Herbaceous Specics Distribution And Canopy Gap Disturbance In Temperate Forest Of Mt. Taibai, The Qinling Mountains

Biodiversity conservation is an urgent matter all over the world. Ecologicaldegradation and its corollary-biodiversity loss-have become pressing global issues.The Qinling Mountains as biology refugia after the Pleistocene glaciations has beendesignated one of the11key regions terresterial "biodiversity hotspots" in China.However, elevational patterns of species richness and mechanisms of speciescoexistence in ecological communities are still not fully known in the region.Therefore, in order to assess the relative importance of local and regional processes instructing herbaceous communities across a regional of Mt. Taibai in the middle part ofQingling Mountains. Using well-documented regional flora, local species richnessand small-scale disturbances information, the purposes of the present study is to:(1)examine the elevational pattern of herbaceous species richness and related hypothesesof mechanisms in Taibai Mountain;(2) evaluate the effects of local and regionalprocesses on herbaceous plant assemblages in temperate forest canopy gaps in TaibaiMountain;(3) detect the effects of natural canopy gap disturbances on herbaceousplant diversity in different temperate forest of Taibai Mountain. The main results wereas follows:1. Herbaceous species diversity totaled1094species in410genera and69families in Mt. Taibai, Qinling Mountains. The species richness of the1094recordedspecies showed a hump-shaped pattern with peak at1200～1300m, and the speciesdistributed in high and low elevations had smaller average elevational range sizes thanthose in mid-elevations accoding to the Rhode's methods. Thus, Rapoport' rule wasnot backed. The best fit models, CARs identified area, geometric constraints,temperature, and drainage density variables as stronger predtctors for overall species,and explained c.75%of the variation in species richness. The area explained46.9%of the richness variance, but the area itself had very low influence when the geometricconstraints was controlled because area and geometric constraints were highlycollinear variables. While the geometric constraints model predictions were well correlated with herbaceous species richness for all species and for large-rangedspecies (R~2=0.601), the explanatory power of the geometric constraints for thesmall-ranged species was lower (R~2=0.007). For small-ranged species, which showeda distribution only strongly correlated with drainage density and temperature. Thus,herbaceous species richness peak deviated notably from geometric constraints modelmay be largely caused by plently of small-ranged species, whose distribution partlyaffected by local-scale rather than regional-scale environmental factors.2. The Non-parametric Brootstrap was used to test the strengths of therelationships between potential regional species richness and local species richness inunderstories and canopy gaps conditions of7different vegetation types in TaibaiMountain. We found that, without canopy gap disturbances, the relationship betweenlocal and regional species richness was weak or nonexistent, suggesting speciessaturation in1m~2small-scale plots; but under canopy gap disturbances, local speciesrichness was positive function of regional species richness, because1m~2small-scaleplots were coloninzed from the potential species pool. These results suggested thatnatural canopy gap disturbances could alter local-regional richness relationships inTaibai Mountain. Thus, to investigate natural canopy gap disturbances may be animportant tool to understanding local and regional processes in determining speciesdiversity.3. We found57herbaceous species in the Quercus aliena var. acuteserratacommunity canopy gaps, and41species within closed canopy sites. The speciesrichness in herbaceous layer in gaps was significantly positively correlated with gapsize (R~2=0.189, P=0.016), but only7of57species displayed gap sizes specialization(>130m~2),87.7%herbaceous species were found across all gap sizes. Nomini-succesional sequence was observed in the herbaceous distribution with the gapsize gradient (P=0.12). Additionally, canonical correspondence analysis and randompermutation tests suggested that only36.3%of herbaceous with abundance≥4wereassociated with environmental variables in canopy gaps. It is concluded thatherbaceous species composition in canopy gaps was not constrainted significantly bygap characteristics in the Quercus aliena var. acuteserrata community.4. We found108herbaceous species in the Betula albosinensis communitycanopy gaps, and74species within closed canopy sites. The mean herbaceous speciesrichness in0.25m~2and1m~2within canopy gaps was correlated with the speciesrichness of the whole gap (r=0.727and r=0.754, respectively). And the two small-scales species richness showed a positive function of gap species richness,respectively. Additionally, there was also a significance correlation between gap sizewith gap species richness and small-scale richness, which might form a spuriousunsaturation local-regional richness relationships. But the unsaturation local-regionalrichness relationships were also found after controlling the effect of gap size inmultiple regression (R2=0.595for0.25m~2, and R2=0.665for1m~2). Moreover,analysis of variance showed that gap size only explained8.0%and1.0%of variationin species richness at0.25m~2and1m~2, whereas gap species richness could explaind27.2%and39.4%, respectively. These results suggested that even relativesmall-scales, local species richness can be constrained by the size of species pool inimmediately surrounding region.5. We found69herbacous species in the Abies fargesii community canopy gaps,and42species within closed canopy sites. Although herbaceous species compositionin gaps significantly differed from closed canopy (ANOSIM, R=0.509, P=0.001),there were no significant differences among gaps of different age groups (ANOSIM,R=0.035, P=0.191) or gaps of different size groups (ANOSIM, R=0.089, P=0.057).Herbaceous species abundance distribution within canopy gaps was well fit by aneutral model (χ2=5.58, P=0.90), showing that relative abundance was qualitativelyconsistent with stochastic processes. Moreover,15of69herbaceous species foundmore commonly in larger gaps (>120m~2), and eight species displayed gap sizespecialization (>146.1m~2). However,88.5%species were observed across the gapsize gradient. Additionally, the CCA ordination suggested that only27%of the55herbaceous species with abundance≥5was associated with environmental variables inthe Abies fargesii community gaps.6. We found84herbaceous species in the Larix chinensis community canopygaps, and52species within closed canopy sites. Herbaceous species-abundancedistribution within canopy gaps and closed canopy sites was well fit by zero-summultinomial, respectively, and no of the species in two of these communities fell outof the95%confidence envelope of the best fit neutral model distribution ofrank-abundance curves. And of the84herbaceous species recorded in the canopygaps,77.3%species were found across all gap sizes, and only5herbaceous speciesdisplayed gap size specialization. An additional14species were more common inlarger gaps but there was no gradient in composition of herbaceous species across gapsize. Additionally, except species of Poa nemoralis, Carex lanceolata, and Thalictrum aquilegiifolium var. sibiricum, the abundances of12early successional species werenot significant differed between canopy gaps and non-gaps. The CCA oridinationshowed that30.9%of68species with abundance≥5was correlated withenvironmental variables in the Larix chinensis community canopy gaps. In summary,the species compostion in gaps was not constrainted significnantly by gap traits;rather species were distributed stochastically, likely through by random dispersal andrecruitment limitation of species from the surrounding available species pool.