Effect of inter-annual climate variability on evapotranspiration and canopy CO₂exchange of a tropical rainforest in Peninsular Malaysia

Abstract

We investigated inter-annual variation of canopy CO 2 exchange (NEE) and evapotranspiration during a 7-year period over a lowland Dipterocarp forest in Pasoh, Peninsular Malaysia, using the eddy covariance method. Annual rainfall fluctuated between 1,451 and 2,235 mm during this period. Annual evapotranspiration estimated by energy budget correction and gap filling using the relationship between latent heat and available energy was 1,287 ± 52 mm. Despite inter-annual variation in rainfall, annual evapotranspiration was stable, except for a slight decrease in the driest year (2009). Evapotranspiration was roughly related to the amount of available energy, but was regulated by stomatal closure to prevent excessive water loss at high vapour pressure deficit. Even during dry periods, no significant decrease in evapotranspiration occurred, as water was supplied from soil layers deeper than 0.5 m. Ecosystem respiration (RE) increased with soil water content. Daytime NEE was also stable during the 7 years, despite climate variability. Afternoon inhibition of canopy photosynthesis was seen every month. Daytime NEE did not become more negative with increasing solar radiation, or with increasing soil water content. During dry periods, gross primary production (GPP) and thus canopy gross photosynthesis decreased slightly, coupled with decreased daytime RE. In this forest, variability in rainfall pattern resulted in seasonal and inter-annual variability in micrometeorology; evapotranspiration, photosynthesis, and RE responded to these changes, and compensated for each other and/or other components of micrometeorology, resulting in rather stable annual evapotranspiration and NEE, even during a very dry year associated with an El Nino Southern Oscillation (ENSO) event.

CTFS‐ForestGEO: a worldwide network monitoring forests in an era of global change

“…At or adjacent to 15 sites, ecosystem-atmosphere gas exchange has been measured using the eddy-covariance technique (e.g., Barford et al, 2001;Kume et al, 2011;Thomas et al, 2011;Kosugi et al, 2012;Soderberg et al, 2012;Wharton et al, 2012;Zhang et al, 2012). There is not a specific CTFS-ForestGEO protocol.…”

Inter-annual variations of net ecosystem productivity of a primeval tropical forest basing on a biometric method with a long-term data in Pasoh, Peninsular Malaysia

“…This study was conducted with filed data about stand dynamics and carbon cycling of a primeval tropical rain forest, which had been obtained at a permanent research plot P1 in the Pasoh Forest Reserve of Peninsular Malaysia under several scientific projects during 1969-2012 (Kira 1987, Yoneda et al 2002, Hoshizaki et al 2004, Kosugi et al 2012. Pasoh forest, situated about 70 km to the southeast of Kuala Lumpur in the state of Negeri Sembilan, is a lowland mixed dipterocarp forest dominated by two genera of Shorea and Dipterocarpus (Davies et al 2003), and the average annual rainfall (1500-2000 mm in 1983-1995 at P1) is less than that in other regions of Peninsular Malaysia .…”

“…CO 2 exchange at the canopy has been observed at a 52 m tower in the expanded (6-ha) P1 since 1995 by ECM . Yearly changes of NEP during 2003-2011 by ECM (Kosugi et al 2012) were compared with results by a biometric method at a fan-shaped area expanded from the tower with a radius of 170 m. This fan-shaped area was divided into six stands by varied distances from the tower (50, 75, 100, 125 and 150 m). All trees in the fanshaped area were sorted to the six stands by their coordinates in the 6-ha plot.…”

“…Spatial-temporal variations of NEP have, however, not been clear because of a less tractable parameter of HTR particularly for coarse woody debris (CWD) and soil organic matter. Eddy covariance method (ECM) for NEP has been adopted to evaluate CO 2 flux from various vegetation to the atmosphere at global scale (FLUXNET 2015), and seasonal and inter-annual changes of NEP have been observed in tropical rain forests (Kim et al 2012, Kosugi et al 2012). To assess a stand dynamics basing on these ECM data, it is necessary to clear a relation between ECM and a biometric method (Miller et al 2004, Goulden et al 2011.…”

“…Fetch length (horizontal distance) for which ＞ 80% of the flux measurements are expected to come from was around 2000 m from the tower to the windward direction, and the contribution was higher at closer sites (Takanashi et al 2010). ECM-based NEP was calibrated by the relation between soil respiration and soil water content for nighttime ecosystem respiration at a neighboring site to the tower (Kosugi et al 2012). These high influences from closer sites suggest that high correlation between two kinds of NEP has been derived from the same phenomenon of a forest ecosystem.…”