| Taken the different age of planting Caragana intermedia in desert steppe in Yanchi county of Ningxia as the research object, taken the sustainable exploitation and utilization of shrub and grass resources as the starting point, and taken the configuration and quality dynamic of the shrub and grass as the breakthrough point, this paper studied the dynamic change, configuration pattern and constraint factors of the vegetation biomass and forage quality of shrub and grass. All of the research is to further understanding and evaluation the status and position of Caragana shrub grassland in the system of desert grassland, to understanding the problem and potential of shrub and grass collocation in actual use condition, finally to provide a theoretical basis for the optimization management of Caragana shrub grassland productivity.The main research results:(1) In the component level,16a,25a and37a planting shrub of Caragana have been in declining stage of development, along with the age growth, biomass decreased obviously of overground part, shrub branches aging, and branching structure tended to be simple.Bearing capacity of all shrub in branches are weak, space resources can be used are relatively more and the competitions are smaller between the branches. Among them,16a shrub have a stronger production branching ability, and the branching pattern of it is the most complex, its ability to occupy the space and the potential use of space resources are high. Along with the age growth and senescence, shrub branching Architecture tends to be simplified, the potential of use of space resources and ecological adaptability are declined.(2) As age increased, the content of crude protein in branches was decreased, and crude protein content decreased first and then increased in leaves. Among them,16a shrub crude protein content in branches and leaves was significantly higher than that of25a and37a.The crude protein content of16a shrub branches decreased in June, and higher in October and March, the overall condition are stability, and the crude protein content of leaves change with time decreased. On the whole, leaf crude protein content higher than branches, the crude protein content of leaf sprouting period of up to29.23%. With increasing shrub branch diameter, branch biomass was significantly reduced, and each size class branch crude protein content increased significantly, different diameter of branch biomass and crude protein content showed significantly negative correlation.The crude protein content of25a planting shrub of Caragana showed the trend of firstly decreased and then increased significantly with the branching increases, however, the crude ash content increases gradually with the increase of branches. At the same time, the crude protein content showed a "W" type change trend from top to bottom, but the crude ash content showed a significant increasing trend. Age has a smaller limit of new branches quality of Caragana shrub, but the effects of growth stage is significant. Along with the growth stage changes, nutrient content of different age shrub branches and leaves are decreased, sprouting period (May) can be determined for the best time to use it because of the highest crude protein.Along with the age increased, the crude protein content first decline after rising in the sprouting period, and just the opposite during the leaf expansion period, and decreased in blossom period and increased in filling stage. Crude ash content increased significantly during the blossom period, while increased first and then decreased in other period. With the change of growth period, content of crude protein in different ages showed an inverted "N" shaped trend, while crude ash content showed a downward trend.(3)The biomass of shrub and vegetation was not significantly affected by age, it showed a typical "J" shape with the growth stage changes.At the same time, the biomass of different age shrub and vegetation was lower than the contrast. In May, the16a and25a biomass in the shrubs is higher than out of the shrubs, the37a’s are similar. In June, the biomass of shrub vegetation in different ages were similar. In August and October, the16a and25a biomass out of shrub is higher than under shrub, and just the opposite of37a.Ages have an little effects on vegetation coverage, height and species number, these factors mainly effected by the growth period. In August, the coverage in the shrubs is higher than out of the shrubs, but to the contrary in October. The height of shrub inside the shrub is higher than outside the shrub, and the vegetation species number and individual number less than the outside shrub. From this point of view, the shrub vegetation species richness, species dominance, species diversity and evenness of species parameters are less than the outside shrub.With the forest age and growth swason change, the vegetation nutrient content changes significantly. In May and June, the content changes of crude protein and crude ash were not obvious. In August and October, with the age increasing, the content of crude protein increased first and then decreased. The crude ash content of different ages was significantly lower than the contrast of natural grassland. In August, crude ash content did not change significantly with age. In October, shrub with age increased significantly inside of the shrub, while first increased and then decreased outside.(4)The main limited factor of Caragana nutrient content of the new branches are wind speed, precipitation and activated carbon, the wind speed and precipitation have a negative influence and the activated carbon has a positive effect.The main factors influencing the characteristics vegetation index inside shrub are organic carbon, temperature, humidity and precipitation, negative correlation with temperature, precipitation and soil organic carbon, positive correlation with moisture. The main factors influencing the characteristics vegetation index outside shrub are soil available nitrogen. temperature, humidity and wind speed, negative correlation with temperature and soil available nitrogen, positive correlation with moisture and wind speed. The main factors influencing the vegetation nutrient content inside shrub are organic carbon and temperature, crude protein and N-P content have a positive correlation with organic carbon and temperature, and just the opposite of crude ash. While the main factors influencing the vegetation nutrient content outside shrub is only temperature, crude protein and N-P content have a positive correlation with the temperature, and just the opposite of crude ash.In summary,16a,25a,37a of Caragana appeared obvious degradation trends. With the growth of shrub structure and its space use capacity degeneration, but its new branches quality did not change with age, and the growth period is the main factor to determine the quality of shrub new branches. Different age Caragana availability is mainly depend on the quantity, rather than quality change,the decline of biomass are the main problem of the ageing of Caragana.In August and October, shrub accumulated more biomass, vegetation height, cover and species diversity indexes are higher. In June, different age forest vegetation nutrient content reached the highest.Comprehensive consideration,6-8months should be the best time of the new branches as the best forage feed, and also is the best time to grazing vegetation.From the viewpoint of the combination of shrub and grass,the relationship is not close of competition and coexistence between the shrub and grass in the object and its spatial-temporal scale.Compared with the contrast check of grass, shrubs extrude the living space of grass, the conservation effect is not sufficient.In the current using condition, the shrub and grass just two random together components, the inherent stability and sustainable productivity of the systems are more disturbed by outside environment factors, including factors climate and soil and so on, and showed a inherent seasonal fluctuation.Caragana continuous aging may be a cause of system shift, but its further development direction is not clear.From the view of sustainable utilization, further inhibit the potential negative effects are equally importantand with shrub renewal measures.Reasonable coexistence relationship between shrub and grass by human induced and consolidate is still the main task and direction for the future management and research. |
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