Seed Rain Dynamics And Seed Dispersal In The Pine-oak Mixed Forests Of Qinling Mountains,China

Quercusaliena var.acuteserrata,Pinustabuliformis and Pinusarmandii are very widely distributed in the Qinling Mountains,they are the predominant species and the mixed forest types are relatively common forest communities in the Qinling Mountains.The pine-oak mixed forests play a very important group of maintaining biodiversity,stability and service function of the forest ecosystems.Seed rain and seed dispersal are the important stages during the process of natural regeneration of forest plant populations and the main measure to self-recolonize and self-repair for forest ecosystem.In this study,a 1.2-ha plot with typical and light disturbance was established in the Huoditang forest region,which is an important habitat of pine-oak mixed forests in the Qinling Mountains.We determined the woody plant species composition and analyzed the seedling regeneration characteristics and spatial distribution pattern of the constructive species of the secondary forests in the pine-oak mixed forests in the middle of south slope in the Qinling Mountians.We monitored the seed rain dynamics of the constructive species using the seed traps,to analyze the seed density and spatial distribution of seed rain in the plot.We also tested the hypothesis whether the seed size effects on the seed dispersal process in the pine-oak mixed forests.We further charified the selection mechanism of microhabitat for removal and predation of rodents on seeds from different tree species.This study aims to illuminate the seed dispersal and developmental dynamics of the pine-oak mixed forests,which can provide a theoretical basis for designing forest developmentaltype and the restoration and reconstruction of vegetation.The main conclusions are as follows:1.Species composition and regeneration characteristics of woody plant seedlings in the pine-oak mixed forests in the Qinling MountainsSeedlings of the main tree species were abundant,but the numbers of later stages differed among the species.There are 32 species in tree layer and they belong to 16 families and 26 genera.A total of 2846 seedlings and saplings were identified,belong to 45 species,37 genera and 25 families.Q.aliena var.acuteserrata had stonger natural regeneration ability than P.tabuliformis and P.armandii in the pine-oak mixed forest.Although Q.aliena var.acuteserrata seedlings mortality is relatively high,it can therefore survive bottlenecks by strong regenerative sprouting to produce a stable population.In contrast,P.tabuliformi seedlings are insufficient,which suffered from intense interspecific competition for light,moisture and nutrients,thereby decreasing regeneration ability during seedlings growth.2.Seed rain dynamics of constructive species in the pine-oak mixed forests in the Qinling MountainsFrom 2015 to 2016,we collected the seeds of Q.aliena var.acuteserrata,P.tabuliformis and P.armandii using the seed traps in the plot,to analyze the seed rain dynamics and spatial distribution.The results showed that there were significant differences in seed rain density of constructive species and seed rain dynamics also were siginficant differences in the pine-oak mixed forests within a year.The results indicated that 2015 may be the relatively harvest seeding year.The fall peak in the number of seed rain of P.tabuliformis was later than other two tree species.The study of seed rain of each category of constructive species showed that the seed rain density of each category was higher in 2015 than in 2016,and the fall peak of sound Q.aliena var.acuteserrata acorns was earlier than the insect-infested acorns.The spatial distribution of seed rain of different tree species had an aggregated distribution and there were significant differences in the plot.With the spatial distribution of seedlings,there was a significant difference between seeds and seedlings.This situation may be due to the different seed dispersal model and intense self-thinning during seedling growth.3.Effects of seed size of Q.aliena var.acuteserrata acorns dispersal in the Qinling Mountains,ChinaThe results showed that Apodemus draco,A.peninsulae,and Sciurotamias davidianus were the main seed dispersers and predators in the forest region.Seed size determine Q.aliena var.acuteserrata acorns dispersal process,and small rodents has preference different foraging strategy with many factors.Large and small size of Q.aliena var.acuteserrata acorns were actively dispersed by rodents in the pine-oak mixed forests.The rodents has preference to removed and cached large Q.aliena var.acuteserrataacorns,and long-distance cached small acorns with long-distance.A great dispersal ability and a strong possessive desire for food resources were showed by rodents.Our findings suggest that small rodents are the main participant in seed dispersal of Q.aliena var.acuteserrata and make a significant contribution to the post-dispersal of Q.aliena var.acuteserrata acorns in the pine-oak mixed forests.Therefore,it plays an improtent role in seed dispersal and seedling germination in the pine-oak mixed forests in the Qinling Mountains.4.Selection mechanism of microhabitat for removal and predation of rodents on seeds from constructive species in the pine-oak mixed forests in the Qinling MountainsRodents has preference in the microhabitat of predation sites and hoarding methods after seeds were dispersed.There are differences in seed dispersal mode of constructive species in the pine-oak mixed forests in Qinling Mountains.Seed dispersal modes of Q.aliena var.acuteserrata are diversified,while that of P.tabuliformis and P.armandii are single,which also has a large pressure of animal predation.Rodents has preference in preying seeds of P.tabuliformis and removing seeds of P.armandii to suitable sites of feeding.Seeds of Q.aliena var.acuteserrata and P.armandii were predation rate tend to decrease during microhabitat change(Shrubs-Grass-Shrub edge-Bare land).Rodents move seeds to specific microhabitats selectively instead of dispersing them randomly.To some extent,rodents provide a good condition of seed dispersal and seedling germination in the pine-oak mixed forests,thereby promoting natural regeneration of Q.aliena var.acuteserrata and P.armandii populations.