黄土高原旱地农业自然生产力潜势评价——兼论旱地农业的出路

本文运用系统工程理论,从理论与实践的结合上,对黄土高原旱地农业自然生态系统的土地、光、热、自然降水等各主要因子的生产潜力进行了评价。从而为开发该地区旱地农业的自然生产力潜势提供了科学依据。本文还通过对旱地农业生态经济系统可控制因素与非可控制因素的分析,以及从人类经济再生产行为方式等角度,对旱地自然生产力蕴藏着巨大潜势和“越穷越垦、越垦越穷”这一历史事实构成的悖论作出了科学解释,否定了“十年九旱”是旱地农业增产的主要制约因素的传统观点,为开发旱地农业资源提供了一条现实的、可供选择的思路。     

Analysis and improving ways for water condition in winter wheat field of dryland in subhumid areas of the Loess Plateau

Based on the soil moisture data from the locating experiments from 1986—1990, and using the water balance method, the water supply and demand state in the field of winter wheat, and the ways for improving water condition in dryland of dry subhumid area of the Loess Plateau were studied. The results suggested that a low precipitation satisfying ratio of 42.9%—58.8% appears in the growing period of winter wheat, and the yield, to a great extent depended on the water that was stored in deep soil layer in the previous rainy season. The filed trial results showed that tillage in the summer fallow period,straw cover, soil moisture regulation with adequate fertilization, crop rotation and proper cropping system could be the efficient ways for improving the water condition,and for the exploitation and utilization of natural water resources(both precipitation and soil water) in the winter wheat field of dryland.      

The interfacial mass transfer resistances of the ozone dry deposition over the field soil of Taichung County in Taiwan

This study aims to design a dry deposition chamber and to measure ozone depletion over the Taichung field soil. This study seeks to verify the phenomena by an experimental and mathematical model. It is demonstrated that interfacial mass transfer resistances of ozone dry deposition involve reactive resistance (R(sr)) and kinetic resistance (R(sk)). It reveals the chemical reaction (O3 + NO --> NO2) to produce the reactive resistance, and verifies that the interfacial mass transfer resistances depend on nitrogen oxide emission and soil temperature. It shows that the interfacial mass transfer resistances are reduced with increasing soil temperature (T(S)). The model profiles are smaller than the observed data within a relative error of 15%. The reactive resistance decreases exponentially with increasing soil temperature; R(sr)(-1) (cm x sec(-1)) = 0.0001 exp (0.1455T(S)). The kinetic resistance decreases linearly with increasing soil temperature; R(sk)(-1)(cm x sec(-1)) = 0.0108T(S) + 1.4012. This model is more accurate with higher soil temperature and larger ozone concentration. Results are consistent with thermodynamics and reaction kinetics. Ozone dry deposition over agricultural soil causes conversion of nitrogen oxide (NO) to nitrogen dioxide (NO2).     

Modelling critical levels of ozone for the forested area of austria modifications of the aot40 concept

GOAL, SCOPE AND BACKGROUND: Ozone is the most important air pollutant in Europe for forest ecosystems and the increase in the last decades is significant. The ozone impact on forests can be calculated and mapped based on the provisional European Critical Level (AOT40 = accumulated exposure over a threshold of 40 ppb, 10,000 ppb x h for 6 months of one growing season calculated for 24 h day(-1)). For Norway spruce, the Austrian main tree species, the ozone risk was assessed in a basis approach and because the calculations do not reflect the health status of forests in Austria, the AOT40 concept was developed. METHODS: Three approaches were outlined and maps were generated for Norway spruce forests covering the entire area of Austria. The 1st approach modifies the AOT40 due to the assumption that forests have adapted to the pre-industrial levels of ozone, which increase with altitude (AOTalt). The 2nd approach modifies the AOT40 according to the ozone concentration in the sub-stomata cavity. This approach is based on such factors as light intensity and water vapour saturation deficit, which affect stomatal uptake (AOTsto). The 3rd approach combines both approaches and includes the hemeroby. The pre-industrial ozone level approach was applied for autochthonous ('natural') forest areas, the ozone-uptake approach for non-autochthonous ('altered') forest areas. RESULTS AND DISCUSSION: The provisional Critical Level (AOT40) was established to allow a uniform assessment of the ozone risk for forested areas in Europe. In Austria, where ozone risk is assessed with utmost accuracy due to the dense grid of monitoring plots of the Forest Inventory and because the continuously collected data from more than 100 air quality measuring stations, an exceedance up to the five fold of the Critical Level was found. The result could lead to a yield loss of up to 30-40% and to a severe deterioration in the forest health status. However, the data of the Austrian Forest Inventory and the Austrian Forest Damage Monitoring System do not reflect such an ozone impact. Therefore, various approaches were outlined including the tolerance and avoidance mechanisms of Norway spruce against ozone impact. Taking into consideration the adaptation of forests to the pre-industrial background level of ozone, the AOT40 exceedances are markedly reduced (1st approach). Taking into account the stomatal uptake of ozone, unrealistic high amounts of exceedances up to 10,000 ppb x h were found. The modelled risk does not correspond with the health status and the wood increment of the Austrian forests (2nd approach). Consolidating the forgoing two approaches, a final map including the hemeroby was generated. It became clear that the less natural ('altered') forested regions are highly polluted. This means, that more than half of the spruce forests are endangered by ozone impact and AOT40 values of up to 30,000 ppb x h occur (3rd approach). CONCLUSIONS: The approaches revealed that a plausible result concerning the ozone impact on spruce forests in Austria could only be reached by combining pre-industrial ozone levels, ozone flux into the spruce needles and the hemeroby of forests.     

Changes in Forest Use Value through Ecological Succession and Their Implications for Land Management in the Peruvian Amazon

Abstract:  Research on local use values of forests across an ecological succession informs land-use decisions and conservation planning. I evaluated use values of three age classes of secondary forest: fallow fields (<5 years old, $8.20/ha/year), young secondary forest (5–20 years old, $20.60/ha/year), and old secondary forest (>20 years old, $6.80/ha/year). I quantified daily forest product use and calculated use values in dollars per hectare per year for three communities in the northern Peruvian Amazon. I made three comparisons between forest types: number of useful species, value based on different use categories, and overall use values. Old secondary forest had the greatest number of total species present and species collected. Wood, food, and medicine were the three most valuable use categories. The value different families extracted from local forests varied enormously, but median forest values were lower for all forest types than potential gains from agricultural land use (e.g., coffee $167/ha/year). Values of different-aged stands on privately owned lands in two communities did not differ significantly, whereas in the third community, young secondary forest had a significantly greater value than other forest types. Old secondary forests were the most valuable source of wood products, and wood was the only use category in which there was any difference in the value of products extracted from different-aged forest stands. The value of all three forest types on open-access (nonprivate) lands was minimal (mean in each forest type, $0/ha/year). Local people can utilize the valuation results to develop land-use strategies that balance forest product use, agricultural productivity, and biodiversity conservation.     

青藏高原东北边缘桦木林木本植物种间联结

青藏高原东北边缘地区位于我国东部季风区、西北干旱区与青藏高原高寒区的交汇地带,该区既兼具3大自然区的特点,又具有边缘地带气候波动不稳定性和自然生态环境的脆弱性,是全球变化重点监测的地区之一。研究青藏高原东北边缘亚高山桦木林的种间联结,不仅有助于更深刻地认识该地区桦木群落的结构、功能和演替,对于维持该地区群落稳定性以及生态恢复具有重要意义。本文选取青藏高原东北边缘桦木林中20个优势种,采用方差比率法(VR)检验多物种间的联结性,2×2列联表分析共同出现百分率(JI)、点相关系数(Ф)、Dice指数(DI)来表示种间联结程度,用重要值的Pearson相关和Spearman秩相关来检验相伴出现的机率等方法分析其种间关联性。结果表明:群落总体联结VR值为1.094,说明20个种群间表现出净正关联,其统计量W值为10.94说明20个种群之间在总体上的正关联不显著;大多数种对的JI值、DI值在0.4以下,说明种对之间联结程度不显著,Φ值大部分处于[-0.2, 0.2]值域内,说明种对之间的正或负的联结性较弱;而Spearman秩相关所测得的正负关联比要大于Pearson相关所测得的,且Spearman秩相关要优于Pearson相关。从以上结果可以看出,青藏高原东北边缘三种桦树天然次生林处于不稳定的状态,即演替的中期阶段,其逐渐会被地带性植被所取代。     

A Spatially Explicit Decision Support Model for Restoration of Forest Bird Habitat

Abstract:  The historical area of bottomland hardwood forest in the Mississippi Alluvial Valley has been reduced by >75%. Agricultural production was the primary motivator for deforestation; hence, clearing deliberately targeted higher and drier sites. Remaining forests are highly fragmented and hydrologically altered, with larger forest fragments subject to greater inundation, which has negatively affected many forest bird populations. We developed a spatially explicit decision support model, based on a Partners in Flight plan for forest bird conservation, that prioritizes forest restoration to reduce forest fragmentation and increase the area of forest core (interior forest >1 km from "hostile" edge). Our primary objective was to increase the number of forest patches that harbor >2000 ha of forest core, but we also sought to increase the number and area of forest cores >5000 ha. Concurrently, we targeted restoration within local (320 km²) landscapes to achieve ≥60% forest cover. Finally, we emphasized restoration of higher-elevation bottomland hardwood forests in areas where restoration would not increase forest fragmentation. Reforestation of 10% of restorable land in the Mississippi Alluvial Valley (approximately 880,000 ha) targeted at priorities established by this decision support model resulted in approximately 824,000 ha of new forest core. This is more than 32 times the amount of core forest added through reforestation of randomly located fields (approximately 25,000 ha). The total area of forest core (1.6 million ha) that resulted from targeted restoration exceeded habitat objectives identified in the Partners in Flight Bird Conservation Plan and approached the area of forest core present in the 1950s.     

Atmospheric Sulfur Deposition onto Different Ecosystems Over China

The regional acid deposition model system (RegADMS) was applied to simulate the air sulfur deposition onto different landuse types over China, in which the dry deposition velocities of SO₂ and sulfate aerosol (SO ₄ ^2– ) were estimated by use of a big leaf resistance analogy model and the wet scavenging coefficients were parameterized in terms of precipitation rate. Investigations show that the annual total sulfur deposition over mainland China is 7.24 mt (1 mt = 10⁶ ton) , in which dry deposition and wet deposition accounts for 56 and 44%, respectively. The sulfur deposition onto agriculture land, grass land, and forest land is 1.09, 3.6 and 1.41 mt, respectively, which sums 6.1 mt and accounts for 84% of the total sulfur deposition. The modeled sulfur deposition was in agreement with the measurement conducted at farmland in Yingtan, a typical read soil region in Jiangxi province of China, during the period of November 1998–October 1999. The total sulfur deposition at the Yingtan site is about 10.3 gm^–2 year^–1 of which 83% is dry deposition. The modeling sulfur deposition at the same site is 8.4 gm^–2 year^–1. Furthermore, the comparison between RegADMS and RAINS-ASIA on modeling regional sulfur deposition shows the consistence of the two models. The correlation coefficient between the simulated sulfur deposition at the medium-large cities reaches 0.72.