Age Structure of Natural Populations of Sabina vulgaris in the Mu Us Sandy Land
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In this study 4 habitat types(bottomland,bottom,slope and ridge of sand dunes)are classified for researching the age structure and its dynamic change of Sabina vulgaris populations based on the local conditions, such as the groundwater regime and terrain in Mu Us sandy land.The aim of the study is to determine how the different habitats affect the stability and development of S.vulgaris populations.The plant age is determined by measuring the number of growth rings with the WinDENDRO~(TM)analyzing system.Regression equations between the basal diameter and the age of S.vulgaris populations are developed for the selected young and mature plant samples,and then the equations are used for estimating the age of individuals across each plot based on measuring the basal diameters. The results show that the proportion of the younger-aged(less than 10 years)plants growing on the bottomland and the bottom of the sand dunes is as high as 94%of the populations,the age structure is in a typical pyramid pattern,and the populations are in an expansion.On the slope of the sand dunes,the age structure of the plants is cone-shaped,the middle-aged(21 to 30 years old)plants are dominant,and the populations are stable. On the ridge of sand dunes,the S.vulgaris populations are dominated by the mature and old plants(51 to 60 years old),and the age structure of the populations is reverse-pyramid-shaped,indicating the typical ageing populations.Keywords:
Basal area
Sand dune stabilization
Pyramid (geometry)
Age structure
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In order to examine how nematodes respond to sand dune succession after stabilisation and reclamation techniques, nematode communities were investigated in sand dunes stabilised for 0, 16, 26, 43, and 51 years in the Tengger Desert, China. Our results revealed that the abundance of nematodes; the proportion of fungivores, omnivores, and predators; maturity index (MI); Shannon index; evenness; and structure index (SI) were affected significantly by the age of stabilised sand dunes, and were correlated with soil physical and chemical properties to different degrees. There were differences in nematode abundance, the proportion of fungivores, Shannon index, and evenness between the shifting dunes and the stabilised dunes, but not within the different succession stages of the stabilised dunes. MI showed a tendency to increase with dune age and SI increased significantly with dune age. MI, and especially SI, could act as robust indicators of stabilised sand dune succession. Redundancy analysis using data on nematode community composition showed that shifting sand dunes were clearly separated from stabilised sand dunes, and younger sand dunes stabilised for 16 and 26 years were also separated from older dunes stabilised for 43 and 51 years to a lesser degree. The results indicated that changes in nematode communities could predict initial sand dune stabilisation due to the planting of artificial vegetation, and clearly differentiate sand dune succession accompanied by vegetation succession and variation of soil properties.
Sand dune stabilization
Primary succession
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To study the interspecific association of plants in interdune lowland is of significance in understanding the responses of plant species to habitat change and the mechanisms of vegetation succession. Sand stabilization may affect the plant interspecific association in interdune lowland, but relevant reports are scare. In this paper, Chi-square test and association coefficient (AC) were used to analyze the interspecific associations of plants in the interdune lowlands with the areas ranging from 0.10 hm2 to 5.64 hm2 in the mobile and stabilized dunes in eastern Inner Mongolia. When the lowland area was smaller than 0.5 hm2, the percentages of |AC|≤0.3 and |AC|≥0.7 species pairs relative to the overall species pairs were somewhat larger in stabilized dunes than in mobile dunes; but when the lowland area was larger than 0.5 hm2, the percentage of |AC|≤0.3 species pairs relative to the overall species pairs was significantly smaller in stabilized dunes than in mobile dunes fields, while that of |AC|≥0.7 species pairs relative to the overall species pairs was in adverse. Sand stabilization less changed the interspecific association in the interdune lowlands smaller than 0.5 hm2, but made the interspecific association closer in the lowlands lager than 0.5 hm2.
Sand dune stabilization
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By the comparative study of the characteristics,age structure and distribution pattern of Ammopiptanthus mongolicus in three different habitat conditions,we got the results that:1) The average density,height,crown and branches of the natural A.mongolicus growing in sunny slope are higher than that growing in shade side of rocky slope;The average density of the plant which growing in fixed sand is smaller,but due to the effection of wind and sand buried,the number of branches are more.2)The main individual growing in rocky slope are young and stable,but the natural regeneration is difficult,there are little seedlings,lacking of reserve resources will be most likely recession;The main individuals growing in fixed sand are old and has no seedlings,they has been declining significantly.3) The habitat conditions of the plants lead to the distribution pattern.The plants growing in sunny rocky slope and fixed sand appear uniformly distribution,while that in shade side of rocky slope appear cluster distribution.
Steep slope
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A description is given of some of the demographic parameters for three populations of dandelions, one in an upland grassland (300 m) two in a lowland roadside verge (1 m). These latter populations differed in the density of dandelions found per square metre. All three populations were stable during the observational period, but differed greatly in the parameters that combined to give this stability. The chance of a seed producing seedling in the uplands was greater (x 23) than in the lowlands. The fecundity of plants in the lowland site was between 50 and 100 times greater than that in the uplands. Seed production in the lowlands was dominated by a few large plants. This was not the case in the uplands. The population turnover time was longest in the lowland high density site (20.5 years) and shortest in the upland site (15 years).
Population density
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Taking root suckers of Hippophae rhamnoides artificial population as the research object,based on the field investigation of produced number of clones,space distribution and growth condition,basic characteristics of ramet and relationship of environmental factors and root suckers were studied systematically in different habitats in Zhifanggou hilly-gully regions.The results showed that the regeneration of H.rhamnoides depended on asexual propagation.Seedlings from seed germination were rarely in investigation area.The artificial population grew vigorously better on shady slope than that on sunny slope;the number of ramet,horizontal extending area and individual growth,and upper mountain slope were superior to lower slope.Deadwood existed in different habitats,the least was on shady slope(5%),and the most was on sunny slope(20%).5~6 years-old ramet revealed the highest dead rate in among different age classes.Spatial distribution showed that dense distributing area was in the surface soils(2~6 cm).Horizontal extension in up slope could reach 3 m,further than lower slope not more than 1.5 m.The spatial distribution of ramets emergence was effected most by slope position,less by slope direction.Although H.rhamnoides forest posses the capability of self-renewing in hilly and gully region,habitats with enough water and loose soil structure should be the first choice to meet the need of growing and soil and water conservation.
Hippophae rhamnoides
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Sand dune stabilization
Environmental gradient
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Sand dune stabilization
Seral community
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Sand dune stabilization
Population density
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Cirsium pitcheri is a threatened plant species endemic to the shoreline sand dunes of the Greak Lakes. In this study, we attempted to identify some of the environmental factors that may limit the growth, survival, and reproduction of its populations. This species occurs as a minor associate among mixed populations of three dominant grass species, Ammophila breviligulata, Calamovilfa longifolia, and Andropogon scoparius in sandy soil of varying texture (fine, medium, coarse, or shingle). It occupies bare areas within stands of grasses on the first and second sand dune ridges and is prevalent in blowouts. The size class distribution based on the number of leaves per plant showed that the population was dominated by young plants (1–5 leaves) and the relative frequency of juveniles in each successive size class decreased from the smallest to the largest size class. Large juveniles were few in number, which suggests that there was high mortality during the juvenile phase. Seedling mortality in individual plots ranged from 11 to 90% in 1993 and 0 to 70% in 1994. Seed production of its populations was severely reduced because of consumption of whole capitula by white-tailed deer. Transition probabilities indicated that the probability of flowering was dependent on the size of the plant based on the longest leaf length. Keywords: survivorship, deer grazing, transition probability, sand texture, Cirsium pitcheri.
Sand dune stabilization
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