Vegetation Change Dynamics Research Articles

Utilizing Sentinel-2 Satellite Imagery for LULC and NDVI Change Dynamics for Gelephu, Bhutan

Gelephu, located in the Himalayan region, has undergone significant development activities due to its suitable topography and geographic location. This has led to rapid urbanization in recent years. Assessing land use land cover (LULC) dynamics and Normalized Difference Vegetation Index (NDVI) can provide important information about urbanization trends and changes in vegetation health, respectively. The use of Geographic Information Systems (GIS) and Remote Sensing (RS) techniques based on various satellite products offers a unique opportunity to analyze these changes at a local scale. Exploring Bhutan’s mandate to maintain 60% forest cover and analyzing LULC transitions and vegetation changes using Sentinel-2 satellite imagery at 10 m resolution can provide important insights into potential future impacts. To examine these, we first performed LULC mapping for Gelephu for 2016 and 2023 using a Random Forest (RF) classifier and identified LULC changes. Second, the study assessed the dynamics of vegetation change within the study area by analysing the NDVI for the same period. Furthermore, the study also characterized the resulting LULC change for Gelephu Thromde, a sub-administrative municipal entity, as a result of the notable intensity of the infrastructure development activities. The current study used a framework to collect Sentinel-2 satellite data, which was then used for pre-and post-processing to create LULC and NDVI maps. The classification model achieved high accuracy, with an area under the curve (AUC) of up to 0.89. The corresponding LULC and NDVI statistics were analysed to determine the current status of the LULC and vegetation indices, respectively. The LULC change analysis reveals urban growth of 5.65% and 15.05% for Gelephu and Gelephu Thromde, respectively. The NDVI assessment shows significant deterioration in vegetation health with a 75.11% loss of healthy vegetation in Gelephu between 2016 and 2023. The results serve as a basis for strategy adaption required to examine the environmental protection and sustainable development management, and the policy interventions to minimize and balance the ecosystem, taking into account urban landscape.

Vegetation Trend Detection Using Time Series Satellite Data as Ecosystem Condition Indicators for Analysis in the Northwestern Highlands of Ethiopia

Vegetation is an essential component of the terrestrial ecosystem and has changed significantly over the last two decades in the Northwestern Highlands of Ethiopia. However, previous studies have focused on the detection of bitemporal change and lacked the incorporation of entire vegetation time series changes, which are considered significant indicators of ecosystem conditions. The Normalized Difference Vegetation Index (NDVI) time series dataset from the Moderate-Resolution Imaging Spectroradiometer (MODIS) is an efficient method for analyzing the dynamics of vegetation change over a lengthy period using remote sensing techniques. This study aimed to utilize time series satellite data to detect vegetation changes from 2000 to 2020 and investigate their links with ecosystem conditions. The time-series satellite processing package (TIMESAT) was used to estimate the seasonal parameter values of NDVI and their correlation across the seasons during the study period. Break Detection for Additive Season and Trend (BFAST) was applied to identify the year of breakpoints, the direction of magnitude, and the number of breakpoints. The results were reported, analyzed, and linked to ecosystem conditions. The overall trend in the study area increased from 0.58 (2000–2004) to 0.65 (2015–2020). As a result, ecosystem condition indicators such as peak value (PV), base value (BV), amplitude (Amp), and large integral (LI) exhibited significant positive trends, particularly for Acacia decurrens plantations, Eucalyptus plantations, and grasslands, but phenology indicator parameters such as start of season (SOS), end of season (EOS), and length of season (LOS) did not show significant trends for almost any vegetation type. The most abrupt changes were recorded in 2015 (24.7%), 2012 (18.6%), and 2014 (9.8%). Approximately 30% of the vegetation changes were positive in magnitude. The results of this study imply that there was an improvement in the ecosystem’s condition following the establishment of the Acacia decurrens plantation. The findings are considered relevant inputs for policymakers and serve as an initial stage for the assessment of the other environmental and climatic implications of Acacia decurrens plantations at the local scale.

Identifying the Main Factors Influencing Significant Global Vegetation Changes

Understanding the dynamics of vegetation change is crucial for comprehending ecosystem functioning and its response to anthropogenic activities and climate change. This study investigates significant vegetation changes worldwide and aims to identify the dominant factors responsible for these changes. By analyzing long-term data on vegetation dynamics and climatic factors, this research identifies regions with significant global vegetation changes and determines the main factors leading to such changes at the grid scale. The results reveal important insights into the drivers of vegetation change. Firstly, the study finds that the area experiencing significant browning from April to July is larger than the area exhibiting significant greening. Secondly, on an annual scale, anthropogenic activity emerges as the main factor driving significant vegetation greening, while climate change becomes the primary factor causing vegetation browning from July to September. Thirdly, in regions dominated by climate change, temperature is identified as the primary climatic factor contributing to significant vegetation greening. Additionally, the study reveals that the primary climatic factors causing significant vegetation browning are temperature followed by soil moisture, with temperature being the main factor in most months. These findings contribute to a deeper understanding of the mechanisms driving global vegetation changes and have implications for sustainable development and climate action.

Spatial Pattern of Changing Vegetation Dynamics and Its Driving Factors across the Yangtze River Basin in Chongqing: A Geodetector-Based Study

Revealing the spatial dynamics of vegetation change in Chongqing and their driving mechanisms is of major value to regional ecological management and conservation. Using several data sets, including the SPOT Normalized Difference Vegetation Index (NDVI), meteorological, soil, digital elevation model (DEM), human population density and others, combined with trend analysis, stability analysis, and geographic detectors, we studied the pattern of temporal and spatial variation in the NDVI and its stability across Chongqing from 2000 to 2019, and quantitatively analyzed the relative contribution of 18 drivers (natural or human variables) that could influence vegetation dynamics. Over the 20-year period, we found that Chongqing region’s NDVI had an annual average value of 0.78, and is greater than 0.7 for 93.52% of its total area. Overall, the NDVI increased at a rate of 0.05/10 year, with 81.67% of the areas undergoing significant expansion, primarily in the metropolitan areas of Chongqing’s Three Gorges Reservoir Area (TGR) and Wuling Mountain Area (WMA). The main factors influencing vegetation change were human activities, climate, and topography, for which the most influential variables respectively were night light brightness (NLB, 51.9%), annual average air temperature (TEM, 47%), and elevation (ELE, 44.4%). Furthermore, we found that interactions between differing types of factors were stronger than those arising between similar ones; of all pairwise interaction types tested, 92.9% of them were characterized by two-factor enhancement. The three most powerful interactions detected were those for NLB ∩ TEM (62.7%), NLB ∩ annual average atmospheric pressure (PRS, 62.7%), and NLB ∩ ELE (61.9%). Further, we identified the most appropriate kind or range of key elements shaping vegetation development and dynamics. Altogether, our findings can serve as a timely scientific foundation for developing a vegetative resource management strategy for the Yangtze River basin that duly takes into account local climate, terrain, and human activity.

Spatiotemporal analysis of trends in vegetation change across an artificial desert oasis, Northwest China, 1975–2010

Vegetation change has become a worldwide environmental concern. Artificial desert oases in the Northwest China are among the most ecologically sensitive environments and are also a repository of ecosystem services by relying on vegetation system. Over the last four decades, land transformation related to anthropogenic activities and climate change is among the main drivers of changing vegetation cover in Northwest China. In an oasis where field-based research is challenging due to diverse landscape and heterogenous relief, quantifying changes in vegetation system using remote sensing can provide available information regarding trends in vegetation cover and its linkages with driving forces. This study aimed to explore spatiotemporal dynamics of vegetation change through examining time series normalized difference vegetation index (NDVI) over the period 1975–2010 in an artificial desert oasis in Northwest China. A time series imagery derived from Landsat product was analyzed for the presence of trends in vegetation change. Using the nonparametric Sen’s and Mann-Kendall methods, over 13.56% of oasis land surfaces were found to exhibit significant increasing trends, and almost 6.07% of oasis land surfaces were found to exhibit significant decreasing trends. The 80.38% spatial distribution of vegetation showed no change trends significantly. The relationships between the detected NDVI trends and land cover also were evaluated by using spatial mapping method. Results showed that the spatiotemporal pattern of vegetation change was consistent with the climate-related change of vegetation growing conditions and implementation of ecosystem management during the study period.

Dynamics of Vegetation Change and Its Relationship with Nature and Human Activities — A Case Study of Poyang Lake Basin, China

ABSTRACT Vegetation coverage directly affects the quality of a regional ecological environment. Current analyzes of the factors driving vegetation coverage do not focus on human activities. Poyang Lake is an internationally important wetland. This study is based on 814 MODIS normalized difference vegetation index (NDVI) data from 2000 to 2017 in the Poyang Lake Basin. Natural effects (temperature, precipitation, terrain niche index) and human activity intensity are employed to analyze the driving forces of NDVI changes. The results demonstrate the following: NDVI in the Poyang Lake Basin fluctuated and increased over the 18 years examined. Spatially, NDVI significantly decreased around the central city, and NDVI significantly increased on both sides of the river. NDVI changes are less affected by topographic factors and are more affected by climatic factors and human activities. Among the climatic factors, the correlation between NDVI and temperature was greater than that between NDVI and precipitation. Climatic factors had a greater impact on NDVI than human activities throughout the study area. However, in areas with significant NDVI changes, the correlation between climatic factors and NDVI was not obvious, and the correlation between human activities and NDVI was more obvious than in other areas. Therefore, from 2000 to 2017, the vegetation coverage of the Poyang Lake Basin generally showed an increasing trend; climatic factors had a greater impact on the overall vegetation coverage of the basin than human activities, but significant changes in vegetation coverage were caused by human activities.

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.

Spatiotemporal Analysis for NDVI Time Series Using Local Binary Pattern and Daubechies Wavelet Transform

NDVI time series has shown to be very efficient for vegetation change dynamic analysis over a long period. However, noise and illumination variations present significant challenges to perform an accurate change detection. This paper aims at capturing global vegetation change dynamics within 16-days MODIS-NDVI time series by considering the inter-annual variations. To determine the appropriate scale that characterizes the long term variation, an efficient way relying on wavelet transform is used. First, the Daubechies 4 wavelet transform is employed to perform a multi-scale decomposition to extract the inter-annual variations and remove noise. Second, critical point theory is used to identify a set of points indicating potential vegetation change within time series, which, allows a time series reduction. Then, for each critical point, LBP code is computed to characterize the corresponding local patterns, which provides the ability to deal with illumination variations. Based on the extracted features, a change map is produced by computing similarity between neighboring time series, assessing dynamic vegetation change over the period of study. Experiment results using NDVI time series show clearly the potential of the proposed approach to detect change.

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.

Holocene dynamics of vegetation change in southern and southeastern Brazil is consistent with climate forcing

At mid to high northern latitudes postglacial vegetation change has often occurred synchronously over large regions triggered mainly by abrupt climate change. Based on 19 pollen diagrams from southern and southeastern Brazil we explore if similar synchronicities in vegetation change were also characteristic for the vegetation dynamics in low latitudes. We used sequence splitting to detect past vegetation change in the pollen diagrams and computed principal curves and rates of change to visually evaluate the changes in composition and dynamics. The results show that vegetation change occurred mostly during the second half of the Holocene with distinct episodes of change. The character of vegetation change is generally consistent with shifts to wetter conditions and agrees with inferred shifts of the South American Monsoon. Speleothems as well as the titanium record from the Cariaco Basin indicate several episodes of rapid shifts in the precipitation regime, which are within the dating uncertainty of the here detected periods of vegetation change (8900, 5900, 2800, 1200 and 550 cal yrs BP). Our results indicate that low latitude vegetation composition follows precession forcing of the hydrology, while change is often triggered and synchronized by rapid climate change much like in high and mid latitudes. Pollen diagrams document changes in the abundance of individual taxa and changes in the amount of woodland cover, while small compositional changes indicate a regional stability of vegetation types during the Holocene.

Climate and abrupt vegetation change in Northern Europe since the last deglaciation

A long-standing question in palaeoecology has been to determine the importance of climate driving vegetation change since the last deglaciation. Here, we investigate the local-to-regional dynamics of vegetation change during the Lateglacial and the Holocene in Northern Europe. We extracted sites from the European Pollen Database and used the squared-chord distance (SCD) dissimilarity metric to identify time periods of high pollen assemblage turnover representing periods of abrupt vegetation change. In addition, a set of generalized additive mixed models were applied to investigate the underlying dynamics of two periods of higher rates of turnover: the Younger Dryas–early Holocene transition (YD-EH; 11.6–9.0 kyr) and early–middle Holocene (EMH; 9.0–6.0 kyr). Results revealed a high frequency of turnover events between 12.75–11.5, 10.75–11, 10.25–10, 7.75–7.25, 3.25–3.0 and 1.75–.25 kyr. Furthermore, there was a strong linear relationship between pollen assemblage turnover and large directional temperature changes during the abrupt climate changes of the Lateglacial–early Holocene transition. In contrast, patterns of turnover during the Holocene were generally site-specific and during the EMH, we found evidence that the vegetation response was non-linear and highly variable across and between regions. Our results have implications for understanding the relationship between threshold dynamics and the amplitude of an extrinsic forcing. Across the Lateglacial–early Holocene boundary, the rate and magnitude of temperature change were large enough to override any site-specific thresholds, resulting in large assemblage turnovers. In contrast, during the Holocene, the vegetation response was mediated by intrinsic factors, which resulted in varying turnover rates between regions. The next research challenge is to attempt to determine whether it is possible to appreciate the velocity and rate of change that is necessary to result in these different responses and whether this rate is the same across biomes.

近10a来蒙古高原植被覆盖变化对气候的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 近10年来蒙古高原植被覆盖变化对气候的响应 DOI: 10.5846/stxb201304100659 作者: 作者单位: 北京师范大学全球变化与地球系统科学研究院地表过程与资源生态国家重点实验室,西北农林科技大学资源环境学院,北京师范大学全球变化与地球系统科学研究院地表过程与资源生态国家重点实验室,北京师范大学全球变化与地球系统科学研究院地表过程与资源生态国家重点实验室,北京师范大学全球变化与地球系统科学研究院地表过程与资源生态国家重点实验室,北京师范大学全球变化与地球系统科学研究院地表过程与资源生态国家重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划（973计划）资助项目（2010CB428502，2011CB952001）；新世纪优秀人才支持计划资助（NCET-09-0227）；国家自然科学基金（41271542）；中央高校基本科研业务费专项资金资助 Response of vegetation coverage to climate change in Mongolian Plateau during recent 10 years Author: Affiliation: State Key Laboratory of Earth Surface Processes and Resource Ecology,College of Global Change and Earth System Science,Beijing Normal University,College of Resources and Environment,Northwest A F University,Yangling,State Key Laboratory of Earth Surface Processes and Resource Ecology,College of Global Change and Earth System Science,Beijing Normal University,State Key Laboratory of Earth Surface Processes and Resource Ecology,College of Global Change and Earth System Science,Beijing Normal University,State Key Laboratory of Earth Surface Processes and Resource Ecology,College of Global Change and Earth System Science,Beijing Normal University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于东亚干旱半干旱地区内蒙古和蒙古国67 个气象站的观测资料和SPOT VEGETATION 归一化植被指数（NDVI）数据，借助线性趋势、MK趋势性检验、最大化合成法和相关分析等常用数理统计方法，研究了内蒙古和蒙古国地区的植被覆盖变化和气候变化及其响应关系。结果表明：① 近49年内蒙古和蒙古国地区年均气温显著上升，降水变化不明显。年均气温在空间上呈现出南高北低的空间分布格局，降水量表现出由西向东递增趋势。② 空间分布上，内蒙的植被覆盖状况好于蒙古国。时间变化上，该地区植被覆盖变化分为2个阶段，1998-2001年NDVI呈整体退化趋势，2002-2012 年波动上升，其中2009-2012 年连续3a上升。空间变化上，内蒙古境内植被退化的区域主要集中在锡林郭勒盟周边地区，蒙古国境内退化的区域分布在中西部地区。③ 蒙古国境内荒漠和草原植被NDVI与降水呈正相关关系，与气温呈负相关。而对于内蒙古而言荒漠和草原植被的NDVI也与降水呈正相关关系，森林植被与气温呈正相关。就政策层面：内蒙古区域近年来受国家重大生态政策退耕还林、退牧还草的影响，大部分东部和西部植被恢复较快。在今后如果增强两国的文化和政策交流学习，将会对未来的游牧民族文化的保留和发展提供契机。 Abstract:Vegetation in the arid/semi arid area is highly sensitive to climate change. The Mongolian Plateau climate is mainly controlled by the east Asia monsoon system. Hence both Inner Mongolia and the state of Mongolia (Hereafter: Mongolia) experience a similar arid/semi arid climate but have different anthropological influences via their separate social and economic development histories. In this study, we analyzed in-situ observations from 67 meteorological stations (50 stations in Inner Mongolia and 17 in Mongolia) and NDVI (Normalized Difference Vegetation Index) product from SPOT (Satellite pour l' observation de la Terre in French) using Mann-Kendall (MK) tests and Maximum Value Composition (MVC). Our results showed that: (1) Temperature is general higher in the south than the north, while precipitation ranges from low in the west to high in the east. There is a significant warming trend over the whole Mongolian Plateau region from 1961 to 2009, while no obvious trends were found for precipitation; (2) Vegetation coverage in Inner Mongolia was generally greater than that in Mongolia. The time series of vegetation coverage change in these two regions can be divided into two periods. The regional averaged NDVI decreased from 1998 to 2001, fluctuated greatly and then increased continuously from 2009 to 2012. The main degraded areas are located in the Xilingol league, central Inner Mongolia, while they are mostly located in the central and western Mongolia; (3) Positive correlations were found between NDVI and precipitation in desert, steppe vegetation and forest areas in Mongolia, while negative relationships were found for temperature. In Inner Mongolia, NDVI are also positively correlated with precipitation in desert and steppe vegetation areas and also positively correlated with temperature in forests. Recently several major national ecological projects were implemented in Inner Mongolia by national central and local governments, including "The Return Cropland to Forest", the "Return Grazing Land to Grassland" (Grain for Green), and the Three North Protection Forest Plantation Project. These projects improved the local environment by stopping grazing/cropping and planting trees. We believe that these policy actions contribute to the vegetation recovery in Inner Mongolia exhibited here in the NDVI. We attribute the different trends and dynamics of vegetation change in Inner Mongolia and Mongolia to human activities since the climate is similar in these two areas. However, the mechanism driving the changes requires further study particularly investigation of the socio-economic drivers of local land use changes. If formal/informal communication between Inner Mongolia and Mongolia are encouraged in scientific research, cultural exchange and policy making of environmental protection at different levels, it will provide more opportunity for preservation and enhancement of the nomadic culture. 参考文献 相似文献 引证文献

Vegetation change in Brazil’s dryland ecoregions and the relationship to crop production and environmental factors: Cerrado, Caatinga, and Mato Grosso, 2001–2009

South America’s drylands remain some of the most threatened ecosystems on the planet. Yet, we know very little about the dynamics of land-use and land-cover change (LUCC) in these understudied regions. Our objective is to map vegetation change in Brazil’s three largest dryland ecoregions – the Cerrado, Caatinga, and Mato Grosso seasonal forests – using MODIS (Moderate Resolution Imaging Spectroradiometer) data from 2001 to 2009 at the scale of the municipality. We then assess the relationship between changes in land use and land cover and changes in crop and animal production and environmental factors using random forest regression. Although deforestation is still the dominant transition in Mato Grosso, portions of the Cerrado and Caatinga are experiencing a return of woody vegetation. Other agricultural production systems such as sugarcane also play a key role in vegetation change dynamics, besides soybean and cattle ranching. Municipalities with low standard deviations of temperature, high annual precipitation totals, and low elevation are most likely to have undergone deforestation from 2001 to 2009. In the Cerrado, sugarcane is positively associated with woody regrowth, but these changes may be resulting in displacement deforestation in Mato Grosso. Increases in rainfall and the decline of agriculture were responsible for the return of woody vegetation in the Caatinga.

A disappearing biome? Reconsidering land‐cover change in the Brazilian savanna

The Cerrado, the tropical savanna covering 22% of Brazil's territory, or approximately 1.783 million km2, has suffered significant human impacts during the past three decades. This paper re‐examines estimates of Cerrado vegetation change dynamics using high‐resolution satellite remote sensing data from an area of interest extracted from eastern Mato Grosso State. This region has undergone a high degree of typical agricultural development since the early 1970s. Results indicate significant loss of original vegetation as well as high levels of regeneration, suggesting Cerrado vegetation may be more resilient to human impacts than catastrophic estimations suggest. The paper concludes with a critical review of Cerrado land‐cover change studies and the implications of evidence for vegetation regeneration, land‐cover dynamism and land‐use intensification, paying particular attention to spatial scale and research methods. The discussion concludes that Cerrado land‐cover change studied at a higher resolution and larger scales (smaller area) is required to represent more effectively the complexity of land conversion for better assessment of human impacts and environmental policy.

Vegetation change shows generic features of non‐linear dynamics

AbstractQuestion:In non‐linear physical, or chemical, systems dynamic instability limits predictability and external fluctuations cause interesting, and sometimes counter intuitive, effects. We ask how these generic properties of complex systems are seen in vegetation change.Methods:An interacting particle system is used to simulate possible developments of a plant community that was observed for 30 years on a test area in the Lüneburger Heide (Germany). We investigate simulated trajectories for five plant types over several decades. The internal updating rule, simulating the interactions between the five plant types, is completely deterministic, the only sources of stochasticity being the initial conditions and the external climatic variations.Results:Though the results of our simulation model share many aspects with those of stochastic models with probabilistic transition matrices, the solution manifold of our non‐linear model goes beyond the possibilities of stochastic models. Among many stable developments, chaotic trajectories were also found. Climatic fluctuations increased the frequency of certain plant types. These properties of vegetation dynamics match the long‐term field observations. They reflect generic features of complex systems.Conclusions:The presented non‐linear model can provide insights into the dynamics of vegetation change, even though the mechanisms observed in the real world are modelled only in a rather general way. The rich behavioural repertoire, resulting from deterministic internal dynamics, can simulate observed properties that are beyond the possibilities of models with probabilistic internal dynamics.

Vegetation change shows generic features of non-linear dynamics

Question: In non-linear physical, or chemical, systems dynamic instability limits predictability and external fluctuations cause interesting, and sometimes counter intuitive, effects. We ask how these generic properties of complex systems are seen in vegetation change. Methods: An interacting particle system is used to simulate possible developments of a plant community that was observed for 30 years on a test area in the Lineburger Heide (Germany). We investigate simulated trajectories for five plant types over several decades. The internal updating rule, simulating the interactions between the five plant types, is completely deterministic, the only sources of stochasticity being the initial conditions and the external climatic variations. Results: Though the results of our simulation model share many aspects with those of stochastic models with probabilistic transition matrices, the solution manifold of our non-linear model goes beyond the possibilities of stochastic models. Among many stable developments, chaotic trajectories were also found. Climatic fluctuations increased the frequency of certain plant types. These properties of vegetation dynamics match the long-term field observations. They reflect generic features of complex systems. Conclusions: The presented non-linear model can provide insights into the dynamics of vegetation change, even though the mechanisms observed in the real world are modelled only in a rather general way. The rich behavioural repertoire, resulting from deterministic internal dynamics, can simulate observed properties that are beyond the possibilities of models with probabilistic internal dynamics.

Are plant functional types relevant to describe degradation in arid, southern Tunisian steppes?

Abstract. In the Tunisian arid zone disturbances (e.g. overgrazing and agriculture) and stresses (e.g. aridity, low fertility) drive changes in the structure and functioning of rangelands, with a decrease in perennial plant cover, changes in floristic composition and erosion. Long‐term monitoring requires (1) an understanding of the dynamics of vegetation change and associated ecological processes and (2) identification of relevant indicators. Using data from the arid zone of southern Tunisia we tested the hypothesis that plant functional response types could be used to address these two goals. We identified plant functional response types in response to a gradient of soil and vegetation types characterized by changes in perennial plant cover, dominant species and associated soil types. Vegetation samples were stratified by contrasted vegetation patch types with varying perennial plant cover (1.6 to 22%). We focused our analysis of trait responses within dwarf–shrubs, which are the dominants in typical steppe ecosystems of south Tunisia. Available trait data concerned morphology (plant height, leaf type), regeneration (dispersal mode, phenology and regeneration mode) and grazing value. Although we found it difficult to recognize ‘indicator response types’ that could be used directly to monitor changes in community composition, we were able to identify plant response syndromes that are relevant to long‐term vegetation changes, and in particular degradation processes, in the region. Two main response types were identified: the decreaser type, made up of small or medium chamaephytes with high grazing palatability and the increaser type with medium to tall chamaephytes and low grazing palatability. These response types are proposed as key elements in a state‐and‐transition model of vegetation dynamics in the context of agropastoral disturbances and climatic and edaphic stresses.

Are plant functional types relevant to describe degradation in arid, southern Tunisian steppes?

Abstract In the Tunisian arid zone disturbances (e.g. overgrazing and agriculture) and stresses (e.g. aridity, low fertility) drive changes in the structure and functioning of rangelands, with a decrease in perennial plant cover, changes in floristic composition and erosion. Long-term monitoring requires (1) an understanding of the dynamics of vegetation change and associated ecological processes and (2) identification of relevant indicators. Using data from the arid zone of southern Tunisia we tested the hypothesis that plant functional response types could be used to address these two goals. We identified plant functional response types in response to a gradient of soil and vegetation types characterized by changes in perennial plant cover, dominant species and associated soil types. Vegetation samples were stratified by contrasted vegetation patch types with varying perennial plant cover (1.6 to 22%). We focused our analysis of trait responses within dwarf–shrubs, which are the dominants in typical ste...

Palaeoclimate versus vegetation reconstruction – palynological investigations on the Oligocene sequence of the Sava Basin, Slovenia

An Oligocene succession from the Slovenian Sava Basin (Zasavje) was analysed to reconstruct climate and vegetation of the interval. Independent quantitative approaches were applied on a detailed palynological data set to reconstruct both parameters separately allowing for a synthesis and interpretation. The reconstruction of palaeoclimate is based on the coexistence approach and documents an equal, warm-temperate, humid climate with low annual variation. Quantitative results indicate values of mean annual temperature of 16–19°C, with winter temperatures of 6–9°C and summer temperatures of 25–28°C, and a mean annual precipitation ranging between 1100 and 1300 mm. In contrast to the very homogeneous climatic signal, the vegetational reconstruction based on multivariate statistical analyses shows distinct changes through time. During intervals of peat accumulation, the environment was a typical swamp vegetation dominated by Taxodiaceae and ferns, in which ephemeral small ponds developed due to changing groundwater levels. With the development of an expanded limnic environment, the Taxodiaceae retreated and a riparian swamp flora dominated. This vegetation, in turn, was displaced by elements of drier mesophytic habitats that increased in abundance during a tectonically forced lowering of the groundwater table. Subsequently, the entire study area was flooded by transgression and overlain by marine sediments. All changes in vegetation can be explained by influences of the basin development on the habitats of the plant communities. The results demonstrate a vegetational change in the Oligocene of the Sava Basin that is independent from climate. Vegetation change dynamics were controlled probably by the regional tectonic–palaeogeographic development within a very equable, warm-temperate, and humid climate.