Systematic conservation planning (SCP) seeks to propose new reserves through a scientifically rigorous process using databases and research selection algorithims. However, SCP exercises have been criticized for “knowing but not doing”, i.e. not implementing the proposed reserve. But there is an additional problem that can be called “knowing but not knowing”, knowing things from databases, but not knowing crucial contextual information about community-based social processes that have supported the high forest cover and biodiversity detected. Examined here is how a common property region of the Sierra Norte of Oaxaca, Mexico has maintained high forest cover in the absence of public protected areas, while multiple SCP exercises have advocated for the creation of public protected areas in communal tropical montane cloud forests and pine forests as strategies for biodiversity conservation and resilience to climate change. Methods included archival research, review of community documents, focus group interviews, semi-structured interviews, participant observation, land use transects, and GIS analysis and remote sensing. Conservation in the region originally occurred because of low population densities, steep slopes and a lack of agricultural subsidies, supported by locally adapted agricultural practices. In the 1990s, a transition from passive to active conservation took place with land use zoning plans, community conservation rules, community forestry enterprises and payments for environmental service programs that consolidated a trend towards high, unthreatened forest cover. Today, the study communities have an average of 88.3% forest cover, with 61% of that in informal conservation based on community land use zoning and rules and another 14% governed by forest management plans approved by the Mexican government. We argue thattruly systematic conservation plans would seek to understand how communities in the region are already managing forests for conservation. It is pointless and uninformed to advocate for top-down conservation interventions of forests that are already robustly conserved and resilient to climate change due to community action.