土壤侵蚀预报模型中的植被覆盖与管理因子研究进展

植被覆盖和土地管理措施是土支离破碎中侵蚀的主要抑制因素之一,通用土壤流失方程（USLE）中的植被覆盖与田间管理因子（C）是评价这种抑制作用的有效指标,并被广泛采用和深入研究。我国在这方面的研究还不能满足土壤侵蚀预报和水土保持规划的要求,在系统回顾该因子的研究历史的基础上,介绍了USLE和RUSLE中C因子估计方法及其不断改进和完善的过程,并概述了中国的覆盖与田间管理因子的研究进展。此外,总结国内在（C）因子估计值以及植被覆盖度,地面覆盖物和植被根系对土壤侵蚀的影响等方面研究成果,分析了目前我国覆盖与田间管理因子研究中存在的3个方面问题,并提出了前景展望。     

气候和土地利用变化影响下生态屏障带水土流失趋势研究

受气候和地形等诸多因素影响,我国"两屏三带"国家生态屏障带中的川滇-黄土高原区域和南方丘陵带水土流失十分严重,自然灾害频发。但是,针对川滇-黄土高原区域和南方丘陵带水土流失时空格局变化,特别是未来气候变化和土地利用变化影响下水土流失变化趋势的研究很少。因此,本研究以川滇-黄土高原区域和南方丘陵带为研究对象,利用修正土壤流失方程（RUSLE）定量分析了该区在2000-2015年水土流失的时空变化规律及其影响因素,并预测了在RCP2.6和RCP4.5的未来气候情景下及土地利用变化条件下水土流失的变化趋势。研究结果表明：（1）黄土高原地区在植被恢复的积极作用下,水土流失显著缓解;（2）川滇地区的西南部因植被盖度的增长和降雨的减少水土流失显著缓解,但四川省境内人口密集区农田面积增加以及降水增加造成水土流失大幅度加剧;（3）南方丘陵带受降水增加影响导致了部分区域的水土流失恶化;（4）在未来气候变化情景下,由于大部分地区降雨将减少使土壤侵蚀趋于缓解,但四川、黄土高原和南方丘陵带大部分地区仍然面临未来农田面积增加带来的水土侵蚀压力。考虑到未来气候变化情景下降雨减少的趋势,建议在黄土高原地区提高草地在土地利用类型中的占比,在减少耗水量的同时维持地表盖度,缓解水土侵蚀;此外,各区域仍需控制农田面积,而且需通过加强坡耕地上保水保土耕作措施降低农田区域的土壤侵蚀压力。     

Oak trees and soil interactions in Mediterranean forests: a positive feedback model

Questions: What is the spectrum of variability of chemical elements in a Mediterranean forest ecosystem across the different compartments? Do co‐existing tree species with different leaf chemical composition and nutrient cycling distinctly modify soil conditions? Could these species‐specific, tree‐generated soil changes create a potential positive feedback by affecting long‐term species distribution? Location: Mixed oak forests of southern Spain, Los Alcornocales Natural Park. Methods: We sampled and chemically analysed five different ecosystem components: leaves, leaf fall, litter and superficial (0–25 cm) and sub‐superficial (25–50 cm) soil beneath the canopies of evergreen Quercus suber and deciduous Q. canariensis trees. We used multiple co‐inertia analysis (MCoA) to conjointly analyse the patterns of variability and covariation of eight macro‐ and micronutrients determined in each of the sampled ecological materials. We implemented a path analysis to investigate alternative causal models of relationships among the chemical properties of the different ecosystem components. Results: Variability in the concentration of chemical elements was related to the nature of their biogeochemical cycles. However, the rank of element concentration was consistent across ecosystem components. Analysis of co‐inertia (MCoA) revealed that there was a common underlying multivariate pattern of nutrient enrichment in the ecosystem, which supported the hypothesis of a separation in biogeochemical niches between the two co‐existing oak species, with Q. canariensis having richer plant tissues and more fertile soil directly under each tree than Q. suber. The feasibility of a potential tree–soil positive feedback model was the only statistically validated among several alternative (non‐feedback) models tested. Conclusions: In the studied Mediterranean forests, oak species distinctly modify soil fertility conditions through different nutrient return pathways. Further investigation is needed to address whether these tree‐generated soil changes could affect seedling establishment and ultimately influence species distribution.     

A model analysis of N and P limitation on carbon accumulation in Amazonian secondary forest after alternate land-use abandonment

Productivity and carbon (C) storage in many mature tropical forests are considered phosphorus (P) limited because of advanced soil weathering. However, disturbance can shift limitation away from P and toward nitrogen (N) because of disproportionately large N losses associated with its mobility relative to P in ecosystems. This shift was illustrated by model analyses in which large disturbances including timber extraction and slash-burn were simulated in a P-limited tropical forest. Re-accumulation of ecosystem C during secondary forest growth was initially N-limited, but long term limitation reverted to P. Mechanisms controlling shifts between N and P limitation included: (1) N volatility during slash combustion produced ash that increased soil solution P more than N, (2) a wide N:P ratio in residual fuel and belowground necromass relative to soil organic matter (SOM) N:P produced a simultaneous P sink and N source during decomposition, (3) a supplemental (to aerosol deposition) external N source via biological N fixation. Redistribution of N and P from low C:nutrient SOM to high C:nutrient vegetation was the most important factor contributing to the resilience of ecosystem C accumulation during secondary growth. Resilience was diminished when multiple harvest and re-growth cycles depleted SOM. Phosphorus losses in particular resulted in long-term reductions of C storage capacity because of slow re-supply rates via deposition and the absence of other external sources. Sensitivity analyses limiting the depth of microbially active SOM in soil profiles further illustrated the importance of elements stored in SOM to ecosystem resilience, pointing to a need for better knowledge on the functioning of deeply buried SOM.     

Potential soil carbon sequestration in a semiarid Mediterranean agroecosystem under climate change: Quantifying management and climate effects

Repeated defoliation and flooding trigger opposite plant morphologies, prostrated and erect ones, respectively; while both induce the consumption of carbohydrate reserves to sustain plant recovery. This study is aimed at evaluating the effects of the combination of defoliation frequency and flooding on plant regrowth and levels of crown reserves of Lotus tenuis Waldst. & Kit., a forage legume of increasing importance in grazing areas prone to soil flooding. Adult plants of L. tenuis were subjected to 40 days of flooding at a water depth of 4 cm in combination with increasing defoliation frequencies by clipping shoot mass above water level. The following plant responses were assessed: tissue porosity, plant height, biomass of the different organs, and utilization of water-soluble carbohydrates (WSCs) and starch in the crown. Flooding consistently increased plant height independently of the defoliation frequency. This response was associated with a preferential location of shoot biomass above water level and a reduction in root biomass accumulation. As a result, a second defoliation in the middle of the flooding period was more intense among plants that are taller due to flooding. These plants lost ca. 90% of their leaf biomass vs. ca. 50% among non-flooded plants. The continuous de-submergence shoot response of frequently defoliated plants was attained in accordance to a decrease of their crown reserves. Consequently, these plants registered only 27.8% of WSCs and 9.1% of starch concentrations with respect to controls. Under such stressful conditions, plants showed a marked reduction in their regrowth as evidenced by the lowest biomass in all plant compartments: shoot, crowns and roots. Increasing defoliation frequency negatively affects the tolerance of the forage legume L. tenuis to flooding stress. Our results reveal a trade-off between the common increase in plant height to emerge from water and the amount of shoot removed to tolerate defoliation. When both factors are combined and defoliation persists, plant regrowth would be constrained by the reduction of crown reserves.     

Correlation between soil characters and forest types: a study in multiple discriminant analysis

Multiple discriminant analysis is a useful multivariate technique in vegetation studies that can be employed for several purposes, even if the underlying statistical assumptions are not satisfied. An example of application of this method is discussed: multiple discriminant analysis was successfully used for evaluating the predictivity of forest types defined by numerical classification of vegetation data with respect to soil variables.Species nomenclature follows Pignatti (1982) for vascular plants and Augier (1966) for mosses.The research has been supported by the IDROSER (Bologna, Italy) and by the Italian C. N. R. (Grant no. 83.02548.04, resp. Prof. A. Pirola). We wish to thank Prof. E. Feoli, Prof. E. van der Maarel, Prof. L. Orlóci and Prof. A. Pirola for suggestions. We are also indebted to Dr N. Filippi who analyzed the soil samples.     

Implications of biofuel policy‐driven land cover change for rainfall erosivity and soil erosion in the United States

Large‐scale conversion of traditional agricultural cropping systems to biofuel cropping systems is predicted to have significant impact on the hydrologic cycle. Changes in the hydrologic cycle lead to changes in rainfall and its erosive power, and consequently soil erosion that will have onsite impacts on soil quality and crop productivity, and offsite impacts on water quality and quantity. We examine regional change in rainfall erosivity and soil erosion resulting from biofuel policy‐induced land use/land cover (LULC) change. Regional climate is simulated under current and biofuel LULC scenarios for the period 1979–2004 using the Weather Research Forecast (WRF) model coupled to the NOAH land surface model. The magnitude of change in rainfall erosivity under the biofuel scenario is 1.5–3 times higher than the change in total annual rainfall. Over most of the conterminous United States (~56%), the magnitude of the change in erosivity is between ?2.5% and +2.5%. A decrease in erosivity of magnitude 2.5–10% is predicted over 23% of the area, whereas an increase of the same magnitude is predicted over 14% of the area. Corresponding to the changes in rainfall erosivity and crop cover, a decrease in soil loss is predicted over 60% of the area under the biofuel scenario. In Kansas and Oklahoma, the states in which a large fraction of land area is planted with switchgrass under the biofuel scenario, soil loss is estimated to decrease 12% relative to the baseline. This reduction in soil loss is due more to changes in the crop cover factor than changes in rainfall or rainfall erosivity. This indicates that the changes in LULC, due to future cellulosic biofuel feedstock production, can have significant implications for regional soil and water resources in the United States and we recommend detailed investigation of the trade‐offs between land use and management options.     

From forest to cropland and pasture systems: a critical review of soil organic carbon stocks changes in Amazonia

The impact of deforestation on soil organic carbon (SOC) stocks is important in the context of climate change and agricultural soil use. Trends of SOC stock changes after agroecosystem establishment vary according to the spatial scale considered, and factors explaining these trends may differ sometimes according to meta‐analyses. We have reviewed the knowledge about changes in SOC stocks in Amazonia after the establishment of pasture or cropland, sought relationships between observed changes and soil, climatic variables and management practices, and synthesized the δ¹³C measured in pastures. Our dataset consisted of 21 studies mostly synchronic, across 52 sites (Brazil, Colombia, French Guiana, Suriname), totalling 70 forest–agroecosystem comparisons. We found that pastures (n = 52, mean age = 17.6 years) had slightly higher SOC stocks than forest (+6.8 ± 3.1 %), whereas croplands (n = 18, mean age = 8.7 years) had lower SOC stocks than forest (?8.5 ± 2.9 %). Annual precipitation and SOC stocks under forest had no effect on the SOC changes in the agroecosystems. For croplands, we found a lower SOC loss than other meta‐analyses, but the short time period after deforestation here could have reduced this loss. There was no clear effect of tillage on the SOC response. Management of pastures, whether they were degraded/nominal/improved, had no significant effect on SOC response. δ¹³C measurements on 16 pasture chronosequences showed that decay of forest‐derived SOC was variable, whereas pasture‐derived SOC was less so and was characterized by an accumulation plateau of 20 Mg SOC ha^?1 after 20 years. The large uncertainties in SOC response observed could be derived from the chronosequence approach, sensitive to natural soil variability and to human management practices. This study emphasizes the need for diachronic and long‐term studies, associated with better knowledge of agroecosystem management.     

The soil quality concept as a framework to assess management practices in vulnerable agroecosystems: A case study in Mediterranean vineyards

Land management aiming to sustain ecosystem services is an important issue, especially in biodiversity hot spots such as found in Mediterranean areas. In Mediterranean areas, viticulture is an important land use. Vineyards are frequently found on inherently poor soils and are submitted to intensive management practices, which threaten soil functioning and associated ecosystem services. To encourage winegrowers and stakeholders to be reflective and adapt their vineyard practices, we evaluated the effects of three soil management practices (inter row plant cover duration, weeding and fertilization strategies) on soil functioning in 146 commercial plots distributed in Southern France, by a complementary set of biological and physico-chemical indicators. We used the concept of soil dynamic quality to evaluate some soil management practices on soil functioning. The influence of inherent soil properties derived from pedogenesis on soil dynamic indicator response was accounted for by considering the response of soil indicators for three soil groups differing in their stoniness and Ca carbonate content. The three soil management practices systematically influenced some nematode-based indicators, whereas other indicators were ascribable to a specific soil type or practice. We demonstrated that the potential of soil management practices to enhance soil functioning is restricted by soil type. In particular for calcareous soils, the soil functioning is very stable limiting effects of soil management practices. The presence of a cover crop, even temporary, in the inter row, is the only practice which benefits soil functioning whatever the soil type whereas organic fertilization and chemical weeding exhibit contrasting results on soil functioning.     

Presence and distribution of insect-associated and entomopathogenic fungi in a temperate pine forest soil: An integrated approach

For decades entomopathogenic fungi have garnered interest as possible alternatives to chemical pesticides. However, their ecology outside of agroecosystems demands further study. We assessed the diversity and abundance of entomopathogenic and insect-associated fungi at a loblolly pine forest in North Carolina, USA using culture-dependent and next-generation sequencing libraries. Fungi were isolated using Galleria mellonella larvae, as well as from soil dilutions plated on a selective medium. Isolates were identified using Sanger sequencing of the ITS and LSU rRNA gene regions, and represented 36 OTUs including Metarhizium, Lecanicillium, and Paecilomyces. Additionally, we assessed the chitinolytic potential of isolates and found widespread, variable ability to degrade chitin within and between genera. Phylogenetic analyses resolved several isolates to genus, with some forming clades with other insect-associated taxa, as well as with fungi associated with plant tissues. Saprophytes were widely distributed in soil, while entomopathogens were less abundant and present primarily in the top two cm of the soil. The similarity between culture-dependent and next-generation sequencing results demonstrates that both methods can be used concurrently in this system to study the ecology of entomopathogenic fungi.     

A simulation model for the fate of pesticide residues in a field soil

The model employed for simulating the fate of pesticides in soil was based on the one dimensional convective-dispersive-reaction equation. The model assumed a constant pore-water velocity (v), linear equilibrium adsorption, and first-order degradation. The adsorption parameter (k_d) was calculated from molecular structure with the help of a first-order molecular connectivity index. On the basis of the results of sensitivity analysis the model was made partially stochastic in order to account for horizontal heterogenity in a field soil. Concentration profiles were obtained by employing the mode, median and mean values of (v, D) while the values of k_d and t_1/2 were kept constants; where D and t_1/2 were the apparent diffusion coefficient and the degradation half-life, respectively. The resulted extremes in concentration profiles were expected to be observed within a relatively small area of the heterogeneous filed soil. A random variable, namely the contaminated depth, was defined so that the soil beneath it would be practically free of pesticide during its entire life-time. The values of (₁, ₂, ₃) under continuous leaching were (0.14, 0.56, 1.00 m), (0.29, 1.50, 2.62 m), and (0.65, 2.25, 4.00m) for DDT, toxaphene and lindane, respectively; where ₁, ₂ and ₃ were values of calculated by employing the mode, median, and mean values of (v, D), respectively. Within a relatively small area the first value would be frequently observed whereas the others would be less pronounced. The depth and shape of the resultant base of the contaminated zone were substantially more sensitive to changes in the surface rates of recharge than to changes in the values of the chemical parameters k_d and t_1/2. The implication of the results for the assesment of pesticide contamination of groundwaters were discussed.     

Landscape dynamics in Mediterranean oak forests under global change: understanding the role of anthropogenic and environmental drivers across forest types

The Mediterranean region is projected to be extremely vulnerable to global change, which will affect the distribution of typical forest types such as native oak forests. However, our understanding of Mediterranean oak forest responses to future conditions is still very limited by the lack of knowledge on oak forest dynamics and species‐specific responses to multiple drivers. We compared the long‐term (1966–2006) forest persistence and land cover change among evergreen (cork oak and holm oak) and deciduous oak forests and evaluated the importance of anthropogenic and environmental drivers on observed changes for Portugal. We used National Forest Inventories to quantify the changes in oak forests and explored the drivers of change using multinomial logistic regression analysis and an information theoretical approach. We found distinct trends among oak forest types, reflecting the differences in oak economic value, protection status and management schemes: cork oak forests were the most persistent (62%), changing mostly to pines and eucalypt; holm oak forests were less persistent (53.2%), changing mostly to agriculture; and deciduous oak forests were the least persistent (45.7%), changing mostly to shrublands. Drivers of change had distinct importance across oak forest types, but drivers from anthropogenic origin (wildfires, population density, and land accessibility) were always among the most important. Climatic extremes were also important predictors of oak forest changes, namely extreme temperatures for evergreen oak forests and deficit of precipitation for deciduous oak forests. Our results indicate that under increasing human pressure and forecasted climate change, evergreen oak forests will continue declining and deciduous oak forests will be replaced by forests dominated by more xeric species. In the long run, multiple disturbances may change competitive dominance from oak forests to pyrophytic shrublands. A better understanding of forest dynamics and the inclusion of anthropogenic drivers on models of vegetation change will improve predicting the future of Mediterranean oak forests.     

Solarization in a forest nursery: effect on ectomycorrhizal soil infectivity and soil receptiveness to inoculation with Laccaria bicolor

 Field experiments were carried out in a forest nursery during the summer of 1994 to examine the effect of soil solarization on ectomycorrhizal soil infectivity (ESI) and soil receptiveness to inoculation with Laccaria bicolor. Soil samples from solarized, steamed, fumigated and untreated plots were periodically collected and assayed for ESI. Untreated soil exhibited high ESI. Solarization was as effective as steaming or fumigation in reducing ESI in the uppermost layer. Solarization with a double layer of polyethylene film and fumigation were the only treatments which reduced ESI deeper in the soil. During July, the temperature of covered beds reached 50  °C at a soil depth of 5 cm. Ectomycorrhizal fungi were among the soil-borne fungi most sensitive to solar heating. Soil solarization provides an effective disinfection method for controlled mycorrhization in forest nurseries. Accepted: 10 April 1997     

基于ETM+影像的森林资源信息提取——以黄土高原丘陵沟壑区水土保持林为例

以森林资源遥感分类为切入点,以黄土高原丘陵沟壑区陕西黄龙县境内的水土保持林作为对象,针对ETM+遥感影像在森林信息提取中存在的大量混合像元的问题,引入一种基于针叶林-阔叶林-灌草(C-B-G)模型的混合像元分解方法,通过这种方法,分别得到研究区针叶林、阔叶林、灌草的覆盖图像,并提取出了针阔混交林的分布情况.采用ERDAS 9.1对分类结果进行精度评价,结果表明针阔混交林的分类精度相对于通用分类方法--监督分类的精度提高了20%,说明该方法可以改善植被信息提取的效果.     

BorealFireSim: A GIS-based cellular automata model of wildfires for the boreal forest of Quebec in a climate change paradigm

Wildfires are the main cause of forest disturbance in the boreal forest of Canada. Climate change studies forecast important changes in fire cycles, such as increases in fire intensity, severity, and occurrence. The geographical information system (GIS) based cellular automata model, BorealFireSim, serves as a tool to identify future fire patterns in the boreal forest of Quebec, Canada. The model was calibrated using 1950–2010 climate data for the present baseline and forecasts of burning probability up to 2100 were calculated using two RCP scenarios of climate change. Results show that, with every scenario, the mean area burned will likely increase on a provincial scale, while some areas might expect decreases with a low emission scenario. Comparison with other models shows that areas forecasted to have an increase in fire likelihood, overlap with predicted areas of higher vegetation productivity. The results presented in this research aid identifying key areas for fire-dependent species in the near future.     

森林土壤有机碳深度分布模型的构建与应用

了解森林土壤有机碳(SOC)的深度分布模式对正确估算森林碳储量,充分发挥森林碳汇功能,减缓全球气候变化有着重要意义。选取寒温带针叶林、温带落叶林、亚热带针阔混交林、热带常绿阔叶林等4类森林生物群系,建立SOC深度分布数据库,构建SOC质量密度的深度分布模型;使用Nash-Sutcliffe效率系数(E)、误差百分比(PE)、决定系数(R~2)等统计参量评定模型的模拟效果;利用构建的深度分布模型外推更深层SOC密度。研究结果表明:(1)本文所构建的森林SOC深度分布模型模拟值与观测值较为吻合,Nash-Sutcliffe效率E、误差百分比PE和决定系数R~2平均为0.74、6.95%、0.88(P0.05),模型模拟能力较高(E0.6),模拟误差值低于可接受的临界值(PE±15%),说明构建的模型可以对该地区森林SOC密度值进行估算;(2)寒温带针叶林0—20 cm层SOC质量密度较高,热带常绿阔叶林较低;20 cm以下则是寒温带针叶林较低,热带常绿阔叶林较高,热带常绿阔叶林具有更深层的SOC分布;用0—100 cm深度的SOC来表征区域SOC储量时结果偏低。若考虑0—200 cm深度,0—100 cm深度SOC值平均偏低约21.8%,在热带地区这种偏低趋势可能更加突出,误差可能更大。(3)模型对表层SOC密度有偏低预测趋势,对深层SOC密度预测值可能偏高;作为一个森林SOC深度分布模拟工具,模型可以在有限区域条件下估算不同深度SOC密度值。     

Species richness of gall-forming insects in a tropical rain forest: correlations with plant diversity and soil fertility

We tested two hypotheses to explain changes in species richness ofgall-forming insects. The first hypothesis proposes that gall-forming insectspecies richness increases as more potential host–plant species areavailable. The second hypothesis implies that soil fertility affects plantcolonization by gall-forming insects. Seven sites, representing strongdifferences in vegetation and soil were chosen at the Lacandona tropical rainforest region, Chiapas, Mexico. Overall, we found 1522 individual plantsbelonging to 340 different plant species. From this, we found gall-forminginsects on 737 (43.9%) plants and on 74 (22%) of total plant species. We found asignificant negative correlation between gall-forming insect species richnessand species richness of plants, which does not support the hypothesis that plantspecies richness is an important factor in generating the radiation ofgall-forming insects. Using phosphorus as an indicator of soil fertility, wefound the lowest number of plants with gall-forming insects and the smallestgall-forming insect load per individual plant in the more fertile soil(alluvial). In contrast, the highest number of plants with galls and the highestgall-forming insect load per plant were found at a savanna-like vegetationsite, where the poorest soil was recorded. These results did not support thesoil fertility hypothesis in terms of species richness, but did with respect toabundance of plants with galls.     

Estimating soil carbon fluxes following land-cover change: a test of some critical assumptions for a region in Costa Rica

Changes in soil carbon storage that accompany land‐cover change may have significant effects on the global carbon cycle. The objective of this work was to examine how assumptions about preconversion soil C storage and the effects of land‐cover change influence estimates of regional soil C storage. We applied three models of land‐cover change effects to two maps of preconversion soil C in a 140 000 ha area of northeastern Costa Rica. One preconversion soil C map was generated using values assigned to tropical wet forest from the literature, the second used values obtained from extensive field sampling. The first model of land‐cover change effects used values that are typically applied in global assessments, the second and third models used field data but differed in how the data were aggregated (one was based on land‐cover transitions and one was based on terrain attributes). Changes in regional soil C storage were estimated for each combination of model and preconversion soil C for three time periods defined by geo‐referenced land‐cover maps. The estimated regional soil C under forest vegetation (to 0.3 m) was higher in the map based on field data (10.03 Tg C) than in the map based on literature data (8.90 Tg C), although the range of values derived from propagating estimation errors was large (7.67–12.40 Tg C). Regional soil C storage declined through time due to forest clearing for pasture and crops. Estimated CO₂ fluxes depended more on the model of land‐cover change effects than on preconversion soil C. Cumulative soil C losses (1950–1996) under the literature model of land‐cover effects exceeded estimates based on field data by factors of 3.8–8.0. In order to better constrain regional and global‐scale assessments of carbon fluxes from soils in the tropics, future research should focus on methods for extrapolating regional‐scale constraints on soil C dynamics to larger spatial and temporal scales.