A comparison of the carbon balance in the soil between a natural forest and a young teak plantation

Transcription

1 Symposium no. Paper no. 7 Presentation: oral A comparison of the carbon balance in the soil between a natural forest and a young teak plantation TAKAHASHI Masamichi (1), LIMTONG Pitayakon (), SUKSAWANG Songtam (3) and HIRAI Keizo (1) (1) Forestry and Forest Products Research Institute, Ibaraki, 35-7, Japan () Land Development Department, Bangkok, Thailand (3) Royal Forest Department, Bangkok, Thailand Abstract The objective of this study was to determine the carbon balance in the soils of tropical seasonal forests, especially for teak, which is widely planted over the country. Soil respiration rates at a natural forest (mixed deciduous forest type) were usually higher than at a young ( years old) teak. In both stands soil respiration rates showed clear seasonal patterns, that is high rates occurred in the wet season from April to November and low in the dry season from December to March. The rates were closely correlated with soil moisture conditions. The amounts of total carbon released by soil respiration annually were estimated to be 19 mg C ha -1 for the natural forest and 13 mg C ha -1 for the teak plantation. A small amount of carbon input though leaf and root litter in the teak plantation was assumed to result in lower carbon sequestration in the soil. In deed, the storage of soil carbon in the natural forest was larger than that in the teak plantation. We concluded that a young teak plantation would not contribute to the accumulation of carbon in the soil. Keywords: soil respiration, soil carbon storage, teak plantation, mixed deciduous forest, Thailand Introduction Recently global worming has become a worldwide concern. The area of tropical forests has been decreasing for last few decades and soil carbon in those areas has deteriorated after exploitation (Dale et al., 1991). Afforestation practice is an important way to store carbon in the terrestrial ecosystems as an organic matter. Especially carbon accumulation in forest ecosystems is expected to mitigate increases in CO concentrations in the atmosphere (Whendee, 199). It is easy to find the effects of afforestation on carbon accumulation in aboveground biomass by measuring the size of planted trees. However, detecting carbon accumulation in the soil is not so easy. Soil organic matter is the largest carbon pool in terrestrial ecosystems and organic matter fixed with minerals exists in a recalcitrant form (Bouwmann and Leemans, 1995). Therefore, carbon in the soil would function as an important pool for carbon that has a long turnover time. To evaluate the carbon balance in soil, it is necessary to find the main pathways of carbon in the soil ecosystem. For example, carbon input by leaf litterfall and by root litterfall, and carbon output by heterotroph respiration should be determined (Nakane et al., 19). However, CO efflux from the soil surface (soil respiration) always contains 7-1

2 17 th WCSS, 1-1 August, Thailand root respiration in addition to heterotroph respiration and the determination of root litterfall is technically difficult. These limitations make us difficult to evaluate actual changes in carbon of soil component in forest ecosystems. This study aimed to determine the carbon balance in the soil of a tropical seasonal forest, especially for teak plantation, which is most widely distributed species in this area. To do this, we compared soil respiration rates between a natural forest and a young teak plantation at Kanchanaburi, Western Thailand. Materials and Methods Sites The study site is located at the Mae Klong Watershed Research Station (Royal Forest Department), Kanchanaburi, Thailand. Soil respiration was determined was determined at a teak plantation and a natural forest. The teak plantation was planted in 199 on the lower slope in the watershed. The density of trees is 53 trees/ha. Average height and GBH in 199 were 11.3 m and 11. cm, respectively. The natural forest site is on the upper slope of a mixed deciduous forest (MDF type). Detail descriptions of the MDF site were given by Yarwudhi et al. (199). Average air temperature in the natural forest is about 5 o C with ranging from 9.3 o C to. o C in the natural forest, about the same as in the teak plantation. The annual precipitation is 1,5 mm, which mostly falls during rainy season, from April to October (Suksawang, 1995: Suksawang et al., 199). The soil type of the Teak plantation is Typic Haplustalfs and that of the natural forest is Typic Paleustalfs. Measurement of soil respiration Soil respiration rates were measured by the closed chamber method (Naganawa, 199). The size of the chamber used was 3 cm in diameter and 3 cm in height. The bottom rim of one chamber (Chamber A) was inserted 3-5 cm into the surface soil. The heights of the chambers from the ground surface were measured to determine their volume, and were done every time soil respiration was measured. A cover with a hole was set on the chamber and the hole and rim of the cover with tightly sealed with plastic tape. After waiting 15 to 3 minutes, CO concentration in the headspace of the chamber was measured by pumping the chamber air (1 L min -1 ) from the hole to an IRGA (ZFP5, Fuji Electronics Co. Ltd, Japan) that connected to the Digital Multimeter for output readings. The hole is wide enough to take open air during measurement, which prevent concentrated soil CO from being withdrawn directly. The highest reading of IRGA, taken for at least seconds, was used as a CO concentration in the chamber. We recorded the exact times that the cover was sealed and CO concentration in the air was measured. The initial CO concentration in the air was measured before and after the measurement. Soil respiration rates were calculated as following equation: Rt = (C - Ct) h / t (1) where Rt is total soil respiration (CO ml h -1 m - ), C; initial CO concentration (mg kg -1 ), Ct is CO concentration (mg kg -1 ) at time t (h), t; time (h) at which CO measured, h is the height of the chamber (m). The CO ml is converted to CO -C mg by CO -C (mg) = CO (ml) x (1 / ) x. 7-

3 17 th WCSS, 1-1 August, Thailand CO source separation Litter respiration and root respiration was estimated by source elimination treatment. Two chambers (Chamber B and C) were set next to the chamber measuring total soil respiration as described above. The organic layers (leaf litter) on the ground were eliminated from Chamber B, which was expected to reduce CO emission from the organic layer. For Chamber C, a trench of 3 cm in depth was dug around the chamber to cut roots in the soil. Plastic sheets were vertically inserted into the trenches and filled with soil in the trench again. The organic layers were also eliminated from the chamber. There were no roots in the organic layers. This treatment was expected to reduce the respiration from the roots and organic layers. We assumed that factors controlling soil, litter, and root respiration rates were the same and that the proportion of these sources in total soil respiration was constant throughout the year. We also assumed that root respiration were constant wherever root were in the soil. From these assumptions, the contributions of litter respiration and root respiration were calculated by the following equations: Chamber A: Rt = Rs + Ro + Rr () where Rt is total soil respiration, Rs is soil respiration, Ro is litter respiration, Rr is root respiration. Rr = Rr1 + Rr (3) where Rr1 is roots in the zone where roots were cut by the trench, and Rr is roots below the cut root zone. The chamber B: Rs + Rr The chamber C: Rs + Rr The litter respiration was Ro = Rt - (Rs + Rr) () hence, the contribution of litter respiration to total soil respiration was Ro/Rt = 1 - (Rs + Rr)/Rt = 1 - R Chamber B /R Chamber A (5) The root respiration was Rr1 = Rt - (Rs + Ro + Rr) = R Chamber B - R Chamber C () The contribution of root respiration to total soil respiration was Rr1/Rt = 1 - (Rs + Ro + Rr)/Rt = 1 - (Rt - Rr1)/Rt = R Chamber B /R Chamber A - R ChamberC /R ChamberA (7) In the chamber C, root respiration was eliminated up to 3 cm deep. We assumed that root respiration in the soil profile was correlated with the distribution of root biomass because root respiration is correlated with root biomass (Katagiri, 19). Rr = abt, Rr1 = ab1, Rr = ab Bt = B1 + B 7-3

4 17 th WCSS, 1-1 August, Thailand where Bt is total root biomass, B1 is root biomass in the cut root zone, B is root biomass below the cut root zone and a is a factor for root respiration rate per unit root biomass. a = Rt/Bt = Rr1/B1 = Rr/B Rr/Rt = (ab1 +ab)/rt = Bt/B1 x Rr1/Rt () When soil respiration was measured, soil (-5 cm) and litter samples were collected for determine moisture content. The samples were dried at 5 o C in an oven. Soil moisture was monitored through a year by TDR (Time domain reflectometry) sensors (Moisture Point TM Model MP-917, Environmental Sensors, Canada). Surface soil moisture was measured at a depth of - 15 cm and was collected every 3 to 7 days. Litterfall and root biomass Litterfall was collected by 1 m litterfall traps set on the natural forest plot. Litterfall at the Teak plantation was assumed to be the same dry weight of fresh leaves of standing trees that was estimated by the allometric equation obtained by Singh et al. (19). Fine root biomass (< mm) was measured by soil column sampling whose sizes were 15 cm x 15 cm area with -3, and 3- cm in depth. The sampling was done three times. Washed and oven dried roots were weighed. Results and Discussion Total soil respiration rates in the natural forest were usually higher than those in the Teak plantation (Figure 1). In both stands soil respiration rates showed clear seasonal patterns, that is, high rates occurred in the wet season from April to November and low in the dry season from December to March. In the natural forest, soil respiration rates were -3 g C m - d -1 during the dry season, and 5- g C m - d -1 during the wet season. The teak plantation showed lower soil respiration than the natural forest. There was large variation among the chambers in the natural forest especially in the rainy season. CO efflux (gc m - d -1 ) Natural Forest J M M J S N J M M J S N CO efflux (gc m - d -1 ) Teak J M M J S N J M M J S N Figure 1 Seasonal changes in total soil respiration at the natural forest and the teak plantation. Soil moisture is high in the rainy season and low in the dry season. The moisture of litter fluctuated even in the rainy season. Compared to air temperature, soil temperature was stable. The range of soil temperature was between to o C throughout the year. 7-

5 17 th WCSS, 1-1 August, Thailand The teak plantation showed the same trend as the natural forest although the range of soil temperature of the former was a little wider. The relationship between CO efflux and environmental factors, moistures and temperatures were analyzed. Because of the small variation in soil temperature, no clear relationship was found (Figure ). Soil moisture was the only factor that had a relationship with CO efflux. Multiple regressions were tested but that did not improve the accuracy of the estimates. Total CO efflux gcm - d -1 Soil Air 3 Temperature o C Litter Soil Y= lnX r=.1 water content % Figure The relationship between total CO efflux and environmental parameters at the natural forest. Clear differences among the treatments were found in MDF (Figure 3). Total CO efflux was always highest and CO efflux from the chamber from which litter and roots were removed showed the lowest rates. In the teak plantation, however, the distinctions are not so clear. CO efflux (gc m - d -1 ) Natural forest J M M J S N J M M J S N CO efflux (gc m - d -1 ) Teak J M M J S N J M M J S N : total : without litter : without litter and roots Figure 3 Seasonal changes in CO efflux with source separation treatments at the natural forest (left) and the teak plantation (right). Figure shows the relationship between total CO efflux and the CO efflux from the chamber without litter, and CO efflux from the chamber without roots and litter. The relationships could be fitted by a linear regression curve with zero intercept. Elimination of CO sources decreased the slope of this formula (equation 5), which indicates the contribution of the sources that were eliminated in the chamber. In the natural forest, litter layer contributed 1% and roots contributed % of the total CO 7-5

6 17 th WCSS, 1-1 August, Thailand efflux. In the teak plantation, 19% of CO was caused by microbial in the litter and only 7% came from the roots. Root respiration was very low in the teak plantation. CO efflux gc m - d - without litter without litter and roots MDF-U y=.19x r=.1 y=.1x r=.77 Total CO efflux CO efflux gc m - d - without litter without litter and roots Teak M y=.1x r=.1 y=.7x r=.1 Total CO efflux Figure The relationship between total CO efflux and CO efflux from source separation treatments at the natural forest (right) and Teak plantation (Left). Upper figures are Chambers A and B, and lower figures are Chambers A and C. Table 1 shows some soil characteristics that relate to CO efflux from the soil. Soil texture, which affected CO gas diffusion coefficient, was not so different. Soil ph at the two sites was similar values. Soil carbon contents of the natural forest are higher than that of the teak plantation. The largest differences were found in fine roots mass. The teak plantation had only around one fifth of the root mass of the natural forest. The low CO efflux rates at the teak plantation probably resulted from low soil carbon content and small fine root mass. Low distinction of CO sources treatment was also likely due to the small root mass. Table 1 Soil properties and fine (< mm) root biomass at the plots. Plot Depth Texture ph Fine root mass Carbon (cm) G m - kg m - Natural -3 SCL forest 3- L teak -3 SCL plantation 3- SCL From the soil moisture data using TDR sensors, total soil respiration can be estimated using the formula obtained above (CO efflux = log (soil moisture v/v%), Figure 5). By integrating the CO effluxes throughout a year, one-year carbon releases from the soil could be determined. The estimation showed that natural forest released 19 mg C ha -1 and the teak plantation release 13 mg C ha -1 from the soil surface in one year. 7-

7 17 th WCSS, 1-1 August, Thailand CO efflux gc m - d - Estimated Observed CO efflux gc m - d - Figure 5 The relationship between observed CO efflux and CO efflux estimated from soil moisture. Figure is a comparison of carbon balance between the natural forest and the teak plantation. Carbon input from leaf litterfall was larger in the natural forest. Root respiration contributes very little to total carbon flux in the teak plantation. We did not measure root litterfall but it would be small in the teak plantation because total root mass is one-fifth of the natural forest. These results indicate that carbon input to the soil in the teak plantation is much lower than that of the natural forest. However, CO efflux in the teak plantation originates mostly from soil microbes, that is, the decomposition of soil organic matter; the value for the teak plantation was only. mg C lower than that of the natural forest. These findings indicate that in spite of low carbon input to the soil, soil organic matter in the teak plantation is decomposing and losing carbon mass in the soil. In deed, soil carbon storage in -3 cm depth was small in the teak plantation. Therefore, we can not expect to accumulate carbon in the soil by planting teak in spite of their rapid aboveground growth, especially in the young stages. Soil respiration 19.3 Litter.9 Soil respiration 13.3 Litter Organic layer.9 Organic layer Root biomass.97 Soil C Root biomass 1. Soil C 3 Natural forest Teak plantation Figure Carbon flows in the soil of the natural forest and the teak plantation. 7-7

8 17 th WCSS, 1-1 August, Thailand Conclusions 1. Soil respiration in the study area was mainly controlled by soil moisture condition.. Litter decomposition and root respiration were contributed 1% and %, respectively, to total CO efflux in the natural forest. At the teak plantation, root respiration contributed only % to total efflux. 3. Annual CO releases from the soil surface were 19 mg C ha -1 at the natural forest, and 13 mg C ha -1 at the teak plantation.. It does not appear that teak plantations accumulate soil carbon in their young stages. Acknowledgements This study was funded by the Science and Technology Agency, Japan and by the National Research Council, Thailand. We thank Dr. U. Kutintara, Dr. D. Marod of Kasetsart University, V. Sunantapongsuk of LDD, and Dr. K. Ishizuka of FFPRI for their suggestions and assistances. References Bouwman, A.F. and R. Leemans The role of forest soils in the global carbon cycle, pp In W.W. McFee and J.M. Kelly (eds.). Carbon Forms and Functions in Forest Soils. Soil Science Society of America, Madison, WI, USA. Dale, V H., R.A. Houghton and C.A.S. Hall Estimating the effects of land-use change on global atmospheric CO concentrations. Can. J. For. Res. 1:7-9. Eswaran, H., E. Van den Berg, P. Reich and J. Kimble Global soil carbon resources, pp In R. Lal, J. Kimble, E. Levine and B.A. Stewart (eds.). Soils and Global Change. Katagiri, S. 19. Estimation of proportion of root respiration in total soil respiration in deciduous broadleaved stands. J. Jpn. For. Soc. 7: Naganawa, T Measurment of soil respiration activity, pp In Society of Soil Microbiology (ed.) Experimental Methods in Soil Microbiology. Yokendo, Tokyo, Japan. (In Japanese). Nakane, K., H. Tsubota and M. Yamamoto. 19. Cycling of soil carbon in a Japanese red pine forest: II. changes occurring in the first year after a clear-felling. Ecol. Res. 1:7-5. Singh, A.K., V.N. PanDey and K.N. Misra. 19. Stand composition and phytomas distribution of a tropical deciduous Teak (Tectona grandis) plantation of India. J. Jpn. For. Soc. : Suksawang, S Site overview: Thong Pha Phum study site, pp In Proceedings of the International Workshop on The Changes of Tropical Forest Ecosystems by El Nino and Ohters. JSTA, NRCT and JISTEC. Suksawang, S., M. Takahashi, T. Nakashizuka, S. Kobayashi and K. Hirai Comparison of microclimate characteristics between a mixed deciduous forest and a young teak plantation in Thailand, pp In Proceedings of the FORTROP'9: Tropical Forestry in the 1 st Century, 5- November 199. Kasetsart University, Bangkok 9, Thailand. 7-

9 17 th WCSS, 1-1 August, Thailand Whendee, L.S The potential effects of elevated CO and climate change on tropical forest soils and biogeochemical cycling. Climate Change 39: Yarwudhi, C., S. Kobayashi, T. Nakashizuka and M. Takahashi Tree population dynamics in a tropical seasonal forest, pp In Proceedings of the international workshop on the Changes of Tropical Forest Ecosystems by El Nino and Others. Kanchanaburi, Thailand. JSTA, NRCT and JISTEC. 7-9