Under a pronounced climate warming, permafrost has been degrading in most areas globally, but it is still unclear in the northwestern part of the Da Xing'anling Mountains, Northeast China. According to a 10-year observation of permafrost and active-layer temperatures, the multi-year average of mean annual ground temperatures at 20 m was −2.83, −0.94, −0.80, −0.70, −0.60, and −0.49 ^∘C, respectively, at boreholes Gen'he4 (GH4), Mangui3 (MG3), Mangui1 (MG1), Mangui2 (MG2), Gen'he5 (GH5), and Yituli'he2 (YTLH2), with the depths of the permafrost table varying from 1.1 to 7.0 m. Ground cooling at shallow depths has been detected, resulting in declining thaw depths in Yituli'he during 2009–2020, possibly due to relatively stable mean positive air temperature and declining snow cover and a dwindling local population. In most study areas (e.g., Mangui and Gen'he), permafrost warming is particularly pronounced at larger depths (even at 80 m). These results can provide important information for regional development and engineering design and maintenance and also provide a long-term ground temperature dataset for the validation of models relevant to the thermal dynamics of permafrost in the Da Xing'anling Mountains. All of the datasets are published through the National Tibetan Plateau Data Center (TPDC), and the link is https://doi.org/10.11888/Geocry.tpdc.271752 (Chang, 2021).

The framework of Quaternary permafrost in China was reconstructed for the first time on the basis of available periglacial, glacial, and other proxies. During the Early Pleistocene (2.68–0.80 Ma BP), permafrost advanced southwards to 47–50° N in northern China and possibly occurred in alpine regions in western China. During the Middle Pleistocene (800–130 ka BP), permafrost occurred extensively on the Qinghai-Tibet Plateau (QTP) and in alpine or mountainous regions of northern, western, central, and northeastern China. The Great Interglacial occurred afterward and before the Last Glaciation, but the evidence of permafrost for this period has been seldom found. Permafrost evolution of the Last Glaciation (72–19 ka BP) in China is divided into: Expansion (72~50 ka BP), degradation (50–26 ka BP), and intensive expansion during the Last Permafrost Maximum (LPMax, 26–19 ka BP) with a permafrost extent of 5.3 × 10⁶~5.4 × 10⁶ km², and when major features of present permafrost took shape. Permafrost fluctuated during the Younger Dryas (12.9–11.7 ka BP). Since the Holocene, permafrost in China expanded and retreated to lesser extents, forming the current permafrost environment. The Holocene evolution of permafrost was divided into: Unstable climate but stable permafrost during the early Holocene (11.7~8.5–7.0 ka BP); permafrost degradation during the Last Permafrost Minimum (LPMin, or the Holocene Megathermal; 8.5–7.0~4.0–3.0 ka BP) and the Medieval Warm Period (MWP; 1.0~0.5 ka BP); permafrost expansion during the Neoglaciation (4.0–3.0~1.0 ka BP) and the Little Ice Age (LIA; 0.5~0.1 ka BP); and recent permafrost degradation (20th century to the present). However, this review paper only provides the framework of Quaternary permafrost in China and some preliminary discussions. Many key questions await further investigations.

Land use and cover changes (LUCC) in permafrost regions have significant consequences on ecology, engineered systems, and the environment. Obtaining more details about LUCC is crucial for sustainable development, land conservation, and environment management. The Hola Basin (957 km²) in the northernmost part of Northeast China, a boreal forest landscape underlain by discontinuous, sporadic, and isolated permafrost, was selected for the case study. The LUCC was analyzed using the Landsat archive of satellite images from 1973 to 2019. A thematic change detection analysis was performed by combining the object-based image analysis (OBIA) and the Support Vector Machine (SVM) algorithm. Four types of LUCC (forest, grass, water, and anthropic) were extracted with an overall accuracy of 80% for 1973 and >90% for 1986, 2000, and 2019. Forest, the dominant class (750 km² in 1973), declined by 88 km² (11.8%) from 1973 to 1986 but had a recovery of 78 km² (12.5%) from 2000 to 2019. Grass, the second-largest class (187 km² in 1973), increased by 86 km² (46.5%) between 1973 and 1986 and decreased by 90 km² (40%) between 2000 and 2019. The anthropic class continuously increased from 10 km² (1973) to 37 km² (2019). Major features in LUCC are attributed to rapid population growth, resource exploitation, agriculture intensification, economic development, and frequent forest fires. Under a pronounced climate warming, these drivers have been accelerating the degradation of permafrost, subsequently triggering natural hazards and deteriorating the ecological environment. This study represents a benchmark for sustainable LUCC management in the Hola Basin, Northeast China.

Degradation of permafrost with a thin overlying active layer can greatly affect vegetation via changes in the soil water and nutrient regimes within the active layer, while little is known about the presence or absence of such effects in areas with a deep active layer. Here, we selected the northeastern Qinghai-Tibet Plateau as the study area. We examined the vegetation communities and biomass along an active layer thickness (ALT) gradient from 0.6 to 3.5 m. Our results showed that plant cover, below-ground biomass, species richness, and relative sedge cover declined with the deepening active layer, while the evenness, and relative forb cover showed a contrary trend. The vegetation indices and the dissimilarity of vegetation composition exhibited significant changes when the ALT was greater than 2.0 m. The vegetation indices (plant cover, below-ground biomass, evenness index, relative forb cover and relative sedge cover) were closely associated with soil water content, soil pH, texture and nutrient content. Soil water content played a key role in the ALT–vegetation relationship, especially at depths of 30–40 cm. Our results suggest that when the ALT is greater than 2.0 m, the presence of underlying permafrost still benefits vegetation growth via maintaining adequate soil water contents at 30–40 cm depth. Furthermore, the degradation of permafrost may lead to declines of vegetation cover and below-ground biomass with a shift in vegetation species.

Pipeline corridors have been rapidly increasing in length and density because of the ever growing demand for crude oil and natural gas resources in hydrocarbon-rich permafrost regions. Pipeline engineering activities have significant implications for the permafrost environment in cold regions. Along these pipeline corridors, the shrubification in the right-of-way (ROW) has been extensively observed during vegetation recovery. However, the hydrothermal mechanisms of this ROW shrubification have seldom been studied and thus remain poorly understood. This paper reviews more than 112 articles mainly published from 2000 to 2022 and focuses on the hydrothermal mechanisms of shrubification associated with environmental changes induced by the rapidly degrading permafrost from pipeline construction and around the operating pipelines under a warming climate. First, the shrubification from pipeline construction and operation and the ensuing vegetation clearance are featured. Then, key permafrost-related ROW shrubification mechanisms (e.g., from the perspectives of warmer soil, soil moisture, soil type, soil nutrients, topography and landscapes, and snow cover) are discussed. Other key influencing factors on these hydrothermal and other mechanisms are hierarchically documented as well. In the end, future research priorities are identified and proposed. We call for prioritizing more systematic and in-depth investigations and surveys, laboratory testing, long-term field monitoring, and numerical modeling studies of the ROW shrubification along oil and gas pipelines in permafrost regions, such as in boreal and arctic zones, as well as in alpine and high-plateau regions. This review can improve our understanding of shrubification mechanisms under pipeline disturbances and climate changes and help to better manage the ecological environment along pipeline corridors in permafrost regions.

Engineering corridors on the Qinghai–Tibet Plateau have substantially modified the regional ecosystem functions and environment, resulting in changes in the alpine ecosystem. In addition, the building and operation of these engineering corridors have led to rapid permafrost degradation, which in turn has impacted local vegetation along these corridors. This study investigated vegetation changes and their driving factors by the methods of coefficient of variation, correlation analysis, and GeoDetector in a 30 km wide buffer zone at each side along the National Highway G214 (G214) at the northern and southern flanks of the Bayan Har Mountains in part of the source area of the Yellow and Yangtze rivers on the southern Qinghai Plateau, West China. The following results were obtained: (1) The Normalized Difference Vegetation Index in Growing Season (NDVI_gs) rose slightly in 2010–2019, with an average annual change rate of 0.006/a. Patterns of NDVI_gs along the G214 exhibited “low at the northern flank and high at the southern flank of the Bayan Har Mountains”. (2) Spatially, average NDVI_gs increased from the first buffer zone at the distance of 0–10 km from the highway centerline to the second buffer zone at 20–30 km perpendicularly away from the G214. Furthermore, the first buffer zone had the lowest coefficient of variation, possibly due to a low vegetation recovery as a result of the greatest influence of the G214 on NDVI_gs at 0–10 km. (3) Furthermore, annual precipitation (AP) was the dominant factor for significantly (p < 0.01) and positively influencing the variations in NDVI_gs (R = 0.75, p < 0.01). Additionally, NDVI_gs was more strongly influenced by the two combined factors than any single one, with the highest q-value (0.74) for the interactive influences of AP and annual average air temperature (AAAT) and followed by that of the AP and mean annual ground temperature (MAGT) at the depth of zero annual amplitude (15 m). Evidently, the construction and operation of the G214 have directly and indirectly affected vegetation through changing environmental variables, with significant impacts on NDVI_gs extended at least 20 km outwards from the highway. This study helps better understand the environmental impacts along the engineering corridors in elevational permafrost regions at mid and low latitudes and their management.