Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Correction to "Spatial and temporal dynamics in eddy covariance observations of methane fluxes at a tundra site in Northeastern Siberia" (Journal of Geophysical Research G: Biogeosciences (2011) 116 (G03016) DOI: 10.1029/2010JG001637)
Parmentier, F.J.W. ; Huissteden, J. van; Molen, M.K. van der; Dolman, A.J. ; Schaepman-Strub, G. ; Karsanaev, S.A. ; Maximov, T.C. - \ 2012
Journal of Geophysical Research: Biogeosciences 117 (2012)1. - ISSN 2169-8953
[1] In the paper “Spatial and temporal dynamics in eddy covariance observations of methane fluxes at a tundra site in northeastern Siberia” by F. J. W. Parmentier et al. (Journal of Geophysical Research, 116, G03016, doi:10.1029/2010JG001637, 2011), a few typographical errors have been brought to our attention which have unfortunately slipped through, and we apologize for any inconvenience they may have caused. [2] In equation (1), the conditions of L > 0 and L <0 were reversed, and in the second part of the equation, a minus was given where a plus should have appeared. However, these mistakes are purely typographical. The same errors were not made in the code used, and all calculations presented in the paper were made with the correct equation, shown here in equation (1). Therefore, both the results and the conclusion of the paper remain unchanged. The correct equation is: [3] Furthermore, in the last sentence of paragraph 21, the word “unstable” was given twice, while the second occurrence should have read “stable.” The correct sentence is: “As a consequence, unstable conditions are expressed in the range 0 <F <1, neutral conditions occur at F = 1, and stable conditions are expressed for values of F > 1.” [4] We'd like to thank Bernard Heinesch and students for bringing these typographical errors to our attention.
Spectral estimation of soil properties in Siberian tundra soils and relations with plant species composition
Bartholomeus, H. ; Schaepman-Strub, G. ; Blok, D. ; Sofronov, R. ; Udaltsov, S. - \ 2012
Applied and Environmental Soil Science 2012 (2012). - ISSN 1687-7667 - 13 p.
Predicted global warming will be most pronounced in the Arctic and will severely affect permafrost environments. Due to its large spatial extent and large stocks of soil organic carbon, changes to organic matter decomposition rates and associated carbon fluxes in Arctic permafrost soils will significantly impact the global carbon cycle. We explore the potential of soil spectroscopy to estimate soil carbon properties and investigate the relation between soil properties and vegetation composition. Soil samples are collected in Siberia, and vegetation descriptions are made at each sample point. First, laboratory-determined soil properties are related to the spectral reflectance of wet and dried samples using partial least squares regression (PLSR) and stepwise multiple linear regression (SMLR). SMLR, using selected wavelengths related with C and N, yields high calibration accuracies for C and N. PLSR yields a good prediction model for K and a moderate model for pH. Using these models, soil properties are determined for a larger number of samples, and soil properties are related to plant species composition. This analysis shows that variation of soil properties is large within vegetation classes, but vegetation composition can be used for qualitative estimation of soil properties.
A laboratory goniometer system for measuring reflectance and emittance anisotropy
Roosjen, P.P.J. ; Clevers, J.G.P.W. ; Bartholomeus, H. ; Schaepman, M.E. ; Schaepman-Strub, G. ; Jalink, H. ; Schoor, R. van der; Jong, A. de - \ 2012
Sensors 12 (2012)12. - ISSN 1424-8220 - p. 17358 - 17371.
bidirectional reflectance - radiance data - albedo - field - brdf - algorithm - surface - model - acquisition - vegetation
In this paper, a laboratory goniometer system for performing multi-angular measurements under controlled illumination conditions is described. A commercially available robotic arm enables the acquisition of a large number of measurements over the full hemisphere within a short time span making it much faster than other goniometers. In addition, the presented set-up enables assessment of anisotropic reflectance and emittance behaviour of soils, leaves and small canopies. Mounting a spectrometer enables acquisition of either hemispherical measurements or measurements in the horizontal plane. Mounting a thermal camera allows directional observations of the thermal emittance. This paper also presents three showcases of these different measurement set-ups in order to illustrate its possibilities. Finally, suggestions for applying this instrument and for future research directions are given, including linking the measured reflectance anisotropy with physically-based anisotropy models on the one hand and combining them with field goniometry measurements for joint analysis with remote sensing data on the other hand. The speed and flexibility of the system offer a large added value to the existing pool of laboratory goniometers.
A new lab facility for measuring bidirectional reflectance/emittance distribution functions of soils and canopies
Clevers, J.G.P.W. ; Bartholomeus, H. ; Schaepman, M.E. ; Schaepman-Strub, G. ; Jalink, H. ; Schoor, R. van der; Jong, A. de; Uiterwijk, M. - \ 2011
In: Proceedings 7th EARSeL Workshop of the Special Interest Group in Imaging Spectroscopy, Edinburgh, Scotland, UK, 11 - 13 April, 2011. - Edinburgh, UK : EARSeL - p. 10 - 10.
Recently, a laboratory measurement facility has been realized for assessing the anisotropic reflectance and emittance behaviour of soils, leaves and small canopies under controlled illumination conditions. The facility consists of an ASD FieldSpec 3 spectroradiometer covering the spectral range from 350 – 2500 nm at 1 nm spectral sampling interval. The spectroradiometer is deployed using a fiber optic cable with either a 1°, 8° or 25° instantaneous field of view (IFOV). These measurements can be used to assess the plant pigment (chlorophyll, xanthophyll, etc.) and non-pigment system (water, cellulose, lignin, nitrogen, etc.). The thermal emittance is measured using a NEC TH9100 Infrared Thermal Imager. It operates in a single band covering the spectral range from 8 – 14 mm with a resolution of 0.02 K. Images are 320 (H) by 240 (V) pixels with an IFOV of 1.2 mrad. A 1000 W Quartz Tungsten Halogen (QTH) lamp is used as illumination source, approximating the radiance distribution of the sun. This one is put at a fixed position during a measurement session. Multi-angular measurements are achieved by using a robotic positioning system allowing to perform either reflectance or emittance measurements over almost a complete hemisphere. The hemisphere can be sampled continuously between 0° and 80° from nadir and up to a few degrees from the hot-spot configuration (depending on the IFOV of the measurement device) for a backscattering target. Measurement distance to targets can be varied between 0.25 and 1 m, although with a distance of more than 0.6 m it is not possible to cover the full hemisphere. The goal is to infer the BRDF (bidirectional reflectance distribution function) and BTDF (bidirectional thermal distribution function) from these multi-angular measurements for various surface types (like soils, agricultural crops, small tree canopies and artificial objects) and surface roughness. The steering of the robotic arm and the reading of the spectroradiometer and the thermal camera are all fully automated.
The Cooling Capacity of Mosses: Controls on Water and Energy Fluxes in a Siberian Tundra Site
Blok, D. ; Heijmans, M.M.P.D. ; Schaepman-Strub, G. ; Ruijven, J. van; Parmentier, F.J.W. ; Maximov, T.C. ; Berendse, F. - \ 2011
Ecosystems 14 (2011)7. - ISSN 1432-9840 - p. 1055 - 1065.
black spruce ecosystems - arctic tundra - shrub expansion - boreal forest - climate - responses - exchange - carbon - vegetation - permafrost
Arctic tundra vegetation composition is expected to undergo rapid changes during the coming decades because of changes in climate. Higher air temperatures generally favor growth of deciduous shrubs, often at the cost of moss growth. Mosses are considered to be very important to critical tundra ecosystem processes involved in water and energy exchange, but very little empirical data are available. Here, we studied the effect of experimental moss removal on both understory evapotranspiration and ground heat flux in plots with either a thin or a dense low shrub canopy in a tundra site with continuous permafrost in Northeast Siberia. Understory evapotranspiration increased with removal of the green moss layer, suggesting that most of the understory evapotranspiration originated from the organic soil layer underlying the green moss layer. Ground heat flux partitioning also increased with green moss removal indicating the strong insulating effect of moss. No significant effect of shrub canopy density on understory evapotranspiration was measured, but ground heat flux partitioning was reduced by a denser shrub canopy. In summary, our results show that mosses may exert strong controls on understory water and heat fluxes. Changes in moss or shrub cover may have important consequences for summer permafrost thaw and concomitant soil carbon release in Arctic tundra ecosystems. Key words: moss; evaporation; ground heat flux; shrub; permafrost; tundra; Arctic; climate change.
The response of Arctic vegetation to the summer climate: relation between shrub cover, NDVI, surface albedo and temperature
Blok, D. ; Schaepman-Strub, G. ; Bartholomeus, H. ; Heijmans, M.M.P.D. ; Maximov, T.C. ; Berendse, F. - \ 2011
Environmental Research Letters 6 (2011)3. - ISSN 1748-9326 - 9 p.
northern alaska - tundra vegetation - siberian tundra - feedbacks - ecosystems - expansion - exchange - trends - forest - map
Recently observed Arctic greening trends from normalized difference vegetation index (NDVI) data suggest that shrub growth is increasing in response to increasing summer temperature. An increase in shrub cover is expected to decrease summer albedo and thus positively feed back to climate warming. However, it is unknown how albedo and NDVI are affected by shrub cover and inter-annual variations in the summer climate. Here, we examine the relationship between deciduous shrub fractional cover, NDVI and albedo using field data collected at a tundra site in NE Siberia. Field data showed that NDVI increased and albedo decreased with increasing deciduous shrub cover. We then selected four Arctic tundra study areas and compiled annual growing season maximum NDVI and minimum albedo maps from MODIS satellite data (2000–10) and related these satellite products to tundra vegetation types (shrub, graminoid, barren and wetland tundra) and regional summer temperature. We observed that maximum NDVI was greatest in shrub tundra and that inter-annual variation was negatively related to summer minimum albedo but showed no consistent relationship with summer temperature. Shrub tundra showed higher albedo than wetland and barren tundra in all four study areas. These results suggest that a northwards shift of shrub tundra might not lead to a decrease in summer minimum albedo during the snow-free season when replacing wetland tundra. A fully integrative study is however needed to link results from satellite data with in situ observations across the Arctic to test the effect of increasing shrub cover on summer albedo in different tundra vegetation types.
What are the main climate drivers for shrub growth in Northeastern Siberian tundra?
Blok, D. ; Sass-Klaassen, U. ; Schaepman-Strub, G. ; Heijmans, M.M.P.D. ; Sauren, P. ; Berendse, F. - \ 2011
Biogeosciences 8 (2011)5. - ISSN 1726-4170 - p. 1169 - 1179.
plant functional types - alaskan arctic tundra - summer temperature - nitrogen mineralization - tree growth - manipulation experiment - environmental-change - cassiope-tetragona - vegetation types - northern alaska
Deciduous shrubs are expected to rapidly expand in the Arctic during the coming decades due to climate warming. A transition towards more shrub-dominated tundra may have large implications for the regional surface energy balance, permafrost stability and carbon storage capacity, with consequences for the global climate system. However, little information is available on the natural long-term shrub growth response to climatic variability. Our aim was to determine the climate factor and time period that are most important to annual shrub growth in our research site in NE-Siberia. Therefore, we determined annual radial growth rates in Salix pulchra and Betula nana shrubs by measuring ring widths. We constructed shrub ring width chronologies and compared growth rates to regional climate and remotely sensed greenness data. Early summer temperature was the most important factor influencing ring width of S. pulchra (Pearson's r=0.73, p
Vegetation feedbacks to permafrost thaw
Blok, D. ; Heijmans, M.M.P.D. ; Schaepman-Strub, G. ; Berendse, F. - \ 2011
Assessing satellite-derived land product quality for earth system science applications: results from the ceos lpv sub-group
Nightingale, J. ; Schaepman-Strub, G. ; Nickeson, J. ; Baret, F. ; Herold, M. - \ 2010
The value of satellite derived land products for science applications and research is dependent upon the known accuracy of the data. CEOS (Committee on Earth Observation Satellites), the space arm of the Group on Earth Observations (GEO), plays a key role in coordinating the land product validation process. The Land Product Validation (LPV) sub-group of the CEOS Working Group on Calibration and Validation (WGCV) aims to address the challenges associated with the validation of global land products. This paper provides an overview of LPV sub-group focus area activities, which cover seven terrestrial Essential Climate Variables (ECVs). The contribution will enhance coordination of the scientific needs of the Earth system communities with global LPV activities.
Spectral estimation of soil properties in the organic layer of tundra soils
Bartholomeus, H. ; Schaepman-Strub, G. ; Blok, D. ; Udalsov, S. ; Sofronov, R. - \ 2010
How does shrub growth relate to local climate and what are potential effects of shrub expansion on permafrost thawing?
Blok, D. ; Schaepman-Strub, G. ; Heijmans, M.M.P.D. ; Sass-Klaassen, U. ; Bartholomeus, H. ; Berendse, F. - \ 2010
Spectral estimation of soil properties in the organic layer of tundra soils
Bartholomeus, H. ; Schaepman-Strub, G. ; Blok, D. ; Udaltsov, S. ; Sofronov, R. - \ 2010
Scaling spectroscopic approaches – from leaf albedo to ecosystems mapping
Schaepman, M.E. ; Kneubühler, M. ; Bartholomeus, H. ; Malenovsky, Z. ; Damm, A. ; Schaepman-Strub, G. ; Hueni, A. - \ 2010
Estimation and extrapolation of soil properties in the Siberian tundra, using field spectroscopy
Bartholomeus, H. ; Schaepman-Strub, G. ; Blok, D. ; Udaltsov, S. ; Sofronov, R. - \ 2010
The Siberian tundra is a complex and sensitive ecosystem. Predicted global warming will be highest in the Arctic and will severely affect permafrost environments. Due to its large spatial extent and large stocks of soil organic carbon, changes to the carbon fluxes in the Arctic will have significant impact on the global carbon cycle. Increased soil temperature, active layer thickness and primary production will cause changes in carbon dioxide and methane fluxes, as well as particulate and dissolved carbon in the rivers discharging into the Arctic Ocean, but this is highly related to changes in permafrost, vegetation development and hydrological conditions. The present soil properties (e.g., organic and inorganic carbon, nutrients, and mineral composition) are an important factor for potential medium-term vegetation development. Because of the difficult access to the Arctic area and the high costs for chemical analysis of soil samples, we investigated the possibilities to use field spectroscopy for a fast assessment of the major soil properties. During a summer 2008 field campaign, soil samples at different levels within the soil core, including frozen parts, vegetation species and cover descriptions were collected, and spectral reflectance measurements (ASD Fieldspec) were made. First, soil properties as derived from a subset of the samples in the laboratory were related to the spectral reflectance properties using partial least squares regression. Reliable soil model calibrations are found for C and K, while moderately accurate models could be constructed for pH and N. Using these models, the soil properties are estimated for a large number of samples, resulting in a dataset that was used to analyze the relation of top soil properties with organic carbon decomposition and vegetation species composition. The established functions of vegetation species composition with top soil properties might be used to extrapolate top soil properties across a larger area. This extrapolation method based on vegetation proxies can account for the small scale hydrological heterogeneity that is typical of Arctic lowlands.
Shrub expansion may reduce summer permafrost thaw in Siberian tundra
Blok, D. ; Heijmans, M.M.P.D. ; Schaepman-Strub, G. ; Kononov, A.V. ; Maximov, T.C. ; Berendse, F. - \ 2010
Global Change Biology 16 (2010)4. - ISSN 1354-1013 - p. 1296 - 1305.
alaskan tussock tundra - litter decomposition rates - arctic tundra - climate-change - northern alaska - boreal forest - energy-exchange - soil-thaw - vegetation - responses
Climate change is expected to cause extensive vegetation changes in the Arctic: deciduous shrubs are already expanding, in response to climate warming. The results from transect studies suggest that increasing shrub cover will impact significantly on the surface energy balance. However, little is known about the direct effects of shrub cover on permafrost thaw during summer. We experimentally quantified the influence of Betula nana cover on permafrost thaw in a moist tundra site in northeast Siberia with continuous permafrost. We measured the thaw depth of the soil, also called the active layer thickness (ALT), ground heat flux and net radiation in 10 m diameter plots with natural B. nana cover (control plots) and in plots in which B. nana was removed (removal plots). Removal of B. nana increased ALT by 9% on average late in the growing season, compared with control plots. Differences in ALT correlated well with differences in ground heat flux between the control plots and B. nana removal plots. In the undisturbed control plots, we found an inverse correlation between B. nana cover and late growing season ALT. These results suggest that the expected expansion of deciduous shrubs in the Arctic region, triggered by climate warming, may reduce summer permafrost thaw. Increased shrub growth may thus partially offset further permafrost degradation by future temperature increases. Permafrost models need to include a dynamic vegetation component to accurately predict future permafrost thaw
Radiometry and Reflectance: From Terminology Concepts to Measured Quantities
Schaepman-Strub, G. ; Schaepman, M.E. ; Martonchik, J.V. ; Painter, T.H. ; Dangel, S. - \ 2009
In: The SAGE Handbook of Remote Sensing / Warner, T.A., Duane Nellis, M., Foody, G., London UK : Sage - ISBN 9781412936163 - p. 215 - 228.
Towards spatial assessment of carbon sequestration in peatlands: spectroscopy based estimation of fractional cover of three plant functional types
Schaepman-Strub, G. ; Limpens, J. ; Menken, M. ; Bartholomeus, H. ; Schaepman, M.E. - \ 2009
Biogeosciences 6 (2009)2. - ISSN 1726-4170 - p. 275 - 284.
spectral reflectance measurements - growth forms - vegetation - sphagnum - leaf - boreal - bog - accumulation - stress
Peatlands accumulated large carbon (C) stocks as peat in historical times. Currently however, many peatlands are on the verge of becoming sources with their C sequestration function becoming sensitive to environmental changes such as increases in temperature, decreasing water table and enhanced nitrogen deposition. Long term changes in vegetation composition are both, a consequence and indicator of future changes in C sequestration. Spatial continuous accurate assessment of the vegetation composition is a current challenge in keeping a close watch on peatland vegetation changes. In this study we quantified the fractional cover of three major plant functional types (PFTs; Sphagnum mosses, graminoids, and ericoid shrubs) in peatlands, using field spectroscopy reflectance measurements (400-2400 nm) on 25 plots differing in PFT cover. The data was validated using point intercept methodology on the same plots. Our results showed that the detection of open Sphagnum versus Sphagnum covered by vascular plants (shrubs and graminoids) is feasible with an R-2 of 0.81. On the other hand, the partitioning of the vascular plant fraction into shrubs and graminoids revealed lower correlations of R-2 of 0.54 and 0.57, respectively. This study was based on a dataset where the reflectance of all main PFTs and their pure components within the peatland was measured at local spatial scales. Spectrally measured species or plant community abundances can further be used to bridge scaling gaps up to canopy scale, ultimately allowing upscaling of the C balance of peatlands to the ecosystem level.
Peatlands and the carbon cycle: from local processes to global implications - a synthesis
Limpens, J. ; Berendse, F. ; Blodau, C. ; Canadell, J.G. ; Freeman, C. ; Holden, J. ; Roulet, N. ; Rydin, H. ; Schaepman-Strub, G. - \ 2008
Biogeosciences 5 (2008). - ISSN 1726-4170 - p. 1475 - 1491.
dissolved organic-carbon - modern methane emissions - northern peatland - interannual variability - ombrotrophic bog - phenol oxidase - blanket peat - elevated co2 - increased n - long-term
Peatlands cover only 3% of the Earth's land surface but boreal and subarctic peatlands store about 15-30% of the world's soil carbon ( C) as peat. Despite their potential for large positive feedbacks to the climate system through sequestration and emission of greenhouse gases, peatlands are not explicitly included in global climate models and therefore in predictions of future climate change. In April 2007 a symposium was held in Wageningen, the Netherlands, to advance our understanding of peatland C cycling. This paper synthesizes the main findings of the symposium, focusing on (i) small-scale processes, (ii) C fluxes at the landscape scale, and (iii) peatlands in the context of climate change. The main drivers controlling most are related to some aspects of hydrology. Despite high spatial and annual variability in Net Ecosystem Exchange ( NEE), the differences in cumulative annual NEE are more a function of broad scale geographic location and physical setting than internal factors, suggesting the existence of strong feedbacks. In contrast, trace gas emissions seem mainly controlled by local factors. Key uncertainties remain concerning the existence of perturbation thresholds, the relative strengths of the CO2 and CH4 feedback, the links among peatland surface climate, hydrology, ecosystem structure and function, and trace gas biogeochemistry as well as the similarity of process rates across peatland types and climatic zones. Progress on these research areas can only be realized by stronger co-operation between disciplines that address different spatial and temporal scales.
Land surface albedo in Northern high latitudes - MODIS satellite-inferred albedo trends for a NE Siberian tundra area
Schaepman-Strub, G. ; Claverie, M. ; Schaepman, M.E. - \ 2008
Peatlands and the carbon cycle: From local processes to global implications - a synthesis
Limpens, J. ; Berendse, F. ; Blodau, C. ; Canadell, J.G. ; Freeman, C. ; Holden, J. ; Roulet, N. ; Rydin, H. ; Schaepman-Strub, G. - \ 2008
Biogeosciences Discussions 5 (2008). - ISSN 1810-6277 - p. 1379 - 1419.
Although peatlands cover only 3% of the Earth's land surface, boreal and subarctic peatlands store about 15¿30% of the world's soil carbon as peat. Despite their potential for large positive feedbacks to the climate system through sequestration and emission of greenhouse gases, peatlands are not explicitly included in global climate models and therefore in predictions of future climate change. In April 2007 a symposium was held in Wageningen, the Netherlands, to advance our understanding of peatland C cycling through integration across disciplines and research approaches and to develop a more synthetic picture of the present and future role of peatlands in the global C cycle and their interactions with the climate system. This paper aims to synthesize the main findings of the symposium, focusing on (i) small-scale processes, (ii) C fluxes at the landscape scale, and (iii) peatlands and climate. The paper concludes with a summary of the main drivers of the C balance of peatlands, and proposes directions for new research to reduce key uncertainties in our knowledge of C cycling in peatlands in order to facilitate the explicit inclusion of these ecosystems in a new generation of earth system models.
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