Spatio-temporal Changes Of Vegetation Research Articles

Analyzing of the spatio-temporal changes of vegetation and its response to environmental factors in north of Fars province, Iran

پوشش گیاهی، یکی از عوامل ضروری در ساختار و عملکرد اکوسیستم‌های خشکی و یکی از حلقه‌های اساسی زنجیر حیاتی آب-خاک-گیاه و اتمسفر[1] است. مطالعات متعدد ثابت کرده است پوشش گیاهی به تغییرات عوامل اقلیمی و ادافیکی حساس است. بر این اساس، تغییر در پوشش گیاهی و رابطه‌اش با عوامل مذکور، از اهمیت بسیاری برخوردار است. تحقیق حاضر به منظور بررسی تغییرات پوشش گیاهی و عوامل موثر بر آن، در حوضه خارستان استان فارس انجام شد. در این رابطه، تصاویر برگرفته از سنجنده ETM لندست 7، طی دوره 2000-2017 و داده‌های اقلیمی‌حاصل از 17 ایستگاه‌ هواشناسی استان استفاده شد. با استفاده از این تصاویر، تغیرات زمانی و مکانی NDVI و آنومالی آن استخراج شد. به منظور استخراج نقشه کاربری اراضی از روش طبقه بندی نظارت شده استفاده شد. در نهایت رابطه NDVI با عوامل اقلیمی، توپوگرافی و انسانی (کاربری اراضی) بررسی شد. رابطه بین این شاخص با عوامل اقلیمی‌و توپوگرافی بر مبنای روش‌های رگرسیون وزن‌دار فضایی[1] و حداقل مربعات معمولی[1] به‌دست آمد. در مجموع، تغییرات زمانی مبین روند افزایش آهسته NDVI بود. آنومالیNDVI در سال‌های قبل از 2008 روند مثبت و برای سال‌های بعد روند منفی را نشان داد. توزیع مکانی NDVI مبین یک روند افزایشی از شمال به سمت مرکز و جنوب غرب منطقه مورد مطالعه بود. نتایج حاکی از تاثیر دو دسته عوامل طبیعی و انسانی بر تغییرات پوشش گیاهی بود. NDVI در اراضی کشاورزی و مرتعی افزایش، همچنین پوشش گیاهی طبیعی بیشتر از پوشش‌های دست کاشت (اراضی کشاورزی و باغی) تحت تاثیر عوامل اقلیمی‌قرار گرفته است. علاوه بر این تغییرات پوشش گیاهی بر حسب ارتفاع، جهت و شیب هم تفاوت داشت. به طوری که از ارتفاع بیشتر از 2500 متر مقدار NDVI کاهش، در شیب‌های کمتر از ˚5، مقدار این شاخص افزایش و در جهت‌های شمال و شرق بیشتر از دامنه‌های جنوبی بود. روند کلی، نشان‌دهنده افزایش دما و کاهش بارندگی در طول دوره مورد مطالعه بود. با توجه به نقش تعیین کننده بارش در مناطق خشک و نیمه‌خشک می‌توان گفت نقش کنترلی بارش بر NDVI بیشتر از دما است. حداکثر همبستگی مثبت و منفی، بین متوسط بارش سالیانه و NDVI با استفاده از روش حداقل مربعات معمولی به ترتیب 93/0 و 83/0 مشاهده شد. همچنین حداکثر همبستگی منفی و مثبت بین NDVI و دما به ترتیب 65/0 و 5/0 بود. بیشترین مقدار ضریب تبیین مکانی (Local R2) بین NDVI با بارندگی و دما به ترتیب 45/0 و 44/0 بود که در بخش‌های مرکزی منطقه مشاهده شد. با توجه به نتایج، می‌توان اظهار داشت که عوامل محیطی نظیر ارتفاع، جهت، شیب، دما و بارش از فاکتورهای تاثیرگذار بر پوشش گیاهی در منطقه خارستان هستند.

Detecting Spatiotemporal Changes in Vegetation with the BFAST Model in the Qilian Mountain Region during 2000–2017

The Qilian Mountain ecosystems play an irreplaceable role in maintaining ecological security in western China. Vegetation, as an important part of the ecosystem, has undergone considerable changes in recent decades in this area, but few studies have focused on the process of vegetation change. A long normalized difference vegetation index (NDVI) time series dataset based on remote sensing is an effective tool to investigate large-scale vegetation change dynamics. The MODerate resolution Imaging Spectroradiometer (MODIS) NDVI dataset has provided very detailed regional to global information on the state of vegetation since 2000. The aim of this study was to explore the spatial-temporal characteristics of abrupt vegetation changes and detect their potential drivers in the Qilian Mountain area using MODIS NDVI data with 1 km resolution from 2000 to 2017. The Breaks for Additive Season and Trend (BFAST) algorithm was adopted to detect vegetation breakpoint change times and magnitudes from satellite observations. Our results indicated that approximately 80.1% of vegetation areas experienced at least one abrupt change from 2000 to 2017, and most of these areas were distributed in the southern and northern parts of the study area, especially the area surrounding Qinghai Lake. The abrupt browning changes were much more widespread than the abrupt greening changes for most years of the study period. Environmental factors and anthropogenic activities mainly drove the abrupt vegetation changes. Long-term overgrazing is likely the main cause of the abrupt browning changes. In addition, our results indicate that national ecological protection policies have achieved positive effects in the study area.

Evaluate the spatio-temporal changes of vegetation and human activities in China’s Wulingyuan Natural World Heritage Site

The Wulingyuan area, in Zhangjiajie, China, is a world natural heritage site famous for quartz sand and rock peak landscape. The assessment of vegetation dynamics and human activities are conducive to protecting the heritage value and to formulating sustainable development plans. Here, we use long-term MODIS data to quantify the spatiotemporal changes of vegetation and the response to environmental variables through three NDVI processing methods. We also analyze human activities and policy changes. The results indicated the following. (i) The vegetation in Wu has been in good condition on average for the past 18 years, with a high vegetation index and high vegetation productivity. (ii) The vegetation in Wu and each subarea shows an overall improvement trend, 71.00% (60.03%, 46.80%), and shows an increase in AM-NDVI (SG-NDVI and STI). Spatially, the vegetation increase area is mainly located in the buffer area, and a very small vegetation decrease area is in the development region. (iii) There are correlations between vegetation and temperature and precipitation, but neither of them passed the significance test. (iv)To comply with the World Heritage Convention, establishing national scenic areas and supplementing woodland protection planning may be the key policies having a positive effect on the vegetation change.

2002-2016年华北平原植被生长状况及水文要素时空特征分析

2002-2016年华北平原植被生长状况及水文要素时空特征分析

Early to mid-Holocene spatiotemporal vegetation changes and tsunami impact in a paradigmatic coastal transitional system (Doñana National Park, southwestern Europe)

Abstract The southern European Donana wetlands host a highly biodiverse landscape mosaic of complex transitional ecosystems. It is one of the largest protected natural sites in Europe, nowadays endangered by intensive agricultural practices, and more recently tourism and human-induced fires. Its present-day spatial heterogeneity has been deeply investigated for the last three decades. However, a long-term perspective has not been applied systematically to this unique landscape. In this new study, a palaeoecological approach was selected in order to unravel patterns of landscape dynamism comparing dry upland and aquatic ecosystems. A 709 cm-long sediment core was retrieved and a multi-proxy approach applied (palynological, microcharcoal, grain size, magnetic susceptibility, loss-on-ignition and multivariate statistical analyses). Pollen signatures show how sensitive aquatic wetland vegetation was to environmental changes while terrestrial vegetation was stable at millennial scale. The impact of several high energy events punctuates the Early and Middle Holocene sequence, two of which relate to the local tsunami record (~ 6.6 and ~ 9.1 cal. kyr BP). Contrasting impacts of these two events in the aquatic and upland ecosystems show the importance of landscape configuration and the contingent history as key elements for coastal protection.

Detecting Historical Vegetation Changes in the Dunhuang Oasis Protected Area Using Landsat Images

Abstract: Given its proximity to an artificial oasis, the Donghu Nature Reserve in the Dunhuang Oasis has faced environmental pressure and vegetation disturbances in recent decades. Satellite vegetation indices (VIs) can be used to detect such changes in vegetation if the satellite images are calibrated to surface reflectance (SR) values. The aim of this study was to select a suitable VI based on the Landsat Climate Data Record (CDR) products and the absolute radiation-corrected results of Landsat L1T images to detect the spatio-temporal changes in vegetation for the Donghu Reserve during 1986–2015. The results showed that the VI difference (ΔVI) images effectively reduced the changes in the source images. Compared with the other VIs, the soil-adjusted vegetation index (SAVI) displayed greater robustness to atmospheric effects in the two types of SR images and was more responsive to vegetation changes caused by human factors. From 1986 to 2015, the positive changes in vegetation dominated the overall change trend, with changes in vegetation in the reserve decreasing during 1990–1995, increasing until 2005–2010, and then decreasing again. The vegetation changes were mainly distributed at the edge of the artificial oasis outside the reserve. The detected changes in vegetation in the reserve highlight the increased human pressure on the reserve.

Spatiotemporal Changes of Vegetation in the Middle Draa Valley Oasis: A Study Case of M’hamid El Ghizlane Oasis (Morocco)

During the last decades, The Middle Draa Valley (Southeast of Morocco) was subjected to various environmental problems which haves caused land degradation especially in the south of the Middle Draa (M’hamid oasis). This study aims to analyze the spatiotemporal changes of vegetation in the M’hamid oasis. Based on the Landsat images belonging to six separate periods during 1984 to 2016 and Geographical Information System (GIS) techniques, the pattern of spatiotemporal changes of vegetation cover in M’hamid oasis was analyzed based to visual interpretation and NDVI (Normalized Difference Vegetation Index) and supervised classified. For easier understanding of the causes and origins of these changes, we exploited statistical data survey from various local administrations (climatological, socio-economic data) and fieldworks. The results show that the total area of the oasis showed an oscillating decrease between 1984-1999 compared to 1999-2013 and a sharp increase after 2003 to 2007 and a moderate decrease from 2003 to 2016, with an area 3 times smaller than the initial date (loss of 22% of oasis area), correlated with a reduction of the habitants (loss of 21% between 1980 and 2016). Mass tourism, construction of the Mansour Eddahbi dam and the irregularities of the rains and the succession of years of drought led to a modification of the oasis ecosystem. Due to these climatic conditions, the oasis population are obliged to emigration thus they leave their fields which are threatened by sand encroachments, therefore accelerating the phenomenon of sand movements and consequently desertification.

Spatiotemporal changes of vegetation and their responses to temperature and precipitation in upper Shiyang river basin

The Shiyang river basin is a typical arid inland river basin in northwestern China, where significant climate change and ecological environment deterioration has been observed over the past several decades. The vegetation in Shiyang river basin is mostly concentrated in its upstream, and plays an important role in ecological environment of this watershed. However, how the regional vegetation responds to such climatic change is poorly understood. To address this question, the spatiotemporal changes of vegetation growth in upper Shiyang river basin together with their responses to climate changes were investigated using SPOT VEGETATION Normalized Difference Vegetation Index (NDVI) and climate datasets from 1999 to 2013. Results reveal that about 81.3% of the study area shows an increasing trend in NDVI. The average NDVI of the study area increases at rates of 7.75% for the growing season (March–November), 11.75% for spring (March–May), 9.62% for summer (June–August), and 5.98% for autumn (September–November) over the study period. The increase of NDVI in spring and autumn suggests the growing season of the vegetation in this study area has been prolonged. The effects of climate changes on vegetation growth vary with the types of vegetation and seasons, which shows a large spatial and temporal heterogeneity. As compared with temperature, precipitation is the dominant climatic factor affecting the interannual variations of vegetation. If the temperature and precipitation continue to increase in the study area, the sensitivity of vegetation growth to temperature and precipitation may decline.

Precipitation does not amplify the efficiency of fencing measures for temperate grassland restoration: A case study in northern China based on remote sensing

Increasing anthropogenic interventions involving utilization and conservation of vegetated ecosystems has attracted considerable attention focused on large-scale assessments of the roles played by human-domination. The effects of specific anthropogenic measures have generally been ignored by large-scale assessments, which has probably resulted in irrational regulations and imprecise understanding of these specific measures. This paper aims to reveal the effect of a grassland restoration measure—fencing in northern China—as well as the spatial patterns of fencing efficiency. Spatially continuous Normalized Difference Vegetation Index (NDVI) data based on remote sensing was used to detect grassland vegetation changes during fencing periods. Using subsequent processes to smooth the impact of precipitation from the current year and by setting thresholds for identifying changed/unchanged NDVI, the spatial vegetation changes were converted into two groups of statistical data: the mean NDVI-increase value in each sample region and the pixel areas with different grassland change types in each sample region. The precipitation lag effect on NDVI increases was assessed by multiple comparison tests, and regions with a significant precipitation lag effect were removed from the fencing effect assessment. Finally, the areas with different grassland change types were related to changes in fenced area using regression analyses under different precipitation gradients. The results indicated that the precipitation lag effect caused by legacy moisture significantly affected the spatio-temporal vegetation changes. By excluding the regions with legacy moisture, the increase in fenced area facilitated an expansion of improved grassland and a reduction in degraded grassland. Fencing efficiency was maximized in the 250–300-mm precipitation zone, where the expansion rate of improved grassland area reached 0.70 (R2=0.54, p<0.01). The second-best and least effective zones lay in the mean annual precipitation (MAP) >300-mm and MAP <250mm zones, respectively. We conclude that a wetter climate does not automatically result in a better fencing effect, and legacy moisture will lead to an overestimation of the fencing effect. A rational fencing implementation should consider the resilience and degradation degree of steppes.

Spatiotemporal Assessment of Vegetation Indices and Land Cover for Erbil City and Its Surrounding Using Modis Imageries

AbstractThe rate of global urbanization is exponentially increasing and reducing areas of natural vegetation. Remote sensing can determine spatiotemporal changes in vegetation and urban land cover. The aim of this work is to assess spatiotemporal variations of two vegetation indices (VI), the Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI), in addition land cover in and around Erbil city area between the years 2000 and 2015. MODIS satellite imagery and GIS techniques were used to determine the impact of urbanization on the surrounding quasi-natural vegetation cover. Annual mean vegetation indices were used to determine the presence of a spatiotemporal trend, including a visual interpretation of time-series MODIS VI imagery. Dynamics of vegetation gain or loss were also evaluated through the study of land cover type changes, to determine the impact of increasing urbanization on the surrounding areas of the city. Monthly rainfall, humidity and temperature changes over the 15-year-period were also considered to enhance the understanding of vegetation change dynamics. There was no evidence of correlation between any climate variable compared to the vegetation indices. Based on NDVI and EVI MODIS imagery the spatial distribution of urban areas in Erbil and the bare around it has expanded. Consequently, the vegetation area has been cleared and replaced over the past 15 years by urban growth.

Spatiotemporal changes of vegetation on the Tibetan Plateau and relationship to climatic variables during multiyear periods from 1982–2012

Understanding the dynamics of vegetation system change is often limited by relatively brief data sequences and the shortage of comparable analyses of variation over longer periods. In this study, GIMMS NDVI and MODIS NDVI datasets were integrated to establish a consistent NDVI time series from 1982 to 2012 on vegetation of the Tibetan Plateau in China. The spatiotemporal patterns of change in seasonal NDVI and their linkage with climatic variables were analyzed at regional and pixel scales over 14 periods ranging from 18 to 31 years and beginning in 1982. On a regional scale, positive trends of growing season and seasonal NDVI were observed during the 14 periods, and the increases were statistically significant for growing season NDVI during all periods, and for summer and autumn NDVI during only the last four and the last two periods, respectively. The rates of NDVI increase in growing season and spring significantly decreased over the 14 periods. NDVI rates slightly decrease in summer and significantly increase in autumn. At a pixel scale, areas with significant greening or significant browning significantly increased over the 14 periods during the growth season and during all seasons except spring, in which the proportion of vegetated area with greening rapidly decreased. Temperature was the primary climatic driver for the observed vegetation changes during multiple periods while precipitation and sunshine duration had significant impacts on vegetation growth only in limited parts of the study area or during spring. Vegetation growth response to climate change varied across seasons and regions. Trend analysis during the multiple nested time series provides a better understanding of NDVI dynamics and may help to forecast future changes. Spring NDVI is likely to continue decreasing, autumn NDVI will continue increasing, and the magnitude of the NDVI increase during growing season will decline in the future.

Monitoring of Vegetation Dynamics in the Mongolia Using MODIS NDVIs and their Relationship to Rainfall by Natural Zone

Vegetation plays a very important role conserving the natural environment and improving the living environment for humans. Thus, investigating spatio-temporal changes in vegetation is a crucial indicator to understand natural environmental changes. We explored the spatio-temporal trends of changing vegetation cover in Mongolia from 2002 to 2010 by investigating changes in the normalized difference vegetation index (NDVI) with rainfall. The 16-day composite NDVI time series Terra MODIS (MOD13A2) and the gridded rainfall data of the Inter-governmental Panel on Climate Change (IPCC) were used to identify the relationship between vegetation dynamics and rainfall. Residual NDVI trends were computed. Following our general procedure, monthly NDVI and annual rainfall were correlated for each pixel. The resulting regression equation represented the statistical association between observed NDVI and rainfall, and the model predicted NDVI according to rainfall. Residuals of NDVI (differences between the observed and predicted NDVI) for each pixel were calculated, and the trends in these residuals was analyzed by linear regression. From the 12 months NDVI and rainfall values they determine a linear regression line for each pixel. The positive or negative slope of this line is considered to reflect an increase or decrease in green biomass. Our results show that vegetation cover changes in Mongolia were caused by both natural factors and human activities. The natural vegetation change, such as those in forests was influenced by climate change, whereas human activities were the main reason for the change in vegetation planted.

Response of Vegetation to Climate Change in the Drylands of East Asia

Over the past 25 years, global climate and environmental changes have caused an unprecedented rate of vegetation change, as exemplified in the drylands of East Asia. In this study, we investigated the spatio-temporal changes of vegetation in this region and analysed their relationship with climate data. Our results show that vegetation productivity significantly increased from 1982 to 2006. This increasing trend was observed for most of the region, particularly for northwest Mongolia and central Inner Mongolia. Grasslands, croplands, forests, and shrublands, all exhibited this trend. The annual growth rate of the grasslands determined using the Normalized Difference Vegetation Index (NDVI) was the largest observed change; reaching 0.07% p.a, followed by shrublands (0.06%), croplands (0.03%), and forests (0.02%). In the different geographic regions, the roles of temperature and precipitation on vegetation growth were shown to be different. Temperature was the dominant factor for the observed NDVI increase in northwest Mongolia and the centre of Inner Mongolia. The combined influences of temperature and precipitation changes have resulted in the promotion of vegetation growth, as seen in eastern GanSu. Temperature change is the primary factor for initiating vegetation growth in spring and autumn because warmer temperatures increase the length of the growing season, and are thus evaluated as an increased NDVI value. Increased precipitation has been shown to play a positive role on vegetation growth during summer.

Spatio-Temporal Changes of Vegetation in Mongolia Based on MODIS-NDVI During 2001-2010

利用2001-2010年的空间分辨率为1km的MODIS-NDVI数据,以蒙古国为研究区域,利用最大值合成法、均值法与差值法、一元线性回归等方法,分析了不同季节下植被覆盖的年内变化、年际变化与波动趋势、空间变化特征。结果表明:MODIS-NDVI对植被的生长变化具有较高的敏感度,可有效应用于植被生态的评估和监测;蒙古国植被季相变化明显,夏秋季植被生长旺盛;近10年里,春季的植被以波动退化为主要趋势,夏季保持稳定,秋、冬季则在波动中趋向改善;前5年的植被变化幅度较小,后5年的植被变化幅度显著,总体上改善幅度略大于退化幅度;蒙古国的植被覆盖在近10年里,呈现出总体保持稳定、局部轻微改善的趋势;从空间上分布看,稳定区分布广泛,改善区主要分布在东部,退化区主要分布在中部。根据以上研究结论,可以看出:蒙古国近几年的植被覆盖变化趋于平缓,并在东部地区呈现轻微的改善趋势,说明该国东部地区加强防治措施初见成效。但与此同时,蒙古国的中部地区出现植被略微退化的趋势,也应引起我国生态环境防治方面的关注。

Vegetation–environment interactions in a sub-arctic primary succession

Biological modification of the physical environment is a characteristic feature of primary succession that is of particular importance in stressful, high-latitude habitats. However, the degree of spatiotemporal variability in biotic reaction is poorly understood. This is a significant gap in our knowledge of primary succession, as spatiotemporal variability in biotic reaction may be linked to divergent development during succession. The aim of this research was to infer long-term, spatiotemporal changes in vegetation and environmental parameters during primary succession from a chronosequence of lava flows in Iceland. Vegetation surveys and measurement of key environmental variables (temperature, relative humidity and wind speed) were carried out on seven lava flows aged 26–848 years. The duration of snow cover was inferred from temperature data using a novel technique. Paired measurements were taken in topographical low and high points, as previous studies in this location have indicated divergent vegetation development according to topographical position. The analysis indicated the long-term amelioration of microclimate. Vegetation development was associated with increased soil temperatures, decreased wind speeds and increased duration of snow-lie. There was also evidence that microenvironmental changes paralleled changes in vegetation structure, although the relationship varied according to the environmental parameter studied. It is likely that positive feedback between shrub development and snow accumulation structures the vegetation on the study sites. These findings have implications for sub-arctic areas where shrub cover is expanding due to climate change and for the development of vegetation on terrain exposed by retreating ice.