The ecology and growth patterns of Cleistogenes species in degraded grasslands of eastern Inner Mongolia, China.
Abstract
Cleistogenes is an important perennial grass genus found in the pastoral steppes of eastern Inner Mongolia. Despite its dominance in many grassland types, the value of Cleistogenes as a key genus for sustainable grassland development has only recently been recognized. To understand better how to manage Cleistogenes-dominant grasslands, an experiment was conducted in China, to characterize the growth patterns of two Cleistogenes species (C. polyphylla) and (C. squarrosa [Kengia squarrosa]) in relation to environmental parameters. Sampling exclosures were established on uniform grasslands at Mangha and Liuhe gachas. Over two growing seasons (1999-2000) vegetation cover, green and dry biomass by species, species height and tiller density of Cleistogenes were measured at about monthly intervals starting in mid-May and ending in mid-October. Cleistogenes polyphylla at Mangha and C. squarrosa at Liuhe accounted for >50% of green biomass. Neither species made any significant growth before late June, even though soil moisture was available and a large number of tillers were present that had survived the subzero winter intact. In contrast, other species (Prunus sibirica, Potentilla spp. Aneurolepidium chinense [Leymus chinensis]) produced up to 500 kg ha-1 biomass in early spring. A relationship between temperature and green weight (wt) tiller-1 indicated that Cleistogenes required an average air temperature >20°C to initiate growth, most probably due to its C4 photosynthetic pathway. In this region, temperatures above 20°C also coincide with periods of most reliable rainfall, which may explain the success of Cleistogenes in grassland degraded by overgrazing. In contrast, competing C3 species (e.g. Stipa spp. and Aneurolepidium chinense) initiate growth earlier in spring when rainfall is highly variable and when small plants are most exposed to severe grazing pressure by livestock emerging from winter in poor condition. Where Cleistogenes spp. completely dominated the grassland, the length of the growing season was shorter and feed shortages in early spring became more acute than for grasslands dominated by C3 species. Livestock producers can minimize this effect by adopting management tactics such as resting pastures in spring to maintain a balance between C3 and C4 perennial grasses. Further research is needed to establish when grazing and strategic rest have most impact on the stability of Cleistogenes-dominant grasslands.