Analysis of the interspecific associations present in an alpine meadow community undergoing revegetation on the railway-construction affected land of the Qinghai-Tibet Plateau

The construction of the Qinghai-Tibet Railway is a centennial project of the People's Republic of China. A large part of this railway is located on alpine meadows( typical vulnerable ecotones characterized by high altitude, low temperatures,and scarce annual precipitation) between the Tanggula Mountains Pass and Damxung County. Because the construction of this railway is inevitably a source of disturbance to the surrounding environment,it is vital to study the revegetation of these severely affected alpine meadows. To understand the community dynamics of the affected alpine meadows,we investigated the vegetation present on the impacted land during the railway construction period( 2005),as well as 4 years( 2009),and 8 years( 2013) after the construction period. Eight 10 m x 40 m plots uniformly located between the Tanggula Mountains Pass( 91[degrees] 43' 31. 4" E,33[degrees] 04' 36. 3" N) and Wumatang( 91[degrees] 32' 11. 95" E,30[degrees] 37' 51.05" N) were sampled,each with 9 quadrants 1 m x 1 m in size. The data collected included species composition,species coverage,species height,and the population size of each species. To this end,a series of variance ratio( VR) tests,[chi]2 tests,and Spearman' s rank correlation coefficient tests were conducted. The results show that the community coverages were( 35. 21 + or - 4. 41) %,( 33. 42 + or - 3. 01) %,and( 43. 41 + or - 3. 26) %,and 71,78,and 85 species recorded in the year 2005,2009,and 2013,respectively. After dropping the species with importance values lower than0.01,we used the 23,27,and 21 dominant species in our subsequent analyses for the respective periods. Overall,species richness and community coverage increased over time,with the overall interspecific association indices( VR) being larger than 1( from 2005 to 2013). In addition,the results of the W statistics( [chi]2_(0.95N) W [chi]2_(0.05N)) showed that the overall associations between species in the community were all significantly positive( P 0.05). The sequential order of association was VR_(2005) VR_(2009)VR_(2013),suggesting that the intensity of the community associations gradually declined over time.Finally,the proportion of positive and negative interspecific associations between the dominated species pairs declined,and the proportion of species pairs achieving significant and highly significant levels tended to increase during the 8 years of revegetation. In addition,the associations between the same species pairs varied significantly am