In this paper,the land use in the region of 32 5 ° 38 0 ° N,100 5 ° 109 0 ° E is classified according to the vegetation index difference in time and space of various vegetations by using NOAA/AVHRR data from 1992 to 1993 The annual variation characteristics of vegetation index of different land use are discussed according to classified results
Results show that the areas of good situation,better situation and general situation of vegetations have been increased,and the change areas are 906.39 km2,593.67 km2,384.13 km2 respectively,the areas of worse and worst situation of vegetation have been decreased,and the change areas are 192.54 km2,348.03 km2 respectively.
Under different vegetations,the size of active carbon pool from surface and subsoil respectively accounts to 0.54%~1.67% and 0.45%~5.48% of total soil organic carbon,and the mean residue time is 11~56 days and 60~88 days;
Soil organic carbon in the 0～20cm and 20～40cm layers was positively correlated with annual precipitation,plant cover, plant productivity, soil water content, and<0.05mm particle content (P<0.001),and negatively correlated with average temperature and soil pH(P<0.001).
Warm season grasses accounted for 48 to 73 percent of the ground cover. Switchgrass (Panicum virgatum) was the dominant warm season species at all sites, with vegetative cover values ranging from 48 to more than 56 percent.
Based on the basic principles of the micrometeorology of atmospheric boundary layers and vegetation canopy, a numerical model of the interaction between forest ecosystems and atmospheric boundary layers was developed.
Increased vegetation cover and change in farming techniques were suggested to prevent and control wind erosion of sand and soil.
Under artificial plantations, the vegetation layer (including roots) had a mean carbon density of 111.3 t/hm2, the litter layer a density of 5.1 t/hm2, and the soil layer a density of 64.9 t/hm2.
The ratios of carbon density among vegetation, litter, and soil pools were 39.6:1.8:58.6 for artificial forests and 57.4:2.7:39.9 for natural forests.
The carbon densities of the vegetation and litter layers increased exponentially with forest age.
The results indicate that undisturbed soils have higher shear resistance and less shear displacement than remolded soils at the same vertical loading, when both soils have the same dry density and water content under the same vegetations.
Initially, vegetations were not detected using transthoracic and transesophageal echocardiography.
Subsequent follow-up using echocardiography is necessary for detection of slowly developing vegetations.
There was a perforation of this aortic root abscess to the left ventricular outflow tract; the aortic and mitral valves however were normal without endocarditic vegetations.
Of five patients from 1995-1998, in whom leads with vegetations or tricuspid valve insufficiency were removed by thoracotomy and cardiopulmonary bypass, one patient died perioperatively.
The species are more likely to prefer sites with plant cover, shrub cover (independent-samples t test, P>amp;lt;0.05), and shrub height (Mann-Whitney U test, P>amp;lt;0.05) in a relatively small range.
Annual photosynthetic carbon sequestration and net ecosystem production in northern Eurasian plant cover
The data on the concentrations of 90Sr and 137Cs in 54 species of lichen and moss with different taxonomic natures, as well as in samples of lichen-moss plant cover, are reported.
Experience in mapping the ecological state of the plant cover
Objectives and methods of mapping the ecological state of the plant cover at different spatial levels-federal, regional, and local-are analyzed.