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Abstract
Grazing disturbs grassland environment through gnawing and treading of livestock, which changes species composition. This study showed that the species richness in communities gradually decreased with the aggravating of grazing intensity from saline-moist meadows to typical steppe communities. The measurement of β-diversity showed that on saline-moist meadows, the intermediate disturbance of species change occurred during the course of light to moderate grazing stage, with a low stability during the whole grazing; while on meadow steppes and typical steppes, it occurred during the course of moderate to heavy grazing stage. Desert steppe showed a high stability throughout grazing system, and the species change from light to over grazing was only 1~3. The stability of grassland community diversity was as follows: desert steppe>typical steppe≥meadow steppe>saline-moist meadow.
... β-Diversity, which indicates the turnover rate of species composition along environmental gradients (Whittaker, 1960), also exhibited a pattern of increase followed by a gradual decrease with rising pika disturbance intensity. The β-diversity index reached its peak at 710 effective openings per hectare, highlighting that pika-induced disturbance can alter species turnover rates and enhance habitat heterogeneity (Li et al., 2021;Yang et al., 1999). These findings underscore the complex role of pika disturbance in shaping plant community diversity. ...
Plateau Pika (Ochotona curzoniae), a key species on the Qinghai-Tibetan Plateau, along with its ecological impact, has been paid extensive attention to. This paper aims to comprehensively assess the ecological impact of pika on vegetation, soil and biodiversity in the Qinghai-Tibet Plateau. Through the review of previous studies, it was found that the foraging behavior of Plateau Pika affected plant community structure and diversity, which decreased plant evenness but increased species richness. Its activities changed soil organic matter, microbial community and greenhouse gas emissions. In terms of animal diversity, it is a food source for many predators and is interdependent with some symbiotic other animals. However, considering pika’s competitiveness with domestic animals for food, population control should be implemented. In order to maintain the ecosystem balance and biodiversity on the Qinghai-Tibet Plateau, self-transmitted contraception control, increasing the planting of non-eating vegetation and controlling the number of livestock and grazing intensity, instead of traditional poisoning method, can be adopted.
... Stocking rate clearly has significant effects, although some relationships are still poorly understood, on plant species diversity, evenness of grazing, productivity and stability of the steppes. Richness and evenness of steppe communities are improved by moderate grazing but reduced by heavy grazing in meadow steppes (Li and Wang 1996;Yang et al. 1999). Although these relationships apply in short-term studies, longer term effects need investigation. ...
Native grassland in China is mostly meadow, typical or desert steppe and comprises 400 million hectares, ∼40% of the land area. We review past research on the meadow steppe of north-east China. Our foci are plant adaptation to climate, edaphic-related and defoliation stresses, vegetation production, grassland management, herbivore foraging behaviour, safe stocking rates, plant-animal interactions, ecosystem functioning, conservation of biodiversity and the influence of climate change on grassland function. Recent studies have provided some insights into ecological processes and functioning of meadow steppe, and have enabled better identification of research opportunities. Key areas identified for future research include plant adaptation, grassland function and value, monitoring of range health, ecological consequences of climate change on biodiversity and ecosystem function.
The grasslands at the northern foot of the Yinshan Mountains are an integral component of the northern grassland ecosystem in China. The ecosystem in this region has low stability and poor resistance to disturbance. In this study, experiments were conducted to evaluate the possible changes in vegetation community structure and soil physicochemical properties due to overgrazing in the grasslands. Completely randomized group experiments were designed with grazing intensity as the single-factor study was conducted using natural grassland located in Xilamuren (in Inner Mongolia, northern China) as the study area. Three blocks were created, each having four plots of different grazing intensities and each block having an area of 100 m × 100 m. The experiments were conducted to evaluate the possible variances both in the structure of the vegetation community and the soil physicochemical properties resulting from overgrazing in the grasslands at the northern foot of Yinshan Mountain. The results were as follows: The importance values of dominant species, such as Heteropappus altaicus and Artimisia gmelinii, exhibited varying degrees of change with an increase in the grazing intensity. The surface vegetation cover decreased significantly with an increase in the grazing intensity. The increasing grazing intensity led to a significant increase in the content of very coarse sand grains in the soil. Severe grazing increased the exposed surface area, intensified the effects of blowing wind and scouring action of water, and led to the coarsening of topsoil particles. At 0–5 cm depth, the bulk density of soil exhibited an increasing tendency with an increase in the grazing intensity. The organic matter content of the soil in the heavily grazed plots decreased by 11.74%, 11.00%, and 14.08%, respectively, when compared to that in the 0–40 cm soil layer with no grazing, light grazing, and moderate grazing. The results emphasized the importance of managing grazing intensity for soil and vegetation restoration. Thus, the effects of short-term grazing (for example, 5 years) on vegetation community composition and species diversity may be less pronounced. This study contributes to our understanding of pasture management and the restoration of grassland species diversity.
Background
Due to the effects of climate change and overgrazing in recent decades, alternative stable states in the alpine Kobresia meadow degradation process have coexisted in the same geographical and climatic environment, with variations occurring among microsites.
Methods
We used a space‐for‐time substitution approach to explore the synergies of microsite variation according to its numerical characteristics and the proportion of each stable state at various stages of succession in alpine Kobresia meadows on the Qinghai–Tibetan Plateau.
Results
(1) The highest average aboveground biomass in summer was 196.2 ± 20.3 g m ⁻² , with significantly higher levels of biomass in ≤3.65 sheep unit ha ⁻¹ than in other levels of grazing intensity, while the parameters showed no significant differences among grazing intensity levels in >3.65 sheep unit ha ⁻¹ . (2) The importance of plant functional groups, aboveground biomass, and niche breadth of Poaceae and Cyperaceae significantly decreased as the grazing intensity increased. (3) The effects of ≥0°C accumulated temperature, total precipitation, altitude, longitude, and latitude cumulatively contributed less than 20% of the variation in the distribution of functional group characteristics across microsites.
Conclusions
(1) Overgrazing decreases primary production in alpine Kobresia meadows, but ecosystem responses regulate plant community structure and botanical components so as to partially counteract grazing disturbance. (2) Overgrazing changed the proportion of microsites, which in turn led to regime shift in the plant community and subsequent synergies between the microsites of plant communities and their stable states.
The Altai Mountain is located at the intersection of cold and arid regions. Climate change and overgrazing directly affect the growth of the grassland ecosystem in this region. This study took the grassland community in the Burqin forest area of the Altai Mountains as an example to analyze the species diversity and productivity of different grassland types based on 50 sampling plots. The relationship between species diversity and the productivity of grassland types at different altitudes was also discussed. The results showed that: (1) In the Burqin forest area, the desert steppe was dominated by Gramineae, Compositae, and Leguminosae. Montane steppe and mountain meadows were dominated by Umbelliferae, Gramineae, and Liliaceae. Gramineae, Ranunculaceae, and Liliaceae were the dominant families in both montane meadows steppe and alpine steppe but occurred in varying proportions. (2) The variation in plant numbers at the family–species level was characterized as montane steppe > alpine meadow > montane meadow steppe > desert steppe > mountain meadows. (3) The similarity in species composition among communities of different grassland types was low. In DS and MM, the number of grasslands and species played a decisive role in determining the biomass. The biomass of MS and AM was determined using the Simpson and Shannon–Wiener indices, and the number of dominant species determined the biomass. The number of grasslands and species did not have a significant impact on the biomass of MMS, which may be due to human factors such as grazing. (4) The dominant species in the grassland at an altitude of 1200–1400 m is prominent. The number of individuals in the dominant species was large and evenly distributed. Margalef peaked at an altitude of 1600–1800 m, but the number of individuals was small, resulting in low biomass and diversity in this range. Most plants survive at an altitude of 2000–2200 m; therefore, in grassland protection and planning management, it is important to consider the specific situation of plant growth under different habitats at different altitudes and make reasonable protection decisions based on local conditions to maintain species diversity and sustainable development of grassland ecosystems. This study provides basic data to support the theoretical basis for the protection and sustainable utilization of grassland resources and the restoration of degraded grasslands in the study region.
Kobresia meadows are the main pastures for animal husbandry on the Qinghai–Tibet Plateau, and may represent alternative steady states associated with different grazing intensities. The ability of other plant communities to succeed these meadows remains unclear. In this study, the historical data of plant communities were analyzed in terms of the soil profile, and the present characteristics were identified by investigating their plant communities. Four types of steady states were identified, corresponding to grazing intensities of >11, 8–11, 5.5–8, and < 5.5 sheep/ha. Drought alpine swamp meadows and shrub meadows could succeed to K. pygmaea meadows and K. humilis meadows under overgrazing, and their total biomass and edible biomass (estimated by Gramineae and Cyperaceae) decreased with increasing grazing intensity. The regime shift of the states occurred at a grazing intensity of 8–11 sheep/ha. This value thus represented the threshold of significant change in the production and ecological service function in the Kobresia meadow succession process. In general, increasing grazing intensities can adversely affect the service ability of meadows for livestock production and ecosystem stabilization. This study revealed the potential degraded succession process of the alpine Kobresia meadow and the succession direction in the restoration process of degraded meadows. Additionally, this study provided a theoretical basis for evaluating the fitness between the livestock bearing capacity and carrying capacity in steady states and academic reference for policy setting pertaining to the utilization of Kobresia meadows in a sustainable development framework.
The relationships between vegetation and environmental factors have always been a core concern of ecologists. The dynamic characteristics of plant communities during the growing season can directly reflect these relationships , so we examined this issue for three typical ecosystems on the Tibetan Plateau. During the growing season, the dominant species remained stable while non-dominant species changed significantly in the alpine meadow and alpine steppe and a mono-dominant community was found in the temperate desert shrub. Due to the seasonal variations of temperature and soil water content, plant species diversity varied significantly during the growing season. Patrick richness, Pielou evenness and Simpson diversity indices differed significantly in the alpine meadow and alpine steppe. The total biomass of these three ecosystems was the largest during the middle growing season. Biomass was greater in the alpine meadow than the alpine steeps or temperature desert. The root-to-shoot ratio was the lowest during the middle growing season for the alpine meadow and alpine steppe and largest during the early growing season for temperate desert shrub. RDA showed the belowground and total biomasses were greatly affected by soil physicochemical factors. Multiple linear stepwise regression showed the above ground biomass was greatly affected by relative atmospheric humidity and belowground and total biomass were greatly affected by soil organic carbon, total nitrogen at 0-20 cm soil depth and pH at 10-20 cm soil depth. These findings provided insights into understanding the relationships between vegetation and environmental factors and to promote sustainable utilization of local grasslands on the Tibetan Plateau.
It is important research fields of global change ecology to study the influence that global climate change has on ecosystem and agroforestry, environmental factor such as water resources. And it is also important scientific basis on which to cope with climate change
, to manage ecosystem adaptively and to make relevant policies. If the change of the earth system’s strength power is the ultimate concern of global climate change study, it will be to focus on questions to recognize the change of ecosystem’s structure, process, and function motivated by climate change and human activities. The earth feeds on massive diverse natural ecosystem, and diverse semi-natural semi-artificial ecosystem, which is already a result of a long-term adaption of the earth to natural environment and human activities. In that case, the adaption research of the ecosystem to the environment change plays a key role in humans getting to know what influence global changes may have on the supporting capacity of earth system. This chapter mainly concerns about the ecosystem’s adaptability. It is defined as the adaptive abilities of lowering environment changes’ negative influence and making good use of favorable opportunities when environment changes but the ecosystem tries to maintain its main functions. And this balance mechanism and adaptability of ecosystem is a basis on which to judge the influence degrees of global changes on ecosystem’s structure and function. To dig into this question, we generally study from two different perspectives, one of which is global changes’ influence on the ecosystem, and the other one is the ecosystem’s responses to these changes, which is the principal framework of this chapter.
This study was conducted in four different habitats of the Alax desert of Inner Mongolia including a grazing-prohibited site, a rotational-grazing site, an over-grazing site and farmland. Rodent communities were sampled using snaptraps for a single day each month during April, July and October from 2002 to 2010, and beta diversity of rodent communities in the different habitats was analyzed. The characteristics of shrub communities also were analyzed to investigate landscape fragmentation under different disturbance conditions. The variation of the four habitats along with gradient were divided into six classes based on the amount of landscape fragmentation. The Jaccard's diversity index, Sorenson's diversity index and Cody diversity index were used to analyze the variation in the beta diversity of the rodent communities. The results showed that the three beta diversity indices differed significantly among all gradients between habitats (P<0.05), and the variance was the most obvious between grazing-prohibited areas and the over-grazing site in the gradient. The Shannon-Wiener index, Simpson index and the species number in the shrub communities were significantly different among studies sites (P<0.01), and showed the following trends: rotational-grazing site>over-grazing site>grazing-prohibited site>farmland. The region was considered a fragmented landscape if the degree of variation for environment conditions and the beta diversity was similar. In addition, the main reason for the landscape fragmentation in the region was the human-caused disturbance, particularly the grazing activities, which drove the heterogeneity of environment significantly. The beta diversity increase along with the increase of environment gradient lead to heterogeneity, which was caused by the increase in difference and variation of the species composition between rodent communities rather than the increase of species in arid desert region.
Structure and biodiversity of herbages were examined using the both transects and quadrats along topographical gradients on both shade and sunny slopes at the core zone of Three Rivers Sources Nature Protection Area. The relationships among richness index, diversity index and environmental factors (altitude, bare patch, slope, soil total carbon, soil total nitrogen, soil pH, soil total dissolved salt), disturbance intensity (rodent destroying and livestock grazing) were analyzed by factor analysis and partial correlation analysis. The results showed that the Margalef richness index of forbs had significant (P<0.01) correlation with the Margalef richness index of all species; the Margalef richness index for this two functional groups presented a peak with higher species diversity index in the communities of middle elevation on the sunny side; there was a positive correlation between the Margalef richness index of forbs and all species and altitude gradient on the shade slope. With the increase of altitude, there was not distinct change on Margalef richness index of grasses and sedges. According to the results of Factor Analysis (FA) and Partial Correlation, the First principal component, including soil patch, rodent disturbance and grazing intensity, significantly affected most of the biodiversity index of total species, except Margalef richness index of Cyperaceae, Simpson index of Gramineae and Pielou evenness index of Gramineae. So, the main factors influenced the diversity of all herbages on the sunny slope were soil patch, rodent disturbance and grazing intensity. Soil total carbon and nitrogen had significant effect on the diversity index and evenness index of grassed on the sunny slope. soil pH, total dissolves salt gathered with slope greatly influenced the richness index of sedges on the sunny slope. Altitude, soil total carbon and nitrogen, soil pH all had major effect on species diversity on the shade slope. The conclusions are that the spatial heterogeneity of species diversity resulted from the interaction of geographical environment (altitude, bare patch, slope), soil condition (soil total carbon, soil total nitrogen, soil pH, soil total dissolved salt) and disturbance intensity (rodent destroying and livestock grazing). At the small scale along the altitude gradient, the effect of the environment factor does not have significant effect on species diversity. Soil circumstance was the main Influencing factor for altering species diversity under no-disturbance or slight disturbance. Under heavy disturbance, intensity of disturbance had more significant influence on species richness and diversity than environmental factors. Reducing the heavy disturb such as grazing and rodent destroy was the first choice for preventing the degradation of alpine grassland and loss of herbage diversity in the alpine region.
Swamp in the Zoige Plateau which was one of the five main pasture regions in China has been threatened by over- grazing for decades ever since 1960s. In this paper, typical degraded swamp was selected to figure out the main characteristics and critical influence factors under the stress of grazing. On the basis of its water,vegetation and soil information, the degraded swamp was classified into five stages, namely:primary swamp, lightly degradation, moderate degradation, severe degradation and extreme degradation. The degradation characteristics and their influence forces were discussed in this paper. The main characteristics of the degraded swamp water were: (1) TN was higher than normal, (2) TN, NO -3, TP, alkaline and the total dissolved solids increased along the degraded gradient,(3)the pH of water is between 8 to 9,(4) HCO -3 is the main contributor to the alkaline. The main changes of the degraded swamp vegetation were: (1) an increase of overall species abundance,(2) a decrease in the important values of helophyte, (3) an increase in the important values of mesophyte, (4) Potentilla ansrina replaced Carex muliensis and C. meyeriana as a dominant species in the community. By comparing the similarity between the communities of different degraded swamps,it was found that the rates of vegetation succession decreased along the swamp degraded gradient. The main changes of the degraded swamp soil along the degraded gradient were: (1)a decrease of soil water content, porosity, TN,(2)an increase of bulk density, TP, TK. The vertical changes of different nutrient contents in the soil profile of degraded swamps were complicated. On the whole, the content of TN and TP decreased along the soil depth gradient,and with the increase of depth,the influence of grazing on the content of TP decreased. In order to find out the main influence factors of swamp degradation under grazing, Principle components analysis (PCA) was employed in this paper. Five vegetation variables,eight water variables and six soil variables involved in PCA were simplified into three components which explained 50. 77%, 30. 50% and 16. 72% of the total variables respectively. There was a significant positive relationship between PC1 and Shannon-Weiner index, the importance value of mesophyte as well as the total phosphorus content of soil and a negative relationship between PC1 and importance value of helophyte, Simpons index, water content as well as total nitrogen content of soil. The significant negative relationship between PC2 and pH of water was also observed. Principle components analysis indicated that water physical properties and nutrient of soil were the main driving factors that caused the swamp degradation in the Zoige Plateau. As the nineteen variables changed obviously along the degradation gradient,they were tried to be used to indicate the degree of swamp degradation. According to the three principle components gaining from PCA, a multiple linear regression model was developed based on the three factor scores which could be used to calculate the score of every kind of degraded swamp and it turned out to be useful in degraded swamp classification.
Artemisia frigida communities on Chinese Inner Mongolia steppe have been grazed by sheep in enclosures for thirteen years under four grazing intensities: zero-grazing (0.00 sheep/hm2), light-grazing (1.33 sheep/hm 2), medium-grazing (4.00 sheep/hm2), and heavy grazing (6.67 sheep/hm2). The plant biodiversity was investigated from July to August in 2002. The results showed that: (1) Under zero grazing, the vegetation density was significantly less than that under light, medium or heavy grazing. The difference of the vegetation density was not significant among the latter three grazing treatments. (2) After thirteen years, the dominant plant became Aneurolepidium chinense under zero grazing, but still was A. frigida under light and medium grazing. However, the population density of Carex duriuscula was largest under above three grazing treatments. Under heavy grazing, Potentilla acaulis became dominant and its population density was largest in the community. With grazing intensities increasing, the population density of indicators of the grassland degradation in different degraded phases first increased, and then decreased for A. frigida, while first sharply increased, then gradually increased, finally sharply increased again for P. acaulis. (3) Diversity and evenness indices were largest under medium grazing, but smallest under zero grazing, which showed that the plant diversity was highest under medium grazing, but lowest under zero grazing. Dominant indices were contrary to the above two indices. Community structure and plant diversity were controlled by the integrated influence of selective browsing of sheep, adaptive strategies of different plants to grazing, interspecific competition, co-evolution between animal and plant and physical and chemical characteristics of the soil changed by grazing. These findings were contributed to provide an insight into the successive theory of the degraded grassland under the continuous disturbance of grazing and provide a theoretical foundation for the protection and restoration of the degraded grassland.
Because ofthe remoteness and harsh conditions of the high-altitude rangelands on the eastern Tibetan Plateau, the relationship between yak grazing and plant diversity has not been so clear although livestock increase was thought as the main issue leading to the degradation of rangeland. In the debate of rangeland degradation, biodiversity loss has been assumed as one of the indicators in the last two decades. In this paper authors measured the effects of different grazing intensities on the plant diversity and the structure of Kobresia pygmaea community in the case-study area, northwestern Sichuan. The results indicated that plant diversity of alpine meadow has different changing trends respectively with the change of grazing intensity and seasons. In June the highest plant diversity occurred in the intensively grazed (HG) plots, but in July and September species biodiversity index of slightly grazed (LG) plots is higher than other experimental treatments. In August the intermediate grazed (IG) plots has the highest biodiversity index. Moreover, it was found that intensively grazing always leads to the increase of plant density, but meanwhile the decrease of community height, coverage and biomass. Over-grazing can change the community structure and lead to the succession from Kobresia pygmaea dominated community to Poa pratensis dominated. Analyzing results comprehensively, it can be suggested that the relationship between grazing intensity and plant diversity is not linear, i.e. diversity index is not as good as other characteristics of community structure to evaluate rangeland degradation on the high altitude situation. The change of biodiversity is so complicated that it can not be explained with the simple corresponding causality.
The invasive Leymus racemosus species is mainly established by ramets (or clonal seedling). A field experiment was conducted in the spring of 2004 to investigate the effects on the surface soil temperature caused by mowing, grazing and grazing exclusion, and the influence of these factors on the ramets emergence characteristics. The primary effect of the treatments was significant changes in soil temperature in the grazing plots due to the mulch cover which was removed by sheep, keeping the daily mean soil temperature above 0 degrees C during the period of the experiment. Grazing had positive impacts on the emergence of ramets, and their final cumulative emergence in the grazing plot significantly increased by 77 and 59% when compared to that in the grazing-exclusion and mowing plots. A linear function model was used to describe the correlation between the cumulative ramets emergence percentage and soil thermal time (theta(T)). Variation in theta(T) explained 98% of the observed variation in cumulative emergence; there were no significant differences in the soil thermal requirements for final ramets emergence completion for the other treatments. Both mowing and grazing exclusion had a significant effect on the invasive L. racemosus species ramets recruitment control.
The diversity of a degraded grassland community on the Chinese Inner Mongolia steppe dominated by Artemisia frigida (Asteraceae) subject to a range of grazing treatments (zero, and light, medium and heavy grazing) for 13 years was studied from July to August 2002. Under zero grazing, percentage total vegetation cover was significantly (P < 0.05) less than under light, medium, and heavy grazing. Although not dominant in any treatments, percentage cover of Carex duriuscula (Cyperaceae) was higher than other species in the zero, light, and medium grazed treatments. Its cover tended to decline as grazing intensity increased (P = 0.49). Aneurolepidium chinense (Poaceae) reasserted its dominant status in the zero grazed grassland; A. frigida remained dominant under light and medium grazing. Under heavy grazing, Potentilla acaulis (Rosaceae) was the dominant species and it provided the highest percentage cover. Zero and heavy grazing resulted in fewer (three‐four) species contributing most of the total cover (cf. six‐seven species for light and medium grazing). This was reflected by indices of diversity and evenness, which were highest for light and medium grazing. The Simpson Dominance Index was highest for the zero and heavily grazed treatments, indicating that at the extremes of the grazing spectrum, single species tended to exclude potential co‐dominants more effectively than at intermediate levels of grazing. Selective grazing was a key process. Grazing increased the proportion of unpalatable and grazing resistant species, and species that although palatable, were relatively inconspicuous. These findings are discussed in terms of their impact on the productivity and long sustainability of grazing. The need to develop a better understanding of underlying processes, and more sustainable forms of grazing management are highlighted.
Four typical successional series in the marsh communities of Sanjiang Plain were selected to investigate the changes of their beta diversity. The results indicated that from the 'starting community' to the 'end community', which had the most and the least moisture level in the series, respectively, the similarity coefficient between each community and 'starting' community decreased with decreasing moisture gradient and increasing horizontal distance. The species turnover speed among the communities in each series had an increasing trend from lowland to upland. In the process of succession, the general trend was that the total number of plant species increased while the common species decreased, with the beta diversity between communities increased gradually. The analysis of succession mechanism supported the 'initial floristics composition hypothesis', and the plant Calamagrostis angustifolia would intensify its dominance in the mash of Sanjiang Plain.
This paper presented the characteristics of the vegetation, soil, and their coupling in the gradient of grazing pressure of the degraded alpine grassland in Sunan county and of the typical arid grassland in Huanxian county, Gansu province. The abundance index of species, Simpson index, Shannon-Wiener index, Cody index, nutrient functional diversity index and life type diversity index increased, while the Bray-Curtis index and nitrogen fixation diversity index decreased with the reduced grazing intensity in both types of degraded grassland. With reduced grazing pressure, the contents of total nitrogen, available nitrogen and organic matter in both grasslands and the content of available phosphorus in arid grassland at 0-40 cm soil depth were increased, and that of total phosphorus in alpine grassland was decreased, while phosphorus concentration in arid grassland showed no regular pattern of change. The total and available nitrogen, available phosphorus and the ratio of available phosphorus to total phosphorus and of organic carbon to nitrogen were all higher in alpine grassland than in arid grassland. The grey correlativity of vertical distribution pattern between soil elements and living root biomass was positively related to grazing pressure, while the coupling intensity of soil-herbage subsystem was increased with decreased grazing pressure. There existed a significant correlation between poor soil elements and abundance of poisonous and poor-nutritional plants in both degraded grasslands. The degradation process of grassland resulted not only from the degeneration of vegetation and soil subsystems, but also from the disappearance of coupling between both subsystems and the development of their discordance. The ecological process could be quantified by coupling intensity and discordance intensity. It is concluded that the studied arid grassland was degraded more seriously than alpine grassland.
Human activities have a major impact on the biodiversity of the earth, while biodiversity change is considered as an important global change in its own right. Elm sparse woods is a climax community distributed on the sandland in temperate steppe zone. Its habitat conditions are much more fragile, and are easily destroyed. Our studies on the effect of human activities on soil environment and plant diversity showed that the main soil environmental factors and plant species diversity had some obvious changes, of which, the changes of man-made pine woods and heavy grazing disturbance were the largest, and the of man-made poplar woods were the in those next place. It is suggested that natural laws and consistency of ecosystem processes in the low and long temporal scale should be considered adequately in the environment management of sandland.
This study on the size and composition of seed bank and its relationship with vegetation showed in Keerqin meadow grassland, the density of soil seed bank was 6158 +/- 1647 grains x m(-2) under grazing and 8312 +/- 2540 grains m(-2) under harvesting. Under grazing, the seed bank was mainly composed of some dwarf and short-life annuals. The seeds of the annuals and biennials accounted for 81.66% of the seeds in seed bank. The four species with largest proportion of seed bank were Chloris virgata, Chenopodium glaucum, Digitaria cilliaris and Setaria viridis, and the proportions were 38.55%, 15.42%, 14.95%, and 9.83%, respectively. The density of perennials in soil seed bank was 1129 +/- 302 grains x m(-2). Under harvesting, the seeds of annuals and biennials accounted for 68.08% of the seed in seed bank, and the proportion of Setaria viridis was 52.7%. In the harvesting meadow grassland, the seed density of perennials was 2653 +/- 811 grains x m(-2). There was no significant correlation between the seed density in soil and the vegetation under grazing, but a significant correlation between the seed density in soil and the species abundance of vegetation under harvesting (r = 0.76, P < 0.01). The index of Shannon-Wiener and richness of grazing meadow grassland were 2.96 and 2.98, respectively, distinctly smaller than 3.10 and 5.09 of harvesting meadow, which showed that free grazing made the diversity of seed bank decrease easily.
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