The results showed that large gaps were more suitable for the regeneration of R.pseudoacacia in the range of 56～225 m~2.2.Influence of latest canopy gap size on microclimateDuring the growing season(July to September),light intensity(16465lx),air temperature(25.95℃),soil temperature(23.08℃)and air humidity(69.7%)were the highest in the large gap.In the gap position,from the center to the edge,light,air temperature and soil temperature decreased significantly(p<0.05).In terms of gap spatial distribution,the central region has the best photothermal conditions and poor humidity,while the northern region has better photothermal conditions than the southern region,and the humidity is opposite.3.Influence of gap size on soil physical and chemical propertiesThe contents of total nitrogen,ammonium nitrogen and nitrate nitrogen in 0-10cm and10-20cm soil layers in large gaps were higher than those in medium and small gaps and closed stands,and the contents of total phosphorus and available phosphorus in different soil layers were lower than those in medium and small gaps and closed stands.There were significant differences in the contents of other soil chemical elements except total nitrogen in the late and middle gaps of different sizes(p<0.05).The contents of other soil chemical elements decreased with the increase of soil depth,except pH.In the late period,the spatial distribution of soil chemical elements was as follows:the contents of nitrogen and organic matter were high in the central area of the gap,the contents of phosphorus were high in the edge area,and the spatial distribution of pH and available potassium were not obvious.4.Main influencing factors of late R.pseudoacacia regenerationAccording to Pearson correlation analysis,the regeneration density of R.pseudoacacia in the late forest gap was significantly positively correlated with light intensity,nitrate nitrogen and ammonium nitrogen(r=0.863,r=0.861,r=0.862),and negatively correlated with total phosphorus and available phosphorus(r=-0.793,r=-0.748).There was no significant positive correlation with total nitrogen,organic matter and available potassium,and no significant negative correlation with pH.Principal component analysis showed that the most important factors affecting the regeneration density of R.pseudoacacia in the gap were light intensity,nitrate nitrogen and ammonium nitrogen,followed by soil temperature,air temperature,organic matter and pH.In conclusion,among the many influencing factors,light intensity,ammonium and nitrate nitrogen may have a certain promotion effect on the regeneration of R.pseudoacacia in the late gap,while total phosphorus and available phosphorus may have a certain restriction effect on the regeneration of R.pseudoacacia in the late gap. |
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