The study sites BMNNR are located within latitude 45˚42' - 46˚03' N and longitude 82˚26' - 83˚13' E. The conservation area covers an area of 115037.3 km² and encompasses a wide range of elevation from 800 to 2800 m asl ( Abdushali , 2013 ). The climate of BMNNR changes from lower to higher altitudes. The average annual temperature is 6.2˚C, with extreme maximum and minimum temperatures of 38.6˚C and −35.9˚C respectively. The annual accumulated temperature ≥ 10.0˚C is 2869˚C, the annual precipitation is 289.2 mm, and the annual evaporation is 1882.7 mm ( Toksun et al., 2024 ).

The vegetation types in the reserve are diverse, shows variation depending on altitude and climate types. Including the subalpine zone (above 2300 m altitude), mid-mountain zone (1400 - 2300 m altitude), low-mountain zone (900 - 1400 m altitude) and the piedmont plain area (500 - 900 m altitude) ( Liu et al., 2010 ; Wang & Abdushali, 2011 ; Abdushali, 2013 ), which provide a variety of habitats for terricolous macrolichens. The unique geographical location, climate conditions, and vegetation types make the BMNNR an ideal area for studying the niche and interspecific association of terricolous macrolichens.

Sample plots were set up along the altitude gradient in the Tuoli Tasite district of BMNNR, with a total of 15 sample plots. Each sample plot is 10 × 10 m in area. In each sample plot, a total of 25 quadrats each with size of 0.5 × 0.5 m were designed at intervals of 1 m, set out to investigate terricolous macrolichens. For each quadrat, the following data was collected: species name of terricolous macrolichens, coverage and frequency ( Table S1 and Table S2 ), and growth forms. We conducted the lichen survey between 8 June to 22 July 2024 to ensure that the terricolous macrolichens were in a relatively stable growth period. During the collection process, photographs were taken of the sample plots and quadrats for future reference.

At each site, we identified common species in the field and took voucher specimens of all other lichens. We identified the lichen specimens morphologically and/or by microscopic examination of their ascospores, as well as by chemical-spot tests and responses to UV light ( Abbas & Wu, 1998 ; Brodo et al., 2001 ; Orange et al., 2010 ).

Niche breadth: the following two indexes were used to calculate the niche breadth of each terricolous macrolichen species.

Levins index (B₁) ( Zhang, 2004 ; Hong et al., 2013 ):

$B_1=\frac{1}{{{\displaystyle \sum }}_{j-1}^r{\left(P_{ij}\right)}^2}$

where B₁ is the niche breadth of species i; n is the number of sample plots, D_i is the important value of individuals in i sample plot.

Shannon-Wiener Index (B₂) ( Zhang, 2004 ; Liu et al., 2019 ):

$B_2=-\underset{j=1}{\overset{r}{{\displaystyle \sum }}}\left(P_{ij}\ln P_{ij}\right)$

where: B₂ is the niche breadth of species i; r is the number of grades of resources; P_ij is the ratio of the utilization of the Jth resource to the utilization of all resources by species i. Considering that important values can better reflect the utilization efficiency of lichen species on environmental resources, P_ij is an important value of species when using this index to calculate the niche breadth.

Niche overlap: Pianka index (O_ij) will be used to calculate the niche overlap between species i and species j. The formula is:

$O_{ij}={\displaystyle \sum \left(P_{ik}{P}_{jk}\right)}/\sqrt{\left[{\displaystyle \sum {\left(P_{ik}\right)}^2}{\displaystyle \sum {\left(P_{jk}\right)}^2}\right]}$, where P_ik and P_jk are the important valuesof species i and j in resources k, respectively ( Wang et al., 1984 ).

Overall association test: The overall association was determined using the variance ratio method proposed by Schluter (1984) , and the significance of the association was tested using the statistic W ( Ma et al., 2019 ).

χ² test used to test the significance of interspecific association. The contingency table will be established based on the presence or absence of species, and the χ² value will be calculated. If χ² > 3.841, it indicates a significant association; if χ² ≤ 3.841, it indicates no significant association ( Zhao et al., 2018 ; Li et al., 2017 )

Association coefficient (AC): Used to measure the degree of interspecific association. The formula is: AC = (ad − bc)/[(a + b) (c + d) (a + c) (b + d)]^(1/2) when ad ≥ bc; AC = (ad − bc)/[(a + b) (a + c)] when ad < bc, where a is the number of quadrats with both species present, b is the number of quadrats with species i present and species j absent, c is the number of quadrats with species i absent and species j present, and d is the number of quadrats with both species absent. The value of AC ranges from −1 to 1, with positive values indicating positive association and negative values indicating negative association ( Ma et al., 2019 ; Xu et al., 2016 ; Huang et al., 2019 ). Statistical software’s such as SPSS 22.0 and R 4.0.0 were used for data processing and analysis.

As a result of collecting and identifying lichen specimens from Tuoli Tasite, B MNNR, 20 species, in 5 genera were identified. Cladonia lichens dominated with a total of 13 species, accounting for 65% of the in terms of growth forms, there are 14 species of fruticose lichens and 6 species of foliose lichens, accounting for 70% and 30% of the total number of terricolous macrolichen species, respectively ( Table 1 ).

The niche breadth is related to the environmental adaptability of the species. Species with a larger niche breadth are usually more adaptable to environmental changes, while species with a smaller niche breadth are more sensitive to environmental changes ( Li & Tumur, 2023 ). In this study, the niche breadth of different terricolous macrolichen species varied. The species with the largest niche breadth was Cladonia gracilis subsp. turbinata, with a Levins and Shannon-Weiner index of 4.609 and 1.693 respectively, following that is Cladonia cornuta, 3.745 and 1.468 indicating that these two species can utilize a variety of resources and adapt to a wide range of environmental conditions. In contrast, Physconia muscigena has a smaller niche breadth (Levins index of 1.241 and Shannon-Weiner index of 0.434), suggesting that it has higher environmental specificity and narrower resource utilization range ( Table 2 ).

The Importance value is an effective indicator for comprehensively measuring the status and role of species in a community. Through the analysis of species important values, we can understand the dynamics of populations in the community. In Tuoli Tasite district of BMNNR the highest importance value for terricolous lichen species is Cladonia cornuta, which is 14%, followed by 10.92 of Cladonia gracilis subsp. turbinata, which is significantly higher than other lichen species. Meanwhile, we found that the importance values of Anaptychia setifera and Cladonia pocillum, are rather low, 5.51 and 5.10 respectively, but their niche breadth are higher. We believe that these two species are “broad but not specialized” in resource utilization, so it is natural that their individual numbers, distribution frequencies or biomass in the community are difficult to predict, in contrast, Cladonia scabriuscula and Phaeophyscia limbata have relatively high importance values but narrow niches. We believe that species with narrow niches usually focus on certain key resources and with long-term adaptation, develop efficient utilization capabilities, this enables them to form high population densities and high dominance in local areas, thus eventually developing high importance values.

In general, the niche overlap between species in the same habitat is higher than that between species in different habitats. This is because species in the same habitat have similar environmental requirements and thus compete for the same resources ( Li & Tumur, 2023 ).

In Tuoli Tasite district of BMNNR, there is a certain degree of niche overlap among terricolous macrolichen species, the overlap value was between 0 and 0.94 ( Table S3 ). The highest niche overlap occurs between C. conista × C. scabriuscula (0.94), C. cenotea × C. scabriuscula (0.93), C. humilis × C. scabriuscula (0.90), P. constipata × P. muscigena (0.89), C. cornuta × C. scabriuscula (0.87), C. acuminata × C. phyllophora (0.85), C. conista × C. phyllophora (0.85), C. acuminata × C. coniocraea (0.83), P. dubia × P. perisidiosa (0.81); indicating that they have similar resource utilization patterns and may have competitive relationships. For example, most Cladonia lichens exhibit the highest niche overlap values, which is related to their similar demands for resources such as soil moisture and light in their habitats. Although Physcia dubia and Physconia perisidiosa do not belong to the same genus, they share the same growth form and thus utilize habitat resources in the same way, leading to a relatively high niche overlap.

Among them, there is a total of 26 pairs of terricolous lichen species with narrow niche overlap values of 0, indicating that there is no common resource demand and the species are distributed in a specific environment. The niche overlap value of 46 pairs of terricolous lichen are also lower than 0.1, indicating that they also have low niche overlap. In the Tuoli Tasite district of BMNNR, as altitude increases, community species diversity gradually increases, which in turn leads to a decrease in the niche breadth of terricolous macrolichen species and causes changes in niche overlap value.

The overall association of the terricolous macrolichen community as shown in Table 3 , the variance ratio of the overall interspecific association in the community VR = 3.653, >1. This indicates that under the condition of the independent null hypothesis, the overall interspecific relationship shows a positive correlation. The statistical test W was used to test the significance of VR, which showed that the interspecific association of macrolichens was significant, and the species distribution was relatively dependent.

The Pearson correlation coefficient and Spearman’s rank correlation coefficient are important indicators reflecting the linear relationship of interspecific covariation between two species, and they can reflect the quantitative change relationship between species ( Li et al., 2017 ; Ma et al., 2019 ). The Pearson’s correlation coefficient shows that there are 59 pairs of species with a positive correlation, accounting for 31.1% of the total pairs. Among them, 22 pairs have a relatively high correlation coefficient, accounting for 11.6% of the total pairs, and 37 pairs have a moderate association degree, accounting for approximately 19.5% of the total pairs. There are 131 pairs with a negative correlation, accounting for 68.9% of the total pairs, among which 26 pairs are extremely significant with a coefficient of −0.14, indicating a weak negative correlation. The Pearson’s index indicates that different species have a strong degree of independence from each other and their correlation is not close ( Table S4 ).

The Spearman’s correlation coefficient shows that, among the 190 species pairs, 97 pairs of species show a positive correlation, accounting for 51% of the total ( Table S5 ). Among them, the correlation of 3 pairs of species are extremely significant (P < 0.01) (C. conista × P. grisea, C. phyllophora × P. muscigena, C. scabriuscula × C. humilis), and 10 pairs of species have significantly correlation (P < 0.05). There are 93 pairs of species negative associations, accounting for 49% of the total. The correlation between C. acuminata × C. cenotea, A. setifera × C. pocillum and C. gracilis subsp. turbinata × P. dubia are significantly negative. The highest coefficient is 0.98 (C. conista × P. grisea), and the lowest coefficient is −0.54 (C. acuminata × C. cenotea), 0.52 (A. setifera × C. pocillum, C. gracilis subsp. turbinata × P. dubia). This indicates that the positive association relationships among the 20 terricolous macrolichen species in the study area are stronger than the negative association relationships.

There are significant differences in the detection results of species pairs under different methods ( Table 4 ).