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The influence of terrestrial ecosystems on climate
Abstract
Terrestrial ecosystems influence climate by affecting how much solar energy is absorbed by the land surface and by exchanging climatically important gases with the atmosphere. Recent model analyses show widespread qualitative agreement that terrestrial ecological processes will have a net positive feedback effect on 21st-century global warming, and, therefore, cannot be ignored in climate-change projections. However, the quantitative uncertainty in the net feedback is large. The uncertainty in 21st-century carbon dioxide emissions resulting from terrestrial carbon cycle-climate feedbacks is second in magnitude only to the uncertainty in anthropogenic emissions. We estimate that this translates into an uncertainty in global warming owing to the land surface of 1.5 degrees C by 2100. We also emphasise the need to improve our understanding of terrestrial ecological processes that influence land-atmosphere interactions at relatively long timescales (decadal-century) as well as at shorter intervals (e.g. hourly).
... Therefore, changes in vegetation and soil coverage strongly influence the temperature and humidity of the surrounding air (Meir et al 2006;Chapin et al 2008), and, generally, the effects on the local and regional climate exceed the recorded variation in air temperature at a global scale, due to the increase in greenhouse gases in the atmosphere (Costa and Foley 2000). ...
... In this study, we found that land use can have a significant impact on the local climate in mountain landscapes in the Andes, as has been demonstrated globally (Meir et al 2006;Chapin et al 2008;Duveiller et al 2018) and in other tropical regions (Osborne et al 2004). As we expected, native forests generate a particular microenvironment, providing more stable weather conditions, which are significantly different from the other land use types (eg planted forests, monocultures, and pastures). ...
Changes in land use affect biodiversity and the biophysical structure of ecosystems, causing negative impacts on ecosystem services, such as climate regulation. However, few studies have evaluated the effect of land use changes on the local climate, particularly in tropical mountain systems such as the Andes. Therefore, this study compares 4 land use types (native forest, planted forest, maize monoculture, and pasture) in a mountain landscape in northern Ecuador as a proxy to assess the impact of land use change on local climate regulation. We estimated gap fraction with photographic techniques and recorded temperature and relative humidity using dataloggers set at 2 heights (0 m and 1 m) above ground level across the land use types. As we expected, native forests provided a more stable microclimate, demonstrating significantly lower temperatures and higher relative humidity values than the other land use types. This effect on microclimate was significantly explained with highest temperatures at intermediate gap fraction levels. In addition, we observed that native forests provided a buffer effect for the variations in mesoclimate; only native forests showed an evident reduction in local temperature over the range of mesoclimates. Local temperature variations registered in human-altered systems (planted forests and pastures) were significantly explained by the mesoclimate variation, with the exception of monocultures that exhibited a mismatch between the 2 scales of climate. These results highlight the importance of native forest for microclimate regulation, an ecosystem service that can act synergistically with other biodiversity and conservation goals to sustainably manage landscapes in Andean mountain systems.
... Wrack freshly deposited during the previous high tide has greater moisture content than bare sand or aged wrack (Gonçalves & Marques, 2011) and this is likely to contribute to an evaporative cooling effect due to interactions with wind in exposed areas (Meir et al., 2006). Furthermore, ocean temperatures would likely be warmer than external early morning ambient temperatures (cf. ...
... Higher temperatures in sheltered locations suggest a reduced effect of evaporative cooling, potentially due to moderation of wind speeds in these positions. However, small variations in substrate colour, aspect and slope, and its influence on radiation load may also contribute to differences in microclimate temperature (Meir et al., 2006). ...
Conservation management to protect coastal ecosystems sometimes overlooks site‐specific fine‐scale heterogeneity. For example, while habitat loss is a known key driver of population declines in many shorebirds, these birds are also dependent on high‐quality habitats to maximize energy stores. Here we describe the microhabitats provided by beach‐cast wrack (washed up macroalgae and seagrasses), a resource threatened by harvesting and beach cleaning, and how shorebirds utilize these.
We measured the temperature and absolute humidity at 10 cm above three substrates (fresh wrack, aged wrack and sand) and then related bird behaviour (roosting vs. foraging) to climatic and environmental data.
Freshly beach‐cast wrack mostly provided cooler and less humid habitats, but warmer temperatures than aged wrack or sand in the early mornings. Microtopography created by shelter from prevailing winds and wrack depth modified these general trends.
Generally, temperature predicted where shorebirds overall and the two most common species, the double‐banded plover Charadrius bicinctus and red‐necked stint Calidris ruficollis, were observed. During most of the day, foraging and roosting were more likely to occur on the warmer aged wrack. In the early morning, when fresh wrack provided the warmer temperatures, birds tended to roost and forage on fresh wrack.
Synthesis and Applications. Beach‐cast wrack creates a complex mosaic of unique microclimates varying in space and time, which allows shorebirds to minimize energy expenditure by selecting the thermally most favourable habitats for roosting and foraging. Removal of beach‐cast wrack for commercial and aesthetic reasons thus reduces habitat quality and increases energy expenditure in shorebirds. Associated declines in energy stores may be contributing to declines in shorebird populations. Management of coastal ecosystems and shorebirds therefore needs to consider and maintain fine‐scale environmental heterogeneity at local scales.
... Warming temperature has proved to have direct physiological effects on photosynthesis and indirect stomatal effects (Meir et al. 2006). Many models included temperature influence on photosynthetic machinery (Doughty 2011). ...
... Greater attention must be given to understanding processes, rather than model projections of the future (Lloyd and Farquhar 2008). Better-constrained predictions of future changes in forest ecosystems and climate will also require improved links between data and models, perhaps through the application of formal data assimilation techniques (Meir et al. 2006;Smith et al. 1992). ...
Forest ecosystems have been identified to be the largest land carbon sink and account for more than half of carbon stored in the terrestrial ecosystems. The influences of climate change on forest ecosystems could have significant implications on global carbon cycling. In this chapter, we reviewed research progresses about climate change impacts on forest ecosystem carbon cycling in the past 20 years. Our review is mostly on field experiments and modeling studies. This chapter starts with a brief description of climate change and forest ecosystems. Different experimental studies are then presented. The impacts of global change such as elevated CO2, global warming, and changes in precipitation and O3 on carbon cycling in forest ecosystems are synthesized. Next, we present some modeling studies of forest ecosystem carbon cycling at ecosystem, regional, and global scales. At the end of the chapter, we make some recommendations for future studies.
... Biochemical feedback between terrestrial ecosystems and climate occur through climateinduced changes in the greenhouse gas exchange [1][2][3]. Their magnitude is still highly uncertain, but it is assumed to be similar to biophysical feedback [4]. The carbon (C) cycle is crucial for the understanding of biochemical feedback since it involves two of the most important greenhouse gases (CO 2 and CH 4 ), and its fluxes are strongly affected by climate change. ...
... The carbon (C) cycle is crucial for the understanding of biochemical feedback since it involves two of the most important greenhouse gases (CO 2 and CH 4 ), and its fluxes are strongly affected by climate change. Generally, a positive C cycle feedback is expected for terrestrial ecosystems accelerating climate change, but its magnitude is uncertain [1,5,6]. ...
Plant–soil interactions are recognized to play a crucial role in the ecosystem response to climate change. We developed a facility to disentangle the complex interactions behind the plant–soil C feedback mechanisms. The MICE (‘Multi-Isotope labelling in a Controlled Environment’) facility consists of two climate chambers with independent control of the atmospheric conditions (light, CO2, temperature, humidity) and the soil environment (temperature, moisture). Each chamber holds 15 plant–soil systems with hermetical separation of the shared above ground (shoots) from the individual belowground compartments (roots, rhizosphere, soil). Stable isotopes (e.g. ¹³C, ¹⁵N, ²H, ¹⁸O) can be added to either compartment and traced within the whole system. The soil CO2 efflux rate is monitored, and plant material, leached soil water and gas samples are taken frequently. The facility is a powerful tool to improve our mechanistic understanding of plant–soil interactions that drive the C cycle feedback to climate change.
... These findings highlight the complex relationship between vegetation cover, precipitation, and land surface temperature variations. Vegetation can have contrasting effects on LSTs: it may cool the surface by increasing evapotranspiration or warm it by reducing albedo (Meir et al., 2006). The net effect depends on which mechanism dominates in a region. ...
Plain Language Summary
Land‐atmosphere interactions are crucial for understanding how regional temperatures change. Here, we looked at land surface temperature (LST) changes by analyzing soil bacterial markers. We found that LST trends varied notably across regions that were close to each other but had different types of vegetation. In the southern and eastern Chinese Loess Plateau (CLP), where vegetation is more abundant, LST changes generally matched patterns of magnetic properties of the soil, organic carbon content, and regional air temperatures. However, in the northern and western CLP, where vegetation is sparse, LSTs showed noticeable differences from air temperatures, with higher LSTs during the Last Glacial Maximum and lower LSTs during the middle Holocene. These spatial differences suggest that regional vegetation variations played a key role in the temperature changes we observed. Our findings are further supported by modern meteorological records, which demonstrate that the influence of vegetation on the temperature disparity between LSTs and air temperatures intensifies as rainfall and vegetation cover decrease, especially when rainfall is less than 600 mm. This study highlights the important role of vegetation in historical LST changes and helps us better understand Holocene temperature trends and land‐atmosphere interactions in East Asia.
... In the 21 st century, plants take in sunlight and engage in gas exchange with their environment, influencing climate change and global warming. Concerns regarding the world's temperature rising by 1.5°C by 2100 largely stem from insufficient accurate data (Meir et al., 2006). ...
Climate change, a long-term alteration in weather patterns, is reshaping ecosystems and industries worldwide, with profound implications for agriculture, biodiversity, and human health. This review paper explores the multifaceted impacts of climate change, emphasizing its effects on global agriculture, forest ecosystems, and marine environments. Rising temperatures, increased carbon dioxide levels, and changing precipitation patterns are leading to decreased crop yields, increased pest populations, and altered ecosystem dynamics. The study highlights the need for global and local adaptation strategies, including improved crop management, sustainable forestry practices, and enhanced carbon sequestration methods. In particular, developing nations like India are facing severe challenges, necessitating robust and immediate adaptation measures to mitigate the adverse effects on food security and economic stability. The review underscores the urgency of interdisciplinary approaches and innovative policies to address the complex and evolving challenges posed by climate change.
... In recent years, the negative terrestrial ecological impacts of climate change have become more apparent and are very likely to intensify over the coming decades [1][2][3]. Forests constitute a crucial segment of land-based ecosystems and are instrumental in sustaining the cycle of carbon on a global scale. They play a key role in counteracting the effects of global warming, enhancing environmental conditions, and maintaining the equilibrium of natural ecosystems [4][5][6]. ...
Forest canopy height is an important indicator of the forest ecosystem, and an accurate assessment of forest canopy height on a large scale is of great significance for forest resource quantification and carbon sequestration. The retrieval of canopy height based on remote sensing provides a possibility for studying forest ecosystems. This study proposes a new method for estimating forest canopy height based on remote sensing. In this method, the GEDI satellite and ICESat-2 satellite, which are different types of space-borne lidar products, are used to cooperate with the Landsat 9 image and SRTM terrain data, respectively. Two forest canopy height-retrieval models based on multi-source remote sensing integration are obtained using a random forest regression (RFR) algorithm. The study, conducted at a forest site in the northeastern United States, synthesized various remote sensing data sets to produce a robust canopy height model. First, we extracted relative canopy height products, multispectral features, and topographic data from GEDI, ICESat-2, Landsat 9, and SRTM images, respectively. The importance of each variable was assessed, and the random forest algorithm was used to analyze each variable statistically. Then, the random forest regression algorithm was used to combine these variables and construct the forest canopy height model. Validation with airborne laser scanning (ALS) data shows that the GEDI and ICESat-2 models using a single data source achieve better accuracy than the Landsat 9 model. Notably, the combination of GEDI, Landsat 9, and SRTM data (R = 0.92, MAE = 1.91 m, RMSE = 2.78 m, and rRMSE = 12.64%) and a combination of ICESat-2, Landsat 9, and SRTM data (R = 0.89, MAE = 1.84 m, RMSE = 2.54 m, and rRMSE = 10.75%). Compared with the least accurate Landsat 9 model, R increased by 29.58%, 93.48%, MAE by 44.64%, 46.20%, RMSE by 42.80%, 49.40%, and the rRMSE was increased by 42.86% and 49.32%, respectively. These results fully evaluate and discuss the practical performance and benefits of multi-source data retrieval of forest canopy height by combining space-borne lidar data with Landsat 9 data, which is of great significance for understanding forest structure and dynamics. The study provides a reliable methodology for estimating forest canopy height and valuable insights into forest resource management and its contribution to global climate change.
... Earth system modelling (ESM, Fig. 1) represents a primary tool for characterizing and quantifying the spatiotemporal variations and internal interactions of the Earth across the past, present and future [5][6][7] . ESMs are composed of a set of physics-based equations that simulate physical, chemical and biological processes within the Earth system, such as carbon and nitrogen cycles, solar radiation dynamics and terrestrial ecosystem dynamics [8][9][10] . These process-based models merge all aspects of the Earth system together, unlike their predecessors (such as global climate models) that just focused on the atmosphere and oceans. ...
Earth system modelling (ESM) is essential for understanding past, present and future Earth processes. Deep learning (DL), with the data-driven strength of neural networks, has promise for improving ESM by exploiting information from Big Data. Yet existing hybrid ESMs largely have deep neural networks incorporated only during the initial stage of model development. In this Perspective, we examine progress in hybrid ESM, focusing on the Earth surface system, and propose a framework that integrates neural networks into ESM throughout the modelling lifecycle. In this framework, DL computing systems and ESM-related knowledge repositories are set up in a homogeneous computational environment. DL can infer unknown or missing information, feeding it back into the knowledge repositories, while the ESM-related knowledge can constrain inference results of the DL. By fostering collaboration between ESM-related knowledge and DL systems, adaptive guidance plans can be generated through question-answering mechanisms and recommendation functions. As users interact iteratively, the hybrid system deepens its understanding of their preferences, resulting in increasingly customized, scalable and accurate guidance plans for modelling Earth processes. The advancement of this framework necessitates interdisciplinary collaboration, focusing on explainable DL and maintaining observational data to ensure the reliability of simulations.
... However, although past changes in marine temperatures are relatively well constrained, much less quantitative temperature data are available for the terrestrial realm. Accordingly, one of the largest uncertainties in predicting the impact of anthropogenic climate change is the response of the terrestrial realm (Meir et al., 2006;Carvalhais et al., 2014). In particular, correctly quantifying the sensitivity of terrestrial climate to natural or anthropogenic climate forcings provides a major challenge for the paleoclimate community (Knight and Harrison, 2012). ...
The scarcity of suitable high-resolution archives, such as ancient natural lakes, that span beyond the Holocene, hinders long-term late Quaternary temperature reconstructions in southern Africa. Here we target two cores from Mfabeni Peatland, one of the few long continuous terrestrial archives in South Africa that reaches into the Pleistocene, to generate a composite temperature record spanning the last ∼43 kyr. The Mfabeni Peatland has previously been proven suitable for temperature and hydrological reconstructions based on pollen and geochemical proxies. Here we use branched glycerol dialkyl glycerol tetraethers (brGDGTs) preserved in the Mfabeni peatland to derive a new quantitative air temperature record for south-east Africa. Our temperature record generally follows global trends in temperature and atmospheric CO2 concentrations, but is decoupled at times. Annual air temperatures during Marine Isotope Stage (MIS) 3 were moderately high (c. 20.5 °C), but dropped by c. 5 °C during the Last Glacial Maximum, reaching a minimum at c.16–15 ka. Asynchronous with local insolation, this cooling may have resulted from reduced sea surface temperatures linked to a northward shift in the Southern Hemisphere westerly winds. Concurrent with the southward retreat of the westerlies, and increasing sea surface temperatures offshore, warming from minimum temperatures (c. 15.0 °C) to average Holocene temperatures (c. 20.0 °C) occurred across the deglaciation. This warming was briefly but prominently interrupted by a millennial-scale cooling event of c. 3 °C at c. 2.4 ka, concurrent with a sudden change in hydrological conditions. The average Holocene temperatures of c. 20.0 °C were similar to those reconstructed for MIS 3, but after the 2.4 ka cooling period, air temperatures in the Mfabeni peat recovered and steadily increased towards the present. In summary, our record demonstrates that land temperature in eastern South Africa is highly sensitive to global drivers as well as nearby sea surface temperatures.
... Terrestrial ecosystems play a critical role in climate systems by regulating exchanges of energy, moisture, and carbon dioxide between the land surface and the atmosphere (Sellers, 1997;Pielke et al., 1998;Meir et al., 2006). In turn, climate change has significantly affected vegetation photosynthesis, water use efficiency, mortality, regeneration, and structure through gradual changes in the temperature and atmospheric CO 2 concentration together with shifts in climate extremes (Keenan et al., 2013;Huang et al., 2015;Brando et al., 2019;McDowell et al., 2020). ...
We developed a demographic vegetation model, BiomeE, to improve the modeling of vegetation dynamics and ecosystem biogeochemical cycles in the NASA Goddard Institute of Space Studies' ModelE Earth system model. This model includes the processes of plant growth, mortality, reproduction, vegetation structural dynamics, and soil carbon and nitrogen storage and transformations. The model combines the plant physiological processes of ModelE's original vegetation model, Ent, with the plant demographic and ecosystem nitrogen processes that have been represented in the Geophysical Fluid Dynamics Laboratory's LM3-PPA. We used nine plant functional types to represent global natural vegetation functional diversity, including trees, shrubs, and grasses, and a new phenology model to simulate vegetation seasonal changes with temperature and precipitation fluctuations. Competition for light and soil resources is individual based, which makes the modeling of transient compositional dynamics and vegetation succession possible. Overall, the BiomeE model simulates, with fidelity comparable to other models, the dynamics of vegetation and soil biogeochemistry, including leaf area index, vegetation structure (e.g., height, tree density, size distribution, and crown organization), and ecosystem carbon and nitrogen storage and fluxes. This model allows ModelE to simulate transient and long-term biogeophysical and biogeochemical feedbacks between the climate system and land ecosystems. Furthermore, BiomeE also allows for the eco-evolutionary modeling of community assemblage in response to past and future climate changes with its individual-based competition and demographic processes.
... WR also reflects the resilience of terrestrial ecosystems to extreme droughts and floods (Zhai & Tao, 2021). However, climate change can affect ecosystems (Jones et al., 2009;Nolan et al., 2018;Meir et al., 2006) and thus can lead to significant changes in the WR of an ecosystem (Bai et al., 2019;Zhai et al., 2018). Therefore, understanding the responses of regional WR to climate change and its potential dynamics under future climate trajectories are critical to water resource management. ...
Identifying the dynamics of water retention (WR) is critical for developing adaptive strategies for effective water resources management under climate change. However, our understanding about the responses of WR to climate change is still limited, which hinders risk assessment and warning of WR under future climate trajectories. In this study, we used the Soil and Water Assessment Tool (SWAT) to quantify the impact of climate change on WR in the upper Heihe River Basin (UHRB), a typical inner headwater basin, and predicted the future trends and potential degradation risks of WR based on climate scenarios under three Representative Concentration Pathways (RCP2.6, RCP4.5, and RCP8.5). Our results showed that the historical (1971-2020) average WR in the UHRB was approximately 91.1 mm, with high WR occurring in the middle and west of the basin and low WR in the north and southeast. Our prediction suggested that the WR may remain stable during the near future (near future, 2021-2060) under the RCP2.6 scenario; however, WR may decrease by 23% and 32% during this period under the RCP4.5 and RCP8.5, respectively. By the end of this century (far future, 2061-2099), the WR may decrease by 10%, 40%, and 69% under the RCP2.6, RCP4.5, and RCP8.5 scenarios, respectively, due to the substantially enhanced evapotranspiration in the warming context, though a slight increase in precipitation may partly offset this negative impact. In brief, this study provides a paradigm for assessing the dynamics and future degradation risk of water retention at watershed scale, and this can be valuable and applicable for other areas.
... Terrestrial ecosystems have an essential role in both global carbon and water cycles by regulating the carbon exchange through photosynthesis and respiration processes and water release to atmosphere through transpiration (Meir et al. 2006;Schimel 1995). These water and carbon exchanges between terrestrial ecosystems and atmosphere has played a crucial role in Earth's past and present. ...
Drought is a frequently occurring hydrometeorological event, which is defined as a reduction in water availability in different hydrologic elements. Over the last century, the hydrologists around the world have put substantial efforts to improve the monitoring and prediction of droughts through the development of new drought indices and prediction models. However, the scarcity of site-based observations has constrained these efforts to date. Remote sensing has emerged as an alternative to supplement these observations and has enabled the progress in drought studies in data-scarce parts of the world. This chapter describes the applicability of remote sensing in evaluation and assessment of drought (i.e., meteorological, agricultural, and hydrological). We also discuss the limitations associated with remote sensing applications (resolution, continuity, and uncertainty) and future perspectives. Further, a case study on remote sensing application in assessment of drought impact on Net Primary Production (NPP) in India is also presented, which highlights the importance of remote sensing in providing information of ecohydrological variables that are difficult to monitor on ground.
... Both biogeochemical and biophysical factors contribute meaningfully to estimating climate regulation value, but the results can be highly variable by the spatialtemporal scale. Solid studies have pointed out that while estimating global scale climate regulation for longer periods, biogeochemical factors are more important, but when focusing on the local scale and within a relatively short period (T ≤ 20 years), the biophysical impacts can dwarf biogeochemical impacts [78][79][80][81][82][83]. Therefore, in estimating the climate regulation value of the local forest ecosystem, studies typically base their estimation solely on the biophysical processes. ...
Suburban forest ecosystems have a great influence on local climate, especially for mitigating urban heat island effects and dry island effects. To quantify the climate regulation value of forest ecosystem, and provide a reference for regional ecosystem accounting and scientific land management, a new estimation method based on actual evapotranspiration (AET) is proposed and applied in this work. Based on remote sensing, meteorological, and soil data in the years 2000, 2010, and 2020, the annual AET of the forest ecosystem and its dynamic changes were calculated in the new urban area, Guanshanhu District, Guiyang, Guizhou Province, SW China. The climate regulation value is derived from differences in the annual AET of forest ecosystems relative to impervious surfaces. The results showed that: (1) the area of forest ecosystem in Guanshanhu District increased from 2000 to 2010 as a result of ecological engineering but decreased from 2010 to 2020 due to the establishment and expansion of the new urban area, while the area of the impervious surface increased rapidly; (2) the differences in annual AET of forest ecosystem relative to the impervious surface were calculated and subdivided according to different forest types. In 2000, 2010, and 2020, coniferous forests contributed the most to the annual AET difference, followed by coniferous and broad-leaved mixed forests, broad-leaved forests, shrubs, and other forests, respectively; (3) the total climate regulation value of forest ecosystem showed an increasing trend, on the whole, the estimation results were ¥8.78 × 10⁸ in 2000, ¥12.62 × 10⁸ in 2010, and ¥14.75 × 10⁸ in 2020; (4) The average per unit area climate regulation value of all types of forests in the area, based on electricity price in the year 2000, was ¥8.06 × 10⁴/ha in 2000, ¥8.11 × 10⁴/ha in 2010, and ¥10.58 × 10⁴/ha in 2020, the highest portion of per unit area climate regulation value was of coniferous forest, as ¥8.59 × 10⁴/ha in 2000, ¥9.28 × 10⁴/ha in 2010, and ¥11.05 × 10⁴/ha in 2020. This study is a beneficial exploration of forest ecosystem climate regulation value estimation in Guanshanhu District, and the results can provide references for ecological construction in new urban areas.
... The scales of these layers can range between 1: 1,200,000 or more. (Meir et al., 2006). The relationships are based on parameters of temperature, precipitation, and those derived from the relationship with vegetation (Arrazola et al., 2000). ...
La importancia de representar los ecosistemas neotropicales surge de la necesidad de generar cartografía que facilite comprender su segregación en el espacio. El objetivo de nuestro trabajo fue diseñar un modelo de representación cartográfica de ecosistemas, a través de procesos que integran los insumos cartográficos y sus respectivas escalas, asociados a un sistema de clasificación jerárquica. Para ello, se determinaron niveles jerárquicos con base en criterios geofísicos y biofísicos, característicos de los ecosistemas neotropicales, se seleccionaron insumos cartográficos en cada nivel jerárquico asociado a su respectiva escala. Se concluye que los ecosistemas neotropicales deben ser representados a mayores escalas, ya que es la única forma de obtener el detalle necesario de los atributos que los caracterizan, esta necesidad está determinada por la complejidad derivada de la diversidad geofísica y biológica de esta región.
... It can be noted based on the analysis of the recent climate changes and the marine and terrestrial ecosystems, that terrestrial communities are rapidly transforming as a result of global warming (Meir et al., 2006;Tylianakis et al., 2008;Zhou and Tung, 2013;Franzke, 2014). This process results the modification of the entire ecosystem (Agiadi and Albano, 2020;Albano et al., 2021). ...
In the present work, well radiocarbon-dated Quaternary malacological and palynological analyses were implemented on 4 cm samples deriving from one of the thickest and best developed last glacial sequences of Central Europe the Madaras brickyard and the borehole of Kolon Lake in the southern part of Hungary. Using a combination of mollusc, anthracological, palynological and climatic proxies evidence preserved within loess, we demonstrate that long-term changes (e.g. the last 39,000 (28,000) years) in paleoclimatic dynamics on the northern edge of the Bácska-Titel loess plateau, on the southern part of the Great Hungarian Plain. These proxy data are reflected in the following ecological changes: a turnover from predominantly cold-tolerant mollusc fauna in a boreal type forest-steppe context under cold conditions during the last glacial then followed by a shift to a predominantly xerotheromphilous land snail fauna in a temperate forest-steppe context under a warm temperate climate in the early Holocene. Certain warm-adapted, Central and SSE European distribution mollusc species such as Caucasotachea vindobonensis and Granaria frumentum, were found to have been associated with temperate forest-steppe in both the Holocene record and the present-day ecosystem.
Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.
... The interaction between terrestrial ecosystems and the ocean and atmosphere is imperative for refining our understanding of modern and ancient climate change, but not well constrained (Meir et al., 2006). So far, little work has been done to understand the impacts of quasiperiodic climate variations on terrestrial coastal Pacific ecosystem development (Guan et al., 2012). ...
Carbon isotope ecology can be used as a measure of plant water stress. Plant water stress is complicated: multiple factors (e.g., evapotranspiration rates, temperature, precipitation, soil texture, and available water) control the magnitude of the isotopic expression. Often, large ocean–atmosphere pressure systems result in the convergence of constructive climate parameters that result in increased plant water stress; for example, El Niño and Pacific Decadal Oscillation (PDO) anomaly phases. We examined the biogeochemistry of three species (Thuja plicata: with a Pacific coastal habitat, Thuja occidentalis: native to the Great Lakes region, and Populus tremuloides: a cosmopolitan species found throughout North America). Coincident analyses of these species allowed for intercomparison between plants in habitats directly impacted by atmospheric–oceanic controls on water availability and those out of Pacific impact range. There are oscillatory patterns in the carbon isotope discrimination values (Δ¹³Cleaf) of Thuja plicata, but no clear patterns in Δ¹³Cleaf values of the other species. We compare the pattern in isotope discrimination of T. plicata with Pacific‐driven multiannual environmental phenomena to determine whether these patterns could be related to the oscillation in Δ¹³Cleaf values. The data demonstrate a regular and significant 14‐ to 19‐year periodicity, aligning most closely with PDO climate patterns. Thuja plicata likely records prolonged stress, like plant available water shortages, which coincide with PDO‐associated shifts in precipitation, humidity, and evapotranspiration. These findings demonstrate that coastal Pacific ecosystems are vulnerable to changes in water availability connected to Pacific teleconnections, providing a new recording tool to examine multiannual climate anomalies.
... Terrestrial vegetation actively participates in the climate system by exchanging mass, momentum and energy with the atmosphere. Plants are known to modify the climate by reducing land surface albedo, and by moderating water and carbon fluxes between the land and atmosphere (Schimel 1995;Meir, Cox & Grace 2006;Bonan 2008). When plants sequester carbon dioxide through photosynthesis, they reduce concentrations of atmospheric CO 2 , potentially affecting climate warming by the greenhouse effect. ...
This dissertation attempts to improve knowledge of the complex interactions of vegetation and climate by addressing two vegetation-atmosphere mass exchanges that are or might be critical to climate: photosynthetic carbon uptake, and biological aerosol emissions. First, a prognostic model of Pollen Emissions for Climate Models (PECM) for use within regional and global climate models is developed to simulate pollen counts over the seasonal cycle based on geography, vegetation type and meteorological parameters. An observation-based parameterization of pollen season phenology is determined using pollen count data to estimate the linear relationship between start and end dates and prior-year annual average temperature. This regression model explains as much as 57% of the variance in pollen phenological dates for many taxa common to the U.S., and it is used to create a “climate-flexible” phenology that can be used to study the response of wind-driven pollen emissions to climate change. The simulated surface pollen concentrations from coupling PECM with a regional climate model are evaluated against observations, and simulated pollen counts are within an order of magnitude of the observed concentrations. Second, the first model of atmospheric pollen grain rupture is developed and implemented in regional climate model simulations over spring pollen season in the United States with a CCN-dependent moisture scheme. The source of SPPs (surface or in- atmosphere) is compared and found to depend on region and sometimes season, due to the distribution of relative humidity and rain. It is shown that upper-bound estimated SPP concentrations can suppress average seasonal precipitation over the continental U.S. by 32% in clean background aerosol conditions, though this effect is smaller (~2%) for polluted air. Finally, the impact of a vertically complex canopy and its microenvironment on carbon uptake is assessed for deciduous broadleaved forests using different model representations of the canopy. Simulations of a multilayer version of Community Land Model (CLM-ml) are compared with CLM4.5 “big-leaf” simulations for the month of July (peak growing season), and evaluated with observed eddy covariance tower fluxes at five FLUXNET deciduous broadleaf forest sites. Four abiotic environmental drivers – air temperature, relative humidity, incoming shortwave radiation and soil moisture – are correlated with GPP inter-annual variations at each site to determine the strength of their influence and the overall sensitivity of GPP to local climate variability. It is found that, even though the models all underestimate GPP and its inter-annual variability, the patterns of GPP IAV and its drivers loosely resemble observed patterns. When using Ball-Berry stomatal conductance and a uniformly applied soil moisture stress factor in CLM-ml, vertical variation in the sensitivity of leaf-level carbon assimilation rate to climate variability is small, and therefore the canopy-scale GPP and its response to climate variability at all five sites are similar between CLM-ml and CLM4.5 simulations. However, using CLM-ml with plant hydraulics with non-uniform water stress, the sensitivity of carbon assimilation rate to climate variability varies with height and canopy-scale GPP is dampened from CLM4.5. Both reduced dependence on soil moisture and opposing climatic forcings on different leaf layers cause such dampening. This research highlights several unknowns in the climate system stemming from vegetation-climate interactions, as well as the importance of model-data integration for solving these unknowns. The results can be used to further the development of more accurate climate prediction to prepare society for the impacts of climate change.
... The scales of these layers can range between 1: 1,200,000 or more. (Meir et al., 2006). The relationships are based on parameters of temperature, precipitation, and those derived from the relationship with vegetation (Arrazola et al., 2000). ...
Provides cartography to represent neotropicals ecosystems helps to understand segregation in space. When mapping ecosystems, ecologists have some problems, some
are related to scales and cartographic inputs. The goal of our work was to design a model of cartographic representation of ecosystems, through processes that integrate cartographic inputs and their respective scales, associated with a hierarchical classification system. For this purpose, we determine hierarchical levels based on geophysical and biophysical criteria, characteristic of Neotropical ecosystems. We select
cartographic inputs in each hierarchical level associated with their respective scale.
We conclude that the Neotropical ecosystems must be represented at greater scales,
since it is the only way to obtain the necessary detail of the attributes that characterize
them, this need is determined by the complexity derived from the geophysical and
biological diversity of this region
... The scales of these layers can range between 1: 1,200,000 or more. (Meir et al., 2006). The relationships are based on parameters of temperature, precipitation, and those derived from the relationship with vegetation (Arrazola et al., 2000). ...
Provides cartography to represent neotropicals ecosystems helps to understand segregation in space. When mapping ecosystems, ecologists have some problems, some
are related to scales and cartographic inputs. The goal of our work was to design a
model of cartographic representation of ecosystems, through processes that integrate
cartographic inputs and their respective scales, associated with a hierarchical classification system. For this purpose, we determine hierarchical levels based on geophysical and biophysical criteria, characteristic of Neotropical ecosystems. We select
cartographic inputs in each hierarchical level associated with their respective scale.
We conclude that the Neotropical ecosystems must be represented at greater scales,
since it is the only way to obtain the necessary detail of the attributes that characterize
them, this need is determined by the complexity derived from the geophysical and
biological diversity of this region.
... In forest ecosystems only 30% of C is situated above ground (Vanguelova et al., 2013). Soil studies are needed to build process based understanding on the changes in soil organic C (SOC) with land use and management, and in response to climatic conditions, that can be used for large scale simulations (Meir et al., 2006;Wiesmeier et al., 2019). Changes in SOC in forest systems are harder to investigate than in arable or grassland systems because management can affect deep soil layers and continue to change for decades to centuries (Hobbie et al., 2013;Poeplau and Don, 2013). ...
Scotland is continuing to afforest land in order to combat climate change, but the long-term capacity for carbon sequestration in forest soils is still uncertain. Here we present measurements that provide comparative estimates of soil organic carbon in grassland and forestry sites at steady state. We develop a new approach to interpret these values based on simulation of organic carbon turnover in soils that are accumulating carbon and use this to determine losses due to management operations associated with afforestation of grassland and deforestation/reforestation of forest stands. Soil organic carbon stock changes were studied in a >120 year-old Scots pine chronosequence and adjacent grassland sites on podzolic soils. Significant carbon accumulation was measured in the top organic soil horizons with forest age, while no changes were noted in the deeper mineral soil horizons. The simulations with the RothC-26.3 model revealed that pine forests on sandy soils could lose a significant amount of soil organic carbon through management operations. The lowest modeled stocks of soil organic carbon were not in the young sites (0–25 years old), but at 43 years since reforestation. Using measured data from our study site, the simulations of grassland afforestation suggested that accumulation of organic carbon under forest occurs mainly in the organic horizons, while the deeper sandy mineral soil horizons are likely to become depleted in organic carbon compared to grasslands. Our simulations suggest that afforestation of grasslands would increase overall soil carbon stocks but may deplete the more stable carbon pools in the deeper mineral horizons of the podzols.
... Many new elements and structures are superimposed upon the landscape, leading to high fragmentation of the landscape and loss of its own unique identity (Antrop 2004). In addition, land cover changes can result in disturbance of biogeochemical and hydrological cycles (Gerten et al. 2004, Bontemps et al. 2008, Gashaw et al. 2018, and have serious impacts on climate change (Pielke et al. 2002), ecological imbalance (Meir et al. 2006), and energy flows (Ryszkowski and Kędziora 1987). More importantly, land cover changes affect various aspects of human society (Vitousek et al. 1997, Foley et al. 2005, such as human settlement (Antrop 2004), water quality (Xiao et al. 2016), and public health (Patz et al. 2004) from local to global scales. ...
Characterizing landscape patterns and revealing their underlying processes are critical for studying climate change and environmental problems. Previous methods for mapping land cover changes largely focused on the classification of remote sensing images. Therefore, they could not provide information about the evolutionary process of land cover changes. In this paper, we developed a spatiotemporal structural graph (STSG) technique for a comprehensive analysis of land cover changes. First, a land cover neighborhood graph was generated for each snapshot to quantify the spatial relationship between adjacent land cover objects. Then, an object-based temporal tracking algorithm was designed to monitor the temporal changes between land cover objects over time. Finally, land cover evolutionary trajectories, pixel-level land cover change trajectories, and node-wise connectivity changes over time were characterized. We applied the proposed method to analyze land cover changes in Suffolk County, New York from 1996 to 2010. The results demonstrated that STSG can not only characterize and visualize detailed land cover changes spatially but also maintain the temporal sequence and relations of land cover objects in an integrated space-time environment. The proposed STSG provides a useful framework for analyzing land cover changes and can be adapted to characterize and quantify other spatiotemporal phenomena.
... This atmospheric moisture eventually returns to the land and contributes about 25-35% of the basin's rainfall and 48-54% of the regional rainfall (Salati and Nobre, 1991;Eltahir and Bras, 1994;Trenberth, 1999;Bosilovich and Chern, 2006;van der Ent et al., 2010;Zemp et al., 2014). When regulating the water cycle in the region, the Amazon forests are a key component of the regional but also global climate system (Foley et al., 2003(Foley et al., , 2005Meir et al., 2006;Snyder, 2010;Anderson-Teixeira et al., 2012). ...
Diese Arbeit beschäftigt sich mit Aerial Rivers („luftgetragenen Flüssen“), den bevorzugten Wegen des Flusses von Feuchte in der Atmosphäre. Ziel ist es, die Voraussetzung für deren Integration in aktuelle Paradigmen der Wasserwirtschaft zu schaffen. Im Mittelpunkt der Arbeit stehen Amazonien und die angrenzenden Gebiete, also Regionen der Erde, in denen sich derzeit der Landnutzungswandel mit am schnellsten vollzieht. Aus theoretischer Sicht wird das Wissen über die Verbindung zwischen Aerial Rivers und Oberflächenflüssen erweitert. Mit Hilfe eines Algorithmus zur Verfolgung des atmosphärischen Feuchtigkeitstransports werden die Auswirkungen von entferntem Landnutzungswandel in Windrichtung auf die Niederschlagsmenge einer Zielregion quantifiziert. Die räumliche Heterogenität des Einflusses der gesamten Quellevapotranspirationsfläche (precipitationsehed) auf die/den empfangene/n Niederschlagsmenge/Oberflächenabfluss der Zielregion wird untersucht und führt zur Identifizierung der „Most Influential Precipitationshed“ (MIP), der für Managementzwecke relevantesten Teilfläche. Ein Aerial River-Managementbeispiel für Santa Cruz (Bolivien) zeigt, dass die strategische Wiederaufforstung im MIP sowohl die Niederschlagsmenge als auch den empfangenen Oberflächenabfluss erhöht und 22%-59% des zukünftigen Wasserbedarfszuwachses einer schnell wachsenden Stadt decken kann. Weiterhin werden sozio-technische Regime entlang von Aerial Rivers, die zu Extremereignissen wie Megadürren beitragen können, mit Hilfe der sozialwissenschaftlichen Methode der Multi-Level-Perspektive (MLP) untersucht. Ursachen wie Bodenpolitik und Marktinterventionen in Brasilien und Bolivien steuern weit entfernte kolumbianische Energieregime und deren Wandel. Aerial Rivers sind also zentral für zukünftiges Gewässermangement einschließlich Wasserkraft; ihr Management erfordert jedoch eine ganzheitliche Betrachtung der gesellschaftlichen Schnittstellen über administrative Grenzen und Sektoren hinweg.
... In the Amazon basin, severe drought in 2005, which was not driven by an ENSO event, caused an increase in the incidence of tree mortality and loss of aboveground biomass in many rainforest sites, thereby converting them from sinks to sources in carbon cycling (Phillips et al. 2009). These studies indicate that hydro-climatic change in the future may induce degradation of tropical forests (Feldpausch et al. 2016;Kumagai and Porporato 2012a;Phillips et al. 2009), in turn affecting feedbacks to the atmosphere (Bonan 2008;Kumagai et al. 2013;Meir et al. 2006;Takahashi et al. 2017). Fauset et al. (2015) demonstrated that, though the abundant species tends to contribute more to the total biomass and productivity in Amazonian forests, species maximum size also strongly influences biomass and productivity. ...
The physiological response of trees to drought is crucial for understanding the risk of mortality and its feedbacks to climate under the increase in droughts due to climate change, especially for the largest trees in tropical rainforests because of their large contribution to total carbon storage and water use. We determined the response of the mean canopy stomatal conductance per unit leaf area (gs) and whole-tree hydraulic conductance (Gp) of the largest individuals (38-53 m in height) of a typical canopy tree species in a Bornean tropical rainforest, Dryobalanops aromatica C.F.Gaertn., to soil moisture reduction by a 4-month rainfall exclusion experiment (REE) based on the measurements of sap flux and leaf water potentials at midday and dawn. In the mesic condition, the gs at vapor pressure deficit (D) = 1 kPa (gsref) was small compared with the reported values in various biomes. The sensitivity of gs to D (m) at a given gsref (m/gsref) was ≥ 0.6 irrespective of soil moisture conditions, indicating intrinsically sensitive stomatal control with increasing D. The REE caused greater soil drought and decreased the mean leaf water potentials at midday and dawn to the more negative values than the control under the relatively dry conditions due to natural reduction in rainfall. However, the REE did not cause a greater decrease in gs nor any clear alteration in the sensitivity of gs to D compared with the control, and induced greater decreases in Gp during REE than the control. Thus, though the small gs and the sensitive stomatal response to D indicate the water saving characteristics of the studied trees under usual mesic conditions, their limited stomatal regulation in response to soil drought by REE and the resulting decline in Gp might suggest a poor resistance to the unusually severe drought expected in the future.
... Ordinary agricultural management model cannot be maintained in the long term because of the recent climate change, inducing higher temperatures, anomalous rainfall trends and lower water reserves [1]. Climate change impacts on ecosystems have been extensively analyzed [2][3][4]. However, only recently climate change effects on crop development production have been documented [5][6][7]. ...
Climate variability is one of the greatest risks for farmers. The ongoing increase of natural calamities suggests that insurance strategies have to be more dynamic than previously. In this work a remote sensing based service prototype is presented aimed at supporting insurance companies with the aim of defining an operative tool to objectively calibrate insurance annual fares, tending to cost reduction able to attract more potential customers. Methodology was applied to the whole Piemonte region (NW Italy) that is greatly devoted to agriculture. MODIS MOD13Q1-v6 image time series were used for this purpose. MODIS data were used to figure out the ongoing climate change trends at regional scale, looking at the NDVI time series ranging from 2000 to 2018; the average phenological behaviour of the main agriculture classes in the area (CORINE Land Cover classes Level 3, CLC2012) was considered looking at the yearly average NDVI value trend in the analysed period. This analysis was intended to describe the yearly tuning of the average insurance risk factor and fares in respect of the reference year (2000). A patch level investigation comparing the NDVI average value of a single CLC2012 patch with its reference class was differently used to map local differences of crops performance, aimed at locally tuning insurance risk and fares around the average one as resulting from the previous step. Proposed methodology proved to be able to describe the average temporal evolution of crop classes performances and to locally tune, at single field and crop type level, the agronomic performances of insured areas.
KeywordsCrop insuranceMODIS NDVIRemote sensing-based services
... Vegetation changes can directly or indirectly influence spatial and temporal variations of soil temperatures in a number of ways through physiological activities underground and changing heat fluxes on and above ground through changing shading (measured by means such as leaf area index, projected leaf area per unit of ground area), ground litter stores, and soil and air moisture 56 . Generally, two opposing vegetation feedback effects may occur on heat fluxes: warming through increased energy absorption (i.e., relatively low albedo) and cooling through increased evaporation 58 . The net impact of vegetation feedback (warming or cooling) that can be registered in the brGDGT-based proxy depends on which influence is predominant. ...
The complicity of long-term land surface temperature (LST) changes has been under investigated and less understood, hindering our understanding of the history and mechanism of terrestrial climate change. Here, we report the longest (800 thousand years) LSTs based on distributions of soil fossil bacterial glycerol dialkyl glycerol tetraethers preserved in well-dated loess-paleosol sequences at the center of the Chinese Loess Plateau. We have found a previously-unrecognized increasing early and prolonged warming pattern toward the northwestern plateau at the onset of the past seven deglaciations, corresponding to the decrease in vegetation coverage, suggesting underlying surface vegetation or lack of has played an important role in regulating LSTs, superimposed on the fundamental global glacial–interglacial changes. Our results support that LSTs in semi-humid and semi-arid regions with little vegetation will be more sensitive to the anticipated global temperature rise, while improving vegetation coverage would reduce LSTs and thus ecological impacts.
... Uncertainty in anthropogenic carbon emissions and carbon cycle-climate feedback are the two main contributors to uncertainty in the temperature effect of climate change to 2100 (Meir et al. 2006). The uncertainty in carbon emissions accompanying land-use change (LUC) (which includes change in forest logging intensity; Luyssaert et al. 2014) remains the most uncertain emissions in the global carbon budget (Canadell et al. 2007). ...
There is high uncertainty in the contribution of land-use change to anthropogenic climate change, especially pertaining to below-ground carbon loss resulting from conversion of primary-to-secondary forest. Soil organic carbon (SOC) and coarse roots are concentrated close to tree trunks, a region usually unmeasured during soil carbon sampling. Soil carbon estimates and their variation with land-use change have not been correspondingly adjusted. Our aim was to deduce allometric equations that will allow improvement of SOC estimates and tree trunk carbon estimates, for primary forest stands that include large trees in rugged terrain. Terrestrial digital photography, photogrammetry and GIS software were used to produce 3D models of the buttresses, roots and humus mounds of large trees in primary forests dominated by Eucalyptus regnans in Tasmania. Models of 29, in situ eucalypts were made and analysed. 3D models of example eucalypt roots, logging debris, rainforest tree species, fallen trees, branches, root and trunk slices, and soil profiles were also derived. Measurements in 2D, from earlier work, of three buttress ‘logs’ were added to the data set. The 3D models had high spatial resolution. The modelling allowed checking and correction of field measurements. Tree anatomical detail was formulated, such as buttress shape, humus volume, root volume in the under-sampled zone and trunk hollow area. The allometric relationships developed link diameter at breast height and ground slope, to SOC and tree trunk carbon, the latter including a correction for senescence. These formulae can be applied to stand-level carbon accounting. The formulae allow the typically measured, inter-tree SOC to be corrected for not sampling near large trees. The 3D models developed are irreplaceable, being for increasingly rare, large trees, and they could be useful to other scientific endeavours.
... This atmospheric moisture eventually returns to the land and contributes about 25-35 % of the basin's rainfall and 48-54 % of the regional rainfall (Salati and Nobre, 1991;Eltahir and Bras, 1994;Trenberth, 1999;Bosilovich and Chern, 2006;Van Der Ent et al., 2010;Zemp et al., 2014). When regulating the water cycle in the region, the Amazon forests are a key component of the regional but also global climate system (Foley et al., 2003(Foley et al., , 2005Meir et al., 2006;Snyder, 2010;Anderson-Teixeira et al., 2012). ...
The abundant evapotranspiration provided by the Amazon forests is an important component of the hydrological cycle, both regionally and globally. Since the last century, deforestation and expanding agricultural activities have been changing the ecosystem and its provision of moisture to the atmosphere. However, it remains uncertain how the ongoing land use change will influence rainfall, runoff, and water availability as findings from previous studies differ. Using moisture tracking experiments based on observational data, we provide a spatially detailed analysis recognizing potential teleconnection between source and sink regions of atmospheric moisture. We apply land use scenarios in upwind moisture sources and quantify the corresponding rainfall and runoff changes in downwind moisture sinks. We find spatially varying responses of water regimes to land use changes, which may explain the diverse results from previous studies. Parts of the Peruvian Amazon and western Bolivia are identified as the sink areas most sensitive to land use change in the Amazon and we highlight the current water stress by Amazonian land use change on these areas in terms of the water availability. Furthermore, we also identify the influential source areas where land use change may considerably reduce a given target sink's water reception (from our example of the Ucayali River basin outlet, rainfall by 5–12 % and runoff by 19–50 % according to scenarios). Sensitive sinks and influential sources are therefore suggested as hotspots for achieving sustainable land–water management.
... Understanding the dynamics of terrestrial vegetation biomass and production is both an interesting and an important topic; vegetation is constantly changing over a range of temporal and spatial scales (Ichii, Kawabata, & Yamaguchi, 2002;Zhu et al., 2016) and it is a key component of the global carbon cycle (Beer et al., 2010;Wieder, Cleveland, Smith, & Todd-Brown, 2015) that is tightly coupled with climate because it directly affects land-atmosphere heat and moisture fluxes (Meir, Cox, & Grace, 2006). Of course vegetation is also the base of the terrestrial food web; hence, the dynamics of vegetation biomass or production is implicated in essentially every area of pure and applied ecology. ...
Aim
Previous work demonstrated a pronounced geography of synchrony for marine phytoplankton and used that geography to infer statistical environmental determinants of synchrony. Here, we determine whether terrestrial vegetation (measured by the enhanced vegetation index, EVI) also shows a geography of synchrony and we infer determinants of EVI synchrony. As vegetation is the basis of the terrestrial food web, changes in spatio‐temporal vegetation dynamics may have major consequences.
Location
The land.
Time period
2001–2014.
Major taxa
Plants.
Methods
Synchrony in terrestrial vegetation is mapped globally. Spatial statistics and model selection are used to identify main statistical determinants of synchrony and of geographical patterns in synchrony.
Results
The first main result is that there is a pronounced and previously unrecognized geography of synchrony for terrestrial vegetation. Some areas, such as the Sahara and Southern Africa, exhibited nearly perfect synchrony, whereas other areas, such as the Pacific coast of South America, showed very little synchrony. Spatial modelling provided the second main result, namely that synchrony in temperature and precipitation were major determinants of synchrony in EVI, supporting the presence of dual global Moran effects. These effects depended on the time‐scales on which synchrony was assessed, providing our third main result, namely that synchrony of EVI and its geography are time‐scale specific.
Main conclusions
To our knowledge, this study is the first to document the geography of synchrony in terrestrial vegetation. We showed that geographical variation in synchrony is pronounced. We used geographical patterns to identify determinants of synchrony. This study is one of very few studies to demonstrate two separate synchronous environmental variables driving synchrony simultaneously. The geography of synchrony is apparently a major phenomenon that has been little explored.
... The interactions among vegetation, climate and hydrology are very complicated (Foley et al., 1996;Meir et al., 2006;Myoung et al., 2011;Potter, 2004). Changes in climatic factors simultaneously affect both hydrological and ecological processes (Donohue et al., 2010;McVicar et al., 2012). ...
Land surface models (LSMs) are widely used to understand the interactions between hydrological processes and vegetation dynamics, which is important for the attribution and prediction of regional hydrological variations. However, most LSMs have large uncertainties in their representations of eco-hydrological processes due to deficiencies in hydrological parameterizations. In this study, the Community Land Model version 4 (CLM4) LSM was modified with an advanced runoff generation and flow routing scheme, resulting in a new land surface-hydrology coupled model, CLM-GBHM. Both models were implemented in the Wudinghe River Basin (WRB), which is a semi-arid basin located in the middle reaches of the Yellow River, China. Compared with CLM, CLM-GBHM increased the Nash Sutcliffe efficiency for daily river discharge simulation (1965-1969) from -0.03 to 0.23 and reduced the relative bias in water table depth simulations (2010-2012) from 32.4% to 13.4%. The CLM-GBHM simulations with static, remotely sensed and model-predicted vegetation conditions showed that the vegetation in the WRB began to recover in the 2000s due to the Grain for Green Program but had not reached the same level of vegetation cover as regions in natural eco-hydrological equilibrium. Compared with a simulation using remotely sensed vegetation cover, the simulation with a dynamic vegetation model that considers only climate-induced change showed a 10.3% increase in evapotranspiration, a 47.8% decrease in runoff, and a 62.7% and 71.3% deceleration in changing trend of the outlet river discharge before and after the year 2000, respectively. This result suggests that both natural and anthropogenic factors should be incorporated in dynamic vegetation models to better simulate the eco-hydrological cycle.
... Such model differences are in substantial part due to remaining unknowns in ecological processes affecting landatmosphere CO 2 fluxes (e.g. Meir et al., 2006). However, common to all models is that climate-carbon cycle feedbacks are positive, that is, the effect of warming on the land surface and oceans is such that it reduces the ability to 'drawdown' extra CO 2 from the atmosphere compared with if these natural components were responding to increased CO 2 only (i.e. ...
... The skill of this numerical weather prediction system therefore is tied partially to the vegetation state and its response to water-stress. A similar argument can be made for Earth System Models used in coupled carbon-climate simulations (Meir et al., 2006;Friedlingstein et al., 2006;Booth et al., 2012), which instead simulate the long-term fate of vegetation and soil carbon pools based on this L-A coupling. With the tropics as dominant region for carbon-climate feedbacks, Joetzjer et al. (2014) illustrated the effect of different drought response function on the simulation of carbon fluxes in the Amazon in one such model (ISBA). ...
Croplands are a managed type of vegetation, with a carbon storage that is highly optimized for food production. For instance, their sowing dates are chosen by the farmers, their genetic potential is bred for high grain yields, and their on-field competition with other species is reduced to the minimum. As a result of human intervention, croplands are a major land cover type (roughly one fifth of the land area over Europe) and they experience a short growing season during which they exchange carbon and water intensively with the atmosphere. Their growth significantly affects the seasonal amplitude of CO2 mole fractions over the globe, interact with extreme weather events such as droughts and heat waves, and impact surface hydrology due to their water consumption. However, and in spite of their relevance, terrestrial biosphere models used in carbon cycle and atmospheric research often assume the phenology of croplands to be similar to the one of grasslands, and they also ignore the impact of crop management. This oversimplification is the motivation for this thesis. We focus on understanding and modeling the key surface and atmospheric processes that shape the cropland water and CO2 exchange, and the resulting impact on the CO2 mole fractions of the atmosphere overhead. We study these processes from the daily to the seasonal scale, for croplands of the mid-latitudes. In the end, we come with recommendations and a new modeling framework to represent the cropland CO2 and water exchange in the Earth System, weather and climate models.
West Africa is undergoing rapid agricultural intensification driven by population growth, leading to significant anthropogenic land use and land cover change (LCC), including both deforestation and afforestation. These changes can profoundly affect the regional climate system by altering the surface energy balance, moisture fluxes, and atmospheric circulation, potentially exacerbating the vulnerability of human, ecological, and economic systems. Despite the ability of climate models to simulate LCC impacts, considerable uncertainties remain, particularly in simulations of precipitation and temperature responses. This study provides the first multidisciplinary systematic review of LCC impacts in West Africa. Data from 26 selected publications were eventually synthesized from an initial pool of nearly 6000 studies. Results indicate that deforestation generally contributes to regional warming, with significant historical temperature increases of +0.26 ± 0.12 °C and projected increases of +0.88 ± 0.25 °C under the future scenarios. Conversely, afforestation could have significantly cooled the climate, lowering temperatures by −0.24 ± 0.14 °C historically and −0.22 ± 0.14 °C in future scenarios, without even accounting for carbon sequestration. Deforestation decreases regional precipitation by 80 ± 58 mm yr⁻¹ historically and −55 ± 102 mm yr⁻¹ in future scenarios, while large-scale afforestation could substantially reduce droughts with increased precipitation, averaging +40 ± 67 mm yr⁻¹ historically and 80 ± 58 mm yr⁻¹ in future scenarios. These results emphasize the need to integrate LCC-induced climate effects into land-based mitigation strategies, climate policy, and assessment frameworks.
TROLL 4.0 is an individual-based forest dynamics model that is capable of jointly simulating forest structure, diversity and ecosystem functioning, including the ecosystem water balance and productivity, leaf area dynamics and the tree community functional and taxonomic composition. It represents ecosystem flux processes in a manner similar to dynamic global vegetation models, while adopting a representation of plant community structure and diversity at a resolution consistent with that used by field ecologists. Specifically, trees are modeled as three-dimensional individuals with a metric-scale spatial representation, providing a detailed description of ecological processes such as competition for resources and tree demography. Carbon assimilation and plant water loss are explicitly represented at tree level using coupled photosynthesis and stomatal conductance models, depending on the micro-environmental conditions experienced by trees. Soil water uptake by trees is also modelled. Physiological and demographic processes are parameterized using plant functional traits measured in the field. Here we provide a detailed description and discussion of the implementation of TROLL 4.0. An evaluation of the model at two tropical forest sites is provided in a companion paper (Schmitt et al., submitted companion paper). TROLL 4.0’s representation of processes reflects the state of the art, and we discuss possible developments to improve its predictive capability and its capacity to address challenges in forest monitoring, forest dynamics and carbon cycle research.
Forests hold a significant proportion of global biodiversity and terrestrial carbon stocks and are at the forefront of human-induced global change. The dynamics and distribution of forest vegetation determines the habitat for other organisms, and regulates the delivery of ecosystem services, including carbon storage. Presenting recent research across temperate and tropical ecosystems, this volume synthesises the numerous ways that forests are responding to global change and includes perspectives on: • the role of forests in the global carbon and energy budgets • historical patterns of forest change and diversification • contemporary mechanisms of community assembly and implications of underlying drivers of global change • the ways in which forests supply ecosystem services that support human lives. The chapters represent case studies drawn from the authors' expertise, highlighting exciting new research and providing information that will be valuable to academics, students, researchers and practitioners with an interest in this field.
Forests hold a significant proportion of global biodiversity and terrestrial carbon stocks and are at the forefront of human-induced global change. The dynamics and distribution of forest vegetation determines the habitat for other organisms, and regulates the delivery of ecosystem services, including carbon storage. Presenting recent research across temperate and tropical ecosystems, this volume synthesises the numerous ways that forests are responding to global change and includes perspectives on: • the role of forests in the global carbon and energy budgets • historical patterns of forest change and diversification • contemporary mechanisms of community assembly and implications of underlying drivers of global change • the ways in which forests supply ecosystem services that support human lives. The chapters represent case studies drawn from the authors' expertise, highlighting exciting new research and providing information that will be valuable to academics, students, researchers and practitioners with an interest in this field.
Forests hold a significant proportion of global biodiversity and terrestrial carbon stocks and are at the forefront of human-induced global change. The dynamics and distribution of forest vegetation determines the habitat for other organisms, and regulates the delivery of ecosystem services, including carbon storage. Presenting recent research across temperate and tropical ecosystems, this volume synthesises the numerous ways that forests are responding to global change and includes perspectives on: • the role of forests in the global carbon and energy budgets • historical patterns of forest change and diversification • contemporary mechanisms of community assembly and implications of underlying drivers of global change • the ways in which forests supply ecosystem services that support human lives. The chapters represent case studies drawn from the authors' expertise, highlighting exciting new research and providing information that will be valuable to academics, students, researchers and practitioners with an interest in this field.
Forests hold a significant proportion of global biodiversity and terrestrial carbon stocks and are at the forefront of human-induced global change. The dynamics and distribution of forest vegetation determines the habitat for other organisms, and regulates the delivery of ecosystem services, including carbon storage. Presenting recent research across temperate and tropical ecosystems, this volume synthesises the numerous ways that forests are responding to global change and includes perspectives on: • the role of forests in the global carbon and energy budgets • historical patterns of forest change and diversification • contemporary mechanisms of community assembly and implications of underlying drivers of global change • the ways in which forests supply ecosystem services that support human lives. The chapters represent case studies drawn from the authors' expertise, highlighting exciting new research and providing information that will be valuable to academics, students, researchers and practitioners with an interest in this field.
Forests hold a significant proportion of global biodiversity and terrestrial carbon stocks and are at the forefront of human-induced global change. The dynamics and distribution of forest vegetation determines the habitat for other organisms, and regulates the delivery of ecosystem services, including carbon storage. Presenting recent research across temperate and tropical ecosystems, this volume synthesises the numerous ways that forests are responding to global change and includes perspectives on: • the role of forests in the global carbon and energy budgets • historical patterns of forest change and diversification • contemporary mechanisms of community assembly and implications of underlying drivers of global change • the ways in which forests supply ecosystem services that support human lives. The chapters represent case studies drawn from the authors' expertise, highlighting exciting new research and providing information that will be valuable to academics, students, researchers and practitioners with an interest in this field.
Forests hold a significant proportion of global biodiversity and terrestrial carbon stocks and are at the forefront of human-induced global change. The dynamics and distribution of forest vegetation determines the habitat for other organisms, and regulates the delivery of ecosystem services, including carbon storage. Presenting recent research across temperate and tropical ecosystems, this volume synthesises the numerous ways that forests are responding to global change and includes perspectives on: • the role of forests in the global carbon and energy budgets • historical patterns of forest change and diversification • contemporary mechanisms of community assembly and implications of underlying drivers of global change • the ways in which forests supply ecosystem services that support human lives. The chapters represent case studies drawn from the authors' expertise, highlighting exciting new research and providing information that will be valuable to academics, students, researchers and practitioners with an interest in this field.
Forests hold a significant proportion of global biodiversity and terrestrial carbon stocks and are at the forefront of human-induced global change. The dynamics and distribution of forest vegetation determines the habitat for other organisms, and regulates the delivery of ecosystem services, including carbon storage. Presenting recent research across temperate and tropical ecosystems, this volume synthesises the numerous ways that forests are responding to global change and includes perspectives on: • the role of forests in the global carbon and energy budgets • historical patterns of forest change and diversification • contemporary mechanisms of community assembly and implications of underlying drivers of global change • the ways in which forests supply ecosystem services that support human lives. The chapters represent case studies drawn from the authors' expertise, highlighting exciting new research and providing information that will be valuable to academics, students, researchers and practitioners with an interest in this field.
Forests hold a significant proportion of global biodiversity and terrestrial carbon stocks and are at the forefront of human-induced global change. The dynamics and distribution of forest vegetation determines the habitat for other organisms, and regulates the delivery of ecosystem services, including carbon storage. Presenting recent research across temperate and tropical ecosystems, this volume synthesises the numerous ways that forests are responding to global change and includes perspectives on: • the role of forests in the global carbon and energy budgets • historical patterns of forest change and diversification • contemporary mechanisms of community assembly and implications of underlying drivers of global change • the ways in which forests supply ecosystem services that support human lives. The chapters represent case studies drawn from the authors' expertise, highlighting exciting new research and providing information that will be valuable to academics, students, researchers and practitioners with an interest in this field.
Emerging negative trends in snow depth and cover days highlight the challenges posed by changing snow patterns around the world. They suggest that snow-dependent regions in southern Europe could be affected by these changes because the number of days with snow on the ground (DSG) determines soil processes and water-flow in rivers, streams, lakes and reservoirs. We present here the first homogeneous, annually-resolved (from October to April), multi-centennial (1681–2018 CE) DSG time-series for the Parma meteorological observatory (OBS), in northern Italy, which to date is also the longest DSG series reconstructed in the world. DSG data are in fact still poorly documented and misunderstood due to the limited and fragmentary data measurements of the past. DSG recording only began in 1938 at Parma OBS. To generate the long-term annual DSG time-series at the study site, we develop a model consistent with calibration (1938–1990 CE) and validation (1991–2018 CE) samples of observed data. We show that the variability of DSG depends on winter precipitation and air temperature, as well as on winter-spring temperature variability, suggesting that long sequences of DSG are dominated by cold air masses in years with cold weather and high variability. Modeled DSG data show a downward trend from the 19th century, in the transition period from the cold of the Little Ice Age to the warmth of modern times, followed by a more rapid decline in the five most recent decades. The DSG at Parma OBS appear to have followed over the last century trends similar to those observed throughout Eurasia and across the Northern Hemisphere, where a marked decline of snow-cover duration has been reported in the transition seasons (spring and autumn).
Climate change is today one of the biggest issues for farmers. The increasing number of natural disasters and change of seasonal trends is making insurance companies more interested in new technologies that can somehow support them in quantifying and mapping risks. Remotely sensed data, with special focus on free ones, can certainly provide the most of information they need, making possible to better calibrate insurance fees in space and time. In this work, a prototype of service based on free remotely sensed data is proposed with the aim of supporting insurance companies’ strategies. The service is thought to calibrate annual insurance rates, longing for their reduction at such level that new customers could be attracted. The study moves from the entire Piemonte region (NW Italy), to specifically focus onto the Cuneo province (Southern Piemonte), which is mainly devoted to agriculture. MODIS MOD13Q1-v6 and Sentinel-2 L2A image time series were jointly used. NDVI maps from MODIS data were useful to describe the midterm phenological trends of main crops at regional level in the period 2000–2018; differently, Sentinel-2 data permitted to map local crop differences at field level in 2016 and 2017 years. With reference to MODIS data, the average phenological behavior of main crop classes in the area, obtained from the CORINE Land Cover map Level 3, was considered using a time series decomposition approach. Trend analyses showed that the most of the crop classes alternated three phases (about 7 years) suggesting that, presently, this is probably the time horizon to be considered to tune mid-term algorithms for risk estimates in the agricultural context. Crop classes trends were consequently split into three phases and each of them modeled by a first-order polynomial function used to update correspondent insurance risk rate. Sentinel-2 data were used to map phenological anomalies at field level for the 2016 and 2017 growing seasons; shifts from class average behavior were considered to locally and temporarily tune insurance premium around its average trend as described at the previous step. Synthesizing, one can say that this approach, integrating MODIS and Sentnel-2 data, makes possible to locally and temporarily calibrate premiums of indexed insurance policies by describing the average trends of crop performance (NDVI) at regional level by MODIS data and refining it at field and specific crop level by Sentinel-2 data.
Este trabajo es una versión extendida de un capítulo que hace parte del Vol. No. 3 de las recomendaciones de la Misión Internacional de Sabios 2019.
Anthropogenic land cover changes (LCC) affect regional and global climate through biophysical variations of the surface energy budget mediated by albedo, evapotranspiration, and roughness. This change in surface energy budget may exacerbate or counteract biogeochemical greenhouse gas effects of LCC, with a large body of emerging assessments being produced, sometimes apparently contradictory. We reviewed the existing scientific literature with the objective to provide an overview of the state-of-the-knowledge of the biophysical LCC climate effects, in support of the assessment of mitigation/adaptation land policies. Out of the published studies that were analyzed, 28 papers fulfilled the eligibility criteria, providing surface air temperature and/or precipitation change with respect to LCC regionally and/or globally. We provide a synthesis of the signal, magnitude and uncertainty of temperature and precipitation changes in response to LCC biophysical effects by climate region (boreal/temperate/tropical) and by key land cover transitions. Model results indicate that a modification of biophysical processes at the land surface has a strong regional climate effect, and non-negligible global impact on temperature. Simulations experiments of large-scale (i.e. complete) regional deforestation lead to a mean reduction in precipitation in all regions, while air surface temperature increases in the tropics and decreases in boreal regions. The net global climate effects of regional deforestation are less certain. There is an overall consensus in the model experiments that the average global biophysical climate response to complete global deforestation is atmospheric cooling and drying. Observed estimates of temperature change following deforestation indicate a smaller effect than model-based regional estimates in boreal regions, comparable results in the tropics, and contrasting results in temperate regions. Regional/local biophysical effects following LCC are important for local climate, water cycle, ecosystems, their productivity and biodiversity, and thus important to consider in the formulation of adaptation policy. However before considering the inclusion of biophysical climate effects of LCC under the UNFCCC, science has to provide robust tools and methods for estimation of both country and global level effects.
Unlike alternative energy sources, or energy efficiency measures, carbon sequestration can only act to reduce CO2 atmospheric concentrations; it does not help solve our energy problems, and may even add to them. Several sequestration approaches are possible. Carbon capture and storage can only be applied to present emissions from large CO2 emitting sources such as power stations. Another possible approach is to capture CO2 directly from the air. Carbon sequestration in forests, soils, or in ocean plankton, are of this type, as is mechanical air capture. Mechanical air capture can in principle also draw down past CO2 emissions into the atmosphere, and even compensate for emissions of other greenhouse gases. However, the energy costs for capture are very high, so that energy availability becomes a problem. The sequestration phase is the same as for CO2 from fossil fuel combustion.
Sequestering CO2 in the deep ocean would lead to both ocean acidification and adverse consequences for marine life. Estimates for the quantity of CO2 that can be ultimately sequestered in geological formations such as disused oil and gas fields, and saline aquifers, both on land and in the seabed, vary by orders of magnitude. But such estimates may be beside the point, since sequestration requires not only that adequate safe geological storage capacity be available, but that CO2 can be safely introduced at the rate desired, which could amount worldwide to tens of Gigatonne of CO2 per year. Furthermore, there is a small risk of catastrophic blowout from injection wells, which means that local citizen opposition could be intense.
Abstract El Niño–La Niña cycles strongly influence dry and wet seasons in the tropics and consequently nitrous oxide (N2O) emissions from tropical rainforest soils. We monitored whole-system and soil chamber N2O fluxes during 5-month-long droughts in the Biosphere 2 tropical forest to determine how rainfall changes N2O production. A consistent pattern of N2O flux changes during drought and subsequent wetting emerged from our experiments. Soil surface drying during the first days of drought, presumably increased gas transport out of the soil, which increased N2O fluxes. Subsequent drying caused an exponential decrease in whole-system (4.0±0.1% day−1) and soil chamber N2O flux (8.9±0.8% day−1; south chamber; and 13.7±1.1% day−1; north chamber), which was highly correlated with soil moisture content. Soil air N2O concentration ([N2O]) and flux measurements revealed that surface N2O production persisted during drought. The first rainfall after drought triggered a N2O pulse, which amounted to 25% of drought-associated reduction in N2O flux and 1.3±0.4% of annual N2O emissions. Physical displacement of soil air by water and soil chemistry changes during drought could not account for the observed N2O pulse. We contend that osmotic stress on the microbial biomass must have supplied the N source for pulse N2O, which was produced at the litter–soil interface. After the pulse, N2O fluxes were consistently 90% of predrought values. Nitrate change rate, nutrient, [N2O], and flux analyses suggested that nitrifiers dominated N2O production during the pulse and denitrifiers during wet conditions. N2O flux measurements in Biosphere 2, especially during the N2O pulse, demonstrate that large-scale integration methods, such as flux towers, are essential for improving ecosystem N2O flux estimates.
Changes in vegetation cover are known to influence the climate system by modifying the radiative, momentum, and hydrologic balance of the land surface. To explore the interactions between terrestrial vegetation and the atmosphere for doubled atmospheric CO{sub 2} concentrations, the newly developed fully coupled GENESIS-IBIS climate-vegetation model is used. The simulated climatic response to the radiative and physiological effects of elevated CO{sub 2} concentrations, as well as to ensuing simulated shifts in global vegetation patterns is investigated. The radiative effects of elevated CO{sub 2} concentrations raise temperatures and intensify the hydrologic cyclic on the global scale. In response, soil moisture increases in the mid- and high latitudes by 4% and 5%, respectively. Tropical soil moisture, however, decreases by 5% due to a decrease in precipitation minus evapotranspiration. The direct, physiological response of plants to elevated CO{sub 2} generally acts to weaken the earth's hydrologic cycle by lowering transpiration rates across the globe. Lowering transpiration alone would tend to enhance soil moisture. However, reduced circulation of water in the atmosphere, which lowers precipitation, leads to more arid conditions overall (simulated global soil moisture decreases by 1%), particularly in the Tropics and midlatitudes.
The physiological response of terrestrial vegetation when directly exposed to an increase in atmospheric carbon dioxide (CO2) concentration could result in warming over the continents in addition to that due to the conventional CO2 “greenhouse effect.” Results from a coupled biosphere-atmosphere model (SiB2-GCM) indicate that, for doubled CO2 conditions, evapotranspiration will drop and air temperature will increase over the tropical continents, amplifying the changes
resulting from atmospheric radiative effects. The range of responses in surface air temperature and terrestrial carbon uptake
due to increased CO2 are projected to be inversely related in the tropics year-round and inversely related during the growing season elsewhere.
PREVIOUS studies1-5 have demonstrated that the
predictions of global climate models are highly sensitive to large
changes in vegetation cover, such as the complete removal of tropical or
boreal forests. Although these studies have illustrated the potential
effects of massive deforestation on the climate system, vegetation
changes of this scale are very unlikely to occur. Investigating past
environments may better illustrate the possible interactions between
climate and vegetation cover. For example, palaeobotanical evidence
indicates that 6,000 years ago boreal forests extended north of the
modern treeline6, apparently in response to high-latitude
warming resulting from variations in the Earth's orbit7,8.
The expanded boreal forests, which took the place of tundra, must also
have affected climate by significantly reducing the surface
albedo5. Here we use a global climate model to examine the
relative effects of orbitally-induced insolation variations and of the
northward extension of boreal forests on the mid-Holocene climate.
Orbital variations alone warm the high latitudes by 2 °C or more in
summer, autumn and winter. The subsequent northward extension of boreal
forests gives rise to an additional warming of approximately 4 °C in
spring and about 1 °C in the other seasons. This suggests that large
positive feedbacks between climate and boreal forests may have taken
place in the recent geological past.
1] Climate-carbon cycle model CLIMBER2-LPJ is run with consistent fields of future fossil fuel CO 2 emissions and geographically explicit land cover changes for four Special Report on Emissions Scenarios (SRES) scenarios, A1B, A2, B1, and B2. By 2100, increases in global mean temperatures range between 1.7°C (B1) and 2.7°C (A2) relative to the present day. Biogeochemical warming associated with future tropical land conversion is larger than its corresponding biogeophysical cooling effect in A2, and amplifies biogeophysical warming associated with Northern Hemisphere land abandonment in B1. In 2100, simulated atmospheric CO 2 ranged from 592 ppm (B1) to 957 ppm (A2). Future CO 2 concentrations simulated with the model are higher than previously reported for the same SRES emission scenarios, indicating the effect of future CO 2 emission scenarios and land cover changes may hitherto be underestimated. The maximum contribution of land cover changes to future atmospheric CO 2 among the four SRES scenarios represents a modest 127 ppm, or 22% in relative terms, with the remainder attributed to fossil fuel CO 2 emissions.
1] A high-resolution mesoscale model was used to investigate the impact of deforestation in Amazonia. Coherent mesoscale circulations were triggered by the surface heterogeneity; synoptic flow did not eliminate the circulations but advected them away from the location where they were generated. This was substantiated by satellite-derived cloud images. These circulations affected the transport of moisture and heat at the synoptic scale and can affect climate. Adequate parameterizations for these processes should be included in GCMs for more accurate climate simulations.
The Amazon River, its huge basin, and the changes in biological processes that are rapidly occurring in this region are unquestionably of global significance. Hence, Global Change Biology is delighted to host a special thematic issue devoted to the Large-scale Biosphere–Atmosphere Experiment in Amazônia (LBA), which is a multinational, interdisciplinary research program led by Brazil. The goal of LBA is no less modest than its subject: to understand how Amazônia functions as a regional entity in the Earth system and how these functions are changing as a result of ongoing changes in land use. This compilation of 26 papers resulting from LBA-related research covers a broad range of topics: forest stocks of carbon (C) and nitrogen (N); fluxes of greenhouse gases and volatile organic compounds from vegetation, soils and wetlands; mapping and modeling land-use change, fire risk, and soil properties; measuring changes caused by logging, pasturing and cultivating; and new research approaches in meteorology to estimate nocturnal fluxes of C from forests and pastures. Some important new synthesis can be derived from these and other studies. The aboveground biomass of intact Amazonian forests appears to be a sink for atmospheric carbon dioxide (CO2), while the wetlands and soils are a net source of atmospheric methane (CH4) and nitrous oxide (N2O), respectively. Land-use change has, so far, had only a minor effect on basin-wide emissions of CH4 and N2O, but the net effect of deforestation and reforestation appears to be a significant net release of CO2 to the atmosphere. The sum of the 100-year global warming potentials (GWP) of these annual sources and sinks of CH4, N2O, and CO2 indicate that the Amazonian forest–river system currently may be nearly balanced in terms of the net GWP of these biogenic atmospheric gases. Of course, large uncertainties remain for these estimates, but the papers published here demonstrate tremendous progress, and also large remaining hurdles, in narrowing these uncertainties in our understanding of how Amazônia functions as a regional entity in the Earth system.
abstractFuture climate change induced by atmospheric emissions of greenhouse gases is believed to have a large impact on the global carbon cycle. Several offline studies focusing either on the marine or on the terrestrial carbon cycle highlighted such potential effects. Two recent online studies, using ocean–atmosphere general circulation models coupled to land and ocean carbon cycle models, investigated in a consistent way the feedback between the climate change and the carbon cycle. These two studies used observed anthropogenic CO2 emissions for the 1860–1995 period and IPCC scenarios for the 1995–2100 period to force the climate – carbon cycle models. The study from the Hadley Centre group showed a very large positive feedback, atmospheric CO2 reaching 980 ppmv by 2100 if future climate impacts on the carbon cycle, but only about 700 ppmv if the carbon cycle is included but assumed to be insensitive to the climate change. The IPSL coupled climate – carbon cycle model simulated a much smaller positive feedback: climate impact on the carbon cycle leads by 2100 to an addition of less than 100 ppmv in the atmosphere. Here we perform a detailed feedback analysis to show that such differences are due to two key processes that are still poorly constrained in these coupled models: first Southern Ocean circulation, which primarily controls the geochemical uptake of CO2, and second vegetation and soil carbon response to global warming. Our analytical analysis reproduces remarkably the results obtained by the fully coupled models. Also it allows us to identify that, amongst the two processes mentioned above, the latter (the land response to global warming) is the one that essentially explains the differences between the IPSL and the Hadley results.
The volume of shade within vegetation canopies is reduced by more than an order of magnitude on cloudy and/or very hazy days compared to clear sunny days because of an increase in the diffuse fraction of the solar radiance. Here we show that vegetation is directly sensitive to changes in the diffuse fraction and we conclude that the productivity and structure of vegetation is strongly influenced by clouds and other atmospheric particles. We also propose that the unexpected decline in atmospheric [CO2] which was observed following the Mt. Pinatubo eruption was in part caused by increased vegetation uptake following an anomalous enhancement of the diffuse fraction by volcanic aerosols that would have reduced the volume of shade within vegetation canopies. These results have important implications for both understanding and modelling the productivity and structure of terrestrial vegetation as well as the global carbon cycle and the climate system.
Recent improvements to the Hadley Centre climate model include the introduction of a new land surface scheme called “MOSES”
(Met Office Surface Exchange Scheme). MOSES is built on the previous scheme, but incorporates in addition an interactive plant
photosynthesis and conductance module, and a new soil thermodynamics scheme which simulates the freezing and melting of soil
water, and takes account of the dependence of soil thermal characteristics on the frozen and unfrozen components. The impact
of these new features is demonstrated by comparing 1×CO2 and 2×CO2 climate simulations carried out using the old (UKMO) and new (MOSES) land surface schemes. MOSES is found to improve the
simulation of current climate. Soil water freezing tends to warm the high-latitude land in the northern Hemisphere during
autumn and winter, whilst the increased soil water availability in MOSES alleviates a spurious summer drying in the mid-latitudes.
The interactive canopy conductance responds directly to CO2, supressing transpiration as the concentration increases and producing a significant enhancement of the warming due to the
radiative effects of CO2 alone.
We use an ocean-atmosphere general circulation model coupled to land and
ocean carbon models to simulate the evolution of climate and atmospheric
CO2 from 1860 to 2100. Our model reproduces the observed
global mean temperature changes and the growth rate of atmospheric
CO2 for the period 1860-2000. For the future, we simulate
that the climate change due to CO2 increase will reduce the
land carbon uptake, leaving a larger fraction of anthropogenic
CO2 in the atmosphere. By 2100, we estimate that atmospheric
CO2 will be 18% higher due to the climate change impact on
the carbon cycle. Such a positive feedback has also been found by Cox et
al. [2000]. However, the amplitude of our feedback is three times
smaller than the one they simulated. We show that the partitioning
between carbon stored in the living biomass or in the soil, and their
respective sensitivity to increased CO2 and climate change
largely explain this discrepancy.
It is generally expected that the Amazon basin will experience at least two major environmental changes during the next few decades and centuries: 1) increasing areas of forest will be converted to pasture and cropland, and 2) concentrations of atmospheric CO2 will continue to rise. In this study, the authors use the National Center for Atmospheric Research GENESIS atmospheric general circulation model, coupled to the Integrated Biosphere Simulator, to determine the combined effects of large-scale deforestation and increased CO 2 concentrations (including both physiological and radiative effects) on Amazonian climate. In these simulations, deforestation decreases basin-average precipitation by 0.73 mm day 21 over the basin, as a consequence of the general reduction in vertical motion above the deforested area (although there are some small regions with increased vertical motion). The overall effect of doubled CO 2 concentrations in Amazonia is an increase in basin-average precipitation of 0.28 mm day21. The combined effect of deforestation and doubled CO2, including the interactions among the processes, is a decrease in the basin-average precipitation of 0.42 mm day21. While the effects of deforestation and increasing CO 2 concentrations on precipitation tend to counteract one another, both processes work to warm the Amazon basin. The effect of deforestation and increasing CO 2 concentrations both tend to increase surface temperature, mainly because of decreases in evapotranspiration and the radiative effect of CO 2. The combined effect of deforestation and doubled CO2, including the interactions among the processes, increases the basin-average temperature by roughly 3.58C.
This paper presents the space-time distribution of terrestrial carbon fluxes for the period 1979-1999 generated by a terrestrial carbon cycle data assimilation system (CCDAS). CCDAS is based around the Biosphere Energy Transfer Hydrology model. We assimilate satellite observations of photosynthetically active radiation and atmospheric CO2 concentration observations in a two-step process. The control variables for the assimilation are the parameters of the carbon cycle model. The optimized model produces a moderate fit to the seasonal cycle of atmospheric CO2 concentration and a good fit to its interannual variability. Long-term mean fluxes show large uptakes over the northern midlatitudes and uptakes over tropical continents partly offsetting the prescribed efflux due to land use change. Interannual variability is dominated by the tropics. On interannual timescales the controlling process is net primary productivity (NPP) while for decadal changes the main driver is changes in soil respiration. An adjoint sensitivity analysis reveals that uncertainty in long-term storage efficiency of soil carbon is the largest contributor to uncertainty in net flux.
Large-scale conversion of tropical forests into pastures or annual crops could lead to changes in the climate. We have used a coupled numerical model of the global atmosphere and biosphere (Center for Ocean-Land-Atmosphere GCM) to assess the effects of Amazonian deforestation on the regional and global climate. We found that when the Amazonian tropical forests were replaced by degraded grass (pasture) in the model, there was a significant increase in the mean surface temperature (about 2.5-degrees-C) and a decrease in the annual evapotranspiration (30% reduction), precipitation (25% reduction), and runoff (20% reduction) in the region. The differences between the two simulations were greatest during the dry season. The deforested case was associated with larger diurnal fluctuations of surface temperature and vapor pressure deficit; such effects have been observed in existing deforested areas in Amazonia. The calculated reduction in precipitation was larger than the calculated decrease in evapotranspiration, indicating a reduction in the regional moisture convergence. There was also an increase in the length of the dry season in the southern half of the Amazon Basin, which could have serious implications for the reestablishment of the tropical forests following massive deforestation since rainforests only occur where the dry season is very short or nonexistent. An empirical bioclimatic scheme based on an integrated soil moisture stress index was used to derive the movement of the savanna-forest boundary in response to the simulated climate change produced by large-scale deforestation. The implications of possible climate changes in adjacent regions are discussed. Pages: 957-988
The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to significant changes in climate. About half of the current emissions are being absorbed by the ocean and by land ecosystems, but this absorption is sensitive to climate as well as to atmospheric carbon dioxide concentrations, creating a feedback loop. General circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and CO2 concentrations from simple carbon-cycle models that do not include climate change. Here we present results from a fully coupled, three-dimensional carbon-climate model, indicating that carbon-cycle feedbacks could significantly accelerate climate change over the twenty-first century. We find that under a 'business as usual' scenario, the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr(-1) is balanced by the terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in uncoupled carbon models, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.
There is significant interannual variability in the atmospheric concentration of carbon dioxide (CO2) even when the effect of anthropogenic sources has been accounted for. This variability is well correlated with the El Nino-Southern Oscillation (ENSO) cycle. This behavior of the natural carbon cycle provides a valuable mechanism for validating carbon cycle models. The model in turn is a valuable tool for examining the processes involved in the relationship between ENSO and the carbon cycle. A GCM coupled climate-carbon cycle model is used to study the mechanisms involved. The model simulates the observed temperature, precipitation, and CO2 response of the climate to the ENSO cycle. Climatic changes over land during El Nino events lead to decreased gross primary productivity and increased plant and soil respiration, and hence the terrestrial biosphere becomes a source of CO2 to the atmosphere. Conversely, during El Nino events, the ocean becomes a sink of CO2 because of reduction of equatorial Pacific outgassing as a result of decreased upwelling of carbon-rich deep water. During La Nina events the opposite occurs; the land becomes a sink and the ocean a source of CO2. The magnitude of the model's response is such that the terrestrial biosphere releases about 1.8 GtC yr-1 for an El Nino with a Nino-3 index of magnitude 1 °C, and the oceans take up about 0.5 GtC yr-1. (1 GtC =1015 g of carbon). The net global response is thus an increase in atmospheric CO2 of about 0.6 ppmv yr-1. This is in close agreement with the sensitivity of the observed CO2 record to ENSO events.
The chemical composition of carbonaceous aerosols collected during the LBA-SMOCC field experiment, conducted in Rondônia, Brazil, in 2002 during the transition from the dry to the wet season, was investigated by a suite of advanced analytical techniques. The period of most intense biomass burning was characterized by high concentrations of submicron particles rich in carbonaceous material and water-soluble organic compounds (WSOC). At the onset of the rainy period, submicron total carbon (TC) concentrations had decreased by about 20 times. In contrast, the concentration of supermicron TC was fairly constant throughout the experiment, pointing to a constant emission of coarse particles from the natural background. About 6?8% of TC (9?11% of WSOC) was speciated at the molecular level by GC-MS and liquid chromatography. Poly-hydroxylated compounds, aliphatic and aromatic acids were the main classes of compounds accounted for by individual compound analysis. Functional group analysis by proton NMR and chromatographic separation on ion-exchange columns allowed characterization of ca. 50?90% of WSOC into broad chemical classes (neutral species/light acids/humic-like substances). In spite of the significant change in the chemical composition of tracer compounds from the dry to the wet period, the functional groups and the general chemical classes of WSOC changed only to a lesser extent. Model compounds representing size-resolved WSOC chemical composition for the different periods of the campaign are then proposed in this paper, based on the chemical characterization by both individual compound analysis and functional group analysis deployed during the LBA-SMOCC experiment. Model compounds reproduce quantitatively the average chemical structure of WSOC and can be used as best-guess surrogates in microphysical models involving organic aerosol particles over tropical areas affected by biomass burning.
Particles from biomass burning and regional haze were sampled in Rondônia, Brazil, during dry, transition and wet periods from September to November 2002, as part of the LBA-SMOCC (Large-Scale Biosphere-Atmosphere Experiment in Amazonia ? Smoke, Aerosols, Clouds, Rainfall, and Climate) field campaign. Water soluble organic and inorganic compounds in bulk (High Volume and Stacked Filter Unit sampler) and size-resolved (Micro Orifice Uniform Deposit Impactor ? MOUDI) smoke samples were determined by ion chromatography. It was found that low molecular weight polar organic acids account for a significant fraction of the water soluble organic carbon (WSOC) in biomass burning aerosols (C2-C6 dicarboxylic acids reached up to 3.7% and one-ring aromatic acids reached up to 2% of fine fraction WSOC during burning period). Short dicarboxylic (C2-C6) acids are dominated by oxalic acid followed by malonic and succinic acids. The largest ionic species is ammonium sulfate (60?70% of ionic mass). It was found that most of the ionic mass is concentrated in submicrometer-sized particles. Based on the size distribution and correlations with K+, a known biomass burning tracer, it is suggested that many of the organic acids are directly emitted by vegetation fires. It is concluded that the dicarboxylic acids are mostly confined to the particulate phase, and no evidence for semi-volatile behavior was observed. Finally, it is shown that the distribution of water soluble species shifts to larger aerosols sizes as the aerosol population ages and mixes with other aerosol types in the atmosphere.
Drought stress in tropical forests can have a major impact on global carbon, water, and energy cycles. This chapter examines drought-induced responses in the processing of carbon and water by intact tropical forest ecosystems over short (physiological) and longer (ecological) timescales. Both levels of understanding should be represented in analyses of climateforest ecosystem feedback. Although limited spatial information on the diversity of the physical properties of soil constrains estimates of drought vulnerability, tree functional convergence across species based on simple measures such as wood density would simplify how drought responses can be represented and linked to changes in forest composition through mortality indices. While insufficient on their own, satellite-derived measurements of ecosystem properties (e.g. leaf area index) and processes (e.g. mortality and photosynthesis) are expected to provide increasingly detailed information that can be used to test understanding of short- and longer-term responses to drought.
The problem of scale has been a critical impediment to incorporating important fine-scale processes into global ecosystem models. Our knowledge of fine-scale physiological and ecological processes comes from a variety of measurements, ranging from forest plot inventories to remote sensing, made at spatial resolutions considerably smaller than the large scale at which global ecosystem models are defined. In this paper, we describe a new individual-based, terrestrial biosphere model, which we label the ecosystem demography model (ED). We then introduce a general method for scaling stochastic individual-based models of ecosystem dynamics (gap models) such as ED to large scales. The method accounts for the fine-scale spatial heterogeneity within an ecosystem caused by stochastic disturbance events, operating at scales down to individual canopy-tree-sized gaps. By conditioning appropriately on the occurrence of these events, we derive a size-and age-structured (SAS) approximation for the first moment of the stochastic ecosystem model. With this approximation, it is possible to make predictions about the large scales of interest from a description of the fine-scale physiological and population-dynamic processes without simulating the fate of every plant individually. We use the SAS approximation to implement our individual-based biosphere model over South America from 15° N to 15° S, showing that the SAS equations are accurate across a range of environmental conditions and resulting ecosystem types. We then compare the predictions of the biosphere model to regional data and to intensive data at specific sites. Analysis of the model at these sites illustrates the importance of fine-scale heterogeneity in governing large-scale ecosystem function, showing how population and community-level processes influence ecosystem composition and structure, patterns of aboveground carbon accumulation, and net ecosystem production.
Past studies have indicated that deforestation of the Amazon basin would result in an important rainfall decrease in that region but that this process had no significant impact on the global temperature or precipitation and had only local implications. Here it is shown that deforestation of tropical regions sig- nificantly affects precipitation at mid- and high latitudes through hydrometeorological teleconnections. In particular, it is found that the deforestation of Amazonia and Central Africa severely reduces rainfall in the lower U.S. Midwest during the spring and summer seasons and in the upper U.S. Midwest during the winter and spring, respectively, when water is crucial for agricultural productivity in these regions. Deforestation of Southeast Asia affects China and the Balkan Peninsula most significantly. On the other hand, the elimination of any of these tropical forests considerably enhances summer rainfall in the southern tip of the Arabian Peninsula. The combined effect of deforestation of these three tropical regions causes a significant decrease in winter precipitation in California and seems to generate a cumulative enhancement of precipi- tation during the summer in the southern tip of the Arabian Peninsula.
Studies of global climate change predict that increases in atmospheric CO2 concentration and temperature are expected to occur over the next century. To help gain an insight into the potential effect of these changes on forests, this book describes how major European tree species respond to experimentally manipulated environmental conditions. The contributors describe the effects on photosynthesis, respiration, and development and use the results to generate models of the likely response of European forests to the predicted changes in climate. The volume encompasses studies carried out under the ECOCRAFT (European Collaboration on CO2 Responses Applied to Forests and Trees) program, focusing on the major tree species found in eight European countries. As such, it provides an authoritative report of the current status of European research into this important area of global environmental biology.
Although the decomposition of plant material in soil is an extremely complex process, relatively simple models can give good fits to the decay process. Thus a two-compartment model gives a close representation, over the first few years, of the decay of C-labelled plant material in soil. A model containing a single homogeneous humus compartment decomposing by a first-order process is surprisingly useful for soil organic nitrogen over periods measured in decades. More sophisticated multicompartmental models are now widely used to represent turnover in soil. One of these, the Rothamsted turnover model, is described in detail and shown to give a useful representation of data from the Rothamsted long-term field experiments.
Although the decomposition of plant material in soil is an extremely
complex process, relatively simple models can give good fits to the
decay process. Thus a two-compartment model gives a close
representation, over the first few years, of the decay of
14C-labelled plant material in soil. A model containing a
single homogeneous humus compartment decomposing by a first-order
process is surprisingly useful for soil organic nitrogen over periods
measured in decades. More sophisticated multicompartmental models are
now widely used to represent turnover in soil. One of these, the
Rothamsted turnover model, is described in detail and shown to give a
useful representation of data from the Rothamsted long-term field
experiments.
(1) Clouds and aerosols alter the proportion of diffuse radiation in global solar radiation reaching the Earth's surface. It is known that diffuse and direct beam radiation differ in the way they transfer through plant canopies and affect the summation of nonlinear processes like photosynthesis differently than what would occur at the leaf scale. We compared the relative efficiencies of canopy photosynthesis to diffuse and direct photosynthetically active radiation (PAR) for a Scots pine forest, an aspen forest, a mixed deciduous forest, a tallgrass prairie and a winter wheat crop. The comparison was based on the seasonal patterns of the parameters that define the canopy photosynthetic responses to diffuse PAR and those that define the responses to direct PAR. These parameters were inferred from half-hourly tower CO2 flux measurements. We found that: (1) diffuse radiation results in higher light use efficiencies by plant canopies; (2) diffuse radiation has much less tendency to cause canopy photosynthetic saturation; (3) the advantages of diffuse radiation over direct radiation increase with radiation level; (4) temperature as well as vapor pressure deficit can cause different responses in diffuse and direct canopy photosynthesis, indicating that their impacts on terrestrial ecosystem carbon assimilation may depend on radiation regimes and thus sky conditions. These findings call for different treatments of diffuse and direct radiation in models of global primary production, and studies of the roles of clouds and aerosols in global carbon cycle. INDEX TERMS: 4806 Oceanography: Biological and Chemical: Carbon cycling; 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 1851 Hydrology: Plant ecology; 1610 Global Change: Atmosphere (0315, 0325); KEYWORDS: diffuse and direct PAR, terrestrial ecosystem productivity, clouds, aerosols, global carbon cycle
Aerosol formation and subsequent particle growth in the ambient air have been frequently observed at the boreal forest site (SMEAR II station), southern Finland. The EU funded project BIOFOR (Biogenic aerosol formation in the boreal forest) has focused on a) the determination of formation mechanisms of aerosol particles in the boreal forest site, and b) the verification of emissions of secondary organic aerosols from the boreal forest site, including the quantification of the amount of condensable vapours produced in photochemical reactions of biogenic volatile organic compounds (BVOC) leading to aerosol formation. Although the exact formation route for 3 nm particles is still unclear, the project results can be summarised as follows: (i) The most probable formation mechanism is ternary nucleation (water-sulphuric acid-ammonia) and the growth to observable sizes is mainly due to condensation of organic vapours. However, we do not have a direct proof of these phenomena, since it is impossible to determine the composition of 1 to 5-nm-size particles using the present state-of-art instrumentation; (ii) If nucleation takes place, it always occurs in cold-air advection in polar and Arctic air masses at low cloudiness, and the nucleation is closely connected to the onset of strong turbulence, convection, and entrainment in the morning-noon transition from a stable to an unstable stratified boundary layer; (iii) The emissions rates for several gaseous compounds have been verified. The model calculations showed that the amount of the condensable vapour needed for observed growth of aerosol particles is in the range 1-5 × 107 cm-3. The estimations for the vapour source rate are in the range 3-8 × 104 cm-3s-1.
TERRESTRIAL ecosystems are thought to play an important role in determining regional and global climate1–6; one example of this is in Amazonia, where destruction of the tropical rainforest leads to warmer and drier conditions4–6. Boreal forest ecosystems may also affect climate. As temperatures rise, the amount of continental and oceanic snow and ice is reduced, so the land and ocean surfaces absorb greater amounts of solar radiation, reinforcing the warming in a 'snow/ice/albedo' feedback which results in large climate sensitivity to radiative forcings7–9. This sensitivity is moderated, however, by the presence of trees in northern latitudes, which mask the high reflectance of snow10,11, leading to warmer winter temperatures than if trees were not present12–14. Here we present results from a global climate model which show that the boreal forest warms both winter and summer air temperatures, relative to simulations in which the forest is replaced with bare ground or tundra vegetation. Our results suggest that future redistributions of boreal forest and tundra vegetation (due, for example, to extensive logging, or the influence of global warming) could initiate important climate feedbacks, which could also extend to lower latitudes.
Previous studies on the Physiology of stomata in higher plants suggest that stomata influence the rate of CO2 fixation in leaf mesophyll tissue. We believe that an equally important stomatal function has not been fully recognised; that stomatal aperture is determined by the capacity of the mesophyll tissue to fix carbon. We altered the capacity of leaves to fix carbon by various means, and found invariably that the diffusive conductance of the epidermis to CO2 transfer, g, (which mainly depends on the number and dimensions of the stomata) changes in nearly the same proportion as the rate of assimilation of CO2. Thus, the intercellular concentration of CO2 (ci), calculated as ci = ca–A/g (where ca is ambient concentration of CO2, A is assimilation rate of CO2), tends to remain constant providing ca is kept constant. We used routine techniques1 to measure A and estimate g in leaves placed singly in chambers. Conductance takes account of CO2 transfer through both stomata and leaf boundary layer, the conductance of the latter being 0.5 mol m−2 s−1.
This chapter is intended as a gentle introduction to models of physiologically structured populations, as developed by Metz and Diekmann (1986) (hereafter, PSP models; the origin of the adjective “physiologically structured” is described in Section 2 after some necessary definitions). You will need a basic knowledge of mathematical modeling but no familiarity with PSP models or the ensuing partial differential equations. My aim is to equip you with enough skills to be able to use moderately complex PSP models for specific biological applications. Hence, I emphasize the formulation of the models, the biological interpretation of the equations, and the tools for studying the models. The mathematical background of the modeling framework and the justification of the equations are discussed only when necessary for a better understanding of the biological aspects of the models.
A number of studies show that significant reductions in solar radiation reaching the Earth’s surface have occurred during the past 50 years. This review analyzes the most accurate measurements, those made with thermopile pyranometers, and concludes that the reduction has globally averaged 0.51±0.05Wm−2 per year, equivalent to a reduction of 2.7% per decade, and now totals 20Wm−2, seven times the errors of measurement. Possible causes of the reductions are considered. Based on current knowledge, the most probable is that increases in man made aerosols and other air pollutants have changed the optical properties of the atmosphere, in particular those of clouds. The effects of the observed solar radiation reductions on plant processes and agricultural productivity are reviewed. While model studies indicate that reductions in productivity and transpiration will be proportional to those in radiation this conclusion is not supported by some of the experimental evidence. This suggests a lesser sensitivity, especially in high-radiation, arid climates, due to the shade tolerance of many crops and anticipated reductions in water stress. Finally the steps needed to strengthen the evidence for global dimming, elucidate its causes and determine its agricultural consequences are outlined.
The possible responses of ecosystem processes to rising atmospheric CO2 concentration and climate change are illustrated using six dynamic global vegetation models that explicitly represent the interactions of ecosystem carbon and water exchanges with vegetation dynamics. The models are driven by the IPCC IS92a scenario of rising CO2 (Wigley et al. 1991), and by climate changes resulting from effective CO2 concentrations corresponding to IS92a, simulated by the coupled ocean atmosphere model HadCM2-SUL. Simulations with changing CO2 alone show a widely distributed terrestrial carbon sink of 1.4–3.8 Pg C y−1 during the 1990s, rising to 3.7–8.6 Pg C y−1 a century later. Simulations including climate change show a reduced sink both today (0.6–3.0 Pg C y−1) and a century later (0.3–6.6 Pg C y−1) as a result of the impacts of climate change on NEP of tropical and southern hemisphere ecosystems. In all models, the rate of increase of NEP begins to level off around 2030 as a consequence of the ‘diminishing return’ of physiological CO2 effects at high CO2 concentrations. Four out of the six models show a further, climate-induced decline in NEP resulting from increased heterotrophic respiration and declining tropical NPP after 2050. Changes in vegetation structure influence the magnitude and spatial pattern of the carbon sink and, in combination with changing climate, also freshwater availability (runoff). It is shown that these changes, once set in motion, would continue to evolve for at least a century even if atmospheric CO2 concentration and climate could be instantaneously stabilized. The results should be considered illustrative in the sense that the choice of CO2 concentration scenario was arbitrary and only one climate model scenario was used. However, the results serve to indicate a range of possible biospheric responses to CO2 and climate change. They reveal major uncertainties about the response of NEP to climate change resulting, primarily, from differences in the way that modelled global NPP responds to a changing climate. The simulations illustrate, however, that the magnitude of possible biospheric influences on the carbon balance requires that this factor is taken into account for future scenarios of atmospheric CO2 and climate change.
• Numerous field studies have measured mycorrhizal dynamics under additions of nitrogen (N), phosphorus (P), or atmospheric CO2 to test the hypothesis that plants should invest in mycorrhizal fungi when soil nutrients are limiting. • Here meta-analyses were used to integrate nutrient responses across independent field-based studies. Responses were compared between ecto- and arbuscular mycorrhizal fungi, and among fertilizer types, methods of measurement, biomes, and lead investigators. Relationships between degree of response and study length, fertilization rates, total amounts of nutrients applied, and numbers of replicates were also tested. • Across studies, mycorrhizal abundance decreased 15% under N fertilization and 32% under P fertilization. Elevated CO2 elicited a 47% increase. Nitrogen effects varied significantly among studies, and P effects varied significantly among lead investigators. Most other factors did not affect mycorrhizal responses. • These results support the plant investment hypothesis, and suggest that global standing stocks of mycorrhizal fungi may increase substantially under elevated CO2 but decline moderately under P additions. Effects of N deposition may be difficult to predict for individual ecosystems, with a slightly negative influence overall.
Carbon cycle feedbacks have been shown to be very important in predicting climate change over the next century. The response of the terrestrial carbon cycle to climate change depends on the competition between increased respiration due to warmer temperatures and increased uptake due to elevated CO2levels. Whether the terrestrial carbon cycle remains a sink for anthropogenic carbon, or switches to become a source, depends particularly on the response of soil respiration to temperature. Here we use observed global atmospheric CO2concentration to constrain the behaviour of soil respiration in a coupled climate–carbon cycle GCM. Copyright © 2001 British Crown Copyright.
In a forest ecosystem at steady state, net carbon (C) assimilation by plants and C loss through soil and litter decomposition by heterotrophic organisms are balanced. However, a perturbation to the system, such as increased mean soil temperature, will lead to faster decay, enhancing CO 2 release from decomposers, and thus upsetting the balance. Recent in situ experiments have indicated that the stimulation of soil respiration following a step increase in annual average soil temperature declines over time. One possible explanation for this decline may be changes in substrate availability. This hypothesis is examined by using the ecosystem model G'DAY, which simulates C and nitrogen (N) dynamics in plants and soil.
We applied the model to observations from a soil‐warming experiment in a Norway spruce ( Picea abies (L.) Karst.) stand by simulating a step increase of soil temperature. The model provided a good qualitative reproduction of the observed reduction of heterotrophic respiration ( R h ) under sustained warming. The simulations showed how the combined effects of faster turnover and reduced substrate availability lead to a transient increase of R h . The simulated annual increase in R h from soil was 60% in the first year after perturbation but decreased to 30% after a decade.
One conclusion from the analysis of the simulations is that R h can decrease even though the temperature response function for decomposition remains unchanged. G'DAY suggests that acclimation of R h to soil warming is partly an effect of substrate depletion of labile C pools during the first decade of warming as a result of accelerated rates of mineralization. The response is attributed mainly to changing levels of C in pools with short time constants, reflecting the importance of high‐quality soil C fractions. Changes of the structure or physiology of the decomposer community were not invoked. Therefore, it becomes a question of definition whether the simulated dynamics of the declining response of CO 2 release to the warming should be named acclimation or seen as a natural part of the system dynamics.
To estimate how tree photosynthesis modulates soil respiration, we simultaneously and continuously measured soil respiration and canopy photosynthesis over an oak-grass savanna during the summer, when the annual grass between trees was dead. Soil respiration measured under a tree crown reflected the sum of rhizosphere respiration and heterotrophic respiration; soil respiration measured in an open area represented heterotrophic respiration. Soil respiration was measured using solid-state CO2 sensors buried in soils and the flux-gradient method. Canopy photosynthesis was obtained from overstory and understory flux measurements using the eddy covariance method. We found that the diurnal pattern of soil respiration in the open was driven by soil temperature, while soil respiration under the tree was decoupled with soil temperature. Although soil moisture controlled the seasonal pattern of soil respiration, it did not influence the diurnal pattern of soil respiration. Soil respiration under the tree controlled by the root component was strongly correlated with tree photosynthesis, but with a time lag of 7–12 h. These results indicate that photosynthesis drives soil respiration in addition to soil temperature and moisture.
We review measured rates of soil respiration from terrestrial and wetland ecosystems to define the annual global CO2 flux from soils, to identify uncertainties in the global flux estimate, and to investigate the influences of temperature, precipitation, and vegetation on soil respiration rates. The annual global CO2 flux from soils is estimated to average (± S.D.) 68 ± 4 PgC/ yr, based on extrapolations from biome land areas. Relatively few measurements of soil respiration exist from arid, semi-arid, and tropical regions; these regions should be priorities for additional research. On a global scale, soil respiration rates are positively correlated with mean annual air temperatures and mean annual precipitation. There is a close correlation between mean annual net primary productivity (NPP) of different vegetation biomes and their mean annual soil respiration rates, with soil respiration averaging 24% higher than mean annual NPP. This difference represents a minimum estimate of the contribution of root respiration to the total soil CO2efflux. Estimates of soil C turnover rates range from 500 years in tundra and peaty wetlands to 10 years in tropical savannas. We also evaluate the potential impacts of human activities on soil respiration rates, with particular focus on land use changes, soil fertilization, irrigation and drainage, and climate changes. The impacts of human activities on soil respiration rates are poorly documented, and vary among sites. Of particular importance are potential changes in temperatures and precipitation. Based on a review of in situ measurements, the Q10 value for total soil respiration has a median value of 2.4. Increased soil respiration with global warming is likely to provide a positive feedback to the greenhouse effect.
A geographically extended model of the dynamics of tree size structure of forests is proposed to simulate the change of forest zonation along latitude in response to global environmental change. To predict the response of forests to global change, it is necessary to construct functional models of forest tree populations. The size-structure-based model requires far less memory and steps of calculation compared with individual-based models, and it is easy to incorporate the dimension of geographic locations into the model to describe large-scale dynamics of forest-type distributions. The effect of increasing size growth rate, expected from increasing atmospheric carbon dioxide, was diminished at the stand-level basal area density, because of regulation by one-sided competition. Model simulations of a century-long global warming at around 3 C predicted that (1) biomass changed in resident forests rather simultaneously in response to warming, and that (2) there was a considerable time lag in movement at the boundaries of different forest types, particularly under the existence of resident forest types that would be finally replaced. It required several thousand years after a century-long warming spell for forest types to attain new steady-state distributions after shifting. As a consequence, global warming created a zigzag pattern of biomass distribution along a latitudinal gradient, i.e., an increase in the cooler-side boundary of forest types and a decrease in the warmer-side boundary.
Results of a simple model of the effects of temperature on net ecosystem production call into question the argument that the large stocks of soil carbon and greater projected warming in the boreal and tu ndra regions of the world will
lead to rapid efflux of carbon from these biomes to the atmosphere. We show that low rates of carbon turnover in these regions and a relatively greater response of net primary production to changes in temperature may lead to carbon storage over some limited range of warming. In contrast, the high rates of soil respiration found in tropical ecosystems are highly sensitive to small changes in temperature, so that despite the less pronounced warming expected in equatorial regions, tropical soils are likely to release relatively large amounts of carbon to the atmosphere. Results for high-latitude biomes are highly sensitive to parameter values used, while the net efflux of carbon from the tropics appears robust.
Over the past decade, the formation and growth of nanometer-size atmospheric aerosol particles have been observed at a number of sites around the world. Measurements of particle formation have been performed on different platforms (ground, ships, aircraft) and over different time periods (campaign or continuous-type measurements). The development during the 1990s of new instruments to measure nanoparticle size distributions and several gases that participate in nucleation have enabled these new discoveries. Measurements during nucleation episodes of evolving size distributions down to 3 nm can be used to calculate the apparent source rate of 3-nm particles and the particle growth rate. We have collected existing data from the literature and data banks (campaigns and continuous measurements), representing more than 100 individual investigations. We conclude that the formation rate of 3-nm particles is often in the range 0.01-10 cm-3 s-1 in the boundary layer. However, in urban areas formation rates are often higher than this (up to 100 cm-3 s-1), and rates as high as 104-10 5 cm-3 s-1 have been observed in coastal areas and industrial plumes. Typical particle growth rates are in the range 1-20 nm h-1 in mid-latitudes depending on the temperature and the availability of condensable vapours. Over polar areas the growth rate can be as low as 0.1 nm h-1. Because nucleation can lead to a significant increase in the number concentration of cloud condensation nuclei, global climate models will require reliable models for nucleation.
A numerical process-based model of terrestrial ecosystem dynamics is described and tested. The model, Hybrid v3.0, treats the daily cycling of carbon, nitrogen, and water within the biosphere and between the biosphere and the atmosphere. It combines a mass-balance approach with the capacity to predict the relative dominance of different species or generalised plant types (such as evergreen needleleaved trees, cold deciduous broadleaved trees, and C3 grasses). The growth of individual trees is simulated on an annual timestep, and the growth of a grass layer is simulated on a daily timestep. The exchange of carbon, nitrogen, and water with the atmosphere and the soil is simulated on a daily timestep (except the flux of tree litter to the soil, which occurs annually). Individual trees and the grass layer compete with each other for light, water, and nitrogen within a ‘plot’. Larger and taller plants shade smaller ones; they also take up a greater proportion of the available water and nitrogen. The above-ground space in each plot is divided into 1 m deep layers for the purposes of calculating irradiance interception; horizontal variation in the plot environment is not treated. The soil is represented as a single layer, with a daily hydrological budget. Decomposition of soil organic matter is calculated using an empirical sub-model. The initial size of each tree seedling is stochastic. To predict the mean behaviour of the model for a particular boundary condition it is necessary to simulate a number of plots. Hybrid v3.0 has been written with three major requirements in mind: (i) the carbon, water, and nutrient cycles must be fully coupled in the soil-plant-atmosphere system; (ii) the internal constraints on the model's behaviour, and the driving forces for the model, must be the same as those which operate in nature (e.g., climate, nitrogen deposition, and the atmospheric concentrations of CO2 and O2); and (iii) the model must be constructed so that it is capable of predicting transient as well as equilibrium responses to climate change. These conditions have largely been met by constructing the model around a set of fundamental hypotheses regarding the general constraints under which plants and soils behave, independently of any particular location or time. The model is thus potentially capable of making reliable predictions of ecosystem behaviour and structure under future, new, atmospheric conditions. The model is tested for a site in eastern North America. A quasi-equilibrium is reached after approximately 250 years with 10 plots. It is found that more plots are not necessary in order to obtain a reliable estimate of mean behaviour. Predictions of productivity, leaf area index, foliage nitrogen, soil carbon, and biomass carbon are all within the range expected for this location. Mortality is shown to be a necessary model component; without it large trees reach a maximum size, and then remain in dynamic equilibrium with the climate, without dying. The model runs at a rate of 0.176 s plot−1 year−1 on a workstation (a 500 year simulation, with 10 plots, thus takes approximately 15 min). A sensitivity analysis demonstrates the importance of the parameterisation of phenology, photosynthesis, and foliage/fine root carbon and nitrogen partitioning for the overall carbon balance of the modelled ecosystem. Hybrid v3.0 has been written with the intention of using it to represent the terrestrial biosphere in a total earth system model. This would be achieved by linking it to models of other components of the earth system, such as the climate and the oceans, in a fully coupled manner. This total earth system model could then be used to answer a large range of questions concerning global environmental change.
High and low affinity methane oxidation potentials were measured for soils under five fully replicated land-use treatments over an entire calendar year. Simultaneous measurements of soil nitrification potential in replicate soil samples were also made. Both high and low affinity CH4 oxidation were significantly reduced in the nitrate-rich soils under alder, compared to the other four vegetation treatments (oak, Norway spruce, Scots pine and grass). However, the effect of land-use was less for high affinity methanotrophy than for low affinity CH4 oxidation. Nitrification rates were highest in alder soils, with the greatest potential for oxidation occurring in the top 5 cm of the soil. No significant relationship between potential nitrification rate and low affinity CH4 oxidation was seen. However, a significant negative relationship between nitrification and high affinity CH4 oxidation was identified. We found vegetation type to be a key determinant of soil-mediated CH4 and oxidation, but found no evidence for significant CH4 oxidation by nitrifying bacteria.
Biological production of the volatile compound dimethylsulfide in the ocean is the main natural source of tropospheric sulfur on a global scale, with important consequences for the radiative balance of the Earth. In the late 1980s, a Gaian feedback link between marine phytoplankton and climate through the release of atmospheric sulfur was hypothesized. However, the idea of microalgae producing a substance that could regulate climate has been criticized on the basis of its evolutionary feasibility. Recent advances have shown that volatile sulfur is a result of ecological interactions and transformation processes through planktonic food webs. It is, therefore, not only phytoplankton biomass, taxonomy or activity, but also food-web structure and dynamics that drive the oceanic production of atmospheric sulfur. Accordingly, the viewpoint on the ecological and evolutionary basis of this amazing marine biota–atmosphere link is changing.
The major source of cloud-condensation nuclei (CCN) over the oceans
appears to be dimethylsulphide, which is produced by planktonic algae in
sea water and oxidizes in the atmosphere to form a sulphate aerosol.
Because the reflectance (albedo) of clouds (and thus the earth's
radiation budget) is sensitive to CCN density, biological regulation of
the climate is possible through the effects of temperature and sunlight
on phytoplankton population and dimethylsulphide production. To
counteract the warming due to doubling of atmospheric CO2, an
approximate doubling of CCN would be needed.
Eleven coupled climate–carbon cycle models used a common protocol to study the coupling between climate change and the carbon cycle. The models were forced by historical emissions and the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A2 anthropogenic emissions of CO2 for the 1850–2100 time period. For each model, two simulations were performed in order to isolate the impact of climate change on the land and ocean carbon cycle, and therefore the climate feedback on the atmospheric CO2 concentration growth rate. There was unanimous agreement among the models that future climate change will reduce the efficiency of the earth system to absorb the anthropogenic carbon perturbation. A larger fraction of anthropogenic CO2 will stay airborne if climate change is accounted for. By the end of the twenty-first century, this additional CO2 varied between 20 and 200 ppm for the two extreme models, the majority of the models lying between 50 and 100 ppm. The higher CO2 levels led to an additional climate warming ranging between 0.1° and 1.5°C.
All models simulated a negative sensitivity for both the land and the ocean carbon cycle to future climate. However, there was still a large uncertainty on the magnitude of these sensitivities. Eight models attributed most of the changes to the land, while three attributed it to the ocean. Also, a majority of the models located the reduction of land carbon uptake in the Tropics. However, the attribution of the land sensitivity to changes in net primary productivity versus changes in respiration is still subject to debate; no consensus emerged among the models.
A model is developed to relate community structure to level of environmental disturbance in systems in which the effects of disturbance are localized in space and time. In general these disturbances create a pattern of spatio-temporal heterogeneity by renewing a limiting resource, thereby permitting utilization by species that are not dominant competitors. The proposed model predicts the frequency distribution of these renewed areas, with regard to size and age (colonization stage). The model thus allows one to relate overall system pattern to the local biology within these areas, to compare various areas with different levels of disturbance, and to predict the effects of new disturbance.