Changes In Vegetation Types Research Articles

A climatological study of the spatio-temporal variability of land surface temperature and vegetation cover of Vadodara district of Gujarat using satellite data

ABSTRACTIn the present study, a comprehensive assessment of the spatio-temporal variation of day-time and night-time land surface temperature (LST) and normalized difference vegetation index (NDVI) of Vadodara district of Gujarat in India from 2001 to 2012 has been carried out using satellite data. A significant cooling trend was observed in the day-time LST, whereas the night-time LST showed a distinct warming trend. The entire geographical extent of Vadodara was classified into different night-time LST classes to quantify the extent of the hot pockets, and it showed a clear-cut warming pattern for all the months of the year with an increase in the geographical areas under higher temperature range. Further analysis of Diurnal Temperature Range (DTR) also revealed a strong impact of the urbanization process, with annual DTR showing a decreasing trend at the rate of 0.29°C year−1. An analysis of the vegetation cover of the district showed that on an average, the NDVI of the district increased during the study period. However, a micro-level examination of NDVI values depicted that the type of vegetation cover had drastically changed. The maximum NDVI values for months from May to December for 2012 were much lower than those of 2001 and 2006, indicating a change in vegetation pattern of the district. An assessment of the area under different NDVI values exhibited that for all the months of the year (except September), the total area with NDVI values of higher range (i.e. +0.5 and above) had substantially decreased from 2001 to 2012. The analysis revealed that for some of the months like February, while in 2001, 45% of district exhibited NDVI values above +0.5, but by 2012, it had decreased to only 18%, showing a drastic change in vegetation type and deterioration of the extent of thick dense vegetation.

The transient response of ecosystems to climate change is amplified by trophic interactions

Studies of ecosystem responses to climate change often focus on potential equilibria in species or community distributions, overlooking the transitions to new equilibrium states. Transient phases can however last for decades or centuries, during which both demography and interspecific interactions are expected to play a crucial role. Here, we investigate the response of vegetation to climate warming at high latitudes involving a shift from open vegetation to either boreal (mainly coniferous) or temperate (mainly deciduous) forests. We specifically address how interactions among browsers and vegetation could affect the shift in dominance of vegetation type after climate warming. We characterize the transient dynamics using five measures: 1) asymptotic resilience, i.e. the rate at which equilibrium is restored, 2) initial resilience, the short‐term rate of change of the ecosystem after climate change, 3) ecosystem exposure, i.e. the shift of the equilibrium due to climate change, 4) sensitivity, or the time to recover equilibrium, and 5) vulnerability, measured as the cumulative amount of changes in vegetation states during the transient phase. We find that plant–herbivore interactions usually extend the length of the transient period and induce more cumulative changes in vegetation types. This result implies that the consideration of multiple interacting species is necessary to provide robust scenarios of how ecosystems will respond to global changes. We furthermore show that plant–herbivore interactions disrupt the correlation between the five measures characterizing the transient dynamics, highlighting the need for a full multidimensional characterization of transients.

Connectivity in riparian plants: influence of vegetation type and habitat fragmentation overrides water flow.

Spatial genetic patterns can be influenced by a broad range of factors across a landscape. The hypothesis that heterogeneous vegetation and habitat fragmentation rather than water flow influence genetic patterns in two riparian plant species with different niches was tested. Genotyping by sequencing was used to assess the genetic diversity and structure of each species at 12 sites across a river catchment. Generalized dissimilarity modelling examined the relative influence that vegetation type and habitat fragmentation had on patterns of genetic differentiation across the landscape. Restricted gene flow in the widespread species, Callistachys lanceolata, resulted in lower genetic differentiation than that exhibited by Astartea leptophylla, a restricted riparian species with high gene flow. Geographic distance and vegetation type explained the patterns of genetic differentiation in the widespread species, whereas habitat fragmentation and, to a lesser extent, vegetation type explained patterns in the restricted species. Water flow was not found to have significant impacts on patterns of genetic diversity in riparian plant species with restricted and widespread distribution. Impacts of vegetation type on genetic differentiation were most likely due to change in canopy density and associated pollinator communities in the vegetation types across the catchment. Reduced connectivity caused by habitat fragmentation was evident in the restricted riparian species, while reduced connectivity in the widespread species was related to the change of vegetation type between sites. Natural causes of reduced connectivity as well as anthropogenic causes need to be considered in future work to predict persistence and resilience under a changing climate.

Dynamics and driving forces of main vegetation types in the Saihanba Nature Reserve, Hebei Province, China

To explore the changes of vegetation landscape pattern and its driving mechanism in Saihanba Nature Reserve, we analyzed vegetation type changes from 1989 to 2013 and the driving factors using random forest and Logistic regression models in conjunction with land dynamic degree indicator, based on three Landsat TM imageries obtained in 1989, 2000 and 2013. The results showed that the proportion of shrubland was always small in this area from 1989 to 2013. During 1989-2013, the proportion of shrubland rapidly decreased and plantation area significantly increased, while the area of grassland and natural secondary forest slightly changed. Key driving factors for the vegetation dynamics were dependent on vegetation type and time. The change of each vegetation type from 1989 to 2000 was significantly influenced by social factors, i.e. distance to road and total investment of afforestation. Since the implementation of the Natural Forest Protection Project and establishment of Saihanba Nature Reserve, the role of natural factors including elevation and aspect gradually became more important during the 2000-2013. The vegetation landscape dynamics were primarily determined by social activities, while the distribution patterns of vegetation types were probably controlled by natural factors in the study area.

Changes in vegetation type on the Chinese Loess Plateau since 75 ka related to East Asian Summer Monsoon variation

Floral communities in terrestrial habitats such as steppes are highly sensitive to regional climate changes. Here, we generated carbon and nitrogen isotope profiles for soil organic matter (SOM) in the Weinan loess-paleosol section in order to investigate changes in floral communities on the Chinese Loess Plateau (CLP) and their relationship to climate variation since 75 ka. δ13CSOM at Weinan ranges from −23.6 to −18.0‰ and δ15NSOM ranges from +3.4 to +5.5‰. Modeling based on the δ13CSOM record suggests that the proportion of C4 plants (%C4) has varied from lower during cold intervals (with minima of 24–32% at 73.1 ka, 20.9 ka (LGM), and 0.6 ka) to higher during warm intervals (with maxima of 62–64% at 53.0 ka and 8.2 ka). The δ13CSOM and δ15NSOM profiles are strongly correlated (r = +0.82; p(α) <0.001), suggesting that the N-isotope composition of SOM was also largely controlled by inputs of C4 versus C3 plants, consistent with known patterns of N-isotope variation among modern plants. The %C4 profile exhibits significant covariation with reconstructed mean annual temperatures (MAT) (r = +0.42; p(α) <0.001), mean annual precipitation (MAP) (r = +0.42; p(α) <0.001), and summer monsoon intensity (r = +0.50; p(α) <0.001), suggesting that paleovegetation was controlled by each of these climate variables to a degree. Comparing the Weinan record to SOM profiles across the CLP region, we identified three zones of varying monsoonal influence, with the East Asian Summer Monsoon (EASM) exerting the strongest influence on the southeastern margin of the CLP, and the East Asian Winter Monsoon (EAWM) greater influence on its northwestern margin. This paper provides new insights into deciphering paleovegetation patterns and their links to paleoclimate change on the basis of paired C- and N-isotope records.

Determinants and rates of land degradation: Application of stationary time-series model to data from a semi-arid environment in Kenya

The causes of land degradation in the African drylands have been shown to vary. Some researchers consider climate to be the major contributor to degradation, with anthropogenic factors playing a minor role. Others reverse the significance of these two factors. A third group attributes land degradation to climate and anthropogenic factors equally. This study was undertaken to establish the factors influencing land degradation in a semi-arid environment in southeastern Kenya and the rate of change in vegetation types for a period of 35 years (1973–2007). The reduction in grassland cover was used as an indicator of land degradation. Causes of land degradation were determined by a multiple regression analysis. A log-linear regression analysis was used to establish the rate of vegetation change. The multiple and log-linear regression analyses showed: (1) woody vegetation, livestock population and cultivated area to be the main contributors of reduction in grassland cover in the area, and (2) an increase in undesirable woody species, livestock population and cultivated area had a significant (P<0.05) negative effect on grassland vegetation. Increased human population, low amounts of rainfall and drought showed no significant negative effect on grassland vegetation cover. In conclusion, human and livestock population growth and increased agricultural land have contributed to intensive crop cultivation and overgrazing in the semi-arid lands. This overuse of the semi-arid rangelands has worsened the deterioration of the natural grassland vegetation.

Prescribed fire and its impacts on ecosystem services in the UK

The impacts of vegetation fires on ecosystems are complex and varied affecting a range of important ecosystem services. Fire has the potential to affect the physicochemical and ecological status of water systems, alter several aspects of the carbon cycle (e.g. above- and below-ground carbon storage) and trigger changes in vegetation type and structure. Globally, fire is an essential part of land management in fire-prone regions in, e.g. Australia, the USA and some Mediterranean countries to mitigate the likelihood of catastrophic wildfires and sustain healthy ecosystems. In the less-fire prone UK, fire has a long history of usage in management for enhancing the productivity of heather, red grouse and sheep. This distinctly different socioeconomic tradition of burning underlies some of the controversy in recent decades in the UK around the use of fire. Negative public opinion and opposition from popular media have highlighted concerns around the detrimental impacts burning can have on the health and diversity of upland habitats. It is evident there are many gaps in the current knowledge around the environmental impacts of prescribed burning in less fire-prone regions (e.g. UK). Land owners and managers require a greater level of certainty on the advantages and disadvantages of prescribed burning in comparison to other techniques to better inform management practices. This paper addresses this gap by providing a critical review of published work and future research directions related to the impacts of prescribed fire on three key aspects of ecosystem services: (i) water quality, (ii) carbon dynamics and (iii) habitat composition and structure (biodiversity). Its overall aims are to provide guidance based on the current state-of-the-art for researchers, land owners, managers and policy makers on the potential effects of the use of burning and to inform the wider debate about the place of fire in modern conservation and land management in humid temperate ecosystems.

Pollen and Sporormiella evidence for terminal Pleistocene vegetation change and megafaunal extinction at Page-Ladson, Florida

Two cores from the Page-Ladson archaeological site, Florida were analyzed for pollen and the dung fungus Sporormiella. The cores contained stratified deposits spanning the Pleistocene-Holocene transition: a period characterized by the widespread extinction of Pleistocene megafauna and abrupt changes in vegetation type and distribution. The disappearance of Sporormiella, a well-established proxy for large herbivore abundance, by ∼12,700 cal BP is consistent with the timing of Terminal Pleistocene megafaunal extinction elsewhere in North America. However, a resurgence of Sporormiella between ∼10,750–10,200 cal BP suggests an Early Holocene incursion of extant megaherbivores such as bison. Pollen evidence from the site also reflects dramatic vegetation changes, which are likely a response to both changing climate and fluctuating herbivore populations. Prior to 14,500 cal BP, the pollen assemblage reflects a relatively cool and dry climate. Between ca. 14,500–12,600 cal BP, the sediments are characterized by an increase in hardwood forest and mesic plant taxa, indicating an increase in both temperature and precipitation. After 12,600 cal BP, a decrease in arboreal pollen, with the exception of oak, alongside an increase in herbaceous pollen, indicates drier, warmer conditions. These results contextualize changes in human behavior at the onset of the Holocene.

Prioritizing forest fuels treatments based on the probability of high-severity fire restores adaptive capacity in Sierran forests.

In frequent fire forests of the western United States, a legacy of fire suppression coupled with increases in fire weather severity have altered fire regimes and vegetation dynamics. When coupled with projected climate change, these conditions have the potential to lead to vegetation type change and altered carbon (C) dynamics. In the Sierra Nevada, fuels reduction approaches that include mechanical thinning followed by regular prescribed fire are one approach to restore the ability of the ecosystem to tolerate episodic fire and still sequester C. Yet, the spatial extent of the area requiring treatment makes widespread treatment implementation unlikely. We sought to determine if a priori knowledge of where uncharacteristic wildfire is most probable could be used to optimize the placement of fuels treatments in a Sierra Nevada watershed. We developed two treatment placement strategies: the naive strategy, based on treating all operationally available area and the optimized strategy, which only treated areas where crown-killing fires were most probable. We ran forecast simulations using projected climate data through 2,100 to determine how the treatments differed in terms of C sequestration, fire severity, and C emissions relative to a no-management scenario. We found that in both the short (20years) and long (100years) term, both management scenarios increased C stability, reduced burn severity, and consequently emitted less C as a result of wildfires than no-management. Across all metrics, both scenarios performed the same, but the optimized treatment required significantly less C removal (naive=0.42 Tg C, optimized=0.25 Tg C) to achieve the same treatment efficacy. Given the extent of western forests in need of fire restoration, efficiently allocating treatments is a critical task if we are going to restore adaptive capacity in frequent-fire forests.

Detailed reconstructions of Holocene climate and environmental changes in the Taman Peninsula (Kuban River delta region) and their correlation with rapid sea-level fluctuations of the Black Sea

The paper presents results of a detailed subdivision of Holocene sediments in the region of the Kuban River delta into climate-stratigraphic units and reconstructions of the vegetation, climate and depositional environment changes on the Taman Peninsula (NE Black Sea region) during the last 7400 years. The reconstructions are based on data from geological-geomorphological and lithological-facies analysis, palynological studies and radiocarbon dating of six sections penetrated by boreholes in various parts of the Kuban River delta. The studied lithological sequences present an assortment of liman, fluvial, lacustrine and marsh sediments, as well as subaerial deposits that accumulated in the course of the delta development.The factual materials thus obtained provided the basis for reconstructing changes in zonal vegetation types and transformations of zonal and intra-zonal formations in the Holocene landscapes of the Taman Peninsula, induced by changes in edaphic conditions and regional climate. Seventeen phases (stages) have been recognized in the evolution of vegetation and climate through the Middle and Late Holocene, and a detailed description is given to every phase. A detailed pollen-climate-chronostratigraphic scheme of the Black Sea level fluctuations over the last 7400 years is proposed.Steppe and forest-steppe landscapes were dominant on the Taman Peninsula over the greater part of the studied period of the Holocene. The warmest and most arid conditions were typical of the phases dominated by steppes with grass, herb and grass, and pigweed-wormwood (Chenopodiaceae-Artemisia) plant communities. Such phases were dated to intervals ∼4660–4400, 3780–3430, 2910–2280, 1540–1230 and 900–830/730 cal yr BP. The most humid intervals within the studied period are dated at ∼5160–4900, 4400–3780, 2280–1540 cal yr BP. They were distinct because of the dominance of broadleaf (mostly beech-oak-hornbeam) forests. Those humid intervals most likely correspond to the maxima of the Kalamitian, Dzemetinian, and Nimphaean Black Sea transgressions.The climatic indexes and zonal attribution of the dominant plant communities can be matched with six transgressive and seven regressive sea level fluctuations of various ranks over the last 7400 years. Of the six transgressive stages, one stage was marked by a relatively cool and humid climate, whereas five others occurred under warm and wet conditions. The regressive stages include four phases of relatively warm and dry climate and three periods of dry and relatively cold (or cool) climate.

Remote Sensing of Spatiotemporal Changes in Wetland Geomorphology Based on Type 2 Fuzzy Sets: A Case Study of Beidagang Wetland from 1975 to 2015

Few studies have considered the spatiotemporal changes in wetland land cover based on type 2 fuzzy sets using long-term series of remotely sensed data. This paper presents an improved interval type 2 fuzzy c-means (IT2FCM*) approach to analyse the spatial and temporal changes in the geomorphology of the Beidagang wetland in North China from 1975 to 2015 based on long-term Landsat data. Unlike traditional type 1 fuzzy c-means methods, the IT2FCM* algorithm based on interval type-2 fuzzy set has an ability to better handle the spectral uncertainty. Four indexes were adopted to validate the separability of classes with the IT2FCM* algorithm. These four validity indexes showed that IT2FCM* obtained better results than traditional methods. Additionally, the accuracy of the classification results was assessed based on the confusion matrix and kappa coefficient, which were high for the analysis of wetland landscape changes. Based on the analysis of separability of classes with the IT2FCM* algorithm using four validity indexes, the classification results, and the membership value images, the long-term series of satellite datasets were processed using the IT2FCM* method, and the study area was classified into six classes. Because water resources and vegetation are two key wetland components, the water resource dynamics and vegetation dynamics, based on the normalized difference vegetation index (NDVI), were analysed in detail according to the spatiotemporal classification results. The results show that the changes in vegetation types have historically been associated with water resource variations and that water resources play an important role in the evolution of vegetation types.

Monitoring the variations of evapotranspiration due to land use/cover change in a semiarid shrubland

Abstract. Evapotranspiration (ET) is an important process in the hydrological cycle, and vegetation change is a primary factor that affects ET. In this study, we analyzed the annual and inter-annual characteristics of ET using continuous observation data from eddy covariance (EC) measurement over 4 years (1 July 2011 to 30 June 2015) in a semiarid shrubland of Mu Us Sandy Land, China. The Normalized Difference Vegetation Index (NDVI) was demonstrated as the predominant factor that influences the seasonal variations in ET. Additionally, during the land degradation and vegetation rehabilitation processes, ET and normalized ET both increased due to the integrated effects of the changes in vegetation type, topography, and soil surface characteristics. This study could improve our understanding of the effects of land use/cover change on ET in the fragile ecosystem of semiarid regions and provide a scientific reference for the sustainable management of regional land and water resources.

黄土丘陵区植被类型与土壤微生物区系及生物量的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 黄土丘陵区植被类型与土壤微生物区系及生物量的关系 DOI: 10.5846/stxb201607311571 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（41411140035，41171419） Relationship among vegetation types and soil microbial biomass in the Loess Hilly region of China Author: Affiliation: 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:以陕西延安黄土丘陵区5种不同植被类型（人工刺槐林、天然侧柏林、天然辽东栎林、灌丛和裸地）为研究对象，分析了土壤微生物生物量碳、氮含量、细菌和真菌的丰度变化规律及其与土壤基本化学性质的关系。结果表明：（1）4种植被类型的土壤质量较之裸地都有不同程度的改善，总体趋势：天然林地 > 人工林地 > 裸地；（2）土壤微生物生物量碳、氮的总体趋势：天然林地最高，人工林次之，裸地最低，且与土壤有机碳（SOC）、全氮（TN）和速效磷（AP）极显著正相关（P < 0.01）；（3）裸地土壤的细菌丰度最低，人工刺槐林真菌含量显著低于天然辽东栎林。细菌丰度与土壤营养状况呈显著正相关（P < 0.05），而真菌与土壤营养无明显相关性，只与土壤pH负相关。说明在该研究区域，植被类型与土壤质量对微生物资源都具有不同程度的作用。 Abstract:To remedy adverse impacts on ecological environments, vegetation restoration has been completed on the Loess Hilly region of China, thus yielding changes in vegetation types, and secondary forests and exotic vegetation have reclaimed most of this area. Vegetation type plays an important role in soil quality, and similar land-use types usually possess similar soil properties and, most likely, similar microbial communities. To assess the effects of vegetation type on soil development, we measured the basic physicochemical properties, microbial biomass carbon (MBC) and nitrogen (MBN), and the number of bacteria and fungi of soils from areas with five different vegetation types, including a secondary natural oak forest, a non-typical natural forest of oriental arborvitae, a natural shrub land, a planted forest of black locust, and a plot of unforested bare land. We found that (1) soil properties improved with the presence of vegetation, compared with the abandoned bare land, and that there were differences in the physicochemical properties of soil from the different land-use types. Soils from the bare land and black locust forest yielded higher pH values than the natural forests, and the overall trend of soil quality was: natural forest > plantation > bare land. This indicated that vegetation coverage, especially natural types, has a beneficial effect on soil nutrient conditions and soil pH. (2) Similar to the trend of the other soil parameters, both MBC and MBN were highest in the oak forest and shrub land and lowest in the bare land and black locust forest. These two indices (MBC and MBN) were also strongly correlated with specific soil properties (soil organic carbon, r2 = 0.725, total nitrogen, r2 = 0.736, and phosphorus, r2 = 0.775; P < 0.001), suggesting that vegetation type and soil properties influence microbial biomass. Thus, microbial biomass can be used to assess soil trophic status and which lower in oligotrophic soils on the Loess Plateau of China. In our study area, the soil was alkaline (pH 8.18-8.48), and the MBC/MBN ratio was ~6, indicating that actinomycetes were dominant, possibly facilitated by the alkaline soil conditions. (3) Bare land harbored the lowest abundance of bacteria, and the abundance of fungi in the black locust was lower than that of the oak forest. The abundance of bacteria exhibited a strong relationship with specific soil properties and was positively correlated with C/N ratio (r2 = 0.754, P < 0.001), soil organic carbon (r2 = 0.636, P < 0.05), total nitrogen (r2 = 0.611, P < 0.05), and phosphorus (r2 = 0.775, P < 0.05), and negatively correlated with pH (r2 = 0.761, P < 0.001). In contrast, the abundance of fungi was only correlated with soil pH, thus confirming previous reports that bacteria and fungi respond to different environmental factors. This discrepancy may result from the different functions of bacteria and fungi. Fungi are primarily responsible for the decomposition of recalcitrant soil organic matter in forest soils. Thus, the overall trend of soil characteristic was: natural forest > plantation > bare land, indicating that the recovery of soil quality differed among plots with different vegetation types, and both soil microorganisms and soil microbial biomass, to a certain extent, can be used as an important index of soil fertility. 参考文献 相似文献 引证文献

Mid-latitude continental temperatures through the early Eocene in western Europe

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are increasingly used to reconstruct mean annual air temperature (MAAT) during the early Paleogene. However, the application of this proxy in coal deposits is limited and brGDGTs have only been detected in immature coals (i.e. lignites). Using samples recovered from Schöningen, Germany (∼48°N palaeolatitude), we provide the first detailed study into the occurrence and distribution of brGDGTs through a sequence of early Eocene lignites and associated interbeds. BrGDGTs are abundant and present in every sample. In comparison to modern studies, changes in vegetation type do not appear to significantly impact brGDGT distributions; however, there are subtle differences between lignites – representing peat-forming environments – and siliciclastic nearshore marine interbed depositional environments. Using the most recent brGDGT temperature calibration (MATmr) developed for soils, we generate the first continental temperature record from central-western continental Europe through the early Eocene. Lignite-derived MAAT estimates range from 23 to 26 °C while those derived from the nearshore marine interbeds exceed 20 °C. These estimates are consistent with other mid-latitude environments and model simulations, indicating enhanced mid-latitude, early Eocene warmth. In the basal part of the section studied, warming is recorded in both the lignites (∼2 °C) and nearshore marine interbeds (∼2–3 °C). This culminates in a long-term temperature maximum, likely including the Early Eocene Climatic Optimum (EECO). Although this long-term warming trend is relatively well established in the marine realm, it has rarely been shown in terrestrial settings. Using a suite of model simulations we show that the magnitude of warming at Schöningen is broadly consistent with a doubling of CO2, in agreement with late Paleocene and early Eocene pCO2 estimates.

Regional energy budget control of the intertropical convergence zone and application to mid-Holocene rainfall

Shifts in the latitude of the intertropical convergence zone—a region of intense tropical rainfall—have often been explained through changes in the atmospheric energy budget, specifically through theories that tie rainfall to meridional energy fluxes. These quantitative theories can explain shifts in the zonal mean, but often have limited relevance for regional climate shifts, such as a period of enhanced precipitation over Saharan Africa during the mid-Holocene. Here we present a theory for regional tropical rainfall shifts that utilizes both zonal and meridional energy fluxes. We first identify a qualitative link between zonal and meridional energy fluxes and rainfall variations associated with the seasonal cycle and the El Nino/Southern Oscillation. We then develop a quantitative theory based on these fluxes that relates atmospheric energy transport to tropical rainfall. When applied to the orbital configuration of the mid-Holocene, our theory predicts continental rainfall shifts over Africa and Southeast Asia that are consistent with complex model simulations. However, the predicted rainfall over the Sahara is not sufficient to sustain vegetation at a level seen in the palaeo-record, which instead requires an additional large energy source such as that due to reductions in Saharan surface albedo. We thus conclude that additional feedbacks, such as those involving changes in vegetation or soil type, are required to explain changes in rainfall over Africa during the mid-Holocene. Shifts in the latitude of the tropical rainfall band are constrained by meridional energy fluxes. Calculations show that combining zonal and meridional energy fluxes can explain past regional rainfall variations like the African Humid Period.

Time trumps habitat in the dynamics of an avian community

AbstractPredictions of change in avian biodiversity often fail to account for the natural dynamism of species assemblages. Information from historical datasets can be useful indicators of how avian communities may change in the future. However, simple comparisons of diversity and abundances over time may overlook additional changes in bird–habitat associations. In 2013, we revisited sites from a unique, highly detailed avian survey from the Willamette Valley, Oregon, conducted in 1952. Our objectives were to quantify and describe the extent of avian community change; relate observed species assemblages to changes in vegetation type and land‐use class; and identify species with specific associations to either survey era. Using nonparametric ordination, we assessed whether the distribution of the avian community within the environmental space varied temporally. We used blocked indicator species analysis to identify species with specific association to historical or modern survey eras. Nonparametric permutation procedures identified both plot, each representing a different major habitat type, and year as significant factors defining communities. Year was more strongly related to the second ordination axis than the other environmental variables examined. Ordination of survey sites in species space confirmed modern avian communities were significantly different from their historical counterparts. Bird species richness increased and community composition changed by at least 50% despite the physiognomic characteristics of each plot's habitat and the surrounding landscape remaining comparatively stable. Because of this, we conclude time trumped, or was more strongly associated with community change, than alterations in physiognomic habitat. These results suggest avian communities are naturally dynamic even in areas with relatively stable habitat conditions. Predictions that only address changes in climate, land use, or vegetation cover type may fail to predict changes in avian community composition. Historical datasets are a valuable means of understanding real‐world changes in avian communities. We suggest additional factors, such as vegetation structure and microhabitat, may predict fine‐scale shifts in avian species assemblages. Nevertheless, major changes in community composition occurred with apparently minor shifts in physiognomic habitat characteristics in our study area.

Water, Rather than Temperature, Dominantly Impacts How Soil Fauna Affect Dissolved Carbon and Nitrogen Release from Fresh Litter during Early Litter Decomposition

Longstanding observations suggest that dissolved materials are lost from fresh litter through leaching, but the role of soil fauna in controlling this process has been poorly documented. In this study, a litterbag experiment employing litterbags with different mesh sizes (3 mm to permit soil fauna access and 0.04 mm to exclude fauna access) was conducted in three habitats (arid valley, ecotone and subalpine forest) with changes in climate and vegetation types to evaluate the effects of soil fauna on the concentrations of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) during the first year of decomposition. The results showed that the individual density and community abundance of soil fauna greatly varied among these habitats, but Prostigmata, Isotomidae and Oribatida were the dominant soil invertebrates. At the end of the experiment, the mass remaining of foliar litter ranged from 58% for shrub litter to 77% for birch litter, and the DOC and TDN concentrations decreased to 54%–85% and increased to 34%–269%, respectively, when soil fauna were not present. The effects of soil fauna on the concentrations of both DOC and TDN in foliar litter were greater in the subalpine forest (wetter but colder) during the winter and in the arid valley (warmer but drier) during the growing season, and this effect was positively correlated with water content. Moreover, the effects of fauna on DOC and TDN concentrations were greater for high-quality litter and were related to the C/N ratio. These results suggest that water, rather than temperature, dominates how fauna affect the release of dissolved substances from fresh litter.

Quantification of Calabrian vegetation in Southern Primory'e (Far East of Russia) using multiple proxies

Early Pleistocene vegetation dynamics in the Russian Far East (southern Primory'e) are studied using multiple quantitative techniques on various palaeobotanical organ types. Vegetation data for this time interval were obtained from a total of 8 macrofloras (fruits and seeds, woods, and leaves) and 18 microfloras collected from a 10m thick, terrigenous succession exposed in the Pavlovskoe brown coal field. According to magnetostratigraphy, the studied section covers the last 250kyr of the Calabrian (1.0 to 0.781Ma) and includes the early/middle Pleistocene boundary. In this first integrative study on quantification of palaeovegetation of the Russian Far East, we apply the following methods: Plant Functional Type (PFT) Approach, Integrated Plant Record (IPR) vegetation analysis, and ecological Coexistence Approach (CAeco) on the different organs, partly originating from the same layer.The investigation documents the following outcomes: 1) Vegetation types obtained from the various methods are proven to be largely consistent. All data indicate the presence of more forested conditions and show no xeric, open woodland throughout the section. 2) Vegetation as reconstructed using the various methods generally is in good agreement with the recently published climate evolution throughout the section. 3) There is a cyclic evolution of PFT diversity which is in line with climate data. 4) The changes of vegetation types obtained from IPR analysis relate to cooling/drying trends of the climate evolution.

Greenhouse gas emissions from natural ecosystems and agricultural lands in sub-Saharan Africa: synthesis of available data and suggestions for further research

Abstract. This paper summarizes currently available data on greenhouse gas (GHG) emissions from African natural ecosystems and agricultural lands. The available data are used to synthesize current understanding of the drivers of change in GHG emissions, outline the knowledge gaps, and suggest future directions and strategies for GHG emission research. GHG emission data were collected from 75 studies conducted in 22 countries (n = 244) in sub-Saharan Africa (SSA). Carbon dioxide (CO2) emissions were by far the largest contributor to GHG emissions and global warming potential (GWP) in SSA natural terrestrial systems. CO2 emissions ranged from 3.3 to 57.0 Mg CO2 ha−1 yr−1, methane (CH4) emissions ranged from −4.8 to 3.5 kg ha−1 yr−1 (−0.16 to 0.12 Mg CO2 equivalent (eq.) ha−1 yr−1), and nitrous oxide (N2O) emissions ranged from −0.1 to 13.7 kg ha−1 yr−1 (−0.03 to 4.1 Mg CO2 eq. ha−1 yr−1). Soil physical and chemical properties, rewetting, vegetation type, forest management, and land-use changes were all found to be important factors affecting soil GHG emissions from natural terrestrial systems. In aquatic systems, CO2 was the largest contributor to total GHG emissions, ranging from 5.7 to 232.0 Mg CO2 ha−1 yr−1, followed by −26.3 to 2741.9 kg CH4 ha−1 yr−1 (−0.89 to 93.2 Mg CO2 eq. ha−1 yr−1) and 0.2 to 3.5 kg N2O ha−1 yr−1 (0.06 to 1.0 Mg CO2 eq. ha−1 yr−1). Rates of all GHG emissions from aquatic systems were affected by type, location, hydrological characteristics, and water quality. In croplands, soil GHG emissions were also dominated by CO2, ranging from 1.7 to 141.2 Mg CO2 ha−1 yr−1, with −1.3 to 66.7 kg CH4 ha−1 yr−1 (−0.04 to 2.3 Mg CO2 eq. ha−1 yr−1) and 0.05 to 112.0 kg N2O ha−1 yr−1 (0.015 to 33.4 Mg CO2 eq. ha−1 yr−1). N2O emission factors (EFs) ranged from 0.01 to 4.1 %. Incorporation of crop residues or manure with inorganic fertilizers invariably resulted in significant changes in GHG emissions, but results were inconsistent as the magnitude and direction of changes were differed by gas. Soil GHG emissions from vegetable gardens ranged from 73.3 to 132.0 Mg CO2 ha−1 yr−1 and 53.4 to 177.6 kg N2O ha−1 yr−1 (15.9 to 52.9 Mg CO2 eq. ha−1 yr−1) and N2O EFs ranged from 3 to 4 %. Soil CO2 and N2O emissions from agroforestry were 38.6 Mg CO2 ha−1 yr−1 and 0.2 to 26.7 kg N2O ha−1 yr−1 (0.06 to 8.0 Mg CO2 eq. ha−1 yr−1), respectively. Improving fallow with nitrogen (N)-fixing trees led to increased CO2 and N2O emissions compared to conventional croplands. The type and quality of plant residue in the fallow is an important control on how CO2 and N2O emissions are affected. Throughout agricultural lands, N2O emissions slowly increased with N inputs below 150 kg N ha−1 yr−1 and increased exponentially with N application rates up to 300 kg N ha−1 yr−1. The lowest yield-scaled N2O emissions were reported with N application rates ranging between 100 and 150 kg N ha−1. Overall, total CO2 eq. emissions from SSA natural ecosystems and agricultural lands were 56.9 ± 12.7 × 109 Mg CO2 eq. yr−1 with natural ecosystems and agricultural lands contributing 76.3 and 23.7 %, respectively. Additional GHG emission measurements are urgently required to reduce uncertainty on annual GHG emissions from the different land uses and identify major control factors and mitigation options for low-emission development. A common strategy for addressing this data gap may include identifying priorities for data acquisition, utilizing appropriate technologies, and involving international networks and collaboration.

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.