Understanding the roles of tropical forest in climate change through ...
Understanding the roles of tropical forest in climate change through the energy/H2O/CO2 exchange processes Abdul Rahim Nik (FRIM) Siti Aisah Shamsuddin (FRIM) Ahmad Abdul Salam(FRIM) Mohd Md Sahat (FRIM)
Makoto Tani (Kyoto Univ.) Yoshiko Kosugi (Kyoto Univ.) Satoru Takanashi (Kyoto Univ.) Naoko Matsuo (Kyoto Univ.) Daizo Tsutsumi (Kyoto Univ.) Takumi Wada (Kyoto Univ.) Tomonori Mitani (Kyoto Univ.) Tatsuya Katayama (Kyoto Univ.) Shoji Noguchi (JIRCAS) Toshinori Okuda (NIES)
INTRODUCTION Roles of forest in CO2 sequestration have been strongly emphasized since the Third Conference of Parties (COP3) of UNFCC held in Kyoto in 1997. CO2 exchange between an ecosystem and the atmosphere is described as a net ecosystem exchange (NEE) representing a difference between the uptake by photosynthesis and the emission by ecosystem respiration. A flux measurement above forest using a micrometeorological method permits a direct computation of the NEE of the forest ecosystem, although CO2 storage between the reference height and the ground should be deduced to calculate the NEE rate in a short period. The NEE can be also estimated as a net ecosystem production (NEP) from a temporal change of biomass through ecological investigations (Fig.1). The NEP is usually calculated as an annual value, because only a long-term biomass change can be detected through investigations on the growth, mortality of trees and the decomposition processes. Both the micrometeorological method and the ecological method have merits and demerits. Usually a time-integration result of CO2 exchange flux measured by the former is validated with a long-term NEP result covering more than one-year period obtained from the latter. Many studies for the both methods have been carried out for tropical forests in the South America. Micro-meteorological studies generally show a net CO2 absorption (Fan et al., 1990; Grace et al., 1995; Malhi et al., 1998), though the data from Cuieras demonstrated NEE in a dry season might be smaller than that in a dry season. About 100 studies on above-ground biomass in Amazon also showed an increase of biomass, suggesting the increase of NEP (Phillips et al., 1998). In the Southeast Asia, very few studies have been initiated to estimate NEE from micro-meteorological observations although NEP has been estimated from ecological studies in study sites including Pasoh Forest Reserve (Hoshizaki et al, 2000, 2002). Only a short -term observation of CO2 flux was conducted in March 1998 in Pasoh (Yasuda et al., 2003). This study showed that CO2 absorption even though it was conducted in a dry season. However, ecological investigations do not support this result. The total amounts of above ground biomass in Pasoh were 475ton ha-1 in 1978, 431-ton ha-1 in 1994, 417 ton ha-1 in 1996 and 403 ton ha-1 in 1998, respectively (Kato et al., 1978; Hoshizaki et al., 2000). A compartment model 5
NEE Biomass change by the ecological investigation
Integration of CO2 flux Leaf photosynthesis and respiration
NEP Above-ground growth
CO2 storage
Litterfall Stem Fallen respiration Microbe tree respiraion Soil Soil Root respiration Organic DOC, DIC Root death matter growth POC Root respiration River
Fig. 1. Schematic diagram of carbon exchange processes in a forest ecosystem. Left: from the aspect of CO2 dynamics. Right: from the aspect of ecosystem production.
developed for Pasoh Forest by Hoshizaki et al. (2002) estimated a slightly negative value of net ecosystem production, that is, carbon source for a primary stand in Pasoh Forest Reserve. Inconsistencies showed by results from Pasoh may be introduced from various kinds of estimation errors such as an underestimation of respiration flux in the nighttime in the flux measurement and an inaccurate estimation of under-ground biomass in the ecosystem investigation. Indeed, both of the gross absorption by photosynthesis and the gross emission by respiration are very large in tropical forest, indicating that it requires a high accuracy and a careful strategy in the observational design to examine the balance sheet of absorption and emission in terms of a small difference of the both gross values. In addition to the estimation errors, heterogeneous properties of the ecosystem also may involve the inconsistency. The representative area, the so-called footprint, of CO2 flux measured at the tower top show changes, reflecting to the wind direction and the other meteorological environments. While some areas in Pasoh Forest are under a growing stage, the area for the biomass investigation is largely consists of big emergent trees with high rate of fallen trees. Considering the previous findings, the new phase of our cooperative project started from 2002 aims to focus the micro-meteorological observations not only on a continuous monitoring of CO2 flux but also on measurements and model evaluations of CO2 dynamics such as the vertical distribution of CO2, the leaf photosynthesis, the leaf and stem respiration, and the horizontal distribution of soil respiration. The ecological investigation in the new phase also aims at quantifying the biomass change paying attention to the heterogeneous properties such as the distributions of fallen trees and decomposition 6
process. Crosschecking analyses are expected in the new phase to understand the carbon sequestration in Pasoh Forest. Within the study plans in the new phase project, this report introduces some preliminary results on energy, H2O and CO2 fluxes above forest as well as the outline of our study designs for evaluating NEE from the micro-meteorological observation in Pasoh Forest.
METHODS Design of our observations in the Pasoh Forest Reserve consists of a long-term continuous monitoring of meteorological factors as well as energy, H2O and CO2 fluxes and shortterm intensive measurements of detailed spatial distributions of micro-meteorological factors and fluxes. The continuous canopy height of the primary lowland mixed dipterocarp forest is about 35 m, although some emergent trees exceed 45 m. The leaf area index (LAI) was 6.52. Monitored factors at the height of 52m of a tower comprise downward and upward radiations for short-wave, long-wave and photosynthetically active radiation ranges, air temperature, humidity, wind direction, wind velocity, and rainfall. The eddy-covariance open-path system consisting of Li-Cor LI7500 gas analyzer and Kaijo SAT550 is used to monitor energy, H2O and CO2 fluxes at the same height. The continuous monitoring is extended to the lower level of the tower and the forest floor. The air temperature, humidity and wind velocity are monitored also at about 46 m height to get their profile above the canopy. The factors monitored on the forest floor are downward and upward radiations in three ranges, air temperature, humidity, soil temperatures, soil water contents, and soil water potentials. Rainfall is monitored also on a bridge connected at the 30 m height between the 52 m tower and another tower with the height of 30 m because data of the rain gauge at the tower top may be influenced by wind. A trough type rainfall collector (400 cm x 14 cm) is used for this measurement. To monitor the fluxes continuously during and after rain events, rainfall within forest canopy, including throughfall and stemflow are monitored on the forest floor using two large rectangular rain gauges (about 4x2 m) as well as 15 pot-type rain gauges and 11 stemflow collectors. We also conduct short-term intensive measurements of detailed spatial distributions of micro-meteorological factors and fluxes to get parameters for applications of the multi-layer model that simulates energy/H2O/CO2 dynamics within and above forest canopy. Vertical distribution of LAI was measured by an optical method, and distribution of a leaf gradient angle was manually measured. Leaf gas exchange for several trees was measured with leaf chamber fluorometer, and soil respiration was measured by a chamber method in a special consideration of the horizontal distribution. The storage fluctuations of sensible heat, latent heat and CO2 in the air below the reference height of 52 m and the storage fluctuation of heat in the stem were also measured in our intensive observation period. The multi-layer model for CO2 and H2O exchange in a C3 broad-leaved plant community (Tanaka, 2001) used for the simulation here is briefly summarized next. The model contains sub-models calculating the following processes: 1) Reynolds stress, sensible heat exchange, CO2 and H2O exchanges of leaves and the ground surface, 2) stomatal conductance and net photosynthesis in individual leaves, 3) radiative transfer within and above canopy, 4) the energy balance of leaves and the ground surface, 5) Atmospheric diffusion within and above the canopy, and 6) the interception of rainfall and the water budget of leaves. This multi-layer model can produce above-canopy fluxes based on detailed processes characterized by the canopy 7
structure and the biochemical processes, supporting our data analyses of NEE.
RESULTS Data quality check Quality of the eddy flux data was checked by power co-spectra and the energy balance closure. Co-spectra of vertical wind velocity and scalars, that is, air temperature, specific humidity and CO2 concentration were similar to each other, indicating moderate conditions for an application of the eddy covariance method (Fig. 2). However, the averaged energy total of the sensible, latent heat and heat storage was
Fc
LHF 1
0.1
0.1
0.1
0.01
0.001
n Cwc/w'c'
1
n Cwq/w'q'
n Cwt/w't'
SHF 1
0.01
0.001
0.001
0.001
0.01
nCwc/w'c' -4/3 line
nCwq/w'q' -4/3 line
nCwt/w't' -4/3 line 0.1
1
10
0.0001 0.0001
0.001
Natural frequency (Hz)
0.01
0.1
1
10
0.0001 0.0001
0.001
0.01
Rn-G vs. SHF+LHF 1000
800
600
400
200
0
Y=0.691X -200 -200
0
200
400
600
800
1000
Rn-G (W m-2)
Fig. 3. Comparison the available energy (net radiation - heat storage) and the total of sensible and latent heat fluxes. 8
0.1
1
Natural frequency (Hz)
Natural frequency (Hz)
Fig. 2. Co-spectra of vertical wind velocity and air temperature (left), vertical wind velocity and specific humidity (center), and vertical wind velocity and CO2 concentration (right).
SHF+LHF (W m-2)
0.0001 0.0001
0.01
10
about 70% of the net radiation (Fig. 3). Various kinds of causes may influence this result, but recent studies (Lee, 1998; Watanabe and Kanda, 2002) show that such an imbalance may inevitably occur due to mass flow even though the measurement includes the minimum errors and the data represent the spatially averaged fluxes. Influences of the imbalance on each flux should be carefully noted for our analyses.
800 600 400 200
0
-1
-200
Date
600
5 10
400
15 200
20
0
25
-200
30
-1 -2
Rainfall (mm 30min )
0
CO2 Flux (mg m s )
-2
Latent Heat Flux (W m ) -2 Sensible Heat Flux (W m )
Eddy fluxes Fluxes monitored by the eddy covariance method are compared with those simulated by the multi-layer model in Fig. 4. Both show that energy is used for latent heat flux. However, the simulated latent heat is generally larger than that observed although the simulated sensible heat is similar to that observed. This suggests the energy imbalance may give only a small influence on the sensible heat in the daytime, whereas the latent heat may be underestimated. For CO2 flux, the observed and simulated uptakes are similar to each other in the daytime but the nighttime emission simulated is much smaller than that observed. This suggests difficulties for the nighttime estimation of CO2 flux as described in previous studies (eg: Goulden et al., 1996). Further checking processes as well as comparisons with soil respiration are necessary to evaluate NEE at this site, but the simulation result of multi-layer model suggests an improvement for the underestimation of nighttime emission, suggesting a
Date
1 0 -1 -2 9/22
9/27
Date
10/2
10/7
Fig. 4. Observed (circle) and simulated (line) 30-minute average fluxes for sensible heat (top), latent heat (middle), and CO2 (bottom). The dotted line and the bar in the middle figure indicate the simulated latent heat flux from the wet canopy and 30-minute rainfall, respectively. 9
positive direction of our NEE estimation because the result is based on a biochemical model with detailed measurements of the model parameters. Concluding remar Generally speaking, an accurate evaluation of CO2 exchange between a forest and the atmosphere is not easy for an eddy correlation monitoring as well as for an ecological investigation. The crosschecking is particularly important for the evaluation. Our results from Pasoh Forest are not the exception. We believe that our application of the multi-layer model with detailed measurements of its parameters is a reliable strategy for validating the CO2 flux before it is crosschecked with a carbon sequestration result by the on-going ecological investigation.
ACKNOWLEDGEMENT We thank the Forestry Department of Negeri Sembilan and Director General of FRIM for giving us permission to work in the Pasoh Forest Reserve. The staff of the Hydrology Unit and Pasoh Station of FRIM is acknowledged for collecting data.
RESEARCH OUTPUT Publications Tani, M., Abdul Rahim N., Ohtani, Y., Yasuda, Y., Mohd Md S., Bharuddin K., Takanashi, S., Noguchi, S., Zulkifli Y. and Watanabe, T., (2003): Characteristics of energy exchange and surface conductance of a tropical rain forest in Peninsular Malaysia. In Okuda, T., Niiyama, K., Thomas, S. C.(Eds.): Pasoh: Ecology and Natural History of a Lowland Tropical Rain Forest in Southeast Asia. Springer, Tokyo, Japan (in press). Tani, M., Abudul Rahim N., Yasuda, Y., Noguchi, S., Siti Aisah S., Mohd Md S., Takanashi, S. (2003): Long-term estimation of evapotranspiration from a tropical rain forest in Peninsular Malaysia. Proceedings of HS02 in IUGG/Sapporo, IHAS Press, Wallingford, (in press).
Conferences/Symposia Tani, M. (2003) Regulation of Weather and Climate - Understanding roles of tropical forest in climate change through the energy/H 2O/CO2 exchange process -. International Symposium on Global Environment and Forest Management, Kyosei Science Center for Life and Nature, Nara Women’s University.
REFERENCES Fan, S.M., Woofs, S., Baking, p. and Jacob, D. (1990) Atmospheric-biosphere exchange of CO2 and O3 in the central Amazon forest, Journal of Geophysical Research 95, 1685116864. Golden, M.L., Monger, J.W., Fan, S.M., Daubed, B.C. and Woofs, S.C. (1996) Measurements of carbon sequestration by long-term eddy covariancew: methods and a critical evaluation of accuracy. Global Change Biology 2: 169-182. Grace, J., Lloyd, J., Mcintyre, J., Miranda, A., Meir, P., Miranda, H., Moncrieff, J. and Massheder, J. (1995) Fluxes of carbon dioxide and water vapour over an undisturbed tropical forest in south-west Amazonia, Global Change Biology 1, 1-12. Hoshizaki, K., Niiyama, K., Kimura, K., Yamashita, T., Bekku, Y., Okuda, T., Takeda, H., Tang, Y., Nur Supardi N., Quah, E.S. and Adachi, N. (1999) Recent biomass change in a tropical primary forest in Pasoh: current status for evaluating carbon-sequestering function, 10
Research report of the NIES/FRIM/UPM Joint Research Project 1999, National Institute for Environmental Studies, Tsukuba, 2-17, 2000. Hoshizaki, K., Adachi, M., Adachi, N., Bekku-Sakata, Y., Koizumi, H., Niiyama, K., Okuda, T., Ymaashita, T., Nur Supardi N., Quah, E.S. and Adachi, N. (2002) Trials for construction of carbon-cycling compartment models in a tropical rainforest, Pasoh Forest Reserve, Research report of the NIES/FRIM/UPM Joint Research Project 2001, National Institute for Environmental Studies, Tsukuba, 127-146. Kato, R., Tadaki, Y. and Ogawa, H. (1978) Plant biomass and growth increment studies in Pasoh Forest. The Malayan Nature Journal, 30, 211-245. Lee, X. (1998) On micrometeorological observations of surface-air exchange over tall vegetation. Agricultural and Forest Meteorology 91: 39-49. Malhi, Y., Nobre, A.D., Grace, J., Kruijt, B., Pereira, M.G.P., Culf, A. and Scott, S. (1998) Carbon dioxide transfer over a Central Amazonian rain forest, Journal of Geophysical Research 103 No. D24, 31593-21612, Phillips, O.L., Malhi, Y., Higuchi, N., Laurance, W.F., Nunez, P.V., Vasquez, R.M., Laurance, S.G., Ferreira, L.V., Stern, M., Brown, S. and Grace, J. (1998) Changes in the carbon balance of tropical forests: evidence from long-term plots, Science 282, 439-442. Tanaka, K. (2001) Multi-layer model of CO2 exchange in a plant community coupled with the water budget of leaf surfaces. Ecological Modelling 147: 85-104. Watanabe T., and Kanda, M. (2002) LES study on the energy imbalance problem with eddy covariance fluxes.II: Analysis for a neutrally stratified surface boundary layer above and within a homogeneous plant canopy. Journal of Japan Society of Hydrology & Water Resources 15: 253-263 (in Japanese with English abstract). Yasuda, Y., Ohtani, Y., Watanabe, T. Okano, M., Yokota, T., Liang, N., Tang, Y., Abdul Rahim, N., Tani, M. and Okuda, T. (2003) Measurement of CO2 flux above a tropical rain forest at Pasoh in Peninsular Malaysia, Agricultural and Forest Meteorology 114, 235-244.
11
Makoto Tani (Kyoto Univ.) Yoshiko Kosugi (Kyoto Univ.) Satoru Takanashi (Kyoto Univ.) Naoko Matsuo (Kyoto Univ.) Daizo Tsutsumi (Kyoto Univ.) Takumi Wada (Kyoto Univ.) Tomonori Mitani (Kyoto Univ.) Tatsuya Katayama (Kyoto Univ.) Shoji Noguchi (JIRCAS) Toshinori Okuda (NIES)
INTRODUCTION Roles of forest in CO2 sequestration have been strongly emphasized since the Third Conference of Parties (COP3) of UNFCC held in Kyoto in 1997. CO2 exchange between an ecosystem and the atmosphere is described as a net ecosystem exchange (NEE) representing a difference between the uptake by photosynthesis and the emission by ecosystem respiration. A flux measurement above forest using a micrometeorological method permits a direct computation of the NEE of the forest ecosystem, although CO2 storage between the reference height and the ground should be deduced to calculate the NEE rate in a short period. The NEE can be also estimated as a net ecosystem production (NEP) from a temporal change of biomass through ecological investigations (Fig.1). The NEP is usually calculated as an annual value, because only a long-term biomass change can be detected through investigations on the growth, mortality of trees and the decomposition processes. Both the micrometeorological method and the ecological method have merits and demerits. Usually a time-integration result of CO2 exchange flux measured by the former is validated with a long-term NEP result covering more than one-year period obtained from the latter. Many studies for the both methods have been carried out for tropical forests in the South America. Micro-meteorological studies generally show a net CO2 absorption (Fan et al., 1990; Grace et al., 1995; Malhi et al., 1998), though the data from Cuieras demonstrated NEE in a dry season might be smaller than that in a dry season. About 100 studies on above-ground biomass in Amazon also showed an increase of biomass, suggesting the increase of NEP (Phillips et al., 1998). In the Southeast Asia, very few studies have been initiated to estimate NEE from micro-meteorological observations although NEP has been estimated from ecological studies in study sites including Pasoh Forest Reserve (Hoshizaki et al, 2000, 2002). Only a short -term observation of CO2 flux was conducted in March 1998 in Pasoh (Yasuda et al., 2003). This study showed that CO2 absorption even though it was conducted in a dry season. However, ecological investigations do not support this result. The total amounts of above ground biomass in Pasoh were 475ton ha-1 in 1978, 431-ton ha-1 in 1994, 417 ton ha-1 in 1996 and 403 ton ha-1 in 1998, respectively (Kato et al., 1978; Hoshizaki et al., 2000). A compartment model 5
NEE Biomass change by the ecological investigation
Integration of CO2 flux Leaf photosynthesis and respiration
NEP Above-ground growth
CO2 storage
Litterfall Stem Fallen respiration Microbe tree respiraion Soil Soil Root respiration Organic DOC, DIC Root death matter growth POC Root respiration River
Fig. 1. Schematic diagram of carbon exchange processes in a forest ecosystem. Left: from the aspect of CO2 dynamics. Right: from the aspect of ecosystem production.
developed for Pasoh Forest by Hoshizaki et al. (2002) estimated a slightly negative value of net ecosystem production, that is, carbon source for a primary stand in Pasoh Forest Reserve. Inconsistencies showed by results from Pasoh may be introduced from various kinds of estimation errors such as an underestimation of respiration flux in the nighttime in the flux measurement and an inaccurate estimation of under-ground biomass in the ecosystem investigation. Indeed, both of the gross absorption by photosynthesis and the gross emission by respiration are very large in tropical forest, indicating that it requires a high accuracy and a careful strategy in the observational design to examine the balance sheet of absorption and emission in terms of a small difference of the both gross values. In addition to the estimation errors, heterogeneous properties of the ecosystem also may involve the inconsistency. The representative area, the so-called footprint, of CO2 flux measured at the tower top show changes, reflecting to the wind direction and the other meteorological environments. While some areas in Pasoh Forest are under a growing stage, the area for the biomass investigation is largely consists of big emergent trees with high rate of fallen trees. Considering the previous findings, the new phase of our cooperative project started from 2002 aims to focus the micro-meteorological observations not only on a continuous monitoring of CO2 flux but also on measurements and model evaluations of CO2 dynamics such as the vertical distribution of CO2, the leaf photosynthesis, the leaf and stem respiration, and the horizontal distribution of soil respiration. The ecological investigation in the new phase also aims at quantifying the biomass change paying attention to the heterogeneous properties such as the distributions of fallen trees and decomposition 6
process. Crosschecking analyses are expected in the new phase to understand the carbon sequestration in Pasoh Forest. Within the study plans in the new phase project, this report introduces some preliminary results on energy, H2O and CO2 fluxes above forest as well as the outline of our study designs for evaluating NEE from the micro-meteorological observation in Pasoh Forest.
METHODS Design of our observations in the Pasoh Forest Reserve consists of a long-term continuous monitoring of meteorological factors as well as energy, H2O and CO2 fluxes and shortterm intensive measurements of detailed spatial distributions of micro-meteorological factors and fluxes. The continuous canopy height of the primary lowland mixed dipterocarp forest is about 35 m, although some emergent trees exceed 45 m. The leaf area index (LAI) was 6.52. Monitored factors at the height of 52m of a tower comprise downward and upward radiations for short-wave, long-wave and photosynthetically active radiation ranges, air temperature, humidity, wind direction, wind velocity, and rainfall. The eddy-covariance open-path system consisting of Li-Cor LI7500 gas analyzer and Kaijo SAT550 is used to monitor energy, H2O and CO2 fluxes at the same height. The continuous monitoring is extended to the lower level of the tower and the forest floor. The air temperature, humidity and wind velocity are monitored also at about 46 m height to get their profile above the canopy. The factors monitored on the forest floor are downward and upward radiations in three ranges, air temperature, humidity, soil temperatures, soil water contents, and soil water potentials. Rainfall is monitored also on a bridge connected at the 30 m height between the 52 m tower and another tower with the height of 30 m because data of the rain gauge at the tower top may be influenced by wind. A trough type rainfall collector (400 cm x 14 cm) is used for this measurement. To monitor the fluxes continuously during and after rain events, rainfall within forest canopy, including throughfall and stemflow are monitored on the forest floor using two large rectangular rain gauges (about 4x2 m) as well as 15 pot-type rain gauges and 11 stemflow collectors. We also conduct short-term intensive measurements of detailed spatial distributions of micro-meteorological factors and fluxes to get parameters for applications of the multi-layer model that simulates energy/H2O/CO2 dynamics within and above forest canopy. Vertical distribution of LAI was measured by an optical method, and distribution of a leaf gradient angle was manually measured. Leaf gas exchange for several trees was measured with leaf chamber fluorometer, and soil respiration was measured by a chamber method in a special consideration of the horizontal distribution. The storage fluctuations of sensible heat, latent heat and CO2 in the air below the reference height of 52 m and the storage fluctuation of heat in the stem were also measured in our intensive observation period. The multi-layer model for CO2 and H2O exchange in a C3 broad-leaved plant community (Tanaka, 2001) used for the simulation here is briefly summarized next. The model contains sub-models calculating the following processes: 1) Reynolds stress, sensible heat exchange, CO2 and H2O exchanges of leaves and the ground surface, 2) stomatal conductance and net photosynthesis in individual leaves, 3) radiative transfer within and above canopy, 4) the energy balance of leaves and the ground surface, 5) Atmospheric diffusion within and above the canopy, and 6) the interception of rainfall and the water budget of leaves. This multi-layer model can produce above-canopy fluxes based on detailed processes characterized by the canopy 7
structure and the biochemical processes, supporting our data analyses of NEE.
RESULTS Data quality check Quality of the eddy flux data was checked by power co-spectra and the energy balance closure. Co-spectra of vertical wind velocity and scalars, that is, air temperature, specific humidity and CO2 concentration were similar to each other, indicating moderate conditions for an application of the eddy covariance method (Fig. 2). However, the averaged energy total of the sensible, latent heat and heat storage was
Fc
LHF 1
0.1
0.1
0.1
0.01
0.001
n Cwc/w'c'
1
n Cwq/w'q'
n Cwt/w't'
SHF 1
0.01
0.001
0.001
0.001
0.01
nCwc/w'c' -4/3 line
nCwq/w'q' -4/3 line
nCwt/w't' -4/3 line 0.1
1
10
0.0001 0.0001
0.001
Natural frequency (Hz)
0.01
0.1
1
10
0.0001 0.0001
0.001
0.01
Rn-G vs. SHF+LHF 1000
800
600
400
200
0
Y=0.691X -200 -200
0
200
400
600
800
1000
Rn-G (W m-2)
Fig. 3. Comparison the available energy (net radiation - heat storage) and the total of sensible and latent heat fluxes. 8
0.1
1
Natural frequency (Hz)
Natural frequency (Hz)
Fig. 2. Co-spectra of vertical wind velocity and air temperature (left), vertical wind velocity and specific humidity (center), and vertical wind velocity and CO2 concentration (right).
SHF+LHF (W m-2)
0.0001 0.0001
0.01
10
about 70% of the net radiation (Fig. 3). Various kinds of causes may influence this result, but recent studies (Lee, 1998; Watanabe and Kanda, 2002) show that such an imbalance may inevitably occur due to mass flow even though the measurement includes the minimum errors and the data represent the spatially averaged fluxes. Influences of the imbalance on each flux should be carefully noted for our analyses.
800 600 400 200
0
-1
-200
Date
600
5 10
400
15 200
20
0
25
-200
30
-1 -2
Rainfall (mm 30min )
0
CO2 Flux (mg m s )
-2
Latent Heat Flux (W m ) -2 Sensible Heat Flux (W m )
Eddy fluxes Fluxes monitored by the eddy covariance method are compared with those simulated by the multi-layer model in Fig. 4. Both show that energy is used for latent heat flux. However, the simulated latent heat is generally larger than that observed although the simulated sensible heat is similar to that observed. This suggests the energy imbalance may give only a small influence on the sensible heat in the daytime, whereas the latent heat may be underestimated. For CO2 flux, the observed and simulated uptakes are similar to each other in the daytime but the nighttime emission simulated is much smaller than that observed. This suggests difficulties for the nighttime estimation of CO2 flux as described in previous studies (eg: Goulden et al., 1996). Further checking processes as well as comparisons with soil respiration are necessary to evaluate NEE at this site, but the simulation result of multi-layer model suggests an improvement for the underestimation of nighttime emission, suggesting a
Date
1 0 -1 -2 9/22
9/27
Date
10/2
10/7
Fig. 4. Observed (circle) and simulated (line) 30-minute average fluxes for sensible heat (top), latent heat (middle), and CO2 (bottom). The dotted line and the bar in the middle figure indicate the simulated latent heat flux from the wet canopy and 30-minute rainfall, respectively. 9
positive direction of our NEE estimation because the result is based on a biochemical model with detailed measurements of the model parameters. Concluding remar Generally speaking, an accurate evaluation of CO2 exchange between a forest and the atmosphere is not easy for an eddy correlation monitoring as well as for an ecological investigation. The crosschecking is particularly important for the evaluation. Our results from Pasoh Forest are not the exception. We believe that our application of the multi-layer model with detailed measurements of its parameters is a reliable strategy for validating the CO2 flux before it is crosschecked with a carbon sequestration result by the on-going ecological investigation.
ACKNOWLEDGEMENT We thank the Forestry Department of Negeri Sembilan and Director General of FRIM for giving us permission to work in the Pasoh Forest Reserve. The staff of the Hydrology Unit and Pasoh Station of FRIM is acknowledged for collecting data.
RESEARCH OUTPUT Publications Tani, M., Abdul Rahim N., Ohtani, Y., Yasuda, Y., Mohd Md S., Bharuddin K., Takanashi, S., Noguchi, S., Zulkifli Y. and Watanabe, T., (2003): Characteristics of energy exchange and surface conductance of a tropical rain forest in Peninsular Malaysia. In Okuda, T., Niiyama, K., Thomas, S. C.(Eds.): Pasoh: Ecology and Natural History of a Lowland Tropical Rain Forest in Southeast Asia. Springer, Tokyo, Japan (in press). Tani, M., Abudul Rahim N., Yasuda, Y., Noguchi, S., Siti Aisah S., Mohd Md S., Takanashi, S. (2003): Long-term estimation of evapotranspiration from a tropical rain forest in Peninsular Malaysia. Proceedings of HS02 in IUGG/Sapporo, IHAS Press, Wallingford, (in press).
Conferences/Symposia Tani, M. (2003) Regulation of Weather and Climate - Understanding roles of tropical forest in climate change through the energy/H 2O/CO2 exchange process -. International Symposium on Global Environment and Forest Management, Kyosei Science Center for Life and Nature, Nara Women’s University.
REFERENCES Fan, S.M., Woofs, S., Baking, p. and Jacob, D. (1990) Atmospheric-biosphere exchange of CO2 and O3 in the central Amazon forest, Journal of Geophysical Research 95, 1685116864. Golden, M.L., Monger, J.W., Fan, S.M., Daubed, B.C. and Woofs, S.C. (1996) Measurements of carbon sequestration by long-term eddy covariancew: methods and a critical evaluation of accuracy. Global Change Biology 2: 169-182. Grace, J., Lloyd, J., Mcintyre, J., Miranda, A., Meir, P., Miranda, H., Moncrieff, J. and Massheder, J. (1995) Fluxes of carbon dioxide and water vapour over an undisturbed tropical forest in south-west Amazonia, Global Change Biology 1, 1-12. Hoshizaki, K., Niiyama, K., Kimura, K., Yamashita, T., Bekku, Y., Okuda, T., Takeda, H., Tang, Y., Nur Supardi N., Quah, E.S. and Adachi, N. (1999) Recent biomass change in a tropical primary forest in Pasoh: current status for evaluating carbon-sequestering function, 10
Research report of the NIES/FRIM/UPM Joint Research Project 1999, National Institute for Environmental Studies, Tsukuba, 2-17, 2000. Hoshizaki, K., Adachi, M., Adachi, N., Bekku-Sakata, Y., Koizumi, H., Niiyama, K., Okuda, T., Ymaashita, T., Nur Supardi N., Quah, E.S. and Adachi, N. (2002) Trials for construction of carbon-cycling compartment models in a tropical rainforest, Pasoh Forest Reserve, Research report of the NIES/FRIM/UPM Joint Research Project 2001, National Institute for Environmental Studies, Tsukuba, 127-146. Kato, R., Tadaki, Y. and Ogawa, H. (1978) Plant biomass and growth increment studies in Pasoh Forest. The Malayan Nature Journal, 30, 211-245. Lee, X. (1998) On micrometeorological observations of surface-air exchange over tall vegetation. Agricultural and Forest Meteorology 91: 39-49. Malhi, Y., Nobre, A.D., Grace, J., Kruijt, B., Pereira, M.G.P., Culf, A. and Scott, S. (1998) Carbon dioxide transfer over a Central Amazonian rain forest, Journal of Geophysical Research 103 No. D24, 31593-21612, Phillips, O.L., Malhi, Y., Higuchi, N., Laurance, W.F., Nunez, P.V., Vasquez, R.M., Laurance, S.G., Ferreira, L.V., Stern, M., Brown, S. and Grace, J. (1998) Changes in the carbon balance of tropical forests: evidence from long-term plots, Science 282, 439-442. Tanaka, K. (2001) Multi-layer model of CO2 exchange in a plant community coupled with the water budget of leaf surfaces. Ecological Modelling 147: 85-104. Watanabe T., and Kanda, M. (2002) LES study on the energy imbalance problem with eddy covariance fluxes.II: Analysis for a neutrally stratified surface boundary layer above and within a homogeneous plant canopy. Journal of Japan Society of Hydrology & Water Resources 15: 253-263 (in Japanese with English abstract). Yasuda, Y., Ohtani, Y., Watanabe, T. Okano, M., Yokota, T., Liang, N., Tang, Y., Abdul Rahim, N., Tani, M. and Okuda, T. (2003) Measurement of CO2 flux above a tropical rain forest at Pasoh in Peninsular Malaysia, Agricultural and Forest Meteorology 114, 235-244.
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