Carbon cycling and budget in a forested basin of southwestern Hokkaido,northern Japan

Quantification of annual carbon sequestration is very important in order to assess the function of forest ecosystems in combatting global climate change and the ecosystem responses to those changes. Annual cycling and budget of carbon in a forested basin was investigated to quantify the carbon sequestration of a cool-temperate deciduous forest ecosystem in the Horonai stream basin, Tomakomai Experimental Forest, northern Japan. Net ecosystem exchange, soil respiration, biomass increment, litterfall, soil-solution chemistry, and stream export were observed in the basin from 1999–2001 as a part of IGBP-TEMA project. We found that 258 g C m^–2 year^–1 was sequestered annually as net ecosystem exchange (NEE) in the forested basin. Discharge of carbon to the stream was 4 g C m^–2 year^–1 (about 2% of NEE) and consisted mainly of dissolved inorganic carbon (DIC). About 43% of net ecosystem productivity (NEP) was retained in the vegetation, while about 57% of NEP was sequestered in soil, suggesting that the movement of sequestered carbon from aboveground to belowground vegetation was an important process for net carbon accumulation in soil. The derived organic carbon from aboveground vegetation that moved to the soil mainly accumulated in the solid phase of the soil, with the result that the export of dissolved organic carbon to the stream was smaller than that of dissolved inorganic carbon. Our results indicated that the aboveground and belowground interaction of carbon fluxes was an important process for determining the rate and retention time of the carbon sequestration in a cool-temperate deciduous forest ecosystem in the southwestern part of Hokkaido, northern Japan.     

Forest structure and biomass of mangroves in the Mgeni estuary,South Africa

Forest structure and biomass were determined in a mangrove stand dominated by Bruguiera gymnorrhiza (L.) Lam. Trees in 5 m² sample plots were harvested at ground level and then further cut into 1 m strata for separation into living wood, dead wood, leaves, reproductive material and pneumatophores. Mean above-ground living biomass was calculated at 94.49±7.83 t dry matter ha^–1, while dead wood contributed a mean mass of 7.63±0.89 t dry matter ha^–1. Excavations of roots yielded a below-ground biomass of 9.67 t dry matter ha^–1 which represented only 9.8% of the above-ground value. There was a mean density of 4700 living stems ha^–1 with plant heights ranging from 0.57 m to 5.80 m. Mean LAI was 4.95±0.80. As a basis for estimating standing biomass, regression lines were fitted to biomass values from individual trees of B. gymnorrhiza and Avicennia marina (Forssk.) Vierh. of various sizes. A comparison of these relationships with methods used by previous workers for estimating biomass suggests that most other methods cannot be applied without modification for local stands of mangroves.     

Culm recruitment,dry matter dynamics and carbon flux in recently harvested and mature bamboo savannas in the Indian dry tropics

Culm recruitment, standing crop biomass, net production and carbon flux were estimated in mature (5 years after last harvest) and recently harvested bamboo (Dendrocalamus strictus (Roxb.) Nees) savanna sites in the dry tropics. During the 2 study years bamboo shoot recruitment was 1711–3182 and 1432–1510 shoots ha⁻¹ in harvested and mature sites, respectively. Corresponding shoot mortality was 66–93% and 62–69%, respectively. Total biomass was 34.9 t ha⁻¹ at the harvested site and 47.4 t ha⁻¹ at the mature site. Harvesting increased the relative contribution of belowground bamboo biomass. Annual litter input to soil was 2.7 and 5.9 t ha⁻¹ year⁻¹ at the harvested and mature sites, respectively. The bulk of the annual litterfall (78–88%) occurred in the cool dry season (November to February). The mean litter mass on the savanna floor ranged from 3.1 to 3.3 t ha⁻¹; at the harvested site wood litter contributed 70% of the litter mass and at the mature site leaves formed 77% of the litter mass. The mean total net production (TNP) for the two annual cycles was 15.8 t ha⁻¹ year⁻¹ at the harvested site and 19.3 t ha⁻¹ year⁻¹ at the mature site. Nearly half (46–57%) of the TNP was allocated to the belowground parts. Short lived components (leaves and fine roots) contributed about four-fifths of the net production of bamboo. Total carbon storage in the system was 64.4 t ha⁻¹ at the harvested site and 75.4 t ha⁻¹ at the mature site, of which 23–28% was distributed in vegetation, 2% in litter and 70–75% in soil. Annual net carbon deposition was 6.3 and 8.7 t ha⁻¹ year⁻¹ at harvested and mature sites, respectively.     

Forest structure and carbon dynamics in Amazonian tropical rain forests

Living trees constitute one of the major stocks of carbon in tropical forests. A better understanding of variations in the dynamics and structure of tropical forests is necessary for predicting the potential for these ecosystems to lose or store carbon, and for understanding how they recover from disturbance. Amazonian tropical forests occur over a vast area that encompasses differences in topography, climate, and geologic substrate. We observed large differences in forest structure, biomass, and tree growth rates in permanent plots situated in the eastern (near Santarém, Pará), central (near Manaus, Amazonas) and southwestern (near Rio Branco, Acre) Amazon, which differed in dry season length, as well as other factors. Forests at the two sites experiencing longer dry seasons, near Rio Branco and Santarém, had lower stem frequencies (460 and 466 ha^–1 respectively), less biodiversity (Shannon–Wiener diversity index), and smaller aboveground C stocks (140.6 and 122.1 Mg C ha^–1) than the Manaus site (626 trees ha^–1, 180.1 Mg C ha^–1), which had less seasonal variation in rainfall. The forests experiencing longer dry seasons also stored a greater proportion of the total biomass in trees with >50 cm diameter (41–45 vs 30% in Manaus). Rates of annual addition of C to living trees calculated from monthly dendrometer band measurements were 1.9 (Manaus), 2.8 (Santarém), and 2.6 (Rio Branco) Mg C ha^–1 year^–1. At all sites, trees in the 10–30 cm diameter class accounted for the highest proportion of annual growth (38, 55 and 56% in Manaus, Rio Branco and Santarém, respectively). Growth showed marked seasonality, with largest stem diameter increment in the wet season and smallest in the dry season, though this may be confounded by seasonal variation in wood water content. Year-to-year variations in C allocated to stem growth ranged from nearly zero in Rio Branco, to 0.8 Mg C ha^–1 year^–1 in Manaus (40% of annual mean) and 0.9 Mg C ha^–1 year^–1 (33% of annual mean) in Santarém, though this variability showed no significant relation with precipitation among years. Initial estimates of the C balance of live wood including recruitment and mortality as well as growth suggests that live wood biomass is at near steady-state in Manaus, but accumulating at about 1.5 Mg C ha^–1 at the other two sites. The causes of C imbalance in living wood pools in Santarém and Rio Branco sites are unknown, but may be related to previous disturbance at these sites. Based on size distribution and growth rate differences in the three sites, we predict that trees in the Manaus forest have greater mean age (~240 years) than those of the other two forests (~140 years).     

Carbon allocation in a Bornean tropical rainforest without dry seasons

To clarify characteristics of carbon (C) allocation in a Bornean tropical rainforest without dry seasons, gross primary production (GPP) and C allocation, i.e., above-ground net primary production (ANPP), aboveground plant respiration (APR), and total below-ground carbon flux (TBCF) for the forest were examined and compared with those from Amazonian tropical rainforests with dry seasons. GPP (30.61 MgC ha^?1 year^?1, eddy covariance measurements; 34.40 MgC ha^?1 year^?1, biometric measurements) was comparable to those for Amazonian rainforests. ANPP (6.76 MgC ha^?1 year^?1) was comparable to, and APR (8.01 MgC ha^?1 year^?1) was slightly lower than, their respective values for Amazonian rainforests, even though aboveground biomass was greater at our site. TBCF (19.63 MgC ha^?1 year^?1) was higher than those for Amazonian forests. The comparable ANPP and higher TBCF were unexpected, since higher water availability would suggest less fine root competition for water, giving higher ANPP and lower TBCF to GPP. Low nutrient availability may explain the comparable ANPP and higher TBCF. These data show that there are variations in C allocation patterns among mature tropical rainforests, and the variations cannot be explained solely by differences in soil water availability.     

Differences in carbon fluxes between forested and cultivated micronesian tropical peatlands

Taro is a staple crop that is often grown in wetlands throughout the Indo-Pacific, but the long-term impacts of its cultivation on wetland ecosystem functions are unknown. The objective of this study was to determine how cultivating taro affects carbon cycling by comparing key pathways in a forested peatland and an adjacent cultivated taro patch. Leaves decomposed rapidly at both sites with roughly 73% remaining after 2 weeks, 53% after 8 weeks, 38% after 17 weeks, and 17% after 36 weeks. Root decomposition proceeded much more slowly with roughly 93% remaining after 2 weeks, 80% after 8 weeks, 71% after 17 weeks, and 66% after 36 weeks. Annual litterfall was 1181 g m^–2 year^–1 and 849 g m^–2 year^–1 for the forested and cultivated sites, respectively. For the two sites combined, litterfall consisted of 78% leaves, 10% reproductive material, 3% branches, and 9% miscellaneous material. Fine root biomass was greater in the forested site than the cultivated site, averaging 205 g m^–2 and 34 g m^–2, respectively. Fine root production was much greater in the forested than the cultivated site, averaging 226 g C m^–2 year^–1 and 48 g C m^–2 year^–1, respectively. Soil respiration averaged 99 mg C m^–2 h^–1 and 55 mg C m^–2 h^–1 at the forested and cultivated sites, respectively. We found that the major change to carbon fluxes in the cultivated site was less carbon was entering the peatland, particularly less root production. Alterations to the carbon cycle caused by cultivation would probably not be permanent, because taro patches are periodically abandoned and allowed to regenerate naturally.     

Aboveground net production and dry matter allocation ofPinus pumila forests in the Kiso mountain range,central Japan

Aboveground net production rates of the subalpine stone pine (Pinus pumila) forests in central Japan were estimated by the summation method; net production was defined as the sum of annual biomass increment and annual loss due to death. In the two pine stands of different scrub heights, P1 (200 cm) and P2 (140 cm), aboveground biomass reached 177 and 126 ton ha⁻¹, respectively. Leaf biomass was about 14 ton ha⁻¹ in each stand. The estimates of aboveground net production during the 2 year period (1987–1989) averaged 4.1 and 3.7 ton ha⁻¹ y⁻¹ in P1 and P2, respectively, which were at the lowest among the pine forests in the world. Two indices of efficiency of energy fixation, that is, the ratio of net production to the total radiation during a growing season and the ratio of net production to total radiation per unit of leaf weight, were evaluated. Both efficiency indices for the twoP. pumila stands fell in the range obtained for other Japanese evergreen conifer forests. This suggested that the low annual net production of the stone pine stands were mainly due to a limitation in the length of the growing season. The pine forests were also characterized by a small allocation (about 17%) of aboveground net production into biomass increment, in comparison with other evergreen conifer forest types. Annual net carbon gain in theP. pumila forests was suggested to be largely invested in leaf production at the expense of the growth of woody parts.     

Transpiration of a 64-year-old maritime pine stand in Portugal

Alpine plant species have been shown to exhibit a more pronounced increase in leaf photosynthesis under elevated CO₂ than lowland plants. In order to test whether this higher carbon fixation efficiency will translate into increased biomass production under CO₂ enrichment we exposed plots of narrow alpine grassland (Swiss Central Alps, 2470 m) to ambient (355 l l^-1) and elevated (680 l l^-1) CO₂ concentration using open top chambers. Part of the plost received moderate mineral nutrient additions (40 kg ha^-1 year^-1 of nitrogen in a complete fertilizer mix). Under natural nutrient supply CO₂ enrichment had no effect on biomass production per unit land area during any of the three seasons studied so far. Correspondingly, the dominant species Carex curvula and Leontodon helveticus as well as Trifolium alpinum did not show a growth response either at the population level or at the shoot level. However, the subdominant generalistic species Poa alpina strongly increased shoot growth (+47%). Annual root production (in ingrowth cores) was significantly enhanced in C. curvula in the 2nd and 3rd year of investigation (+43%) but was not altered in the bulk samples for all species. Fertilizer addition generally stimulated above-ground (+48%) and below-ground (+26%) biomass production right from the beginning. Annual variations in weather conditions during summer also strongly influenced above-ground biomass production (19–27% more biomass in warm seasons compared to cool seasons). However, neither nutrient availability nor climate had a significant effect on the CO₂ response of the plants. Our results do not support the hypothesis that alpine plants, due to their higher carbon uptake efficiency, will increase biomass production under future atmospheric CO₂ enrichment, at least not in such late successional communities. However, as indicated by the response of P. alpina, species-specific responses occur which may lead to altered community structure and perhaps ecosystem functioning in the long-term. Our findings further suggest that possible climatic changes are likely to have a greater impact on plant growth in alpine environments than the direct stimulation of photosynthesis by CO₂. Counter-intuitively, our results suggest that even under moderate climate warming or enhanced atmospheric nitrogen deposition positive biomass responses to CO₂ enrichment of the currently dominating species are unlikely.     

Carbon cycling and net ecosystem production at an early stage of secondary succession in an abandoned coppice forest

Secondary mixed forests are one of the dominant forest cover types in human-dominated temperate regions. However, our understanding of how secondary succession affects carbon cycling and carbon sequestration in these ecosystems is limited. We studied carbon cycling and net ecosystem production (NEP) over 4 years (2004–2008) in a cool-temperate deciduous forest at an early stage of secondary succession (18 years after clear-cutting). Net primary production of the 18-year-old forest in this study was 5.2 tC ha^?1 year^?1, including below-ground coarse roots; this was partitioned into 2.5 tC ha^?1 year^?1 biomass increment, 1.6 tC ha^?1 year^?1 foliage litter, and 1.0 tC ha^?1 year^?1 other woody detritus. The total amount of annual soil surface CO₂ efflux was 6.8 tC ha^?1 year^?1, which included root respiration (1.9 tC ha^?1 year^?1) and heterotrophic respiration (RH) from soils (4.9 tC ha^?1 year^?1). The 18-year forest at this study site exhibited a great increase in biomass pool as a result of considerable total tree growth and low mortality of tree stems. In contrast, the soil organic matter (SOM) pool decreased markedly (?1.6 tC ha^?1 year^?1), although further study of below-ground detritus production and RH of SOM decomposition is needed. This young 18-year forest was a weak carbon sink (0.9 tC ha^?1 year^?1) at this stage of secondary succession. The NEP of this 18-year forest is likely to increase gradually because biomass increases with tree growth and with the improvement of the SOM pool through increasing litter and dead wood production with stand development.     

Production,standing biomass and natural abundance of <Superscript>15</Superscript>N and <Superscript>13</Superscript>C in ectomycorrhizal mycelia collected at different soil depths in two forest types

Nutrient uptake by forest trees is dependent on ectomycorrhizal (EM) mycelia that grow out into the soil from the mycorrhizal root tips. We estimated the production of EM mycelia in root free samples of pure spruce and mixed spruce-oak stands in southern Sweden as mycelia grown into sand-filled mesh bags placed at three different soil depths (0–10, 10–20 and 20–30 cm). The mesh bags were collected after 12 months and we found that 590±70 kg ha^–1 year^–1 of pure mycelia was produced in spruce stands and 420±160 kg ha^–1 year^–1 in mixed stands. The production of EM mycelia in the mesh bags decreased with soil depth in both stand types but tended to be more concentrated in the top soil in the mixed stands compared to the spruce stands. The fungal biomass was also determined in soil samples taken from different depths by using phospholipid fatty acids as markers for fungal biomass. Subsamples were incubated at 20°C for 5 months and the amount of fungal biomass that degraded during the incubation period was used as an estimate of EM fungal biomass. The EM biomass in the soil profile decreased with soil depth and did not differ significantly between the two stand types. The total EM biomass in the pure spruce stands was estimated to be 4.8±0.9×10³ kg ha^–1 and in the mixed stands 5.8±1.1×10³ kg ha^–1 down to 70 cm depth. The biomass and production estimates of EM mycelia suggest a very long turnover time or that necromass has been included in the biomass estimates. The amount of N present in EM mycelia was estimated to be 121 kg N ha^–1 in spruce stands and 187 kg N ha^–1 in mixed stands. The ¹³C value for mycelia in mesh bags was not influenced by soil depth, indicating that the fungi obtained all their carbon from the tree roots. The ¹³C values in mycelia collected from mixed stands were intermediate to values from pure spruce and pure oak stands suggesting that the EM mycelia received carbon from both spruce and oak trees in the mixed stands. The ¹⁵N value for the EM mycelia and the surrounding soil increased with soil depth suggesting that they obtained their entire N from the surrounding soil.     

Fire in the Brazilian Amazon: 1. Biomass,nutrient pools,and losses in slashed primary forests

Deforestation in the Brazilian Amazon has resulted in the conversion of >230,000 km² of tropical forest, yet little is known on the quantities of biomass consumed or the losses of nutrients from the ecosystem. We quantified the above-ground biomass, nutrient pools and the effects of biomass burning in four slashed primary tropical moist forests in the Brazilian Amazon. Total above-ground biomass (TAGB) ranged from 292 Mg ha^-1 to 436 Mg ha^-1. Coarse wood debris (>20.5 cm diameter) was the dominant fuel component. However, structure of the four sites were variable. Coarse wood debris comprised from 44% to 69% of the TAGB, while the forest floor (litter and rootmat) comprised from 3.7 to 8.0% of the TAGB. Total biomass consumption ranged from 42% to 57%. Fires resulted in the consumption of >99% of the litter and rootmat, yet <50% of the coarse wood debirs. Dramatic losses in C, N, and S were quantified. Lesser quantities of P, K, and Ca were lost by combustion processes. Carbon losses from the ecosystem were 58–112 Mg ha^-1. Nitrogen losses ranged from 817 to 1605 kg ha^-1 and S losses ranged from 92 to 122 kg ha^-1. This represents losses that are as high as 56%, 68%, and 49% of the total above-ground pools of these nutrients, respectively. Losses of P were as high as 20 kg ha^-1 or 32% of the above-ground pool. Losses to the atmosphere arising from primary slash fires were variable among sites due to site differences in concentration, fuel biomass, and fuel structure, climatic fluctuations, and anthropogenic influences. Compared to fires in other forest ecosystems, fires in slashed primary tropical evergreen forests result in among the highest total losses of nutrients ever measured. In addition, the proportion of the total nutrient pool lost from slash fires is higher in this ecosystem compared to other ecosystems due to a higher percentage of nutrients stored in above-ground biomass.     

Woody debris contribution to the carbon budget of selectively logged and maturing mid-latitude forests

Woody debris (WD) is an important component of forest C budgets, both as a C reservoir and source of CO₂ to the atmosphere. We used an infrared gas analyzer and closed dynamic chamber to measure CO₂ efflux from downed coarse WD (CWD; diameter≥7.5 cm) and fine WD (FWD; 7.5 cm>diameter≥2 cm) to assess respiration in a selectively logged forest and a maturing forest (control site) in the northeastern USA. We developed two linear regression models to predict WD respiration: one based on WD temperature, moisture, and size (R ²=0.57), and the other on decay class and air temperature (R ²=0.32). WD respiration (0.28±0.09 Mg C ha⁻¹ year⁻¹) contributed only ≈2% of total ecosystem respiration (12.3±0.7 Mg C ha⁻¹ year⁻¹, 1999–2003), but net C flux from CWD accounted for up to 30% of net ecosystem exchange in the maturing forest. C flux from CWD on the logged site increased modestly, from 0.61±0.29 Mg C ha⁻¹ year⁻¹ prior to logging to 0.77±0.23 Mg C ha⁻¹ year⁻¹ after logging, reflecting increased CWD stocks. FWD biomass and associated respiration flux were ≈7 times and ≈5 times greater, respectively, in the logged site than the control site. The net C flux associated with CWD, including inputs and respiratory outputs, was 0.35±0.19 Mg C ha⁻¹ year⁻¹ (net C sink) in the control site and −0.30±0.30 Mg C ha⁻¹ year⁻¹ (net C source) in the logged site. We infer that accumulation of WD may represent a small net C sink in maturing northern hardwood forests. Disturbance, such as selective logging, can enlarge the WD pool, increasing the net C flux from the WD pool to the atmosphere and potentially causing it to become a net C source.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

An estimation of CO<Subscript>2</Subscript> fixation capacity in mangrove forest using two methods of CO<Subscript>2</Subscript> gas exchange and growth curve analysis

In many coastal areas of South-East Asia, attempts have been made to revive coastal ecosystem by initiating projects that encourage planting of mangrove trees. Compared to the terrestrial trees, mangrove trees possess a higher carbon fixation capacity. It becomes a very significant option for clean development mechanism (CDM) program. However, a reliable method to estimate CO₂ fixation capacity of mangrove trees has not been established. Acknowledging the above fact, we decided to set up an estimation method for the CDM program, using gas exchange analysis to estimate mangrove productivity, we put into consideration the net CO₂ fixation of reforested Kandelia candel (5-, 10-, and 15-year-old stand). This was estimated by gas exchange analysis and growth curve analysis. In growth curve analysis, we drew a growth curve of a single stand using data of above- and below-ground biomass. In the gas exchange analysis, we calculated CO₂ fixation capacity by (1) measuring respiration rate of each organ of stand and calculating respiratory CO₂ emission from above- to below-ground biomass. (2) Measuring the single-leaf photosynthetic rate in response to light intensity and calculating the photosynthetic CO₂ absorption. (3) We also developed a model for the diurnal changes in temperature, and monthly averages based on one-day estimation of CO₂ absorption and emission, which we corrected by this model in order to estimate the net CO₂ fixation capacity in response to temperature. Comparing the biomass accumulation of the two methods constructed for the same forest, the above-ground biomass accumulation of 10-year-old forest (34.3 ton ha⁻¹ yr⁻¹) estimated by gas exchange analysis was closely compared to those of growth curve analysis (26.6 ton ha⁻¹ yr⁻¹), suggesting that the gas exchange analysis was capable of estimating mangrove productivity. The validity of the estimated CO₂ fixation capacity by the gas exchange analysis and the growth curve analysis was also discussed.     

The effect of sewage-enriched river Ganga water on the biomass production of theAzolla-Anabaena complex

The biomass formation ofAzolla was greatly enhanced by water of the River Ganga and by prevailing environmental conditions. It increased gradually from January to April (first maximum 2.409 g.m^–2.day^–1), declined during June (1.185 g.m^–2.day^–1), and reached a second its maximum during September (2.629 g.m^–2.day^–1). The biomass formation was related to the nutrient availability in the medium in a particular season (measured were: nitrate-N, available phosphorus, total suspended solids, and conductivity). The average annual production of 6.73 ton.ha^–1.yr^–1 is equivalent to the average production of 0.025 ton.ha^–1.yr^–1 phosphorus, 0.252 ton.ha^–1.yr^–1 nitrogen, and 1.57 ton.ha^–1.yr^–1 crude protein.     

Calibration and validation of an empirical approach to model soil CO<Subscript>2</Subscript> efflux in a deciduous forest

Soil respiration (Rs) was monitored periodically throughout 2001 and 2003 in a pedunculate oak (Quercus robur L.) stand located in the Belgian Campine region. An empirical model originally developed for a neighboring pine stand, that accounts for variation in temperature, soil moisture, rewetting of the surface layers by rain during dry periods and seasonal fresh litter inputs, was fitted to the data. The model explained 92% and 94% of the temporal variability in Rs during 2001 and 2003 respectively. Monthly measurements of Rs can suffice to build a robust empirical model if temperature is the main controlling factor. However, during the driest period of the year a weekly sampling schedule was needed to capture the combined effect of temperature, soil water content (SWC) and the short-term effect of rewetting played. Although the model was developed for gap-filling purposes it also showed a remarkable predictive ability for this site and these conditions. Annual emissions of carbon (C) estimated with the model were significantly higher in 2001 than in 2003 (7.8 and 5.9 ton C ha⁻¹ year⁻¹, respectively). The severe drought during most of the growing season in 2003 caused a high fine root mortality and a decrease in microbial activity, and was likely the main responsible factor of the almost 2 ton C ha⁻¹ year⁻¹ differences in Rs between both years. Pulses of Rs during drying/rewetting cycles accounted for a substantial fraction of the total flux, especially during the driest year. Finally, our results show that quality of the substrate may play an important role in both the intensity of the rewetting pulses of CO₂ and the seasonality of Rs.     

Estimating seasonal and annual carbon inputs,and root decomposition rates in a temperate pasture following field 14C pulse-labelling

Using a ¹⁴C pulse-labelling technique, we studied the seasonal changes in assimilation and partitioning of photoassimilated C in the plant–root–soil components of a temperate pasture. Pasture and soil samples were taken after 4-h, and 35-day chase periods, to examine these seasonal ¹⁴C fluxes. Total C and ¹⁴C were determined in the shoot, root and soil system. The amounts of C translocated annually to roots and soil were also estimated from the seasonal ¹⁴C distribution and pasture growth. The in situ field decomposition of newly formed roots during different seasons, also using ¹⁴C-labelling, was studied for one year in undisturbed rhizosphere soil. The ¹⁴C-labelled roots were sampled five times and decomposition rates were calculated assuming first-order decomposition.Annual pasture production at the site was 16 020 kg DM ha^–1, and pasture growth varied with season being highest (75–79 kg ha^–1 d^–1) in spring and lowest (18–20 kg ha^–1 d^–1) in winter. The above- and below-ground partitioning of ¹⁴C also varied with the season. The respiratory ¹⁴C–CO₂ losses, calculated as the difference between the total amounts of ¹⁴C recovered in the soil-plant system at 4 h and 35 days, were high (66–70%) during the summer, autumn and winter season, and low (37–39%) during the spring and late-spring season. Pasture plants partitioned more C below-ground during spring compared with summer, autumn and winter seasons. Overall, at this high fertility dairy pasture site, 18 220 kg C/ha was respired, 6490 kg remained above-ground in the shoot, and 6820 kg was translocated to roots and 1320 kg to soil. Root decomposition rate constant (k) differed widely with the season and were the highest for the autumn roots. The half-life was highest (111 days) for autumn roots and lowest (64 days) for spring roots. About one-third of the root label measured in the spring season disappeared in the first 5 weeks after the initial 35 Day of allocation period. The late spring, summer, late summer and winter roots had intermediate half-lives (88–94 days). These results indicate that seasonal changes in root growth and decomposition should be accounted for to give a better quantification of root turnover.     

Productivity and carbon fluxes of tropical savannas

Aim (1) To estimate the local and global magnitude of carbon fluxes between savanna and the atmosphere, and to suggest the significance of savannas in the global carbon cycle. (2) To suggest the extent to which protection of savannas could contribute to a global carbon sequestration initiative. Location Tropical savanna ecosystems in Africa, Australia, India and South America. Methods A literature search was carried out using the ISI Web of Knowledge, and a compilation of extra data was obtained from other literature, including national reports accessed through the personal collections of the authors. Savanna is here defined as any tropical ecosystem containing grasses, including woodland and grassland types. From these data it was possible to estimate the fluxes of carbon dioxide between the entire savanna biome on a global scale. Results Tropical savannas can be remarkably productive, with a net primary productivity that ranges from 1 to 12 t C ha⁻¹ year⁻¹. The lower values are found in the arid and semi‐arid savannas occurring in extensive regions of Africa, Australia and South America. The global average of the cases reviewed here was 7.2 t C ha⁻¹ year⁻¹. The carbon sequestration rate (net ecosystem productivity) may average 0.14 t C ha⁻¹ year⁻¹ or 0.39 Gt C year⁻¹. If savannas were to be protected from fire and grazing, most of them would accumulate substantial carbon and the sink would be larger. Savannas are under anthropogenic pressure, but this has been much less publicized than deforestation in the rain forest biome. The rate of loss is not well established, but may exceed 1% per year, approximately twice as fast as that of rain forests. Globally, this is likely to constitute a flux to the atmosphere that is at least as large as that arising from deforestation of the rain forest. Main conclusions The current rate of loss impacts appreciably on the global carbon balance. There is considerable scope for using many of the savannas as sites for carbon sequestration, by simply protecting them from burning and grazing, and permitting them to increase in stature and carbon content over periods of several decades.     

Effect of winter fire on primary productivity and nutrient concentration of a dry tropical savanna

Burning increased the mean annual canopy and belowground biomass of a dry tropical savanna by 40% and 12%, respectively, while littermass was reduced by 85% in comparison to control savanna. Mean annual aboveground and belowground net primary production were 471 and 631 g m^-2 in control, and 584 and 688 g m^-2 in burned savanna, respectively. Fire caused an increase in mean aboveground net production of 24% and in belowground net production of 9%.Concentration of carbon, nitrogen and phosphorus in vegetation of unburned plots ranged between 34.01–38.59%, 0.85–1.53% and 0.04–0.11% and in soil from 0.95–1%, 0.011–0.13% and 0.017–0.02%, respectively. Fire increased the mean concentrations of N and P by 16% and 42% in vegetation and 18.18% and 17.65% in soil, respectively. Thus winter fire can be an important tool for the management of dry tropical savanna with respect to biomass production and nutritive quality.     

Annual and monthly carbon balance in an intensively managed Mediterranean olive orchard

At present, research activities on the role of orchard systems in sequestering atmospheric CO₂ remain scarce. This paper aimed to contribute to assessing the carbon balance of a Mediterranean olive (Olea europea) orchard. The net ecosystem exchange, the ecosystem respiration and the gross primary production were computed for two consecutive years through eddy covariance, and the different biomass accumulation terms were also inferred in the same period through an inventorial method. The net carbon exchange ranged from 13.45 t(C) ha^?1 year^?1 to 11.60 t(C) ha^?1 year^?1. Very similar values [12.2 and 11.5 t(C) ha^?1 year^?1] were found with the direct carbon accumulation inventory. The intensive farming management (irrigation included) and the young age of the plants (12–16 years old), still in an active growing phase, led the olive plantation to be a higher carbon sink with respect to other evergreen orchards reported in the literature.     

Biomass carbon storage and net primary production in different habitats of Hunshandake Sandland, China

Terrestrial ecosystems are playing important roles in global carbon cycling. However, the information is still limited with regard to the semi-arid sandland or desert area, compared with the thorough studies on forest and grassland. We here estimated the biomass carbon storage, net primary production (NPP) and rain use efficiency (RUE) of Hunshandake Sandland, a semi-arid sandy region in Inner Mongolia covered with vegetation of Siberian elm (Ulmus pumila L.) sparse forest grassland. Five main habitats, i.e. fixed dunes, semi-fixed dunes, shifting dunes, lowland, and wetland, were compared to analyze the patterns of carbon storage and NPP distribution. The average biomass (9.19 Mg C ha^?1) and NPP (4.79 Mg C ha^?1 yr^?1) of the sparse forest grassland were respectively 82% and 54% higher than the mean level of the surrounding temperate grassland. Governed by the same climate, sparse forest grassland ecosystem had RUE almost twice that of surrounding grassland. The ratio of below to aboveground biomass was 3.5: 1 in the sandland, indicating that most of the vegetational carbon was stored in belowground pool. Although trees were functionally critical in maintaining the integrity of sparse forest grassland, they accounted for only 10.6% and 1.2% of the biomass and NPP, respectively. The sparse forest grassland in Hunshandake Sandland should be recognized as a temperate savanna ecosystem which is distinctively different from typical temperate grassland in the same region as evidenced by the higher NPP and vegetation carbon storage. Well designed management and restoration efforts can potentially sustain ecosystem services in both forage production and carbon sequestration.