**1. Introduction**

Community assembly has been one of the major over-arching topics in community ecology with species distributions being fundamental to understanding community assembly [1]. In general, two processes are thought to be fundamental in shaping the spatial distributions of species in plant communities: niche and neutral processes [2]. Niche processes allows survival of species that are adapted to local habitats. Much prior research has examined how the distribution of species is the outcome of niche processes such as interactions between biological and ecological processes [3]. In contrast to niche processes, neutral processes suggest that plant communities can be modeled without regard for species identity resulting in random species distributions [4]. Recent studies suggest that both niche and neutral processes affect species distributions [5]. Thus so far, there are many studies examining processes and phenomena of community assembly assume species to be independent from one another. However, a species, especially a dominant species, may have directional and endogenous relationships with neighboring species and their distribution.

Ecological dominance is the degree to which a taxon within an ecological community is more numerous either numerically or by biomass [6]. For tree species in forests, species with most numerous and of largest size is considered as the dominant species. Phylogenetic relationships between a dominant species and its neighbors depend on the relative importance of the ecological mechanisms of community assembly involved. The study of these relationships is called "community phylogenetics" [7]. Considering that most traits are phylogenetically conserved niche conservatism was supported dominantly [8], although counter examples exist [9]. A descriptive statistic that indicates the strength of phylogenetic signal was derived [10], then used to quantify whether there was phylogenetic signal in plant-habitat associations – information critical for inferring which ecological process has influenced community assembly the most [11]. Close relatives to a neighbor species may represent the effects of environmental filtering given niche conservatism, while more distant relatives may represent the effects of competition for limited resources. Close relatives with similar phenotypes are filtered into a community from the regional species pool, and therefore, utilize analogous resources. Under limited resources, survival necessitates repulsion among closely related species thus preventing local coexistence [12]. Conversely, resource competition and predation or disease limit coexistence of close relative individuals and is widely acknowledged as negative density-dependence. Uriarte et al. [13] studied how neighbors influenced sapling growth in the Barro Colorado Island (BCI) plot finding that confamilial neighbors exerted stronger negative effects than non-confamilial neighbors. Both environmental filtering and negative density-dependence can be categorized into niche process, which differs from the neutral process of biodiversity proposed by Hubbell [1]. Thus, a third possibility is that neighbor species are neutral (random) in relationship to the dominant species. Predicted responses based on theory between phylogenetic distance of a dominant species and its neighbors are summarized in Table 1.


**Table 1.** Predicted effects of different ecological processes on community structure of a dominant species relative to the phylogenetic distance of its neighbors.

On the other hand, community assembly is recognized as a dynamic progression, one of which means as community succession. Community succession is a process of ecological change in the species structure of an ecological community over time [14]. Faith proposed that communities at early successional stages are expected to be colonized by the pioneer species that are well dispersed, and can tolerate harsh environments, while their competition interactions within communities are

weak [15]. As succession proceeds and later arriving species are established, some ecologists found that the importance of biotic interactions would be increased [16]. That is, the interplay between environmental heterogeneity and competition interactions can have complex effects on the long-term persistence of the interacting species.

Dominant species play a key role in community structure, influencing the survival and distribution of others species [17]. Phylogenetic information helps resolve the multitude of processes structuring community assembly and the importance of evolution in the assembly process [7,18]. However, few studies focused on phylogenetic relationships between a dominant species and its neighbors, which could be a useful way to explore the mechanisms in community assembly. To address this gap, we explored, at the community level, the effect of a dominant species *Castanopsis chinensis* on their neighbor species in a 20 ha species-rich subtropical forest (Dinghushan Plot, DHS Plot) in southern China. *C. chinensis* is one of the most dominant tree species in lower subtropical China. It is a canopy species with its establishment providing subsequent suitable microenvironments for later successional species [5,19]. Based on the prediction in Table 1, we reason that environment filtering would lead to positive relationship between *C. chinensis* and phylogenetic distance of neighbor species and the abundance of closely related species will more than expected randomly distribution. Conversely, negative density-dependence lead to negative relationship between *C. chinensis* and phylogenetic distance of neighbor species and the abundance of distantly related species will more than expected randomly distribution. Our objectives here were to: (1) explore the distribution of neighbor species to the dominant species *C. chinensis* based on phylogenetic distance to test hypotheses with respect to relationships between dominant species and their neighbors (i.e., environmental filtering, negative density-dependence or neutrality; Table 1); and (2) test whether this relationship will be consistent across the successional stages of community development (i.e., successional and mature forests).
