Characteristics of dominant tree species and their niches in the middle section of the Nanling Mountains with altitudinal gradient

This study established 45 ecological monitoring plots in well-preserved natural forests within an altitudinal range of 400–1 800 m in the middle section of the Nanling Mountains. These plots were classified into four forest vegetation types based on elevation range and species composition. This study assessed the differences in dominant tree species and their niche characteristics along various altitudinal gradients by surveying key ecological niche parameters and evaluating the niche resource utilization hypothesis. Results indicated that: (1) Dominant species varied at different altitudes, with more pronounced differences in species composition observed at higher altitudinal differences; (2) In the evergreen broad-leaved dwarf forest at higher altitudes, dominant species exhibited a high degree of uniformity in resource requirements, accompanied by intense interspecific competition; (3) A weak positive correlation was found between the niche width of dominant species and their importance value, while a significant negative correlation was observed with the coefficient of variation of importance value. Although niche width was related to niche overlap and similarity, no clear pattern was established; (4) Species with higher importance values, larger niche widths, and smaller coefficients of variation included Castanopsis eyrei (Champ.) Tutch, Cyclobalanopsis glauca (Thunb.) Oerst, and Schima superba Gardn. et Champ., suggesting that these species are the primary constructive species in the middle section of the Nanling Mountains. These findings provide theoretical support for the sustainable management of forest ecosystems and the conservation of plant diversity in the middle section of the Nanling Mountains and beyond; (5) The division of resource utilization in forest stands at middle and low altitudes aligned more closely with the random niche boundary hypothesis in the resource utilization hypothesis of niche theory; in high-altitude areas, the resource utilization mode of forest stands conformed to the niche priority occupation hypothesis.