Growth Variation and Early Selection of Betula Platyphylla in Natural Stands

The stem analysis of Betula platyphylla in natural forest at the Maoershan Forest Experimental Station of Northeast Forestry Universitu. showed that the growth variation of the trees. including height and diameter breast height decreaseswith the increase of the age. There is the turning point for the growth variation of the tree from acute change to relative sta-bility when the trees are in eighteen years old. There are signiticant difttrences among the height. diameter and volumegrowth of the trees at that time. Theretbre. the optimal age for carly seleetion of this species in natural stands is eighteenyears old (18 a). Diameter is used as main index for eary seleclion and height growth as auxiliary one.

Research on the Change of GDP Growth,Monetary Growth and Price Index based on VAR and IRF

In this paper,we use the macro data from the first quarter of 2001 to the first quarter of 2015,through vector autoregressive(VAR)model,Granger causality analysis,impulse response function(RFI)and variance decomposition analysis of quantitative analysis methods,to research on the relationship among China’s real growth variation of gross domestic product(GDP),Money supply growth rate and consumer price index.We find that the money supply growth has impact on China’s real growth variation of GDP in short-term,but there is no long-term significant effect.Economic growth is the main factor to promote the consumer price index growth,money growth is not the main factor driving the change in the price index.China’s currency growth is affected significantly by the change of the economic growth.

Root production, mortality and turnover in soil profiles as affected by clipping in a temperate grassland on the Loess Plateau

Aims Clipping or mowing for hay,as a prevalent land-use practice,is considered to be an important component of global change.Root production and turnover in response to clipping have great implications for the plant survival strategy and grassland ecosystem carbon processes.However,our knowledge about the clipping effect on root dynamics is mainly based on root living biomass,and limited by the lack of spatial and temporal observations.The study aim was to investigate the effect of clipping on seasonal variations in root length production and mortality and their distribution patterns in different soil layers in semiarid grassland on the Loess Plateau.Methods Clipping was performed once a year in June to mimic the local spring livestock grazing beginning from 2014.The minirhizotron technique was used to monitor the root production,mortality and turnover rate at various soil depths(0–10,10–20,20–30 and 30–50 cm)in 2014(from 30 May to 29 October)and 2015(from 22 April to 25 October).Soil temperature and moisture in different soil layers were also measured during the study period.Important Findings Our results showed that:(i)Clipping significantly decreased the cumulative root production(P<0.05)and increased the cumulative root mortality and turnover rates of the 0–50 cm soil profile for both years.(ii)Clipping induced an immediate and sharp decrease in root length production and an increase in root length mortality in all soil layers.However,with plant regrowth,root production increased and root mortality decreased gradually,with the root production at a depth of 30–50 cm even exceeding the control in September–October 2014 and April–May 2015.(iii)Clipping mainly reduced root length production and increased root length mortality in the upper 0–20 cm soil profile with rapid root turnover.However,roots at deeper soil layers were either little influenced by clipping or exhibited an opposite trend with slower turnover rate compared with the upper soil profile,leading to the downward transport of root production and living root biomass.These findings indicate that roots in deeper soil layers tend to favour higher root biomass and longer fine root life spans to maximize the water absorption efficiency under environmental stress,and also suggest that short-term clipping would reduce the amount of carbon through fine root litter into the soil,especially in the shallow soil profile.