The 850ha on the Surrey-Hampshire border is home to Alice Holt Lodge, one of the main research stations of Forest Research, the scientific agency of the Forestry Commission, which manages the land.
A spokesperson said the huge bank of knowledge and data built up from work there over the past 50 years would now be available to outside researchers.
Forest Research chief executive Professor Jim Lynch said: “Particularly in topics such as climate change we can no longer afford to think in terms of national boundaries and we welcome this step to work more closely with the wider international scientific community.”
The forest incorporates working woodland and recreational areas, and an area of old-growth woodland more than 200 years old.