Disturbance-dependent Variations In Species And Functional Diversity Relationships Across Spatial Scales And Vegetation Layers In Tiantong National Forest Park,Zhejiang Province

Biodiversity is a central topic in ecology,where species and functional diversity are the two main components.Although ecologists typically focus on species diversity or functional diversity differences across forest types(undisturbed forests and human-disturbed forests)and spatial scales,the potential variation in the relationship between species diversity versus functional diversity across forest types and spatial scales is rarely studied.Since species’ functional traits are closely linked to ecosystem functioning,investigating the relationship between plant species and functional diversity can offer valuable insights into biodiversity conservation benefits concerning ecosystem health,functions,and stability,potentially guiding forest management and conservation decisions.The study was conducted at Tiantong National Forest Park in East China’s Zhejiang province.Using sample plots of 10 m × 10 m,20m × 20 m,and 20 m × 100 m,I collected data about overstory woody species(trees and shrubs)and understory non-woody species(herbs)from relatively intact(undisturbed)mature forests and human-disturbed shrublands and plantations.Then,I used seven empirically measured leaf traits(specific leaf area SLA,dry matter content LDMC,leaf thickness LT,leaf succulence LS,leaf carbon LC,leaf nitrogen LN,and leaf phosphorus contents LP)and chose species richness(S),species evenness(Evar),and Shannon-Wiener diversity index(H)as species diversity indices,and functional evenness(FRic),functional evenness(FEve),Rao quadratic entropy index(RaoQ)as functional diversity indices.I employed mixed-effect modeling to assess the dependency of the species and functional diversity relationships(species richness versus functional richness,species evenness versus functional evenness,and Shannon-Wiener species diversity versus RaoQ functional diversity)on disturbance,spatial scale and vegetation layer and further explore the potential roles of community-level functional redundancy,specieslevel functional uniqueness among forests and spatial scales in driving any such dependency.The main results are as follows:(1)Species richness versus functional richness relationships were significantly positive.However,although the relationship varied among disturbed versus undisturbed forests and vegetation layers,it did but not vary among spatial scales of observation.Slopes of the relationship between species richness versus functional richness were generally steeper in human-disturbed shrublands and plantations than in relatively intact mature forests.Meanwhile,slopes of the relationship were steep in woody layers in shrublands and plantations and at small and moderate spatial scales;however,slopes did not vary in non-woody layers among disturbed versus undisturbed forests and spatial scales.(2)Species evenness versus functional evenness relationships were positive and varied among spatial scales and vegetation layers.Although the relationship’s slopes increased with spatial scales,slopes did not vary among disturbed versus undisturbed forests.In woody layers,relationships were significantly positive and varied among disturbed versus undisturbed forests(i.e.,slopes were steeper in shrublands and plantations than mature forests)but not among spatial scales.In nonwoody layers,species evenness and functional evenness relationships were positive in shrublands but negative in mature forests and plantations.(3)Species and functional diversity relationships were significantly positive and did not vary among disturbed versus undisturbed forests,spatial scales,and vegetation layers.(4)Interestingly,community-level functional redundancy and species-level functional uniqueness significantly vary among disturbed versus undisturbed forests but not among spatial scales of observation,potentially explaining the disturbance-dependent variation in the relationships between species and functional diversity indices.In summary,studying the relationships between species and functional diversity can help understand biodiversity in subtropical evergreen broad-leaved forests and determine which forest or spatial scale is more beneficial to forest management and conservation.Due to steeper slopes of species and functional diversity relationships in disturbed forests,especially shrublands,or at smaller spatial scales,forest managers should focus on biodiversity changes in disturbed forests,especially shrublands or at small spatial scales to keep good ecosystem functions and health in practices.In addition,species and functional diversity relationships in woody layers are often more susceptible to forests and spatial scales than in non-woody layers,which reminds forest managers to pay more attention to biodiversity changes among forests and at spatial scales in woody layers.