The landscapes of Inner Mongolia are widely known for the vast Stipa krylovii steppes. However, overgrazing and other improper land uses have extensively degraded the Stipa krylovii steppe ecosystem in recent decades. Knowledge about the soil seed banks and the remaining vegetation in these damaged ecosystems is crucial for guiding all future restoration efforts. Using a germination method, this project sought to examine the size, composition, and species richness of the soil seed banks in three ï¬eld types: overgrazed steppe, enclosed steppe and abandoned crop ï¬eld. It was found that the abandoned crop ï¬eld had the largest soil seed bank with mostly annual and weedy plant species. Seeds of desirable perennial grass species were impoverished by the intensive cultivation in the abandoned crop ï¬eld. The lack of desirable perennial species in the abandoned ï¬eld was a critical limiting factor for restoration. Grazing decreased the size of the seed bank in the overgrazed steppe. But seeds of desirable grassland species were present in both the overgrazed and the enclosed steppes. As indicated by the Sorenson’s indices of community similarity (50 – 67%), plant species abundance and composition in the soil seed banks were closely related to the corresponding vegetation for each of the three sites.
Country or Territory:
Grasslands & Savannas - Temperate
Primary Causes of DegradationAgriculture & Livestock
The primary factors degrading the ecosystem has been overgrazing, expansion of crop cultivation, and hasty development, combined with possible climate change, which has resulted in a fast decline of the original ecosystems, severe soil erosion, and more frequent sandstorms. Because of overgrazing and indiscriminate cultivation in recent decades about 60% of the land has become severely degraded. Most of the steppe has been used for livestock grazing for centuries. The grazing intensity has increased substantially during the past decades. Livestock grazing has been stopped in the enclosed steppe since the year 2001. The old crop ï¬eld was abandoned in 2001, before which wheat and oats were the main crops.
Reference Ecosystem DescriptionThe landscape is steppe, woodland and cropland. The steppe is dominated by the perennial bunch grass, Stipa krylovii, with is the major vegetation type in the region. The vegetation of Stipa krylovii steppe mainly consists of Stipa krylovii, Artemisia sieversiana, Artemisia frigida, Agropyron cristatum, Allium bidentatum and Salsola collina.
Due to the increasing desertification and degraded nature of the project lands, the project sought to establish the condition of the soil seed banks as a precondition for further restoration interventions. The project was motivated by the understanding that any restoration required a more complete picture of the conditions at the site in order to guide and inform future efforts.
The project does not have a monitoring plan.
The Chinese government decided to ban grazing and cultivation on most of the degraded land, hoping for natural recovery. However, because it was unknown what an acceptable speed for the recovery process would be active ecological restoration studies were encouraged to evaluate what might be necessary to accelerate that process.
Description of Project Activities:
Soil seed bank sampling was performed at the end of March, 2004, just prior to natural germination of seeds. Four 20 x 20 sq m -plots were chosen at each of the three ï¬eld types. Sixteen soil cores (6 cm in diameter) were sampled randomly to a depth of 5 cm from each plot. Seed banks were determined using a germination method, which is a commonly used and convenient approach for the ï¬eld survey of soil seed banks. After removing gravels, litter and roots, the soil sample from each soil core was spread to form a thin layer (about 2 cm) over a thick layer of seed-free sand in a nursery pot. Three other pots ï¬lled with only seed-free sand were used as controls to monitor the occurrence of airborne seeds. The sand used in the germination test was pre-baked for 4 h at 150 C in the oven. All pots were randomly arranged in a glasshouse (temperature ranging between 12 and 22C) and allowed to germinate under natural light conditions. All pots were watered once or twice daily to keep the surface moist. As seedlings emerged, they were identiï¬ed and then removed from the pots, while those that could not be identiï¬ed were further transplanted to other pots and kept growing until they could be identiï¬ed. Soil in each pot was mixed once every 2 weeks to maximize possible germination. Germination trials lasted for approximately 4 months. Vegetation was investigated twice by recording the species present in eight 0.5 m x 0.5 m- quadrats randomly located in each ï¬eld types. The ï¬rst survey was conducted on 30 May, 2004 when the steppe plants were still in vegetative growth, and the second was on 4 August when steppe plants were at their reproductive stage.
Ecological Outcomes Achieved
Eliminate existing threats to the ecosystem:
No seedlings were found in the control pots, indicating that there were no airborne seed contaminants. Altogether 3276 seedlings belonging to 34 species were germinated, which resulted in a calculated mean of 6035 seeds per sq m. The largest seed bank was found in the abandoned ï¬eld, the smallest seed bank was found in the grazed steppe, and intermediate in the enclosed steppe. Annual grasses only found in the soil seed bank of the abandoned ï¬eld. Annual forbs dominated in the abandoned ï¬eld soil seed bank. Perennial grasses occurred more in the soil seed bank of grazed steppe and enclosed steppe, and perennial forbs occurred more in the enclosed steppe soil seed bank. The number of species was the largest in soil samples from the abandoned ï¬eld, intermediate in the enclosed steppe, and the lowest in soils from the grazed steppe. Perennial forbs and perennial grasses dominated in the soil seed banks of both the enclosed steppe and the grazed steppe, while annual forbs and annual grasses were present almost exclusively in the abandoned ï¬eld soil seed bank. Comparisons of the species similarity between the seed bank and the vegetation for the three sites were made by employing Sorenson's index for community similarity. The species similarity indices between the soil seed bank and the established vegetation in the three sites ranged from 50% to about 67%. The dominant species in the soil seed bank of the abandoned ï¬eld were Artemisia sieversiana, Polygonum divaricatum and Chenopodium aristatum, accounting for 68.1% of the total seedlings for the site, while in the grazed steppe and the enclosed steppe the most abundant species were Artemisia frigida and Stipa krylovii, accounting for 55.8% and 52.5% of their respective totals. The species composition in the soil seed bank of the abandoned ï¬eld was different from that of both the grazed steppe and the enclosed steppe, only 7 of the 23 species in the soil seed bank of the abandoned ï¬eld were found in that of both the grazed steppe and the enclosed steppe. Artemisia sieversiana, P. divaricatum and C. aristatum, the dominated species in the soil seed bank of the abandoned ï¬eld, were not found in grazed steppe and enclosed steppe. Artemisia frigida and Stipa krylovii were the dominant species in the seed bank of both grazed steppe and enclosed steppe, but no seeds of Artemisia frigida and only 9 seeds of Stipa krylovii were found in the soil seed bank of the abandoned ï¬eld. The grazed steppe and the enclosed steppe were relatively similar in soil seed bank composition, 10 species occurred both in the soil seed bank of grazed steppe and that of enclosed steppe, and the dominated species were the same. The species composition in the soil seed bank of the abandoned ï¬eld is different from that of both the grazed steppe and the enclosed steppe. The seed banks of grassland species have been impoverished by agricultural intensiï¬cation and tend to be replaced by annual and weedy species in the abandoned ï¬eld. Based on these results researchers accepted their working hypothesis-II: stopping grazing in the enclosed ï¬eld increases the overall density and species richness of the soil seed bank as compared to the grazed treatment. The seed bank of Chenopodium glaucum was found to beneï¬t from grazing. Artemisia frigida and Stipa krylovii were abundant, Leymus chinensis and some other desirable species were also presented in the soil seed banks of the grazed steppe and the enclosed steppe, indicating that restoration of this heavily grazed steppe is not seed-limited. Stopping livestock grazing for 3 years increased the number of perennial forbs in the seed bank. After enclosure for 3 years, the vegetation in the enclosed steppe was obviously taller and richer in litter, which was in contrast to the thin and short vegetation in the grazed steppe.
Factors limiting recovery of the ecosystem:
The lack of seeds of desirable perennial grasses has usually been the key factor limiting for restoring diverse grassland communities from an abandoned field. The introduction of desirable species by sowing, seed cutting, and grazing management and some other techniques should be applied to overcome this biotic constraint in the restoration of Stipa krylovii steppe from the abandoned ï¬eld. High proportions of annual forbs in both the soil seed bank and in the vegetation of the abandoned ï¬eld suggest that it is still in the early stage of succession. The lack of seeds of desirable perennial grasses in the abandoned ï¬eld may prevent the restoration of this land back to the original steppe. The impoverishment of desirable grassland species in the soil seed bank has not occurred in the overgrazed steppe. Therefore, the researchers were inclined to partially accept their working hypothesis that the impoverished seed bank in the abandoned ï¬eld limits the restoration of the degraded Stipa krylovii steppe. Compared to the enclosed steppe, we can see the decrease in seed density in the soil seed bank in the grazed steppe.
Socio-Economic & Community Outcomes Achieved
Economic vitality and local livelihoods:
In this project, more plant species were found in the above-ground vegetation than in the soil seed bank for both the enclosed steppe and the grazed steppe. This result indirectly suggested that asexual reproduction was a primary mean of reproduction in the two sites. If this is true for all steppe ecosystems, the preservation of perennial vegetation may play a more important role in grassland recovery than soil seed banks. This further implies that there might a threshold in remaining vegetative storage for natural recovery. Once the remaining vegetative storage for asexual reproduction drops below a certain threshold, natural recovery is severely hindered. Finding this threshold in remaining vegetative storage for reproduction should be an important task for future research. The species composition and the dominant species in the soil seed bank in the grazed steppe are similar to that in the enclosed steppe. This result implies that it might be easier to restore the bunch grass steppe damaged by overgrazing than to restore the abandoned ï¬eld back to the native vegetation status by natural means. For the abandoned ï¬eld, manipulated measures, e.g. reseeding desirable species, cutting and grazing management, etc, will be required to speed up the restoration after a long period of intensive cultivation in the agro-pastoral eco-tone of north China.
Sources and Amounts of Funding
The study was supported by the Innovative Group Project of Natural Science Foundation of China (NSFC:30521002) and the Outstanding Overseas Chinese Scientists Team Program of the Chinese Academy of Sciences.
Zhan, X, L. Li, and W. Cheng. 2007. Restoration of Stipa krylovii steppes in Inner Mongolia of China: Assessment of seed banks and vegetation composition. Journal of Arid Environments, 68: 298-307.