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We defined gas exchange phenology as the seasonality of the gas exchange characteristics of a forest canopy, and investigated how the gas exchange phenology could be directly detected from an eddy covariance (EC) dataset and its influence on the canopy fluxes within an evergreen Japanese cypress forest. For the detection of gas exchange phenology, we derived three bulk parameters of the extended big-leaf model (Kosugi et al. ) inversely from EC flux data over a 7-year period: surface conductance ( g), maximum rate of carboxylation of the 'big leaf' ( V), and intercellular CO concentration of the 'big leaf' ( C). The relationship between g and the vapor pressure deficit declined in winter and spring. The relationship between the daily ecosystem respiration and air temperature was greater in the spring than in the other seasons. The temperature dependence curve of V decreased substantially in the winter and was different from that of an evergreen broadleaved forest. A decrease in C was occasionally coupled with the decrease in canopy gross primary production during April and August, indicating that stomatal closure was responsible for a decline in canopy photosynthesis. Gas exchange phenology should be quantified when understanding the determining factors of the seasonality of canopy fluxes at evergreen coniferous forests. [ABSTRACT FROM AUTHOR]

ABSTRACT The object of this study was to elucidate the seasonal patterns of energy partitioning of net radiation into sensible and latent heat fluxes and carbon dioxide (CO2) flux at a tropical deciduous forest site, i.e. a teak plantation in northern Thailand. In general, latent heat flux was more prominent than sensible heat flux in the wet (growing) season, whereas in the dry (dormant) season, sensible heat was the main form of energy emitted to the atmosphere. More specially, latent heat flux began to increase before leaf-out of teak trees and decreased 1 month earlier than leaf-fall initiation. Daytime net CO2 uptake appeared to increase with increasing amount of leaves but only at the beginning of the wet season; values peaked during the early part of wet season; and declined thereafter. This decline occurred about 3 months earlier than when latent heat flux began to decrease about 4 months earlier than the leaf-fall initiation. These results indicate that the seasonality of water and CO2 exchanges between the atmosphere and the tropical deciduous forest was substantially decoupled during the late wet season. This decoupling of the seasonality of water and carbon exchanges may be particularly important when modelling the ecohydrology of this tropical deciduous forest. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT In a tropical deciduous forest in northern Thailand, an area affected by the Asian monsoon, we made soil respiration measurements for 4 years to determine their inter-annual variability. We also made continuous measurements of soil moisture, soil temperature, and soil CO2 concentration. Annual soil respiration rates were estimated using two methods: multiple regression analysis and Fick's first law of diffusion. During the study period, between June 2000 and December 2004, the annual rainfall and the length of the wet period showed considerable year-to-year variation, differing by 1162-1435 mm year−1 falling over 146-189 days, respectively. In response to the inter-annual variability in rainfall, annual soil respiration rates estimated by the two models also showed large inter-annual variations for the 4 years (coefficient of variation = 14-17%). The range in the inter-annual variation for soil respiration was comparable with values for net ecosystem exchange reported in other Southeast Asian tropical forests. Historical rainfall records at this site showed further large inter-annual variations that occurred in times other than in the study period, suggesting that long-term monitoring would be required for a better understanding of the C balance at this site. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We tested the effect of general flowering ( GF), community-wide masting, and drought stress on current-year tree diameter growth and aboveground biomass increment ( ABI). General flowering but not drought had a marginally significant negative effect on tree growth and ABI at the community level. Analyses of dominant species clarified this pattern. [ABSTRACT FROM AUTHOR]

We examined the impact of both seasonal and year-to-year variations in precipitation on simulated soil moisture dynamics at a tropical rain forest (TRF) site and a tropical seasonal forest (TSF) site in Southeast Asia, between which there is a clear difference in the precipitation regime, through a probabilistic ecohydrological model. All model parameters have apparent physical meaning and were obtained by field observations. Rainfall statistics as the primary model forcing terms were constructed from long-term rainfall records, and their analysis revealed a close relationship between drought and El Niño events at the TRF site and a long-term drying trend at the TSF site. The model results further demonstrated that the studied ecosystem's robustness (mainly concerning the plant water availability) are attributed to functional factors such as soil texture for the TRF site and rooting depth and the dry season use of water from the preceding wet season for the TSF site. [ABSTRACT FROM AUTHOR]

To our knowledge, there is no information on the canopy conductance of Cryptomeria japonica plantations, although such forests are very common in Japan. We examined the canopy conductance Gc of a C. japonica plantation based on 1-year sap-flow data using the simplified Penman-Monteith equation. After selecting data based on the criterion proposed in part 1 of this study (Komatsu et al., 2006. Hydrological Processes 20: this issue), we now examine Gc responses to meteorological factors. Gc was expressed using functions of solar radiation S (W m-2), the vapour pressure deficit D (kPa), and air temperature T (°C). The resulting functions were f1(S) = [(1000 + 30)S]/[1000(S + 30)], f2(D) = exp(-0.54D)/exp(-0.54), and f3(T) = {[(30 - 5) + 14](T - 5)}/{(30 - 5)[(T - 5) + 14]), where f1(S), f2(D), and f3(T) are functions expressing the Gc responses to S, D, and T respectively. The functions were characterized by comparing general functions for coniferous forests, which showed that it was necessary to consider f3(T) to reproduce the 1-year transpiration at the site, and that f1(S) and f2(D) determined here were not very different from the general functions. This paper is the first to determine Gc responses to meteorological factors for a C. japonica plantation. When predicting transpiration from a C. japonica plantation using hydrological or ecological models, the functions determined here should be used instead of the default functions of the models. [ABSTRACT FROM AUTHOR]

To our knowledge, no one has examined the canopy conductance of a Cryptomeria japonica plantation, although such forests are very common in Japan. We plan to examine the canopy conductance of a Cryptomeria japonica plantation (canopy height 8 m) based on 1-year sap-flow data using the simplified Penman-Monteith equation. This study examines the effect of the aerodynamic control of transpiration before calculating canopy conductance using the simplified Penman-Monteith equation, because the equation assumes that the effect of aerodynamic control is negligible. To examine the effect of aerodynamic control, we examined the dependency of the relationship between the vapour pressure deficit (VPD) and transpiration on wind speed, when solar radiation, air temperature, and soil water content do not limit transpiration greatly. The relationship between VPD and the heat pulse velocity measured 11 m above the ground was dependent on wind speed only when the wind speed was < 0.7 m s-1. This suggests that the effect of aerodynamic control was negligible when the wind speed was < 0.7 m s-1, but that the effect was not negligible when the wind speed was < 0.7 m s-1. Therefore, we should use data from when the wind speed was ≥ 0.7 m s-1 for calculating canopy conductance Gc, based on the simplified Penman-Monteith equation. Although this criterion is site specific, the methods used to develop it are applicable to other sites. [ABSTRACT FROM AUTHOR]

This study emphasizes the importance of canopy drying time (CDT) after rainfall in a lowland tropical rain forest. In this study, we estimate CDT using sap flow velocities measured by a heat-pulse method in an emergent tree in a lowland mixed-dipterocarp forest. Estimated CDT (ECDT) for each rain event has been defined as the time from rainfall cessation to the specific time derived from the difference between diurnal courses of sap flow velocities on a rainy day versus bright days. ECDT could be derived for 22 rain events that were grouped into two types, depending on whether rainfall ceased before or after noon. The ECDTs were distributed more widely and with greater values when rainfall ceased before noon (Type 1) than after noon (Type 2). The ECDTs of both Type 1 and Type 2 decreased with increases in net radiation (Rn) and vapour pressure deficit (VPD) after rainfall. This result shows that ECDT is determined mainly by post-rainfall evaporation rates. The sap flow velocity as a detector of canopy wetness worked out well because of the specific rainfall characteristics at this site. The practical limitations of the method using sap flow velocities are discussed in relation to rainfall characteristics and time lags between transpirations and sap flow velocities. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]