Structure and biomass of larch stands regenerating naturally after clearcut logging

Variations in the succession following cutting of a herbaceousLarix sibirica Ledeb. phytocoenosis along the southern boundary of boreal forests in southern Siberia and in Eastern Hentey, Mongolia, were studied. Morphometric methods were used to determine the dimensional hierarchies of coenopopulation individuals. Structure and productivity of the aboveground components including standing wood, herbaceous cover and litter were studied. The maximum aboveground phytomass was measured as 212.3 Mg ha^?1 (oven dry mass). The highest total aboveground biomass productivity rate of aLarix sibirica phytocoenosis located at its southern limit exceeds 7 Mg ha^?1 per year. The maximum annual phytomass increment was found to be 4.4 Mg ha^?1 for the overstorey trees, 2.1 Mg ha^?1, for the herbaceous layer and 0.7 Mg ha^?1 for forest litter.     

Influence of acid deposition on element cycling in mature sugar maple forest,Algoma, Canada

Forestry studies were undertaken within the Turkey Lakes Watershed to determine the impact of long-range transport of air pollutants on biogeochemical processes in old-growth sugar maple forest on shallow Precambrian-derived till soils in the Algoma District of Ontario, Canada. Distributions of organic matter and macroelements were determined in the tree- and field-layer vegetation, the forest floor and the mineral soil of the study site. Annual tree growth was largely offset by mortality, resulting in a relatively stable standing stock of ca. 245 t ha^?1. Annual aboveground litter production averaged 3.7 t ha^?1 yr^?1, chiefly in the form of deciduous leaf fall. The average pH of the precipitation (4.3) was reduced considerably by contact with the forest canopy. Throughfall was enriched with other elements, principally K and, to a lesser extent, Ca and Mg. The cationic composition of the forest-floor percolates, on the other hand, was dominated primarily by Ca and only to a lesser extent by Mg and K. The stand receives moderate acid deposition, mainly from average inputs of 33–36 kg ha^?1 yr^?1 of SO₄ ^2? and 24–29 kg ha^?1 yr^?1 of NO₃ ^? distributed throughout the year. Atmospheric inputs add to substantial natural NO₃ ^? production, notably within the forest floor and upper mineral soil, and contribute to leaching of bases, principally Ca and Mg, from the rooting zone. Active recycling of elements together with weathering of primary minerals should assist in preserving the base status of the site.     

The effects of burning forest biomass on the yield of plantain (cv. Ebang,Musa spp. AAB,false horn) after hot-water and boiling-water treatment in southern Cameroon

Plantain grown after forest slash-and-burn raises concerns due to the release of CO₂ and the destruction of biodiversity. Plantain yields are presented after forest biomass was burned or retained in combination with sucker sanitation versus traditional planting. Biomass burning did not affect plant crop and total yield. Soil chemical properties were weakly positively affected by burning. Sucker sanitation increased total yield at one site from 6.2 to 9.7 Mg ha^?1 (p = 0.015), without effects on root health. In the second site, sucker sanitation had no effect on fresh bunch yield (mean 8.59 Mg ha^?1), yet significantly improved root health parameters. Thus, at the first site, sucker sanitation elicited a positive response via a mechanism different from nematode control. At the second site, by contrast, nematode control was not the most important factor in yield formation. These data do not support the notion that retaining biomass increases plantain production. Other factors related to labor requirements and later weed infestation are probably more important in farmers' decision making on biomass management.     

Simulation of mixedwood management of aspen and white spruce in northeastern British Columbia

FORECAST, an ecosystem simulation model, was calibrated for aspen (Populus tremuloides Michx) and white spruce (Picea glauca (Moench) Voss) stands using data collected in the Boreal White and Black Spruce biogeoclimatic zone in northeastern British Columbia and published data. Simulations were undertaken to examine the effects of initial density of aspen on yield of white spruce in an aspen and spruce mixedwood stand, and to compare the predicted stemwood biomass yields of aspen, white spruce and mixedwood stands. Results of the simulations suggest that mixedwood management regimes on the same medium quality site should have higher stemwood yield compared to pure white spruce stand. Simulated stemwood biomass yield of pure aspen stands over 240 years on medium site varied from 682.5 Mg ha^?1 to 239.1 Mg ha^?1 for different rotation lengths (30 to 120 years). Repeated rotations of monoculture white spruce produced much less stemwood biomass, simulated yields over 240 years ranging from 877.3 Mg ha^?1to 248.4 Mg ha^?1 for rotation lengths of 60 to 240 years. Simulated aspen and white spruce mixedwood stands produced higher stemwood biomass yields than the pure white spruce stands, but less than the pure aspen stands; from 217.4 Mg ha^?1 to 292.8 Mg ha^?1 over 240 years. Variations in initial densities of aspen did not affect spruce stemwood biomass yield over the simulation period. This model shows potential for comparing the relative effects of different management strategies on harvestable volume and variety of other ecosystem variables. A calibrated version of the model should be useful as both a management simulator and a research tool. However, shortcomings in the representation of the canopy architecture of mixed species stands suggested the need to develop an individual tree version of this ecosystem management model for application to mixed species stands.     

Soil carbon stocks and their primary origin at mature mangrove ecosystems in the estuary of Fukido River,Ishigaki Island,southwestern Japan

ABSTRACT

Mangrove ecosystems play an important role in carbon (C) accumulation in tropical and subtropical regions. Below-ground deep anoxic soil is especially important for C accumulation. However, quantitative data on below-ground soil C stocks in mangrove ecosystems are lacking compared with data on above-ground biomass. In addition, soil C accumulation processes in mangrove ecosystems have not been sufficiently clarified. In this study, we quantified soil C stocks and focused on the mass of fallen litter and below-ground roots, which are produced by tree and that may directly influence soil C stocks in a mature subtropical mangrove in the estuary of Fukido River, Ishigaki Island, southwestern Japan. The principal species in this study site were Bruguiera gymnorhiza and Rhizophora stylosa, and total above-ground biomass at the site was 80.7 ± 1.3 (mean ± SD) Mg C ha^?1 over the period from 2014 to 2016. Litter was collected in six litter traps from May 2013 to November 2016, it ranged from 7.8 to 11.5 Mg C ha^?1, with the major proportion of litter being from foliage (leaves and stipules). The root C density at 90-cm depth was 27.1 ± 11.3 Mg C ha^?1. The soil C stock in the mangrove forest at a depth of 90 cm at the study site was 251.0 ± 34.8 Mg C ha^?1, and it seems to be lower value in the tropical region but it to be higher in subtropical East Asian mangrove sites. Dead roots, especially dead fine roots, but not fallen litter, were significantly positively correlated with soil C stocks. The δ¹³C values obtained from soils ranged from ?29.3‰ to ?27.0‰; these values are consistent with those for below-ground fine roots. These results strongly suggest that dead fine roots could be a main factor controlling soil C stocks at this study site.     

Simulation of forest and wood product carbon budget under a changing climate in Finland

Flows of carbon (C) in the forest ecosystem were simulated with a gap-phase dynamics type model, while flows of C in wood products were simulated using a model that processes raw material into final products. In southern Finland, the ratio between gross production and total storage for the 500 year period was 3052–3572 Mg C ha^?1: 192–223 Mg C ha^?1 under the current climate and 4257–5096 Mg C ha^?1: 260–318 Mg C ha^?1 under the predicted changing climate. In northern Finland, the respective ratios were 1721–2021 Mg C ha^?1: 103–134 Mg C ha^?1 and 3409–4475 Mg C ha^?1: 212–244 Mg C ha^?1. The average total C storage in southern Finland over the 500 year period was 174–181 Mg C ha^?1 under the current climate, and 206–217 Mg C ha^?1 under the changing climate. In northern Finland, average total storage was 101 Mg C ha^?1 under the current climate, and 191–198 Mg C ha^?1 under the changing climate. The average C storages in unmanaged forest ecosystems under the current climate and under changing climate were 200 and 191 Mg C ha^?1 respectively in southern Finland, and 142 and 193 Mg C ha^?1 in northern Finland. Approximately 27–43% of total C was stored in wood products over a 500 year period. Wood products contributed 15–22% of the total emissions to the atmosphere. Over short periods, C sequestration potentials are much greater than over longer periods.     

Potential of mine land reclamation for soil organic carbon sequestration in Ohio

Soils are an effective sink for carbon storage and immobilization through biomass productivity and enhancement of soil organic carbon (SOC) pool. The SOC sink capacity depends on land use and management. Degraded lands lose large amounts of C through SOC decomposition, erosion, and leaching. Thus, restoration of disturbed and degraded mine lands can lead to increase in biomass productivity, improved soil quality and SOC enhancement and sequestration. Reclamation of mined lands is an aggrading process and offers significant potential to sequester C. A chronosequence study consisting of 0‐, 5‐, 10‐, 15‐, 20‐ and 25‐year‐old reclaimed mine soils in Ohio was initiated to assess the rate of C sequestration by pasture and forest establishment. Undisturbed pasture and forest were used as controls. The SOC pool of reclaimed pasture sites increased from 15·3 Mg ha⁻¹ to 44·4 Mg ha⁻¹ for 0–15 cm depth and from 10·8 Mg ha⁻¹ to 18·3 Mg ha⁻¹ for 15–30 cm depth over the period of 25 years. The SOC pool of reclaimed forest sites increased from 12·7 Mg ha⁻¹ to 45·3 Mg ha⁻¹ for 0–15 cm depth and from 9·1 Mg ha⁻¹ to 13·6 Mg ha⁻¹ for 15–30 cm depth over the same time period. The SOC pool of the pasture site stabilized earlier than that of the forest site which had not yet attained equilibrium. The SOC sequestered in 0–30 cm depth over 25 years was 36·7 Mg ha⁻¹ for pasture and 37·1 Mg ha⁻¹ for forest. Copyright © 2000 John Wiley & Sons, Ltd.     

Nutrient balance in Scots pine (Pinus sylvestris L.) forest. 5. Tree growth in a field plot experiment

A field plot experiment on fertilization with N, Mg and P in Scots pine forest was established. The experiment had a factorial design with three levels of N (0, 30 and 90 kg ha^?1), two levels of Mg (0 and 1.5 kg ha^?1) and two levels of P (0 and 5.3 kg ha^?1). The application was done annually. There was a significant growth increase for the two N treatments. During a period of 5-years the mean increase in volume increment was 2.3 and 4.5 m³ ha^?1 for the 30 N and 90 N kg ha^?1 yr^?1 treatments, respectively. This represents a percentage increase in volume increment of 53 and 102% compared to the untreated control plots. No significant growth effect of P and Mg application was detected, either alone or in combination with N. The needle nutrient concentrations have been followed along with the annual measurements. An increase in N-concentration was detected after the first growing season in the N treated trees. After five years the Mg concentrations in the needles are lower in these treatments. The one year old needles have concentrations as low as 0.05% Mg. No visible deficiency symptoms have been observed. The field experiment effects demonstrates that N is still the most limiting nutrient under these conditions and that there is a relative large potential for N accumulation in these forest types without negative effects.     

Soil carbon pools of reclaimed minesoils under grass and forest landuses

Minesoils are characterized by low soil organic matter and poor soil physicochemical environment. Mine soil reclamation process has potential to restore soil fertility and sequester carbon (C) over time. Soil organic C (SOC) pool and associated soil properties were determined for reclaimed minesoils under grass and forest landuses of varied establishment year. Three grassland sites of 30, 9, and 1 years after reclamation (G30, G9, and G1) and two forest sites, 11 years after reclamation (RF) and undisturbed stand of 40 years (UF), were selected within four counties (Morgan, Muskingum, Noble, and Coshocton) of southeastern Ohio. Soil bulk density (BD) of reclaimed forest (RF) soil was significantly higher than undisturbed forest (UF) soils within 10–40 cm soil depth profile. Reclamation process increased soil pH from slightly acidic to alkaline and decreased the soil EC in both landuses. Among grassland soils, significant changes in SOC and total soil N contents were observed within 0–10 cm soil depth. SOC contents of G30 (29.7 Mg ha⁻¹) and G9 (29.5 Mg ha⁻¹) were significantly higher than G1 soils (9.11 Mg ha⁻¹). Soil N content was increased from G1 (0.95 Mg ha⁻¹) to G9 (2.00 Mg ha⁻¹) site and then the highest value was found under G30 (3.25 Mg ha⁻¹) site within 0–10 cm soil depth. UF soils had significantly higher SOC and total N content than RF soils at 0–10 and 10–20 cm soil depths. Copyright © 2009 John Wiley & Sons, Ltd.     

The effect of post-fire stand age on the boreal forest energy balance

Fire in the boreal forest renews forest stands and changes the ecosystem properties. The successional stage of the vegetation determines the radiative budget, energy balance partitioning, evapotranspiration and carbon dioxide flux. Here, we synthesize energy balance measurements from across the western boreal zone of North America as a function of stand age following fire. The data are from 22 sites in Alaska, Saskatchewan and Manitoba collected between 1998 and 2004 for a 150-year forest chronosequence. The summertime albedo immediately after a fire is about 0.05, increasing to about 0.12 for a period of about 30 years and then averaging about 0.08 for mature coniferous forests. A mature deciduous (aspen) forest has a higher summer albedo of about 0.16. Wintertime albedo decreases from a high of 0.7 for 5- to 30-year-old forests to about 0.2 for mature forests (deciduous and coniferous). Summer net radiation normalized to incoming solar radiation is lower in successional forests than in more mature forests by about 10%, except for the first 1–3 years after fire. This reduction in net radiative forcing is about 12–24 W m⁻² as a daily average in summer (July). The summertime daily Bowen ratio exceeds 2 immediately after the fire, decreasing to about 0.5 for 15-year-old forests, with a wide range of 0.3–2 for mature forests depending on the forest type and soil water status. The magnitude of these changes is relatively large and may affect local, regional and perhaps global climates. Although fire has always determined stand renewal in these forests, increased future area burned could further alter the radiation balance and energy partitioning, causing a cooling feedback to counteract possible warming from carbon dioxide released by boreal fires.     

Influence of forest disturbance on CO2, CH4 and N2O fluxes from larch forest soil in the permafrost taiga region of eastern Siberia

Abstract

To evaluate the effect of increasing forest disturbances on greenhouse gas budgets in a taiga forest in eastern Siberia, CO₂, CH₄ and N₂O fluxes from the soils were measured during the growing season in intact, burnt and clear-felled larch forests (4–5 years after the disturbance). Soil temperature and moisture were higher at the two disturbed sites than at the forest site. A 64–72% decrease in the Q ₁₀ value of soil CO₂ flux from the disturbed sites compared with the forest site (5.92) suggested a reduction in root respiration and a dominance of organic matter decomposition at the disturbed sites. However, the cumulative CO₂ emissions (May–August) were not significantly different among the sites (2.81–2.90 Mg C ha^?1 per 3 months). This might be because decreased larch root respiration was compensated for by increased organic matter decomposition resulting from an increase in the temperature and root respiration of invading vegetation at the disturbed sites. The CH₄ uptake (kg C ha^?1 per 4 months [May–September]) at the burnt site was significantly higher (–0.15) than the uptake at the forest (–0.045) and clear-felled sites (0.0027). Although there were no significant differences among the sites, N₂O emission (kg N ha^?1 per 4 months) was slightly lower at the burnt site (0.013) and higher at the clear-felled site (0.068) than at the forest site (0.038). This different influence of burning and tree felling on CH₄ and N₂O fluxes might result from changes in the physical and chemical properties of the soil with respect to forest fire.     

Comparison of two methods to assess the carbon budget of forest biomes in the Former Soviet Union

The sink of CO₂ and the C budget of forest biomes of the Former Soviet Union (FSU) were assessed with two distinct methods: (1) ecosystem/ecoregional, and (2) forest statistical data. The ecosystem/ecoregional method was based on the integration of ecoregions (defined with a GIS analysis of several maps) with soil/vegetation C data bases. The forest statistical approach was based on data on growing stock, annual increment of timber, and FSU yield tables. Applying the ecosystem/ecoregional method, the area of forest biomes in the FSU was estimated at 1426.1 Mha (10⁶ ha); forest ecosystems comprised 799.9 Mha, non-forest ecosystems and arable land comprised 506.1 and 119.9 Mha, respectively. The FSU forested area was 28% of the global area of closed forests. Forest phytomass (i.e., live plant mass), mortmass (i.e., coarse woody debris), total forest plant mass, and net increment in vegetation (NIV) were estimated at 57.9 t C ha^?1, 15.5 t C ha^?1, 73.4 t C ha^?1, and 1.0 t C ha^?1 yr^?1, respectively. The 799.9 Mha area of forest ecosystems calculated in the ecosystem/ecoregional method was close to the 814.2 Mha reported in the FSU forest statistical data. Based on forest statistical data forest phytomass was estimated at 62.7 t C ha^?1, mortmass at 37.6 t C ha^?1; thus the total forest plant mass C pool was 100.3 t C ha^?1. The NIV was estimated at 1.1 t C ha^?1 yr^?1. These estimates compared well with the estimates for phytomass, total forest plant mass, and NIV obtained from the ecosystem/ecoregional method. Mortmass estimated from the forest statistical data method exceeded the estimate based on the ecosystem/ecoregional method by a factor of 2.4. The ecosystem/ecoregional method allowed the estimation of litter, soil organic matter, NPP (net primary productivity), foliage formation, total and stable soil organic matter accumulation, and peat accumulation (13.9 t C ha^?1, 125.0 t C ha^?1, 3.1 t C ha^?1 yr^?1, 1.4 t C ha^?1 yr^?1, 0.11, and 0.056 t C ha^?1 yr^?1, respectively). Based on an average value of NEP (net ecosystem productivity) from the two methods, and following a consideration of anthropogenic influences, FSU forests were estimated to be a net sink of approximately 0.5 Gt C yr^?1 of atmospheric C.     

Dynamics of the dead wood carbon pool in northwestern Russian boreal forests

Our study examines dead wood dynamics in a series of permanent plots established in closed, productive second-growth forest stands of north-west Russia and in temporary plots that represent different successional stages and types of disturbance. Dead wood stores measured on 63 plots 0.2–1.0 ha in size range from 1–8 Mg C ha^?1 in young to mature intensively managed stands, 17 Mg C ha^?1 in an old-growth forest, 20 Mg C ha^?1 on a clear-cut, and 21–39 Mg C ha^?1 following a severe windthrow. A total of 122 logs, snags, and stumps aged by long-term plot records was sampled for decay rates and to develop a system of decay classes. Annual decomposition rates are: 3.3% for pine, 3.4% for spruce, and 4.5% for birch. Based on these decay rates the average residence time of carbon (C) in the dead wood pool is 22–30 years. The mortality input on the permanent plots was 23–60 Mg C ha^?1 over 60 years of observation or 15–50% of the total biomass increment. This data suggests a dead wood mass of 10–22 Mg C ha^?1 would be expected in these mature forests if salvage had not occurred. In old-growth forests, dead wood comprised about 20% of the total wood mass, a proportion quite similar to the larger, more productive forests of the Pacific Northwest (USA). If this proportioning is characteristic of cool conifer forests it would be useful to estimate potential dead wood mass for old-growth forests without dead wood inventories. However, the use of a single live/dead wood ratio across the range of successional stages, a common practice in C budget calculations, may substantially over-or under-estimate the dead wood C pool depending upon the type of disturbance regime. Intensive forest management including short harvest rotations, thinning and wood salvage reduces dead wood C stores to 5–40% of the potential level found in undisturbed old-growth forest. In contrast, natural disturbance increases dead wood C pool by a factor of 2–4.     

Biomass production and N fixation of five Mucuna pruriens varieties and their effect on maize yields in the forest zone of Cameroon

Mucuna has been tested intensively in past years as green manure for intensive maize production in West Africa. However, information is missing about the yield effect of different existing mucuna varieties. Five Mucuna pruriens varieties were grown for 40 weeks followed by sole maize (Zea mays L.) in order to determine differences in biomass production, nitrogen fixation, and effects on maize yield. Mucuna varieties differed in length of growing period, total biomass production (5.9—8.8 Mg ha^—1), seed production (0.65—1.3 Mg ha^—1), nitrogen (N) uptake (147—222 kg ha^—1), N fixation (87—171 kg ha^—1), and the amount of N retained in residues (138—218 kg ha^—1). The grain yield of maize grown immediately after the short mucuna fallow was significantly higher after mucuna vars. jaspaeda (4.60 Mg ha^—1), utilis (3.49 Mg ha^—1), and cochinchinensis (3.44 Mg ha^—1), compared with a non‐fertilized control (1.93 Mg ha^—1) which had a maize crop and vegetation regrowth before. After mucuna vars. ghana and veracruz, 2.90 and 2.65 Mg ha^—1 of maize grain were produced, respectively. No significant correlation between mucuna biomass and its N uptake and maize grain yield was found, whereas maize stover yield showed a significant positive correlation. Application of 30, 60, and 90 kg ha^—1 N as <?tw=98%>urea on sub‐plots of the control yielded 2.20, 3.19, and 3.46 Mg ha^—1 <?tw>of maize grain in the first year. Only the difference between 0 and 90 kg ha^—1 N was significant. Fertilizer N equivalent values for mucuna varieties ranged from 41 to 148 kg ha^—1. The yield advantage of vars. jaspaeda, utilis, and cochinchinensis versus the control without N fertilizer application was confirmed in the following year, with no significant difference in maize grain yield between mucuna and the control with N fertilizer application.<?show $6#>     

Nitrogen Fixation,Soil Nitrogen Availability,and Biomass in Pure and Mixed Plantations of Alder and Pine in Central Korea

ABSTRACT

Rates of nitrogen (N) fixation, soil N availability, and aboveground biomass were measured in 27-year-old pure and mixed Alnus hirsuta and Pinus koraiensis plantations in central Korea. Nodule biomass and N fixation were 179.3 kg ha^{? 1} and 46.6 kg ha^{? 1}yr^{? 1} for the pure A. hirsuta plantation (PA) and 95.2 kg ha^{? 1} and 41.1 kg ha^{? 1}yr^{? 1} for the mixed A. hirsuta + P. koraiensis plantation (MAP), respectively. A. hirsuta seemed to provide more than two thirds of annual N requirement for P. koraiensis.Rates of acetylene reduction were significantly related to soil temperature (R² = 0.51, P < 0.001), but not to soil moisture content. Total inorganic N [ammonium (NH₄ ⁺)plus nitrate (NO₃ ^?)] availability measured using ion exchange bags were significantly higher under PA (27.91 μ g-N bag^{? 1}) and MAP (31.34 μ g-N bag^{? 1}) than under the pure P. koraiensis plantation (PP) (14.31 μ g-N bag^{? 1}). Especially soils under the influence of A. hirsuta showed at least 2 fold increase in resin total inorganic N concentrations. Total aboveground biomass (Mg ha^{? 1}) was 147.3 for PA, 145.8 for MAP, and 174.8 for PP, respectively, and was not significantly different among plantations. A. hirsuta significantly increased soil N availability; however, the influence of N fixation on aboveground biomass was not significant for the study plantations.     

The impact of cultivation on carbon fluxes in woody savannas of Southern Africa

The rapid transition from miombo woodland and savanna to maize-based agriculture in Southern Africa results in a near universal loss of total system and biomass carbon. Forests and savannas occupy approximately 3.1 million km² in southern Africa. Two natural ecosystems, a miombo woodland (Zimbabwe) and a broadleafed dry savanna (South Africa), contained 48 and 94 Mg C ha^?1, respectively. Clearing of the miombo and establishment of maize-based agriculture on a sandy Alfisol resulted in a decline in total soil organic carbon from 28 to as little as 9 Mg ha^?1. This decline is not related to the annual aboveground productivities which, in many cases is greater in the cropping system than in the savanna or forest. Severe declines in total soil organic matter resulting from shifting cultivation were also observed in coastal Mozambique. The CENTURY plant/soil simulation model was used to simulate long-term carbon dynamics a miombo woodland and maize-based cropping system in Marondera, Zimbabwe. The miombo woodland continues to accumulate total system C but shifting cultivation and commercial cultivation of maize result in annual carbon losses of 0.15 and 0.14 Mg ha^?1 yr^?1. Increases in temperature (2° C) accompanied by 25% increases in photosynthetic efficiency did not effect the decline in total system carbon, however, improved organic matter management within the agroecosystem reduced the losses in total system carbon within the agroecosystem by 57% under the climate change scenario.     

Pedotransfer function to predict density of forest soils in Switzerland

Soil density is an important soil property, but respective measurements are usually scarce. With data from 559 mineral soil horizons (134 sites) we developed a linear regression pedotransfer function (PTF) for the density of forest soils (sieved to ≤ 2 mm). The field estimate of density was the most important covariate. RMSE of 0.205 Mg m^?3 and R² of 0.67, calculated on independent data (131 horizons), were better than the statistics obtained by published, recalibrated PTF (RMSE 0.271–0.324 Mg m^?3; R² 0.28–0.42).     

A simulation model of the water uptake of a beech forest: testing variations in root biomass and distribution

A validated mathematical model was used to simulate the effects of roots biomass and distribution on the water uptake of a 120-year old beech (Fagus silvatica L.) stand located at Solling (West Germany). The modell was based on the soil-water movement equation including an extraction term to account for the water uptake of the root system. This extraction term varies with the meteorological conditions, root density and soil water potential. Root biomass values considered were: 500 kg. ha^?-1, 1000 kg. ha^?-1, 2000 kg. ha^?-1, 4000kg. ha^?-1 and 6000 kg. ha^?-1. For each of these values, five different distributions were tested. These ranged between a soil profile 0.40m deep with high root concentration to a 1.00m soil profile with idealized uniform root distribution. The model was run under two different rainfall conditions: i) an uncommon dry year (1971), (ii) a hypothetical normal year without a dry period. The model showed the fundamental importance of the root distribution under the given meteorological conditions. This was more evident when the root biomass was low and medium. A good root distribution throughout the profile allowed the forest to overcome long dry periods. With the maximum root biomass value the distribution had no effect on the forest water uptake.     

Coniferous afforestation increases soil carbon in maritime sand dunes

Afforestation of grasslands can increase C sequestration and provide additional economic and environmental benefits. Pine plantations, however, have often been found to deplete soil organic C and trigger detrimental effects on soils. We examined soil characteristics under a 45-year-old Pinus radiata stand and under adjacent grassland on maritime dunes in temperate Argentina. Soil under the pine plantation had greater soil organic C (+93%), total N (+55%) and available P (+100%) concentrations than under grassland. Carbon was stored under the pinestand at an estimated mean accretion rate of 0.64 Mg ha^?1 y^?1. At 0- to 25-cm depth, soil C amounted to 61 Mg ha^?1 under pine and 27 Mg ha^?1 under grassland. Soil C accumulated more on dune slopes (35 Mg ha^?1 y^?1) than on ridges(29 Mg ha^?1 y^?1) and bottoms (12 Mg ha^?1 y^?1). Compared with the grassland, soil acidity, cation-exchange capacity, base losses (K > Ca = Mg) and C/N ratio increased under pine. Spatial heterogeneity in soil characteristics was greater under pine than under grassland. Such variability was non-systematic and did not support the ‘single-tree influence circle’ concept. Afforestation increased C in soil, forest floor and tree biomass in dunes with ustic climate regime.     

Multiple measurements constrain estimates of net carbon exchange by a Eucalyptus forest

Net ecosystem exchange of carbon (F_NEE) was estimated for a temperate broadleaf, evergreen eucalypt forest ecosystem at Tumbarumba in south-eastern Australia to investigate the processes controlling forest carbon sinks and their response to climate. Measurements at a range of temporal and spatial scales were used to make three different estimates of F_NEE based on: (1) the difference between fluxes of carbon input by photosynthesis and output by autotrophic plus heterotrophic respiration, (2) changes over time in the carbon pools in the above- and below-ground biomass, soil and litter, and (3) micrometeorological flux measurements that provide a continuous estimate of the net exchange. A rigorous comparison of aggregated component fluxes and the net eddy fluxes within a flux tower source area was achieved based on an inventory of the site and a detailed sampling strategy. Measurements replicated in space and time provided mean values, confidence limits and patterns of variation of carbon pools and fluxes that allowed comparisons within known limits of uncertainty. As a result of comparisons between nighttime eddy flux and chamber measurements of respiration, a revised micrometeorological method was developed for estimating nighttime carbon flux using flux tower measurements. Uncertainty in the final estimate of F_NEE was reduced through mutual constraints of each of these measurement approaches. F_NEE for the period October 2001–September 2002, with average rainfall, was an uptake of 6.7 (5.1–8.3) tC ha^?1 yr^?1 estimated from component fluxes, and 5.4 (3.0–7.5) tC ha^?1 yr^?1 estimated from the revised eddy flux method. Biomass increment was 4.5 (3.7–5.4) tC ha^?1 yr^?1 and the remaining 0.9–2.2 tC ha^?1 yr^?1 could represent a carbon sink in the soil and litter pools or lie within the confidence limits of the measured fluxes. F_NEE was reduced to ?0.1 to 2.4 tC ha^?1 yr^?1 during a period of drought and insect disturbance in October 2002–September 2003, with biomass increment being the main component reduced. The forest is a large carbon sink compared with other forest ecosystems, but this is subject to high-annual variability in response to climate variability and disturbance.