Ecophysiological Adaptive Strategies Of Elm (Ulmus Pumila L.) In Hunshandak Sandland

There are many elms (Ulmus pumila L.) distributing on the dunes of Hunshandak Sandland. The Sparse-elm grassland was the climax community of vegetation succession in this region. Recently, the number of elm trees decreased sharply, especially the young elms and seedlings, leading to the Sparse-elm grassland ecosystem degrade severely.Based on literatures and our field investigation along a 2,500 km transect in August 2002 in North China as well as our ecological restoration experimentation in Huanshandak Sandland from 2001 to 2003, the distribution and origin of elms were firstly emphasized, and the serial changes of Sparse-elm grasslands vegetation and their degradation and reconstruction were discussed. Moreover, some ecophysiological features were measured, with main results as follows:1) The sparse-elm grassland ecosystem in North ChinaElm is common specie in North China, while Qinling-Huaihe River is their northern boundary of natural distribution areas. They have been acclimated to the cool, drought, high irradiance and sandy environments, where other tree species hardly live together with them. The possible origin of elms might be in Siberia Region. The Sparse-elm grasslands in China, however, only distribute in Hunshandak Sandland, Kerqin Sandland and Hulunber Sandland.2) Ecological degradation and reconstruction of sparse-elm grasslandCase study in Zhenglan Banner, the hinterland of Hunshandak Sandland showed that: 1) the degradation of sparse-elm grassland ecosystem caused mainly by overgrazing, while climate change only the secondary. 2) The enclosed Sparse-elm grassland could be naturally recovered in 2 or 3 yrs. 3) The utilization of artificial grassland could product grass about 100 fold higher and which might be considered as a new approach to restore the degraded ecosystems there. 4) The adjustment of stockbreeding industrial management is vital for the sustainable development of economic in Hunshandak Sandland3) Impacts of human disturbance on sparse-elm grasslandThree typical disturbed sites were investigated with the results indicating that: 1) About 30% adult elms had been deforested by local inhabitants to enclose their rangelands, and those elms were 30-70 years old, which answers the question well why the adult elms decreased sharply. 2) There were no enough fodder for livestock in the heavy disturbed grassland and they had to eat elm seedlings and young elms, this result in further sharp decrease of the quantity of seedlings and young elms. 3) Because of heavy human disturbance, the vegetation coverage has decreased sharply, most of the elm seeds lost the stability for sprouting and no seeding could establish.4) Chlorophyll fluorescence characteristics of different species in Hunshandak Maximum quantum efficiency values (Fv/Fm) of 99 native plant species distributed inHunshandak Sandland have measured. Values of Fv/Fm showed that deep-rooted plant species (tree, shrub and perennial grass) had higher Fv/Fm values than shallow-rooted plant species (annual grass), suggesting that soil droughty is the major environmental stress but Ulmus pumila could tolerant the droughty much better than other species. This finding provides a sound physiological base for understanding the adaptive strategies for elm trees in most sandy lands of China.5) Comparison of responses to drought between elm and exotic treesUlmus pumila and Malus baccata are both the dominant trees distributed in dunes. While Populus spp. and Salix matsuadana are exotic trees introduced by human being for their fast growth characteristics. Different responses of these trees to droughty compared in the field in order to find out their special adaptive strategies. The results showed that those physiological traits of native and exotic trees differ greatly when soil became drier. Leaf water potential, photochemistry efficiency, stomata conductance (gs) and net photosynthetic rate (Pn) of the exotic trees decreased more sharply than those native species, but transpiration rate (E) changed slightly. Water use efficiency (WUE) of the native tre...