The Impact of Arid Climate Change on Agriculture of Dry Valley in Southwest China and Its Adaptive Countermeasures

The eco-environmental vulnerability and underdevelopment of the agriculture in Southwest China would strengthen its disadvantage conditions further on the condition of arid climate change.It is necessary to deal with the relations between resource utilization and eco-environment finely and ascertain the adaptive principles on the dry valley agriculture to the arid climate change in order to change the extensive utilization of the special agricultural resources.The paper gave some adaptive countermeasures that develop modern rangeland husbandry,strengthening the special agriculture and agricultural industrialization,emphasis on the ecological agriculture development,constructing the extension system of water-saving modern agriculture,encouraging the service industry related to ＂agriculture,peasants and the countryside＂,constructing water utilization facilities,and exploiting the renewable energies.

Effect of altitude and climatic parameters on shrub-meadow community composition and diversity in the dry valley region of the eastern Hengduan Mountains,China

Because of the“foehn effect”,deeply incised gorges of major rivers in the Hengduan Mountains(commonly called dry valleys)have semiarid or arid climate.Harsh environment and difficult access have so far obstructed the systematic inventory and documentation of the flora of these dry valleys.This is particularly problematic for efforts towards the conservation of endemic and valuable plant species.Therefore,102 shrub-meadow community survey plots were set up along four dry valleys in Ganzi prefecture,located in the eastern Hengduan Mountains,China.The compositions,richness,diversity of these communities were calculated and assessed using sample plot survey and phytosociological approach.Overall,244 plant species were recorded,consisting of subtropical(48.77%)and temperate(38.83%)species,47.13%of which were endemic to southwest China.Obvious differences in species composition and structure along the altitude gradient were observed.The variations of richness,diversity,and evenness followed a bimodal-hump shaped pattern with increasing altitude,with peak occurring at mid-level altitude(3501–4000 m)and valley occurring at 2501–3000 m altitude.The regions at 2501–3000 m altitudes were more sensitive to global climate change and biological interference,and were found to have the highest protection value.The impacts of altitude gradients and climatic parameters on the features of this shrubmeadow community were also evaluated using principal component and multiple linear stepwise regression analysis methods.Altitude and temperature-related variables were the most important drivers of both species richness and cover.Speciesα-diversity here only depended on the precipitation frequency.This founding could help to understand the impact of the very harsh environment and altitude gradient on plant-plant interactions in a variety of natural systems.

Impacts of reforestation on woody species composition,species diversity and community structure in dry-hot valley of the Jinsha River,southwestern China

To understand the impacts of reforestation on woody species composition,species diversity and community structure,seven plantation forests in dryhot valley of the Jinsha River in Southwest China were investigated,with adjacent wastelands,natural shrub grassland and a natural forest as references.Species importance value,species richness,species heterogeneity and Sorenson similarity index between plantations and the natural forest were analyzed.Results indicated that compared to wastelands and natural shrub grassland,reforestation improved species diversity and community structure,and more forest woody species found suitable habitats in plantations.Species diversity in understory of plantations and Sorenson similarity index were significantly negatively correlated with stem density in mature plantations(26-31 years old).Higher species diversity and Sorenson similarity index existed in mature sparse plantations due to lower stem density and more tree species planted initially.In contrast,reference natural forest,with species heterogeneity of 2.28 for shrub layer,showed the highest species diversity.It would take a long time for species composition and diversity to recover through reforestation in a dry-hot valley.Therefore,it was essential to protect remnant natural forests strictly and reforest with suitable management such as lower stem density and increasing genetic diversity of trees planted.

Survey of damaging pests and preliminary assessment of forest health risks to the long term success of Pinus radiata introduction in Sichuan, southwest China

Pinus radiata was introduced to the summer rainfall environments of Sichuan Province, China in the 1990s as a part of an afforestation pmgram for soil and water conservation in the arid and semi-arid river valley area of Aba Prefecture. Within this region a total area of 26 000 ha have been identified through climate matching as suitable and a further 63 000 ha potentially suitable for environmental plantings of P. radiata. The plantations are being established in widely separated small patches on steep and degraded slopes along the dry river valley The newly introduced P. radiata are exposed to two kinds of forest health risks： they may be attacked by （a） indigenous pathogens and pests against which they may not possess any resistance or （b） by inadvertently introduced foreign pests or pathogens. This paper presents a survey of the potential damaging pests and a preliminary assessment of forest health risks facing the P. radiata plantations over a much longer timeframe than the initial phase of introduction and early plantation establishment. An empirical appmach was adopted to evaluate forest health risks by a combination of literature review, examination of historical records of pest and disease outbreaks in the surrounding conifemus forests, field surveys and inspections, specimen collection and identification, and most importantly, expert analysis of the likelihood of attack by specific pests and pathogens and the subsequent impact of such attacks. The assessment identified some specific forest health risks to the long-term success of P. radiata introduction in this area. These risks are closely associated with the indigenous pests and pathogens of the two native pine species, P. tabulaeformis and P. armondii since these pests and pathogens are considered more likely to establish on P. radiata over time. Exotic pests and pathogens are of a quarantine concern at present. Based on the results of assessment, recommendations are pmvided to improve forest vigour and to reduce the forest health risks posed by indigenous as well as exotic pests and pathogens to the introduced P. radiata. Ways to increase the ability to manage the forest health risks once a particular pest infestation and disease eventuates are also recommended. Although detrimental to the survival and growth of the introduced P. radiata, the impact of identified forest health risks are not considered to be fatal to the long term success ofP. radiata in this area.

Evaluation of Soil Fertility Under Different Cupressus chengiana Forests Using Multivariate Approach

The distribution and growing conditions of Cupressus chengiana forests along with the physical and chemical properties of soils in Northwest Sichuan were studied in 2002 to investigate the conditions and characteristics of soil fertility of C. chengiana and to compare and investigate differences of soil fertility for six C. chengiana populations and their relationships with vegetation, climate and disturbance. The results of the study at 0-20 cm soil depth showed that 1) significant differences (P < 0.05) existed among populations for soil bulk density, soil total porosity, capillary porosity, maximum water-holding capacity, capillary water-holding capacity and topsoil natural water content; 2) chemical characteristics of soil organic matter, total N, total P, alkali-hydrolyzable N, available P, available K and cation exchange capacity were significantly different among the populations; and 3) based on the significant effect of soil fertility factors on forest growth, soil physical and chemical characteristics could be selected as an integrated fertility index (IFI) for evaluation of different C. chengiana populations. Principal component and cluster analyses showed significant differences probably due to the difference of vegetation conditions, management measurements, human-induced disturbances and environmental factors. In order to protect the soil ecological functions in fragile ecological regions, C. chengiana could be used in programs enclosing the hill for natural afforestation, natural forest protection programs, and programs replacing agriculture with afforestation measures.

Introduction of Pinus radiata for afforestation:a review with reference to Aba, China

Pinus radiata D. Don, native to a Californian coastal environment, has been introduced to many parts of the world as an exotic species for afforestation. It is now a major plantation species in the Southern Hemisphere. In 1990, it was introduced to the heavily degraded, dry Min river valley area in Aba prefecture of Sichuan Province, P. R. China. Survival and growth of young trees planted at several sites appear to be reasonable. This review is to serve as an introduction to the large body of literature on P. radiata for forest scientists in China. It covers the following aspects: P. radiata in its native environment and in ex situ plantations, provenance and genetic variations, environmental limitations and climate niche, diseases and pests, lessons from unsuccessful introductions, and the use of P. radiata for ecological restoration. The early growth of P. radiata planted in the dry river valley area is briefly described. Potential problems associated with the introduction of P. radiata in Aba and future research needs are also identified.

Impacts of native vegetation on the hydraulic properties of the concentrated flows in bank gullies

To quantify the impacts of native vegetation on the spatial and temporal variations in hydraulic properties of bank gully concentrated flows,a series of in situ flume experiments in the bank gully were performed at the Yuanmou Gully Erosion and Collapse Experimental Station in the dry-hot valley region of the Jinsha River,Southwest China.This experiment involved upstream catchment areas withone-and two-year native grass(Heteropogon contortus)and bare land drained to bare gully headcuts,i.e.,Gullies 1,2 and 3.In Gully 4,Heteropogon contortus and Agave sisalana were planted in the upstream catchment area and gully bed,respectively.Among these experiments,the sediment concentration in runoff in Gully 3 was the highest and that in Gully 2 was the lowest,clearly indicating that the sediment concentration in runoff obviously decreased and the deposition of sediment obviously increased as the vegetation cover increased.The concentrated flows were turbulent in response to the flow discharge.The concentrated flows in the gully zones with native grass and bare land were sub-and supercritical,respectively.The flow rate and shear stress in Gully 3 upstream catchment area were highest among the four upstream catchment areas,while the flow rate and shear stress in the gully bed of Gully 4 were lowest among the four gully beds,indicating that native grass notably decreased the bank gully flow rate and shear stress.The Darcy–Weisbach friction factor(resistance f)and flow energy consumption in the gully bed of Gully 4 were notably higher than those in the other three gully beds,clearly indicating that native grass increased the bank gully surface resistance and flow energy consumption.The Reynolds number(Re),flow rate,shear stress,resistance f,and flow energy consumption in the gully beds and upstream areas increased over time,while the sediment concentration in runoff and Froude number(Fr)decreased.Overall,increasing vegetation cover in upstream catchment areas and downstream gully beds of the bank gully is essential for gully erosion mitigation.

Geomorphological Features of Ancient Volcanic Terrain of Mars

The article considers geological and morphological features of a volcanic relief of a surface of a planet Mars. Effusive magmatism processes at early stages of planet crust forming come out in structure of solidified relief forms of Mars. Volcanic relief of a planet represents relic ancient line oriented forms, areal and central lava flooding. Linear forms generate shield volcanoes, chains of volcanic mountains and radial-concentric faults. This article deals with geological and morphological characteristics of the volcanic terrain of Mars. Hypsometric altitude profiles of volcanoes have been built based on the MOLA （Mars orbiter laser altimeter） of the spacecraft MGS （Mars global surveyor）. The gradient of volcano flanks has been calculated. The relative age of the volcanic terrain was estimated by the classical method of counting of the density of impact craters. Names of the volcanic landforms of Mars are given in the article in accordance with the name nomenclature system approved by the International Astronomical Union. Research results make it possible to compare the scientific and technical information about the planet and analyze the materials of satellite imagery of Mars.