Age structure of dominant plant populations is vital to forecast community dynamics during vegetation restoration. Pennisetum flaccidum, a perennial grass with long rhizomes, is widely distributed in the northeast and western regions as well as the Inner Mongolian Plateau of China. In the Kerqin grassland region, P. flaccidum is one of several native plant species that are used to restore coal ash storage pools generated by Coal Power Plants. In 2003, we located three ash storage pools (from here on referred to as‘plots’) that differed in age (12, 8, and 5 years old) and contained P. flaccidum. We found that natural colonization had successfully restored these plots, with the average herbaceous cover for all three plots reaching 85%-90%. We sampled the P. flaccidum population. Due to relaxed oversight at the storage pools following a change in the managing entity in 2005, the plots were grazed by livestock. In 2007, we resampled the same plots and found that the total vegetation coverage had decreased to 30%-50%.
In late August of 2003 and 2007, three to five replicate quadrats (each 0.25 x 0.25 m in area and 50 cm deep) in each plot were sampled by taking soil cores, including all aboveground shoots and belowground rhizomes, to maintain the inherent links among tillers and rhizomes. Age classes of tillers and tillering buds were classified according to vegetative propagation generations of tillering nodes and their numbers were counted. Age structure of tillers, tiller buds, tiller matter productivity and tiller vegetative propagation capability of P. flaccidum populations were studied during different vegetation restoration years in the coal ash storage plots of Coal Power Plant in the Kerqin grassland region. Structure changes of P. flaccidum tillers were analyzed under different restoration years (spot 1: 1992-1993; spot 2: 1996-1997; spot 3: 1999-2000) and livestock disturbance (the beginning of 2005). Number and biomass of P. flaccidum tillers showed expanding age structures in both spot 1 and spot 2 and it was stable in spot 3 in 2003. After two years livestock disturbed with different intensities since 2005, P. flaccidum tillers showed stable age structures in all three spots. Every age class and total tiller buds were significantly higher in 2007 after disturbing than those in 2003 as enclosed. Dry matter productivity of same age class tillers was not significantly different among three spots in 2003. Dry matter productivity of 1a tillers and average of each age class in spot 2 and spot 3 in 2007 were significantly fewer than those in 2003. Vegetative propagation capability of tillers of both 1a and average of all age classes were all higher in spot 3 than those in spot 1 and spot 2 in 2003 (P< 0.05). Vegetative propagation capability of tillers of 1a, 3a and average of all age classes in spot 3 were all significantly fewer than those in spot 1 and spot 2 in 2007 after livestock disturbance. Vegetative propagation capability of every age class tillers and their average value in 2007 was higher than those in 2003. There were significant differences between 2003 and 2007 at vegetative propagation capability of 1a age class tillers in every spot, 2a age class tillers in spot 1 and average vegetative propagation capability. Sustaining fence to coal ash storage pools of Coal Power Plant is an effective way to vegetation restoration in the arid Kerqin grassland region.