Community forest management (CFM) is one way used to mitigate deforestation and forest degradation which have been occurring for more than half a century, particularly in northern Thailand. The collaboration in CFM, especially at multiple scales (e.g. subdistrict, district, or provincial levels) is essential to improve a forest ecosystem status and avoid forest degradation risks in the future. Recently, integrative and participatory modelling methodologies, specifically the Companion Modelling (ComMod), have been implemented in the context of sustainable common-pool resource management in several regions of the world. However, the application of this approach in CFM across institutional scales has still been challenging. Therefore, this research aimed to assess community forest ecosystem functions at the seven villages of Lainan Subdistrict, Wiang Sa District, Nan Province, and conduct a participatory modelling and simulation process to promote collaborative CFM at the subdistrict scale. Ecologically conventional and participatory assessments of ecosystem functions were performed to assess community forest ecosystem status. Lainan's community forests have officially been operating for nearly 50 years. There were 67 tree species, 18 orders of soil fauna, 105 wild mushroom species, and 183 non-timber forest products (NTFPs). Among these diverse NTFPs, Melientha suavis, Oecophylla smaragdina's queen broods, and wild edible mushrooms were identified as the three common NTFPs at this site with the productivity of 2, 12, and 2 kg/ha/y, respectively. The results from the participatory assessment showed that the forest status scores of all villages ranged from 233 to 322 of 500 points. Only village 3 obtained “good” for its community forest ecosystem status while the other villages' status was “moderate”. However, all villages were still facing forest degradation risks. Following this preliminary diagnostic analysis, a ComMod process including two participatory modelling an