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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Modelling the combined effect of moisture and temperature on secondary infection in a coupled host-pathogen FSPM
    Streit, Katarina ; Evers, Jochem B. ; Renton, Michael - \ 2019
    In: Proceedings - 2018 6th International Symposium on Plant Growth Modeling, Simulation, Visualization and Applications, PMA 2018. - Institute of Electrical and Electronics Engineers Inc. - ISBN 9781538678152 - p. 61 - 68.
    disease modelling - functional-structural plant modelling - leaf wetness duration - moisture - tan spot - temperature - yellow spot

    Weather conditions are an important driver of disease development. For example for yellow spot in wheat, warm and moist conditions favour secondary infection. Although the relationship between environment and disease development is the basis of many epidemiological models, changes in plant architecture and growth have an effect on disease progress and severity as well. Functional-structural plant models (FSPMs) are well suited to study the interactions between pathogen, climatic conditions and growing host crop. In this study we focused on simulating the effect of weather conditions on the progression of secondary infection in yellow spot and the interaction with growing wheat canopy. Simulations were performed using a coupled host-pathogen FSPM with standard meteorological data input. The model develops on previous coupled host-pathogen FSPMs by combining response functions to temperature and wetness duration and calculating the hourly progression of secondary infection. The simulated diseased area differed with different combinations of temperature and moisture response models. Changes in dispersal pattern were observed mainly in relation to spore release rate.

    Voorkomen vochtschokken beste remedie om bladrandjes te vermijden
    Voogt, Wim - \ 2016
    horticulture - greenhouse horticulture - vegetables - tomatoes - plant disorders - calcium absorption - nutrient accounting system - chlorine - iron - climatic factors - illumination - nutrient solutions - moisture - agricultural research
    Effect of temperature on biomass allocation in seedlings of two contrasting genotypes of the oilseed crop Ricinus communis
    Ribeiro de Jesus, P.R. ; Zanotti, R.F. ; Deflers, C. ; Fernandez, L.G. ; Castro, R.D. De; Ligterink, W. ; Hilhorst, H.W.M. - \ 2015
    Journal of Plant Physiology 185 (2015). - ISSN 0176-1617 - p. 31 - 39.
    abiotic stress tolerance - plant-responses - heat-stress - castor-oil - acid gaba - growth - metabolomics - arabidopsis - pathways - moisture
    Ricinus communis is becoming an important crop for oil production, and studying the physiological and biochemical aspects of seedling development may aid in the improvement of crop quality and yield. The objective of this study was to assess the effect of temperature on biomass allocation in two R. communis genotypes. Biomass allocation was assessed by measuring dry weight of roots, stems, and cotyledons of seedlings grown at three different temperatures. Root length of each seedling was measured. Biomass allocation was strongly affected by temperature. Seedlings grown at 25 ¿C and 35 ¿C showed greater biomass than seedlings grown at 20 ¿C. Cotyledon and stem dry weight increased for both genotypes with increasing temperature, whereas root biomass allocation showed a genotype-dependent behavior. Genotype MPA11 showed a continuous increase in root dry weight with increasing temperature, while genotype IAC80 was not able to sustain further root growth at higher temperatures. Based on metabolite and gene expression profiles, genotype MPA11 increases its level of osmoprotectant molecules and transcripts of genes encoding for antioxidant enzymes and heat shock proteins to a higher extent than genotype IAC80. This might be causal for the ability to maintain homeostasis and support root growth at elevated temperatures in genotype MPA11.
    Remote sensing of epibenhtic shellfish using synthetic aperture radar satellite imagery
    Nieuwhof, S. ; Herman, P.M.J. ; Dankers, N.M.J.A. ; Troost, K. ; Wal, D. van der - \ 2015
    Remote Sensing 7 (2015)4. - ISSN 2072-4292 - p. 3710 - 3734.
    bare soil surfaces - mussel beds - wadden sea - ecosystem engineers - intertidal flats - tidal flats - sar data - roughness - classification - moisture
    On intertidal mudflats, reef-building shellfish, like the Pacific oyster and the blue mussel, provide a myriad of ecosystem services. Monitoring intertidal shellfish with high spatiotemporal resolution is important for fisheries, coastal management and ecosystem studies. Here, we explore the potential of X- (TerraSAR-X) and C-band (Radarsat-2) dual-polarized SAR data to map shellfish densities, species and coverage. We investigated two backscatter models (the integral equation model (IEM) and Oh’s model) for inversion possibilities. Surface roughness (vertical roughness RMSz and correlation length L) was measured of bare sediments and shellfish beds, which was then linked to shellfish density, presence and species. Oysters, mussels and bare sediments differed in RMSz, but because the backscatter saturates at relatively low RMSz values, it was not possible to retrieve shellfish density or species composition from X- and C-band SAR. Using a classification based on univariate and multivariate logistic regression of the field and SAR image data, we constructed maps of shellfish presence (Kappa statistics for calibration 0.56–0.74 for dual-polarized SAR), which were compared with independent field surveys of the contours of the beds (Kappa statistics of agreement 0.29–0.53 when using dual-polarized SAR). We conclude that spaceborne SAR allows one to monitor the contours of shellfish-beds (thus, distinguishing shellfish substrates from bare sediment and dispersed single shellfish), but not densities and species. Although spaceborne SAR cannot replace ground surveys entirely, it could very well offer a significant improvement in efficiency.
    Glastuinbouw waterproof grondgebonden : stand van zaken lysimeter en vochtsensoren
    Voogt, Wim - \ 2014
    greenhouse horticulture - cropping systems - lysimeters - moisture - moisture meters - air conditioning - greenhouse soils - greenhouse experiments - tomatoes - chrysanthemum
    Lupine and rapeseed protein concentrate in fish feed: a comparative assessment of the techno-functional properties using a shear cell device and an extruder
    Draganovic, V. ; Boom, R.M. ; Jonkers, J. ; Goot, A.J. van der - \ 2014
    Journal of Food Engineering 126 (2014). - ISSN 0260-8774 - p. 178 - 189.
    trout oncorhynchus-mykiss - rainbow-trout - wheat gluten - glass-transition - kernel meal - starch - extrusion - products - moisture - quality
    The techno-functional properties of soy, lupine and rapeseed protein concentrates (SPC, LPC and RPC, respectively) in fish feed were evaluated relative to fish meal (FM). The effects were studied using a shear cell device and an extruder with emphasis on the added moisture content. Six diets were formulated: an SPC-based diet with 300 g SPC kg-1, diets containing 100 and 200 g LPC kg-1 or 100 and 200 g RPC kg-1 and an FM-based diet with 450 g FM kg-1. Each diet was extruded with an added moisture content of 29%, 25% and 22% of the mash feed rate. It was found that the technological properties of LPC closely resemble FM, being high solubility, low water-holding capacity (WHC) and low paste viscosity. The LPC 100 and 200 g kg-1 diets could be extruded at 22% moisture, which gives an extrudate with reduced drying requirements. In addition, less specific mechanical energy was needed for extrusion. In contrast, both SPC and RPC have high WHC and paste viscosity. This explains the higher feed moisture required during extrusion. The properties of the feeds containing RPC could be well within the ranges acceptable for commercial fish feed use at even higher moisture content compared with SPC. The results of the extrusion trials confirmed the observations made from the shear cell device. Thus, the shear cell device can be used to study processing conditions that are close to extrusion conditions.
    Oven-drying reduces ruminal starch degradation in maize kernels
    Ali, M. ; Cone, J.W. ; Hendriks, W.H. ; Struik, P.C. - \ 2014
    Animal Feed Science and Technology 193 (2014). - ISSN 0377-8401 - p. 44 - 50.
    physicochemical properties - microwave irradiation - gas-production - rumen fluid - corn-silage - digestibility - grain - degradability - moisture - protein
    The degradation of starch largely determines the feeding value of maize (Zea mays L.) for dairy cows. Normally, maize kernels are dried and ground before chemical analysis and determining degradation characteristics, whereas cows eat and digest fresh material. Drying the moist maize kernels (consisting mainly of starch) at high temperatures can influence their physical properties and thus their degradation dynamics in the rumen. We compared the in vitro degradability of dried maize kernels with that of fresh kernels after incubation in rumen fluid. Maize kernels were obtained from genotypes diverse in starch structure, composition and type of endosperm. These genotypes were grown in greenhouses at different temperatures during starch accumulation, and harvested at different maturity stages, in two experiments. Starch content was assessed using the amyloglucosidase method. Fermentation in rumen fluid was measured using an in vitro gas production technique. Starch degradation of the kernels was calculated after 6, 12 and 20 h of incubation in rumen fluid. Oven-drying influenced (P <0.0001) the in vitro degradation of starch in maize kernels at the different incubation times, with more starch being degraded in the fresh than in the oven-dried maize kernels, although the differences were small (11–15%). There was a consistent interaction (P <0.009 to 0.0002) between oven-drying and genotype, with the high-amylose genotype showing larger effects of oven-drying than the other genotypes. The vitreous genotype showed a lower starch degradation than the non-vitreous type. At earlier maturity stages, the difference between oven-dried and fresh kernels was larger than at later maturity stages. The temperature during grain filling affected (P <0.0001) starch degradation but did not affect the difference between fresh and oven-dried samples. Oven-drying reduced the in vitro rumen starch degradation of maize kernels regardless of growing conditions, genotype and maturity stage, but its effect depends on genotype and maturity.
    Mega-heatwave temperatures due to combined soil desiccation and atmospheric heat accumulation
    Miralles, D. ; Teuling, A.J. ; Heerwaarden, C.C. van; Vilà-Guerau de Arellano, J. - \ 2014
    Nature Geoscience 7 (2014). - ISSN 1752-0894 - p. 345 - 349.
    boundary-layer - land-surface - summer - europe - evaporation - extremes - moisture - impact - wave
    The recent European mega-heatwaves of 2003 and 2010 broke temperature records across Europe1, 2, 3, 4, 5. Although events of this magnitude were unprecedented from a historical perspective, they are expected to become common by the end of the century6, 7. However, our understanding of extreme heatwave events is limited and their representation in climate models remains imperfect8. Here we investigate the physical processes underlying recent mega-heatwaves using satellite and balloon measurements of land and atmospheric conditions from the summers of 2003 in France and 2010 in Russia, in combination with a soil–water–atmosphere model. We find that, in both events, persistent atmospheric pressure patterns induced land–atmosphere feedbacks that led to extreme temperatures. During daytime, heat was supplied by large-scale horizontal advection, warming of an increasingly desiccated land surface and enhanced entrainment of warm air into the atmospheric boundary layer. Overnight, the heat generated during the day was preserved in an anomalous kilometres-deep atmospheric layer located several hundred metres above the surface, available to re-enter the atmospheric boundary layer during the next diurnal cycle. This resulted in a progressive accumulation of heat over several days, which enhanced soil desiccation and led to further escalation in air temperatures. Our findings suggest that the extreme temperatures in mega-heatwaves can be explained by the combined multi-day memory of the land surface and the atmospheric boundary layer
    Mapping a priori defined plant associations using remotely sensed vegetation characteristics
    Roelofsen, H.D. ; Kooistra, L. ; Bodegom, P.M. van; Verrelst, J. ; Krol, J. ; Witte, J.M.P. - \ 2014
    Remote Sensing of Environment 140 (2014). - ISSN 0034-4257 - p. 639 - 651.
    ellenberg indicator values - continuous floristic gradients - hyperspectral imagery - imaging spectroscopy - endmember selection - tropical forests - aviris data - classification - regression - moisture
    Incorporation of a priori defined plant associations into remote sensing products is a major challenge that has only recently been confronted by the remote sensing community. We present an approach to map the spatial distribution of such associations by using plant indicator values (IVs) for salinity, moisture and nutrients as an intermediate between spectral reflectance and association occurrences. For a 12 km2 study site in the Netherlands, the relations between observed IVs at local vegetation plots and visible and near-infrared (VNIR) and short-wave infrared (SWIR) airborne reflectance data were modelled using Gaussian Process Regression (GPR) (R2 0.73, 0.64 and 0.76 for salinity, moisture and nutrients, respectively). These relations were applied to map IVs for the complete study site. Association occurrence probabilities were modelled as function of IVs using a large database of vegetation plots with known association and IVs. Using the mapped IVs, we calculated occurrence probabilities of 19 associations for each pixel, resulting in both a crisp association map with the most likely occurring association per pixel, as well as occurrence probability maps per association. Association occurrence predictions were assessed by a local vegetation expert, which revealed that the occurrences of associations situated at frequently predicted indicator value combinations were over predicted. This seems primarily due to biases in the GPR predicted IVs, resulting in associations with envelopes located in extreme ends of IVs being scarcely predicted. Although the results of this particular study were not fully satisfactory, the method potentially offers several advantages compared to current vegetation classification techniques, like site-independent calibration of association probabilities, site-independent selection of associations and the provision of IV maps and occurrence probabilities per association. If the prediction of IVs can be improved, this method may thus provide a viable roadmap to bring a priori defined plant associations into the domain of remote sensing.
    Comparison of Soil Respiration in Typical Conventional and New Alternative Cereal Cropping Systems on the North China Plain
    Gao, B. ; Ju, X.T. ; Su, F. ; Gao, F.B. ; Cao, Q.S. ; Oenema, O. ; Christie, P. ; Chen, X.P. ; Zhang, F.S. - \ 2013
    PLoS ONE 8 (2013)11. - ISSN 1932-6203
    carbon-dioxide - water-content - temperature - nitrogen - dependence - ecosystem - tillage - forest - management - moisture
    We monitored soil respiration (Rs), soil temperature (T) and volumetric water content (VWC%) over four years in one typical conventional and four alternative cropping systems to understand Rs in different cropping systems with their respective management practices and environmental conditions. The control was conventional double-cropping system (winter wheat and summer maize in one year - Con. W/M). Four alternative cropping systems were designed with optimum water and N management, i.e. optimized winter wheat and summer maize (Opt. W/M), three harvests every two years (first year, winter wheat and summer maize or soybean; second year, fallow then spring maize - W/M-M and W/S-M), and single spring maize per year (M). Our results show that Rs responded mainly to the seasonal variation in T but was also greatly affected by straw return, root growth and soil moisture changes under different cropping systems. The mean seasonal CO2 emissions in Con. W/M were 16.8 and 15.1 Mg CO2 ha(-1) for summer maize and winter wheat, respectively, without straw return. They increased significantly by 26 and 35% in Opt. W/M, respectively, with straw return. Under the new alternative cropping systems with straw return, W/M-M showed similar Rs to Opt. W/M, but total CO2 emissions of W/S-M decreased sharply relative to Opt. W/M when soybean was planted to replace summer maize. Total CO2 emissions expressed as the complete rotation cycles of W/S-M, Con. W/M and M treatments were not significantly different. Seasonal CO2 emissions were significantly correlated with the sum of carbon inputs of straw return from the previous season and the aboveground biomass in the current season, which explained 60% of seasonal CO2 emissions. T and VWC% explained up to 65% of Rs using the exponential-power and double exponential models, and the impacts of tillage and straw return must therefore be considered for accurate modeling of Rs in this geographical region.
    Beheersing Botrytis in Cyclaam
    Vries, Rozemarijn de - \ 2013
    ornamental plants - cyclamen - botrytis - plant pathogenic fungi - cropping systems - moisture - fertilizer application - infection - trials
    Satellite based radar interferometry to estimate large-scale soil water depletion from clay shrinkage: possibilities and limitations
    Brake, B. te; Hanssen, R.F. ; Ploeg, M.J. van der; Rooij, G.H. de - \ 2013
    Vadose Zone Journal 12 (2013)3. - ISSN 1539-1663 - 13 p.
    synthetic-aperture radar - sar interferometry - land subsidence - texas vertisols - earths surface - level changes - moisture - volume - insar - field
    Satellite-based radar interferometry is a technique capable of measuring small surface elevation changes at large scales and with a high resolution. In vadose zone hydrology, it has been recognized for a long time that surface elevation changes due to swell and shrinkage of clayey soils can serve as an estimate for soil water storage change. Therefore, satellite-based radar interferometry can potentially offer an alternative methodology to estimate soil water storage change at field or regional scales. This paper introduces principles of satellite-based radar interferometry and identifies limitations and potential applications of the technique to measure surface elevation changes from clay shrinkage. In situ measurements were performed and a linear relation between soil water storage depletion and layer shrinkage was obtained. Data from the TerraSAR-X satellite over the measurement area were analyzed to identify the most favorable conditions for radar interferometry to measure vertical shrinkage. High-quality phase observations over clayey areas in polders with limited vegetation can be explained from differences in land use and soil type. Signal noise over sparsely vegetated agricultural fields was successfully reduced by multilooking over agricultural fields at the cost of spatial resolution. Good resemblance between in situ measured shrinkage and differential phase change was found in a test period. Based on this study, we expect that radar interferometric processing of data from the future satellite mission Sentinel-1 can play a crucial role in providing much-needed observations of vadose zone processes at the field scale and beyond.
    Met goede hygiëne en vochtbeheersing Erwinia in paprika te lijf (onderzoek van Jantineke Hofland-Zijlstra en Rozemarijn de Vries)
    Arkesteijn, M. ; Hofland-Zijlstra, J.D. ; Vries, R.S.M. de - \ 2012
    Onder Glas 9 (2012)12. - p. 44 - 45.
    capsicum - plantenplagen - erwinia - vruchtrot - plantenziekten - gewasbescherming - bedrijfshygiëne - vocht - glastuinbouw - groenten - capsicum - plant pests - erwinia - fruit rots - plant diseases - plant protection - industrial hygiene - moisture - greenhouse horticulture - vegetables
    Zomer 2010 had een groot aantal paprikabedrijven verspreid over het hele land last van Erwinia vruchtrot. Waar komt Erwinia vandaan en wat is er tegen te doen? Met deze vragen gingen onderzoekers Jantineke Hofland- Zijlstra en Rozemarijn de Vries aan de slag. Hygiëne, een goede vochtbeheersing en mogelijk antagonisten inzetten zijn de antwoorden die ze vonden op deze vragen.
    Satellite-based herbicide rate recommendation for potato haulm killing
    Evert, F.K. van; Voet, P. van der; Valkengoed, E. van; Kooistra, L. ; Kempenaar, C. - \ 2012
    European Journal of Agronomy 43 (2012). - ISSN 1161-0301 - p. 49 - 57.
    nitrogen application - moisture - wheat - crop
    When using variable-rate application (VRA), tractor-mounted sensors are typically used to measure crop status. Crop status can also be measured with a satellite-based sensor. In both cases a vegetation index derived from the sensor measurements is used as an indicator of the amount of crop biomass. The first objective of this study was to establish a relationship between the Weighted Difference Vegetation Index (WDVI) in potato as measured with a nearby, ground-based crop reflectance meter on the one hand and WDVI as measured with remote, satellite-based sensors on the other hand. It was found that groundbased WDVI and satellite-based WDVI are strongly and linearly related, thus making it feasible to calculate herbicide rates for potato haulm killing on the basis of satellite-based measurements. The scale at which VRA is applied is an important determinant of the reduction in input use. The second objective was to estimate the potential to reduce herbicide use for potato haulm killing as a function of the size of decision units, using the above-mentioned relationship, satellite imagery of 13 potato fields and a previously developed decision rule for herbicide rate. It was found that when the size of the decision unit was 15 m × 15 m (the size of an ASTER pixel), a reduction in herbicide use of at least 50% would be achieved in one out of every two of the fields, and a reduction of at least 33% would be achieved in all fields. When the size of the decision unit was 30 m × 30 m, a reduction of at least 33% would be achieved in one out of every two of the fields. In conclusion, satellite-based crop reflectance measurements can be used instead of ground-based measurements for determining herbicide rate for potato haulm killing. When the size of the decision unit is not larger than 30 m ×30 m, a 50% reduction in herbicide use for potato haulm killing can be achieved with VRA
    Some observational evidence for dry soils supporting enhanced relative humidity at the convective boundary layer top
    Westra, D. ; Steeneveld, G.J. ; Holtslag, A.A.M. - \ 2012
    Journal of Hydrometeorology 13 (2012). - ISSN 1525-755X - p. 1347 - 1358.
    diurnal time scales - land-surface - cumulus onset - vertical diffusion - model - precipitation - entrainment - prediction - moisture - column
    The tendency of the relative humidity at the top of a clear convective boundary layer (RHtop) is studied as an indicator of cloud formation is studied over a semi-arid region within the conceptual framework introduced by Ek and Holtslag (2004). Typically the tendency of RHtop increases if the evaporative fraction at the land surface increases, which supports boundary layer moistening but only when boundary-layer growth is limited by atmospheric factors. This regime was supported by Cabauw observations in the original study. Here we provide new observational evidence that the tendency of RHtop can also increase as the surface becomes more dry as is consistent with another regime of the conceptual framework. The observations used are from the AMMA intensive observational campaign near Niamey, Niger, June 20-25, 2006. In addition, we evaluate whether various versions of the WRF single-column model confirm the different regimes of the conceptual framework for a typical day in the AMMA campaign. It appears that the model confirms that dryer soils can support cloud formation.
    Jantineke Hofland-Zijlstra: "We moeten de plant opnieuw leren begrijpen" : Vochtbeheersing bij Het Nieuwe Telen helpt tegen Botrytis (interview met Jantineke Hofland-Zijlstra)
    Arkesteijn, M. ; Hofland-Zijlstra, J.D. - \ 2012
    Onder Glas 9 (2012)3. - p. 66 - 67.
    glastuinbouw - teelt onder bescherming - teeltsystemen - schimmelziekten - vocht - klimaatregeling - milieubeheersing - botrytis - fytosanitaire maatregelen - greenhouse horticulture - protected cultivation - cropping systems - fungal diseases - moisture - air conditioning - environmental control - botrytis - phytosanitary measures
    Het Nieuwe Telen is ontwikkeld om energie te besparen. Deze manier van telen verandert het teeltklimaat én daardoor zijn er meer mogelijkheden om te sturen. Dit heeft gevolgen voor de plant en de ziekteverwekkers. Jantineke Hofland- Zijlstra van Wageningen UR Glastuinbouw neemt drie belangrijke met vocht gerelateerde schimmels onder de loep: Botrytis, meeldauw en Mycosphaerella.
    Voordelen Het Nieuwe Telen wegen nog onvoldoende op tegen investeringen: Meer kwaliteitsverbetering nodig en minder slappe stelen (interview met Hans Kok)
    Stijger, H. ; Kok, B.J. - \ 2012
    Onder Glas 9 (2012)3. - p. 62 - 63.
    glastuinbouw - teelt onder bescherming - cultuurmethoden - klimaatregeling - gewaskwaliteit - besluitvorming - doelstellingen - agrarische bedrijfsvoering - proeven - vocht - lelies - snijbloemen - greenhouse horticulture - protected cultivation - cultural methods - air conditioning - crop quality - decision making - objectives - farm management - trials - moisture - lilies - cut flowers
    Bij Imanse Quality Lillies liep deze winter de tweede proef met Het Nieuwe Telen Lelie. Aanleiding voor deze proeven zijn de vochtproblemen in de winter, die tot gebreksverschijnselen kunnen leiden. Uitgangspunt van het onderzoek is om zonder kwaliteitsverlies een hogere plantdichtheid aan te kunnen houden.
    Process-based proxy of oxygen stress surpasses indirect ones in predicting vegetation characteristics
    Bartholomeus, R.P. ; Witte, J.P.M. ; Bodegom, P.M. van; Dam, J.C. van; Becker de, P. ; Aerts, R. - \ 2012
    Ecohydrology 5 (2012)6. - ISSN 1936-0584 - p. 746 - 758.
    vegetatietypen - ecohydrologie - klimaatverandering - vegetation types - ecohydrology - climatic change - ellenberg indicator values - climate-change - hydraulic conductivity - species richness - soil-conditions - plant-roots - moisture - temperature - models - growth
    Robust relationships among soil, water, atmosphere and plants are needed to reliably forecast the plant species composition. In this paper, we show the need for, and the application of, a process-based relationship between soil moisture conditions and vegetation characteristics. We considered 366 groundwater-dependent sites, where oxygen stress, caused by a surplus of soil moisture, codetermines plant performance. We compared two existing indirect proxies for the soil oxygen status – namely mean spring groundwater level (MSL) and sum exceedence value (SEV) – with our newly developed process-based proxy, viz. root respiration stress (RS). The two indirect proxies and the process-based proxy for oxygen stress performed equally well in describing vegetation characteristics for the Netherlands under the current climate. However, relationships based on MSL and SEV appeared to produce systematic prediction errors when applied outside their calibration range, in contrast to the relationship based on RS. Hence, the two indirect proxies cannot be used in projections, such as in predicting effects of climate change on vegetation composition, all the more because they – unlike RS – do not account for essential parameters that determine oxygen stress (e.g. temperature and extreme rainfall events in the growing season). We advocate using RS for estimating vegetation impacts in climate projections to increase the reliability and effectiveness of adaptive strategies
    Relative Greenness Index for assessing curing of grassland fuel
    Newnham, G.J. ; Verbesselt, J. ; Grant, I.F. ; Anderson, S.A.J. - \ 2011
    Remote Sensing of Environment 115 (2011)6. - ISSN 0034-4257 - p. 1456 - 1463.
    ndvi time-series - vegetation index - avhrr data - modis data - bidirectional reflectance - fire - moisture - models - derivation - australia
    Knowledge of the proportion of live and dead herbaceous fuel in grasslands is important in determining fire danger. This paper examines the Relative Greenness approach for quantifying these live and dead proportions. Relative Greenness places the Normalized Difference Vegetation Index (NDVI) in the context of a time series of measurements. The parameters used to describe the temporal distribution of NDVI and the time interval over which this distribution is assessed impact Relative Greenness and the inferred characteristics of the vegetation. In this paper, the Relative Greenness approach was investigated using different NDVI distribution parameters derived from eight-day composites of surface reflectance from the Moderate Resolution Imaging Spectroradiometer (MODIS). We assessed the accuracy of Relative Greenness for predicting the degree of curing (equivalent to the dead proportion of herbaceous fuel) measured at 25 grassland sites in Australia from 2005 to 2009. Results showed that Relative Greenness explained a greater proportion of the variance and provided a more accurate estimate of the degree of curing than linear regression against NDVI Relative Greenness was further improved using alternative parameters of the NDVI distribution and by selecting an appropriate time interval over which this distribution was assessed.
    Natural and fire-induced soil water repellency in a Portugese Shrubland
    Stoof, C.R. ; Moore, D. ; Ritsema, C.J. ; Dekker, L.W. - \ 2011
    Soil Science Society of America Journal 75 (2011)6. - ISSN 0361-5995 - p. 2283 - 2295.
    coarse-textured soils - forest soils - pine forests - hydrological behavior - eucalyptus-globulus - spatial variability - prescribed fire - sandy soil - hydrophobicity - moisture
    Post-fire land degradation is often attributed to fire-induced soil water repellency, despite the fact that soil water repellency is a natural phenomenon in many soils and is therefore not necessarily caused by fire. To improve our understanding of the role of soil water repellency in causing fire-induced land degradation, a long-term monitoring study was performed in which the temporal variation of topsoil water repellency (0–2.5-cm depth) was captured in a Portuguese shrubland before and after fire between November 2007 and March 2010. In addition, similarities and dissimilarities between changes following burning and clipping were assessed in a plot experiment. Soil water repellency appeared to be the rule rather than the exception, both before and after fire, and was strongly related to soil moisture and organic matter content. Surprisingly, despite the low soil temperatures during the fire (60°C) and the lack of direct soil moisture changes, fire significantly increased the persistence of soil water repellency (the water drop penetration time). Vegetation removal by burning and clipping played a key role in determining post-fire water repellency in litter and at the soil surface and considerably reduced the time needed to both develop and eliminate water repellency of the litter and surface soil. Where pre-fire (or “natural”) soil water repellency is abundant, an increase in erosion after fire cannot be solely caused by soil water repellency. Nevertheless, fire-induced removal of the protective canopy cover may increase the hydrologic significance of soil water repellency in burned landscapes
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