Long-term Vegetation Dynamics Research Articles

Holocene Paleoecology in the Neotropical Savannas of Northern South America (Llanos of the Orinoquia Ecoregion, Colombia and Venezuela): What Do We Know and on What Should We Focus in the Future?

We provide an overview of the Holocene paleoecology of the Llanos ecoregion. A region that captured the attention of researchers for more than 200 years, as it exhibits a high heterogeneity in landscapes and vegetation, where savanna and forest mosaics exist. Located in an area influenced by the seasonal migration of the Intertropical Convergence Zone (ITCZ), it provides a unique area for understanding long-term dynamics of climate, vegetation and human history. Twelve locations have been paleoecologically studied, showing general vegetation and climate changes trends since the Last Glacial Maximum (LGM). During LGM savanna herbs were dominant, indicating dry climatic conditions. The transition of the Holocene was characterized by a slight increase in forest taxa, suggesting a transition to a wetter climate. Between ∼10,000 and 7,000 cal yr BP, grasslands were abundant, and few forest taxa, including Mauritia were also common but rare, pointing to a warm and humid climate. After ∼7,000 cal yr BP, the gallery forest started to expand, suggesting a change to a wetter climate. Mauritia palms increased markedly after 4,000–3,000 cal yr BP, possibly driven by higher mean annual precipitation and/or longer wet season. The start of human occupation remains unclear, but it has been linked to the time of expansion of Mauritia, a period in which fires, possibly of anthropogenic origin, were more frequent. To understand patterns of change in these ecosystems, it is necessary to improve the chronological control of the sediments in future studies and increase the resolution and proxies used to reconstruct their history.

Vegetation dynamics in response to climate change and human activities in the Hulun Lake basin from 1981 to 2019

Monitoring long-term vegetation dynamics is essential for developing adaptation strategy to address the challenges to the ecosystem posed by climate change and human activities. This study analyzed spatio-temporal changes of normalized difference vegetation index (NDVI) in the Hulun Lake Basin (HLB) from 1981 to 2019, and explored the relationship between climatic factors and NDVI datasets. Furthermore, the residual trend (RESTREND) method was used to distinguish between the impacts of changes in climate and human activities on vegetation dynamics. The results showed that NDVI of the basin initially increased to the 1990s, then decreased to the mid-2000s, and finally rebounded to 2019 owing to the periodic fluctuations in precipitation. There were 28.32% of the NDVI pixels significantly increasing and 13.85% of the pixels significantly decreasing. The increase proportion of vegetation coverage in forest, wetland and cultivated land was higher than other vegetation types. NDVI in the China Grass Zone (CGZ) significantly degraded by 20.39% compared with the Mongolia Grass Zone (MGZ) significantly degraded by 5.60%. NDVI was significantly correlated with precipitation and weakly correlated with temperature in the HLB, and precipitation was the principal factor influencing vegetation coverage. The results of RESTREND revealed that farmland reclamation, over-grazing, and open-pit mining led to greater browning of vegetation in the CGZ than in the MGZ. Meanwhile, the implementation of ecological protection and restoration projects have helped the greening of the vegetation in the CGZ (20.91%) compared with the MGZ (7.45%). China’s ecological restoration projects are important for Mongolia to reverse the trend of serious ecological degradation. Our results can provide scientific decision-making for the local government to formulate differentiated vegetation ecological protection and restoration measures.

Growing-season vegetation coverage patterns and driving factors in the China-Myanmar Economic Corridor based on Google Earth Engine and geographic detector

Although previous studies have shown that the construction of the China-Myanmar Economic Corridor (CMEC) has caused critical deforestation, few studies have monitored the long-term vegetation dynamics in corridor regions. Recent studies have revealed vegetation greening trends at different scales but have failed to further explore whether these trends are due to the restoration of natural vegetation or the large-scale planting of artificial crops. To investigate the vegetation dynamics and influencing factors during the growing season between 2001 and 2020 in the CMEC area, trend analysis, the random forest (RF) classifier at Google Earth Engine platform, and the geographic detector were employed to quantitatively analyze the patterns of distribution and change in vegetation coverage and its driving factors. Note that we distinguished between natural vegetation areas and artificial crop areas using the RF classification algorithm in an attempt to improve the drawback that most previous studies confused the contribution of natural vegetation and artificial vegetation to macro vegetation change. We discovered that (1) the growing-season average fractional vegetation cover (FVC) was 0.7033, which was relatively low in central and southern regions. The FVC increased by 0.21% yr−1 from 2001 to 2020, and areas with an increasing trend in FVC were 16.67% more than those with a decreasing trend. (2) Although forests and grasslands were reduced by 0.68%, the cropland that prominently clustered in the central and southern regions contributed 50.37% to an increase in FVC, and the decreasing effects on natural vegetation were offset by the increase in artificial crops. (4) The factors that influence FVC distribution were ranked in descending order: land use/land cover (LULC) > climate > topography > anthropogenic activity; factors that influence FVC change were ranked as: anthropogenic activity > climate > LUCC. Note that the grain yield influence on the FVC distribution increased 0.31% yr -1, which was also the most important factor driving FVC change, indicating that agricultural activities increasingly facilitated vegetation greening.

Revisiting the Past: Replicability of a Historic Long-Term Vegetation Dynamics Assessment in the Era of Big Data Analytics

Open and analysis-ready data, as well as methodological and technical advancements have resulted in an unprecedented capability for observing the Earth’s land surfaces. Over 10 years ago, Landsat time series analyses were inevitably limited to a few expensive images from carefully selected acquisition dates. Yet, such a static selection may have introduced uncertainties when spatial or inter-annual variability in seasonal vegetation growth were large. As seminal pre-open-data-era papers are still heavily cited, variations of their workflows are still widely used, too. Thus, here we quantitatively assessed the level of agreement between an approach using carefully selected images and a state-of-the-art analysis that uses all available images. We reproduced a representative case study from the year 2003 that for the first time used annual Landsat time series to assess long-term vegetation dynamics in a semi-arid Mediterranean ecosystem in Crete, Greece. We replicated this assessment using all available data paired with a time series method based on land surface phenology metrics. Results differed fundamentally because the volatile timing of statically selected images relative to the phenological cycle introduced systematic uncertainty. We further applied lessons learned to arrive at a more nuanced and information-enriched vegetation dynamics description by decomposing vegetation cover into woody and herbaceous components, followed by a syndrome-based classification of change and trend parameters. This allowed for a more reliable interpretation of vegetation changes and even permitted us to disentangle certain land-use change processes with opposite trajectories in the vegetation components that were not observable when solely analyzing total vegetation cover. The long-term budget of net cover change revealed that vegetation cover of both components has increased at large and that this process was mainly driven by gradual processes. We conclude that study designs based on static image selection strategies should be critically evaluated in the light of current data availability, analytical capabilities, and with regards to the ecosystem under investigation. We recommend using all available data and taking advantage of phenology-based approaches that remove the selection bias and hence reduce uncertainties in results.

Comprehensive Assessment of Performances of Long Time-Series LAI, FVC and GPP Products over Mountainous Areas: A Case Study in the Three-River Source Region, China

Vegetation biophysical products offer unique opportunities to examine long-term vegetation dynamics and land surface phenology (LSP). It is important to understand the time-series performances of various global biophysical products for global change research. However, few endeavors have been dedicated to assessing the performances of long-term change characteristics or LSP extraction derived from different satellite products, especially in mountainous areas with highly fragmented and rugged surfaces. In this paper, we assessed the time-series characteristics and LSP detections of Global LAnd Surface Satellite (GLASS) leaf area index (LAI), fractional vegetation cover (FVC), and gross primary production (GPP) products across the Three-River Source Region (TRSR). The performances of products’ temporal agreements and their statistical relationship as a function of topographic indices and heterogeneous pixels, respectively, were investigated through intercomparison among three products during the period 2000 to 2018. The results show that the phenological differences between FVC and two other products are beyond 10 days over more than 35% of the pixels in TRSR. The long-term trend of FVC diverges significantly from GPP and LAI for 13.96% of the total pixels, and the percentages of mismatched pixels between FVC and two other products are 33.24% in the correlation comparison. Moreover, good agreements are observed between GPP and LAI, both in terms of LSP and interannual variations. Finally, the LSP and long-term dynamics of the three products exhibit poor performances on heterogeneous surfaces and complex topographic areas, which reflects the potential impacts of environmental factors and algorithmic imperfections on the quality and performances of different products. Our study highlights the spatiotemporal disparities in detections of surface vegetation activity in mountainous areas by using different biophysical products. Future global change studies may require multiple high-quality satellite products with long-term stability as data support.

Legacies of past human activities on one of the largest old-growth forests in the south-east European mountains

The Dinaric Mountains are a region considered as a hotspot for late-successional montane mixed Abies alba-Fagus sylvatica-Picea abies old-growth forests. This is likely due to historical deforestation levels being presumably lower than in other European regions. This paper provides new insights into the long-term vegetation dynamics and possible legacies of past human activities in old-growth forests in the montane zone of the Dinaric Mountains. Our extensive ground survey and the detailed land-cover types map show that the mixed A. alba-F. sylvatica old-growth forest with sparse P. abies is surrounded by almost pure F. sylvatica stands at Biogradska Gora. The well-dated stand-scale palaeoecological records (pollen, spores, stomata, macrofossils, macroscopic charcoal, and magnetic susceptibility) show that land use (cereal crop cultivation, cattle herding, and fire) during the Middle Ages caused a reduction of the A. alba and P. abies-dominated forest. After a major land abandonment around the Black Death pandemic (mid-14th century) and weaker land-use phases, F. sylvatica-dominated stands developed in the more accessible areas surrounding the old-growth forest. The legacy of past land uses is still visible as the almost pure F. sylvatica stands show less old-growth characteristics than other European beech-dominated old-growth forests. Markedly in contrast to decreasing tree cover elsewhere in the region, tree cover increased several centuries before the formal protection of the forest (1878 ce). These results support the view that historical land-use pressures played an important role for the small extent and the continuity of disturbance-sensitive A. alba and P. abies-dominated old-growth forest stands.

Vertical Differences in the Long-Term Trends and Breakpoints of NDVI and Climate Factors in Taiwan

This study explored the long-term trends and breakpoints of vegetation, rainfall, and temperature in Taiwan from overall and regional perspectives in terms of vertical differences from 1982 to 2012. With time-series Advanced Very-High-Resolution Radiometer (AVHRR) normalized difference vegetation index (NDVI) data and Taiwan Climate Change Estimate and Information Platform (TCCIP) gridded monthly climatic data, their vertical dynamics were investigated by employing the Breaks for Additive Seasonal and Trend (BFAST) algorithm, Pearson’s correlation analysis, and the Durbin–Watson test. The vertical differences in NDVI values presented three breakpoints and a consistent trend from positive (1982 to 1989) to negative at varied rates, and then gradually increased after 2000. In addition, a positive rainfall trend was discovered. Average and maximum temperature had similar increasing trends, while minimum temperature showed variations, especially at higher altitudes. In terms of regional variations, the vegetation growth was stable in the north but worse in the central region. Higher elevations revealed larger variations in the NDVI and temperature datasets. NDVI, along with average and minimum temperature, showed their largest changes earlier in higher altitude areas. Specifically, the increasing minimum temperature direction was more prominent in the mid-to-high-altitude areas in the eastern and central regions. Seasonal variations were observed for each region. The difference between the dry and wet seasons is becoming larger, with the smallest difference in the northern region and the largest difference in the southern region. Taiwan’s NDVI and climatic factors have a significant negative correlation (p < 0.05), but the maximum and minimum temperatures have significant positive effects at low altitudes below 500 m. The northern and central regions reveal similar responses, while the south and east display different feedbacks. The results illuminate climate change evidence from assessment of the long-term dynamics of vegetation and climatic factors, providing valuable references for establishing correspondent climate-adaptive strategies in Taiwan.

Long-term dynamics of aquatic vegetation and the state of ecosystems of soda lakes in southeastern Transbaikalia

The cyclical nature of long-term changes in the annual amounts of atmospheric precipitation in Transbaikalia controls most of the processes in ecosystems. The paper briefly describes the long-term vegetation dynamics of soda lakes in the southeast of Transbaikal territory. These dynamics are driven by changes in abiotic parameters of the lakes, mainly water salinity and pH values. When the values of these indicators increase, the perennial succession series of vegetation of higher plants is as following: Helophytes + Neustophytes + Hydatophytes → Helophytes + Hydatophytes → Helophytes. The succession series of macrophytic algae is as following: Stigeoclonium sp. or Spirogyra sp. → Cladophora fracta + Charophyta → Enteromorpha intestinalis.

Long term changes of the inner-alpine steppe vegetation: the dry grassland communities of the Vinschgau (South Tyrol, Italy) 40–50 years after the first vegetation mapping

Aims: The Vinschgau is the driest inner-alpine valley in the Eastern Alps and harbours a unique steppe vegetation. We studied these dry grassland communities and aimed to answer the following questions: Which plant communities can be found currently? Do the syntaxa described by Braun-Blanquet in the 1960s still prevail in the area? Has there been any change in species composition over the last 40–50 years?Study area: Along an approximately 40 km transect, the south-facing slopes of the Vinschgau valley (South Tyrol, Italy) from Mals to Plaus were investigated.Methods: For the classification, 92 relevés were sampled in 2019 and compared with 76 relevés from the 1960s and ´70s by means of vegetation tables and ordinations (Detrended Correspondence Analysis).Results: Based on our investigation, the majority of dry grassland communities can be classified asFestuco-Caricetum supinae. Three subassociations were defined by the dominant speciesStipa capillata,Bothriochloa ischaemumandStipa pennataagg. The comparison of new and old relevés shows an increase in species from the classSedo-Scleranthetea(e.g.Trifolium arvense,Erodium cicutarium) and the associationArtemisieto-Agropyretum. In addition, ruderal elements (e.g.Erigeron annuus,Convolvulus arvensis) have also migrated into dry grasslands. A shift in the dominance over time can be recognized as well. In particular,Festuca rupicolaand to some extent alsoStipa capillata, have increased in abundance and frequency.Conclusions: We suggest to include the investigated closed dry grasslands in the allianceFestucion valesiacae. The rank of the character species at association, alliance and order level should be re-analysed. In order to obtain a better syntaxonomic overview of western and eastern alpine dry grassland communities in relation to Eastern European dry grasslands, a comprehensive study is absolutely necessary. Furthermore, long-term vegetation dynamics and vegetation change need to be studied in more detailed future studies.Taxonomic reference: Fischer et al. (2008).Syntaxonomic references: Mucina et al. (2016) for syntaxa from alliance to class level; Braun-Blanquet (1961) for associations.Abbreviations: agg. = aggregate; cf. = confer (means ‘compare’); DCA = Detrended Correspondence Analysis; s. lat. = sensu lato; s. str. = sensu stricto

Long-term forest vegetation dynamics in Nanda Devi Biosphere Reserve, Indian west Himalaya: evidence from repeat studies on compositional patterns.

It has been established that resurvey of historical vegetation stands, even those not marked permanently, could foster our understanding of vegetation dynamics and changes in structure and composition over time. However, such studies are poorly available, particularly in remote landscapes of the Indian Himalaya. There exists a complete lack of resurveys, which has limited our ability to provide reliable evidence of changes over the decades. This study, for the first time in the Indian Himalaya, considered repeat surveys (nearly after 25years) of vegetation stands in eleven forest communities of the buffer zone of NDBR (Nanda Devi Biosphere Reserve). Thirty historical forest stands, earlier studied in 1988-1990, were revisited during 2012-2014 and investigated using the same survey methods as used in the previous study. We found that previously reported dominant tree species, i.e., Alnus nepalensis, Acer cappadocicum, Quercus floribunda, Quercus semecarpifolia, Hippophae salicifolia, and Betula utilis, in nine out of eleven communities in the study area are continuing to exhibit dominance in the community. However, a significant increase in species richness and density in the seedling and sapling layer in Quercus floribunda, Quercus semecarpifolia, Rhododendron arboreum, and Abies pindrow is indicative of the ongoing process of change in forest composition. The compositional features of plant communities, when analyzed through Community Change Sensitivity (CCS) approach, identified Quercus floribunda, mixed Quercus-deciduous spp., Hippophae salicifolia, and Abies pindrow as the most change-sensitive communities in the study area and thus can be prioritized as the long-term ecological monitoring sites in the west Himalaya to understand intensity and patterns of changes. The potential changes based on the ecological information from two time period compositional data sets, having conservation and management implications, should be accommodated in the long-term perspective plans of the reserve.

Multi-proxy indications of depositional evolution and paleo-natural disasters (flooding and fire) in the southern part of the Korean Peninsula during the Holocene

Understanding paleoenvironmental changes and corresponding driving forces can provide valuable information for predicting and preparing for future climate change. However, under the complex climate system, the driving mechanisms behind hydroclimatic variability in terms of timescales and magnitude are still unclear, and the various ecological responses are not clear. Here, we reconstruct the history of swamp evolution and climate changes in the southern part of the Korean Peninsula during the Holocene based on multi-proxy data (palynomorphs, microscopic charcoal, diatoms, grain size, total organic carbon, C/N ratio, and δ13CTOC data). The climatic conditions in the study area gradually became cold and dry due to the weakening East Asian summer monsoon (EASM) after ca. 5400 cal yr BP, as evidenced by the shift in vegetation communities from temperate broad-leaved forests dominated by Quercus to mixed conifer and deciduous broad-leaved forests with increased cold/dry-tolerant taxa. After ca. 4700 cal yr BP, microscopic charcoal concentration to terrestrial pollen concentration values are relatively high together with a sharp decrease in palynomorph concentrations and the proportions of arboreal pollen, representing open forest with fewer plants due to frequent wildfires. In addition, the quasi-millennial frequencies of seasonal fires (dry spring) and flooding (summer rainfall) were identified in our study area during the Late Holocene, which correspond to lower sea surface temperatures of the western tropical Pacific and stronger El Niño Southern Oscillation (ENSO) activity periods. After ca. 8200 cal yr BP, the depositional environment underwent gradual backswamp expansion due to high precipitation, strengthened EASM, and relative sea-level rise during the Early to Middle Holocene. During the Late Holocene, ENSO-driven extreme hydroclimatic variability, such as frequent flooding and fire, had significant impacts on not only swamp development with large fluctuations in water level but also long-term vegetation and aquatic ecosystem dynamics.

Analysis of the Response of Long-Term Vegetation Dynamics to Climate Variability Using the Pruned Exact Linear Time (PELT) Method and Disturbance Lag Model (DLM) Based on Remote Sensing Data: A Case Study in Guangdong Province (China)

The dynamic change and spatial–temporal distribution of vegetation coverage are of great significance for regional ecological evolution, especially in the subtropics and tropics. Identifying the heterogeneity in vegetation activities and its response to climate factors is crucial for projecting ecosystem dynamics. We used long-term (2001–2018) satellite-derived enhanced vegetation index (EVI) datasets and climatic factors to analyze the spatiotemporal patterns of vegetation activities in an experimental area in Guangdong Province (China), as well as their links to changes in temperature (TEM), relative humidity (HUM), precipitation (PRE), sunshine duration (SUN), and surface runoff. The pruned exact linear time change point detection method (PELT) and the disturbance lag model (DLM) were used to understand the detailed ecological coverage status and time lag relationships between the EVI and climatic factors. The results indicate the following. (1) At the whole regional scale, a significant overall upward trend in the EVI variation was observed in 2001–2018. More specifically, there were two distinct periods with different trends, which were split by a turning point in 2005. PRE was the main climate-related driver of the rising EVI pre-2005, and the increase in TEM was the main climate factor influencing the forest EVI variation post-2006. (2) A three-month time lag effect was observed in the EVI response to relative humidity. The same phenomenon was found in the sunshine duration factor. (3) The EVI of farmlands (one type of land use) exhibited the largest lags between relative humidity and the sunshine duration factor, followed by grasslands and forests. (4) The comprehensive index of surface runoff could explain the time lags of vegetation activities, and the surface runoff value showed an apparently negative relationship with the vegetation coverage change.

Influence of taxonomic resolution on the value of anthropogenic pollen indicators

The taxonomic resolution of palynological identification is determined by morphological criteria that are used to define pollen types. Different levels of taxonomic resolution are reached in palynology, depending on several factors such as the analyst’s expertise, the palynological school, the aim of the study, the preservation of the pollen grains, the reference collections and the microscope facilities. Previous research has suggested that attaining pollen records with high taxonomic resolution is important to reconstruct correctly past land use and human impact. This is in turn central to disentangling past human activities from other drivers of long-term vegetation dynamics such as natural disturbance or climate variability. In this study, we assess the impact of taxonomic resolution on the indicative capacity of anthropogenic pollen types. To achieve this, we attribute the pollen types of sixteen sedimentary records, located along a latitudinal gradient spanning from Switzerland to Italy, to three levels of taxonomic resolution previously proposed at the European scale. Our results show that higher taxonomic resolution improves the identification of human impact by enhancing the indicative power of important pollen indicators widely used in the research field. Our results may contribute to the improvement of palynological reconstructions of land use and human impact by identifying key pollen types whose determination requires particular attention.

The influence of climatic change, fire and species invasion on a Tasmanian temperate rainforest system over the past 18,000 years

We aim to understand how did cool temperate rainforest respond to changes in climate and fire activity over the past 18 kcal yrs, interrogating the role that flammable plant species (such as Eucalyptus) have in the long-term dynamics of rainforest vegetation. We used high-resolution pollen and charcoal analysis, radiometric dating (lead and carbon), modern pollen-vegetation relationships, detrended correspondence analysis, rarefaction (palynological richness), rate of change and granger causality to understand the patterns and drivers of change in cool temperate rainforest from the sediments of Lake Vera, southwest Tasmania through time. We record clear changes in key rainforest taxa in response to climatic change throughout the record. The spread of rainforest through the lake catchment in the early and mid-Holocene effectively negated disturbance from fire despite a region-wide peak in fire activity. An anomalously dry period in the late-Holocene resulted in a local fire that facilitated the establishment of Eucalyptus within the local catchment. Granger causality tests reveal a significant lead of Eucalyptus over fire activity in the Holocene, indicating that fires were enhanced by this pyrogenic taxon following establishment.

Relative pollen productivity estimates of savanna taxa from southern Africa and their application to reconstruct shrub encroachment during the last century

To understand the resilience of African savannas to global change, quantitative information on the long-term dynamics of vegetation is required. Past dynamics can be reconstructed with the REVEALS model, which requires pollen productivity estimates (PPE) that are calibrated using surface pollen and vegetation data. Here we calculated PPE values for five savanna taxa using the extended R-value (ERV) model and two pollen dispersal options: the Gaussian plume model (GPM) and the Lagrangian stochastic model (LSM). The ERV calculations failed to produce a reliable PPE for Poaceae. We therefore used Combretaceae as the reference taxon – although values obtained with Poaceae as the reference taxon are presented in the supplement. Our results indicate that Combretaceae is the taxon with the highest pollen productivity and Grewia the taxon with the lowest productivity. Acacia and Dichrostachys are intermediate pollen producers. We find no clear indication of whether the GPM PPEs or the LSM PPEs are more realistic, but the differences between these values confirmed that the pollen fall speed has a greater effect in the modelling of GPM than in the LSM. We also applied REVEALS to the pollen record of Lake Otjikoto (northern Namibia) and obtained the first quantitative reconstruction of the last 130 years of vegetation history in the region. Cover estimates for Poaceae indicate the predominance of a semi-open landscape throughout the 20th century, while cover values below 50% since the 21st century correspond to a thick savanna. This change in grass cover is associated with the spread of Vachellia, Senegalia and Grewia reflecting an encroached state.

Examining long-term natural vegetation dynamics in the Aral Sea Basin applying the linear spectral mixture model.

BackgroundAssociated with the significant decrease in water resources, natural vegetation degradation has also led to many widespread environmental problems in the Aral Sea Basin. However, few studies have examined long-term vegetation dynamics in the Aral Sea Basin or distinguished between natural vegetation and cultivated land when calculating the fractional vegetation cover.MethodsBased on the multi-temporal Moderate Resolution Imaging Spectroradiometer, this study examined the natural vegetation coverage by introducing the Linear Spectral Mixture Model to the Google Earth Engine platform, which greatly reduces the experimental time. Further, trend line analysis, Sen trend analysis, and Mann–Kendall trend test methods were employed to explore the characteristics of natural vegetation cover change in the Aral Sea Basin from 2000 to 2018.ResultsAnalyses of the results suggest three major conclusions. First, the development of irrigated agriculture in the desert area is the main reason for the decrease in downstream water. Second, with the reduction of water, the natural vegetation coverage in the Aral Sea Basin showed an upward trend of 17.77% from 2000 to 2018. Finally, the main driving factor of vegetation cover changes in the Aral Sea Basin is the migration of cultivated land to the desert.

NDVI Indicates Long-Term Dynamics of Vegetation and Its Driving Forces from Climatic and Anthropogenic Factors in Mongolian Plateau

In recent years, global warming and intense human activity have been responsible for significantly altering vegetation dynamics on the Mongolian Plateau. Understanding the long-term vegetation dynamics in this region is important to assess the impact of these changes on the local ecosystem. Long-term (1982–2015), satellite-derived normalized difference vegetation index (NDVI) datasets were used to analyse the spatio-temporal patterns of vegetation activities using linear regression and the breaks for additive season and trend methods. The links between these patterns and changes in temperature, precipitation (PRE), soil moisture (SM), and anthropogenic activity were determined using partial correlation analysis, the residual trends method, and a stepwise multiple regression model. The most significant results indicated that air temperature and potential evapotranspiration increased significantly, while the SM and PRE had markedly decreased over the past 34 years. The NDVI dataset included 71.16% of pixels showing an increase in temperature and evaporation during the growing season, particularly in eastern Mongolia and the southern border of the Inner Mongolia Autonomous region, China. The proportion indicating the breakpoint of vegetation dynamics was 71.34% of pixels, and the trend breakpoints mainly occurred in 1993, 2003, and 2010. The cumulative effects of PRE and SM in the middle period, coupled with the short-term effects of temperature and potential evapotranspiration, have had positive effects on vegetation greening. Anthropogenic factors appear to have positively impacted vegetation dynamics, as shown in 81.21% of pixels. We consider rapid economic growth, PRE, and SM to be the main driving factors in Inner Mongolia. PRE was the main climatic factor, and combined human and livestock populations were the primary anthropogenic factors influencing vegetation dynamics in Mongolia. This study is important in promoting the continued use of green projects to address environmental change in the Mongolian Plateau.

Evaluating natural experiments in ecology: using synthetic controls in assessments of remotely sensed land treatments.

Many important ecological phenomena occur on large spatial scales and/or are unplanned and thus do not easily fit within analytical frameworks that rely on randomization, replication, and interspersed a priori controls for statistical comparison. Analyses of such large-scale, natural experiments are common in the health and econometrics literature, where techniques have been developed to derive insight from large, noisy observational data sets. Here, we apply a technique from this literature, synthetic control, to assess landscape change with remote sensing data. The basic data requirements for synthetic control include (1) a discrete set of treated and untreated units, (2) a known date of treatment intervention, and (3) time series response data that include both pre- and post-treatment outcomes for all units. Synthetic control generates a response metric for treated units relative to a no-action alternative based on prior relationships between treated and unexposed groups. Using simulations and a case study involving a large-scale brush-clearing management event, we show how synthetic control can intuitively infer treatment effect sizes from satellite data, even in the presence of confounding noise from climate anomalies, long-term vegetation dynamics, or sensor errors. We find that accuracy depends on the number and quality of potential control units, highlighting the importance of selecting appropriate control populations. Although we consider the synthetic control approach in the context of natural experiments with remote sensing data, we expect the methodology to have wider utility in ecology, particularly for systems with large, complex, and poorly replicated experimental units.

Exploring the long-term vegetation dynamics of different ecological zones in the farming-pastoral ecotone in northern China.

The vegetation in the farming-pastoral ecotone in northern China is influenced by both natural and anthropogenic factors and has undergone drastic changes in the past decades. The farming-pastoral ecotone is the transition zone from agriculture to animal husbandry. The ecological environment of this ecotone is complex and fragile. Most researches have primarily focused on the entire farming-pastoral ecotone, seldomly considering the differences between different ecological zones characterized by soil, climate, and biome conditions. Based on the long time series of leaf area index (LAI) data, meteorological data, and land-use dataset, this study analyzed LAI variation trends, the correlations between LAI and climate factors, and the impact of land-use type change on vegetation in the farming-pastoral ecotone in northern China. Moreover, this paper makes a full study of the changes of the whole study area from the perspective of the differences between different ecological zones. The results showed that over 36years, areas with vegetation improvements were considerably larger than those with degradations. However, there were still 49.56% of the total area showing no significant vegetation change. There are differences in vegetation change and response to climate between the forest ecological zones and the grassland ecological zones. The vegetation improvement trends of the forest ecological zones were larger and more sensitive to temperature, while the vegetation improvements of the grassland ecological zones were relatively small, and were more sensitive to precipitation. Human activities promote LAI changes in areas close to the forest ecological zones. The change of land use indicates that the decrease of the overall natural vegetation area has not resulted in decreasing LAI. And there is a growing trend of woodland area in the grassland ecological zones. The study provides a theoretical basis for the management of the environment and vegetation in the farming-pastoral ecotone in northern China.

Tree Composition, Diversity, and Stand Structure of Mid-montane Forest in Sipit Watershed, Mount Makiling Forest Reserve ASEAN Heritage Park, Philippines

This study aimed to establish benchmark data and assess diversity, stand structure, and identify species and habitats that need immediate protection and conservation and monitor ecosystems dynamics through time. A 2-ha long-term ecological research (LTER) plot was established in the mid-montane forest in Sipit Watershed of Mount Makiling Forest Reserve ASEAN Heritage Park (MMFR AHP). Fifty 20 m x 20 m subplots were established from the said 2-ha LTER plot and oriented 100 m north and 200 m east. Trees with diameter at breast height (DBH) of ≥ 10 cm were measured in fifty 20 m x 20 m plots. A total of 1,055 tree individuals belonging to 73 species among 49 genera and 33 families were inventoried. The importance value index (IVI) shows dominant species – namely, Antidesma pleuricum Tul. (40.40), Neolitsea vidalii Merr. (34.14), Palaquium philippense C.B.Rob. (27.77), Micromelum minutum (G.Forst) Wight & Arn. (27.50), and Syzygium barnesii (Merr.) Merr. (16.16). Further, the inventory recorded a total of 11 threatened species thriving in the area and several species suspected to be unique in the area or can only be found abundant therein. The study reveals that the population of P. philippense was maintained intact and preserved within the Sipit Watershed for about a hundred years. Findings also reveal a very high diversity at 3.32 Shannon diversity index with an evenness of 0.28 and relatively high endemism, where 44% (32 species) of the 73 species are endemic. The study is very significant in long-term vegetation dynamics for sustainable management and conservation of protected areas like MMFR AHP, as well as for future research and studies for biodiversity conservation, climate change, and protection of other mountain ecosystems.