Introduction
The objective of this study is to examine the applicability of the thermodynamic equations presented in the theoretical section (Theoretical basis) for description of a plant community ecologically restored at a manganese tailing site. Remediation of a damaged ecosystem should be a manipulated process well-designed with proper measures and explicit targets (Baldera et al., 2018; Laughlin, 2014; Zhao et al., 2016; Haapalehto et al., 2017; Tongkoom et al., 2018) that can maximize the benefits and minimize the damages that are currently existed and that can possibly be brought into the site due to use of improper methods (González et al., 2014; Wallace et al., 2017; Garrouj et al., 2019). Performing a thermodynamic analysis focusing on changes in individual, population and community traits in the restoration process can provide useful information not only for assessment of the remediation effect but also for development of relevant knowledge and technology (Hesse et al., 2018; Kollmann & Mahy, 2018; Fiedler et al., 2018).
Biomass quantity C , individual number m and species numberN are the three basic parameters that can be directly used as indicators for, respectively, productivity, species abundance and species richness. Other parameters developed for describing a specific state of an ecosystem, such as the Shannon-Wiener and Simpson indexes (Ricklefs & Relyea, 2014), exergy (Jørgensen, 2010; Jørgensen et al., 2016) and entropy-based indicators (Laner et al., 2017; Ludovisi & Scharler, 2017), etc., are all presented as functions of C ,m or N , or a combination of them. Accounted for by their additive nature, C , m and N are extensive properties of an ecosystem. Thus, as primary state variables of an ecosystem, C , m and N all have fixed values at a given state and their changes can be uniquely determined by their difference between states regardless of the process history. It follows that all indexes presented as functions of either C , m orN are also state variables with defined meanings in thermodynamics. The conventional indexes are useful and sufficient if one is only interested in assessing the remediation effect. They are not, however, sufficient enough if one is also interested in revealing their related mechanisms and apprehending their significances in ecology. The difference, for an example, in mathematical expressions between the Shannon-Wiener index (or the Shannon form of information entropy) as a function of m and N (Harte & Newman, 2014; Newman et al., 2014) and entropy S as a function of C andN will lead to differences in advantages and disadvantages of their applications. Analysis of their difference using the obtained experimental data can offer a better understanding of the restoration process reflected by the changes in C , m and N .
Two fast-growing tree species P. fortunei andK. bipinnata were used as dominant species in the implemented restoration project. Analysis of their thermodynamic behaviors and the changes in their contribution rates with increase in species richness and abundance should be a meaningful approach to determine the causes that lead to the changes in the internal energy state of the restored plant community. Due to limited scope, the present analysis will be focused on identification of the key thermodynamic factors related to spontaneous changes and biodiversity of the restored plant community.