Investigating the spatial distributions and associations of tree populations provides better insights into the dynamics and processes that shape the forest community. Korean pine (Pinus koraiensis) is one of the most important tree species in broad-leaved Korean pine mixed forests (BKMFs), and little is known about the spatial point patterns of and associations between Korean pine and community-level woody species groups such as coniferous and deciduous trees in different developmental stages. This study investigated the spatial patterns of Korean pine (KP) trees and then analyzed how the spatial associations between KP trees and other tree species at the community level vary in different BKMFs. Extensive data collected from five relatively large sample plots, covering a substantial area within the natural distribution range of KP in northeastern China, were utilized. Uni- and bivariate pair correlation functions and mark correlation functions were applied to analyze spatial distribution patterns and spatial associations. The DBH (diameter at breast height) histogram of KP trees in northeastern China revealed that the regeneration process was very poor in the Changbai Mountain (CBS) plot, while the other four plots exhibited moderate or expanding population structures. KP trees were significantly aggregated at scales up to 10 m under the HPP null model, and the aggregation scales decreased with the increase in size classes. Positive or negative spatial associations were observed among different life stages of KP trees in different plots. The life history stages of the coniferous tree group showed positive spatial associations with KP saplings and juvenile trees at small scales, and spatial independence or negative correlations with larger KP trees at greater scales. All broad-leaved tree groups (canopy, middle, and understory layers) exhibited only slightly positive associations with KP trees at small scales, and dominant negative associations were observed at most scales. Our results demonstrate that mature KP trees have strong importance in the spatial patterns of KP populations, and site heterogeneity, limited seed dispersal, and interspecific competition characterize the spatial patterns of KP trees and community-level spatial associations with respect to KP trees, which can serve as a theoretical basis for the management and restoration of BKMFs in northeastern China.

In the dynamic monitoring fixed sample plot of 25 ha of coniferous broad-leaved mixed forest in the temperate zone of Northeast China, we used the data from two surveys (2013 and 2018) and microtopography data of the sample plot, and the mycorrhizal type data of tree species to explore whether the different microtopography types and single terrain factors will affect the radial growth of tree species with different mycorrhizal types on a regional scale. We studied the adaptability of tree species with different mycorrhizal types in the north end of Changbai Mountain and the south slope of Laoyeling mountain, and which provided basis for further revealing the response mechanism of tree species with different mycorrhizal types to the microtopography in this area. We found that: the tree species with different mycorrhizal types have higher radial growth rates on gentle slopes than on steep slopes. Tree species on sunny slopes have higher growth rates and survival rates than tree species of the same mycorrhizal type on shady slopes. The quantity and radial growth of AM (Arbuscular mycorrhiza) type, EcM (Ectomycorrhiza) type, and ErM (Ericoid mycorrhiza) type tree species were significantly positively correlated with different microtopography types. The quantity and radial growth of AM type tree species and EcM type tree species were significantly positively correlated with slope. The quantity of AM type tree species, EcM type tree species and the radial growth of EcM type tree species were significantly negatively correlated with slope aspect. The quantity and radial growth of ErM type tree species and radial growth of EcM type tree species the were significantly positively correlated with slope position. We believe that the reasons for these conclusions may be caused by the differences in soil temperature, humidity, and water distribution caused by different slopes.

: Foundation species play important roles in structuring forest communities and ecosystems. Foundation species are difficult to identify without long-term observations or experiments and their foundational roles rarely are identified before they are declining or threatened. We used new statistical criteria based on size-frequency distributions, species diversity, and spatial codispersion among woody plants to identify potential (“candidate”) foundation species in 12 large forest dynamics plots spanning 26 degrees of latitude in China. We used these data to identify a suite of candidate foundation species in Chinese forests; test the hypothesis that foundation woody plant species are more frequent in the temperate zone than in the tropics; and compare these results with comparable data from the Americas to suggest candidate foundation genera in Northern Hemisphere forests. We identified more candidate foundation species in temperate plots than in subtropical or tropical plots, and this relationship was independent of the latitudinal gradient in overall species richness. Two species of Acer , the canopy tree Acer ukurunduense and the shrubby treelet Acer barbinerve were the only two species that met both criteria in full to be considered as candidate foundation species. When we relaxed the diversity criteria, Acer, Tilia , and Juglans spp., and Corlyus mandshurica were frequently identified as candidate foundation species. In tropical plots, the tree Mezzettiopsis creaghii and the shrubs or treelets Aporusa yunnanensis and Ficus hispida had some characteristics associated with foundation species. Species diversity of co-occurring woody species was negatively associated with basal area of candidate foundation species more frequently at 5- and 10-m spatial grains (scale) than at a 20-m grain. Conversely, Bray-Curtis dissimilarity was positively associated with basal area of candidate foundation species more frequently at 5-m than at 10- or 20-m grains. Our data support the hypothesis that foundation species should be more common in temperate than in tropical or boreal forests, and suggest that in the Northern Hemisphere that Acer be investigated further as a foundation tree genus.

Fagaceae trees dominate in the temperate and subtropical forests in East Asia. Understanding the spatial patterns of their carbon contents and the influencing factors can support high-precision forest carbon accounting. A comprehensive understanding of the changes in carbon in multiple organs of trees such as Fagaceae trees is still lacking at a large scale. This study investigated the inter-tissue variation, spatial patterns, and climatic drivers of carbon fraction across nine tissues (leaves, branches, bark, sapwood, heartwood, stump, coarse roots, medium roots, and fine roots) in 41 Fagaceae species (5 genera) from 12 sites across China’s major forest biomes. The sampling sites ranged from northern temperate to northern-tropical and covered an elevation range of 1200 m. The carbon fraction was measured with dry combustion after dried at 60 °C. Variance decomposition revealed that geographical location was the dominant source of variation (16%–55%), outweighing differences at the species and genus levels. Significant disparities in carbon fraction were observed among tissues, following a general pattern of leaves (517 mg g⁻¹) ≈ fine roots (516 mg g⁻¹) > heartwood (510 mg g⁻¹) > sapwood (504 mg g⁻¹) > branches (501 mg g⁻¹) ≈ medium roots (500 mg g⁻¹) > bark (495 mg g⁻¹) > coarse roots (488 mg g⁻¹) ≈ stump (487 mg g⁻¹). This indicated a “high-at-both-ends” arcuate pattern from leaves to fine roots. Spatially, carbon fractions in most tissues exhibited significant declining trends with increasing latitude and eastward longitude. Generalized additive models identified mean annual temperature and precipitation as the most influential factors for most above-ground tissues, while fine roots were primarily regulated by temperature seasonality. These findings help us understand the differences in tree carbon fraction from an organ perspective, highlighting the critical importance of multi-tissue sampling protocol. We recommend integrating the spatial and climatic drivers for refining forest carbon accounting. More species should be included to separate the species and climatic effects in the future.