Soil organic carbon stock in the Belgian Ardennes as affected by afforestation and deforestation from 1868 to 2005

The effects of historical land use changes on the global C cycle have mainly been studied by means of bookkeeping models. Here, we investigate with such models the impact of afforestation and deforestation on soil organic carbon (SOC) stocks. This approach, using field-based estimates of the response of SOC upon land use changes, is applied to a pilot area in the Belgian Ardennes over one and a half century (1868–2005). After a small initial decline during the 1868–1888 period due to deforestation for agricultural use, mean SOC stocks increased steadily up to 1990, due essentially to the conversion of deciduous to coniferous forests (in the study area, deciduous forests stored less SOC than coniferous) and the reclamation of heathland, which occurred both at the turn of the 19th and 20th centuries. Simulations showed that SOC stocks decreased recently (1990–2005) because of the slow down of sequestration in coniferous forests and a reversion of some of the coniferous plantations to deciduous forests. Over the entire period, afforestation resulted in a net sequestration of carbon (0.16 t C ha⁻¹ year⁻¹). Monte Carlo simulations demonstrated that the model was highly sensitive to its inputs (initial SOC stocks for each land use) both in term of predicted SOC stocks and rates of SOC stocks change. However, the sensitivity of the model was not large enough to revert the main trends of SOC changes observed. Compared to the amount of carbon sequestered in the biomass, the contribution of soils to the C sink in forest is small. Despite several sources of errors, a detailed reconstruction of land use changes combined with realistic SOC response curves upon land use conversion are required to be able to quantify the contribution of soils to terrestrial carbon fluxes.     

Long term effects of fire on ectomycorrhizas and soil properties in Nothofagus pumilio forests in Argentina

The forests of Nothofagus pumilio have historically been affected by forest fires. The effects of fire on certain above and belowground, biotic and abiotic components of these ecosystems have been previously documented, albeit belowground components have received much less attention. It has been suggested that the effects observed in the short-term after a fire usually differ from the longer-term effects. The long-term effects of fire (i.e. >5 years after burning) on belowground components in Nothofagus forests are currently unknown. In the present study we evaluated the long-term effect of fire on ectomycorrhiza (ECM) colonization and morphotype composition in N. pumilio roots, as well as soil chemical properties in temperate forests in Patagonia. Sampling was conducted in three mature monospecific forests. In each, nearby burned and unburned sites were selected. The time since the occurrence of fires differed between areas (i.e. 6-10 years). Within each site, 3 transects of 40 m were established randomly along which 5 samples of roots and soil were collected in spring and autumn. The main results were: (1) in comparison with the unburned site, ECM colonization was lower in the burned site in the area with the shorter time length since fire occurrence and no effects in the other two areas were observed; (2) richness and diversity were not significantly affected by fire but there was a significant effect of season for both parameters, being higher in spring; (3) ECM dominance was significantly higher in the unburned than in the burned site in Tronador, while in Challhuaco the opposite was observed, mainly in autumn; (4) in general carbon, nitrogen and phosphorous decreased while pH increased in the burned sites; (5) ECM colonization positively correlated with NH⁴⁺ and phosphorus and negatively with pH but was not significantly correlated with organic matter or any other soil variable. Altogether the results suggest that effects of fire on ectomycorrhiza and soil properties in N. pumilio forests are probably related to the time elapsed since fire occurrence combined with site characteristics. In addition, the direct and indirect effects of fire in these forest systems may persist for more than 10 years.     

不同土地利用方式对土壤有机碳、氮含量的影响

土壤有机C、N的定量动态变化是评价不同土地利用方式对土壤质量影响的重要内容。本文比较了研究地区种植黑麦草(Lolium multiflorum Lam．)、百喜草(Paspalum notatum Flugge．)、桔树(Citrus reticulata Blanco．)和马尾松(Pinus Massoniana Lamb．)的四种土地利用方式对植物生物量和土壤有机C、N多年变化的影响。试验初期，四种土地利用方式的植物生物量几乎处于同一水平。经过10年长期试验后，黑麦草和百喜草的累计生物量分别是桔树的3．68和3．75倍，马尾松的2．06和2．14倍。地下部生物量的差异更为明显，黑麦草和百喜草两种草类地下部累计生物量都较桔树和马尾松高10倍之多。这表明草类较之乔木更有利于提高土壤有机C、N的含量。土壤有机C、N的含量变化主要发生在0．40cm土层。统计计算表明，10年期问，种植黑麦草和百喜草可使土壤有机C、N贮量每公顷分别约增加1．5吨和0．2吨，而种植桔树使土壤有机C、N贮量每公顷分别约减少1．2吨和0．02吨，种植马尾松使土壤有机C、N贮量每公顷分别约减少0．4吨和0．04吨。表4参10。     

The influence of land-use change on the organic carbon distribution and microbial respiration in a volcanic soil of the Chilean Patagonia

Land-use changes can modify soil carbon contents. Depending on the rate of soil organic matter (SOM) formation and decomposition, soil-vegetation systems can be a source or sink of CO₂. The objective of this study was to determine the influence of land-use change on SOM distribution, and microbial biomass and respiration in an Andisol of the Chilean Patagonia. Treatments consisted of degraded natural prairie (DNP), thinned and pruned Pinus ponderosa plantations (PPP), and unmanaged second-growth Nothofagus pumilio forest (NPF). The soil was classified as medial, amorphic, mesic Typic Hapludands. Soil microbial respiration and microbial biomass were determined in the laboratory from soil samples taken at 0–5, 5–10, 10–20 and 20–40 cm depths obtained from three pits excavated in each treatment. Physical fractionation of SOM was performed in soil of the upper 40 cm of each treatment to obtain the three following aggregate-size classes: macroaggregates (>212 μm), mesoaggregates (212–53 μm) and microaggregates (<53 μm). Plant C content was 68% higher in PPP than in DNP and 635% higher in NPF than in PPP. Total soil and vegetation C content in both DNP and PPP were less than half of that in NPF. Total SOC at 0–10 cm depth decreased in the order DNP (7.82%) > NPF (6.16%) > PPP (4.41%), showing that land-use practices affected significantly (P < 0.01) SOC stocks. In all treatments, microbial biomass C and respiration were significantly higher (P < 0.05) in the upper 5 cm. Soil microbial respiration was also correlated positively with microbial biomass C and SOC. The different land uses affect the formation of organic matter, SOC and microbial biomass C, which in turn will affect soil microbial respiration. Conversion of DNP to PPP resulted in a 44% decrease of SOC stocks in 0–10 cm mineral soil. The largest amount of SOC was stabilized within the mesoaggregate fraction of the less disturbed system, NPF, followed by PPP. In the long term, formation of stable mesoaggregates in soils protected from erosion can behave as C sinks.     

岷江上游不同森林类型土壤有机碳含量及密度特征

本文研究了岷江上游云杉人工林、紫果冷杉人工林、岷江冷杉人工幼龄林、高山栎天然次生林4种森林类型土壤有机碳含量及密度。结果表明:4种森林类型不同土层有机碳含量和有机碳密度均差异显著,都随土层深度增加而逐渐减小,且土壤有机碳集中分布在表层土(0~20 cm)中;4种森林类型土壤有机碳含量从高到低排序为:云杉人工林(5.896 g.kg-1)紫果冷杉人工林(5.479 g.kg-1)高山栎天然次生林(5.019 g.kg-1)岷江冷杉人工幼龄林(2.245 g.kg-1);土壤有机碳密度从高到低为:云杉人工林(0.03541 kg.m-2)高山栎天然次生林(0.03134 kg.m-2)紫果冷杉人工林(0.02474 kg.m-2)岷江冷杉人工幼龄林(0.01573 kg.m-2)。说明林分起源、树种组成、植物根系、地表枯落物和人类活动等因素影响着土壤有机碳含量及碳密度。     

Soil organic carbon and aggregation under poplar based agroforestry system in relation to tree age and soil type

The poplar based agroforestry system improves aggregation of soil through huge amounts of organic matter in the form of leaf biomass. The extent of improvement may be affected by the age of the poplar trees and the soil type. The surface and subsurface soil samples from agroforestry and adjoining non-agroforestry sites with different years of poplar plantation (1, 3 and 6 years) and varying soil textures (loamy sand and sandy clay) were analyzed for soil organic carbon, its sequestration and aggregate size distribution. The average soil organic carbon increased from 0.36 in sole crop to 0.66% in agroforestry soils. The increase was higher in loamy sand than sandy clay. The soil organic carbon increased with increase in tree age. The soils under agroforestry had 2.9–4.8 Mg ha⁻¹ higher soil organic carbon than in sole crop. The poplar trees could sequester higher soil organic carbon in 0–30 cm profile during the first year of their plantation (6.07 Mg ha⁻¹ year⁻¹) than the subsequent years (1.95–2.63 Mg ha⁻¹ year⁻¹). The sandy clay could sequester higher carbon (2.85 Mg ha⁻¹ year⁻¹) than in loamy sand (2.32 Mg ha⁻¹ year⁻¹). The mean weight diameter (MWD) of soil aggregates increased by 3.2, 7.3 and 13.3 times in soils with 1, 3 and 6 years plantation, respectively from that in sole crop. The increase in MWD with agroforestry was higher in loamy sand than sandy clay soil. The water stable aggregates (WSA >0.25 mm) increased by 14.4, 32.6 and 56.9 times in soils with 1, 3 and 6 years plantation, respectively, from that in sole crop. The WSA >0.25 mm were 6.02 times higher in loamy sand and 2.2 times in sandy clay than in sole crop soils.     

Biomass and carbon sequestration of ponderosa pine plantations and native cypress forests in northwest Patagonia

Fast growth tree plantations and secondary forests are considered highly efficient carbon sinks. In northwest Patagonia, more than 2 million ha of rangelands are suitable for forestry, and tree plantation or native forest restoration could largely contribute to climate change mitigation. The commonest baseline is the heavily grazed gramineous steppe of Festuca pallescens (St. Yves) Parodi. To assess the carbon sequestration potential of ponderosa pine (Pinus ponderosa (Dougl.) Laws) plantations and native cypress (Austrocedrus chilensis (Don) Flor. et Boutl.), individual above and below ground biomass models were developed, and scaled to stand level in forests between 600 and 1500 annual rainfall. To calculate the carbon sequestration baseline, the pasture biomass was simulated. Also, soil carbon at two depths was assessed in paired pine-cypress-pasture sample plots, the same as the litter carbon content of both forest types. Individual stem, foliage, branch and root log linear equations adjusted for pine and cypress trees presented similar slopes (P>0.05), although some differed in the elevations. Biomass carbon was 52.3 Mg ha⁻¹ (S.D.=30.6) for pine stands and 73.2 Mg ha⁻¹ (S.D.=95.4) for cypress forests, given stand volumes of 148.1 and 168.4 m³ ha⁻¹, respectively. Soil carbon (litter included) was 86.3 Mg ha⁻¹ (S.D.=46.5) for pine stands and 116.5 Mg ha⁻¹ (S.D.=38.5) for cypress. Root/shoot ratio was 19.5 and 11.4%, respectively. The low r/s value for cypress may account for differences in nutrient cycling and water uptake potential. At stand level, differences in foliage, taproot and soil carbon compartments were highly significative (P<0.01) between both forest types. In pine stands, both biomass and soil carbon were highly explained by the rainfall gradient (r²=0.94). Nevertheless, such a relationship was not found for cypress, possibly due to stand and soil disturbances in sample plots. The carbon baseline estimated in pasture biomass, including litter, was 2.6 Mg ha⁻¹ (S.D.=0.8). Since no differences in soil carbon were found between pasture and both forest types, additionality should be accounted only by biomass. However, the replacement of pasture by pine plantations may decrease the soil carbon storage, at least during the first years. On the other hand, the soil may be a more relevant compartment of sequestered carbon in cypress forests, and if pine plantation replaces cypress forests, soil carbon losses could cause a negative balance.     

柳杉人工林皆伐后初期土壤有机碳和微生物量碳动态

本文研究了华西雨屏区柳杉人工林皆伐后1年内土壤有机碳和微生物量碳动态。结果表明:柳杉人工林皆伐林地土壤平均有机碳含量比对照(未皆伐林地)减小2.01 gC.kg-1,但差异不显著,而土壤平均有机碳储量及微生物量碳分别比对照减少20.97 tC.hm-2、6.68 mg.kg-1(P0.05);皆伐林地土壤有机碳含量及微生物量碳均随季节的变化而逐渐降低,但有机碳储量随季节的变化无明显减少趋势;皆伐林地土壤四季的有机碳含量、碳储量和微生物量碳差异不显著。皆伐对柳杉人工林土壤有机碳储量的影响主要表现在0~20 cm土层(P0.05);皆伐林地和对照在0~40 cm土层的微生物量碳和有机碳含量都表现出显著相关性(P0.05),但对照的相关性高于皆伐林地。总之,柳杉人工林转变为采伐迹地后,其初期土壤有机碳储量和微生物量碳都明显减少。     

The decline of Austrocedrus chilensis forests in Patagonia, Argentina: soil features as predisposing factors

The forests of Austrocedrus chilensis in southern Argentina suffer mortality from “mal del ciprés”, whose causes remain unknown. The purpose of this work was to establish the relation of soil features with the occurrence of the disease. In Río Grande Valley, Chubut Province, Argentina, 14 areas with “mal del ciprés” were selected for study. The spatial pattern of the decline varied among the different areas and was classified as aggregated and disaggregated. In each area, symptomatic and asymptomatic plots were established and characterized by 11 edaphic and topographic variables. Three forest areas where the disease was totally absent were also included. Site features were related to the occurrence of the decline using principal component analysis and cluster analysis. Results indicated that soil properties related to poor internal drainage, such as the proximity to water streams, non-allophanized soils of fine textures, and redoximorphic features, act as predisposing factors to the development of “mal del ciprés”. Poor soil drainage was strongly associated not only with the occurrence of the disease, but also with its spatial pattern. Symptomatic and asymptomatic plots presented similar edaphic features in areas with a disaggregated distribution of the decline and were grouped together in the multivariate analysis. This result suggests that large areas with such a pattern are prone to develop the decline.     

青冈栎次生林土壤活性有机碳对间伐强度的响应

目的 探索不同间伐强度对青冈栎次生林土壤活性有机碳的响应。 方法 以湖南省天心阁林场青冈栎次生林为研究对象,于2018年设置4种间伐强度（对照：0%;弱度间伐：15%;中度间伐：30%;强度间伐：50%）,探讨不同间伐强度下4种土壤活性有机碳（土壤微生物量碳、可溶性有机碳、颗粒有机碳和易氧化有机碳）含量变化及其在总有机碳中的分配比例。 结果 （1）与对照样地相比,中度间伐和强度间伐显著提高了土壤总有机碳含量,弱度间伐降低了土壤总有机碳含量;（2）间伐提高了土壤微生物量碳的含量,降低了可溶性有机碳的含量,土壤颗粒有机碳和易氧化有机碳含量在不同间伐处理下的变化趋势与总有机碳一致;（3）不同间伐强度下土壤微生物量碳、可溶性有机碳、颗粒有机碳和易氧化有机碳的分配比例分别为：0.23%～0.54%、0.40%～0.78%、16.54%～47.30%和6.46%～14.29%,强度间伐显著提高了微生物量碳、颗粒有机碳和易氧化有机碳分配比例,降低了可溶性有机碳的分配比例,表明间伐提高了不稳定碳的比例,且颗粒有机碳对间伐处理更敏感;（4）相关性分析表明,土壤总有机碳与各活性有机碳组分间呈极显著正相关,且活性有机碳与土壤含水量和总氮含量呈正相关;土壤活性组分碳间转化依赖于总有机碳量的变化,且在一定的水分和氮素条件下易发生分解转变。 结论 不同间伐处理对土壤有机碳及其活性组分的含量有显著影响,强度间伐显著提高土壤有机碳及其活性组分的含量,加快土壤中的碳素循环。     

Soil characteristics below <Emphasis Type="Italic">Erythrina poeppigiana</Emphasis> in organic and conventional Costa Rican coffee plantations

The impact of Erythrina poeppigiana on soil characteristics, at three different positions relative to the shade tree and from three different soil depths, was evaluated in pairs of comparable Costa Rican coffee farms (organic and conventional) in 2000 and 2004. In the conventional system at 0–5 cm, higher C and N concentrations were found close to the shade tree versus the positions 2 m from the trunk (5.04 vs. 4.18%). This positive effect could influence only 20% of the farm area when high population of E. poeppigiana were used. This finding highlighted the importance of E. poeppigiana in maintaining SOM levels. In contrast, the organic system showed similar C and N concentrations for all positions probably due to an even distribution of pruning residues and to the use of organic amendments. A trend to higher total C and N concentrations for organic farms in comparison to conventional farms was found. No significant temporal changes in soil C or N concentrations were found between 2000 and 2004.     

Changes in soil P chemistry as affected by conversion of natural secondary forests to larch plantations

To assess the impact of conversion of native forests to monocultural larch plantations on soil chemical properties, we compared the total and various fractions of soil phosphorus (P) and acid phosphatase activity (APA) between natural secondary forests (NSF) and Larix olgensis plantations (LOP) on a montane forest site in eastern Liaoning Province, Northeast China. We found that the concentrations of total P (TP), inorganic P, and iron-bound P (Fe-P) were significantly higher, and the concentrations of microbial biomass P (MBP), sodium bicarbonate-extractable organic P (NaHCO₃-Po), and APA were significantly lower, in the LOP stands than in the NSF stands; whilst organic P, sodium bicarbonate-extractable inorganic P (NaHCO₃-Pi), aluminum-bound P (Al-P) and calcium-bound P (Ca-P) were comparable between the two forest types. Our study also showed that the ratios of MBP/TP, NaHCO₃-Pi/TP, NaHCO₃-Po/TP, and APA significantly varied with time during the growing season. Moreover, the concentrations of NaHCO₃-Pi, NaHCO₃-Po, and MBP had significant (P < 0.01) and positive linear relationships with APA. Overall, results from this study suggest that conversion of native forests to larch plantations in the region is more likely to cause compositional change in soil P than to result in reduction in overall P availability.     

Carbon sequestration by forests and soils on mined land in the Midwestern and Appalachian coalfields of the U.S.

Carbon (C) accreditation of forest development projects is one approach for sequestering atmospheric CO₂, under the provisions of the Kyoto protocol. The C sequestration potential of reforested mined land is not well known. The purpose of this work was to estimate and compare the ecosystem C content in forests established on surface, coal-mined and non-mined land. We used existing tree, litter, and soil C data for fourteen mined and eight adjacent, non-mined forests in the Midwestern and Appalachian coalfields to determine the C sequestration potential of mined land reclaimed prior to the passage of the Surface Mining Control and Reclamation Act (1977). We developed statistically significant and biologically reasonable models for ecosystem C across the spectrum of site quality and stand age. On average, the highest amount of ecosystem C on mined land was sequestered in pine stands (148 Mg ha⁻¹), followed by hardwood (130 Mg ha⁻¹) and mixed stands (118 Mg ha⁻¹). Non-mined hardwood stands sequestered 210 Mg C ha⁻¹, which was about 62% higher than the average of all mined stands. Our mined land response surface models of C sequestration as a function of site quality and age explained 59, 39, and 36% of the variation of ecosystem C in mixed, pine, and hardwood stands, respectively. In pine and mixed stands, ecosystem C increased exponentially with the increase of site quality, but decreased with age. In mined hardwood stands, ecosystem C increased asymptotically with age, but it was not affected by site quality. At rotation age (60 yr), ecosystem C in mined hardwood stands was less on high quality sites, but similar for low quality sites compared to non-mined hardwood stands. The overall results indicated that the higher the original forest site quality, the less likely C sequestration potential was restored, and the greater the disparity between pre- and post-mining C sequestration stocks.     

凋落物和铵态氮添加对亚热带罗浮栲和杉木林土壤碳氮淋溶的影响

目的 凋落物是森林土壤碳氮的主要来源,通过分析凋落物或土壤淋溶碳氮的变化,揭示凋落物分解通过淋溶对土壤碳氮的影响及氮添加情况下这种影响的变化,进而探究凋落物分解与土壤碳氮的关系。 方法 以亚热带天然阔叶林和人工针叶林土壤和凋落物为对象,设置6种处理：凋落物、土壤、凋落物 + 土壤、凋落物 + 氮、土壤 + 氮和凋落物 + 土壤 + 氮,每个处理3重复。氮添加量（NH4 + -N/土壤）为120 mg·kg−1 ,针、阔叶林凋落物添加量分别为12.1、19.7 g·kg−1,凋落物放置在土壤或石英石表面,土壤湿度控制在60%饱和持水量,于25 ℃暗培养箱中,采用氮淋溶模拟氮沉降的方法,进行室内培养试验。培养期间,氮溶液分5次不等氮量淋溶,每次110 mL溶液（按照淋溶次数分配依次为80、10、10、10、10 mg NH4 + -N）,收集淋溶液,测定其溶解性有机碳（DOC）、氮（DON）和无机氮。 结果 凋落物淋溶液有较低的无机氮和DON,较高的DOC;凋落物添加分别降低针阔叶土壤淋溶液中NO3−-N 22.6%和29.9%、提高针叶林土壤淋溶液中DOC 181.4%,但是降低阔叶林土壤淋溶液中DON 39.2%和阔叶林土壤MBN 53.2%。氮添加后,凋落物对添加氮的截留较少,且阔叶林凋落物截留高于针叶林;凋落物通过淋溶输入土壤的DOC减少,而DON增加。氮添加增加土壤可淋溶的无机氮量和针叶林土壤淋溶液DON,但凋落物降低土壤氮淋溶的作用在氮添加情况下没有减弱。 结论 凋落物具有减缓土壤NO3−-N输出对水环境的负面影响,氮添加可通过改变针阔叶林凋落物DOC和DON 的输出影响土壤氮变化。     

四川森林土壤有机碳储量估算方法选择

土壤碳是陆地碳库的重要成分,森林土壤有机碳储量的变化对全球气候变化产生重要影响。对森林土壤有机碳储量的正确估计是编制2005年IPCC国家温室气体清单的重要任务之一,也是其中的难点。本文简要介绍了森林土壤有机碳储量的各种估算方法并对各自的优缺点做了进一步的分析,指出了不确定性产生的主要原因。在分析了四川森林土壤的基本特征后,从满足编制IPCC温室气体清单高层次的方法上考虑,指出四川森林土壤有机碳储量估算的合理方法是土壤类法和生命带法相结合的办法。     

氮沉降对米槠天然林土壤有机碳及微生物群落结构的影响

目的 研究氮（N）沉降对亚热带常绿阔叶天然林土壤有机碳和微生物群落结构的影响,为亚热带森林生态系统碳循环过程的研究提供依据。 方法 选取中亚热带典型米槠天然林为研究对象,采用随机区组试验设计,设3个N沉降水平：对照（CK,0 kg·hm−2·a−1）、低N（LN,40 kg·hm−2·a−1）和高N（HN,80 kg·hm−2·a−1）。 结果 在0～10 cm土层,与对照相比,高N和低N处理总微生物生物量显著增加,低N处理土壤有机碳含量增加27.4%,而高N对土壤有机碳无显著影响;在10～20 cm土层,N沉降（低N和高N处理）对土层有机碳含量和总微生物及各类群生物量均无显著影响。相关分析和随机森林模型结果分析表明,N沉降导致土壤可溶性有机碳（DOC）、全氮（TN）、C/N和微生物生物量增加是驱动表层土壤有机碳累积的关键因子;主成分分析表明,N沉降显著改变0～10 cm土层土壤微生物群落结构,而对10～20 cm土层土壤微生物群落结构无显著影响。 结论 在亚热带常绿阔叶天然林中,短期低N沉降增加能够提高土壤碳储量,但长期N沉降对土壤碳吸存的影响仍不清楚。     

Soil organic carbon status and sustainability of slash-and-burn cultivation in India

ABSTRACT

The study was carried out (a) to identify the changes in the soil organic carbon (SOC) content during the different phases of slash-and-burn cultivation—i.e., before slash-and-burn (Phase 1), after slash-and-burn (Phase 2), and after harvest (Phase 3); and (b) to determine the status of soil organic carbon content in the primary undisturbed forest (Site 1) and in the secondary forests, where slash-and-burn cultivation was taken up ~25 yr (Site 2), 15 yr (Site 3), and 5 yr back (Site 4). The undisturbed forest holds the largest amount of SOC % (5.25) followed by 25 yr (3.07), 5 yr (2.86), and 15 yr (2.27) fallow. The mean percentages of SOC in the 0- to 15-cm layer fell from 3.07 in Phase 1 to 2.53 and 2.37, respectively, in Phases 2 and 3; in the subsurface 15- to 30-cm layer, they fell from 1.95 to 1.62 and 1.63, respectively. Although, the SOC in Phase 3 still seems sufficient to support another round of cultivation, further studies are needed to examine crop yields in successive cultivation cycles, suitability of other rice varieties, and weed and pest types and rates of invasion. Tribal population dynamics is another major concern, which needs assessment for monitoring future land requirements.     

Replacement of wildfire by whole-tree harvesting in jack pine forests: Effects on soil fertility and tree nutrition

Large areas of northern coniferous forests once naturally maintained by stand-replacing wildfires have shifted to an anthropogenic disturbance regime of clearcut harvesting followed by natural or artificial regeneration, with unknown consequences for soil biogeochemical processes. We used a comparative approach to investigate the effects of whole-tree harvesting (WTH) vs. stand-replacing wildfire (WF) on soil C and nutrient availability, and nutrition and growth of the succeeding stand, in jack pine (Pinus banksiana) forests of northern Lower Michigan. We compared total carbon (C), total nitrogen (N), potential N mineralization, and extractable phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) among stands regenerated via WTH or WF in two age classes (4–7 years and 12–18 years). We also measured jack pine foliar nutrition and height growth in these same stands, as well as estimating the contribution of legacy dead wood to ecosystem nutrient capital in young stands. We found some evidence in support of our hypothesis that WTH would leave behind greater pools of soil C and N, but lower pools of P and base cations. However, the differences we observed were confined entirely to surface organic horizons, with the two disturbance regimes indistinguishable when viewed cumulatively to our maximum sampling depth of 30 cm. Estimates of nutrient pools in legacy wood inherited by young jack pine stands were also small in comparison to total soil pools (ranging from 1 to 9% depending on the element), suggesting that decomposition and nutrient release from this material is not likely to result in noticeable differences in soil fertility later in stand development. Similar levels of soil nutrients between WTH- and WF-origin stands were reflected in our measures of jack pine foliar nutrition and height growth, which were both unaffected by mode of stand origin. Results from this study suggest that soil nutrient levels following WTH fall within the natural range of variation produced by WF in these jack pine forests; however, comparison with a similar study on boreal jack pine suggests that latitudinal effects on O-horizon nutrient capital may influence the degree to which WTH matches the effects of WF on soil nutrient availability.     

模拟氮沉降对长白山兴安落叶松林土壤有机碳库的短期影响

以净月潭国家森林公园兴安落叶松林为研究对象,以NH4NO3为原料模拟4个强度的氮沉降,分析土壤总有机碳(TOC)、易氧化有机碳(ROC)、溶解性有机碳(DOC)和微生物量碳(MBC)的动态变化。研究结果表明:低氮沉降量(L,50 kg N yr^-1 ha^-1)提高了TOC、ROC、DOC和MBC浓度,但除MBC外均未达到显著性水平;中氮沉降量(M,100 kg N yr^-1 ha^-1)提高了TOC和DOC浓度,降低了ROC和MBC浓度;高氮沉降量(H,150 kg N yr^-1 ha^-1)提高了ROC和MBC浓度,降低了TOC和DOC浓度。