Typhoon Haiyan’s Effects on Interception Loss from a Secondary Tropical Forest near Tacloban, Leyte, the Philippines

Abstract:

Typhoon Haiyan made landfall in the central Philippines on November 8, 2013 as one of the strongest tropical cyclones ever recorded with maximum windspeeds of 314 km h^-1. It affected humans, infrastructure and forests, including the 22-year-old community-managed secondary forest at Manobo near Tacloban on Leyte island. As part of a larger investigation of the impacts of secondary forests on streamflow, gross rainfall (P), throughfall (TF) and stemflow (SF) were monitored between June 2013 and June 2014 using 2 tipping bucket rainfall gauges, 2 large (200 cm by 30 cm) throughfall gutters connected to tipping buckets, 24 roving throughfall gauges (491 cm² each) and 12 stemflow collectors. Leaf Area Index (LAI) above each of the throughfall collectors was measured regularly using a Canopy Analyzer. Average throughfall, stemflow, and interception loss (I) were determined for three different periods:(i) pre-Haiyan (reference), (ii) damaged canopy post Haiyan, and (iii) recovered canopy. Before the forest was disturbed, average TF/P, SF/P and I/P ratios were 0.83 ± 0.22, 0.03 ± 0.01 and 0.15 ± 0.22, respectively. During the period with the damaged canopy, the respective ratios were 0.91 ± 0.18, 0.004 ± 0.01 and 0.09 ± 0.15, while 3 months after the passage of Haiyan the forest canopy had recovered more or less in terms of leaf surface area with average TF/P, SF/P and I/P ratios of 0.86 ± 0.22, 0.01 ± 0.06,and 0.13 ± 0.21, respectively. The respective trends reflected the changes in LAI, which dropped from 5.24 ± 0.79 to 3.80 ± 0.80 right after Haiyan, recuperating to 4.69 ± 0.62 after recovery. These changes in rainfall partitioning after typhoon Haiyan are less pronounced than those reported previously for hurricane-affected forests in the Caribbean and the Pacific, possibly because the Manobo forest was relatively sheltered topographically.