Progress of physical geography in China: Toward elements correlated,processes coupled,and spatial integrated research

Physical geography focuses on the Earth surface system and is dedicated to revealing how people affect the environment and how the environment reacts to people (Peng et al., 2020). Physical geography emphases on principles of field-based observation and generalization, classification, and understanding of processes and dynamics of environmental systems (Aspinall, 2010). Physical geography is regarded as the cornerstone of comprehensive geographical study (Fu et al., 2019). It has the strong identity for the geographical approach to the earth and environmental sciences and the spatio-analytical approach integrating deductive and inductive studies (Gregory et al., 2002). The outstanding feature of physical geography is the comprehensiveness and regionality, which can be specified as using a spatial integrated perspective to understand correlated environmental elements and coupled environmental processes (Figure 1). It is certain that interactions, especially those brought out by attention to human in the environment at regional or landscape scale, will increase the impact of physical geography (Clifford and Malanson, 2019).OPEN IN VIEWER

Emphasizing the harmony between human and nature, China highly values environmental protection under the Ecological Civilization thought and provides good opportunities for the development of physical geography (Peng et al., 2020). Physical geography in China has experienced fast development in recent years and provided disciplinary support for regional and national sustainable development (Chen et al., 2019; Fu and Pan, 2016; Fu et al., 2019). Chinese geographers’ efforts towards meeting the sustainable development include: the sensitive process capture of regional responses and feedbacks to global change; the cognition and geographical solution of human–environment conflicts; and the mutual promotion of spatial governance and geographical practices (Liu et al., 2019). Some typical geographical units, such as the world’s highest plateau - the Tibetan Plateau, have provided unique and valuable scientific evidence on the research of element correlation and processes coupling in Earth system (Chen et al., 2021). However, reviews on the new regional findings and contributions to sustainable development in specific branches of China’s physical geography are relatively lacked, especially for international geographers. In this special issue, seven selected reviews and articles are published as the front-edged progress of physical geography in China, demonstrating China’s physical geography is gradually toward elements correlated, processes coupled, and spatial integrated research.

China is rich in diverse aquatic environments. Understanding key N biogeochemical processes and N₂O dynamics is critical for uncovering the responses of China’s aquatic environments to human activities. Hou et al. (2022) found that the response of N transformations to oxygen level was not completely consistent and was affected by substrate availability among different aquatic ecosystems; and the biogeochemical processes and microbial activities of sediment in a unit volume might be higher than those of the water body, but the total volume of the water column in aquatic environments was larger than that of sediment with intensively biogeochemical processes. The research frontier is gaining interdisciplinary modeling efforts by incorporating biogeochemical processes and microbial data to understand the N cycle and related environmental implications in China’s diverse aquatic environments.

The Critical Zone is the Earth’s skin. Nitrogen dynamics at ecosystem level profoundly impact the Earth’s surface system, while the nitrogen dynamics in the soil-water system in the Critical Zones of China has not been well summarized. Li et al. (2022) found the nitrogen accumulated in the deep soils of cropland ecosystems due to China’s intensive fertilizer applications, which potentially harmed soil functions and water quality; and there were serious nitrogen pollution issues in some surface waters and groundwater areas, which could be addressed by reducing the fast leaching and considerable nitrogen accumulation in the vadose zone. The long-term Critical Zones Observatories networks are advocated for evaluating ecosystems that support appropriate environmental management strategies.

Vegetation phenology is one of the observable responses of vegetation to climate change, and China’s phenological research has accumulated abundant scientific evidence. However, the large regional differences of vegetation phenology trends in China have not been well summarized. Zhang et al. (2022) found the trends in the spring and autumn phenology were spatially specific during 1982–2020; and in the Northern region, Northwestern region, Qinghai–Tibet region, and Southern region, the change in spring phenology was −0.16, −0.46, −0.18, and −0.13 days/year, respectively, while the change in autumn phenology was 0.02, 0.32, 0.09, and 0.28 days/year, respectively. Temperature was the dominant factor for spring phenology in cold regions, while precipitation, radiation, and temperature co-determined spring phenology in warm regions; and the effect of temperature was larger than that of radiation and precipitation on the autumn phenology across all regions. The research frontier is further revealing phenological feedback mechanisms, such as the agricultural eco-hydrological effects, especially under future extreme climate events to ensure national food security and ecological security.

Vegetation production plays crucial roles in sustaining carbon balance, reducing atmospheric CO₂ concentration, and mitigating global climate change. Chinese scientists have investigated the spatial and temporal patterns of vegetation production using diverse models. Yuan et al. (2022b) summarized that the accuracy and capability of China’s vegetation production datasets were comparable to those of other international datasets; and the drivers of vegetation production change in China were included but not limited to atmospheric CO₂ concentration, atmospheric nitrogen deposition, temperature, precipitation, and radiation, according to the large land use change caused by human activities. The research frontier is improving light use efficiency models, as well as the quantity and quality of forcing data on environmental variables and canopy structure.

China’s experimental manipulation studies also contributed to the understanding of typical ecosystems in the world, such as the high-altitude alpine ecosystems. According to the linkage between cold biome ecosystems and global changes demonstrating high spatial heterogeneity, Bhattarai et al. (2022) used meta-analysis to compare ecosystem responses to warming and altered precipitation between two cold biome ecosystems. It was shown that high-latitude ecosystems were sensitive to warming, and high-altitude alpine ecosystems was sensitive to precipitation. The evidence implies geographical differences on the specific ecosystem traits and particular environmental constraining factors for these two cold biome ecosystems.

Paleoenvironmental change is an area of thriving research in China, as is all manner of physical geography research on the Tibetan Plateau. Yuan et al. (2022a) reported an investigation of lake level fluctuations since the last deglaciation. It was shown that lake level changes were complicated responses to climate and hydrology, and a cautious interpretation was warranted. Multiple proxy indicators, focusing on sediment chemistry in addition to shorelines, were brought to bear to illustrate the complexities. This evidence is an exemplar of using sedimentary proxies for paleoenvironmental reconstruction.

There are abundant evidences on China’s living environment and human lifestyles from the early Holocene. However, considering China’s large territorial area, the spatial differences in human–environment interaction in Neolithic and Bronze Age periods are not yet well understood. Dong et al. (2022) found that human settlement intensities in the northern East Asia Monsoon Region and south China were relatively low during 10,000–6500 BP, with a small peak during ∼8000–7500 BP, and evidently increased since ∼6500 BP, whereas farming groups began to settle intensively on the Tibetan Plateau and the inland arid region since ∼5200 BP and ∼4000 BP, respectively. The spatial differences in the impact of human activities shed light on the evolution of the human–environment relationship in China during 10,000–2200 BP.

To conclude, the great challenges of sustainable development highlight an urgent need to systematically understand the mechanisms linking humans and nature, and promotion of physical geography enables a more comprehensive and in-depth understanding of regional environmental changes relevant to assuring a more sustainable global development (Fu et al., 2021). This special issue is expected to share the new findings of progress of physical geography in China within selected topics, as well as promote global attentions on the scientific questions in China’s physical geography. It is delightful that Chinese physical geographers has a good early harvest of spatial integrated scientific evidences on correlating environmental elements and coupling environmental processes for national and global sustainable development. For the future development of physical geography in China, it is expected to take spatial integration research as the basic perspective, and human-environment interaction as the core content, along with the combination of deductive and inductive approaches and the strengthening of interregional integration, all under the goal of sustainability (Peng et al., 2020).