*4.3. Effects of Climatic and Non-Climatic Factors on the Plant Diversity Altitudinal Pattern*

Although environmental factors can influence species distribution, plants can have positive effects on each other [52]. In this study, we focused mainly on the effects of environmental factors on the altitudinal pattern of plant species. Using partial analysis, we evaluated the contribution of climatic (temperature and precipitation) and non-climatic (slope, Hfp, Hii, NPP, population density, pH, and VWC%) factors to the altitudinal patterns of plant diversity. Partial methods are often used to analyze the effects of the main environmental variables and covariates on species distribution. We measured the contribution of climatic and non-climatic factors to plant distribution along the altitudinal gradient by partial CCA. The results showed that the interpretation rate of climatic factors on the altitudinal distribution of plant species (28.89%) was less than that of non-climatic factors (44.51%), which indicated that non-climatic factors were the main driving forces of plant altitudinal distribution in the central Taihang Mountain region. Ohmann and Spies [53] noted that the contribution of climate to species distribution in an Oregon forest was the most significant factor, which contrasted with the results in this study. The joint contribution of climatic and non-climatic factors was 13.72%, and 12.88% of the altitudinal pattern could not be explained by climatic and non-climatic factors (Figure 5). These results implied that the plant distribution pattern was more significantly influenced by altitudinal gradients than by temperature and precipitation gradients.

**Figure 5.** Venn diagram showing the contributions of climatic and non-climatic factors to plant altitudinal distribution in the central Taihang Mountain region, northern China.

By using the Monte Carlo significance test of CCA ordination (Table 2), it was noted that the climatic factors (temperature and precipitation) had the most significant effect on plant altitudinal distribution patterns; moreover, the coefficients of temperature and precipitation reached the most significant and extremely significant levels, respectively. The coefficients of non-climatic factors, including Hfp, Hii, and population density, reached extremely significant levels, implying that these factors also had an important effect on plant altitudinal distribution patterns in the study area. The coefficients of slope, NPP, and soil pH were not significant (Pr > 0.05), implying that these factors were not the dominant drivers of the plant altitudinal distribution in the study area. According to the results of partial CCA, non-climatic factors played a more important role than climatic factors in the plant altitudinal pattern. Among the non-climatic factors, coefficients of Hfp, Hii, and human population density reached an extremely significant level, and the coefficient of water soil content reached a significant level, which implied the anthropogenic factors (Hfp, Hii, and population density) had more important effects than the other non-climatic factors on the plant altitudinal pattern in the central Taihang Mountain region of northern China.


**Table 2.** Monte Carlo significance test of the environmental factors and plant species altitudinal distribution.

Notes: \*\*\* represents the most significant level; \*\* represents an extremely significant level; \* represents a significant level.

### **5. Conclusions**

In conclusion, climatic and non-climatic factors both had important effects on the plant altitudinal pattern. Non-climatic factors were the more significant drivers of plant distribution along the altitudinal gradient compared to climatic factors in the central Taihang Mountain region. In addition, among the non-climatic factors, the anthropogenic factors were the main driving forces of the plant altitudinal distribution. To a certain degree, both climatic and non-climatic factors drove the altitudinal distribution of species richness in the study area. The results of the study suggested that in the central Taihang Mountain region, even in the sub-alpine zone, human disturbance was still a critical factor driving the altitudinal distribution of species richness. From the perspective of sustainable development, in the mountain vegetation protection and management, it is strongly recommended to reduce the impact of human interference.

**Author Contributions:** Conceptualization, J.L. and H.L.; methodology, H.L.; software, T.F.; validation, H.G. and H.L.; formal analysis, H.L.; investigation, H.G.; resources, T.F. and M.L.; data curation, H.L.; writing—original draft preparation, H.L.; writing—review and editing, J.L.; visualization, T.F.; supervision, J.L.; project administration, H.L.; funding acquisition, J.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Key Programme of National Natural Science Foundation of China (No. 41930651).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data supporting the reported results are included in the manuscript text.

**Acknowledgments:** We thank Hongjun Li for the statistics analysis, Jiancheng Zhao and Lin Li for their excellent technical support, and Huijun Gao and Fei Qi for the support in the field survey. We also thank LetPub (www.letpub.com, accessed on 28 October 2022) for its linguistic assistance during the preparation of this manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

### **References**


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