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.     

Influence of rainfall and grazing on herbage dynamics in a seasonally dry tropical savanna

Species composition and herbage dynamics in relation to rainfall variability and cattle grazing were studied in permanently protected, grazed, and temporarily fenced treatments on three sites in a seasonally dry tropical savanna. Permanently protected sites, established between 1979 and 1984, were 55–79% similar with each other in species composition, and 14–25% similar with grazed sites during the period 1986–1988. Similarity among grazed sites was only 36–43%. Number of species was greater in the grazed treatment than in the permanently protected treatment. The percentages of annual grasses and non-leguminous forbs were greater in grazed savanna than in permanently protected savanna. Species diversity was higher in grazed savanna than in the corresponding permanently protected savanna. Species the two annual cycles studied, peak live shoot biomass was 614 g m^-2 in permanently protected savanna, 109 g m^-2 in grazed savanna, and 724 g m^-2 in temporarily fenced savanna. Live shoot biomass in temporarily fenced savanna was 18 to 44% greater than in permanently protected savanna. Peak canopy biomass ranged from 342 to 700 g m^-2 in permanently protected savanna. It was related with total rainy season rainfall, and was particularly sensitive to late rainy season rainfall. On the other hand, peak canopy biomass in grazed savanna ranged from 59 to 169 g m^-2 and was related to grazing intensity rather than either total rainy season rainfall or late rainy season rainfall. Coefficient of variation of green biomass in permanently protected savanna was related with rainfall variability indicating it to be a pulsed system which responds quickly to rainfall events. Biomass of woody species ranged from 2466 to 5298 g m^-2 in permanently protected savanna and from 744 to 1433 g m^–2 in the grazed savanna. Green foliage biomass was 3.7 to 6.4% of the woody biomass in permanently protected and 5.6 to 5.9% in grazed savanna, and supplements substantially the fodder resource during the dry periods of the year.     

Belowground structure and production in a Mediterranean sand dune shrub community

Belowground structure and annual production in an open Mediterranean scrub were studied on a sandy substrate which had not been harvested or exposed to fire during the last 30–40 years. Estimated belowground biomass (1328 ± 93.4 g m^-2) and production (548 ± 246.9 g m^-2 yr^-1) were lower than in other Mediterranean scrubs. However, the energy investment in belowground structures was high (root biomass/ shoot biomass = 2.7; annual belowground production/ annual aboveground production = 7.1), which is associated with a high density of fine roots in the top soil (the average distance between the fine roots = 0.76 cm). A very simple model based on nutrient diffusion was considered to analyse the resource constrains of the community. The results underline the importance of nutrients (and more specifically phosphorus) rather than water, as possible determinants of the structure and dynamics of the root system, as well as for the primary production of the community during the vegetative period.     

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.     

Net Primary Production and Carbon Stocks for Subarctic Mesic–Dry Tundras with Contrasting Microtopography, Altitude, and Dominant Species

Mesic–dry tundras are widespread in the Arctic but detailed assessments of net primary production (NPP) and ecosystem carbon (C) stocks are lacking. We addressed this lack of knowledge by determining the seasonal dynamics of aboveground vascular NPP, annual NPP, and whole-ecosystem C stocks in five mesic–dry tundras in Northern Sweden with contrasting microtopography, altitude, and dominant species. Those measurements were paralleled by the stock assessments of nitrogen (N), the limiting nutrient. The vascular production was determined by harvest or in situ growing units, whereas the nonvascular production was obtained from average species growth rates, previously assessed at the sites. Results showed that aboveground vascular NPP (15–270 g m⁻²), annual NPP (214–282 g m⁻² or 102–137 g C m⁻²) and vegetation biomass (330–2450 g m⁻²) varied greatly among communities. Vegetation dominated by Empetrum hermaphroditum is more productive than Cassiope tetragona vegetation. Although the large majority of the apical NPP occurred in early-mid season (85%), production of stems and evergreen leaves proceeded until about 2 weeks before senescence. Most of the vascular vegetation was belowground (80%), whereas most of the vegetation production occurred aboveground (85%). Ecosystem C and N stocks were 2100–8200 g C m⁻² and 80–330 g N m⁻², respectively, stored mainly in the soil turf and in the fine organic soil. Such stocks are comparable to the C and N stocks of moister tundra types, such as tussock tundra. Author Contributions  Matteo Campioli, Anders Michelsen, Roeland Samson, Raoul Lemeur—conceived and designed study, Matteo Campioli, Anders Michelsen, Andreas Demey, Annemie Vermeulen—performed research, Matteo Campioli—analyzed data, and Matteo Campioli—wrote the paper.     

The effect of charcoal production on carbon cycling in African biomes

Using biomass for charcoal production in sub-Saharan Africa (SSA) may change carbon stock dynamics and lead to irreversible changes in the carbon balance, yet we have little understanding of whether these dynamics vary by biome in this region. Currently, charcoal production contributes up to 7% of yearly deforestation in tropical regions, with carbon emissions corresponding to 71.2 million tonnes of CO₂ and 1.3 million tonnes of CH₄. With a projected increased demand for charcoal in the coming decades, even low harvest rates may throw the carbon budget off-balance due to legacy effects. Here, we parameterized the dynamic global vegetation model LPJ-GUESS for six SSA biomes and examined the effect of charcoal production on net ecosystem exchange (NEE), carbon stock sizes and recovery time for tropical rain forest, montane forest, moist savanna, dry savanna, temperate grassland and semi-desert. Under historical charcoal regimes, tropical rain forests and montane forests transitioned from net carbon sinks to net sources, that is, mean cumulative NEE from −3.56 ± 2.59 kg C/m² to 2.46 ± 3.43 kg C/m² and −2.73 ± 2.80 kg C/m² to 1.87 ± 4.94 kg C/m² respectively. Varying charcoal production intensities resulted in tropical rain forests showing at least two times higher carbon losses than the other biomes. Biome recovery time varied by carbon stock, with tropical and montane forests taking about 10 times longer than the fast recovery observed for semi-desert and temperate grasslands. Our findings show that high biomass biomes are disproportionately affected by biomass harvesting for charcoal, and even low harvesting rates strongly affect vegetation and litter carbon and their contribution to the carbon budget. Therefore, the prolonged biome recoveries imply that current charcoal production practices in SSA are not sustainable, especially in tropical rain forests and montane forests, where we observe longer recovery for vegetation and litter carbon stocks.     

No changes in soil organic carbon and nitrogen following long-term prescribed burning and livestock exclusion in the Sudan-savanna woodlands of Burkina Faso

Fire and overgrazing reduce aboveground biomass, leading to land degradation and potential impacts on soil organic carbon (SOC) and total nitrogen (TN) dynamics. However, empirical data are lacking on how prescribed burning and livestock exclusion impact SOC in the long-term. Here we analyse the effects of 19 years of prescribed annual burning and livestock exclusion on tree density, SOC and TN concentrations in the Sudanian savanna ecoregion at two sites (Tiogo and Laba) in Burkina Faso. Results revealed that neither livestock exclusion nor prescribed burning had significant impact on SOC and TN concentrations. The results at both sites indicate that 19 years of livestock and fire exclusion did not result in a significant increase in tree density compared to grazing and annual prescribed burning. The overall mean (± SEM) of SOC stocks in the 0–50 cm depth increment in the unburnt (53.5 ± 4.7 Mg C ha⁻¹) and annually burnt (56.4 ± 4.3 Mg C ha⁻¹) plots at Tiogo were not statistically different. Similarly, at Laba there was no significant difference between the corresponding figures in the unburnt (37.9 ± 2.6 Mg ha⁻¹) and in the annually burnt plots (38.6 ± 1.9 Mg ha⁻¹). Increases in belowground inputs from root turnover may have countered changes in aboveground biomass, resulting in no net change in SOC and TN. We conclude that, contrary to our expectation and current policy recommendations, restricting burning or grazing did not result in increase in SOC stocks in this dry savanna ecosystem.     

Regional Variations in Biomass Distribution in Brazilian Savanna Woodland

The Cerrado, the savanna biome in central Brazil, mostly comprised of woodland savanna, is experiencing intense and fast land use changes. To understand the changes in Cerrado carbon stocks, we present an overview of biomass distribution in different Cerrado vegetation types (i.e., grasslands, shrublands and forestlands). We surveyed 26 studies including 170 Cerrado sites. The grasslands presented mean total biomass of 24 Mg/ha, with 70 percent allocated in the belowground portion. In shrublands, the mean total biomass was 58 Mg/ha being 58 percent in the belowground portion. Finally, in forestlands the mean total biomass was 98 Mg/ha with 18 percent as belowground biomass. The surveyed studies presented 12 allometric equations for biomass estimate, most involving both diameter and height. Data on wood density for Cerrado shrubs and trees are not abundant and the average value was 0.66 g/cm³, similar to that found in the central portion of the Amazon Forest. We also examined the relationship between total precipitation and dry‐season intensity with biomass variation in the Cerrado shrubland using data from tropical rainfall measurement mission (TRMM) for the period 2000–2010. Dry‐season precipitation amount in cerrado areas in severe drought regions explained 29 percent of the variation in aboveground woody biomass. This finding is important in the face of the predictions of longer and more severe dry seasons in the region due to climate change.     

Element storage in native,agri-, and silvicultural ecosystems of the Brazilian savanna. II. Metals

Conversion of native savanna in Brazil, the Cerrado, to agri- and silvicultural land use causes changes in metal storages of the ecosystems. To evaluate the sustainability of land use these changes have to be known. Therefore, we examined the Al, Ca, Fe, K, Mg, Mn, Na, and Zn storages in above- and belowground biomass, the organic layer, and the top 2 m of the mineral soil (Anionic Acrustoxes) of three replicate plots in each of six native and land-use systems. The systems were native Cerrado, Pinus caribaea Morelet plantations, productive and degraded Brachiaria decumbens Stapf pastures, and conventional and no-tillage soybean cultivation. The total metal storage varied little among the studied systems except for Ca, K, and Mg. All land-use systems had larger Ca storages (cropping systems 202–205 g m^–2, productive pasture: 112, degraded pasture: 84, Pinus: 81) than the Cerrado (62 g m^–2). The K storage was smaller in the pastures (17–18 g m^–2) than in Cerrado and Pinus stands (22–24) and largest in the cropping systems (26). The Mg storages were largest in the cropping systems (65–69) and productive pasture (59 g m^–2); those in the Pinus stands (52), the degraded pasture (51), and the Cerrado (53) were similar. For most metals, the aboveground biomass contained up to 1% of the total storage including the top 2 m of the soil (<5% if the lower ecosystem boundary was set at 0.3 m soil depth). However, the aboveground biomass stored up to 12% of Ca, K, and Mg down to 2 m soil depth (41% if the lower ecosystem boundary was set at 0.3 m soil depth). In the Pinus stands, the storage of most metals was larger in the below- than in the aboveground biomass; for the other systems the reverse was true. Metal storages in soil were little affected by land use except that liming resulted in increased Ca and Mg storages in the topsoil. The comparison between known inputs of Ca, K, and Mg and mean annual change rates of their storages revealed that there were considerable base metal losses by leaching, grazing, and removal with the harvest. After 12–20 years, the land-use impact on metal storages is restricted to Ca, Mg, and K. Generally, all land-use systems tend to be richer in these nutrients except for the significant depletion in K of the pastures.     

Allocation of carbon in a mature eucalypt forest and some effects of soil phosphorus availability

Pools and annual fluxes of carbon (C) were estimated for a mature Eucalyptus pauciflora (snowgum) forest with and without phosphorus (P) fertilizer addition to determine the effect of soil P availability on allocation of C in the stand. Aboveground biomass was estimated from allometric equations relating stem and branch diameters of individual trees to their biomass. Biomass production was calculated from annual increments in tree diameters and measurements of litterfall. Maintenance and construction respiration were calculated for each component using equations given by Ryan (1991a). Total belowground C flux was estimated from measurements of annual soil CO₂ efflux less the C content of annual litterfall (assuming forest floor and soil C were at approximate steady state for the year that soil CO₂ efflux was measured). The total C content of the standing biomass of the unfertilized stand was 138 t ha^-1, with approximately 80% aboveground and 20% belowground. Forest floor C was 8.5 t ha^-1. Soil C content (0–1 m) was 369 t ha^-1 representing 70% of the total C pool in the ecosystem. Total gross annual C flux aboveground (biomass increment plus litterfall plus respiration) was 11.9 t ha^-1 and gross flux belowground (coarse root increment plus fine root production plus root respiration) was 5.1 t ha^-1. Total annual soil efflux was 7.1 t ha^-1, of which 2.5 t ha^-1 (35%) was contributed by litter decomposition.The short-term effect of changing the availability of P compared with C on allocation to aboveground versus belowground processes was estimated by comparing fertilized and unfertilized stands during the year after treatment. In the P-fertilized stand annual wood biomass increment increased by 30%, there was no evidence of change in canopy biomass, and belowground C allocation decreased by 19% relative to the unfertilized stand. Total annual C flux was 16.97 and 16.75 t ha^-1 yr^-1 and the ratio of below- to aboveground C allocation was 0.43 and 0.35 in the unfertilized and P-fertilized stands, respectively. Therefore, the major response of the forest stand to increased soil P availability appeared to be a shift in C allocation; with little change in total productivity. These results emphasise that both growth rate and allocation need to be estimated to predict changes in fluxes and storage of C in forests that may occur in response to disturbance or climate change.     

Dynamics of dry matter production in a mixed-grass prairie in western North Dakota

Summary Above- and belowground biomass of primary producers were estimated by the harvest method on 10 dates in 1969 in a mixed-prairie grassland. A range of estimates of above- and belowground net primary production is established using several methods of calculation. The range for aboveground production is 240 to 302 g·m^-2 and 931 to 1221 g·m^-2 for belowground production. Correlation analysis indicated that above- and belowground biomass dynamics are significantly (0.05) related to air and soil temperature, soil water, precipitation, and vapor pressure deficit. Analysis of energy flow through primary producers indicates a net storage of energy in the standing dead, litter, and belowground compartments. Accumulation in the standing dead was 63% of inputs, in the litter 8%, and belowground 37%. Belowground decomposition was 57% of belowground production and the same value aboveground was 50%.     

Regional Patterns in Carbon Cycling Across the Great Plains of North America

The large organic carbon (C) pools found in noncultivated grassland soils suggest that historically these ecosystems have had high rates of C sequestration. Changes in the soil C pool over time are a function of alterations in C input and output rates. Across the Great Plains and at individual sites through time, inputs of C (via aboveground production) are correlated with precipitation; however, regional trends in C outputs and the sensitivity of these C fluxes to annual variability in precipitation are less well known. To address the role of precipitation in controlling grassland C fluxes, and thereby soil C sequestration rates, we measured aboveground and belowground net primary production (ANPP-C and BNPP-C), soil respiration (SR-C), and litter decomposition rates for 2 years, a relatively dry year followed by a year of average precipitation, at five sites spanning a precipitation gradient in the Great Plains. ANPP-C, SR-C, and litter decomposition increased from shortgrass steppe (36, 454, and 24 g C m^–2 y^–1) to tallgrass prairie (180, 1221, and 208 g C m^–2 y^–1 for ANPP-C, SR-C, and litter decomposition, respectively). No significant regional trend in BNPP-C was found. Increasing precipitation between years increased rates of ANPP-C, BNPP-C, SR-C, and litter decomposition at most sites. However, regional patterns of the sensitivity of ANPP-C, BNPP-C, SR-C, and litter decomposition to between-year differences in precipitation varied. BNPP-C was more sensitive to between-year differences in precipitation than were the other C fluxes, and shortgrass steppe was more responsive than were mixed grass and tallgrass prairie.     

Biomass and production of a naturally regenerated oak forest in southern Korea

Biomass and production of two stands with Quercus variabilis Bl. as the dominant species (stands 1 and 3) and one with Q. mongolica Fisch. as the dominant species (stand 2) were investigated in southern Korea. Stands 1 and 3 naturally occurred on sites with southerly aspects while stand 2 naturally occurred on northerly aspects; stand ages were similar for the three stands (36–38 years old). Total above- and belowground biomass including understory vegetation (Mg ha^–1) was 108.4 for stand 1, 115.6 for stand 2, and 132.0 for stand 3, respectively. Understory vegetation constituted 17.4% of the total biomass in stand 1 but only 3.7–4.5% in stand 2 and stand 3. Roots constituted 20.1–24.6% of the biomass of the overstory vegetation. Although stand 3 showed the highest total biomass, net production was highest in stand 2 at 12.6 (Mg ha^–1 year^–1); net production levels for stands 1 and 3 were 11.7 and 11.1 (Mg ha^–1 year^–1), respectively. It appeared that the differences in site conditions related to aspect influenced the distribution of naturally regenerated oak species within a relatively small area and resulted in differences in biomass and production among the stands.     

Root biomass of a dry deciduous tropical forest in Mexico

The deciduous tropical dry forest at Chamela (Jalisco, Mexico) occurs in a seasonal climate with eight rainless (November through June) and four wet months (700 mm annual precipitation). The forest reaches a mean height of 10 m. Tree density in the research area was 4700 trees per ha with a basal area at breast height of 23 m² per ha. The above-and below-ground biomass of trees, shrubs, and lianas was 73.6 Mg ha^–1 and 31 Mg ha^–1, respectively. A root:shoot biomass ratio of 0.42 was calculated. Nearly two thirds of all roots occur in the 0–20 cm soil layer and 29% of all roots have a diameter of less than 5 mm.     

Plant diversity and dry-matter dynamics of peri-urban plant communities in an Indian dry tropical region

The emergence of variety of land-use changes due to continuous anthropogenic pressure in peri-urban areas may concomitantly result in modification of the structure of associated plant communities for their sustainable growth. In the present study, plant diversity, and above- and belowground biomass distribution among species were investigated to understand their dynamics across different season, soil, and site conditions in a dry tropical peri-urban region in India. From four study sites that covered contrasting land uses: abandoned brick kiln (ABK), grazing land (GL), Kali river bank (KRB), and agricultural land (AL), a total of 360 monoliths were randomly extracted in three seasons, and dry weights were estimated for aboveground and belowground parts of species individuals. Seasonal soil samples of the sites were analyzed for physico-chemical characteristics. Of the total 87 recorded species that were mainly annual weeds and ruderals, 77% were forbs and 23% grasses. The ranges of plant biomass recorded across all sites and seasons were: aboveground 228–738 g m⁻², belowground 83–288 g m⁻², and a total of 344–1,026 g m⁻². The dominance of species differed between above- and belowground; some species dominated only above- or belowground, and others dominated in both layers. Above- and belowground biomass of the sites, differential community-biomass allocation to above- and belowground parts and species dominants varied significantly with site and season. ABK and AL sites showed lower species diversity and soil nutrients compared to GL and KRB sites. Belowground biomass significantly declined with increasing soil organic C and total N, indicating altered dry matter allocation under resource-scarce habitat conditions. Higher diversity occurred at both low- and high-biomass sites, reflective of enhanced ability of these plant communities to exploit resources maximally in spatio-temporal pattern.     

Productivity and water relations of burnt and long-unburnt semi-arid shrubland in Western Australia

This study provides a comparison between vegetation of relatively recent and long-unburnt shrubland in terms of structural and functional groups, annual net primary productivity and water relations. Adjacent areas of vegetation long-unburnt or burnt 5 years previously were compared within a remnant block of Acacia–Allocasuarina–Melaleuca arid shrubland at Kalannie, south west Western Australia. Species were classified according to growth and life form, fire response, phenology and rooting morphology and densities, mean plant above-ground dry weights and shoot:root dry mass ratios of each assessed. Species compositions, seedling densities and absence of recruitment in the long-unburnt area suggested marked dependence on fire in maintenance of biodiversity. Comparisons of above-ground standing dry biomass and annual net primary productivity of total (above-ground plus below-ground) dry matter showed the 4.09 kg m^–2 biomass of long-unburnt vegetation to be increasing at 0.52 kg m^–2 year^–1 versus 0.45 and 0.18 kg m^–2 year^–1 for vegetation of the burnt area. Water relations of soils indicated consistently wetter profiles in burnt than long-unburnt areas and no deep drainage during the year of study. Lower water stress of key species in burnt than long-unburnt areas were indicated by less negative pre-dawn water potentials and higher stomatal conductance during the year of study and more negative carbon-isotope composition (¹³C) in wood laid down over the past 5 years. Budgets for water use were estimated for both sites and compared with annual net primary productivities. Data suggested much greater transpiration loss per unit dry matter gain by the rapidly growing plants at the burnt site (437 ml H₂O g^–1 DM) than by the plants of the long-unburnt community (92 ml H₂O g^–1 DM). Results are discussed in relation to composition and functioning of other Western Australian ecosystems. It is clear that time since fire affects productivity and water-use of vegetation of semi-arid shrublands and is therefore an important consideration for management and protection of remnant vegetation.     

Elevation effects on the carbon budget of tropical mountain forests (S Ecuador): the role of the belowground compartment

Carbon storage and sequestration in tropical mountain forests and their dependence on elevation and temperature are not well understood. In an altitudinal transect study in the South Ecuadorian Andes, we tested the hypotheses that (i) aboveground net primary production (ANPP) decreases continuously with elevation due to decreasing temperatures, whereas (ii) belowground productivity (BNPP) remains constant or even increases with elevation due to a shift from light to nutrient limitation of tree growth. In five tropical mountain forests between 1050 and 3060 m a.s.l., we investigated all major above‐ and belowground biomass and productivity components, and the stocks of soil organic carbon (SOC). Leaf biomass, stemwood mass and total aboveground biomass (AGB) decreased by 50% to 70%, ANPP by about 70% between 1050 and 3060 m, while stem wood production decreased 20‐fold. Coarse and large root biomass increased slightly, fine root biomass fourfold, while fine root production (minirhizotron study) roughly doubled between 1050 and 3060 m. The total tree biomass (above‐ and belowground) decreased from about 320 to 175 Mg dry mass ha^?1, total NPP from ca. 13.0 to 8.2 Mg ha^?1 yr^?1. The belowground/aboveground ratio of biomass and productivity increased with elevation indicating a shift from light to nutrient limitation of tree growth. We propose that, with increasing elevation, an increasing nitrogen limitation combined with decreasing temperatures causes a large reduction in stand leaf area resulting in a substantial reduction of canopy carbon gain toward the alpine tree line. We conclude that the marked decrease in tree height, AGB and ANPP with elevation in these mountain forests is caused by both a belowground shift of C allocation and a reduction in C source strength, while a temperature‐induced reduction in C sink strength (lowered meristematic activity) seems to be of secondary importance.     

Carbon balance of a tropical savanna of northern Australia

Through estimations of above- and below-ground standing biomass, annual biomass increment, fine root production and turnover, litterfall, canopy respiration and total soil CO₂ efflux, a carbon balance on seasonal and yearly time-scales is developed for a Eucalypt open-forest savanna in northern Australia. This carbon balance is compared to estimates of carbon fluxes derived from eddy covariance measurements conducted at the same site. The total carbon (C) stock of the savanna was 204±53 ton C ha^–1, with approximately 84% below-ground and 16% above-ground. Soil organic carbon content (0–1 m) was 151±33 ton C ha^–1, accounting for about 74% of the total carbon content in the ecosystem. Vegetation biomass was 53±20 ton C ha^–1, 39% of which was found in the root component and 61% in above-ground components (trees, shrubs, grasses). Annual gross primary production was 20.8 ton C ha^–1, of which 27% occurred in above-ground components and 73% below-ground components. Net primary production was 11 ton C ha^–1 year^–1, of which 8.0 ton C ha^–1 (73%) was contributed by below-ground net primary production and 3.0 ton C ha^–1 (27%) by above-ground net primary production. Annual soil carbon efflux was 14.3 ton C ha^–1 year^–1. Approximately three-quarters of the carbon flux (above-ground, below-ground and total ecosystem) occur during the 5–6 months of the wet season. This savanna site is a carbon sink during the wet season, but becomes a weak source during the dry season. Annual net ecosystem production was 3.8 ton C ha^–1 year^–1.     

Primary production and nutrient budgets of Sarcocornia perennis ssp. alpini (Lag.) Castroviejo in the salt marsh of the Palmones River estuary (Southern Spain)

Biomass, primary production and nutrient budgets associated to Sarcocornia perennis subspecies (ssp.) alpini were studied in the Palmones River estuary salt marsh (Southern Spain) to evaluate the nutrient sequestration capacity of the low marsh. Above- and belowground living and dead biomass, as well as carbon, nitrogen and phosphorus content were monitored during 1 year. Additionally, the fate of aboveground detritus was evaluated in an experiment on litter decomposition. The detritus production of S. perennis ssp. alpini was almost equivalent to its annual primary production indicating a rapid turnover of biomass. We calculated that only 12% of the aboveground detritus was exported out of the low marsh while the rest was decomposed in the sediment with a rate of 0.8 year⁻¹. Changes in concentrations of total carbon, nitrogen and phosphorus in the sediment showed patterns related to S. perennis ssp. alpini belowground biomass. Our results suggested that the sediment functions as a net sink for nutrients accumulating 550 g C m⁻² year⁻¹, 55 g N m⁻² year⁻¹, and 13 g P m⁻² year⁻¹.     

Forest vegetation in relation to surface water chemistry in the North Branch of the Moose River,Adirondack Park,N.Y.

The Regional Integrated Lake-Watershed Acidification Study (RILWAS) was conducted to identify and to quantify the environmental factors controlling surface water chemistry in forested watersheds of the Adirondack region of New York. The RILWAS vegetation research was designed to: (1) compare the quantitative patterns of forest cover and tree community structure in the study catchments of the Moose River drainage system; and (2) identify important vegetation differences among study watersheds that might help to explain inter-watershed differences in water chemistry and aquatic responses to acidic deposition. Field transect data indicated that the overall drainage system includes 50% mixed forest cover, 38% hardwood forest, 10% coniferous forest, and 2% wetland cover. Major tree species include yellow birch, red spruce, American beech, sugar maple, eastern hemlock, and red maple. Analysis of forest structure indicated that mean weighted basal area estimates ranged two-fold from 24–48 m²ha^–1 among watersheds. Likewise, mean weighted estimates for aboveground biomass and aboveground annual productivity ranged among watersheds from 160 to 320 MT ha^–1 and from 8 to 18 MT ha^–1 yr^–1, respectively. Results showed that differences in surface water chemistry were independent of vegetation differences among watersheds.