**1. Introduction**

Forests are important biological resources as they provide habitat for many of the world's species [1]. Forests also provide timber and non-timber forest products such as bamboo and rattan and food ranging from fruits, mushrooms, honey, and a wide variety of traditional medicines that are critical for human survival [2]. Furthermore, they are key component of many species' habitats, providing nourishment, shelter, and structural features needed for communication, surveillance, and other activities [3]. They also provide significant ecosystem services in terms of nutrients, water cycling, prevention of erosion, sequestration of carbon as well as performing of range of other physical and biological functions. Forests are the main filters in the earth since there are many pollutions from human activities such as industry and motor transportation are disposed, i.e., carbon dioxide (CO2), water (H2O), nitrogen (N), nitrogen dioxide (NO2), and sulfur dioxide (SO2) (National Research Council U.S., 1972). These pollutants can be filtered by plants for its life cycle, thereby reducing pollution at the atmosphere, although CO2 and H2O become main material for their photosynthesis [4]. Results from photosynthesis of plants are the main energy resources for all animal life including human. It is a substantial ecosystem service in terms of providing nutrients, water recycling, prevention of erosion, and carbon storage in the terrestrial ecosystem as well as sequestering CO2 in the atmosphere [5–8].
