Comparing tree seedling composition and distribution patterns under different sampling intensities in the 24 ha Gutianshan forest dynamics plot
As the seedling stage is the bottleneck in forest tree regeneration,knowledge of the composition and structure of seedlings is crucial to understanding the mechanisms of community assemblage and diversity maintenance.However,based on the limited sampling intensity common in previous studies,seedling census datasets are representative of common species,but are ineffective for monitoring rare species.In this study,we established a new seedling monitoring network in the 24 ha Gutianshan (GTS) forest dynamics plot (FDP) consisting of 285 seedling plots (5 m × 5 m) in 2012.In the seedling pots,all woody plants (DBH ＜ 1 cm and height ≥ 10 cm) were tagged,mapped and measured every two years.We used the first census data to investigate seedling composition,species diversity patterns,seedling,and non-seedling species habitat association.Our results showed that:(1) There were 138 species,consisting of a total of 20,581 individuals in 285 seedling plots of 5 m × 5 m.The Shannon-Wiener diversity index and Rarefied species richness were higher than those of the 1 m × 1 m seedling plots and 24 ha FDP census (DBH ≥ 1 cm).Similar results were found when using rarefaction approach.Compared with 1 m × 1 m seedling plots,the number of species showed a significant increase and the species-area curve became more asymptotic.(2) The relationship between seedling abundance and tree species exhibited negative allometry,suggesting that the mortality rate of plants in the seedling stage was relatively high compared with the rate found in the non-seedling stage due to the negative density dependence.(3) Sampling intensity and selection of DBH cutoffs influence the definition of rare species.Some rare species defined by trees with DBH ≥ 1 cm were not actually rare when individuals with DBH ＜ 1 cm were considered (i.e.Ardisia crenata,Litsea cubeba,Lespedeza thunbergii subsp.formosa).(4) The indicator species of the 5 m × 5 m seedling plots were different from those found in the 24 ha FDP and the 1 m × 1 m seedling census.13 species was significantly correlated with single habitat type in these 5 m × 5 m seedling plots,which shared only three species that identified as indicator species for 1 m ×1 m seedling plots and two species for non-seedling plots.In conclusion,sampling intensity influenced patterns of tree seedling composition and community diversity,and increasing sampling intensity can provide deeper insights into the processes of diversity maintenance.
Gutianshan (GTS)tree seedlingsampling intensityrare speciesmechanisms of maintenance of species diversity
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