Recent systematic analyses of these forests, combining field surveys with extensive literature reviews, have revealed the complex community structures and species compositions that define these ecosystems. The research identifies two distinct vegetation associations based on the dominant species in each vertical layer. The first is the Pinus densiflora var. ussuriensis – Rhododendron dauricum – Carex callitrichos association, found in the drier, higher-altitude regions of the Muling River Basin. The second is the Pinus densiflora var. ussuriensis + Quercus mongolica – Lespedeza bicolor – Carex caespitosa association, located on the lower hillocks between the Xingkai Lakes. These classifications provide a foundational framework for understanding the ecological dynamics and conservation needs of these rare pine stands.

Floristic surveys within these natural forests have recorded a total of 134 vascular plant species, belonging to 59 families and 104 genera. The composition is dominated by angiosperms, with 131 species, alongside two gymnosperm species and one fern species. Among the plant families, Asteraceae is the most species-rich, containing 18 species across 11 genera, followed by Rosaceae with 12 species and Fabaceae with 9 species. The life form composition of the forest is heavily skewed toward terrestrial herbs, which account for nearly 80% of the total species count. Within this herbaceous layer, erect forbs are the most prevalent, making up about 40% of the total species, while woody plants constitute only about 20% of the community.

The Pinus densiflora var. ussuriensis + Quercus mongolica – Lespedeza bicolor – Carex caespitosa association is characterized by a more complex stand structure and higher species richness, with approximately 102 vascular plant species recorded. This association is distributed on hillocks at altitudes of 80 to 100 meters, typically on sunny slopes with gradients of 10 to 20 degrees. The tree layer has a cover of about 70%, with an average diameter at breast height of 15 cm and a height of 13 meters. The presence of broad-leaved trees such as Quercus mongolica, Populus davidiana, and Acer pictum indicates a mixed forest structure. The shrub and herbaceous layers are relatively sparse but diverse, featuring drought-tolerant species like Carex rigescens and Artemisia gmelinii, as well as vines such as Vitis amurensis that add complexity to the community.

In contrast, the Pinus densiflora var. ussuriensis – Rhododendron dauricum – Carex callitrichos association is found in the low mountain hills of the Muling River Basin at higher altitudes of 300 to 600 meters, on steeper slopes of 40 to 60 degrees. This association is characterized by large areas of pure Pinus densiflora var. ussuriensis forest on dry, barren stony soils. The tree layer is uniform, with a cover of about 70% and an average height of 10 meters. The shrub layer is sparse, with a cover of only 20%, and the herbaceous layer is even less dense, with a cover of about 15%. The species composition is simpler, with only 74 vascular plant species, and the community lacks vines entirely. This association is considered the climax vegetation of its specific habitat, exhibiting stability and good natural regeneration.

The ecological dynamics of these two associations differ significantly due to varying environmental conditions and disturbance regimes. The forests on the Xingkai Lake hillocks are currently in decline, facing threats from changing soil conditions, bank collapse, and human disturbance. The rising water level of Xingkai Lake has reduced the width of the hillocks by nearly 50% over the past 30 years, leading to frequent collapses that damage the vegetation. Additionally, the increasing soil moisture in this area favors the establishment of broad-leaved trees, which may eventually transform the pine forest into a broad-leaved mixed forest. This shift underscores the fragility of the Ussuri red pine in the face of hydrological changes.

Human activities have also played a role in the degradation of the Xingkai Lake pine forests. Prior to the implementation of conservation regulations in 2011, intense activities such as soil excavation, land use, and road construction caused considerable damage to the forest on the hillocks. These disturbances have led to irreversible changes in soil conditions and living environments, further threatening the survival of the Pinus densiflora var. ussuriensis in this region. The combination of natural and anthropogenic pressures highlights the urgent need for conservation measures to preserve the remaining stands of this rare pine variant.

Conservation strategies for the declining Xingkai Lake association must focus on preserving germplasm resources and strengthening breeding technology research. Establishing seed orchards and nurseries, along with implementing ex-situ conservation measures, is essential to safeguard the genetic diversity of the species. In contrast, the Muling River Basin association, which is relatively stable and far from human settlements, requires dynamic monitoring to formulate scientific conservation measures and rational utilization plans. The high proportion of seedlings and saplings in this area, reaching 40%, indicates a healthy regeneration process that can be supported through careful management.

The study of Pinus densiflora var. ussuriensis forests provides valuable insights into the ecological resilience and vulnerability of coniferous species in adverse environments. By understanding the specific conditions that support these forests, researchers and conservationists can develop targeted strategies to protect them from further decline. The findings emphasize the importance of maintaining the delicate balance between soil moisture, vegetation composition, and human impact in these unique ecosystems. As climate change and human activities continue to alter landscapes, the preservation of such rare and ecologically significant forests becomes increasingly critical for biodiversity conservation in Northeast China.

Subject of Research: Pinus densiflora var. ussuriensis Forest Alliance

Article Title: Pinus densiflora var. ussuriensis Forest Alliance

Article References: Zhang, Y., Sui, Y., Jin, G., & Wang, H. (2024). Pinus densiflora var. ussuriensis Forest Alliance. One Ecosystem, 9, Article e127449. https://doi.org/10.3897/oneeco.9.e127449

Image Credits: AI Generated

DOI: 10.3897/oneeco.9.e127449

Keywords: Pinus, densiflora, ussuriensis, Forest, Alliance, scientific research