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China (Posted on 1997-03-03)

Studies On Characteristics Of Grasshopper Communities And Mathematical Models In The Desert Steppe Ecosystem Of China

He D H

Titre : Studies On Characteristics Of Grasshopper Communities And Mathematical Models In The Desert Steppe Ecosystem Of China

Auteur : He D H

Posted on : 1997-03-03

Grade : Doctor (Dissertation)

Résumé (partiel)
Grasshoppers are the most important primary consumers among invertebrates and are often functionally dominant phytophagous insects in temperate grassland ecosystems( Anderson 1964 ; Joem 1979 ; Rodell et al 1977) . The feeding of grasshoppers forms a key link in the material circulation and energy conversion in a grassland ecosystem. While outbreaks of grasshoppers can cause severe defoliation of grasses and forbs, it also severely hinders the development of animal husbandry. Several volume of studies have been conducted on individual species of Acridoidea at home and abroad(e.g Uvrov 1966 1977 ; Chapman & Joem 1990 ; Guo Fu 1992),but these only aimed at the bioecology and control methods of several pests, locusts and grasshoppers. In the past few years, many detailed studies were made on the grasshopper community ecology on the typical steppe in Nei Monggol(Kang et al 1992,1994a, 1994b, 1994c, 1995a, 1995b). However, ocurrence and distribution of grasshoppers are influenced exceedingly by variable environmental factors such as vegetation type and structure, geographical characters, climatic conditions in microhabitat and so on (Torell 1978) . Little work has been done on the community ecology of grasshoppers on .desert steppes, which make up the main part of grasslands in the Northwestern China, the author has studied some grasshopper community patterns, and effects of environmental factors on these patterns, as well as their models in the desert steppe ecosysem in 1986 1996.1 Physical environment of the grasslands in NingxiaNingxia grasslands are situated in the middle - eastern Asia belonging to inland region at N 35° 17’ 39°22’ and E 104°17’ 107°39’ with an area of around 30100km2, and it includes 11 different types of grassland, that is, meadow steppe, arid steppe, desert steppe, siccideserta, prairie deserta, montane meadow, moistand bottemland meadow, shrub meadow, shrub steppe, swamp meadow, steppe savanna, and several larger areas which, include meadon steppe, arid steppe, desert steppe,siccideserta. These were distributed zonally in horizon from the south to the north. Among them the desert steppe is the largest in area, about 55% of total natural grassland area in Ningxia ; and the arid steppe, 37.0% ; the siccideserta, 1.8% ; the others are of smaller area.In the grassland region, the topology ranges from 1090 m in the northern, to 3350 m in the southern region. The complex and diversified natural environment and vegetation forms on which the variety number of grasshopper species and population depended for their existence is caused by topographic patterns and widely irrgular distribution of mountains, plains, plateaus, deserts, sand dune and water area etc.In spite of small areas of grassland in Ningxia, it has evident climatic characteristics of the three major natural regions, e. g. , the monsoon climatic region, Nei Monggol - Xinjiang plateau region and Qinghai - Xizang plateau region, as well as the general wind in our country. Effects of temperature factors on vegetation types and distribution with increase in latitude are not obvious because that the topography in the region is falling from the south to the north. The annual precipitation is dropping from the southern region, e. g. the rangeland of Liupan mountains, 450mm - 700mm of precipitation, belonged to semihumia climate, to the northern region, e.g. the middle and northern region of Helan mountains, 220mm 400 mm, below 200 mm of precipitation, and belongs to the arid - semi arid climate ; the index of gridity (Ratio of aporation/ precipitation) is increasing from 1 to 5.5 times and the vegetative landscapes are changing from the forest type to the desert steppe type from the south to the north.There are more than one thousand natural plants in Ningxia grasslands, of which there are approximately one hundred species of good forage grass and 200 species of major forage plant, among them species of grass and legume are 1/5 and 1/ 3 of total forage plants respectively.

Présentation (Globethesis)

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