Abstract
Clematis tientaiensis is a rare and endangered plant species endemic to Zhejiang Province, China, characterized by weak natural regeneration and a scarce extant population. To elucidate its endangerment mechanisms and formulate scientific conservation strategies, this study collected data from its natural community using the quadrat sampling method, with C. tientaiensis and its associated dominant species from the shrub layer (n = 19) and herb layer (n = 19) as the research subjects. By comprehensively applying niche analysis (niche breadth and overlap), interspecific association tests (overall association, 
-test, association coefficient, Pearson and Spearman correlation analyses), and cluster analysis, we systematically revealed the resource utilization strategies and interaction patterns between the target species and its associated plants. The results showed that a total of 133 associated plant species were recorded in the C. tientaiensis community, belonging to 107 genera in 58 families. The proportion of liana species accounted for only 6.77%, and a shortage of seedlings was observed. C. tientaiensis belongs to the endemic Chinese distribution type, while 83.46% of the associated species or 70.00% of the dominant species belonged to the East Asian distribution type. In both the shrub and herb layers, C. tientaiensis exhibited the widest niche breadth (BL = 10.756 and BS = 2.508), but this ecological attribute did not enhance its population survival. The niche overlap among dominant associated species was generally low (mean value < 0.30), indicating weak interspecific resource competition. Furthermore, the overall associations among dominant species were not significantly negative. The ratios of positively associated species pairs to negatively associated species pairs were all below 1.00 in the 
, AC, Pearson, and Spearman test results. According to the hierarchical clustering analysis results, C. tientaiensis was suitable for constructing a stable shrub community with associated plants such as Rubus idaeus, Lespedeza davidii, Mallotus apelta, and Oplismenus undulatifolius. In conclusion, the C. tientaiensis community is characterized by high species richness and a relatively complete structure, currently in the early unstable stage of positive succession with independent niche differentiation and loose interspecific associations. The majority of associated species, sharing similar resource requirements, created a niche monopoly effect that significantly inhibited resource acquisition by plants from other floristic regions. This may be a primary reason for the endangered status of C. tientaiensis. For the conservation and restoration of its native habitat, in situ protection of individuals should be implemented to enhance niche occupation, accompanied by appropriate replanting and optimization of associated species composition to improve community stability.
Supplementary Information
The online version contains supplementary material available at 10.1186/s12862-026-02510-2.
Keywords: Floristic region, Interspecific competition, Community succession, Endangerment mechanisms, Ecological species group
Introduction
With the intensification of global climate change and habitat fragmentation, the conservation of endangered plants has emerged as a core issue in biodiversity maintenance [1]. There exists a close linkage between endangered plants and community ecology, where the theories and methodologies of community ecology provide scientific foundations for understanding the survival mechanisms of endangered plants, formulating conservation strategies, and conducting ecological restoration [2, 3]. Community ecology primarily focuses on aspects such as species composition, niche differentiation, interspecific interactions, community stability, and community succession [2]. Among these, niche theory, as a key tool to reveal species’ resource utilization strategies, effectively deciphers the functional roles of plants within communities. By quantifying the niche breadth and overlap characteristics of dominant associated species, it clarifies the sources of survival competition pressure on endangered plants, which holds significant scientific value for understanding their endangerment mechanisms [4, 5]. Interspecific associations, as a fundamental basis for maintaining community stability, enable the analysis of association strength and coevolutionary patterns between endangered plants and their dominant associated species. This not only reveals the biological interaction mechanisms underlying their ecological adaptability, but also provides theoretical support for constructing scientific artificial conservation communities [6, 7]. While niche theory emphasizes “resource competition”, interspecific associations reflect “biological interactions”. Their integration systematically uncovers the survival limiting factors of endangered plants, offering a basis for formulating differentiated conservation strategies (e.g., competition mitigation or symbiosis enhancement). In recent years, research on niche and interspecific associations has been widely applied in the conservation of endangered plants.
Wang et al. showed that the survival strategy of Thuja sutchuenensis was based on its strong adaptability to harsh environments to avoid interspecific competition [8]. Chang et al. demonstrated that interspecific competition limited the regeneration capacity of Taxus chinensis populations, and moderate anthropogenic disturbance can reduce competitive pressure between Taxus chinensis and other species [9]. Shao and Zhang found that Zelkova serrata exhibited strong ecological adaptability, with weak or independent associations among its companion species, indicating that the Zelkova serrata community is in the early stage of succession [10]. Investigating niche characteristics and interspecific associations within endangered plant communities is crucial for understanding species interactions and maintaining community stability, providing a scientific theoretical foundation for formulating targeted conservation measures.
The genus Clematis L. (Ranunculaceae) is a large genus predominantly composed of woody lianas, with approximately 355 species worldwide (including subspecies, varieties, and other infraspecific taxa) [11]. China is home to 147 naturally wild species, with 32 species distributed in Zhejiang Province [12]. C. tientaiensis is an endemic species to Zhejiang Province, China, listed in the Catalogue of Key Protected Wild Plants in Zhejiang Province (First Batch) issued by the Zhejiang Provincial People’s Government in 2012. It is mainly distributed in eastern Zhejiang, growing in forests and shrublands on mountain slopes at an altitude of 800–1000 m. C. tientaiensis has a flower diameter of up to 15 cm, with a flowering period from May to June. In natural environments, besides the common white flowers, there are also blue variant types, possessing high ornamental and garden application values [13]. It also exhibits significant ecological values in microhabitat construction, soil and water conservation, and microclimate regulation [14]. Therefore, rational utilization of its ecological characteristics in ecological restoration and urban greening can achieve a win-win situation between landscape benefits and ecological service functions.
Currently, there are no reports on surveys of the native communities or studies on the endangerment mechanisms of C.tientaiensis. Research on the roles of niche and species associations in plant endangerment mechanisms has mainly been applied to trees, shrubs, and herbs such as Taxus cuspidata [9], Camellia luteoflora [15], and Gymnadenia conopsea [16], with few reports on lianas. Based on field surveys of wild populations of C.tientaiensis in Tiantai County, Taizhou City, and Pan’an County, Jinhua City, Zhejiang Province, this study aims to reveal the interaction among dominant associated species and the mechanisms underlying community stability maintenance in C. tientaiensis communities, providing a theoretical basis for in situ conservation, ex situ conservation, and population reintroduction of this species.
Materials and methods
Study area
From May to June 2024, surveys of C. tientaiensis communities were conducted in Huading National Forest Park, Tiantai County, Taizhou City, and Dapan Mountain National Nature Reserve, Pan’an County, Jinhua City, Zhejiang Province, China (Fig. 1). Both regions are located in the subtropical monsoon climate zone, characterized by hot and rainy summers and mild, relatively dry winters. The mean annual temperatures in Huading National Forest Park and Dapan Mountain National Nature Reserve are 16–18 °C and 15–17 °C, respectively, with average annual precipitation of 1300–1500 mm and 1400–1600 mm, respectively. Surveys revealed that within the plots established at Huading National Forest Park, the common tree species primarily included Pinus hwangshanensis, Castanopsis sclerophylla, and Quercus glauca, with the plant community type dominated by mixed evergreen and deciduous broadleaf forest. In contrast, within the survey plots at Dapan Mountain Nature Reserve, the prevalent tree species were Cunninghamia lanceolata, Sassafras tzumu, and Platycarya strobilacea, and the plant community type was categorized as deciduous broadleaf forest. We obtained official permission from the Natural Resources and Planning Bureau of Tiantai County, Taizhou City, Zhejiang Province, China to conduct the study and collect samples on this public land. The base map of China was provided by Ministry of Natural Resources with map approval number: GS (2022) 4308.
Fig. 1.
Overview of the study area and sample distribution
Experimental design
Surveys were conducted using the quadrat method. A total of 16 permanent quadrats (5 m×5 m each) were established in typical habitats of the target species, C. tientaiensis (Fig. 1). Within each quadrat, a complete stratified census was performed for all vascular plants, which were categorized as follows for sampling: trees (diameter at breast height [DBH] ≥ 1 cm), shrubs (DBH < 1 cm or without a distinct main stem), herbs (non-woody plants), and lianas (climbing plants, recorded separately). For trees, we recorded species name, individual count, height (m), DBH (cm), and crown width (m); for shrubs and herbs, we recorded species name, individual/clump count, average height (cm), and canopy coverage (%, visually estimated to the nearest 5%). Environmental variables recorded at each quadrat included geographic coordinates and altitude (GPS), aspect (°), slope (°), slope position (upper/middle/lower), and canopy closure (%, estimated with a spherical densiometer). All plants were identified in the field using the Flora of China. Species identification was further verified with the assistance of experts from Zhejiang Agriculture and Forestry University.A voucher specimen has been deposited in the Herbarium of Zhejiang Agriculture and Forestry University (Voucher Number: ZJFC Cl. 235).
Research methods
Importance value
The importance value is a comprehensive quantitative index reflecting a species’ status and role in the community, serving as an indicator for screening dominant species [17]. We selected the top 20 species with the highest importance values that also occurred in at least two quadrats as the dominant associated species for analysis. The calculation formula is as follows:
Relative coverage (RC) = (Coverage of a species/Total coverage of all species) × 100%.
Relative abundance (RA) = (Abundance of a species/Total abundance of all species) × 100%.
Relative frequency (RF) = (Frequency of a species/Total frequency of all species) × 100%.
Importance value = (RC + RA + RF)/3.
Where: Coverage represents the projected area of a species within a quadrat (visually estimated to the nearest 5%). Abundance is the count of individuals or clumps. Frequency is the percentage of quadrats in which the species was present.
Niche index calculation
Niche breadth and niche overlap are two key indices for quantifying niches. Niche breadth was calculated using Levins’ index (BL) and Shannon’s index (BS), while niche overlap was calculated using Pianka’s index (
) [18–20].
 |
Where: N is the number of quadrats; Pij and Pkj are the proportions of the importance value of species i and k in quadrat j to their respective total importance values across all quadrats.
Overall connection test
The variance ratio (VR) method proposed by Schluter [21] was used to test the overall association between species in community, and the statistic W was used to test whether the overall association was significant [22]. The formula is as follows:
 |
In the formula: N is the total number of quadrats, Tj is the number of species appearing in the quadrat j, t is the average number of species in the quadrat, S is the total number of all species, ni is the number of quadrats where species i appears, 
is the variance of the number of species in the quadrat, and 
is the variance of the occurrence frequency of all species. If VR = 1, there is no correlation between species as a whole; VR > 1, the overall association is positive; if VR < 1, the overall association is negative. W is an index to test the significance of VR. When 
(0.95, N) < W < 
(0.05, N), the overall correlation is significant (P < 0.05); when W < 
(0.95, N) or W > 
(0.05, N), it is not significant (P > 0.05).
Interspecific association analysis
The 
test was used to examine the significance of qualitative interspecific associations, with the Yates’ continuity correction formula employed for calculating the 
value [23]. Since the 
test cannot accurately determine the association of nonsignificant species pairs, the association coefficient (AC) can reflect the relative strength of interspecific associations between species pairs [24]:
 |
Where: N is the number of quadrats. a is the number of quadrats where both species co-occur; b and c are the numbers of quadrats where only one of the two species occurs; d is the number of quadrats where neither species occurs. When ad > bc, the interspecific association is positive; when ad < bc, it is negative; and when ad = bc, there is no interspecific association. Regarding the significance of interspecific associations: if 
< 3.841, the association is not significant (P > 0.05); if 3.841 < 
< 6.635, the association is significant (0.01 < P < 0.05); if 
>6.635, the association is extremely significant (P < 0.01). The value range of AC is [-1, 1]. The closer the value is to 1, the stronger the positive interspecific association; the closer to -1, the stronger the negative interspecific association.
In addition to qualitative analysis, quantitative analysis is also necessary. The main testing methods for quantitative analysis are the Pearson correlation coefficient (rp) and the Spearman rank correlation coefficient (rs). Pearson correlation testing belongs to parametric tests, which require species data to conform to a continuous normal distribution [25]. In contrast, Spearman rank correlation testing is a non-parametric test that has no requirements for the distribution form of species data, exhibits higher sensitivity, and is more suitable for application in communities under natural distribution states [24].
 |
Where: N is the number of quadrats; 
and 
are the quantitative values of species 
and 
in quadrat (
); 
and 
are the mean values of the quantitative values of species (
) and (
) across all quadrats, respectively.
Ecological species group division method
To identify species assemblages with similar ecological habits and resource utilization strategies, this study performed hierarchical clustering on dominant species in both shrub and herbaceous layers. The clustering was based on a similarity matrix derived from the Spearman rank correlation coefficients (rs) between species, combined with indicators of niche overlap (Oik) and interspecific associations (AC and 
) [26]. Ward’ s method was employed for clustering, and a threshold of rs ≥ 0.5 together with Oik ≤ 0.5 was used to delineate ecological species groups [27]. The clustering results were visualized using dendrograms, and each group was named and interpreted in light of the ecological traits of the constituent species, such as light preference, water requirement, and other relevant adaptive characteristics.
Statistical analyses
Data organization and calculation of species importance values were performed in Microsoft Excel 2021. Niche indices (including niche breadth and niche overlap) and interspecific association metrics (overall association, 
test, association coefficient, Pearson and Spearman correlation coefficients) were computed in R 4.2.0, primarily using functions from the “spaa” package [28]. Visualization of analytical results, including hierarchical cluster analysis, was conducted in Origin 2024, and geographic maps depicting the study area and quadrat distribution were generated using ArcGIS 10.8.1.
Results and analysis
Species composition and floristic characteristics
As shown in the Fig. 2, the associated plants in the C. tientaiensis community consist of 133 species belonging to 58 families and 107 genera (Supp. Table S1). Among them, tree species include 29 species from 24 genera in 17 families, shrub species comprise 42 species from 30 genera in 19 families, herbaceous plants include 53 species from 45 genera in 26 families, and liana species consist of 9 species from 9 genera in 7 families. The C. tientaiensis community is species-rich and diverse in life forms, but lianas are fewer in species and lack seedlings. According to the classification standard for distribution types of Chinese seed plant genera [29], associated species are divided into six distribution types: East Asian, North Temperate, Pantropical, Worldwide, Tropical Asian, and North American distributions. C. tientaiensis belongs to the unique distribution type of China, with East Asian distribution being the most common among associated species (Family = 54, G = 96, S = 111). Families such as Poaceae, Fabaceae, Rosaceae, and Lauraceae exhibit relatively high relative frequency (RF ≥ 0.02) and species richness (G ≥ 2, S ≥ 5), serving as the main components of the C. tientaiensis plant community. The community structure was relatively complete, with the highest species richness in the understory layer (S = 104), but the distribution types of associated species were extremely unbalanced.
Fig. 2.
The associated species composition characteristics and floristic characteristics of Clematis tientaiensis community
Importance value and niche breadth of dominant species
The survey results showed that the tree layer had high species richness (S = 29), with a mean relative frequency (RF) of 0.007 (Supp. Table S2). Among them, 62.07% of tree species had an RF of only 0.004, and species such as Sassafras tzumu, Liquidambar formosana, and Tilia tuan, among others. appeared in quadrats only once. These tree species were relatively evenly distributed in space, with no single or few tree species dominating or concentrating in multiple quadrats. As a herbaceous climbing liana, C. tientaiensis vertically spans both the shrub and herb layers due to its climbing growth habit. Therefore, in the niche analysis conducted in this study, it was compared with the main associated species from the shrub and herb layers to provide a comprehensive assessment of its functional role and adaptive potential within the community.
As shown in Tables 1 and 2, the niche analysis of the dominant associated species in the shrub and herb layers demonstrated that the floristic composition of both layers was dominated by East Asian elements (65% and 70% of species, respectively). Within this biogeographic context, C. tientaiensis, as the only species with an unique distribution in China, exhibits a significant ecological advantage. It ranked first in relative frequency (RF = 0.059) and importance value (IV = 0.028) within the shrub layer. Its niche breadth (BL=10.756, BS=2.508) was markedly greater than that of other species in the same layer, measuring approximately 2.1 times that of the second-ranked species, Eurya japonica. In the herb layer, while its importance value was not the highest, it maintained a notably high relative frequency. Crucially, its niche breadth was substantially larger than that of all other herb-layer species, reaching about 3.7 times that of the second-ranked species, Ophiopogon japonicus. These results indicate that through its unique climbing growth form, C. tientaiensis effectively transcends the floristic and structural boundaries between layers, integrating resources across vertical strata. It has developed a broader adaptive capacity than species confined to a single layer or the dominant East Asian floristic group, thereby securing a keystone structural and functional role within the community.
Table 1.
Importance values and niche width of the dominant species in the shrub layer
| Number | Species | Distribution area | Relative frequency (RF) | Importance value (IV) | Niche breadth | |
|---|---|---|---|---|---|---|
| BL | BS | |||||
| S1 | Clematis tientaiensis | C | 0.059 | 0.028 | 10.756 | 2.508 |
| S2 | Hydrangea chinensis | E | 0.032 | 0.019 | 4.188 | 1.675 |
| S3 | Rubus trianthus | E | 0.008 | 0.004 | 1.471 | 0.500 |
| S4 | Corylopsis sinensis | E | 0.024 | 0.016 | 4.592 | 1.640 |
| S5 | Eurya japonica | T | 0.028 | 0.022 | 5.042 | 1.685 |
| S6 | Staphylea bumalda | E | 0.004 | 0.004 | 1.000 | 0.000 |
| S7 | Camellia cuspidata | E | 0.020 | 0.014 | 3.379 | 1.376 |
| S8 | Rubus idaeus | N | 0.004 | 0.003 | 1.636 | 0.684 |
| S9 | Rhododendron simsii | N | 0.024 | 0.016 | 4.349 | 1.590 |
| S10 | Rubus buergeri | E | 0.012 | 0.011 | 1.940 | 0.677 |
| S11 | Lindera erythrocarpa | E | 0.004 | 0.002 | 1.000 | 0.000 |
| S12 | Litsea cubeba | T | 0.012 | 0.028 | 2.172 | 0.917 |
| S13 | Rubus corchorifolius | N | 0.012 | 0.008 | 2.051 | 0.860 |
| S14 | Lespedeza davidii | E | 0.012 | 0.010 | 2.283 | 0.916 |
| S15 | Eurya rubiginosa var. attenuata | E | 0.008 | 0.008 | 1.471 | 0.500 |
| S16 | Litsea pungens | E | 0.012 | 0.010 | 2.133 | 0.900 |
| S17 | Clerodendrum cyrtophyllum | E | 0.008 | 0.006 | 1.988 | 0.690 |
| S18 | Berchemia sinica | E | 0.008 | 0.005 | 1.923 | 0.673 |
| S19 | Aralia elata | E | 0.008 | 0.004 | 1.600 | 0.562 |
| S20 | Mallotus apelta | E | 0.008 | 0.005 | 1.600 | 0.562 |
Note: “C”represents the unique distribution area in China, and the other letters represent different distribution zone types (see Fig. 2)
Table 2.
Importance values and niche width of the dominant species in the herbaceous layers
| Number | Species | Distribution area | Relative frequency (RF) | Importance value (IV) | Niche breadth | |
|---|---|---|---|---|---|---|
| BL | BS | |||||
| H1 | Clematis tientaiensis | C | 0.059 | 0.028 | 10.756 | 2.508 |
| H2 | Oplismenus undulatifolius | P | 0.012 | 0.062 | 1.672 | 0.650 |
| H3 | Lophatherum gracile | E | 0.012 | 0.032 | 1.825 | 0.800 |
| H4 | Polygonatum filipes | E | 0.008 | 0.007 | 1.988 | 0.690 |
| H5 | Erigeron canadensis | W | 0.008 | 0.006 | 1.180 | 0.287 |
| H6 | Lagotis Gaertn | E | 0.004 | 0.005 | 1.000 | 0.000 |
| H7 | Pseudocyclosorus esquirolii | E | 0.012 | 0.018 | 1.733 | 0.758 |
| H8 | Youngia heterophylla | E | 0.008 | 0.003 | 2.000 | 0.693 |
| H9 | Tripterospermum chinense | E | 0.016 | 0.014 | 2.785 | 1.169 |
| H10 | Ophiopogon japonicus | E | 0.012 | 0.012 | 2.904 | 1.081 |
| H11 | Eleusine indica | P | 0.008 | 0.012 | 1.062 | 0.136 |
| H12 | Phaenosperma globosum | E | 0.012 | 0.009 | 2.111 | 0.839 |
| H13 | Lygodium japonicum | P | 0.012 | 0.008 | 2.778 | 1.055 |
| H14 | Euphorbia hylonoma | E | 0.004 | 0.005 | 1.000 | 0.000 |
| H15 | Viola diffusa | E | 0.004 | 0.008 | 1.000 | 0.000 |
| H16 | Disporum uniflorum | E | 0.008 | 0.005 | 1.960 | 0.683 |
| H17 | Osmunda japonica | E | 0.004 | 0.004 | 1.000 | 0.000 |
| H18 | Cyclosorus parasiticus | E | 0.004 | 0.004 | 1.000 | 0.000 |
| H19 | Erigeron acris | W | 0.004 | 0.004 | 1.000 | 0.000 |
| H20 | Veratrum schindleri | E | 0.004 | 0.004 | 1.000 | 0.000 |
Niche overlap of dominant species
The average niche overlap (Oik) values among dominant species in the shrub and herb layers (Fig. 3a-b) were 0.17 and 0.25, respectively. There were 22 and 23 species pairs with Oik ≥ 0.50, accounting for 11.58% and 12.10%; 60 and 25 pairs with 0.10 ≤ Oik < 0.50, accounting for 31.58% and 13.16%; and 108 and 142 pairs with Oik < 0.10, accounting for 56.84% and 74.74%. C. tientaiensis had higher niche overlap values with Hydrangea chinensis (0.53), Rhododendron simsii (0.51), Litsea cubeba (0.52), and Oplismenus undulatifolius (0.58), forming obvious competition, and also exhibited competitive relationships for environmental resources with other associated species. Overall, more than 50% of plant pairs in both the shrub and herb layers showed weak competitive relationships.
Fig. 3.
Niche overlap of dominant species in shrub and herb layers. a - the niche overlap of shrub layer, b - the niche overlap of herb layer. Note : The letters in the figures are the numbers of companion species, and the species represented by the numbers are shown in Tables 1 and 2 ( the same below)
The overall connectivity of community species
The variance ratios (VR) of both the shrub and herb layers were less than 1 (Table 3). The critical chi-square values were 
(0.95,16)=7.96, 
༈0.05,16༉=26.30. Using the test statistic W to examine the significance of VR deviation, the statistics for the shrub and herb layers were 12.72 and 14.22, respectively - both falling between 
(0.95,16) and 
(0.05,16). This indicates that the associations among dominant associated species in both the shrub and herb layers showed nonsignificant negative correlations, suggesting that the C. tientaiensis community is in an unstable stage.
Table 3.
Overall connection between the dominant associated species in the shrub and herb layers
| Layer | Variance ratio (VR) | Statistic W |
 threshold (0.95, 16) |
 threshold (0.05, 16) |
Results |
|---|---|---|---|---|---|
| Shrub | 0.85 | 12.72 | 7.96 | 26.30 | Not significant negative correlation |
| Herb | 0.95 | 14.22 | Not significant negative correlation |
Comparison of multiple association test results of dominant species
As shown in Table 4 and Fig. 4, among the 190 species pairs formed by dominant associated species in the shrub/herb layer community, the ratios of positive to negative associations from 
, AC, Pearson and Spearman tests were 0.74/0.36, 0.76/0.43, 0.43/0.22, and 0.67/0.39, respectively. The ratios of significant to nonsignificant associations were 22.21%/13.68%, 77.89%/94.74%, 17.37%/14.21%, and 29.47%/18.42%, respectively. C. tientaiensis showed significant negative associations with Corylopsis sinensis, Eurya japonica, Rubus buergeri, Litsea pungens, Youngia heterophylla, and Eleusine indica (P ≤ 0.05), and significant positive associations with Staphylea bumalda, Lindera erythrocarpa, Litsea cubeba, Mallotus apelta, Oplismenus undulatifolius, Lophatherum gracile, Pseudocyclosorus esquirolii, and Lygodium japonicum. The AC test was more sensitive to quadrat data, with a significant rate approximately threefold higher than other methods, though it did not fully align with results from other tests. The combined results from the four tests indicated that within the C. tientaiensis community, negative associations accounted for the majority of interspecific relationships among the dominant species in both the shrub and herb layers. Furthermore, the number of nonsignificant species pairs substantially exceeded that of significant pairs, reflecting overall weak interspecific associations.
Table 4.
Comparison of the results of multiple association tests for the predominant associated species
| Layer | Method | Positive association (Pa) | Negative association (Na) | Pa/Na | Significance rate | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| P ≤ 0.01 | P ≤ 0.05 | P > 0.05 | Total | P ≤ 0.01 | P ≤ 0.05 | P > 0.05 | Total | ||||
| Shrub |
|
7 | 18 | 56 | 81 | 4 | 17 | 88 | 109 | 0.74 | 22.21% |
| AC | 28 | 29 | 25 | 82 | 92 | 2 | 14 | 108 | 0.76 | 77.89% | |
| Pearson | 20 | 4 | 33 | 57 | 1 | 8 | 124 | 133 | 0.43 | 17.37% | |
| Spearman | 19 | 13 | 44 | 76 | 9 | 15 | 90 | 114 | 0.67 | 29.47% | |
| Herb |
|
4 | 10 | 36 | 50 | 0 | 12 | 128 | 140 | 0.36 | 13.68% |
| AC | 39 | 8 | 10 | 57 | 133 | 0 | 0 | 133 | 0.43 | 94.74% | |
| Pearson | 25 | 1 | 8 | 34 | 0 | 1 | 155 | 156 | 0.22 | 14.21% | |
| Spearman | 25 | 4 | 24 | 53 | 1 | 5 | 131 | 137 | 0.39 | 18.42% | |
Fig. 4.
Test results of various species between dominant associated species. Note: In the figure, 
test, AC test, Pearson correlation test, and Spearman rank correlation test for the shrub/herb layers are represented by a/b, c/d, e/f, and g/h, respectively. " *** " and " ** " indicate extremely significant levels (P ≤ 0.001 and p ≤ 0.01), while " * " indicates significance (P ≤ 0.05). Blue squares and pie charts represent positive correlations, and red squares and pie charts represent negative correlations. In pie charts, clockwise directions indicate positive correlations, and counterclockwise directions indicate negative correlations
Ecological species group
Hierarchical clustering analysis classified the dominant species (including C.tientaiensis and its associated species) in the shrub and herb layers into five ecological species groups, respectively (Fig. 5a-b). Further analysis showed that each ecological species group showed obvious intra-group similarity and inter-group difference in light availability, soil pH, and soil properties(Supp. Table S3). To therefore translate the clustering results into functional units with explicit ecological meaning and practical relevance, we developed a habitat-based nomenclature system. This system is founded on the shared ecological traits of each group and the specific environmental conditions they indicate. These groups were classified and named as follows: Open Slope Group (OSG): Dominated by heliophytes, indicating sun-exposed slopes with acidic, nutrient-rich soils; Forest Gap Group (FGG): Dominated by shade-tolerant species, indicating moist, nutrient-rich forest gaps or riparian zones with moderate light; Sparse Thicket Group (STG): Dominated by species tolerant of nutrient poverty and drought, indicating acidic, nutrient-poor, and open shrublands; Disturbed Edge Group (DEG): Dominated by generalist or pioneer species, indicating frequently disturbed habitats such as forest margins and roadsides; Understory Group (UG): Dominated by sciophytes, indicating a shaded understory environment with moist, near-neutral soils. In both the shrub and herb layers, C. tientaiensis exhibited positive associations with dominant companion species such as Rubus idaeus, Lespedeza davidii, Mallotus apelta, Oplismenus undulatifolius, and Erigeron canadensis. These species all belong to the Open Slope Group and share highly similar habitat preferences, indicating considerable niche overlap under natural conditions and the potential for stable coexistence.
Fig. 5.
Cluster plots of the ecospecies groups. Note: a shows the clustering diagram of the dominant species in the shrub layer, and b shows the clustering diagram of the dominant species in the herb layer
Discussions
Species composition and floristic characteristics of Clematis tientaiensis community
The endangered status of plants is the result of the synergistic effect of multiple ecological factors, which may include resource competition, niche restriction, reproductive difficulties, environmental changes, or anthropogenic disturbances [30–33]. In the C. tientaiensis community, the species diversity of lianas was significantly lower than that of other life-form plants, and environmental conditions for seed germination and seedling growth (such as light, temperature, moisture, etc.) were lacking, indicating that C. tientaiensis may face certain competitive pressures in terms of living space and resource acquisition within the community [34]. Floristic region, as the collection of all plant species in a specific ecosystem or community, emphasizes the functional combination of species and their associations with environmental factors, which can indicate ecosystem stability and biodiversity [35]. In plant communities, plants with the same floristic region share similar ecological adaptation strategies; if they dominate in species abundance and richness, they can intensify interspecific competition, restrict resource acquisition by other species, and increase the risk of endangerment [36–38]. In this study, 83.46% of associated species with C.tientaiensis belonged to the East Asian distribution type, yet results from niche overlap and overall association tests showed that competition among associated species was not significant. This indicates that community succession has passed the stage of intense resource competition [3], and plants within the same floristic region have mitigated competitive pressures through niche differentiation (e.g., differences in height, root distribution depth, and resource utilization timing), leading to weak competitive relationships [39–40]. However, the remaining resources after competition may be insufficient to support the growth, spread, and reproductive renewal of C. tientaiensis, which could contribute to its endangered status.
Niche and interspecific association characteristics
Importance value and niche breadth are crucial data indicators reflecting the survival status of a population within a community and its ability to utilize resources [41]. It is generally believed that endangered plants can only adapt to and depend on extremely limited and specific ecological environmental conditions, and the range of available ecological resources is narrow [42]. This is inconsistent with the fact that C. tientaiensis has the largest niche breadth in this study. This result might be due to the limited sampling plot area, which overestimates the niche breadth of this species at the regional scale [14]. Furthermore, quadrat survey data in this study indicated that C. tientaiensis exhibited an extremely low population density, with only 1–2 individuals recorded per quadrat, presenting a typically sparse distribution pattern. This indicates that its broader ecological niche did not translate into a survival advantage for the population. The wide niche breadth of C. tientaiensis may represent an ecological strategy wherein, under constrained reproductive success, the species sustains population persistence by enhancing individual survivability [43]. Previous studies have shown that there is a positive correlation between the importance value and niche breadth [44–45], indicating that the larger (smaller) the importance value, the larger (smaller) the niche breadth. In this study, a generally positive correlation was observed between the importance value and niche breadth of dominant shrub species, meaning that species with higher importance values (IV ≥ 0.01) typically exhibited greater niche breadth. However, this trend was not consistent in the herbaceous layer. A notable exception was found in Oplismenus undulatifolius, which had the highest importance value (IV = 0.062) but displayed a narrower niche breadth compared to Polygonatum filipes, which had a significantly lower importance value (IV = 0.007). These findings indicate that the relationship between importance value and niche breadth is not simply linear and should be interpreted in the context of species-specific biological traits and microenvironmental conditions. However, some studies have suggested that the distribution frequency of species can more effectively reflect the breadth of species’ resource utilization and explain the changes in its niche breadth [26].
Interspecific associations can reveal the interactive effects among species and the dynamic changes of communities, and community stability is an expression of interspecific associations [24]. Generally, in the initial stage of community succession, species tend to be independently distributed, with weak connectivity, and majority of species pairs show negative correlations. However, as the community succession reaches a relatively stable stage, species are positively and closely connected to maintain the coexistence mechanism. The higher the ratio of positive to negative correlations, the more stable the community [46]. In this study, based on the comprehensive results of niche overlap, overall association tests, qualitative tests (
, AC), and quantitative tests (Pearson, Spearman), it can be concluded that the community successions of the shrub layer and herb layer in the C. tientaiensis community are both in the initial stage. The niche overlap among species is small, the degree of association is low, and the community is unstable, being easily disturbed by external factors. This was primarily due to the high degree of functional similarity among the co-occurring species in this community. This low functional diversity, which could be linked to the East Asian distribution of most species in the community, diminished the community’s resilience to environmental changes [47]. Secondly, it is related to the fact that the habitat of C. tientaiensis is mostly located along roadsides and is vulnerable to human interference. In addition, the results of the AC test do not match those of other test methods. This is because when two species do not co-occur in a sample plot, the AC value must be 0, which leads to an increase in the number of species pairs with extremely significant negative correlations obtained from the AC test [48]. This indicates that the AC test of the association coefficient is highly sensitive and easily affected by other factors. Interspecific associations can reflect the similarities and differences in the utilization of environmental resources by species. If the habitat requirements of two species are similar, they are likely to attract and gather with each other, forming a positive association; if the requirements are very different, they will repel each other, showing a negative association [49]. The niche overlap can not only display the competition situation when different species utilize the same resources but also reflect the degree of similarity in the requirements for ecological factors among species [50]. Therefore, numerous studies have shown that the niche overlap is significantly positively correlated with the Pearson correlation test and Spearman rank correlation test indices [48, 51–52]. This rule exists among most dominant species in this study. For example, C. tientaiensis and Oplismenus undulatifolius have a high niche overlap, and their interspecific association is significantly positive, indicating that they can achieve niche differentiation and interspecific mutualism through adaptation and competition, forming a stable community for species coexistence [39].
Ecological species group
An ecological species group refers to a combination of species in a community that have similar ecological habits and requirements for survival [53]. This study conducted hierarchical clustering analysis based on the Spearman rank correlation coefficient and established a habitat-based nomenclature system by integrating species ecological characteristics. This habitat-naming approach overcomes the limitation of traditional clustering methods that focus solely on species composition similarity, thereby providing actionable guidance for vegetation restoration and species conservation [54]. When the interspecific association of dominant species is positive, the species are in a coexistence relationship. Conversely, when it is negative, there is a phenomenon of mutual exclusion and resource competition. When configuring species in a plant community, species pairs with a significant positive correlation should be selected, which can improve the community stability of vegetation to a greater extent [46]. The investigation found that C. tientaiensis is mainly distributed in areas with relatively sufficient light at the forest edge. It needs to climb and grow by relying on the branches of surrounding shrubs and blooms at the tops of branches with sufficient light [13]. In this study, C. tientaiensis has a significant positive association with these shrub plants (Staphylea bumalda, Lindera erythrocarpa, Litsea cubeba, and Mallotus apelta) (P ≤ 0.05), and it can be planted in combination with any one of them alone. However, when multiple shrub plants are planted in combination, it is necessary to ensure that C. tientaiensis has a positive association with associated species or among associated species (P > 0.05 or P ≤ 0.05) and a weak resource competition relationship (Oik < 0.5). In this study, C. tientaiensis meets the above conditions with these three shrub plants (Rubus idaeus, Lespedeza davidii, and Mallotus apelta), and can be planted in a mixed manner with them, which can provide a supporting role for C. tientaiensis in the community and enhance community stability. Secondly, among the dominant species in the herb layer, plants such as Lophatherum gracile, Lygodium japonicum, or Pseudocyclosorus esquirolii can create a shaded environment for the roots of C.tientaiensis. Therefore, when C. tientaiensis is reintroduced into the wild or the native environment is restored, attention should be paid to the ecological requirements of various configured plants. It is necessary to appropriately remove associated species with a strong negative association and replant or configure native plants with a strong positive association to increase the ratio of positive and negative associations among species and the stability of the community.
Conclusion
The interspecific associations among common plant species in the C. tientaiensis community are loose, with weak correlations. The community succession is in the initial stage and in a dynamic process of positive succession. The associated species of C. tientaiensis are mainly of the East Asian distribution type, which may monopolize limited resources. Meanwhile, the shortage of C. tientaiensis seedlings indicates that its growth and natural regeneration capabilities are restricted, and the population is at risk of decline. Therefore, when restoring the native habitat, it is necessary to combine artificial nurturing measures, moderately clear competitive species in the herb layer such as Youngia heterophylla and Ophiopogon japonicus, as well as invasive species (Erigeron canadensis and Eleusine indica), to improve the conditions for seed germination and seedling growth, optimize the proportion of associated species in different floras, and increase the ratio of positive and negative associations among species and the stability of the community. At the same time, artificially breed C. tientaiensis plants, select suitable sites and habitats (communities of species such as Rubus idaeus and Lespedeza davidii) for local reintroduction and ex-situ conservation, expand the population distribution range, and promote the enhancement of the C. tientaiensis population.
Supplementary Information
Below is the link to the electronic supplementary material.
Acknowledgements
My special thanks go to Professor Ji Mengcheng and Professor He Yunhe for their support during the field investigation and collection of Clematis germplasm resources. I also extend my sincere appreciation to Shi Dujuan for her constructive feedback during the paper revision, and to Associate Professor Yang Liyuan for her invaluable assistance in the writing of this thesis.
Author contributions
Shunyun He: Conceptualization, Methodology, Software, Investigation, Formal analysis, Writing-original draft. Zhigao Liu: Conceptualization, Funding acquisition, Resources, Supervision, Writing-review & editing. Hanxi Yang: Data curation, Writing-original draft. Jichen Wang: Visualization, Investigation. Xinli Zeng: Visualization, Writing-review & editing. Duojie Wei: Visualization, Investigation.
Funding
The research was supported by Zhejiang Science and Technology Major Program on Agricultural New Variety Breeding [2021C02071-6-4] and Major science projects for agriculture (floriculture) new variety breeding of Zhejiang province [2016C02056-13-4].
Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
Not obtained - either because the research does not involve human participants or their data, or for some other reason. We obtained official permission from the Natural Resources and Planning Bureau of Tiantai County, Taizhou City, Zhejiang Province, China to conduct the study and collect samples on this public land.
Consent for publication
We, the undersigned authors, declare that all authors have read and approved the final version of the manuscript entitled ‘Analysis of niche and interspecific associations of dominant associated species in the community of the rare and endangered plant Clematis tientaiensis’ and agree to its submission to BMC Ecology and Evolution. We confirm that there are no conflicts of interest that could affect the publication of this work, and all authors consent to the publication of the manuscript in the aforementioned journal.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Supplementary Materials
Data Availability Statement
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.