Study of the height growth dynamic based on tree-ring data in Populus euphratica from the lower reach of the Heihe River, China

In recent years, the Populus euphratica Oliv population has shown signs of degradation that are hypothesized to reflect decreases in surface water. Based on the analysis of tree-ring data and field inventories for P. euphratica populations in 14 study sites in the lower reach of the Heihe River, China, this paper assesses (1) age–height growth relationships, (2) tree growth levels, and (3) effects of stand type, soil type, water condition and river runoff on rate of change in tree height growth.There is a close relationship between tree height and age in P. euphratica, but the extent of this relationship varies at different growth stages and at different locations in the lower reach of the Heihe River. In this area, most of the natural P. euphratica forest is currently at a suppressed growth level with an unfavorable growing condition. The height growth in particular appears to be quite sensitive and variable in terms influences of internal and external factors over the tree lifespan, with changes in the water–soil conditions, wind action and gravity being particularly detrimental. In general, tree height growth rate was higher when growth conditions were favorable than in poorer growth conditions; however, the actual differences in growth between trees in the same area was more variable under good growth conditions and could be less variable for trees growing in poor conditions. In addition, the correlation between P. euphratica height growth and river runoff was not significant.These findings should be helpful in determining forestry management measures for the sustainable development and maintenance of natural P. euphratica forests in this study area and for overall environmental evaluation and monitoring of ecosystems of inland river basins of arid areas.