Phytosociological Study of Pteroceltis tatarinowii Forest in the Deciduous-Forest Zone of Eastern China

Abstract

Pteroceltis tatarinowii is a Chinese endemic tree species belonging to the family Ulmaceae. This species likes high-calcium soil, can tolerate drought and barren environmental conditions, has strong rooting ability, and is regarded as one of the important tree species for vegetation restoration on limestone mountains in the warm-temperate zone (sensu sinico) of eastern China. But existing Pteroceltis tatarinowii forests have survived mostly in small areas, and so far there have been only rare phytosociological studies of Pteroceltis tatarinowii forest reported. To clarify the phytosociological characteristics of Pteroceltis tatarinowii forest in eastern China, this study selected five sites in the main distribution areas of Pteroceltis tatarinowii forest and recorded 28 vegetation samples, using Braun-Blanquet methodology. Field data were also collected for Quercus forests in the same region (including Quercus variabilis forest and Quercus acutissima forest), in order to determine the position of Pteroceltis tatarinowii forest in the hierarchical syntaxonomic system of deciduous broad-leaved forests. Data on Pteroceltis tatarinowii forest were classified by tabular comparison and summarized in a synoptic table, along with typical Quercus forests occurring in the same region. The different geographical distributions of Pteroceltis tatarinowii forest and deciduous Quercus forests were demonstrated by de-trended canonical correspondence analysis (DCCA). The compared results show that Pteroceltis tatarinowii forest in eastern China can be recognized as a new alliance in the Quercetea variabilis class, named Moro australis-Pteroceltidion tatarinowii. This new alliance can be subdivided into two associations (i.e. Isodo rubescens-Pteroceltido tatarinowii ass. nov. and Pteroceltido tatarinowii-Quercetum variabilis) and one community (i.e. Platycladus orientalis-Pteroceltis tatarinowii community). The results of DCCA show that suitable environmental ranges of Pteroceltis tatarinowii forest are narrower than for Quercus forests and the different geographical distributions can be explained by the geographical and climate conditions. Compared with Quercus forests, Pteroceltis tatarinowii forest is more likely to occur in relatively harsh habitats at low altitudes, on steep cliffs or hillsides, on dry slopes with much exposed rock, and on calcium-rich limy soils. The constituent species of Pteroceltis tatarinowii communities are not many, the average number being about 34, because most species are unable to tolerate unfavorable dry, rocky, or barren environments. The structure of Pteroceltis tatarinowii communities is relatively simple, but many seedlings and clonal ramets of Pteroceltis tatarinowii appeared in the understory, so natural regeneration of Pteroceltis tatarinowii populations is better in forests. The structure and species composition of Pteroceltis tatarinowii forests showed significant differences along with environmental temperature and humidity. The community types of Pteroceltis tatarinowii forest in the study area change from Isodo rubescens-Pteroceltido tatarinowii to a Platycladus orientalis-Pteroceltis tatarinowii community, and then to Pteroceltido tatarinowii-Quercetum variabilis, with increasing environmental temperature and decreasing humidity (from north to south).