Exotic tree species may help re-establish forests in the Philippines as these species have better productivity traits and physiological characteristics than native species.
Dr. Marilyn S. Combalicer’s study entitled Physiological Characteristics of Nitrogen-fixing Tree Species in Mt. Makiling and La Mesa Watershed, Philippines made use of the exotic tree species Acacia auriculiformis (Auri) and Acacia mangium (Mangium). These two species were compared with the native Pterocarpus indicus (Narra). She picked the three species for their substantial nitrogen-fixing abilities.
The three species were compared across age classes (2-, 10-, and 20-year-old specimens) based on their aboveground biomass and productivity traits. Some of the characteristics measured were the stand densities, basal areas, carbon content, litter production, resource use, soil analyses, and weather data.
For most of these categories, the 20-year-old Mangium and Auri trees had better results, according to Dr. Combalicer. She also observed that higher densities of trees resulted in slower individual tree growth rates. This is because of the greater number of organisms competing for the nutrients. However, according to her, the results of the research are incomparable with other studies, since the rate of biomass and carbon stored in the forest is dependent on the type and age of the forest and the size class of the trees.
The Auri, Mangium, and Narra were also compared based on their physiological characteristics, such as the stomata size and number, leaf anatomical features, chlorophyll content, net photosynthesis, photosynthetic nitrogen use efficiency, transpiration, stomatal conductance, and water use efficiency. Patterns of physiological responses of the specimens were also determined.
For future researches, Dr. Combalicer recommends including a wider range of exotic and native species with different age classes. This would help in understanding the general physiological patterns of these species and assess their ecological effects.
Dr. Combalicer, former assistant professor from the College of Forestry in Nueva Vizcaya State University and now programme consultant at the Korea Forest Service, presented her study at SEARCA’s Agriculture and Development Seminar on 23 August 2011. (Amy Christine S. Cruz)