Objective At present, the protection of historic campus is generally scattered and insufficient overall. Particularly, insufficient attention is paid to the landscape of historic campus with rich historical information and cultural connotation but relatively few material remains, which aggravates the problems of isolation of architectural heritage and fragmentation of historical information in the protection of historic campuses. From the perspective of historic urban landscape (HUL), this research aims to explore the framework and method for landscape evolution and protection value assessment of historic campus, which integrates nature and culture, physical and spiritual elements, as well as historical and present values.

Methods Based on the overall time-space view and dynamic stratification concept, this research, from the perspective of HUL, constructs a framework for landscape evolution and protection value identification of university historical campus, which involves the four aspects of landscape composition analysis (including landscape pattern, landscape elements and associated information), landscape evolution combing, landscape stratification analysis, and plot-based protection value assessment (including historical record value, artistic aesthetic value and spiritual and cultural value). Then the case study of Chongqing University is carried out. Firstly, the landscape composition and evolution of the historic campus of Chongqing University are analyzed based on the interpretation of historical graphics and literature. The landscape in the aforesaid historical campus can be divided into the three parts of landscape pattern, landscape element, and associated information, with landscape pattern being subdivided into macro-regional landscape pattern and campus pattern, landscape element subdivided into three categories (buildings and structures, spatial places, and environmental landscapes) and 10 sub-categories, and associated information divided into the three categories of important historic events, celebrity deeds, and commemorative activities. On this basis, the period of landscape evolution is divided according to the historical chronology. In each historical period, the composition, corresponding characteristics, and overall evolution of landscapes in the historic campus are analyzed. Secondly, the driving force for the landscape evolution of the historic campus of Chongqing University is analyzed, and the plot-based stratification models are summarized. The stratification models of landscape elements can be summarized into three categories: maintenance, coverage, and collage. Finally, the ArcGIS superposition analysis method is used in protection value identification, which combines the qualitative interpretation and quantitative assessment of value characteristics.

Results 1) In terms of landscape evolution, the landscape in the historic campus of Chongqing University was initially built along the river under the influence of natural factors such as landscape environment, and then gradually expanded to the interior area under the influence of social and humanistic factors such as special historical events including the Anti-Japanese War, as well as urban development and talent training needs. As a whole, the depth of historic stratification shows a decrease from the riverfront area to the interior area, with the overall landscape pattern remaining stable in the riverfront teaching area and the gully area (composed of Tuanjie Square, Siqun Square and Minzhu Lake), which confirms the important role of campus landscape in the protection and inheritance of campus history and culture. 2) In terms of protection value, the plots with certain landscape protection value account for 43.3% of the total campus area. Specifically, the plots with the highest comprehensive protection value account for 3.7% of the total area, those with high value account for 11%, those with medium value account for 5.3%, and those with low value accounts for 23.3%. Specifically, the plots with the highest or high value are distributed in the riverfront teaching area and the gully area. And most of them are public open spaces or important buildings that have been built for a long time, serving as the carrier of a lot of activities for teachers and students. In terms of value type, most land values are dominated by historic recording value and spiritual and cultural value, while artistic and aesthetic values are relatively low.

Conclusion The research results may provide theoretical reference and technical support for the identification of landscape protection value of historic campuses in Chongqing and the formulation of classified protection and management measures in spatial planning. In general, differentiated protection and management measures should be formulated according to different importance levels and types of protection value, and the protection and renewal of campus landscape should be comprehensively considered in the overall campus planning. In addition, the research may also provide reference for the protection of other historic campuses and even urban historical areas.