%0 Journal Article
%T The Study on Establishing Growth Patterns of Grassland Yields and Analysis of its Ecological Formations Using New PPR<br>利用PPR新方法建立草地产量增长模型及生态成因机理研究
%A LI Jian-Long
%A <br>李建龙
%J 生态学报
%D 2002
%I 
%X Using the Projection Pursuit Regression (PPR) method, the multivariate regression statistical and PPR analysis were made between the grassland yields and six other relative ecological factors observed on the desert steppe in the northern slope of Tianshan, Xinjiang in 1992~1994. The PPR regression models of herbage growth were set up, and the formations of grassland yields were analyzed and theoretically explained about them. The results showed that hay yields regularly varied according to precipitations and possessed a bimodal distribution in common years. Among the three factors (precipitation ( PR ), accumulated temperature ( AT ) and light duration affected the herbage yield formations), precipitation was the chief ecological one. However, the growth conditions and patterns of herbages were resulted jointly by hydrothermal factors, soil textures, ecological habits and species compositions. While setting up the growth models of grassland yields and analyzing the yield formations with PPR method, the dimensional curses brought about by rarefaction of nonnormal and nonlinear higher dimensional data points and the interference of independent factors and anthropogenic factors were automatically eliminated. Thus, the precision and effectiveness of setting up growth models were enhanced by the PPR method. The study also offered the results and contribution of each variance in the PPR model, and scientifically brought out the internal structural characters and regularity of the data indiscoverable than other multivariate regression statistical methods. The real grassland yields were estimated and that fitted well with the PPR regressive estimating model in 5 types. The estimating precisions were above 90%. The models passed the effective verification and the statistical analysis of contributive rates was done. Among the 6 variances, growth periods ( T ) had the greatest contributive rate to herbage yields, and soil water contents ( SW ), precipitations ( PR) , accumulated temperatures ( AT ), soil temperatures ( ST ), grassland types ( GT ) followed decreasingly in succession. Our results provided foundations for reasonable utilization of grassland and understanding of the yield formative mechanism in grassland ecological systems.
%K PPR new method
%K grassland in Tianshan
%K setting up of PPR model
%K yield formative effect analysis<br>PPR新方法
%K 草地
%K 产量增长模型
%K 天山
%K PPR模型
%K 生态成因
%K 机理分析
%U http://www.alljournals.cn/get_abstract_url.aspx?pcid=90BA3D13E7F3BC869AC96FB3DA594E3FE34FBF7B8BC0E591&jid=FE163E5DB2274E5937319DE98913EC37&aid=C824F3EB1FC12093&yid=C3ACC247184A22C1&vid=BC12EA701C895178&iid=DF92D298D3FF1E6E&sid=1B519D9EB22393DB&eid=90C2E72D2E105FF5&journal_id=1000-0933&journal_name=生态学报&referenced_num=2&reference_num=30