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Forest planets would provide habitats very suitable for complex life over much of the surface, resulting in life more diverse than there are on Earth. Around Sun-like stars, forest planets appear mostly green from space. Such planets are estimated to be rare in the universe and may comprise less than 0.1% of all planets in the Milky Way Galaxy. At present, the prospects of finding evidence of forests on exoplanets are slim.

The average height of trees, shrubs and other organisms around the planet depend on the strength of planet's gravity. Gravity affects how organisms grow and develop in certain ways. Because gravity acts as breaking mechanism for tree growth, shorter trees tend to be grown in higher gravity environments, while taller trees tend to be grown in lower gravity enviroments. The same mechanism also applies to animals; in addition, they're stronger on higher gravity planets than in counterparts on Earth, and vice versa.

Forest planets tend to have atmospheres thicker than Earth's but with similar proportions of gases, like nitrogen, oxygen, carbon dioxide, and methane. The combination between thicker atmosphere and greater amounts of greenhouse gases would mean heating be distributed more evenly around the planet. As a result, climate would be similar worldwide, allowing forests and wildlife to thrive over much of the planet's surface.

Chlorophyll is a pigment causing plants to appear green on Earth. However, plants on other worlds don't have to be green, depending on the color of parent stars. Planets orbiting around F, G, K, and M-type stars would be suitable for vegetation, but stars brighter than F would emit too much light for plants to absorb energy and thus would not survive. Around late K and M-type stars, plants would need to absorb nearly all of visible light wavelengths, resulting in gray to black plants, and corresponding forest planets would appear dark from space with geometric albedo less than 0.1. Around early to mid F-type stars, vegetations would need to absorb less energy and reflect more light, thus making plants light in color, and corresponding forest planets would appear bright from space with geometric albedo greater than 0.7. Around solar-type stars (from late F to mid G-type star), plants would be green like they are on Earth, but on planets orbiting late G to early K-type stars, vegetations would be brown.