Maps of historical forests in France and their temporal continuity since the first half of the 19th century

Nationwide digitisation of the French General Ordnance survey (1818–1866) yields a 19th-century forest vector layer covering 99.6% of mainland France, with mean survey date 1843.

• Why it matters: Reliable historical forest baselines are needed to interpret present-day ecosystem dynamics and support conservation planning under the EU Biodiversity Strategy for 2030.
• What they did: The 976 1:40,000 manuscript sheets were scanned, georeferenced, and vectorised, using local elastic transformations on 21% of territory to reduce positioning error from 60 m to 34 m.
• The result: Compared with the Napoleonic cadastre across 600+ municipalities, forest cover percentages were highly correlated (r>0.9), enabling four land-use trajectories and revising historical minimum forest area to 9.9 million ha.