Diversity, physiological, and morphological attributes of indigenous tropical tree species for rehabilitation, climate change adaptation and mitigation of Upper Marikina River Basin protected landscape

Due to anthropogenic actions (shifting cultivation, small scale mining, timber-cutting and poaching) and forest fires, almost half of the land area of the Upper Marikina River Basin Protected Landscape in Rizal Province, Philippines, has been degraded, ushering the need for immediate rehabilitation. This study aimed to assess the potential of indigenous species as part of rehabilitation strategies and enhancement of climate change adaptation and mitigation in the area, as well as to characterize the morphological and physiological attributes of indigenous trees and their carbon stock potential. Eleven-month old indigenous species of Alahan (Guioa koelreuteria), Dungon (Tarrietia sylvatica), Palosapis (Anisoptera thuriftera), Syzygium (Syzygium malaccense), Yakal (Shorea astylosa) and Narra (Pterocarpus indicus) as border strips, were planted in the field in February 2014 following Randomized Complete Block Design (RCBD). Seedlings were planted in three blocks at three (upper, middle and lower) elevations with a 4-m x 5-m spacing between seedlings and a gap of 5-m in between blocks. Growth parameters (diameter, height, number of leaves and buds, fresh and dry weight, root-shoot ratio, leaf anatomy and survival rate) were measured and physiological attributes (net photosynthesis, transpiration rate and stomatal conductance, size and number) were determined. Results revealed that the most diverse species were Palosapis, followed by Syzgium and Dungon, which garnered the highest overall performance in the three sites. These tree species performed the best in most of morphological aspects (height, diameter, number of buds), growth performance (fresh weight and oven dry wieght of roots and shoots), survival and other attributes (average number of branches, root branching, secondary roots, and length of stem, secondary roots). Meanwhile, Syzygium, Palosapis aspects (net photosynthesis, transpiration, stomatal conductance) due to their high net photosynthesis coupled with increased light intensities brought about by their small-sized stomata that provides high resistance to transpiration. Dungon, Polasapis and Syzgium exhibited very strong correlation for net photosynthesis and fresh and dry weight. Likewise, chlorophyll content was correlated to fresh weight and leaf area. Similarly, fresh and dry weight is highly correlated with net photosynthesis. Lastly, stomata number and size were also highly correlated to stomatal conductance and transpiration. It was found that Dungon is best planted at almost all elevations of Mt. Baetangan, Mt. Campanan and Mt. Pamitinan. Meanwhile, Polasapis thrives best in Mt. Campanan and Mt. Pamitinan, particularly at the upper elevation. Syzygium is best suited for Mt. Baetangan and Mt. Pamitinan, and at blocks 2 and 3 in Mt. Campanan. These three species are ideal for the reforestation and rehabilitation of grasslands,marginal and denuded areas. Dungon, Palosapis and Syzygium showed high growth performance and exhibited the best potential for biomass production to support climate change adaptation and mitigation. Syzygium, in particular, is best for the enhancement of biodiversity in the area, serving as a shelter for avian species,among others. Thus, the results of this one-year study identified Dungon, Palosapis and Syzygium as showing excellent early-stage growth and physiological characteristics, giving them high potential for carbon sequestration and sxcellent biomass production for continuing reforestation program in the area.