Phosphorus dynamics and solubilizing microorganisms in acid soils under different land uses of Lesser Himalayas of India

Although chemical and some soil physical properties have been studied under different land uses of the Lesser Himalayas of India, very limited information is available on soil biochemical properties. Hence we investigated phosphorus (P) fractions [total P (TP), inorganic P (P_i), organic P (P_o), available P, microbial biomass P (MBP)], enzyme activities [dehydrogenase, phosphatases, phytase], phosphate solubilizing bacteria (PSB) and fungi (PSF), and their correlations of acid soils (0–15 and 15–30 cm depths) under different land uses (viz, organic farming, maize–wheat, apple orchard, undisturbed oak forest and uncultivated land of the Indian Himalayas). All land use systems differed significantly for the P fractions, except TP. The highest values for TP, P_i, available P and MBP were found in soils under oak forest and lowest in uncultivated land. However, P_o content was highest in apple orchard. The organic farming (organic manures field under garden pea-french bean cropping system for > 10 years) maintained highest activities of dehydrogenase, acid phosphatase and alkaline phosphatase. The highest phytase activity and highest numbers of PSB (99 × 10³ g^?1 soil) and PSF (30 × 10³ g^?1 soil) were observed in the rhizosphere soils of oak forest. Significant relationships between soil P fractions and enzyme activities, except alkaline phosphatase, were recorded in surface soil layer. PSB and PSF population were also correlated significantly with P fractions and enzyme activities. This would lead us to understand the level of degradation of P pools due to cultivation over forest system and the suitable management practices needed for soil quality restoration.     

Responses of labile soil organic carbon and enzyme activity in mineral soils to forest conversion in the subtropics

Aims

Globally, extensive areas of native forest have been almost replaced by plantations to meet the demands for timber, fuel material and other forest products. This study aimed to evaluate the effects of forest conversion on labile soil organic C (SOC), soil respiration, and enzyme activity, and to quantify their relationship in subtropical forest ecosystems.

Methods

Surface mineral soil (0–20 cm) was collected from a Cunninghamia lanceolata Hook. plantation, Pinus massoniana Lamb. plantation, Michelia macclurei Dandy plantation, and an undisturbed native broadleaf forest. Soil microbial biomass C, dissolved organic C, permanganate-oxidizable C, basal respiration, and six enzyme activities were investigated.

Results

Soil microbial biomass C was higher by 45.9 % in native broadleaf forest than that in M. macclurei Dandy plantation. The ratio of soil microbial biomass C to total SOC was 27.6 % higher in the M. macclurei Dandy plantation than in the native broadleaf forest. The soil respiration increased by 25.2 % and 21.7 % after conversion from native broadleaf forest to P. massoniana Lamb. and M. macclurei Dandy plantations respectively. The effects of forest conversion on the soil enzyme activities differed among the tree species. Soil microbial biomass C had higher correlation with soil respiration than with the other SOC fractions. Moreover, soil microbial biomass C was positively correlated with urease and negatively correlated with cellulase activity. Soil respiration had higher correlation with soil microbial biomass C, dissolved organic C and permanganate-oxidizable C.

Conclusion

Forest conversion affected the soil microbial biomass C, soil respiration, invertase, cellulase, urease, catalase, acid phosphatase, and polyphenol oxidase activities, but their response depended on tree species. Soil respiration was mainly controlled by labile SOC, not by total SOC.     

Soil carbon sequestration in agroforestry systems: a meta-analysis

Agroforestry systems may play an important role in mitigating climate change, having the ability to sequester atmospheric carbon dioxide (CO₂) in plant parts and soil. A meta-analysis was carried out to investigate changes in soil organic carbon (SOC) stocks at 0–15, 0–30, 0–60, 0–100, and 0 ≥ 100 cm, after land conversion to agroforestry. Data was collected from 53 published studies. Results revealed a significant decrease in SOC stocks of 26 and 24% in the land-use change from forest to agroforestry at 0–15 and 0–30 cm respectively. The transition from agriculture to agroforestry significantly increased SOC stock of 26, 40, and 34% at 0–15, 0–30, and 0–100 cm respectively. The conversion from pasture/grassland to agroforestry produced significant SOC stock increases at 0–30 cm (9%) and 0–30 cm (10%). Switching from uncultivated/other land-uses to agroforestry increased SOC by 25% at 0–30 cm, while a decrease was observed at 0–60 cm (23%). Among agroforestry systems, significant SOC stocks increases were reported at various soil horizons and depths in the land-use change from agriculture to agrisilviculture and to silvopasture, pasture/grassland to agrosilvopastoral systems, forest to silvopasture, forest plantation to silvopasture, and uncultivated/other to agrisilviculture. On the other hand, significant decreases were observed in the transition from forest to agrisilviculture, agrosilvopastoral and silvopasture systems, and uncultivated/other to silvopasture. Overall, SOC stocks increased when land-use changed from less complex systems, such as agricultural systems. However, heterogeneity, inconsistencies in study design, lack of standardized sampling procedures, failure to report variance estimators, and lack of important explanatory variables, may have influenced the outcomes.     

Shifting cultivation on the tidal floodplains of Amazônia: impacts on soil nutrient status

Studies of the impact of traditional agroforestry practices on soil nutrient status in the Amazon Basin have largely been limited to upland sites, many of which are oligotrophic. However, rural population density in Amazonia is highest on the floodplains of the major rivers and shifting cultivation has been practiced on the floodplains for millennia. We established a slash-and-burn cultivation plot and an untreated forest plot in tidal floodplain successional forest in the Islands of Abaetetuba, Pará, Brazil, and sampled soils (0–10 cm) during four phases of the agroforest cycle (n = 9 in each plot for each sampling period): (1) prior to clearing, (2) following burning, (3) harvest one (rice at four months), and (4) harvest two (sugar cane at 15 months). During the course of this pilot experiment, background temporal variability in SOC, total N and available mineral nutrient pools (P, K, Ca, Mg) exceeded treatment effects, suggesting that soil nutrient pools in this environment are well-buffered against the effects of shifting cultivation. These results contrast markedly with those reported for Amazonian upland sites where nutrient pulses and declines associated with the agroforest cycle have been demonstrated and may restrict the potential for low-input, continuous cultivation. Physical limitations imposed by flooding and fluvial erosion, rather than nutrient constraints, restrict the potential of agricultural intensification in the tidal floodplains. This revised version was published online in June 2006 with corrections to the Cover Date.     

Long-term development of soil organic carbon and nitrogen stocks after shelterwood- and clear-cutting in a mountain forest in the Bavarian Limestone Alps

Forest soils store large stocks of soil organic matter (SOM) and are of vital importance for the ecosystem supply with nutrients and water. According to the available literature, depending on management regime and site properties, different negative and positive effects of forest management (particularly of forest thinnings and shelterwood cuttings) on soil organic carbon (SOC) and nitrogen (N) stocks are observed. To elucidate the long-term impact of different shelterwood systems and small clear-cuttings on the OC and N stocks of shallow calcareous soils in the Bavarian Alps, we conducted soil humus inventories on different plots of a mixed mountain forest management experiment started in 1976. The silvicultural multi-treatment experiment consists of a NW-exposed Main Experiment (ME) site with eight plots of different cutting intensity (two unthinned controls, two light shelterwood cuttings = 30 % of basal tree area removed, two heavy shelterwood cuttings = 50 % removed, and two clear-cuttings = 100 % removed) on Triassic dolostone. Additionally, plots were installed at a N-exposed dolostone (ND) site and two sites (FL, FH) on Flysch sandstone (each with one unthinned control and one heavy shelterwood cutting). The shelterwood cuttings from 1976 were repeated in 2003 to re-establish the overstorey basal area as produced by the first cutting in the different plots. Thirty-five years after the first treatments, forest floor SOC and N stocks were significantly decreased (up to ?70 %) at the different shelterwood and clear-cut treatments compared to the unthinned control at the ME site despite vigorous development of natural rejuvenation. Also significantly smaller topsoil (forest floor plus mineral soil 0–10 cm depth) OC stocks (between ?16 and ?20 %) were detected at the thinned compared to the control plots. Differences in topsoil N stocks were also considerable (between ?3 and ?14 %), but substantially smaller than OC stock changes. For the total soil down to 30 cm depth, OC stocks in the differently thinned plots were consistently smaller compared to the unthinned control plots. Comparable to our findings at the ME site, heavy shelterwood plots at the three other sites (ND, FL, and FH) showed significant losses of OC in the forest floor (up to 43 %), mineral soil (up to 38 %), topsoil (up to 38 %), and total soil (up to 34 %). Significant large absolute and relative SOC decreases coincided with sites characterized by large initial humus stocks. Moreover, significant effects of heavy shelterwood cuttings on SOC and N stocks (on average 23 % SOC loss and 13 % soil N loss for the forest floor plus the uppermost 10 cm mineral soil) were detected on a regional level. Our results show that different shelterwood systems are accompanied with a considerable long-term decrease in OC and N stocks in shallow calcareous forest soils of the Bavarian Alps. However, a comparison with a windthrown forest stand at a nearby similar site indicates that SOM losses after thinning operations are small compared to decreases following windthrow or other calamities with subsequent large soil erosion and increased mineralization processes.     

Soil organic carbon stock in relation to aggregate size and stability under tree-based cropping systems in Typic Ustochrepts

The growing of tree crops along with the field crops is a common practice in foothills of lower Himalayas with the twin objective of checking soil erosion by water and covering the risk of crop failure due to frequently occurring droughts. A study was conducted to evaluate dry and water stable aggregates for their soil organic carbon (SOC) stocks under different tree-based cropping systems. The treatments consisted of three cropping systems viz. maize-wheat (sole crop), agroforestry and agrohorticulture (tree-based) in the similar soil texture and in 6 year old plantations. The soil samples were obtained from different layers (0–15, 15–30, 30–60, 60–90 and 90–120 cm) and analyzed for SOC. The undisturbed aggregate samples (as big clods) were collected from 0–15 and 15–30 cm soil layer for dry and wet aggregate stability. The data so obtained was analyzed by using CRD factorial deigns at LSD (P ≤ 0.05). The SOC concentration decreased with soil depth, the decrease was higher (89.6%) in soils under maize-wheat than in soils under agrohorticulture (81.3%) and agroforestry (77.8%). The mean SOC concentration decreased with the size of the dry stable aggregates (DSA) and water stable aggregates (WSA). In DSA, the mean SOC concentration was 58.06 and 24.2% higher in large and small macroaggregates than in microaggregates respectively; in WSA it was 295.6 and 226.08% higher in large and small macroaggregates than in microaggregates respectively in surface soil layer. The mean SOC concentration in surface soil was higher in DSA (0.79%) and WSA (0.63%) as compared to bulk soil (0.52%). The SOC concentration and stock being highest in soils under agroforestry resulted in higher SOC concentration in dry as well as WSA.     

Soil carbon stock assessment in the tropical dry deciduous forest of the Sathanur reserve forest of Eastern Ghats,India

Climate change and carbon mitigation through forest ecosystems are some of the important topics in global perspective. Tropical dry forests are one of the most widely distributed ecosystems in tropics, which remain neglected in research. The soil organic carbon (SOC) stock was quantified on a large scale (30 1-ha plots) in the dry deciduous forest of the Sathanur reserve forest of Eastern Ghats. The SOC stock ranged from 16.92 to 44.65 Mg/ha with a mean value of 28.26 ± 1.35 Mg/ha. SOC exhibited a negative trend with an increase in soil depth. A significant positive correlation was obtained between SOC stocks and vegetation characteristics viz. tree density, shrub basal area, and herb species richness, while a significant negative correlation was observed with bulk density. The variation in SOC stock among the plots obtained in the present study could be due to differences in tree abundance, herb species richness, shrub basal area, soil pH, soil bulk density, soil texture etc. The present study generates a large-scale baseline data of dry deciduous forest SOC stock, which would facilitate SOC stock assessment at the national level as well as to understand its contribution on a global scale.     

Forest-type shift and subsequent intensive management affected soil organic carbon and microbial community in southeastern China

In this study, we investigated the effect of forest types changes (from coniferous and broadleaf mixed forest (CBMF) to plantation forests of bamboo (Phyllostachys pubescens forest, MBF) and hickory (Carya cathayensis forest, CHF)) combined with intensive management on soil organic carbon (SOC) and microbial community structure, using the ¹³C-nuclear magnetic resonance (NMR) and phospholipid fatty acid (PLFA). The results indicated that soil organic carbon significantly decreased by 30.7 and 28.5% in MBF and CHF, respectively. The aromatic C and aromaticity also significantly decreased in MBF and CHF (P < 0.05), while alkyl, O-alkyl and carbonyl C contents increased (P > 0.05). Significant changes of the soil microbial community were found after the forest type changed from CBMF to MBF and CHF. Total soil microbial PLFAs, soil bacteria PLFAs, fungus PLFAs, actinobacteria PLFAs, arbuscular mycorrhizal fungi PLFAs and protozoan PLFAs ranked as follows: CBMF > CHF > MBF (P < 0.05). The ratio of soil fungus to bacteria was in the order of MBF (0.78) > CHF (0.66) > CBMF (0.49) (P < 0.05), while an opposite order was found for ratio of G+/G− values (CBMF > CHF > MBF, P < 0.05). The converting CBMF into MBF and CHF combined with fertilization and tillage significantly changed the SOC and microbial community. Therefore, necessary measures should be taken to improve the SOC and soil fertility in the MBF and CHF.

     

Pasture or permanent crops after slash-and-burn cultivation? Land-use choice in three Amazon colonies

Land use was examined in three settlements – Pedro Peixoto in Acre and Theobroma in Rondonia, Brazil, and Pucallpa, in Peru. Research aimed at characterizing the differences in land use after initial slash-and-burn, and presenting hypotheses to assess the feasibility of improved land uses. Settlers in the Amazon practice slash-and-burn agriculture in forest lands to produce annual crops. After cropping, lands are converted to pasture, or planted with perennial crops, or fallowed in anticipation of future annual crop production. Land use after slash-and-burn cultivation in forest lands differed among the colonies examined. Whereas colonists in Pedro Peixoto converted lands to pasture for cattle production, settlers in Theobroma adopted a strategy encompassing both dual-purpose (milk and meat) cattle and perennial crop production. The more heterogeneous settlers in Pucallpa, who included small-scale cattle ranchers and riverine and forest slash-and-burn farmers, gave more importance to perennial crops. Hypotheses are suggested regarding the described land use differences, and implications for the adoption of agroforestry are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Tree structure and diversity of lowland Atlantic forest fragments: comparison of disturbed and undisturbed remnants

This study describes the tree community structure of three moist lowland Atlantic Forest fragments in Rio de Janeiro State, southeastern Brazil. Two fragments were disturbed and an undisturbed one was used as reference. Our hypothesis was that disturbed fragments show distinct structural patterns in comparison with undisturbed stands due to past disturbance practices and forest fragmentation. Four 100 ×5 m sampling plots were demarcated in each fragment and all live and dead trees with DBH C 5 cm were located, measured and identified. The results supported our hypothesis, due to the high values found for standing dead trees, an increase of dominance of a few pioneer species, lower values of large trees and species richness in disturbed fragments in comparison with the undisturbed one. The advanced fragmentation process in the Southern Brazilian lowland areas and the high species richness in undisturbed areas highlight these forest fragments as priority areas for conservation and management.     

Effect of land-use conversion from forest to cocoa agroforest on soil characteristics and quality of a Ferric Lixisol in lowland humid Ghana

Soil fertility decline caused by deforestation, soil degradation and low input use has become a primary factor limiting sustainable utilization of soil resources in cocoa agroforestry systems on acid soils in lowland humid Ghana. Changes in and responses of soil physico-chemical properties and soil quality to land-use change was investigated along a chronosequence of farm fields on a Ferric Lixisol in the Ashanti region of Ghana. Soil bulk density increased significantly only in the top 0–10 cm soil layer. Concentrations and stocks of soil organic carbon (SOC) and total N decreased significantly in the top 0–10 and 10–20 cm soil depths. By 30 years after forest conversion, cocoa system had re-accumulated up to 38.8 Mg C ha^?1 or 85 % of initial forest carbon stock values. Total porosity (%) decreased significantly in shaded-cocoa fields in comparison with the natural semi-deciduous forest. An assessment of soil deterioration using degradation indices (DIs) revealed that total soil quality (0–20 cm) deteriorated significantly (DI = –60.6) in 3-year-old of cocoa system but improved in 15 and 30-year-old systems. Available P stocks declined consistently while soil exchangeable Ca, K and Mg stocks as well as cation exchange capacity (CEC) and base saturation remained more or less stable with a tendency to improve. The inclusion of leguminous shade trees during early plantation development, development of mechanisms for the integration of cover crops and enhancement of farmer capability in improved farm management are required to maintain high C and nutrient base, minimize soil quality degradation during plantation development phase and sustain long-term productivity.     

Conversion of tropical moist forest into cacao agroforest: consequences for carbon pools and annual C sequestration

Tropical forests store a large part of the terrestrial carbon and play a key role in the global carbon (C) cycle. In parts of Southeast Asia, conversion of natural forest to cacao agroforestry systems is an important driver of deforestation, resulting in C losses from biomass and soil to the atmosphere. This case study from Sulawesi, Indonesia, compares natural forest with nearby shaded cacao agroforests for all major above and belowground biomass C pools (n = 6 plots) and net primary production (n = 3 plots). Total biomass (above- and belowground to 250 cm soil depth) in the forest (approx. 150 Mg C ha^?1) was more than eight times higher than in the agroforest (19 Mg C ha^?1). Total net primary production (NPP, above- and belowground) was larger in the forest than in the agroforest (approx. 29 vs. 20 Mg dry matter (DM) ha^?1 year^?1), while wood increment was twice as high in the forest (approx. 6 vs. 3 Mg DM ha^?1 year^?1). The SOC pools to 250 cm depth amounted to 134 and 78 Mg C ha^?1 in the forest and agroforest stands, respectively. Replacement of tropical moist forest by cacao agroforest reduces the biomass C pool by approximately 130 Mg C ha^?1; another 50 Mg C ha^?1 may be released from the soil. Further, the replacement of forest by cacao agroforest also results in a 70–80 % decrease of the annual C sequestration potential due to a significantly smaller stem increment.     

Reforestation with loblolly pine can restore the initial soil carbon stock relative to a subtropical natural forest after 30 years

We hypothesized that long-term loblolly pine (Pinus taeda L.) land-use restores SOC stock and lability of a subtropical Cambisol to the original levels of the natural forest (NF). Additionally, we hypothesized that roots are the major contributor to SOC and that soil stores most of the ecosystem total carbon (ETC). We investigated a chronosequence of loblolly pine land-use of 17 (first rotation) and 32 years (second rotation, unthinned or thinned) following clearing of the NF. The original SOC stock to 100 cm of NF (209?±?9.4 Mg C ha^?1) was depleted by 22% after 17 years of pine, possibly because of intense soil disturbance and low quantity and quality of the residue inputted during the pine stand implementation. However, the SOC stock was restored to the original stock of NF after 32 years of pine, with the input of above and belowground biomass at harvest of the first rotation possibly playing a role in this recovery. Thinning did not affect SOC stocks after 1 year. The POM-C reduced after 17 years and was not recovered after 32 years. We could not ascertain in 5-year evaluation whether root or litter was the major contributor to SOC. Soil held 72% of the ETC in NF and 48–59% in pine plantations, confirming that it stores most of the ETC. Overall, long-term loblolly pine land-use seems to restore the original soil carbon stock in this subtropical site, regardless of some lability losses.     

Soil Carbon and Nitrogen Stocks Under Plantations in Gambo District,Southern Ethiopia

The effect of six plantation species in comparison to natural forest (NF) on soil organic carbon (SOC) and total nitrogen (TN) stocks, depth-wise distribution, biomass carbon (C), and N was investigated on plantations and cultivated lands on an Andic paleudalf soil in Southern Ethiopia. The SOC, N, and bulk density were determined from samples taken in 4 replicates from 10-, 20-, 40-, 60-, and 100-cm depth under each site. Similarly, the biomass C and N of the plantation species and understory vegetation were also determined. The SOC and N were concentrated in the 0- to 10-cm depth and decreased progressively to the 1-m depth. Next to the NF, Juniperous procera accrued higher SOC and N in all depths than the corresponding plantations. No evidence of significant difference on SOC and N distribution among plantations was observed below the 10-cm depth with minor exceptions. The plantations accrue from 133.62 to 213.73 Mg ha^–1 or 59.1 to 94.5% SOC, 230.4 to 497.3 Mg ha^–1 or 6.9 to 14.9% TBC and 420.37 to 672.80 Mg ha^–1 or 12.5 to 20% total C-pool of that under the NF. The N stock under Juniperous procera was the highest, while the lowest was under Eucalyptus globulus and Cupressus lusitanica. We suggest that SOC and N sequestration can be enhanced through mixed cropping and because the performance of the native species Juniperous procera is encouraging, it should be planted to restock its habitat.     

关帝山森林土壤有机碳和氮素的空间变异特征

在庞泉沟自然保护区选择3个生态功能区设置典型样地,运用经典统计学和地统计学方法研究了森林土壤有机碳、全氮及碳氮比的空间变异特征及分布格局.结果表明,随着生态系统由人工林→次生演替早期杨桦阔叶林→次生演替中后期云杉、杨、桦混交林顺向演替,土壤有机碳和全氮平均值先增加后减小,碳氮比平均值呈逐渐减小趋势.3指标变异系数在11...     

Coarse woody debris of Fagus sylvatica produced a quantitative organic carbon imprint in an andic soil

Coarse woody debris (CWD) is involved in important forest ecosystem functions and processes, e.g., habitat provision, water retention, and organic matter decomposition. However, a quantitative, CWD-produced soil organic carbon (SOC) imprint has not yet been detected, possibly due to lack of free adsorption sites on soil minerals. To circumvent this potential constraint, we selected plots with and without CWD in a beech (Fagus sylvatica L.) primeval forest in the West Carpathian volcanic range (Slovakia). Local andic soil contains abundant allophane and amorphous Fe-compounds as important SOC binding agents. The C concentration in the fine earth of sampled soils was determined by the dry combustion method. We established that organic carbon concentration decreased with depth from 0.20 kg kg^?1 (0.0–0.3 m) to 0.11 kg kg^?1 (0.3–0.5 m) in soil with CWD and from 0.13 kg kg^?1 (0.0–0.3 m) to 0.07 kg kg^?1 (0.3–0.5 m) in soil without CWD. The respective average differences in soil organic carbon concentration (0.07 kg kg^?1) and stock (15.84 kg m^?2) between the two series of plots within the upper 0.3 m were significant according to the t test (P < 0.05 or P < 0.01, respectively). Also, corresponding differences within the 0.3–0.5 m layer (0.04 kg kg^?1 and 5.51 kg m^?2) were significant (P < 0.05, P < 0.001). Our results represent the first indication that CWD-produced SOC imprint may reach deeper than just a few centimeters in soils featuring high adsorption capacity, such as Andosols.     

The farming system and traditional agroforestry systems in the Maya community of San Jose, Belize

Shifting slash-and-burn agriculture is likely one of the main causes of forest degradation in southern Belize. Although many development projects have attempted to reduce the impacts of agriculture on the tropical rainforest, the situation is still a cause for concern. A study of the farming system of the San Jose Maya community was therefore carried out to examine agricultural production in its social, cultural, economic, and political context. Results demonstrate that agricultural production contributes to forest degradation because of the limited availability of agricultural land, the low level of investment in agricultural production, the land tenure system, limited marketing opportunities, and the exclusion of Mayas from the country's political and economic domains. Agroforestry could, however, offer a partial solution to the problem of forest degradation. Three types of traditional agroforestry systems are practised in San Jose: the milpa (a slash-and-burn agriculture system), cacao (Theobroma cacao) cultivation under shade trees, and the homegarden. These traditional agroforestry systems almost entirely meet a family's needs for food and wood, and generate at least 62% of family income. Improving the productivity of these systems could help to reduce pressure on the forest in southern Belize.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nestedness and modularity in fragmented Shasha Forest Reserve,southwestern Nigeria

Species co-occurrence and nestedness pattern in Shasha forest reserve were investigated with a view to determining the effect of interactions to species contribution. Three distinct sites (Gmelina arborea plantation, undisturbed forest, and Pinus carribaea (plantation) were selected in the forest reserve. Four 25 m × 25 m plots were established in each of the site within the forest reserve. Species enumeration, identification,, and distribution into families of the standing vegetation were carried out. Woody species represented the most diverse life form. Plant species diversity was highest in UF and lowest in Gmelina plantation. Differences in woody species composition among the three forest types were determined by non-metric multidimensional scaling (NMDS) analysis, analysis of similarity (ANOSIM), and similarity of percentages. Using z-score and NODF (a nestedness metric based on overlap and decreasing fill). Three modules were detected and modularity score Q = 0.2. The composition analyses (NMDS and ANOSIM) revealed a significant difference in the woody species composition among the forest types. Our research may contribute to understand species assemblage in one of the diverse forests of Africa. Current work highlighted species occurrence in Shasha forest and highlighted the importance of non-random pattern which could serve as framework for conservation perspective.     

海南岛尖峰岭半落叶季雨林生态效应的研究Ⅳ—游耕农业的地力分析

本文根据在海南岛尖峰岭林区半落叶季雨林—褐色砖红壤上所进行的游耕农业生态后果的实验研究,论证了热带森林土壤资源退化的四个方面:凋落物层烬失,使土壤养分补给源和水文功能减弱;水土流失严重;水分的输导、涵贮能力降低;上壤理化性状劣变,肥力下降。文章提出了废除游耕制,建立以木本植物为主的林—农制;合理规划和经营热带林;停止炼山全垦法,推行生态造林技术等项建议,以培育和保持地力,保护热带森林土壤资源。     

Active organic carbon pool of coniferous and broad-leaved forest soils in the mountainous areas of Beijing

In order to explore the effects of different forest types on active soil carbon pool, the amounts and density of soil organic carbon (SOC) were studied at different soil horizons under typical coniferous and broad-leaved forests in the mountainous area of Beijing. The results showed that the amount of total SOC, readily oxidizable carbon and particulate organic carbon decreased with increasing depths of soil horizons and the amounts at depths of 0–10 cm and 10–20 cm in broad-leaved forest was clearly higher than that in coniferous forests. The trend of a decrease in SOC density with increasing depth of the soil horizon was similar to that of the amount of SOC. However, no regular trend was found for SOC density at different depths between coniferous forest and broad-leaved forests. The ratio of readily oxidizable carbon to total amount of SOC ranged from 0.36–0.45 and the ratio of particulate organic carbon to total amount of SOC from 0.28–0.73; the ratios decreased with increasing depths of soil horizons. Active SOC was significantly correlated with total SOC; the relationship between readily oxidizable carbon and particulate organic carbon was significant. A broad-leaved forest may produce more SOC than a coniferous forest.