Background The Daqing river basin is an important component of the water resource security system in Xiong'an New Area and a key area for governance in the 14th Five-Year Plan. However, due to arid climate and severe soil erosion, the upstream of the basin has experienced flow interruption and frequent river dry-ups, resulting in low vegetation coverage and poor water conservation function. Therefore, comprehensive basin governance is urgently needed, with a focus on providing technical support for "appropriate tree species in appropriate areas" and "scientific forest management" to the upstream water conservation forests.

Methods The present study was carried out in the Dalan small watershed located in the upper reaches of the Daqing river basin. Through field surveys and indoor experiments, eight site factors, including topography and soil, were obtained for research.By employing correlation analysis, principal component analysis, and ArcGIS overlay analysis, the primary factors that impacted the site type division were identified and site type maps were generated. The index weight was determined using the mean square deviation and analytic hierarchy process. Kriging interpolation was used to convert the sample point data into surface data, which was then standardized using the fuzzy membership method. The site quality grade map was generated by overlaying the index weight using raster calculator, and subsequently, reclassified and graded.

Results 1) Elevation, slope, aspect and soil type are the dominant site factors. 2) Dalan small watershed is divided into 26 site types, and the site type of hilly gentle sunny slope cinnamon soil is the main one, accounting for 16.37%.3) There is no "excellent" site in the small watershed, with "good" site types accounting for 50.47% and "medium" site types accounting for 48.48%. The "poor" site type accounts for 1.05%.

Conclusions When constructing water source conservation forests based on the principle of "suitable land and suitable trees, " attention should be paid to the classification and quality evaluation of the site types. For different types and qualities of sites, appropriate afforestation tree species and spatial allocation schemes should be selected to improve the productivity of forest land. This can provide theoretical guidance for the scientific afforestation of the relatively tree-poor regions in the Beijing-Tianjin-Hebei area in northern China.