草原土地利用变化多智能体仿真模型

国内草原生态系统正面临着利用方式不合理、生态压力不断加剧等一系列严重问题。据此采用多智能体建模思想,基于Repast Simphony平台设计并构建草原土地利用变化仿真模型,以模拟和预测草原土地在复杂性、非线性和交互性等多种影响因素下的状态反馈和变化过程。模型针对内蒙古鄂温克旗地区草原土地利用变化实例,详细定义了地理栅格、空间环境以及牧民、牧户和政府三类智能体。采用遗传算法优化草原效益函数,从而对每个地理栅格实现综合效益最优的牧业生产模式探索,以此实现政府智能体行为决策的优化。针对不同情景进行了仿真实验,仿真结果表明牧业劳动力转移、草原利用模式以及政府政策对于草原生态的可持续发展具有重要影响。模型对现有多智能体系统存在的过度简化与仿真度低等问题具有良好的完善补充作用,且具有较高实用价值,可为政府管理草原和牧民合理利用草原提供决策支持。

Seasonal Dynamics of Biomass under Different Land Use Patterns

[Objective] The aim was to study seasonal dynamics of biomass under different land use patterns. [Methed] Aboveground biomass and underground biomass of plants under 3 different surface cover conditions of Stipa krylovii, Leymus chinensis and farmland were determined in growing season （ from May to October） of 2008. [ Result ] The aboveground biomass of Stipa krylovii, Leymus chinensis and farmland in August all reached the highest value, which of Stipa krylovii, Leymus chinensis and farmland was 287.91,117.05 and 193.59 g/m2, respectively. The total biomass of plant roots of the 3 plots in July all reached the highest value, which of Stipa krylovii, Leymus chinensis and farmland was 1 683.9, 1 601.9 and 513.9 g/m2, respectively. Leymus chinensis had the biggest biomass ratio of upper plant roots （0 - 15 cm） to lower plant roots （15 -30 cm）, Stipa krylovii took second place, and farmland had the smallest one. ~ Conclusion The research provides theoretical basis for the ecological environment protection of ecological fragile area.

Land Use/Cover Changes and Environmental Consequences in Songnen Plain,Northeast China

The Songnen Plain in Northeast China,one of the key national bases of agricultural production,went through remarkable land use/cover changes in recent years.This study aimed to explore the long-term land use/cover changes and the effects of these changes on the environment.The Landsat-based analysis showed that,during 1986-2000,cropland,built-up land and barren land had increased,among which cropland had the largest increase of 9,198km2 with an increase rate of 7.5%.Woodland,grassland,water body and swampland had decreased correspondingly,among which grassland had the most dramatic decrease of 6,127km2 with a decrease rate of 25.6%.The transition matrix results revealed that grassland,woodland and swampland were the three main land use types converted to cropland.Climate warming created the potential environment for the conversion of grassland and swampland into cropland.Land resources policy made by central and provincial governments of China affected the pattern and intensity of land use.Land use/cover changes accompanied by climatic variation brought out a series of environmental consequences,such as sand desertification of land,land salinization and alkalinization,grassland degradation,and more frequent floods.Under this circumstance,optimized land use structure and restoration measures are needed.

Soil N Pools and Transformation Rates Under Different Land Uses in a Subalpine Forest-Grassland Ecotone

Soil nitrogen pools (NP), denitrification (DN), gross nitrification (GN), N2O and CO2 flux rates with their responses to temperature increases were determined under five different land uses and managements in a subalpine forest-grassland ecotone of the eastern Tibetan Plateau. Land uses consisted of 1) sparse woodland, 2) shrub-land, 3) natural pasture, 4)fenced pasture, and 5) tilled pasture mimicking a gradient degenerating ecosystem under grazing impacts. The NO3--N content was higher than the NH4+-N content. Comparing tilled pasture with fenced pasture showed that higher intensive management (tillage) led to a significant decrease of soil organic matter (SOM) (P ＜ 0.05) in the soils, which was in contrast to the significant increases (P ＜0.05) of DN, GN, N2O and CO2 flux rates. GN (excluding tilled pasture) and CO2 flux rates increased with a temperature rise, but DN and N2O flux rates normally reached their maximum values at 12-14 ℃ with tilled pasture (the highest management intensity) being very sensitive to temperature increases. There was a difference between net nitrification and GN, with GN being a betterindicator of soil nitrification.

Ecological Consequences of Land Use Change: Forest Structure and Regeneration across the Forest-grassland Ecotone in Mountain Pastures in Nepal

The ecotone, the spatial transition zone between two vegetation communities, is claimed to have more species than the adjoining communities. However, empirical studies do not always confirm higher richness at the ecotone. The ecotone position and structure are dynamic over time and space and it is driven by the changes in climate, land use or their interaction. In this context, we assessed the forest- grassland ecotone of temperate mountains in central Nepal by i） comparing species composition and richness across the ecotone, ii） analyzing if the forestgrassland ecotone is shifting towards the grassland center by colonizing them with trees, and iii） discussing the consequence of changed disturbance regime in the dynamics of this ecotone and the surrounding grasslands. We analyzed vegetation data sampled from belt transects laid across the forest- grassland ecotone in semi-natural grassland patches. Vegetation data consisting of species richness and composition, and size structure and regeneration of the two most dominant tree species, namely Rhododendron arboreum and Abies spectabilis, from the transects, were used to analyze the trend of the forest-grassland ecotone. Forest and grasslands were different in terms of floristic composition and diversity. Vascular plant speciesrichness linearly increased while moving from forest interior to grassland center. Spatial pattern of tree size structure and regeneration infers that forest boundary is advancing towards the grasslands at the expense of the grassland area, and tree establishment in the grasslands is part of a suceessional process. Temporally, tree establishment in grasslands started following the gradual decline in disturbance. We argue that local processes in terms of changed land use may best explain the phenomenon of ecotone shift and consequent forest expansion in these grasslands. We underpin the need for further research on the mechanism, rate and spatial extent of ecotone shift by using advaneed tools to understand the process indepth.

Correlation between the Diversity and Land Use in Cleared Grassland Areas in the Pannon Mountains

Nowadays, mowing has an increasing role in the management of semi-natural and nature conservation areas. Semi-dry grasslands have been planted on cleared areas of forest in the Pannon Mountains, which would be reclaimed by forest without use of the areas by humans. In our work we analysed cleared grasslands. The questions we tried to answer were which changes were caused by different land use, how favourable mowing can be for the purpose of grassland management and nature protection, do the composition of the plant species and the diversity vary within two years when conditions of precipitation are different. In four sampling areas, in 4 × 10 quadrats we registered the plant species and their cover values. We performed a site assessment in April, June and October, 2013-2014. We analysed the data by using cluster and ordination processes and we compared the sampling areas on the basis of the humidity preference and Shannon＇s index of diversity. According to the results, the composition of species and diversity on the analysed areas used for different purposes considerably deviate from each other. Further, we found a difference between two portions of the area whose had minor deviation in water management.