Luzon is the largest and northernmost major island of the Philippines, located in the western Pacific Ocean.

Even when glacial advances during the Pleistocene caused sea levels to fall over 100 meters worldwide, this only connected Luzon to the modern islands of Polillo, Marinduque, and Catanduanes.

[2] This long period of isolation and complex internal geography is a primary cause for the great biodiversity and high degree of endemism found on the island of Luzon.

The Zambales Mountains and northern Central Cordillera highlands are more strongly seasonal with a longer dry period and slightly less rainfall generally.

[3] The dipterocarp trees of the lowlands are gradually replaced by oak and laurel forest species with increasing altitude.

[3] With the decreasing temperature from increasing altitude, decomposition is slowed and results in a forest floor thick with humus.

[3] Many endemic animal species reside in the thick, matty soil of the upper montane forests.