The Effect Of Tending On The Undergrowth Vegetation Biodiversity Of Pinus Tabulaeformis Plantations In The Loess Plateau

Biodiversity has played an indelible role in the survival and development of human beings.As the largest ecosystem on land,forest ecosystems,compared with other ecosystems,have rich species diversity,complex spatial structure and powerful ecological functions.In order to protect natural forest resources and satisfy human's production,life and spiritual needs,a lot of defective plantation cultivation has been carried out in recent decades.The restoration of understory vegetation biodiversity has become one of the main objectives of forest management in the present plantation.More and more studies show that maintaining the biodiversity of understory herb and shrub layers plays a crucial role in improving the overall function of the whole forest ecosystem.The geographic environment is special on the Loess Plateau,which has resulted in the poor availability of effective understory tending measures.In previous studies,the diversity of understory vegetation was compared mostly after 3 years or even longer duration of different tending intensities.However,there are few studies on the variation of the vegetation diversity after one year of tending.And previous studies on changes of understory vegetation diversity in post-tending forests have mostly focused upon species diversity,but rarely upon functional diversity.The present study is the first time to investigate the changes of understory vegetation biodiversity after one year of tending from the perspective of functional traits and functional diversity.We discussed the influence of tending on functional traits and functional diversity of understory vegetation by analyzing the effects of tending on species richness,species diversity,functional traits,functional richness,functional evenness and functional divergence of understory herb and shrub layers.We explicated the influence of tending on the understory vegetation in the artificial forest ecosystem of the Loess Plateau and hoped to explain the regeneration of the understoty vegetation and the function of the ecosystem better from the perspective of functional diversity.It not only laid a foundation for long-term follow-up study of forest biodiversity after tending,but also provided an example reference for the study of influence of tending on functional diversity of understory vegetation.And the results of this study have vital practical significance for tending management of Pinus tabuliformis plantation,and also provide theoretical basis for the regeneration,succession and development of artificial forest ecosystem.(1)Under the tended forest,the soil temperature,humidity,salinity and ISF under forest were improved.The soil temperature,soil moisture and soil salinity under the tended forest were all higher than that under the non-tended forest.The strength of sanitation cutting is smaller than that of thinning,which only improves the ISF(Indirect Site Factors).Cleaning the understory shrubs and herbs was beneficial to the accumulation of soil moisture and nutrients.The surface temperature of soil under forest was also slightly increased with the increase of ISF.(2)Tending improved the species diversity of the herb layer,but had no significant effect on the shrub layer.The tended forest has better conditions of light,water and heat,and provided more available resources and growth space for understory vegetation.Therefore,species richness index and the Shannon-Wiener index of the herb layer in the tended forest were significantly higher than that in the non-tended forest.But the effect of tending on the shrub layer was not significant.On the one hand,the root of shrub was not planed.When the species investigation was carried out,many sprouting branches had been sprouted at their roots,resulting in no significant difference in species richness and diversity of shrub layer.On the other hand,the growth characteristics of herbs and shrubs were closely related to the diffusion mechanism of herbs and shrubs at the initial stage of community reconstruction.(3)The effects of tending on the functional characters of the leaves of the herb layer were very significant,but the influences on the shrub layer were not obvious.Area of a leaf(LA),leaf dry-matter content(LDMC),leaf thickness(Lth)traits in the tended forest were higher than those in the non-tended forest.The improvement of soil and water conditions reduced the competition among species,thus LA and Lth in the tended forest were significantly higher than those in the non-tended forest.The effective accumulation of nutrients increased the LDMC significantly.The specific leaf area(SLA)is positively related to the potential relative growth rate(RGR)of the plant.The SLA of the understory herb layer was significantly less than that of the non-tended forest,indicating that the resources of the herb layer under the tended forest were not fully utilized enough to provide more plants to growth.The Lth in the tended forest was significantly greater than that in the non-tended forest.The results showed that the effects of tending on the herb layer under the plantation of Pinus tabuliformis were more effective than that of the shrub layer.On the one hand,it is related to the chance of species random intrusion(Random Niche Hypothesis),which will be occupied by a large number of one year species in the early stage.On the other hand,tending does not exert a great influence on environment under the forest,and it is not enough to affect the growth of shrubs.(4)Tending increased FRci of LA,SLA and Lth in the herb layer,FRO of SLA and LDMC,and also increased FRci of Lth,and FDvar of SLA in the shrub layer.And tending raised FEve and FRic of the herb and reduced the FEve and FDiv of the shurb.Functional richness(FRci)of LA,SLA and Lth of the herb layer in the tended forest were significantly higher than that in the non-tended forest,and Fci of Lth of the shrub layer in the tended forest were significantly higher than that in the non-tended forest,indicating that the improvement of the richness of LA,SLA and Lth in the herb layer and Lth in the shrub layer were in their single niche space.The results show that the community productivity was higher,and the niche space of the community was also more stable.Functional regularity(FRO)of SLA and LDMC of the herb layer in the tended forest were significantly lower than that in non-tended forest.The result shows that SLA and LDMC of the herb layer in the tended forest occupied by the distribution of niche space the evenness was lower than that in the non-tended forest.There were niche space and the use of space to spread the other species and promote forest vegetation renewal and growth.Functional divergence(F Dvar)of SLA of the shrub layer in the tended forest was significantly higher than that in the non-tended forest.The result indicates that SLA of the shrub layer in the tended forest had a higher degree of differentiation in its niche space.It indicates that there was less competition among species in the SLA niche space under the tended forest.There were enough resources and spaces to be utilized to growth.For multi-trait functional diversity indices,functional richness(FRic)of the herb layer in the tended forest was significantly higher than that in the non-tending forest and functional evenness(FEve)and functional divergence(FDiv)were significantly less than that in the non-tended forest.The results show that tending improved functional richness of herb layer leaves,but leaves in the functional niche space distribution uniformity and leaves functional traits differentiation were lower than that in the non-tending forest.In other words,the plants under the tended forest had more space and more resources.FEve of the shrub layer in the tended forest was significantly higher than that in the non-tended forest.The result shows that the distribution of leaves characters in the shrub layer under the tended forest was even higher in the functional space.(5)ISf was the main factor affecting the functional diversity of the herb layer,while soil condition was the main factor that affects the functional diversity of the shrub layer.The environmental factors that influence the functional diversity index of the herb layer and the shrub layer were different.ISF significantly affected FRci of LA and Lth and FDiv in the herb layer.ST significantly affected FRci of SLA and FRic and FEve in the herb layer,and the FRci of SLA in the shrub layer.