| Improving forest quality,maintaining the long-term productivity of plantation and other ecosystem services,improving forest species diversity and enhancing the ability of plantation to resist climate change and natural disasters have become the strategic needs of the construction of ecological civilization in China.In this study,the Pinus massoniana plantation in Huaying City,a low mountain area of eastern Sichuan,was taken as the research object.Three crop tree densities of 100,150,200 trees /hm~2 and gaps of 50,100,200,667 m~2 were used as natural restoration,supplemented by setting up control stands.After 3 years of implementation,In October 2018,two close-to-nature management modes were studied on plant diversity,niche breadth,niche overlap and soil physical and chemical properties of Pinus massoniana plantation under different treatments.The results are as follows:(1)The crop tree management had a significant effect on the plant species richness of the shrub and herb layer under the Pinus massoniana plantation.Compared with the control,a large number of new species appeared in the crop tree treatment.With the increase of the degree of treatment,the shrub layer diversity index of Pinus massoniana plantation increased significantly.Compared with CK,the pielou index of shrub layer decreased significantly in the crop tree management with the crop tree density of 100 trees / hm~2 and 200 trees / hm~2.The crop tree management had a significant impact on each index of plant diversity in the herb layer of Pinus massoniana plantation,showing an increasing trend.The dominant species of shrub layer under different management measures were different,but there were overlapping dominant species.Cinnamomum camphora L.,Mallotus barbatus,Quercus serrata,Litsea pungens and Ficus pandurata were dominant in the four samples,indicating that these species have a better ability to utilize various resources than other plants in the current ecosystem.Under the crop tree management of shrub layer,the degree of niche overlap between 100 trees /hm~2 and 150 trees /hm~2 was not high compared with that among the main populations of CK,while the niche overlap among shrub species under 200 trees /hm~2 was larger,indicating that this treatment had higher similarity in resource utilization and higher degree of sharing of environmental resources.There was no significant difference in the niche breadth of the dominant species in the herb layer,showing that the dominant species had the same ability to utilize the current resources.The niche overlap index of dominant species in herb layer under each treatment was relatively small,indicating that herbaceous plants almost occupy space environment resources independently,there is no competition,and only form their own local growth advantage.(2)The crop tree management had a significant effect on the physical and chemical properties of the topsoil of Pinus massoniana plantation.Compared with the control,there were significant differences in soil organic matter content,soil available phosphorus content,soil hydrolyzed nitrogen content,soil available potassium content,soil moisture content and soil bulk density,which were closely related to the plant diversity index of shrub and grass layer(P < 0.05).The principal component analysis of crop tree management on soil physical and chemical properties and plant diversity of Pinus massoniana plantation was 200 trees /hm~2 > 100 trees /hm~2 > 150 trees /hm~2 > CK.The results showed that all kinds of crop tree management significantly improved the surface soil physical and chemical properties and plant diversity,among which the treatment with crop tree density of 200 trees / hm~2 played the most prominent role in giving full play to the ecosystem service function of Pinus massoniana plantation.(3)After the transformation of the forest gap,the plant species in the shrub layer of Pinus massoniana plantation increased,and the dominant species in the shrub layer were Cinnamomum camphora,Aralia chinensis L.,and Urena lobata Linn.,and the pteridophytes accounted for a large proportion under the herb layer.The gaps of Pinus massoniana plantation had a significant effect on each index of plant diversity in shrub layer.The simpson index and pielou index of herb layer were significantly lower than LCK,richness index and shannon-wienner index were significantly higher than LCK.Cinnamomum camphora and Aralia chinensis L.used to be the dominant species under five different treatments,and occupied a certain niche breadth under their respective treatments.There was no obvious law between niche breadth and niche overlap.Species with larger niche breadth not only had larger niche overlap,but also had smaller niche overlap,so niche overlap could not be determined only by niche breadth.Most of the shrubs were in small niche overlap,and the proportion of high niche overlap in treatment100 m~2 and 200 m~2 was higher than that of the control.Arthraxon hispidus occupied an important position in 50 m~2 treatment,100 m~2 treatment and 667 m~2 treatment,indicating that this herb was the main dominant species in the study area,had strong environmental adaptability and occupies most of the available resources.The total niche overlap of dominant species in the herb layer of Pinus massoniana plantation was lower than that of CK,in small gap(50 m~2 treatment)and large gap(667 m~2 treatment),and higher than CK in middle gap(100 m~2 and 200 m~2 treatment).(4)There were significant differences in soil p H,soil organic matter content,soil hydrolyzed nitrogen content,soil available potassium content,soil moisture content and soil bulk density under different gaps of Pinus massoniana plantation.The diversity of shrub layer was mainly driven by the content of soil available potassium,and soil bulk density also significantly affected the Simpson index,pielou index and shannon index of herb layer.Pielou index of herb layer was positively correlated with soil available potassium content and soil moisture content,shannon index of herb layer was closely correlated with soil organic matter content and soil hydrolyzable nitrogen content,and soil moisture content was only positively correlated with simpson index and pielou index of herb layer.The comprehensive expression of soil physical and chemical properties and plant diversity in different gap treatments of Pinus massoniana plantation was 200 m~2 >100 m~2 > 50 m~2 > 667 m~2 > LCK,which indicated that the gap transformation had obvious improvement on soil physical and chemical properties and undergrowth plant diversity,among which the gap with 200 m~2 size had the best performance.To sum up,close-to-nature management not only improved the plant diversity of shrub and herb layer,but also significantly changed the plant community structure,promoted the development of the whole community to a more stable structure,and improved the physical and chemical properties of surface soil.These research results provide theoretical support and technical guidance for improving the ecosystem service function of Pinus massoniana plantation and realizing the accurate improvement plan of forest quality.The results showed that both crop tree management and forest gap can significantly improve the plant community and environment under Pinus massoniana plantation,but the crop tree density was 200 trees / hm~2,gap area was 200 m~2 treated Pinus massoniana plantation had the best performance in shrub and herb layer’ plant diversity,niche distribution and internal environment,which improvement could cultivate an environment that was more suitable for plant growth than other treatments.It was suggested that 200 trees/ hm~2 should be implemented under similar conditions,and the gap area of 200 m~2 was the best gap size. |
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