Changes In Vegetation Types Research Articles

Distribución altitudinal de la riqueza y composición de ensamblajes de aves en una zona montañosa al sur de Nayarit, México

Elevation gradient studies have strengthened the evaluation of changes in richness and composition of bird assemblages. They also provide information on environmental variables that determine bird distribution, and the variables that define their population structure. Our aim was to describe their variation through an elevational cline in Southern Nayarit, Mexico. To analyze the behavior of richness across the gradient, we gathered information through point counts in nine elevational intervals (300 m from each other) from sea level to 2 700 m of elevation. With a standardized sampling effort, we produced rarefaction curves and analyzed changes in species composition by hierarchical classification using the TWINSPAN technique. In order to identify variables associated with richness changes, we examined the effect of precipitation and habitat structure via regression trees. An analysis of nonmetric multidimensional scaling (NMDS) was implemented with the purpose to determine if the changes in composition correspond to changes in vegetation types. Species richness varied significantly across the gradient: high in the lower parts of the gradient, reached its peak in the middle, and decreased monotonically with elevation. Species responded to changes in the cline and were grouped in three elevational zones. Analyses suggest that changes in richness and species composition are influenced by vegetation, its structure and precipitation regime, as well as various aspects related to habitat features and disturbance. These aspects should be taken into account in order to design appropriate strategies for the conservation of the birds of Nayarit.

Chaparral recovery following a major fire with variable burn conditions

ABSTRACTWildfires are a common occurrence in California shrublands, maintaining ecosystem functions with the regeneration of key shrub species. The Cedar Fire of 2003 in southern California was unique in that a portion of it burned with wildfire accelerated by dry, strong northeasterly Santa Ana winds that later subsided, while the remaining area burned under an onshore, westerly wind of lower velocity and higher humidity. These nearby areas, having similar terrain, fuel type, and environments, burned under these different conditions. Our goal is to understand the connection between vegetation response to extreme fire events by analysing life-form regrowth in chaparral from the Santa Ana wind driven, Santa Ana backing, and non-Santa Ana fire types. Study sites representing these three fire conditions were based on fire progression maps generated from Moderate Resolution Imaging Spectroradiometer (MODIS) hotspot data. Shrub cover before and six years after the fire were mapped based on a spatial contextual classifier applied to colour infrared orthoimagery, and analysed per slope aspect and angle, elevation, and fire characteristic categories to isolate shrub regrowth patterns. Six years after the fire, shrub cover in the Santa Ana wind driven site was substantially lower than in the other two sites. Such differences in shrub cover at the landscape scale may have resulted from different wind speed, direction, and humidity during the fire, coupled with terrain differences on wildfire behaviour and different rates of recovery associated primarily with moisture availability to plants. The information gathered from this study can help land managers assess shrub regrowth and possibility of vegetation type change after extreme fire events in southern California shrubland ecosystems.

Carbon emission along a eutrophication gradient in temperate riverine wetlands: effect of primary productivity and plant community composition

Summary Eutrophication increases primary productivity and favours the predominance of floating vegetation in wetlands. Carbon (C) fluxes in wetlands are strongly driven by primary productivity and can differ by vegetation type. However, to the best of our knowledge, the role of eutrophication in C fluxes has rarely been assessed. Consequently, we aimed to measure the seasonal variation in carbon dioxide (CO2) and methane (CH4) fluxes at six aquatic sites in four temperate wetlands, ranging along a gradient of sediment total phosphorus content, and determine whether C fluxes correlate with above‐ground net primary productivity (ANPP) and plant community composition along this eutrophication gradient. Daytime CO2 emissions were significantly and negatively correlated with wetland net primary productivity as a result of the greater C fixation by photosynthesis during the peak of production. Conversely, CH4 emissions were significantly and positively correlated with wetland ANPP, possibly due to higher litter production and anaerobic decomposition. The highest CH4 emissions were observed above floating vegetation, which favoured hypoxic conditions in the water column. CH4 emissions including ebullition were higher above macroalgal belts than above vascular plants with floating leaves. CH4 emissions without ebullition (i.e. resulting from plant transport and diffusion) better correlated with the abundance of macroalgae than with the abundance of vascular plants with floating leaves. Our results suggest that eutrophication may greatly modify CO2 and CH4 emissions from wetlands through changes in vegetation type and productivity.

Pedological and Botanical Records of Environment Changes of Yamskaya Steppe (Belgorod Oblast, Russia) in Holocene

In the natural reserve “Belogorie” at the Yamskaya Steppe site, located in the south of the Central-Russian Upland, a wide range of subjects were studied aiming identification and analysis of paleo-pedological and paleobotanical indicators of environmental change in different historical periods of the Holocene. The study subjects included paleosoil buried under the earth mound of the Bronze Age, background virgin Chernozem near the mound, soil buried under the cast of marmot, and the soils in the ravine-gully deposits on bottom of gully. Using a complex of methods, including soil-archaeological, palynological, microbiomorphic, pedoanthracological, radiocarbon and paleogeographic reconstructions, was allowed to reveal a complicated combination of natural and human-induced changes in the meadow and meadowsteppe landscapes of the Yamskaya Steppe site in the Holocene. Watershed spaces were characterized by contrasting changes of vegetation types during studied period. The high degree of natural afforestation was observed for 6000−6500 yrs BP. Later, up to nowadays, on the watersheds the meadow-steppe type of landscape was dominated. The phase of increased afforestation was also observed in the beginning of the Subboreal period of Holocene (before 4600 years ago), but this time the development of forests was limited by their spread in the ravines. The Late Holocene was heterogeneous in relation to bioclimatic conditions with alternating wet and relatively dry phases, but their exact identification is complicated by the increasing of anthropogenic impacts on vegetation. Starting with the Subboreal period of Holocene the anthropogenic disturbance of landscapes became apparent, first in the form of periodic burning of steppes, and in the Sub-Atlantic period of Holocene – as a combination of burning and cultivation of agricultural crops on individual plots within the study area. Thus, the meadow-steppe environments in the south of the Central-Russian Upland, preserved nowadays only in the reserves, had a complex history of development in the past including climatogenic and anthropogenic transformation of soils and vegetation.

Vegetation changes in the agricultural-pastoral areas of northern China from 2001 to 2013

Climate change and human activity have resulted in increasing change of vegetation growth globally. Numerous studies have been conducted on extreme climate events and analyses of ecological environment evolution. However, such studies have placed little emphasis on vegetation change and spatial variation in this type of ecotone. Accordingly, this study analyzed the changes in vegetation type and growth using the 16-d composite MOD13A1 product with 1-km resolution and MOD12Q1 product with 1-km resolution. We used the mean, maximum, standard deviation normalized-difference vegetation index (NDVI) values, and the rate of change (ROC) of NDVI value to explain vegetation changes within the studied ecotone. Our results showed that significant vegetation type and growth changes have occurred in the study area. From 2001 to 2013, for example, with the exception of 2001, 2004 and 2009, a certain extent of grassland area was converted to cropland. Drought severity index (DSI) results indicate that there exists drought in 2001, 2004 and 2009. Such temporal changes in cropland and grassland area confirmed the ecological vulnerability of the ecotone. At the same time, vegetation varied spatially from west to east and from south to north. The mean, maximum and standard deviation NDVI values were all sorted in descending order based on differences in latitude and longitude, as follows: NDVI2013>NDVI2009>NDVI2004>NDVI2001

How will climate change affect wildland fire severity in the western US?

Fire regime characteristics in North America are expected to change over the next several decades as a result of anthropogenic climate change. Although some fire regime characteristics (e.g., area burned and fire season length) are relatively well-studied in the context of a changing climate, fire severity has received less attention. In this study, we used observed data from 1984 to 2012 for the western United States (US) to build a statistical model of fire severity as a function of climate. We then applied this model to several (n = 20) climate change projections representing mid-century (2040–2069) conditions under the RCP 8.5 scenario. Model predictions suggest widespread reduction in fire severity for large portions of the western US. However, our model implicitly incorporates climate-induced changes in vegetation type, fuel load, and fire frequency. As such, our predictions are best interpreted as a potential reduction in fire severity, a potential that may not be realized due human-induced disequilibrium between plant communities and climate. Consequently, to realize the reductions in fire severity predicted in this study, land managers in the western US could facilitate the transition of plant communities towards a state of equilibrium with the emerging climate through means such as active restoration treatments (e.g., mechanical thinning and prescribed fire) and passive restoration strategies like managed natural fire (under suitable weather conditions). Resisting changes in vegetation composition and fuel load via activities such as aggressive fire suppression will amplify disequilibrium conditions and will likely result in increased fire severity in future decades because fuel loads will increase as the climate warms and fire danger becomes more extreme. The results of our study provide insights to the pros and cons of resisting or facilitating change in vegetation composition and fuel load in the context of a changing climate.

Influence of coniferous and deciduous vegetation on major and trace metals in forests of northern New England, USA

Climate change and land-use are predicted to shift coniferous stands to deciduous stands in northern New England. This change in vegetation type may modify plant-soil cycling of major and trace metals, potentially affecting soil fertility and contaminant transport. We studied eight pairs of adjacent coniferous- and deciduous-dominated forest stands across northern New England, USA. We estimated the mean residence time (MRT) of each metal in organic horizons using calculated litterfall from allometric equations and interpolated atmospheric deposition rates. Coniferous stands had 30–50 % smaller organic horizons pools of Ca, K, Mg, Mn, and Zn than deciduous stands. Mineral horizon metal pools were similar between vegetation types. Foliar metal concentrations and pools were smaller at coniferous stands than deciduous stands. The organic horizon MRT for Ca, Cd, Cu, K, Mg, and Mn was predicted to be 40–200 % longer for coniferous stands than deciduous stands. Based upon our findings, we conclude that a shift from coniferous to deciduous vegetation could decrease the accumulation and retention of major metals in the organic horizons. Further investigations into the effect of vegetation type on mineral horizons are needed to constrain regional changes.

Effects of permafrost aggradation on peat properties as determined from a pan‐Arctic synthesis of plant macrofossils

AbstractPermafrost dynamics play an important role in high‐latitude peatland carbon balance and are key to understanding the future response of soil carbon stocks. Permafrost aggradation can control the magnitude of the carbon feedback in peatlands through effects on peat properties. We compiled peatland plant macrofossil records for the northern permafrost zone (515 cores from 280 sites) and classified samples by vegetation type and environmental class (fen, bog, tundra and boreal permafrost, and thawed permafrost). We examined differences in peat properties (bulk density, carbon (C), nitrogen (N) and organic matter content, and C/N ratio) and C accumulation rates among vegetation types and environmental classes. Consequences of permafrost aggradation differed between boreal and tundra biomes, including differences in vegetation composition, C/N ratios, and N content. The vegetation composition of tundra permafrost peatlands was similar to permafrost‐free fens, while boreal permafrost peatlands more closely resembled permafrost‐free bogs. Nitrogen content in boreal permafrost and thawed permafrost peatlands was significantly lower than in permafrost‐free bogs despite similar vegetation types (0.9% versus 1.5% N). Median long‐term C accumulation rates were higher in fens (23 g C m−2 yr−1) than in permafrost‐free bogs (18 g C m−2 yr−1) and were lowest in boreal permafrost peatlands (14 g C m−2 yr−1). The plant macrofossil record demonstrated transitions from fens to bogs to permafrost peatlands, bogs to fens, permafrost aggradation within fens, and permafrost thaw and reaggradation. Using data synthesis, we have identified predominant peatland successional pathways, changes in vegetation type, peat properties, and C accumulation rates associated with permafrost aggradation.

Analyzing nonlinear variations in terrestrial vegetation in China during 1982-2012.

Quantifying the long-term trends of changes in terrestrial vegetation on a large scale is an effective method for detecting the effects of global environmental change. In view of the trend towards overall restoration and local degradation of terrestrial vegetation in China, it is necessary to pay attention to the spatial processes of vegetative restoration or degradation, as well as to clarify the temporal and spatial characteristics of vegetative growth in greater geographical detail. However, traditional linear regression analysis has some drawbacks when describing ecological processes. Combining nonparametric linear regression analysis with high-order nonlinear fitting, the temporal and spatial characteristics of terrestrial vegetative growth in China during 1982-2012 were detected using the third generation of Global Inventory Modeling and Mapping Studies (GIMMS3g) dataset. The results showed that high-order curves could be effective. The region joining Ordos City and Shaanxi Gansu Ningxia on the Loess Plateau may have experienced restoration-degradation-restoration processes of vegetative growth. In the Daloushan Mountains, degradation-restoration processes of vegetative growth may have occurred, and the occurrence of several hidden vegetative growth processes was located in different regions of eastern China. Changes in cultivated vegetation were inconsistent with changes in other vegetation types. In southern China and some high-altitude areas, temperature was the primary driver of vegetative growth on an interannual scale, while in the north, the effect of rainfall was more significant. Nevertheless, the influence of climate on vegetation activity in large urban areas was weak. The trend types of degradation-restoration processes in several regions were inconsistent with the implements of regional land development and protection strategy. Thus, the role of human activity cannot be ignored. In future studies, it will be still necessary to quantify the effects of human management on spatial patterns, develop trend-fitting methods, and explore more refined methods of analyzing the driving forces affecting large-scale changes in vegetative growth.

Climatic and Landscape Influences on Fire Regimes from 1984 to 2010 in the Western United States.

An improved understanding of the relative influences of climatic and landscape controls on multiple fire regime components is needed to enhance our understanding of modern fire regimes and how they will respond to future environmental change. To address this need, we analyzed the spatio-temporal patterns of fire occurrence, size, and severity of large fires (> 405 ha) in the western United States from 1984–2010. We assessed the associations of these fire regime components with environmental variables, including short-term climate anomalies, vegetation type, topography, and human influences, using boosted regression tree analysis. Results showed that large fire occurrence, size, and severity each exhibited distinctive spatial and spatio-temporal patterns, which were controlled by different sets of climate and landscape factors. Antecedent climate anomalies had the strongest influences on fire occurrence, resulting in the highest spatial synchrony. In contrast, climatic variability had weaker influences on fire size and severity and vegetation types were the most important environmental determinants of these fire regime components. Topography had moderately strong effects on both fire occurrence and severity, and human influence variables were most strongly associated with fire size. These results suggest a potential for the emergence of novel fire regimes due to the responses of fire regime components to multiple drivers at different spatial and temporal scales. Next-generation approaches for projecting future fire regimes should incorporate indirect climate effects on vegetation type changes as well as other landscape effects on multiple components of fire regimes.

Silica gossan as a prospective guide for amethyst geode deposits in the Ametista do Sul mining district, Paraná volcanic province, southern Brazil

A new frontier of amethyst geode deposits (amethyst, agate, gypsum, calcite and zeolites) driven by the prospective guide termed silica gossan may change the metallogenetic scenario previously known in the Paraná volcanic province. Silica gossans, which are related to basalt, basaltic andesite and rhyodacite, occur throughout this province. In this study, we focus on the Ametista do Sul mining district, Rio Grande do Sul, Brazil, the largest producer of amethyst geodes in the world (400t/month). In this district, a silica gossan occurs at the top of the Coogamai flow above the Mina do Museu. This basalt (47.9wt.% SiO2) flow belongs to the intermediate-Ti Paranapanema magma type (2.25wt.% TiO2 and Ti/Y=416) exhibiting columnar jointing. The gossan as prospective guide displays polygonal shape associated with the enrichment of clay minerals at the surface, the concentration of iron oxides and the presence of silicified sandstones. In addition, marshes with ponds and a change in surface color (ocher to brownish) and vegetation type were observed. A gamma spectrometry survey at the Mina do Museu silica gossan showed negative anomalies in %K, eU and eTh above the amethyst deposit with values of 55 counts per second (cps) outside the silica gossan and 43cps within it. These anomalies are caused by hydrothermal events and subsequent weathering of the silica gossan. Bulk rock analyses of the silica gossan demonstrate a loss on ignition up to 1.8wt.% whereas this value is around 0.5wt.% for rocks outside the silica gossan. SiO2, K2O, MgO, CaO and Na2O display negative correlations with loss on ignition. X-ray diffraction proved the presence of smectites and kaolinite in the soil on the silica gossan. In addition, dioctahedral and trioctahedral interlayered smectites were identified. Mg-smectite is present in the silica gossan whereas K-smectite occurs in the Coogamai flow.

The hustle and bustle of city life: monitoring the effects of urbanisation in the African lesser bushbaby.

Urbanisation has become a severe threat to pristine natural areas, causing habitat loss and affecting indigenous animals. Species occurring within an urban fragmented landscape must cope with changes in vegetation type as well as high degrees of anthropogenic disturbance, both of which are possible key mechanisms contributing to behavioural changes and perceived stressors. We attempted to elucidate the effects of urbanisation on the African lesser bushbaby, Galago moholi, by (1) recording activity budgets and body condition (body mass index, BMI) of individuals of urban and rural populations and (2) further determining adrenocortical activity in both populations as a measure of stress via faecal glucocorticoid metabolite (fGCM) levels, following successful validation of an appropriate enzyme immunoassay test system (adrenocorticotropic hormone (ACTH) challenge test). We found that both sexes of the urban population had significantly higher BMIs than their rural counterparts, while urban females had significantly higher fGCM concentrations than rural females. While individuals in the urban population fed mainly on provisioned anthropogenic food sources and spent comparatively more time resting and engaging in aggressive interactions, rural individuals fed almost exclusively on tree exudates and spent more time moving between food sources. Although interactions with humans are likely to be lower in nocturnal than in diurnal species, our findings show that the impact of urbanisation on nocturnal species is still considerable, affecting a range of ecological and physiological aspects.

Different altitude effect of leaf wax n-alkane δD values in surface soils along two vapor transport pathways, southeastern Tibetan Plateau

Here we present 76 hydrogen isotope values for leaf wax-derived n-alkanes (δDwax, being the abundance-weighted average δD values of C29 and C31n-alkanes) in surface soils along two vapor transport pathway transects running across the southeastern Tibetan Plateau (TP). The first is the South Himalayan (SH) Transect (with an altitude range of 1660–5050m∗ above sea level, and representing the Southern Himalayan air mass), and the second a combination of the Zayu–Bomi (ZB; altitude 1468–4800m) and Bayi-Lhasa (BL; altitude 3050–4970m) transects, together representing the Brahmaputra–Yarlung Zangbo river valley air mass. δDwax values and their relation to altitude did exhibit some variability. Nonetheless, altitude was the predominant factor in determining soil δDwax values, with a lapse rate of −2.2‰/100m (R2=0.78; n=76) based on overall soil δDwax values, despite changes in precipitation amount, relative humidity (RH) and vegetation type. Furthermore, our εwax/rw values (the isotopic fractionation between the δDwax and δD values of river water (δDrw)) remained approximately constant at −104.5‰ (ranging between −99‰ and −110‰), confirming that the relation between altitude and isotopic hydrology (river water and precipitation) controls the n-alkane δDwax altitudinal gradients for all of the sample localities in the Southern Himalaya (SH) and the southern TP. This endorses the efficacy of using δDwax to reconstruct paleoelevation. Along the SH Transect, soil δDwax values varied from −151‰ to −264‰, with an altitudinal lapse rate of −2.4‰/100m (R2=0.84, n=32). This was due to the significant change in altitude over short distances. Along the ZB Transect, soil δDwax values varied from −174‰ to −263‰, with a lower lapse rate of −1.9‰/100m (R2=0.68, n=29). The altitudinal lapse rate was −3.3‰/100m above 3000m (R2=0.63, n=19), and −1.35‰/100m below 3000m (R2=0.64, n=10); in the lower sub-transect, the latitudinal effect significantly counteracted the altitude effect. Along the BL Transect, soil δDwax values varied from −205‰ to −244‰, with an altitudinal lapse rate of −1.4‰/100m (R2=0.74, n=15). The lower lapse rate for soil δDwax reflects a combination of local continental and altitudinal effects. The differences we observed in soil δDwax altitudinal lapse rates along the two vapor transport pathways imply that they are affected by subtle local environmental conditions, moisture sources, latitude and topography. This should be considered fully during any reconstruction of paleoelevation.

Seasonal variations in labile soil organic matter fractions in permafrost soils with different vegetation types in the central Qinghai–Tibet Plateau

Labile soil organic matter (SOM) plays a crucial role in nutrient and carbon cycling, particularly in permafrost ecosystems. Understanding its variation is therefore very important. In the present study, we evaluated the seasonal patterns of labile SOM from April 2013 to March 2014 under alpine swamp meadow (ASM), meadow (AM), steppe (AS) and desert (AD) vegetation in permafrost regions of the China's Qinghai–Tibet Plateau. The fractions (0 to 10cm depth) included dissolved organic carbon (DOC), light-fraction carbon (LFC) and nitrogen (LFN), and microbial biomass carbon (MBC) and nitrogen (MBN). These fractions showed dramatic seasonal patterns in ASM and AM soils, but were relatively stable in AD soil. Soil DOC concentrations in the ASM, AM, and AD soils increased from April to May 2013, then increased again from July to August 2013 and from February to March 2014. The LFC and LFN concentrations in all four vegetation types were higher from June to August 2013. The highest MBC and MBN concentrations in the ASM, AM, and AS soils all occurred in the summer and the ASM soil showed a second peak in October or November 2013. Seasonal changes in climatic factors, vegetation types, and permafrost features were great causes of labile SOM variations in this study. Throughout the entire sampling period, the ASM soil generally had the highest labile SOM, followed by the AM, AS, and AD soils; thus, the ASM soil is the best system conserving soil nutrient (especially labile fractions) and microbial activity. Correlation analysis indicated that these fractions were not related to soil moisture and temperature in AS or AD soils, but soil temperature and moisture were significantly related to MBC and MBN in AM soil and DOC in ASM soil. Thus, the response of the labile SOM fractions in this high-altitude permafrost soils to climate change depended strongly on vegetation types.

Effect of climatic change and afforestation on water yield in the Rocky Mountain Area of North China

Aim of study: We studied effects of climatic variability and afforestation on water yield to make a quantitative assessment of the hydrological effects of afforestation on basin water yield in the Rocky Mountain Area of North China.Area of study: Seven typical forest sub-watersheds in Chaobai River watershed, located near Beijing's Miyun Reservoir, were selected as our study object. Material and methods: Annual water yield model and Separate evaluation method were applied to quantify the respective contributions of changes in climate and different vegetation types on variations in runoff. Main results: Statistical analysis indicated precipitation did not vary significantly whereas the annual runoff decreased significantly in the past decades. Although forest increased significantly in the late 20th century, climatic variations have the strongest contribution to the reductions in runoff, with the average contribution reaching 63.24%, while the remainder caused by human activities. Afforestation has a more positive impact on the reduction in runoff, with a contribution of 65.5%, which was more than the grassland of 17.6% and the farmland of 16.9%. Research highlights: Compared to the impact of climatic change, we believe the large-scale afforestation may not be the main reason for the reductions in basin water yield.Keywords: Annual water yield model; Separate evaluation method; North China.Abbreviations: AWY-Annual water yield model; AET-actual evapotranspiration; Y-annual water yield; P-precipitation; R-runoff; T-temperature.

Surface pollen and its relationships with modern vegetation and climate in the Tianshan Mountains, northwestern China

A dataset consisting of 70 surface pollen sam- ples from forest, alpine meadow, alpine steppe, temperate steppe, desert steppe, shrub/semi-shrub steppe and desert sites in the Tianshan Mountains, northwestern China pro- vides an opportunity to study the relationships between surface pollen assemblages and modern vegetation and climate in this region. Redundancy analysis (RDA), the human influence index (HII) and pollen ratios were used to facilitate analysis of the pollen data. The modern pollen assemblages are primarily composed of Picea, Artemisia, Chenopodiaceae, Poaceae, Asteraceae, Nitraria and Ephedra. The results suggest that the surface pollen assemblages of different vegetation types largely represent the modern vegetation in terms of the primary taxa and dominant types. The RDA indicates that the mean annual precipitation (MAP) and the July temperature (TJuly) are the major climate variables that control the modern pollen assemblages. Picea, Artemisia, Poaceae, Cyperaceae, Fabaceae, Asteraceae, Polygonaceae and Apiaceae pollen assemblages are positively correlated with MAP and negatively correlated with TJuly, while the pollen ratios for certain other types, such as Chenopodiaceae, Ephedra and Nitraria, are negatively correlated with MAP and positively correlated with TJuly. The arboreal/non-arboreal ratios are notably high in the forest samples, indicating a sensitive response to forest vegetation. Moreover, the Artemisia/Chenopodiaceae pollen ratios are generally cor- related with the vegetation type and annual precipitation change, suggesting that these factors could be useful indicators of moisture variability in arid regions. However, it is difficult to distinguish between steppe and steppe de- sert based on this ratio, due partly to human disturbance. The HII is significantly correlated with certain pollen taxa, including Poaceae, Plantago, Polygonaceae and Elaeag- naceae, particularly in the alpine meadow and steppe samples. Our results have implications for interpreting the available fossil pollen data in the study region and other arid and semi-arid regions.

The impact of Sahara desertification on Arctic cooling during the Holocene

Abstract. Since the start of the Holocene, temperatures in the Arctic have steadily declined. This has been accredited to the orbitally forced decrease in summer insolation reconstructed over the same period. However, here we present climate modelling results from an Earth model of intermediate complexity (EMIC) that indicate that 17–40% of the cooling in the Arctic, over the period 9–0 ka, was a direct result of the desertification that occurred in the Sahara after the termination of the African Humid Period. We have performed a suite of sensitivity experiments to analyse the impact of different combinations of forcings, including various vegetation covers in the Sahara. Our simulations suggest that over the course of the Holocene, a strong increase in surface albedo in the Sahara as a result of desertification led to a regional increase in surface pressure, a weakening of the trade winds, the westerlies and the polar easterlies, which in turn reduced the meridional heat transported by the atmosphere to the Arctic. We conclude that during interglacials, the climate of the Northern Hemisphere is sensitive to changes in Sahara vegetation type.

Toward Estimating Wetland Water Level Changes Based on Hydrological Sensitivity Analysis of PALSAR Backscattering Coefficients over Different Vegetation Fields

Synthetic Aperture Radar (SAR) has been successfully used to map wetland’s inundation extents and types of vegetation based on the fact that the SAR backscatter signal from the wetland is mainly controlled by the wetland vegetation type and water level changes. This study describes the relation between L-band PALSAR and seasonal water level changes obtained from Envisat altimetry over the island of Île Mbamou in the Congo Basin where two distinctly different vegetation types are found. We found positive correlations between and water level changes over the forested southern Île Mbamou whereas both positive and negative correlations were observed over the non-forested northern Île Mbamou depending on the amount of water level increase. Based on the analysis of sensitivity, we found that denser vegetation canopy leads to less sensitive variation with respect to the water level changes regardless of forested or non-forested canopy. Furthermore, we attempted to estimate water level changes which were then compared with the Envisat altimetry and InSAR results. Our results demonstrated a potential to generate two-dimensional maps of water level changes over the wetlands, and thus may have substantial synergy with the planned Surface Water and Ocean Topography (SWOT) mission.

Arctic greening can cause earlier seasonality of Arctic amplification

AbstractAs global temperatures rise, vegetation types will change, particularly in the northern high latitudes. Under a warming scenario, shrub and grasslands over the Arctic are expected to shift to boreal forests. This study compares the impact of such a change in Arctic vegetation type with that of CO2 doubling on the seasonality of Arctic warming. Even though vegetation is changed throughout the year, the effect of the surface albedo change is maximum in boreal summer when the incoming solar radiation is largest. Evapotranspiration changes are also maximized in the summer, when the photosynthesis rate is highest. As a result, when Arctic vegetation change is considered in addition to doubled CO2, Arctic amplification is maximized earlier in the annual cycle.

Extractable nitrogen and microbial community structure respond to grassland restoration regardless of historical context and soil composition.

Grasslands have a long history of invasion by exotic annuals, which may alter microbial communities and nutrient cycling through changes in litter quality and biomass turnover rates. We compared plant community composition, soil chemical and microbial community composition, potential soil respiration and nitrogen (N) turnover rates between invaded and restored plots in inland and coastal grasslands. Restoration increased microbial biomass and fungal : bacterial (F : B) ratios, but sampling season had a greater influence on the F : B ratio than did restoration. Microbial community composition assessed by phospholipid fatty acid was altered by restoration, but also varied by season and by site. Total soil carbon (C) and N and potential soil respiration did not differ between treatments, but N mineralization decreased while extractable nitrate and nitrification and N immobilization rate increased in restored compared with unrestored sites. The differences in soil chemistry and microbial community composition between unrestored and restored sites indicate that these soils are responsive, and therefore not resistant to feedbacks caused by changes in vegetation type. The resilience, or recovery, of these soils is difficult to assess in the absence of uninvaded control grasslands. However, the rapid changes in microbial and N cycling characteristics following removal of invasives in both grassland sites suggest that the soils are resilient to invasion. The lack of change in total C and N pools may provide a buffer that promotes resilience of labile pools and microbial community structure.