Drought monitoring over India through Normalized Difference Vegetation Index (NDVI)

Normalized Difference Vegetation Index (NDVI) is a simple index to monitor the state of vegetation (stressed/unstressed) which can be derived from satellite data. Hence an attempt is made to find out the vegetation responses to rainfall through NDVI over the study area. Applicability of NDVI in drought monitoring is discussed using the NDVI and rainfall data for the period 1982-2003. The anomaly of NDVI is compared with the percentage departure of rainfall of corresponding years. Results showed a significant relation between the NDVI with the percentage departure of rainfall. The time series plots of averaged NDVI and seasonal rainfall (June-September) are done for NW India (21° N - 31° N, 68° E - 78° E), Central India (22° N - 27° N, 70° E - 77° E) and Peninsular India (16° N - 21° N, 74° E - 79° E) over the period 1982-2003 to analyze changes in vegetation pattern of India during the last two decades. Results indicated a clear linear relationship over NW and Central India. NDVI anomalies and the corresponding cumulative rainfall showed significantly linear correlation of 0.69 over NW India and 0.57 over Central India significant at 1% level but the correlation is found to be insignificant over Peninsular India which was only 0.04. Trend analysis of averaged NDVI over India showed that during last two decades the vegetation status had quite improved over the dry farming tracts of India.

Pattern Dynamics of Vegetation Growth With Saturated Water Absorption

Regular pattern is a typical feature of vegetation distribution and thus it is important to study the law of vegetation evolution in the fields of desertification and environment conservation. The saturated water absorption effect between the soil water and vegetation plays an crucial role in the vegetation patterns in semi-arid regions, yet its influence on vegetation dynamics is largely ignored. In this paper, we pose a vegetation-water model with saturated water absorption effect of vegetation. Our results show that the parameter 1/P, which is conversion coefficient of water absorption, has a great impact on pattern formation of vegetation: with the increase of P, the density of vegetation decrease, and meanwhile it can induce the transition of different patterns structures. In addition, we find that the increase of appropriate precipitation can postpone the time on the phase transition of the vegetation pattern. The obtained results systematically reveal the effect of saturated water absorption on vegetation systems which well enrich the findings in vegetation dynamics and thus may provide some new insights for vegetation protection.

Soil Erosion and Controls in the Slope-Gully System of the Loess Plateau of China: A Review

The Loess Plateau has long been suffering from serious soil erosion of which erosion from the slope-gully system is now dominant. The slope-gully system is characterized with distinctive erosion distribution zones consisting of inner and inter gully areas wherein erosion patterns spatially vary, acting as both sediment source and the dominant sediment and water transport mechanism. In this paper, a substantial body of research is reviewed concentrating on the soil erosion processes and control practices in the slope-gully system. The inner gully area is identified as the main sediment source while runoff and sediment from the inter-gully upland is found to significantly affect down slope erosion processes. Correspondingly, the protective vegetation pattern and coverage should be strategically designed for different erosion zones with an emphasis on the critical vegetation cover and pattern to reduce sediment yield of the whole slope-gully system. Check-dam could change the base level of erosion and reduce the slope length of the gully side, which will further decrease the possibility and magnitude of gravity erosion. We concluded that understanding the erosion processes and implementing erosion practices for the slope-gully system are of importance and require more research efforts that emphasize: 1) the influence of upland runoff on erosion processes at downslope; 2) the relationship between hydraulic characteristics of overland flow and erosion process at a slope-gully system scale; 3) physical mechanisms of different vegetation patterns on the slope-gully erosion process.

Soil moisture in forest island and adjacent ecosystems in Sub-Saharan Region

Forest islands are widely distributed throughout West Africa savanna landscape. Stated as direct outcome of anthropogenic activity, these mosaics are often found around villages and are known for their unique and luxuriant characteristics of tropical rainforest. Althought significant studies focus on their ecology, works on edaphic factors that govern their establishment are very scare. The objective of the current study was to evaluate soil moisture dynamics in forest islands compared to that of surrounding savannas and farmlands at five sites located along a precipation gradient in Burkina Faso. For two years, from 2016 to 2017, soil moisture was monitored at a depth of 0-80 cm using a neutron probe. The results highlighted a seasonal pattern ranging from 42±2% during the heavy rainy month (August) to 16±1% during the dry season (October-November). Significant differences in soil moisture content soil water profile and water stock at depth 0 to 80 cm were recorded between locations and land use patterns. In general, soil moisture was on average 58% less in forest island than in croplands across sites. Soil moisture content was lower in topsoil (0-20 cm) compared to deeper soil (40-80 cm). The Study demonstrated evident link of soil moisture dynamic with rainfall and the vegetation pattern.

Effect of Protection of Mountainous Vegetation against Over-Grazing and Over-Cutting in South Sinai, Egypt

In this study, we evaluated the species diversity, density, cover, and size index of plant species within and outside 37 enclosures in the South Sinai mountainous region (Egypt), which had been protected for six years (March 2012–March 2018) against over-grazing and over-cutting for medicinal and fuel purposes. Within and outside the enclosures, the plant species were recorded, and their density (individuals per 100 m2) and cover (cm per 100 cm) were estimated using the line-intercept method. The biovolume of each individual of each species was calculated as the average of its height and diameter. The species richness was calculated as the average number of species per enclosure, and the species turnover was calculated as the ratio between the total number of species and the species richness. The relative evenness was calculated using the Shannon–Weaver index, whereas the relative concentration of dominance was calculated using the Simpson index. Detrended correspondence analysis (DCA) was applied to ordinate the vegetation inside and outside the enclosures depending on the species cover. The unpaired t-test was applied to assess the statistically significant differences in the species density, cover, and biovolume inside and outside the enclosures. By the end of the six-year period, the vegetation pattern inside the enclosures became more or less stable, presumably because of the stopping of grazing and cutting, which also led to an increase in the plant diversity, density, and cover. In general, the protection of vegetation in South Sinai improved its diversity, density, and cover. In addition, the topographic and physiographic heterogeneity in this region results in microclimatic variations, which play a major role in governing its natural vegetation.

How spatial vegetation distribution affects soil erosion and sediment transport

<p>There are a multitude of factors that affect soil erosion and the process of sediment movement. One particular factor known to have a considerable impact is vegetation coverage within catchment areas.  Previous studies have examined the impact of vegetation cover on erosion. However, there is a lack of research on how the spatial distribution of vegetation influences erosion rates.</p><p>A greater understanding of hillslope erosion is fundamental in modelling previous and future topographic changes under various climate conditions. Here, the physical based erosion model EROSION 3D © is used to evaluate the impact of a variety of vegetation patterns and degrees of vegetation cover on sediment erosion and transport. The model was applied on a natural catchment in La Campana (Central Chile). For this purpose, three different vegetation patterns were created: (i) random distribution, (ii) water-dependent distribution (TWIR) and (iii) banded vegetation pattern distribution. Additional to this, the areas covered by vegetation generated in the first step were expanded by steps of 10% [0...100%]. The Erosion3D © model then was applied on all vegetation patterns and degrees of cover.</p><p>Our results show an initial increase of soil erosion with increasing plant coverage within the catchment up to a certain cover threshold ranging between 10 and 40%. At larger vegetation cover soil erosion rates decline. The strength of increase and decline, as well as the cover-threshold is strongly conditioned by the spatial vegetation pattern. In the light of this, future research should pay particular attention to the properties of the plants and their distribution, not solely on the amount of biomass within catchment areas.</p>

Dominant role of the global monsoon intensity on large-scale Holocene vegetation transitions

<p><span>We give an overview on the global change in mid-to late Holocene vegetation pattern derived from a transient MPI-ESM1.2 simulation and discuss the vegetation trend in the context of the simulated Holocene climate change. The model captures the main trends found in reconstructions. Most prominent are the southward retreat of the northern treeline, coinciding the strong reduction of forest cover in the high northern latitudes during the Holocene, and the vast increase of the Sahara desert that is embedded in a general decrease and equator-ward retreat of the vegetation in the northern hemispheric monsoon margin regions. In contrast, large parts of the extratropical North American continent experience a greening during the Holocene, caused by an increase in forest and grass cover. </span></p><p><span>While the broad forest decline in the high northern latitudes can mainly be explained by the cooling of the warm season climate, precipitation is the driving factor for the tropical and extratropical vegetation trends on the northern hemisphere south of 60°N. The model indicates that most of the changes in rainfall can be related to the weakening of the northern hemispheric monsoon systems and the response of the global atmospheric circulation to this weakening. </span></p><p><span>The southern hemisphere is less affected by changes in total vegetation cover during the last 8000 years, but the monsoon related increase in precipitation and the insolation-induced cooling of the winter climate lead to shifts in the vegetation composition, mainly in between the woody plant functional types (PFTs).</span></p><p><span>The simulated large-scale global vegetation pattern almost linearly follow the subtle, approximately linear orbital forcing. Non-linear and more rapid changes in vegetation cover occur only on a regional level. The most striking area is the western Sahel-Sahara domain that experiences a rapid vegetation decline to a rather desertic state, in line with a strong decrease in moisture availability. The model also indicates rapid shifts in the vegetation composition in some regions in the high northern latitudes, in South Asia and in the monsoon margins of the southern hemisphere. These rapid transitions are mainly triggered by changes in the winter temperatures, which go into, or move out of, the bioclimatic tolerance range of the individual PFTs defined in the model and therefore have to be interpreted differently. </span></p><p><span>In summary, our model results identify the global monsoon system as the key player in Holocene climate and vegetation history and point to a far greater importance of the monsoon systems on the extra-monsoonal regions than previously assumed. </span></p>

Correspondence Between Vegetation Patterns and Soils in Wet and Wet-mesic Grasslands of Hanság and Tóköz (Hungary)

Our research focused on the causes responsible for the fine mosaic pattern of plant associations on wet and wet-mesic meadows. The study area is located in the Little Hungarian Plain, including the former swamp basins of Hanság and Tóköz in Hungary. The vegetation survey data were evaluated by statistical methods (TWINSPAN method), and vegetation maps of the areas were prepared. Topsoil samples near the relevés were gathered for further laboratory tests. Soil profiles were opened by a Pürckhauer soil sampler for on-site description of the soil horizons and classification. Surface models provided a base for the preparation of contour maps that could be compared with the vegetation pattern. We found that of the two dominant vegetation types, mesotrophic wet meadows were associated with Mollic Gleysols, while non-tussock sedge beds were associated with Histic Gleysols. At the transitions of the two soil classes, the subgroup of non-tussock sedge beds is the dominant type. The soil class only determined the plant association on a habitat level, but it could not reason the fine pattern of the plant communities on the same soil class. Canonical correspondence analysis (CCA) was performed to investigate the relationship between the distribution of dominant species and soil parameters. Several soil parameters combined have a significant effect on the distribution of dominant species. In conclusion, we found that the formation of association types strongly depends on the soil characteristics of the area, and that it is closely related to it. However, in the formation of the fine mosaic pattern, the driving ecological factors are the microrelief and the length of the saturated or flooded soil conditions.