Spectra of plant life forms as a reflection of structure of forest communities

Abstract

Along with the species composition and richness of species, an important component of the communities structure is the ratio of groups of species that perform similar functions, the so-called functional diversity (Ackerly and Cornwell, 2007; Diaz et al., 2007; Vasilevich, 2016). Functional diversity is assessed by a set of species properties, one of the commonly used species traits is the life form of species. Life forms (LF) reflect the adaptation of plants to macro- and microecological habitat conditions and characterize the structure of communities. When classifying communities, a taxonomic only approach may have limitations (Mucina, 1997), but despite this, the use of species traits to assess community type and structure is not sufficient. The main questions of this paper: 1) How do the spectra of life forms (biomorphological spectra) look like in different types of forest communities? 2) Are differences in species composition reflected in the biomorphological spectra of forest communities? And how are differences in life form spectra exhibited for different categories of the classification system? 3) Are secondary forests different from native forests by their biomorphological spectra? The study of the structure of syntaxa is based on the forest communities of the Moscow Region (Morozova et al., 2017, 2021, 2022 a, b; Chernenkova et al., 2018), located in the center of the Russian Plain. According to remote sensing data, the forests cover 51 % of region area (Chernenkova et al., 2020). Classification of forests was performed by the Braun-Blanquet approach. The forests of the Moscow Region belong to 10 associations of 4 classes of forest vegetation: Vaccinio-Piceetea Br.-Bl. in Br.-Bl. et al. 1939, Carpino-Fagetea Jakucs ex Passarge 1968, Alnetea glutinosae Br.-Bl. et Tx. ex Westhoff et al. 1946, Alno–Populetea albae P. Fukarek et Fabijanic 1968. More than a third part of the forests are secondary, they represent the facies of zonal associations, which they replaced. Taking into account the facies of secondary forests, the analysis was performed for 15 syntaxa. The classification of LF was carried out according to the Serebryakov system with additions (Zhmylev et al., 2017). The variety of LF of vascular plants was summarized in 13 large groups according to the state of skeletal axes, type of root system, and life longivity (Table 1). The shares of LF groups were calculated as weighted by coverage. To compile a “complete” portrait of communities, we included the proportion of bryophytes in the spectrum. Differences between syntaxa in terms of LF shares were analyzed using analysis of variance (ANOVA). A clear connection was revealed between the number of LF and the number of species of vascular plants in the communities: the more species, the more LF. For logarithmic values, it has a linear form (Fig. 1), however, to assert or refute the universality of the direct relationship between species and functional diversity, it is necessary to expand the testing units from different vegetation classes. For the considered syntaxa, the proportions of LF groups in communities differ significantly (F = 21.971, p = 0.00001). Basically, differences appear between syntaxa of different classes, i.e. within the same class, syntaxa according to the corresponding LF may not be differentiated (Table 2, Figs. 2–4). Formulas for the highest classification units have been compiled according to the predominant LF groups. Thus, in LF spectra of the Carpino-Fagetea class, trees LF (Tr) predominate; second and third places are occupied by long-rhizome herbaceous perennials (LR) and shrubs (Shrub), followed by short rhizome herbaceous perennials (SR) (Fig. 3). In general, the spectrum of syntaxa of this class can be represented as Tr–LR–Shrub or или Tr–LR–Shrub. The Carpino-Fagetea syntaxa are also characterized by the highest proportion of taproots (S), an increased proportion of bulbs/stem tubers (Bu) and root sprouting (R) species among herbaceous perennials in at least one of the syntaxa of the class. According to the biomorphological spectra, secondary forests of the Moscow Region differ slightly from the communities of native forests, which emphasizes their relatively good state and the possibility of transition to native forests in the course of further succession. In the Vaccinio-Piceetea, trees predominate, followed by mosses and dwarf shrubs (SShr) or shrubs. The generalized formula for the spectrum of mesophytic syntaxa of this class is Tr–Mosses–SShr/Shrub (Fig. 4). A significant proportion of tufted LF species (Tu) is recorded in this class compared to other forest classes. However, the biomorphological spectra of different communities of this class differ greatly, which reflects the modern view on the syntaxa system. In contrast to the mesophytic communities of the boreal forest class, the spectra of associations of the order Vaccinio uliginosi–Pinetalia sylvestris Passarge 1968are dominated by mosses, followed by either shrubs (ass. Vaccinio uliginosi–Pinetum de Kleist 1929) or trees LF (ass. Vaccinio uliginosi–Betuletum Libb. 1933). Structure formula of the syntaxon of sphagnum pine forests is Mosses–SShr–Tr. This indicates a clear transitional character of boggy pine communities and the possibility of placing the association both in the class of boreal forests and in the class of open sphagnum bogs of the class Oxycocco-Sphagnetea Br.-Bl. et Tx. ex Westhoff et al. 1946 (Table 4). However, according to the results of comparison of biomorphological spectra between boggy pine forests and forested open bogs (Fig. 6), sphagnum pine forests of the Moscow Region are assigned to ass. Vaccinio uliginosi–Pinetum of the class Vaccinio-Piceetea. The spectrum formula of associations included in the class of black alder forests Alnetea glutinosae is Tr–LR–SR, with mosses on the fourth place (Fig. 4). A similar biomorphological spectrum is for a syntaxon from the class Alno–Populetea albae, but in these communities, shrubs are on the fourth place, and among the all considered forest syntaxa of the Region, the proportion of annuals/biennials (An/Bi) is the highest here. The revealed patterns can be used to characterize communities, they adequately reflect the species richness, structure of communities and emphasize the ecological differences of syntaxa and can be an additional argument for placing the syntaxon in the system of higher units.