Temporal Variation Of Vegetation Research Articles

Characterizing multiscale effects of climatic factors on the temporal variation of vegetation in different climatic regions of China

Vegetation dynamics are sensitive to climatic warming and are affected by individual or combined climatic factors at different temporal scales with different intensities. Previous studies have unraveled the relationships between vegetation dynamics and individual climatic factors; however, it is unclear whether the effects of single or combined climatic factors on vegetation dynamics are dominant for different temporal scales, vegetation types, and climatic regions. The objective of this study was to explore scale-specific univariate and multivariate controls on vegetation over the period 1982–2015 using bivariate wavelet coherence (BWC), multivariate wavelet coherence (MWC), and multidimensional empirical mode decomposition (MEMD). The results indicated that significant vegetation dynamics were located mainly at scales of 1, 0.5, and 0.3 years. Vegetation variations were divided into seasonal (≤ 1 year), short-term (1–4 years), medium-term (4–8 years), and long-term (> 8 years) scales. The combined explanatory powers of seven climatic factors on the vegetation were greater at the short-term and long-term scales, whereas individual climatic factors, such as precipitation or temperature, might affect vegetation dynamics in some climatic regions at the seasonal and medium-term scales. The combined effect of climatic factors in the grassland of the Tibetan Plateau (TP) and the temperate grassland of Inner Mongolia (TGIM) were the greatest, which were 65.06% and 59.53%, respectively. The explanatory powers of climate on crop dynamics in both temperate humid and subhumid Northeast China and the TP were around 47%, whereas the controls of climate on crops in both the TGIM and the temperate and warm-temperate desert of Northwest China were around 39%. Cropland farming practices could alleviate the spatial variation of the relationships between climate and vegetation while enhancing the temporal difference of their relationships. Additionally, the dominant influencing factor among different regions varied greatly at the medium-term scale. Collectively, the results might provide an alternative perspective for understanding vegetation evolution in response to climatic changes in China.

From land cover to land use: Applying random forest classifier to Landsat imagery for urban land-use change mapping

The extensive record of Landsat imagery is commonly used to map urban land-cover and land-use change. Random forest (RF) classification was applied for mapping more detailed urban land-use and change categories than is typically attempted with Landsat data. Two dates of Landsat imagery (1990 and 2015) were utilized with surface reflectance, Vegetation-Impervious-Soil (V-I-S) fractions, grey-level cooccurrence matrix (GLCM) of V-I-S, and temporal variation of V-I-S inputs. GLCM V-I-S and temporal variation of Vegetation as input features of RF classifiers slightly improved accuracies of land use maps. A change map derived from an overlay analysis between the 2015 map and a Landsat-derived urban expansion map was more accurate than one from post-classification comparison of 1990 and 2015 maps. For the Taiwan study area, Transportation Corridor land use tended to lead conversion to Residential and Employment types in relatively undeveloped districts, and extensive urban land-use change occurred in peri-urban areas.

Spatiotemporal Analysis of Vegetation Cover in Kurdistan Region-Iraq using MODIS Image Data

The rapidly and wide use of remote sensing and accurately obtain information on the spatiotemporal distribution of large-scale vegetation is of great significance for improving and managing the Environment. To assess and analyze the spatiotemporal variation of vegetation status in Kurdistan Region of Iraq (KRGI), we used time series NDVI-based vegetation that are extracted from MOD13Q1 MODIS product over 20 years (2000 - 2019). The results showed that vegetation was mainly distributed in the north-east to south-east of the KRGI, while west region has less distributed and almost no vegetation. This is clearly remarkable in the south-west part of the region (Garmian administration). While, the most dominated vegetation province was Duhok province in KRGI during study period. There is a noticeable temporal variation in vegetation over a period of 20-year in the KRGI. The lower vegetated cover area is observed in the years 2000, 2008, and 2009. The increase/decrease of vegetated cover area is not only effected by climate conditions. The anthropogenic resource is also one of the main resources that has a major influence on the increase/decrease of vegetation.

Temporal variation of vegetation at two operating landfills and its implications for landfill phytoremediation

ABSTRACTLandfilling is a popular method to dispose of solid waste around the world, but this practice is associated with inevitable negative consequences such as air and water pollution and potential health hazards. Phytoremediation is an economical and promising technology to address these problems. To select suitable species for restoring landfills in China, the vegetation characteristics and their physiological activities were investigated in two different landfills. The results showed that the vegetation coverage of the two landfills both increased with the closure time. The species diversity decreased with the closure time in the Chongming landfill, whereas it showed the opposite trend in the Jiangcungou landfill. Five dominant species (Conyza canadensis, Setaria viridis, Sesbania cannabina, Suaeda glauca, and Phragmites australis) and four dominant species (Festuca elata Keng, Amaranthus retroflexus, Lolium multiflorum, and Kochia scoparia) were identified in the Chongming landfill and Jiangcungou landfill, respectively, and these dominant species were mainly annual plants. In addition, the net photosynthetic rate of P. australis and K. scoparia was the highest in the Chongming landfill and Jiangcungou landfill, respectively. Their photosynthetic rates were influenced significantly by stomatal conductance. Based on the overall results, among the dominant species identified, P. australis and K. scoparia represent potentially well suited plants to use in the remediation of landfills in China, because of their strong adaptability to landfill environments and natural occurrence in landfills.

Spatial-temporal Evolution of Vegetation Coverage and Analysis of it’s Future Trends in Wujiang River Basin

Vegetation coverage dynamics is affected by climatic, topography and human activities, which is an important indicator reflecting the regional ecological environment. Revealing the spatial-temporal characteristics of vegetation coverage is of great significance to the protection and management of ecological environment. Based on MODIS NDVI data and the Maximum Value Composites (MVC), we excluded soil spectrum interference to calculate Fractional Vegetation Coverage (FVC). Then the long-term FVC was used to calculate the spatial pattern and temporal variation of vegetation in Wujiang River Basin from 2000 to 2016 by using Trend analysis and Hurst index. The relationship between topography and spatial distribution of FVC was analyzed. The main conclusions are as follows: (1) The multi-annual mean vegetation coverage reveals a spatial distribution variation characteristic of low value in midstream and high level in other parts of the basin, owing a mean value of 0.6567. (2) From 2000 to 2016, the FVC of the Wujiang River Basin fluctuated between 0.6110 and 0.7380, and the overall growth rate of FVC was 0.0074/a. (3) The area of vegetation coverage tending to improve is more than that going to degrade in the future. Grass land, Arable land and Others improved significantly; karst rocky desertification comprehensive management project lead to persistent vegetation coverage improvement of Grass land, Arable land and Others. Residential land is covered with obviously degraded vegetation, resulting of urban sprawl; (4) The spatial distribution of FVC is positively correlated with TNI. Researches of spatial-temporal evolution of vegetation coverage have significant meaning for the ecological environment protection and management of the Wujiang River Basin.

The spatial distribution and temporal variation of desert riparian forests and their influencing factors in the downstream Heihe River basin, China

Abstract. Desert riparian forests are the main restored vegetation community in Heihe River basin. They provide critical habitats and a variety of ecosystem services in this arid environment. Since desert riparian forests are also sensitive to disturbance, examining the spatial distribution and temporal variation of these forests and their influencing factors is important to determine the limiting factors of vegetation recovery after long-term restoration. In this study, field experiment and remote sensing data were used to determine the spatial distribution and temporal variation of desert riparian forests and their relationship with the environmental factors. We classified five types of vegetation communities at different distances from the river channel. Community coverage and diversity formed a bimodal pattern, peaking at the distances of 1000 and 3000 m from the river channel. In general, the temporal normalized difference vegetation index (NDVI) trend from 2000 to 2014 was positive at different distances from the river channel, except for the region closest to the river bank (i.e. within 500 m from the river channel), which had been undergoing degradation since 2011. The spatial distribution of desert riparian forests was mainly influenced by the spatial heterogeneity of soil properties (e.g. soil moisture, bulk density and soil particle composition). Meanwhile, while the temporal variation of vegetation was affected by both the spatial heterogeneity of soil properties (e.g. soil moisture and soil particle composition) and to a lesser extent, the temporal variation of water availability (e.g. annual average and variability of groundwater, soil moisture and runoff). Since surface (0–30 cm) and deep (100–200 cm) soil moisture, bulk density and the annual average of soil moisture at 100 cm obtained from the remote sensing data were regarded as major determining factors of community distribution and temporal variation, conservation measures that protect the soil structure and prevent soil moisture depletion (e.g. artificial soil cover and water conveyance channels) were suggested to better protect desert riparian forests under climate change and intensive human disturbance.

Time–space characterization of vegetation in a semiarid mining area using empirical orthogonal function decomposition of MODIS NDVI time series

There are always different patterns of temporal variation determined by the heterogeneity of the surface coverage and influence factors at regional scale. Identification of the temporal patterns and positioning their spatial distribution are critical for rational use of nature resources and ecological protection. In this study, the empirical orthogonal function decomposition (EOFD) was proposed for the time–space characterization of vegetation in a semiarid mining area using 206 MODIS-NDVI images with a spatial resolution of 250 m and temporal resolution of 16 days. Four kinds of temporal patterns of the vegetation were decomposed, which are annual cycle, desertification, increase and degradation. Moreover, the spatial distributions of the decomposed temporal patterns were mapped. As a result, a much stronger relationship was found between the NDVI and rainfall, which is the key factor controlling the vegetation growth in the study area. The spatial distribution of the impacts on the vegetation from the underground coal mining, open-pit mining, and vegetation reconstruction was identified with the EOFD method and verified by site investigations. These results demonstrated that the EOFD method can decompose the whole temporal variation of vegetation into several different patterns of variations and help to distinguish between the influences from natural factors or anthropogenic activities. The EOFD method is determined by the temporal variations of the study area without human intervention; therefore, it is a promising methodology for time–space characterization with the aid of satellite images time series at a large scale.

Temporal Variation of Vegetation in Songmuxicuo Basin as Detected by MODIS Remote Sensing during 2001~2010

Temporal Variation of Vegetation in Songmuxicuo Basin as Detected by MODIS Remote Sensing during 2001~2010

Vegetation vis-à-vis climate and glacier history during 12,400 to 5,400 yr BP from Dokriani valley, Garhwal Himalaya, India

Palynological analysis from a 10 m deep sediment profile from Dokriani valley, Garhwal Himalaya, provides temporal variation of vegetation vis-a-vis climate and glacier history of the region. This study reveals that between 12,406 and 10,633 cal yr BP vegetation was sparse when the climate was cool-dry and the glacier snout might had been located at lower elevations in comparison to its present position. Subsequently around 10,633 cal yr BP, an increase in the growth of diversified taxa close to the site, indicates the early Holocene climatic amelioration when glacier might have retreated at faster rate. Further, within Holocene some intermittent cool-dry episodes were recorded around 9,670 to 9,000 cal yr BP and 7,100 cal yr BP when glacier might have shown reduction in retreat rate or came to stagnation.

On the relationship between the environmental history and the epidemiological situation of Argentine hemorrhagic fever

AbstractThe aim of this work was to establish the relationship between different Argentine hemorrhagic fever (AHF) epidemiological situations found at different sites and the related large‐scale environmental conditions. Large‐scale environmental records (vegetation index, temperature, precipitation and elevation) were obtained from a series of monthly NOAA satellite images and global databases considered suitable for modeling climatic and other environmental determinants of large‐scale biogeographical regions. The temporal variation in vegetation for cycles of winter‐summer showed a greater variation in the nonendemic region than in the other two regions. On the other hand, the average of the temporal variation in precipitation in cycles of spring–autumn was more different in the historic region than in the other two regions, and land surface temperatures in cycles of spring–autumn showed differences between the epidemic region and the other two regions. We found good separation among the epidemic, historic and nonendemic sites, with the greatest difference found between epidemic and nonendemic sites. The classification of sites showed a tendency for grouping according to the epidemiological situation, but there was some variation. It seems possible to establish a close relationship between the state of AHF incidence and the environmental history of sites suggesting the possibility of predicting epidemiological behavior using environmental conditions derived from satellite data.

Using soil profiles of seeds and molecular markers as proxies for sawgrass and wet prairie slough vegetation in Shark Slough, Everglades National Park

We measured the abundance of Cladium jamaicense (Crantz) seeds and three biomarkers in freshwater marsh soils in Shark River Slough (SRS), Everglades National Park (ENP) to determine the degree to which these paleoecological proxies reflect spatial and temporal variation in vegetation. We found that C. jamaicense seeds and the biomarkers Paq, total lignin phenols (TLP) and kaurenes analyzed from surface soils were all significantly correlated with extant aboveground C. jamaicense biomass quantified along a vegetation gradient from a C. jamaicense to a wet prairie/slough (WPS) community. Our results also suggest that these individual proxies may reflect vegetation over different spatial scales: Paq and kaurenes correlated most strongly (R2 = 0.88 and 0.99, respectively) with vegetation within 1 m of a soil sample, while seeds and TLP reflected vegetation 0–20 m upstream of soil samples. These differences in the spatial scale depicted by the different proxies may be complementary in understanding aspects of historic landscape patterning. Soil profiles of short (25 cm) cores showed that downcore variation in C. jamaicense seeds was highly correlated with two of the three biomarkers (Paq, R2 = 0.84, p<0.005; TLP, R2 = 0.97, p<0.0001), and all four of the proxies indicated a recent increase in C. jamaicense biomass at the site. Using a preliminary depth-to-age relationship based on matching charcoal peaks with available ENP fire records (1980-present) specific to our coring site, we found that peak-depths in C. jamaicense seed concentration appeared to correspond to recent minimum water levels (e.g., 1989 and 2001), and low seed abundance corresponded to high water levels (e.g., 1995), consistent with the known autecology of C. jamaicense. In summary, the combination of C. jamaicense seeds and biomarkers may be useful for paleoecological reconstruction of vegetation change and ultimately in guaging the success of ongoing efforts to restore historic hydrologic conditions in the South Florida Everglades.

Interannual Covariability Found in Evapotranspiration and Satellite-derived Vegetation Indices over Northern Asia

Temporal variation in vegetation over a large area induces temporal variation in the landatmosphere water budget through evapotranspiration activity. To examine this relationship interannually, normalized difference vegetation index (NDVI) and evapotranspiration (ET) values collected from 1982 to 2000 over northern Asia were investigated. Monthly global NDVI values were acquired from Pathfinder AVHRR land data. Monthly ET was estimated from NCEP/NCAR assimilated atmospheric data and CMAP global precipitation data. All calculations were made for 2:5 × 2:5-degree grid boxes in the study region on a monthly basis. The correlation coefficient of the 19-year time series of ET and NDVI anomalies showed the annual maximum correlation in June, and high correlation generally distributed over the region except for southern arid areas and the most northern areas. Although interannual variations in temperature and precipitation anomalies also showed some relation to ET in the warm season, they did not exhibit high correlation in a specific month. Since the vegetation is probably most active in June, it is considered that vegetation variability contributed significantly to ET through its transpiration activity.

Monitoring dioxins and furans near an old municipal solid waste incinerator: Temporal variation in vegetation

To determine the temporal variation in the levels of polychlorinated dibenzo‐p‐dioxins (PCDDs) and dibenzofurans (PCDFs) in vegetation grown near an old municipal solid waste incinerator (Montcada, Barcelona, Spain), 24 herbage samples were collected at the same sampling points in which samples had been taken one year before. While in the previous survey PCDD/F concentrations ranged from 1.07 to 3.05 ng I‐TEQ/kg (dry matter) (median value: 1.88 ng I‐TEQ/kg, mean value: 1.92 ng I‐TEQ/kg), in the current samples PCDD/F levels ranged from 0.75 to 1.95 ng I‐TEQ/kg (dry matter) (median value: 1.27 ng I‐TEQ/kg, mean value: 1.30 ng I‐TEQ/kg). An individual comparison between PCDD/F concentrations in samples collected in both studies shows a decrease in all the sampling points with an average reduction of 32.3%. This reduction can be due to general abatement actions for PCDD/F emissions.