The spatial relationship between salt marsh vegetation patterns,soil elevation and tidal channels using remote sensing at Chongming Dongtan Nature Reserve, China

The analysis of vegetation-environment relationships has always been a study hotspot in ecology. A number of biotic, hydrologic and edaphic factors have great influence on the distribution of macrophytes within salt marsh.Since the exotic species Spartina alterniflora（S. alterniflora） was introduced in 1995, a rapid expansion has occurred at Chongming Dongtan Nature Reserve（CDNR） in the Changjiang（Yangtze） River Estuary, China.Several important vegetation-environment factors including soil elevation, tidal channels density（TCD）,vegetation classification and fractional vegetation cover（FVC） were extracted by remote sensing method combined with field measurement. To ignore the details in interaction between biological and physical process,the relationship between them was discussed at a large scale of the whole saltmarsh. The results showed that Scirpus mariqueter（S. mariqueter） can endure the greatest elevation variance with 0.33 m throughout the marsh in CDNR. But it is dominant in the area less than 2.5 m with the occurrence frequency reaching 98%. S. alterniflora has usually been found on the most elevated soils higher than 3.5 m but has a narrow spatial distribution. The rapid decrease of S. mariqueter can be explained by stronger competitive capacity of S. alterniflora on the high tidal flat. FVC increases with elevation which shows significant correlation with elevation（r=0.30, p〈0.001）. But the frequency distribution of FVC indicates that vegetation is not well developed on both elevated banks near tidal channels from the whole scale mainly due to tidal channel lateral swing and human activities. The significant negative correlation（r=–0.20, p〈0.001） was found between FVC and TCD, which shows vegetation is restricted to grow in higher TCD area corresponding to lower elevation mainly occupied by S. mariqueter communities. The maximum occurrence frequency of this species reaches to 97% at the salt marsh with TCD more than 8 m/m2.

Vegetation patterns and nature reserve construction in an extremely-arid desert in Anxi, NW China's Gansu Province

Anxi County is located in the northwestern part of the Hexi Corridor in Gansu Province and has the sole national level nature reserve of extremely arid desert in China. Phytosociological methods (Braun Blanquet, 1964) are used to classify plant community types in this area. Eleven are distinguished, including six of deserts, four of oases and one transitional type between deserts and oases. Direct gradient analysis(DCA) is employed to correlate the distribution of plant communities to physiogeographic conditions. This study makes clear that water is the most important ecological factor for the distribution of plant species and communities in this area. The effects of water have been demonstrated in different ways. A vegetation gradient from lower altitude to higher altitude in the southern part of the reserve is driven by a precipitation gradient. The effects of the depth of ground water table contribute to the differentiation of vegetation from desert to oasis in the flat area. In a finer scale, the washed gullies have obviously higher species richness and also higher vegetation cover than the surround gobi surfaces, possibly caused by the effects of floods. The vegetation patterns demonstrate that the area of Anxi County is a complete landscape unit. The range of the current nature reserve is not large enough for the purpose of conserving the unique biodiversity in this area.

Effects of shrub-grass patterns on soil detachment and hydraulic parameters of slope in the Pisha sandstone area of Inner Mongolia,China

The characteristics of soil holding capacity for different shrub-grass patterns are important to research the mechanisms regulating vegetation on slopes.The objective of this study was to describe the characteristics and mecha-nisms of soil erosion and hydraulic parameters under differ-ent vegetation patterns in the Pisha sandstone area of Inner Mongolia on lands of 8°slope gradient.We carried out field scouring experiments on five different shrub-grass patterns as treatments,viz no shrubs(GL),shrubs on the upper part of the slope(SU),middle part of the slope(SM)and lower part of the slope(SL).We designated bare slope(BL)as the control.We employed three different water flow rates(15,20,30 L·min^(−1)).Our results showed that the contribution of plant root systems to slope sediment reduction ranged from 64 to 84%.The root systems proved to be the main contributing factor to reduction of erosion by vegetation.The relationship between soil detachment rate,stream flow power,and flow unit stream power under different scouring discharge rates showed that soil detachment declined in rank order as:BL>GL>SU>SM>SL.The SL pat-tern had the lowest soil detachment rate(0.098 g·m^(−2)·s^(−1)),flow stream power(2.371 W·m^(−2)),flow unit stream power(0.165 m·s^(−1))and flow shear stress(16.986 Pa),and proved to be the best erosion combating pattern.The results of decision coefficient and path analysis showed that stream power was the most important hydraulic parameter for describing soil detachment rate.The combination of stream power and shear stress,namely Dr=0.1ω−0.03τ−0.56(R^(2)=0.924),most accurately simulated the soil detachment characteristics on slopes.Our study suggests that the risk of soil ero-sion can be reduced by planting shrub-grass mixes on these slopes.Under the conditions of limited water resources and economy,the benefit of sediment reduction can be maxi-mized by planting shrubbery on the lower parts of slopes.

Response of vegetation restoration to climate change and human activities in Shaanxi-Gansu- Ningxia Region

The ＂Grain for Green Project＂ initiated by the governments since 1999 were the dominant contributors to the vegetation restoration in the agro-pastoral transitional zone of northern China. Climate change and human activities are responsible for the improvement and degradation to a certain degree. In order to monitor the vegetation variations and clarify the causes of rehabilitation in the Shaanxi-Gansu-Ningxia Region, this paper, based on the MODIS-NDVI and climate data during the period of 2000-2009, analyzes the main charac- teristics, spatial-temporal distribution and reasons of vegetation restoration, using methods of linear regression, the Hurst Exponent, standard deviation and other methods. Results are shown as follows. （1） From 2000 to 2009, the NDVI of the study area was improved progres- sively, with a linear tendency being 0.032/10a, faster than the growth of the Three-North Shelter Forest Program （0.007/10a） from 1982 to 2006. （2） The vegetation restoration is characterized by two fast-growing periods, with an ＂S-shaped＂ increasing curve. （3） The largest proportion of the contribution to vegetation restoration was observed in the slightly improved area, followed by the moderate and the significantly improved area; the degraded area is distributed sporadically over southern part of Ningxia Hui Autonomous Region as well as eastern Dingbian of Shaanxi province, Huanxian and Zhengyuan of Gansu province. （4） Climate change and human activities are two driving forces in vegetation restoration; more- over anthropogenic factors such as ＂Grain for Green Project＂ were the main causes leading to an increasing trend of NDVI on local scale. However, its influencing mechanism remains to be further investigated. （5） The Hurst Exponent of NDVI time series shows that the vegetation restoration was sustainable. It is expected that improvement in vegetation cover will expand to the most parts of the region.

Relationship between Remotely Sensed Vegetation Change and Fracture Zones Induced by the 2008 Wenchuan Earthquake, China

The Wenchuan earthquake triggered cascading disasters of landslides and debris flows that caused severe vegetation damage. Fracture zones can affect geodynamics and spatial pattern of vegetation damage. A segment tracing algorithm method was applied for identifying the regional fracture system through lineament extractions from a shaded digital elevation model with 25 m mesh for southern Wenchuan. Remote sensing and geographic information system techniques were used to analyze the spatiotemporal vegetation pattern. The relationship between vegetation type identified from satellite images and lineament density was used to characterize the distribution patterns of each vegetation type according to fracture zones. Broad-leaved forest, mixed forest, and farmland persist in areas with moderate lineament density. Deciduous broad-leaved and coniferous forest persists in less frac- tured areas. Shrub and meadow seem to be relatively evenly distributed across all lineament densities.Meadow, farmland, and shrub persist in the fractured areas. Changes of spatial structure and correlation between vegetation patterns before and after the earthquake were examined using semivariogram analysis of normalized difference vegetation indices derived from Landsat enhanced thematic mapper images. The sill values of the semivariograms show that the spatial heterogeneity of vegetation covers increased after the earthquake. Moreover, the anisotropic behaviors of the semivariograms coincide with the vegetation changes due to the strikes of fracture zones.

Vegetation distribution pattern in the dam areas along middle-low reach of Lancang-Mekong River in Yunnan Province, China

Lancang-Mekong River Basin is one of ecoregions with rich biodiversity and high ecological values in the world. The basin has been strongly affected by human activities, particularly by dam construction. This study was conducted to investigate the vegetation distribution patterns in the dam areas along middle-low reach of the Lancang-Mekong River in Yunnan Province of China, where eight cascade dams have been planned or are being constructed. To identify the vegetation composition and structure, we sampled 126 quadrats along the transects arrayed vertically to both side of river channel from the year of 2004 to 2010. We found that the forest, shrub and grass communities were widely spread along the riverside. In low reach watershed of the Lancang-Mekong River, the dominated vegetations were grasses and shrubs which were severely disturbed by human activity. In middle reach of the Lancang-Mekong River, the dry-hot valley vegetation was found in the low valley. At high altitude, the pine forest and semi-evergreen seasonal forest were found. As a result of dam construction and operation, the structure and compositions of riparian vegetation were strongly changed. Some plants declined or disappeared due to the alteration of their habitats. The protection or restoration interventions are urgently needed to mitigate the risk of vegetation damage associated with dam projects along middle and low reach of the Lancang-Mekong River.

A study on the relationship between vegetation pattern and environment in the upstream of Minjiang River,China

The vegetation pattern in the upstream of Minjiang River,and its relationship with environment factors,such as landscape position(elevation,slope,aspect),precipitation and temperature and soil are analyzed in this paper.The data used in this paper were based on the landscape map derived from 1994 TM imagery.The results were as follows:1)dominant landscape types were forest,shrub land and grassland,which were very similar in terms of area ratio(32.87%,31.85%and 28.44%,respectively);2)the patch shape of conifer forest and mixed forest was complicated while that of broad-leaved forest and cultivated land was simple;3)the fragmentation of conifer forest and mixed forest was serious in contrast with low fragmentation of broad-leaved forest and cultivated land;and 4)closed scrub and grassland had a high contagion and good connectivity while mixed forest had a lower contagion and bad connectivity.In addition,the vegetation distribution pattern of upstream of Minjiang River was closely related with elevation and temperature,but the relationship between vegetation and precipitation was not statistically significant.

Analysis of the contributions of human factors and natural factors affecting the vegetation pattern in coastal wetlands

Introduction:Accurate identification of the dominant factors affecting coastal wetlands can provide a reference for vegetation rehabilitation.In this study,quantitative analysis was performed on the Yancheng coastal wetland using ANOVA and geostatistical methods.Outcomes/other:The results indicated that in the directions perpendicular and parallel to the coastline,the soil moisture and salinity in the study area exhibited relatively significant(p<0.05)spatial variability.Vegetation in the southern experimental zone was in a low-moisture,low-salinity ecological niche,whereas vegetation in the northern experimental zone was in a high-moisture,high-salinity ecological niche.Soil salinity exhibited higher spatial variability than soil moisture,and it was most correlated with unvegetated mudflats,followed by areas with Spartina alterniflora,Suaeda glauca,and Phragmites australis.Discussion:The fitting of the semivariogram showed that the nugget and sill of the ratio were relatively low(<25%)for soil moisture and salinity in the northern experimental zone and northern buffer zone,whereas these values were relatively high(>75%)for soil moisture and salinity in the southern experimental zone and southern buffer zone.Conclusion:Compared with the northern study area,the contribution of human disturbance to the spatial heterogeneity of soil moisture and salinity in the southern study area is higher.

Spatial Variability of Soil Saturated Hydraulic Conductivity in a Small Watershed of Loess Hilly Region,China

Saturated hydraulic conductivity (Ks) is an important soil hydraulic parameter for charactering the rate of water flow across the soils and is mainly related to its high spatial variability. In a small watershed with the area of 0.27 km2 in the Loess Plateau, Ks of 197 soil samples under different vegetations and landforms were measured. Ks had a moderate variability for total samples. The forestland had high Ks with low coefficient of variation (CV), but the grassland in the watershed bottom had low Ks with big CV. Ks had moderate correlation in space distribution and combined both structural and random factors. At the N-S and E-W directions of watershed being parallel and normal to the stream valley, Ks had relatively weak correlation, indicating that the random factor was the dominate reason causing spatial variance. At the NE-SW and SE-NW directions, Ks had relatively strong correlation due to structural factors such as geomorphology and vegetation distribution patterns. Kriging optimal estimation method was used to produce Ks contour map. The Kriging standard deviation (SD) was the lowest near the sampling points, and increased along with the distance to sampling points. In the Loess Plateau region, soil texture is relatively even, and the vegetation distribution pattern was the key factor affecting spatial variability of Ks.