Influences of tree characters on throughfall and stemflow from rainfall and fog in Popa Mountain Park, Myanmar

Available water for communities is insufficient in the central part of Myanmar due to limited rainfall and surface water resources. Over the last two decades, afforestation and reforestation projects have been implemented in this region to provide sufficient water to local communities, expecting forested areas to store more rainwater than other land uses. However, there has been no research and very limited information on rainfall partitioning into throughfall (TF) and stemflow (SF), particularly concerning tree characters. Gross rainfall, TF under different canopy types, and SF of different tree types were measured in 2019. TF and SF were frequently observed even without rain but under foggy conditions. Therefore, both were partitioned into TF and SF from rainfall and fog individually. Sparser canopies resulted in larger TF from rainfall than denser canopies. However, a denser canopy delivered larger TF from fog than a sparser one. TF rates from rainfall in sparser and denser canopies were 54.5% and 51.5%, respectively, while those from fog were 15.2% and 27.2%, respectively. As a result, total TF rate in the denser canopy (70.7%) was significantly larger than that from the sparser one (64.3%). Short trees with small crown projection area and smooth bark (Type I) resulted in larger SF from rainfall than taller trees with large crown projection area and rough bark (Type II). However, Type II trees resulted in larger SF from fog. SF rates by rainfall from Type I and II trees were 17.5% and 12.2%, respectively, while those by fog were 22.2% and 39.5%, respectively. No significant total SF rates were found for Type I (22.5%) and II trees (20.1%). A denser canopy results in larger TF, and Type I trees result in larger SF. In an area where foggy conditions occur frequently and for a lengthy period, however, Type II trees will result in larger SF. These three tree characters (dense canopies, short trees with small crown projection area and smooth bark, and tall trees with large crown projection area and rough bark) should be considered for afforestation and reforestation projects in the Popa Mountain Park to enhance net water input by forests.