Dynamic response of a Philippine dipterocarp forest to typhoon disturbance

Abstract

AbstractQuestionsNatural hazards can wreak catastrophic damage to forest ecosystems. Here, the effects of typhoon disturbance on forest structure and demography of the 16‐ha Palanan Forest Dynamics Plot in the northeast Philippines were examined by comparing census intervals with (1998–2004) and without (2004–2010) a strong typhoon. Category 4 Typhoon Imbudo, with wind gusts exceeding 210 kph, hit Palanan in July 2003. In this study, we ask: (1) was there an effect of the typhoon on stand structure and biomass; (2) was there an impact on species diversity; (3) did annual mortality, growth and recruitment change significantly between typhoon and non‐typhoon periods; and (4) did the typhoon's impact vary with local topography, from leeward to windward sides of a ridge?LocationLowland mixed dipterocarp forest, Palanan, Isabela, Philippines.MethodsCensus data from 1998, 2004 and 2010 for all trees ≥1 cm DBH in a 16‐ha permanent plot in Palanan, Isabela, were used to assess tree demography. Recorded in the census were species identification and measurements of DBH and tree locations. Biomass was calculated from published allometry.ResultsSpecies diversity and stand structure remained stable, except for an increase in small‐sized trees (1–2 cm) recorded in the census conducted within a year of the typhoon disturbance. Tree mortality was significantly higher during the typhoon interval at 2.27%·yr−1 and more so in windward than leeward habitats. Above‐ground biomass loss in the typhoon interval was minimal (2.64%) and biomass exceeded pre‐typhoon levels after 6 yrs. Recruitment rate during the typhoon interval was almost four times the rate in the non‐typhoon interval that followed, attributed to the rapid growth of seeds and seedlings of pioneer species due to the open, defoliated canopy. Negative population growth was recorded for the early successional species in the non‐typhoon interval. Significantly higher growth rates of trees in the non‐typhoon interval also contributed to biomass gain.ConclusionsMortality, recruitment and growth rates vary across a heterogeneous landscape and are related to typhoon disturbances. The relatively low mortality and fast recovery of the Palanan forest demonstrates the resistance and resilience of the forest to intense episodic typhoon disturbances.