Forêt de Mare Longue, Protected rainforest in Saint-Philippe, Réunion Island, France.

Forêt de Mare Longue is a protected tropical rainforest on Réunion Island that covers steep volcanic slopes with exceptional plant diversity found nowhere else. The vegetation consists of ferns, mosses, and rare trees adapted to the misty highland conditions at this elevation.

The forest stands on a lava flow roughly 300 to 400 years old on the lower slopes of the Piton de la Fournaise. It was classified as a biological reserve in 1958 over 23 hectares, then enlarged to 68 hectares in 1981, when it became the first nature reserve of Réunion. It is managed by the Office national des forêts.

The name Mare Longue comes from the village of Mare Longue below the forest, in Saint-Philippe; it is not a description of highland waters. Locals call this low-altitude rainforest "bois de couleurs des Bas", after the coloured woods it yields. Access to the reserve itself is regulated, but a botanical trail laid out beside it and a botanical guide let visitors see the endemic species.

A marked walking path guides visitors through the forest interior where they can observe native plants in their natural setting. The terrain includes slopes, so sturdy shoes and a reasonable pace are recommended for exploring comfortably.

The reserve covers 68 hectares on a lava flow only 300 to 400 years old, between 150 and 700 metres up the slopes of Piton de la Fournaise. It protects one of the last remnants of the Mascarene lowland rainforest, a formation that once covered the whole windward side below 800 metres and survives on under 5% of its former area.