Carbon storage in biomass,litter, and soil of different native and introduced fast-growing tree plantations in the South Caspian Sea

Replantation of degraded forest using rapidgrowth trees can play a significant role in global carbon budget by storing large quantities of carbon in live biomass,forest floor,and soil organic matter.We assessed the potential of 20-year old stands of three rapid-growth tree species,including Alnus subcordata,Populus deltoides and Taxodium distichum,for carbon(C) storage at ecosystem level.In September 2013,48 replicate plots(16 m × 16 m) in 8 stands of three plantations were established.36 trees were felled down and fresh biomass of different components was weighed in the field.Biomass equations were fitted using data based on the 36 felled trees.The biomass of understory vegetation and litter were measured by harvesting all the components.The C fraction of understory,litter,and soil were measured.The ecosystem C storage was as follows: A.subcordata(626.5 Mg ha~(-1)) [ P.deltoides(542.9Mg ha~(-1)) [ T.distichum(486.8 Mg ha~(-1))(P \ 0.001),of which78.1–87.4% was in the soil.P.deltoides plantation reached the highest tree biomass(206.6 Mg ha~(-1)),followed by A.subcordata(134.5 Mg ha~(-1)) and T.distichum(123.3 Mg ha~(-1)).The highest soil C was stored in theplantation of A.subcordata(555.5 Mg ha~(-1)).The C storage and sequestration of the plantations after 20 years were considerable(25–30 Mg ha~(-1) year~(-1)) and broadleaves species had higher potential.Native species had a higher soil C storage while the potential of introduced species for live biomass production was higher.     

Effects of afforestation on soil carbon and its fractions: a case study from the Loess Plateau,China

Afforestation has been implemented to reduce soil erosion and improve the environment of the Loess Plateau,China.Although it increased soil organic carbon(SOC),the stability of the increase is unknown.Additionally,the variations of soil inorganic carbon(SIC) following afforestation needs to be reconfirmed.After planting Robinia pseudoacacia,Pinus tabuliformis,and Hippophae rhamnoides on bare land on the Loess Plateau,total soil carbon(TSC) was measured and its two components,SIC and SOC,as well as the light and heavy fractions within SOC under bare lands and woodlands at the soil surface(0–20 cm).The results show that TSC on bare land was 24.5 Mg ha~(-1) and significantly increased to 51.6 Mg ha~(-1) for R.pseudoacacia,47.0 Mg ha~(-1) for P.tabuliformis and 39.9 Mg ha~(-1) for H.rhamnoides.The accumulated total soil carbon under R.pseudoacacia,P.tabuliformis,and H.rhamnoides,the heavy fraction(HFSOC) accounted for 65.2,31.7 and 76.2%,respectively; the light fraction(LF-SOC) accounted for 18.0,52.0 and 4.0%,respectively; SIC occupied 15.6,15.3 and 19.7%,respectively.The accumulation rates of TSC under R.pseudoacacia,P.tabuliformis,and H.rhamnoides reached159.5,112.4 and 102.5 g m~(-2) a~(-1),respectively.The results demonstrate that afforestation on bare land has high potential for soil carbon accumulation on the Loess Plateau.Among the newly sequestrated total soil carbon,the heavy fraction(HF-SOC) with a slow turnover rate accounted for a considerably high percentage,suggesting that significant sequestrated carbon can be stored in soils following afforestation.Furthermore,afforestation induces SIC sequestration.Although its contribution to TSC accumulation was less than SOC,overlooking it may substantially underestimate the capacity of carbon sequestration after afforestation on the Loess Plateau.     

Biomass production,carbon sequestration and nutrient characteristics of 22-year-old support trees in black pepper (<Emphasis Type="Italic">Piper nigrum</Emphasis>. L) production systems in Kerala,India

Diverse kinds of fast growing multipurpose trees are traditionally grown as support trees (standards) for trailing black pepper vines in the humid tropics of India. Apart from differential black pepper yields, such trees exhibit considerable variability to accumulate biomass, carbon and nutrients. An attempt was made to assess the biomass production, carbon sequestration potential (tree + soil) and nutrient stocks of six multipurpose tree species (age: 22 years) used for trailing black pepper vines (Acacia auriculiformis, Artocarpus heterophyllus, Grevillea robusta, Macaranga peltata, Ailanthus triphysa and Casuarina equisetifolia). Results indicate that G. robusta showed the highest total biomass production (365.72 Mg ha^?1), with A. triphysa having the least value (155.13 Mg ha^?1). Biomass allocation among tissue types followed the order stemwood > roots > branchwood > twigs > leaves. Total C stocks were also highest for G. robusta (169 Mg C ha^?1), followed by A. auriculiformis (155 Mg C ha^?1). Mean annual carbon increment also followed a similar trend. Among the various tissue fractions, stemwood accounted for the highest N, P and K stocks, implying the potential for nutrient export from the site through wood harvest. All the support trees showed significantly higher soil carbon content compared to the treeless control. Soil N, P and K contents were higher under A. auriculiformis than other species. Nitrogen fixation potential, successional stage of the species, stand age and tree management practices such as lopping may modify the biomass allocation patterns and system productivity.     

Carbon storage in agroforestry systems in the semi-arid zone of Niayes,Senegal

Agroforestry is an ancient practice widespread throughout Africa. However, the influence of Sahelian agroforestry systems on carbon storage in soil and biomass remains poorly understood. We evaluated the carbon storage potential of three agroforestry systems (fallow, parkland and rangeland) and five tree species (Faidherbia albida, Acacia raddiana, Neocarya macrophylla, Balanites aegyptiaca and Euphorbia balsamifera) growing on three different soils (clay, sandy loam and sandy) in the Niayes zone, Senegal. We calculated tree biomass carbon stocks using allometric equations and measured soil organic carbon (SOC) stocks at four depths (0–20, 20–50, 50–80 and 80–100 cm). F. albida and A. raddiana stored the highest amount of carbon in their biomass. Total biomass carbon stocks were greater in the fallow (40 Mg C ha^?1) than in parkland (36 Mg C ha^?1) and rangeland (29 Mg C ha^?1). More SOC was stored in the clay soil than in the sandy loam and sandy soils. On average across soil texture, SOC stocks were greater in fallow (59 Mg C ha^?1) than in rangeland (30 Mg C ha^?1) and parkland (15 Mg C ha^?1). Overall, the total amount of carbon stored in the soil + plant compartments was the highest in fallow (103 Mg C ha^?1) followed by rangeland (68 Mg C ha^?1) and parkland (52 Mg C ha^?1). We conclude that in the Niayes zones of Senegal, fallow establishment should be encouraged and implemented on degraded lands to increase carbon storage and restore soil fertility.     

Optimal rotation length for carbon sequestration in <Emphasis Type="Italic">Eucalyptus</Emphasis> plantations in subtropical China

Most Eucalyptus plantations are intensively managed as short-rotation plantations and carbon (C) storage in plants and soils in stands older than 10 years is not well understood. We examined the changes in plant biomass C and soil organic C (SOC) storage across a chronosequence of E. urophylla × E. grandis forests (4-, 7-, 10-, 13-, and 21-year-old) in subtropical China. Biomass C stock significantly increased with stand age. SOC storage increased initially after afforestation, peaking in 10-year-old stands, and declined gradually. Ecosystem C pools in the five development stages were 111.76, 167.66, 234.04, 281.00, and 299.29 Mg ha^?1, respectively. Trees and soils were the dominant C pools across all stand ages with the contribution of tree biomass C storage significantly increasing and SOC storage decreasing with age. Eucalyptus plantations are still in vigorous growth phase and have great potential for C sequestration at the end of the current rotation length (within 7 years). Considering the sharp decrease of annual biomass C increment rate and the gradual loss of SOC storage in stands older than 13 years, we recommend the optimal length for one full Eucalyptus plantation cycle should be 12–15 years in subtropical China to maximize land-use value and carbon sink value.     

Quantification of organic carbon and primary nutrients in litter and soil in a foothill forest plantation of eastern Himalaya

The present study was an effort to understand the amount of litter fall and its subsequent decomposition and quantify the release of available nutrients and soil physicochemical characteristics in plantations of four forest tree species(Lagerstroemia parviflora, Tectona grandis, Shorea robusta and Michelia champaca) in the Chilapatta Reserve Forest of the Cooch Behar Wildlife Division in the Terai zone of West Bengal, India. The most litter(5.61 Mg ha~(-1))was produced by T. grandis plantation and the least(4.72 Mg ha~(-1)) by L. parviflora. The material turnover rate to the soil through decomposition from total litter was fastest during the first quarter of the year and subsequently decreased during the next two quarters. The material turnover rate was only 1 year, which indicates that more than90% of the total litter produced decomposed within a year.The available primary nutrient content in litter varied across the four plantations over the year. The plantations generally did not significantly influence the soil physical characteristics but did significantly influence the availability of primary nutrients and organic carbon at two depths(1–15 and16–30 cm) over the year. The availability of soil primary nutrients in the four plantations also increased gradually from the first quarter of the year to the third quarter and then decreased during the last quarter to the same level as in the first quarter of the year at both depths. The availability for soil organic carbon in the plantations followed a similar trend. The amount of litter produced and the material turnover in the soil in the different plantations differed, influencing the nutrient availability and organic carbon at the plantations. The amount of soil organic carbon was highest for T. grandis(2.52 Mg ha~(-1)) and lowest for L. parviflora(2.12 Mg ha~(-1)). Litter is the source of soil organic matter,and more the litter that is produced by the plantations, the higher will be the content and amount of soil organic carbon in the plantation.     

Soil organic carbon stocks and fractions in different orchards of eastern plateau and hill region of India

Soil organic carbon (SOC) plays an important role in soil fertility and productivity. It occurs in soil in labile and non-labile forms that help in maintaining the soil health. An investigation was undertaken to evaluate the dynamics of total soil organic carbon (C _tot), oxidisable organic carbon (C _oc), very labile carbon (C frac ₁), labile carbon (C frac ₂), less labile carbon (C frac ₃), non-labile carbon (C frac ₄), microbial biomass carbon (C _mic) and SOC sequestration in a 6-year-old fruit orchards. The mango, guava and litchi orchards caused an enrichment of C _tot by 17.2, 12.6 and 11 %, respectively, over the control. The mango orchard registered highest significant increase of 20.7, 13.5 and 17.4 % in C frac ₁, C frac ₂ and C frac ₄, respectively, over control. There is greater accumulation of all the C fractions in the surface soil (0–0.30 m). The maximum total active carbon pool was 36.2 Mg C ha^?1 in mango orchard and resulted in 1.2 times higher than control. The passive pool of carbon constituted about 42.4 % of C _tot and registered maximum in the mango orchard. The maximum C _mic was 370 mg C kg^?1 in guava orchard and constituted 4.2 % of C _tot. The carbon management index registered 1.2 (mango orchard)- and 1.13 (guava and litchi orchard)-fold increase over control. The mango orchard registered highest carbon build rate of 1.53 Mg C ha^?1 year^?1 and resulted in 17.3 % carbon build-up over control. Among the carbon fractions, C frac ₁ was highly correlated (r = 0.567**) with C _mic.     

A generalized algebraic difference approach allows an improved estimation of aboveground biomass dynamics of <Emphasis Type="Italic">Cunninghamia lanceolata</Emphasis> and <Emphasis Type="Italic">Castanopsis sclerophylla</Emphasis> forests

Key message

A generalized algebraic difference approach (GADA) developed in this study improved the estimation of aboveground biomass dynamics of Cunninghamia lanceolata (Lamb.) Hook and Castanopsis sclerophylla (Lindl.) Schott forests. This could significantly improve the fieldwork efficiency for dynamic biomass estimation without repeated measurements.

Context

The estimation of biomass growth dynamics and stocks is a fundamental requirement for evaluating both the capability and potential of forest carbon sequestration. However, the biomass dynamics of Cunninghamia lanceolata and Castanopsis sclerophylla using the generalized algebraic difference approach (GADA) model has not been made to date.

Aims

This study aimed to quantify aboveground biomass (AGB, including stem, branch and leaf biomass) dynamics and AGB increment in C. lanceolata and C. sclerophylla forests by combining a GADA for diameter prediction with allometric biomass models.

Methods

A total of 12 plots for a C. lanceolata plantation and 11 plots for a C. sclerophylla forest were selected randomly from a 100 m × 100 m systematic grid placed over the study area. GADA model was developed based on tree ring data for each stand.

Results

GADA models performed well for diameter prediction and successfully predicted AGB dynamics for both stands. The mean AGB of the C. lanceolata stand ranged from 69.4 ± 7.7 Mg ha^?1 in 2010 to 102.5 ± 11.4 Mg ha^?1 in 2013, compared to 136.9 ± 7.0 Mg ha^?1 in 2010 to 154.8 ± 8.0 Mg ha^?1 in 2013 for C. sclerophylla. The stem was the main component of AGB stocks and production. Significantly higher production efficiency (stem production/leaf area index) and AGB increment was observed for C. lancolata compared to C. sclerophylla.

Conclusion

Dynamic GADA models could overcome the limitations posed by within-stand competition and limited biometric data, can be applied to study AGB dynamics and AGB increment, and contribute to improving our understanding of net primary production and carbon sequestration dynamics in forest ecosystems.

     

Improving maize production through nitrogen supply from ten rarely-used organic resources in Ghana

Where there is limited availability of conventional fertilizers, the use of organic materials is considered a viable alternative to increase the productive capacity of soils. Many potential plant residues remain underutilized due to limited research on their use as a nutrient source. In this study, the nitrogen supplying capabilities of ten rarely-used leaf biomass sources (Acacia auriculiformis, Baphia nitida, Albizia zygia, Azadirachta indica, Senna siamea, Senna spectabilis, Tithonia diversifolia, Gliricidia sepium, Leucaena leucocephala and Zea mays) were tested based on their nutrient content, N mineralization patterns and effect on maize yield (in comparison with inorganic fertilizer). N mineralization was studied in the laboratory using an incubation experiment. Field trials were also established using a randomized complete block design. Plant residues were applied at 5 t dry matter ha^?1 a week before planting maize while fertilizer was split-applied at 90 kg N ha^?1 on designated plots. From the results on plant residue chemistry, most of the plant residues recorded relatively high N concentration (≥24.9 g kg^?1) and low C/N ratio (≤20.1) although neither N content nor C/N ratio significantly (p > 0.05) affected their N mineralization patterns. Leaf biomass application of B. nitida, A. auriculiformis, A. zygia and maize stover resulted in an initial net N immobilization that lasted for 14 days. Application of all plant materials significantly increased the biological yield and N uptake of maize with G. sepium and T. diversifolia producing the greatest impact especially in the major rainy season. Relative to the control, total grain yield after four cropping seasons was comparable between inorganic fertilizer (9.2 t ha^?1), G. sepium (8.8 t ha^?1) and T. diversifolia (9.4 t ha^?1) treatments. The results on maize biological yield were significantly correlated with the effects of the treatments on N uptake. The findings suggest that in locations where inorganic fertilizers are limited, leaf biomass from G. sepium and T. diversifolia could offer the most suitable option in comparison with the other species used in this study.     

Long-term response to area of competition control in <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> plantations

Numerous studies have quantified the responses to vegetation management in Eucalyptus plantations but most publications have reported early responses in tree growth and a gap in knowledge exist about the magnitude and duration of growth responses throughout the whole rotation. We evaluated the long-term response (9 years-old) of E. globulus across a gradient of sites to different intensity levels of free area of competing vegetation around individual tree seedlings. Competing vegetation intensity levels considered free areas ranging between 0 (control) to 2.54 m² plus a treatment with total weed control. Competing vegetation biomass production during the first growing season was 2.9, 6.5, 2.2 and 12.9 Mg ha^?1, for sites ranging from low to high annual rainfall. Across sites, maximum response in stand volume ranged between 58 and 262 m³ ha^?1 at age 9 years and was proportional to the amount of competing biomass controlled during the first growing season. Total competing vegetation control showed the largest response in stand volume at sites with 2.9 and 12.9 Mg ha^?1 of competing vegetation. However, the 2.54 m² vegetation control treatment showed the maximum response for sites with 2.2 and 6.5 Mg ha^?1 of competing vegetation. The duration of response for vegetation control treatments ranged between 5 and 9 years. However, at the site with the largest accumulation of competing vegetation biomass the response to vegetation control showed a sustained and divergent response. Our results suggest that vegetation control improved site resources acquisition increasing long-term stand productivity by reducing environmental limitations to tree growth differentially at each site.     

Predictive models for biomass and carbon stocks estimation in Grewia optiva on degraded lands in western Himalaya

Grewia optiva Drummond is one of important agroforestry tree species grown by the farmers in the lower and mid-hills of western Himalaya. Different models viz., monomolicular, logistic, gompetz, allometric, rechards, chapman and linear were fitted to the relationship between total biomass and diameter at breast height (DBH) as independent variable. The adjusted R² values were more than 0.924 for all the seven models implying that all models are apparently equally efficient. Out of the six non-linear models, allometric model (Y = a × DBH ^b ) fulfils the validation criterion to the best possible extent and is thus considered as best performing. Biomass in different tree components was fitted to allometric models using DBH as explanatory variable, the adjusted R² for fitted functions varied from 0.872 to 0.965 for different biomass components. The t values for all the components were found non-significant (p > 0.05), thereby indicating that model is valid. Using the developed model, the estimated total biomass varied from 6.62 Mg ha^?1 in 4 year to 46.64 Mg ha^?1 in 23 year old plantation. MAI in biomass varied from 1.66–2.05 Mg ha^?1 yr^?1. The total biomass carbon stocks varied from 1.99 Mg ha^?1 in 4 year to 15.27 Mg ha^?1 in 23 year old plantation. Rate of carbon sequestration varied from 0.63–0.81 Mg ha^?1 yr^?1. Carbon storage in the soil up to 30 cm soil depth varied from 25.4 to 33.6 Mg ha^?1.     

Similar carbon density of natural and planted forests in the Lüliang Mountains,China

Key message

The carbon density was not different between natural and planted forests, while the biomass carbon density was greater in natural forests than in planted forests. The difference is due primarily to the larger carbon density in the standing trees in natural forests compared to planted forests (at an average age of 50.6 and 15.7 years, respectively).

Context

Afforestation and reforestation programs might have noticeable effect on carbon stock. An integrated assessment of the forest carbon density in mountain regions is vital to evaluate the contribution of planted forests to carbon sequestration.

Aims

We compared the carbon densities and carbon stocks between natural and planted forests in the Lüliang Mountains region where large-scale afforestation and reforestation programs have been implemented. The introduced peashrubs (Caragana spp.), poplars (Populus spp.), black locust (Robinia pseudoacacia), and native Chinese pine (Pinus tabulaeformis) were the four most common species in planted forests. In contrast, the deciduous oaks (Quercus spp.), Asia white birch (Betula platyphylla), wild poplar (Populus davidiana), and Chinese pine (Pinus tabulaeformis) dominated in natural forests.

Methods

Based on the forest inventory data of 3768 sample plots, we estimated the values of carbon densities and carbon stocks of natural and planted forests, and analyzed the spatial patterns of carbon densities and the effects of various factors on carbon densities using semivariogram analysis and nested analysis of variance (nested ANOVA), respectively.

Results

The carbon density was 123.7 and 119.7 Mg ha^?1 for natural and planted forests respectively. Natural and planted forests accounted for 54.8% and 45.2% of the total carbon stock over the whole region, respectively. The biomass carbon density (the above- and belowground biomass plus dead wood and litter biomass carbon density) was greater in natural forests than in planted forests (22.5 versus 13.2 Mg ha^?1). The higher (lower) spatial carbon density variability of natural (planted) forests was featured with a much smaller (larger) range value of 32.7 km (102.0 km) within which a strong (moderate) spatial autocorrelation could be observed. Stand age, stand density, annual mean temperature, and annual precipitation had statistically significant effects on the carbon density of all forests in the region.

Conclusion

No significant difference was detected in the carbon densities between natural and planted forests, and planted forests have made a substantial contribution to the total carbon stock of the region due to the implementation of large-scale afforestation and reforestation programs. The spatial patterns of carbon densities were clearly different between natural and planted forests. Stand age, stand density, temperature, and precipitation were important factors influencing forest carbon density over the mountain region.

     

Biomass allocation in five semi-arid afforestation species is driven mainly by ontogeny rather than resource availability

Key message

The changes in the relative biomass allocation to roots in juvenile stands of fast-growing ( Leucaena leucocephala Lam., Moringa oleifera Lam., and Jatropha curcas L.) and slow-growing ( Anacardium occidentale L. and Parkia biglobosa Jacq.) afforestation species are driven mainly by ontogeny rather than resource availability. However, silvicultural management aiming at increasing availability of water and particularly nutrients enhances biomass production in all species.

Context

Understanding the patterns of biomass allocation among tree species in response to ontogeny and to variation in resource availability is key to the successful restoration of degraded land using forest plantations.

Aims

This study assessed the effects of resource availability and ontogeny on biomass accumulation and partitioning in five semi-arid afforestation species.

Methods

The aboveground and belowground biomass production of fast-growing Leucaena leucocephala Lam., Moringa oleifera Lam., and Jatropha curcas L. and slow-growing Anacardium occidentale L. and Parkia biglobosa Jacq. was monitored following the application of manure (1 kg plant^?1) and/or supplemental irrigation (0.5 L per sapling daily) during the first two rainy seasons and the intervening dry season on degraded cropland in Northern Benin.

Results

Biomass accumulation in the fast-growing species was positively impacted by fertilization and irrigation during both rainy seasons. The slow-growing species responded positively to the silvicultural treatments during the dry and second rainy season. The application of fertilizer alone increased the biomass of P. biglobosa by up to 335% during the dry season. Fifteen months after planting, manure-treated L. leucocephala accumulated the most biomass (2.9 kg tree^?1). The root fraction decreased with increasing tree size in all species. The comparison of root versus shoot allocation in trees of equal size indicated that the treatment-induced shifts in biomass partitioning were controlled by ontogeny, which explained 86–95% of the variation in root-shoot biomass relationships.

Conclusion

While ontogeny was the main driver of biomass partitioning, increased resource availability induced a larger production of biomass, overall leading to greater aboveground production in all species.

     

Stocks and dynamics of soil organic carbon and coarse woody debris in three managed and unmanaged temperate forests

The effect of forest conservation on the organic carbon (C) stock of temperate forest soils is hardly investigated. Coarse woody debris (CWD) represents an important C reservoir in unmanaged forests and potential source of C input to soils. Here, we compared aboveground CWD and soil C stocks at the stand level of three unmanaged and three adjacent managed forests in different geological and climatic regions of Bavaria, Germany. CWD accumulated over 40–100 years and yielded C stocks of 11 Mg C ha^?1 in the unmanaged spruce forest and 23 and 30 Mg C ha^?1 in the two unmanaged beech–oak forests. C stocks of the organic layer were smaller in the beech–oak forests (8 and 19 Mg C ha^?1) and greater in the spruce forest (36 Mg C ha^?1) than the C stock of CWD. Elevated aboveground CWD stocks did not coincide with greater C stocks in the organic layers and the mineral soils of the unmanaged forests. However, radiocarbon signatures of the O _e and O _a horizons differed among unmanaged and managed beech–oak forests. We attributed these differences to partly faster turnover of organic C, stimulated by greater CWD input in the unmanaged forest. Alternatively, the slower turnover of organic C in the managed forests resulted from lower litter quality following thinning or different tree species composition. Radiocarbon signatures of water-extractable dissolved organic carbon (DOC) from the top mineral soils point to CWD as potent DOC source. Our results suggest that 40–100 years of forest protection is too short to generate significant changes in C stocks and radiocarbon signatures of forest soils at the stand level.     

Litterfall,decomposition and nutrient release of <Emphasis Type="Italic">Shorea robusta</Emphasis> and <Emphasis Type="Italic">Tectona grandis</Emphasis> in a sub-tropical forest of West Bengal,Eastern India

We studied leaf litter fall, decomposition and nutrient release patterns of Shorea robusta and Tectona grandis by using a litter bag technique to better understand the release pattern of nutrients to soil from leaf litter. Annual litterfall varied from 13.40 ± 2.56 t ha^?1 a^?1 for S. robusta to 11.03 ± 3.72 t ha^?1 a^?1 for T. grandis and the decay constant (k) of decomposed leaf litter was distinctly higher for T. grandis (2.70 ± 0.50 a^?1) compared to S. robusta (2.41 ± 0.30 a^?1). Biomass loss was positively correlated with the initial litter C, WSC, C/N and ash content in S. robusta and N, P and K concentration for T. grandis. Biomass was negatively correlated with lignin and L/N ratio for S. robusta and L, WSC, L/N and C/N ratio for T. grandis (P < 0.01). Nutrient use efficiency (NUE) and nutrient accumulation index (NAI) of S. robusta was higher than for T. grandis. The retranslocation of bioelements from senescent leaves ranked as P > N > K. Annual N, P and K input to soil through litterfall differed significantly between the two species in the following order: N>K>P. S. robusta was superior in terms of K and P return and T. grandis was superior in terms of N return. The two tree species showed a similar patterns of nutrient release (K > P > N) during decomposition of their leaf litter. Nutrients of N, K and P were the primary limiting nutrients returned to soil through litterfall with important roles in soil fertility and forest productivity.     

Soil carbon stocks in planted woodlots and Ngitili systems in Shinyanga,Tanzania

Our understanding of the processes influencing the storage and dynamics of carbon (C) in soils under semi-arid agroforestry systems in Sub-Saharan Africa (SSA) is limited. This study evaluated soil C pools in woodlot species of Albizia lebbeck (L.) Benth., Leucaena leucocephala (Lam.) de Wit, Melia azedarach (L.), and Gmelina arborea Roxb.; and in farmland and Ngitili, a traditional silvopastoral system in northwestern Tanzania. Soil organic carbon (SOC) was analyzed in the whole soil to 1 m depth and to 0.4 m in macroaggregates (2000–250 μm), microaggregates (250–53 μm), and silt and clay-sized aggregates (<53 μm) to provide information of C dynamics and stabilization in various land uses. Synchrotron-based C K-edge x-ray absorption near-edge structure (XANES) spectroscopy was also used to study the influence of these land use systems on the soil organic matter (SOM) chemistry to understand the mechanisms of soil C changes. Whole soil C stocks in woodlots (43–67 Mg C ha^?1) were similar to those in the reserved Ngitili systems (50–59 Mg C ha^?1), indicating the ability of the planted woodlots on degraded lands to restore SOC levels similar to the natural woodlands. SOC in the woodlots were found to be associated more with the micro and silt-and clay-sized aggregates than with macroaggregates, reflecting higher stability of SOC in the woodlot systems. The continuous addition of litter in the woodlots preserved recalcitrant aromatic C compounds in the silt and clay-sized aggregates as revealed by the XANES C K-edge spectra. Therefore establishment of woodlots in semi-arid regions in Tanzania appear to make significant contributions to the long-term SOC stabilization in soil fractions.     

Developing individual tree-based models for estimating aboveground biomass of five key coniferous species in China

Estimating individual tree biomass is critical to forest carbon accounting and ecosystem service modeling. In this study, we developed one- (tree diameter only) and two-variable (tree diameter and height) biomass equations, biomass conversion factor (BCF) models, and an integrated simultaneous equation system (ISES) to estimate the aboveground biomass for five conifer species in China, i.e., Cunninghamia lanceolata (Lamb.) Hook., Pinus massoniana Lamb., P. yunnanensis Faranch, P. tabulaeformis Carr. and P. elliottii Engelm., based on the field measurement data of aboveground biomass and stem volumes from 1055 destructive sample trees across the country. We found that all three methods, including the one- and two-variable equations, could adequately estimate aboveground biomass with a mean prediction error less than 5%, except for Pinus yunnanensis which yielded an error of about 6%. The BCF method was slightly poorer than the biomass equation and the ISES methods. The average coefficients of determination (R ²) were 0.944, 0.938 and 0.943 and the mean prediction errors were 4.26, 4.49 and 4.29% for the biomass equation method, the BCF method and the ISES method, respectively. The ISES method was the best approach for estimating aboveground biomass, which not only had high accuracy but also could estimate stocking volumes simultaneously that was compatible with aboveground biomass. In addition, we found that it is possible to develop a species-invariant one-variable allometric model for estimating aboveground biomass of all the five coniferous species. The model had an exponent parameter of 7/3 and the intercept parameter a ₀ could be estimated indirectly from stem basic density (a ₀ = 0.294 ρ).     

Response of nitrogen mineralization dynamics and biochemical properties to litter amendments to soils of a poplar plantation

Understanding the impact of plant litters on soil nitrogen(N) dynamics could facilitate development of management strategies that promote plantation ecosystem function.Our objective was to evaluate the effects of different litter types on N mineralization and availability,microbial biomass, and activities of L-asparaginase and odiphenol oxidase(o-DPO) in soils of a poplar(Populus deltoides) plantation through 24 weeks of incubation experiments.The tested litters included foliage(F), branch(B), or root(R) of poplar trees, and understory vegetation(U) or a mixture of F, B, and U(M).Litter amendments led to rapid N immobilization during the first 4 weeks of incubation, while net N mineralization was detected in all tested soils from 6 to 24 weeks of incubation, with zeroorder reaction rate constants(k) ranging from 7.7 to9.6 mg N released kg~(-1) soil wk~(-1).Moreover, litter addition led to increased microbial biomass carbon(C) 49–128% and increased MBC:MBN ratio by 5–92%,strengthened activities of L-asparaginase and o-DPO by14–74%; Up to about 37 kg N ha~(-1) net increase in mineralized N in litter added soils during 24 weeks of incubation suggests that adequate poplar and understory litter management could lead to reduced inputs while facilitate sustainable and economic viable plantation production.     

Stand structure,phenology and litterfall dynamics of a subtropical mangrove <Emphasis Type="Italic">Bruguiera gymnorrhiza</Emphasis>

We evaluated the phenology and litterfall dynamics of the mangrove Bruguiera gymnorrhiza (L.) Lamk along the Okukubi River, Okinawa Island, Japan. Over 3 years, this species showed the highest litterfall of leaves and stipules in summer and the lowest litterfall in winter. From Kendall’s coefficient of concordance, the monthly changes in leaf, stipule, and branch were strongly and significantly concordant among years. Leaf and stipule litterfall could be governed by monthly maximum wind speed, monthly day length, and monthly mean air temperature. Branch litterfall depended on monthly maximum wind speed and monthly rainfall, and increased exponentially with increasing monthly maximum wind speed. Mean total litterfall was 11.8 Mg ha^?1 yr^?1, with the largest component being leaf litterfall (65.8 %). Annual leaf litterfall per plot was almost constant regardless of the tree density of the plot. Mean leaf longevity was 18 months. Flower and mature propagule litterfall might be influenced by monthly mean air temperature, monthly day length and monthly mean air temperature. The average development periods from flower buds to flowers and flower buds to mature propagules were 1 and 8 months, respectively. Except for leaf and branch, all vegetative and reproductive organ litterfall had clear annual cycles. B. gymnorrhiza showed a positive correlation between leaf production and reproductive organ production.     

Carbon sequestration capability of <Emphasis Type="Italic">Fagus sylvatica</Emphasis> forests developing in the Majella National Park (Central Apennines,Italy)

Terrestrial ecosystems represent a major sink for atmospheric carbon (C) and temperate forests play an important role in global C cycling, contributing to lower atmospheric carbon dioxide (CO₂) concentration through photosynthesis. The Intergovernmental Panel of Climate Change highlights that the forestry sector has great potential to decrease atmospheric CO₂ concentration compared to other sectoral mitigation activities. The aim of this study was to evaluate CO₂ sequestration (CO₂S) capability of Fagus sylvatica (beech) growing in the Orfento Valley within Majella National Park (Abruzzo, Italy). We compared F. sylvatica areas subjected to thinning (one high-forest and one coppice) and no-management areas (two high-forests and two coppices). The results show a mean CO₂S of 44.3 ± 2.6 Mg CO₂ ha^?1 a^?1, corresponding to 12.1 ± 0.7 Mg C ha^?1 a^?1 the no-managed areas having a 28% higher value than the managed areas. The results highlight that thinning that allows seed regeneration can support traditional management practices such as civic use in some areas while no management should be carried out in the reserve in order to give priority to the objective of conservation and naturalistic improvement of the forest heritage.