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Article

Uniqueness and Contributing Factors of Main Tree Species Distribution in Kunyu Mountain

by
Shidong Li
1,
Jiming Che
2,
Zhenkai Liu
3,4,
Ran Qiu
3,4,
Can Yang
3,4 and
Yongxia Li
3,4,*
1
Department of Science and Technology, National Forestry and Grassland Administration, Beijing 100714, China
2
Kunyushan Forest Farm of Yantai, Yantai 264100, China
3
Ecology and Nature Conservation Institute, Chinese Academy of Forestry, Beijing 100091, China
4
Kunyushan Forest Ecosystem Observation and Research Station, Yantai 264100, China
*
Author to whom correspondence should be addressed.
Forests 2025, 16(11), 1751; https://doi.org/10.3390/f16111751
Submission received: 10 August 2025 / Revised: 17 November 2025 / Accepted: 18 November 2025 / Published: 20 November 2025
(This article belongs to the Section Forest Biodiversity)
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Abstract

Located in a transitional climatic zone surrounded by sea on three sides, Kunyu Mountain provides an ideal region to study the drivers of plant distribution. The study examined the distribution patterns and environmental drivers of three dominant tree species—Pinus densiflora, Cunninghamia lanceolata, and Pinus koraiensis—using data from 55 permanent plots. A total of 52 plant species were recorded, primarily in warm-temperate areas, with some in other climatic zones. While the native P. densiflora was widespread, the introduced C. lanceolata and P. koraiensis showed limited distribution, with lower richness and growth rates than in their core ranges, yet both regenerated naturally. C. lanceolata mainly occurred below 400 m on sunny slopes, whereas P. koraiensis was concentrated at 400–500 m on shaded slopes. Climate similarity analysis confirmed that local microhabitats created by transitional climate and complex topography offer suitable conditions for both species. These findings improve the understanding of microhabitat roles in species distribution and offer insights for future species introduction strategies.

1. Introduction

Plant distribution follows zonal patterns primarily governed by thermal and moisture gradients. However, local ecological factors, particularly topography, often generate plant assemblages that differ from those typical of the prevailing climatic zone. The mechanisms of species coexistence and biodiversity maintenance have long been fundamental scientific questions in ecology. Different principles have been proposed to explain the phenomenon, with habitat heterogeneity being one of the most prominent drivers [1]. Mountains often exhibit high habitat heterogeneity, which offer diverse niches for plants [2]. However, mountain regions are more vulnerable to global climate change and human activities, thereby affecting the distribution of regional species [3]. Consequently, microhabitat heterogeneity in mountains drives distinct distribution patterns [4]. For example, the distribution of vegetation on Dinghu Mountain is primarily determined by topographic features [5]. Microtopographic variations create pronounced gradients in temperature, humidity, and other critical environmental factors [6,7]. Research demonstrates that topography induces mean thermal variations of 5–8 °C between adjacent sites at equivalent elevations [4]. Furthermore, topography significantly buffers extreme seasonal temperatures, reducing summer maxima by up to 8 °C in shaded valley bottoms and winter minima by up to 4.5 °C on sun-exposed slopes [8].
Located on the Shandong Peninsula, Kunyu Mountain represents a notable ecotone where northern and southern floristic elements converge. Its unique geographical setting, surrounded by sea on three sides, covering a total area of 1750 km2 with a main peak elevation of 923 m, and influenced by a warm-temperate monsoon climate, supports a diverse array of vegetation types [9]. Native warm-temperate species such as Pinus densiflora and Quercus spp. dominate the landscape, while introduced species like Cunninghamia lanceolata (a subtropical native with its natural northern limit along the Qinling Mountains-Huai River line) and Pinus koraiensis (a typical mid-temperate species primarily distributed in Heilongjiang, Jilin, and Liaoning) have also established populations, forming distinct distribution enclaves [9]. This convergence of northern and southern flora establishes Kunyu Mountain as a significant biogeographic ecotone, providing an ideal system for investigating drivers of plant distribution across climatic transitions.
Previous studies in Kunyu Mountain have examined community ecology [9,10], population regeneration dynamics [11,12], interspecific relationships with structural diversity across tree, shrub, and herb layers [13,14] and impacts of vegetation types on soil bacterial community [15]. Recent advancements in species distribution modeling and microclimatic analysis have further highlighted the importance of topographic mediation in creating microrefugia [16,17]. However, despite these efforts, the specific environmental factors enabling the persistence of non-native species such as C. lanceolata and P. koraiensis remain unclear. In particular, the roles of microtopography (e.g., slope aspect, elevation, slope position) and local climate in facilitating their establishment, including whether microhabitats in Kunyu Mountain meet the bioclimatic requirements of these species, have not been quantitatively assessed.
To address this gap, this study systematically investigates the distribution patterns of three key tree species—P. densiflora (native warm-temperate), C. lanceolata (introduced subtropical), and P. koraiensis (introduced mid-temperate)—in Kunyu Mountain through surveys of 55 permanent 30 m × 30 m plots. The specific objectives are: (1) To compare the community characteristics and growth performance of these species in Kunyu Mountain with those in other distribution regions; (2) To identify the key environmental factors (climatic and topographic) influencing their distribution; (3) To evaluate the role of microhabitats in supporting the successful introduction and natural regeneration of these species. By integrating field surveys, climatic analysis, and comparative studies, we elucidates the mechanisms underlying their unique distributional patterns in Kunyu Mountain, significantly advancing understanding of regional phytogeography and floristic evolution.

2. Materials and Methods

2.1. Geographic and Climatic Boundaries

Kunyu Mountain (121°41′−121°48′ E, 37°11′−37°17′ N) is located in the eastern part of the Jiaodong Peninsula, straddling the cities of Yantai and Weihai in Shandong Province, and serves as a vital ecological barrier for the Shandong Peninsula. It covers a total area of 1750 km2, with its main peak reaching an elevation of 923 m. The region experiences a warm-temperate monsoon climate, characterized by a mean annual temperature of 12.3 °C, with extremes ranging from −14.3 °C in January to 37.2 °C in July. The highest monthly mean temperature occurs in July, while the lowest is in January. Mean annual precipitation is 800–1200 mm, concentrated primarily from June to September, accounting for 70% of the annual total. The frost-free period spans 210 days per year. The bedrock consists mainly of Cambrian granite, with minor occurrences of gneiss and quartz porphyry. Soils are classified as forest brown soils (Haplic Luvisols), predominantly sandy loams with an acidic reaction.

2.2. Methods and Data Acquisition

Based on the structure, function, and environmental characteristics of Kunyu Mountain’s forest ecosystems, fifty-five 30 m × 30 m permanent plots were established in 2006. The distribution map of the sample plots is shown in Figure 1. Within each plot, all tree individuals with a diameter at breast height (DBH) ≥ 5 cm were recorded, including species identification, count, DBH, height, and crown width. Five 5 m × 5 m shrub subplots were positioned at the four corners and the center of each main plot to record shrub layer species, abundance, coverage, and height. Environmental factors documented for each plot included geographic coordinates, elevation, slope gradient, slope aspect, slope position, and soil depth.
Meteorological data were obtained from the long-term environmental monitoring records (2015–2024) of the Kunyu Mountain Ecological Station. This station continuously monitors parameters including rainfall, wind speed, atmospheric pressure, air temperature, air humidity, sunshine duration, total solar radiation, photosynthetically active radiation, and soil temperature and moisture, with data recorded at 30 min intervals.
Elevation gradient covered 110–800 m (the full range of woody vegetation distribution in Kunyu Mountain), including low elevations (<400 m, target for C. lanceolata), mid-elevations (400–500 m, target for P. koraiensis), and high elevations (>500 m, target for native P. densiflora). Slope aspect included sunny slopes (135–225°, south/east-facing), shaded slopes (315–360°/0–45°, north/northwest-facing), and semi-sunny slopes (45–135°/225–315°, east/west-facing) to capture microclimatic differences.
To standardize data collection, each 30 m × 30 m plot was divided into a 6 × 6 grid (comprising 5 m × 5 m subplots), and vegetation surveys were conducted across three layers (tree, shrub, herb) from May to October 2023 (the peak growing season) to ensure accurate species identification: For the tree layer (individuals with diameter at breast height, DBH ≥ 5 cm), all individuals were recorded for species name (verified using Flora of China and local botanical guides), DBH (measured at 1.3 m above ground with a diameter tape, precision of 0.1 cm; for forked trunks, measured below the lowest fork), height (measured using a Vertex IV ultrasonic hypsometer (Haglöf, Långsele, Sweden), precision of 0.1 m, with 3 measurements per individual in east, west, and south directions averaged), and crown width (measured as east–west and north–south diameters with a tape measure, precision of 0.1 m, and crown area calculated as π × (EW/2) × (NS/2)); for the shrub layer (individuals with height ≥ 1 m and DBH < 5 cm), five 5 m × 5 m subplots were placed at the four corners and center of each main plot, where records included species name, abundance (number of individuals), coverage (estimated via the line-intercept method: 2 diagonal lines per subplot, with the length of shrub canopy intersecting the lines recorded), and average height (measured for 5 random individuals per species); for the herb layer (individuals with height < 1 m), one 1 m × 1 m herb subplot was placed at the center of each shrub subplot (resulting in a total of 5 per main plot), with records including species name, coverage (visual estimation with 1% increments), and average height (measured for 10 random individuals per species).
For each main plot, the following environmental factors were measured to characterize microhabitats: geographic coordinates and elevation were recorded using a Garmin GPSmap 66st (Garmin Ltd, Olathe, KS, USA, with a horizontal precision of <3 m and a vertical precision of <1 m), and elevation was cross-validated against a 1:5000 topographic map; slope gradient was measured using a Suunto PM-5/360PC clinometer (Suunto, Vantaa, Finland, with a precision of 0.5°) at 3 random locations per plot, and the measured values were averaged; slope aspect was measured using a compass (with a precision of 1°) and then quantified into categorical variables for analysis, including sunny (135–225°), semi-sunny (45–135°/225–315°), and shaded (315–360°/0–45°); slope position was classified as lower (0%–33% of the mountain height), middle (34%–66%), or upper (67%–100%) based on the relative elevation within the local watershed; soil depth was measured using a 1 m-long soil auger at 5 random points per plot (drilled to the bedrock or hardpan), and the measured values were averaged to represent the plot-level soil depth.
Data for locations outside Kunyu Mountain were primarily sourced from: Chinese Virtual Herbarium (CVH) (www.cvh.ac.cn/), Plant Science Data Center (PSDC) (www.plantplus.cn/cn/ibcas, accessed on 5 July 2025), National Forestry and Grassland Scientific Data Center (NFGSDC) (www.forestdata.cn/), Chinese Ecosystem Research Network (CERN) (http://www.forestcen.cn), Observation data from the Kunyu Mountain Forest Ecosystem National Positioning Observation and Research Station and Literature retrieval.

2.3. Data Analysis

Plant species were categorized and analyzed by family, genus, species, and associated climatic zone. Meteorological data were processed to extract key climatic factors influencing plant distribution: Annual mean temperature, Maximum temperature of warmest month, Minimum temperature of coldest month, Annual precipitation, Precipitation of wettest month, Precipitation of driest month, and Frost-free period.
To assess the environmental similarity for specific species (C. lanceolata and P. koraiensis in this study), the degree of correspondence between the climatic requirements (optimal range of climatic factors) of the organism and the actual climatic conditions of Kunyu Mountain was evaluated. A smaller calculated similarity value indicates greater climatic similarity between Kunyu Mountain and the species’ natural range.
As the meteorological variables have different units, they were first nondimensionalized to enable comparison on a common scale:
x k i ′ = x k i − x ¯ k σ k
where xki (k = 1,…,m; i = 1,…,n): the value of climate variable, m: the number of climate variables, n: the number of climate variables.
Following variable standardization, the relative distance (dij) between any two points in the multidimensional space can be computed. A smaller dij value indicates greater climatic similarity. The distance metric is calculated as follows:
d i j = ∑ k = 1 m ( x k i ′ − x k j ′ ) 2

3. Results

3.1. Floristic Composition of Kunyu Mountain

Field surveys across 55 plots documented 5676 woody individuals (trees and shrubs), representing 52 species from 35 genera and 27 families. These included 44 tree species and 8 shrub or small tree species. The flora exhibited complex climatic zonation (Figure 1); warm-temperate species (40 species) dominated, followed by cold-temperate (17 species), subtropical (8 species), and tropical taxa (2 species). Dominant tree species were P. densiflora, P. thunbergii, Quercus acutissima, and C. lanceolata, while shrubs were primarily represented by Rhus chinensis and Symplocos tanakana. This combination reflects the transitional position of Kunyu Mountain between northern and southern climate zones, underscoring its role as a regional convergence zone of floristic elements (Figure 2 and Table 1). The dominance of P. densiflora and the presence of both C. lanceolata and P. koraiensis, otherwise absent from neighboring mountain systems, indicate that Kunyu Mountain provides unique conditions for species beyond their typical ranges.
In comparison to Mount Luzhongnan (Shandong) and Mount Lingkong (Shanxi) within the same vegetation-climate zone, P. densiflora serves as the group species in Kunyu Mountain, while C. lanceolata and P. koraiensis occur exclusively in this region (Table S1). P. densiflora exhibits only scattered distribution in the Mountains of Luzhongnan, where shrub layers are dominated by Ziziphus jujuba var. spinosa and Vitex negundo var. heterophylla. Conversely, Mount Lingkong in Shanxi features P. tabuliformis and Q. wutaishanica as its primary tree species, with minimal presence of P. densiflora. Its shrub communities consist predominantly of Rhamnus davurica and Euonymus alatus. These differences point to the specific ecological and topographic conditions in Kunyu Mountain that support atypical species assemblages (Table S1).

3.2. Community Characteristics of Typical Plant Species: P. densiflora, C. lanceolata, and P. koraiensis in Kunyu Mountain

P. densiflora is primarily distributed in eastern Heilongjiang, the Changbai Mountains of Jilin, central to eastern Liaoning, the Jiaodong Peninsula of Shandong, and the Yuntai Mountains of northeastern Jiangsu, with its highest concentration on the Jiaodong and Liaodong Peninsulas. Compared to the Liaodong Peninsula and the Changbai Mountains region, Kunyu Mountain features P. densiflora as the dominant species in its forests. Its broadleaved forests are dominated by Q. acutissima, with shrubs primarily consisting of S. tanakana, Lespedeza bicolor, and Rosa rubus. In contrast, the Liaodong Peninsula is dominated by Quercus wutaishanica, with shrubs mainly including Zanthoxylum schinifolium, L. bicolor, and Rhododendron micranthum. The Changbai Mountains region, however, is characterized by Quercus mongolica and Fraxinus rhynchophylla as primary trees, with shrubs such as Corylus mandshurica, Eleutherococcus senticosus, and Deutzia scabra being common (Table S2).
C. lanceolata is a significant native tree species in subtropical China, with the Qinling Mountains-Huai River line marking its northern distribution limit. Compared to its core subtropical distribution areas in Hunan and Jiangxi, C. lanceolata communities in Kunyu Mountain exhibit lower species richness and a distinct temperate component. The tree layer consists of monodominant C. lanceolata stands, while the shrub layer is represented by Lindera obtusiloba and S. tanakana. Conversely, C. lanceolata communities in Hunan and Jiangxi display higher species richness and a greater proportion of tropical and subtropical elements. The tree layer includes not only C. lanceolata but also scattered individuals of other species such as Vernicia montana, Cinnamomum camphora, and Pinus massoniana, all growing robustly. The shrub layer is dominated by Maesa japonica with a clumped distribution pattern and contains numerous saplings of deciduous and evergreen trees, like Litsea pungens and Alniphyllum fortunei (Table S3).
P. koraiensis, a typical mid-temperate species, is primarily distributed in Heilongjiang, Jilin, and Liaoning. Compared to its core distribution areas on the Liaodong Peninsula and in the Changbai Mountains, P. koraiensis communities in Kunyu Mountain show lower species richness. The tree layer comprises P. koraiensis associated with P. densiflora and Q. acutissima. The shrub layer features Indigofera kirilowii, Diospyros lotus, and R. chinensis, while the herbaceous layer is dominated by Convallaria majalis. In the Liaodong Peninsula and Changbai Mountains, P. koraiensis is the dominant species in the tree layer, mixed with Fraxinus mandshurica and Tilia amurensis. The shrub layer consists of E. senticosus, Ribes mandshuricum, and E. alatus (Table S4).

3.3. Growth Characteristics of Typical Tree Species in Kunyu Mountain: P. densiflora, C. lanceolata, and P. koraiensis

The diameter at breast height (DBH) and height growth rates of P. densiflora exhibit a progressive decline southward along the latitudinal gradient. For approximately 30-year-old P. densiflora stands in Kunyu Mountain, the mean DBH is 9.8 cm and mean height is 5.7 m, values lower than those observed in the Liaodong Peninsula and Changbai Mountains region (Table 2 and Table S2). C. lanceolata and P. koraiensis were introduced to Kunyu Mountain in the 1950s. After several decades of acclimatization and cultivation, both species now demonstrate natural growth and reproductive regeneration within the Kunyu Mountain area. However, their growth performance remains inferior to that observed in their core distribution ranges. Specifically, the mean annual volume increment of C. lanceolata stands in Kunyu Mountain ranges from 3 to 6 m3/ha/yr, significantly lower than the increments recorded in Mount Funiu, Henan (7–10 m3/ha/yr), Mount Dagang, Jiangxi (9–13 m3/ha/yr), and Mount Fanjing, Guizhou (7–12 m3/ha/yr) (Table 2 and Table S3). The mean annual DBH increment of P. koraiensis stands in Kunyu Mountain is 0.3 cm. This growth rate is lower compared to its natural core distribution areas: 0.6 cm in the Liaodong Peninsula and 0.72 cm in the Changbai Mountains, Jilin (Table 2 and Table S4).

3.4. Environmental Factor Characteristics of Kunyu Mountain Overall and the Distribution Areas of C. lanceolata and P. koraiensis

The overall mean annual temperature (MAT) of Kunyu Mountain is 12.3 °C, with mean annual precipitation (MAP) of 1000 mm. These values are higher than those of the Liaodong Peninsula (MAT 8.9 °C, MAP 799 mm) and the Changbai Mountains region (MAT 4.7 °C, MAP 900 mm). Within the C. lanceolata distribution area in Kunyu Mountain, MAT and MAP (14.4 °C, 1150 mm) are lower than in its core distribution area in Jiangxi (16.0 °C, 1591 mm) but higher than at its natural northern distribution limit in Henan (14.0 °C, 886 mm). The MAT in the P. koraiensis distribution area of Kunyu Mountain (11.7 °C) is higher than in its natural range (Liaodong Peninsula: 6.5 °C; Changbai Mountains: 4.7 °C), while MAP remains comparable at approximately 900 mm (Table 3).
Significant differences exist in topographic indicators (elevation, slope gradient, slope aspect, slope position) for the distributions of P. densiflora, C. lanceolata, and P. koraiensis between Kunyu Mountain and their natural ranges (Table 3). P. densiflora is widely distributed throughout Kunyu Mountain, occurring from ~110 m to 800 m elevation, primarily on middle-lower slope positions, with no marked preference between sunny and shaded slopes. In contrast, within its natural ranges on the Liaodong Peninsula and Changbai Mountains, it concentrates on sunny south- and southeast-facing slopes at low-to-middle elevations (200–600 m). C. lanceolata in Kunyu Mountain is restricted to elevations below 400 m, predominantly on sunny and semi-sunny slopes (south- and east-facing aspects) at lower slope positions. Conversely, in its core natural distribution areas (e.g., Henan and Jiangxi), it occurs up to 1000 m elevation (locally reaching 2000 m) and occupies diverse slope aspects and positions. P. koraiensis in Kunyu Mountain is confined to shaded, mid-slope positions at higher elevations (400–500 m). This elevational range is lower than in its core distribution area in the Changbai Mountains (500–1200 m).

3.5. Analysis of Drivers Underlying the Specific Plant Distribution in Kunyu Mountain

Kunyu Mountain is situated within a transitional zone between the warm-temperate monsoon climate and the subtropical humid climate. This region exhibits subtropical characteristics—high temperatures and abundant rainfall in summer—alongside warm-temperate features—cold, dry winters. This climatic duality facilitates the coexistence of flora from northern and southern phytogeographic regions. Furthermore, the east–west orientation of the Kunyu Mountain range creates numerous north–south branching ridges and valleys. The intricate network of ravines dissects the landscape into diverse microtopographic units, generating significant microenvironmental heterogeneity. These microhabitats are critical for the successful introduction and establishment of both southern (e.g., C. lanceolata) and northern (e.g., P. koraiensis) plant species.
To further elucidate the role of microhabitats, climate similarity distances were calculated based on three key climatic factors: mean annual temperature (MAT), mean annual precipitation (MAP), and mean annual frost-free period (FFP). This analysis assessed the climatic similarity between the distribution areas of C. lanceolata and P. koraiensis in Kunyu Mountain and their respective natural ranges (Table 4). The results show: The climate similarity distances between Kunyu Mountain and the core distribution areas of C. lanceolata (Jiangxi and Guizhou) are 2.38 and 1.88, respectively. These values are lower than the distances between its current reported northern limit (Henan) and the core areas in Jiangxi (3.0) and Guizhou (2.27). The climate similarity distance between the P. koraiensis distribution area in Kunyu Mountain and its core area in Jilin is 3.35. This value approaches the distance between its natural southern distribution limit (Liaoning) and the core area in Jilin (3.26). These findings confirm that the microclimatic conditions (microhabitats) within the distribution areas of C. lanceolata and P. koraiensis in Kunyu Mountain satisfy the bioclimatic requirements for their growth and persistence.
Together, these findings demonstrate that Kunyu Mountain is not merely a repository of species but a dynamic ecological laboratory where transitional climate and microtopography interact to produce unique distributional enclaves. The results highlight mechanistic drivers of distribution, providing evidence for the role of microhabitats in sustaining species beyond their primary ranges.

4. Discussion

4.1. Uniqueness of Vegetation Distribution in Kunyu Mountain

Habitat heterogeneity can be influenced in different dimensions that correspond to the biological requirements of the species, such as climate, topography, geological history, and human activities, thereby generating distinct species-specific distribution patterns [18,19,20]. Kunyu Mountain lies within the warm-temperate deciduous broadleaf forest zone, where natural vegetation typically features Quercus-dominated deciduous forests. The Mountains of South-Central Shandong exemplify this zone, supporting extensive Q. acutissima forests [21]. While Kunyu Mountain exhibits deciduous broadleaf characteristics, it uniquely harbors large-scale P. densiflora stands, forming natural secondary forests co-dominated by P. densiflora and Quercus species. Field investigations reveal diverse floristic elements in Kunyu Mountain: warm-temperate species (e.g., P. densiflora) predominate, complemented by cold-temperate, subtropical, and tropical components. This aligns with Shandong’s overall floristic composition but distinguishes itself through pronounced dominant families/genera, complex phytogeographic origins, relict characteristics, and high richness of rare/endangered plants [22].
Among Kunyu’s vegetation types, P. densiflora, C. lanceolata, and P. koraiensis are most representative. P. densiflora constitutes Kunyu’s iconic vegetation type, forming China’s largest and best-preserved natural stands. The significant presence of subtropical and tropical elements positions Kunyu as the northern distribution limit for numerous evergreen/semi-evergreen subtropical plants [13,22]. C. lanceolata naturally reaches its northern limit along the Qinling-Huai River line; its successful introduction to Kunyu extends this species’ range to its current northernmost boundary. P. koraiensis naturally occurs southward to the Liaodong Peninsula-historically connected to Shandong Peninsula-where vegetation similarities exist. However, P. koraiensis does not naturally occur on Shandong Peninsula; its establishment in Kunyu now marks the species’ southernmost distribution limit [23,24].
Within the warm-temperate deciduous forest zone, P. densiflora occurs sporadically outside Kunyu, while C. lanceolata and P. koraiensis are restricted in Kunyu, forming distinct distribution enclaves. Since C. lanceolata and P. koraiensis are absent or rare in other parts of the same vegetation-climate zone, the presence of these species in Kunyu Mountain further underscores its ecological uniqueness. This pattern is consistent with the concept of microrefugia, where local topography and microclimate create suitable conditions for species beyond their typical ranges [4,8]. Our findings support the view that Kunyu Mountain serves as a significant biogeographic ecotone, facilitating the coexistence of northern and southern floristic elements.

4.2. Drivers of Specific Plant Distribution in Kunyu Mountain

As a unique ecosystem, a mountain region features a highly complex environmental heterogeneity resulting from the interplay between climate and topography. This interaction creates numerous local microclimates that diverge from the regional climate [25]. Both C. lanceolata and P. koraiensis exhibit natural regeneration and have established self-sustaining populations in Kunyu, indicating suitable growth conditions. C. lanceolata primarily occupies elevations below 400 m on south- and east-facing slopes, while P. koraiensis concentrates on north-facing slopes at 400–500 m. This distribution reflects Kunyu’s complex microtopography, which generates local microclimates distinct from regional conditions. Climate similarity analysis (integrating temperature/precipitation metrics) confirms microclimatic congruence between Kunyu and these species’ native ranges, enabling Kunyu to serve as a convergence zone for northern and southern flora.
Temperature and precipitation govern C. lanceolata and P. koraiensis distributions [26,27]. Kunyu’s warm-temperate monsoon climate-moderated by maritime influences and ample rainfall-largely satisfies both species’ climatic requirements. C. lanceolata, a subtropical species, faces range-limiting cold/drought stress at northern margins. Kunyu’s winter frost killed C. lanceolata saplings planted on northwest slopes > 500 m after its 1952 introduction [11]. Consequently, it persists only on sub-400 m south/east slopes, minimizing cold exposure. This aligns with findings that cold avoidance is critical for its survival at northern distribution limits [11,26]. Similarly, the confinement of P. koraiensis to north-facing slopes at higher elevations echoes its preference for cooler and more humid microhabitats, as reported in studies from its native range [28]. Furthermore, decades of species introductions (Table S5) have effectively filled ecological niches, facilitating north–south floristic integration. Significant warming and shifts in precipitation patterns have been documented across numerous mountain ecosystems over recent decades [29]. Given this context, the climate sensitivity of transitional vegetation in Kunyu Mountain (e.g., C. lanceolata and P. koraiensis) lends it exceptional significance for studying the response dynamics of plant communities to a changing climate.

4.3. Limitations of the Study

While this study provides valuable insights into the distribution drivers of key tree species in Kunyu Mountain, several limitations should be acknowledged. First, the sample size of 55 plots, though representative, may not capture the full heterogeneity of the region. Second, the reliance on static climatic and topographic data may overlook dynamic processes such as climate change impacts or successional shifts. Third, although the flora of Kunyu Mountain includes elements from multiple climatic zones, this study focused specifically on the distribution mechanisms of three dominant tree species rather than on overall floristic diversity. Future studies could benefit from long-term monitoring, remote sensing, comprehensive taxonomic and ecological surveys, and species distribution modeling to predict future range shifts under climate scenarios and to show regional floristic richness.

5. Conclusions

This study demonstrates that Kunyu Mountain supports a unique combination of tree species, including native P. densiflora and introduced C. lanceolata and P. koraiensis. Native species (P. densiflora, Quercus spp.) occupy primary ecological space, while subtropical C. lanceolata thrives in low-elevation valleys/slopes, and cold-temperate P. koraiensis persists on mid-elevation north slopes, establishing distinct distribution enclaves for both species. The coexistence of these species is facilitated by the area’s transitional climate, complex topography, and targeted human introductions, which together create suitable microhabitats that meet their bioclimatic requirements. These findings enhance our understanding of how microhabitats can enable species to persist outside their core ranges, with implications for assisted migration, species introduction, and conservation planning under climate change. This unique configuration establishes Kunyu Mountain as a critical floristic convergence zone between northern and southern China—an exceptional natural ecological museum and invaluable genetic reservoir for rare species.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/f16111751/s1, Table S1: Comparison of vegetation community characteristics between Kunyu Mountain and the same vegetation zone; Table S2: Comparison of vegetation community characteristics in major distribution areas of P. densiflora; Table S3: Comparison of vegetation community characteristics of C. lanceolata in Kunyu Mountain and natural distribution regions; Table S4: Comparison of vegetation community characteristics of P. koraiensis in Kunyu Mountain and natural distribution regions; Table S5: Successful introduction of trees in Kunyu Mountain [21,23,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47].

Author Contributions

Conceptualization, S.L. and Y.L.; writing—original draft preparation, Z.L., C.Y., R.Q. and J.C.; writing—review and editing, S.L. and Y.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by [Ecological Station Monitoring and Operation Project] grant number [KS2025160004].

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Forests 16 01751 g001
Figure 1. Distribution map of sampling plots in Kunyu Mountain. The yellow area indicates the boundary of the protected area, the blue area indicates the boundary of the ecological buffer zone, the red area indicates the core zone of the protected area, and the green area indicates the area of the artificial forest farm. The numbers in the figure represent the plot numbers The geographic coordinate system uses East Longitude. Data source: Ministry of Natural Resources of the People’s Republic of China.
Figure 1. Distribution map of sampling plots in Kunyu Mountain. The yellow area indicates the boundary of the protected area, the blue area indicates the boundary of the ecological buffer zone, the red area indicates the core zone of the protected area, and the green area indicates the area of the artificial forest farm. The numbers in the figure represent the plot numbers The geographic coordinate system uses East Longitude. Data source: Ministry of Natural Resources of the People’s Republic of China.
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Forests 16 01751 g002
Figure 2. Vegetation community characteristics in Kunyu Mountain. (A) species composition; (B) proportion of arbors and shrubs; (C) number of species across climatic zonation.
Figure 2. Vegetation community characteristics in Kunyu Mountain. (A) species composition; (B) proportion of arbors and shrubs; (C) number of species across climatic zonation.
Forests 16 01751 g002
Table 1. Distribution of plant families and genera.
Table 1. Distribution of plant families and genera.
Plant TypeNo. of FamiliesNo. of GeneraNo. of SpeciesPercentage of Total Species (%)
Arbor21294484.6
Shrub66815.4
Total273552
Table 2. Comparison of growth characteristics among P. densiflora, C. lanceolata, and P. koraiensis in Kunyu Mountain and other natural distribution regions.
Table 2. Comparison of growth characteristics among P. densiflora, C. lanceolata, and P. koraiensis in Kunyu Mountain and other natural distribution regions.
P. densifloraDiameter (cm)Height (m)C. lanceolataAnnual Timber Stock Increment (m3/ha/a)P. koraiensisAnnual DBH Growth (cm)Annual Tree Height Growth (m)
Kunyu Mountain9.85.7Kunyu Mountain3–6Kunyu Mountain0.300.15
Liaodong Peninsula15.08.6Henan Funiu Mountain7–10Liaodong Peninsula0.600.40
Changbai Mountain18.112.5Jiangxi Dagang Mountain9–13Changbai Mountain0.720.48
Jianghuai region8.97.4Guizhou Fanjing Mountain7–12
Table 3. Comparison of topographic factors among P. densiflora, C. lanceolata, and P. koraiensis in Kunyu Mountain and other natural distribution regions.
Table 3. Comparison of topographic factors among P. densiflora, C. lanceolata, and P. koraiensis in Kunyu Mountain and other natural distribution regions.
SpeciesRegionAnnual Mean Air Temperature (°C)Mean Annual Precipitation (mm)Frost-Free Period (d)Altitude (m)Slope AspectSlope Position
P. densifloraKunyu Mountain12.31000210110–800All slopes, but optimal at eastern/northern/northwestern slopesMiddle-Lower Slope
Liaodong Peninsula8.9799182200–600Southern/southeastern slopesMiddle-Lower Slope
Changbai Mountain4.7900100200–550Southwestern/southeastern slopesMiddle-Lower Slope
C. lanceolataKunyu Mountain14.41150220285–400Southern/eastern slopesLower Slope
Henan Funiu Mountain14.0886220300–600Southern slopeMiddle-Lower Slope
Jiangxi Dagang16.01591268500–1000All slopes, but optimal at southern slopeMiddle-Lower Slope
Guizhou Fanjing Mountain14.51326275500–2000All slopes, but optimal at southern slopeMiddle-Lower Slope
P. koraiensisKunyu Mountain11.7890200400–500Northwestern slopesMiddle Slope
Liaodong Peninsula6.5900189200–800Northern/northeastern slopesMiddle-Lower Slope
Changbai Mountain4.7900100500–1200Northern/northwestern slopesMiddle Slope
Table 4. Comparison of climate similarity in C. lanceolata and P. koraiensi between Kunyu Mountain and their natural distribution regions.
Table 4. Comparison of climate similarity in C. lanceolata and P. koraiensi between Kunyu Mountain and their natural distribution regions.
C.lanceolataKunyu MountainHenan Funiu MountainJiangxi Dagang MountainGuizhou Fanjing MountainP. koraiensisKunyu MountainLiaodong PeninsulaChangbai Mountain
Kunyu Mountain0.000.812.381.88Kunyu Mountain0.00
Henan Funiu Mountain 0.003.002.27Liaodong Peninsula2.270.00
Jiangxi Dagang Mountain 0.001.39Changbai Mountain3.353.260.00
Guizhou Fanjing Mountain 0.00
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Li, S.; Che, J.; Liu, Z.; Qiu, R.; Yang, C.; Li, Y. Uniqueness and Contributing Factors of Main Tree Species Distribution in Kunyu Mountain. Forests 2025, 16, 1751. https://doi.org/10.3390/f16111751

AMA Style

Li S, Che J, Liu Z, Qiu R, Yang C, Li Y. Uniqueness and Contributing Factors of Main Tree Species Distribution in Kunyu Mountain. Forests. 2025; 16(11):1751. https://doi.org/10.3390/f16111751

Chicago/Turabian Style

Li, Shidong, Jiming Che, Zhenkai Liu, Ran Qiu, Can Yang, and Yongxia Li. 2025. "Uniqueness and Contributing Factors of Main Tree Species Distribution in Kunyu Mountain" Forests 16, no. 11: 1751. https://doi.org/10.3390/f16111751

APA Style

Li, S., Che, J., Liu, Z., Qiu, R., Yang, C., & Li, Y. (2025). Uniqueness and Contributing Factors of Main Tree Species Distribution in Kunyu Mountain. Forests, 16(11), 1751. https://doi.org/10.3390/f16111751

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