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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    Environmental drivers of Sphagnum growth in peatlands across the Holarctic region
    Bengtsson, Fia ; Rydin, Håkan ; Baltzer, Jennifer L. ; Bragazza, Luca ; Bu, Zhao Jun ; Caporn, Simon J.M. ; Dorrepaal, Ellen ; Flatberg, Kjell Ivar ; Galanina, Olga ; Gałka, Mariusz ; Ganeva, Anna ; Goia, Irina ; Goncharova, Nadezhda ; Hájek, Michal ; Haraguchi, Akira ; Harris, Lorna I. ; Humphreys, Elyn ; Jiroušek, Martin ; Kajukało, Katarzyna ; Karofeld, Edgar ; Koronatova, Natalia G. ; Kosykh, Natalia P. ; Laine, Anna M. ; Lamentowicz, Mariusz ; Lapshina, Elena ; Limpens, Juul ; Linkosalmi, Maiju ; Ma, Jin Ze ; Mauritz, Marguerite ; Mitchell, Edward A.D. ; Munir, Tariq M. ; Natali, Susan M. ; Natcheva, Rayna ; Payne, Richard J. ; Philippov, Dmitriy A. ; Rice, Steven K. ; Robinson, Sean ; Robroek, Bjorn J.M. ; Rochefort, Line ; Singer, David ; Stenøien, Hans K. ; Tuittila, Eeva Stiina ; Vellak, Kai ; Waddington, James Michael ; Granath, Gustaf - \ 2020
    Journal of Ecology (2020). - ISSN 0022-0477
    climate - global change - net primary production - nitrogen deposition - PAR - peat mosses - plant–climate interactions - structural equation model

    The relative importance of global versus local environmental factors for growth and thus carbon uptake of the bryophyte genus Sphagnum—the main peat-former and ecosystem engineer in northern peatlands—remains unclear. We measured length growth and net primary production (NPP) of two abundant Sphagnum species across 99 Holarctic peatlands. We tested the importance of previously proposed abiotic and biotic drivers for peatland carbon uptake (climate, N deposition, water table depth and vascular plant cover) on these two responses. Employing structural equation models (SEMs), we explored both indirect and direct effects of drivers on Sphagnum growth. Variation in growth was large, but similar within and between peatlands. Length growth showed a stronger response to predictors than NPP. Moreover, the smaller and denser Sphagnum fuscum growing on hummocks had weaker responses to climatic variation than the larger and looser Sphagnum magellanicum growing in the wetter conditions. Growth decreased with increasing vascular plant cover within a site. Between sites, precipitation and temperature increased growth for S. magellanicum. The SEMs indicate that indirect effects are important. For example, vascular plant cover increased with a deeper water table, increased nitrogen deposition, precipitation and temperature. These factors also influenced Sphagnum growth indirectly by affecting moss shoot density. Synthesis. Our results imply that in a warmer climate, S. magellanicum will increase length growth as long as precipitation is not reduced, while S. fuscum is more resistant to decreased precipitation, but also less able to take advantage of increased precipitation and temperature. Such species-specific sensitivity to climate may affect competitive outcomes in a changing environment, and potentially the future carbon sink function of peatlands.

    Does functional trait diversity predict aboveground biomass and productivity of tropical forests? Testing three alternative hypotheses
    Finegan, B. ; Peña Claros, M. ; Oliviera, A. de; Alarcón, A. ; Ascarrunz, N. ; Bret-Harte, M.S. ; Carreño-Rocabado, G. ; Casanoves, F. ; Díaz, S. ; Eguiguren Velepucha, P. ; Fernandez, F. ; Licona, J.C. ; Lorenzo, L. ; Salgado Negret, B. ; Vaz, M. ; Poorter, L. - \ 2015
    Journal of Ecology 103 (2015)1. - ISSN 0022-0477 - p. 191 - 201.
    net primary production - basin-wide variations - rican rain-forest - amazon forest - growth-rates - nutrient limitation - economics spectrum - species richness - plant diversity - tree
    Tropical forests are globally important, but it is not clear whether biodiversity enhances carbon storage and sequestration in them. We tested this relationship focusing on components of functional trait biodiversity as predictors. Data are presented for three rain forests in Bolivia, Brazil and Costa Rica. Initial above-ground biomass and biomass increments of survivors, recruits and survivors + recruits (total) were estimated for trees =10 cm d.b.h. in 62 and 21 1.0-ha plots, respectively. We determined relationships of biomass increments to initial standing biomass (AGBi), biomass-weighted community mean values (CWM) of eight functional traits and four functional trait variety indices (functional richness, functional evenness, functional diversity and functional dispersion). The forest continuum sampled ranged from ‘slow’ stands dominated by trees with tough tissues and high AGBi, to ‘fast’ stands dominated by trees with soft, nutrient-rich leaves, lighter woods and lower AGBi. We tested whether AGBi and biomass increments were related to the CWM trait values of the dominant species in the system (the biomass ratio hypothesis), to the variety of functional trait values (the niche complementarity hypothesis), or in the case of biomass increments, simply to initial standing biomass (the green soup hypothesis). CWMs were reasonable bivariate predictors of AGBi and biomass increments, with CWM specific leaf area SLA, CWM leaf nitrogen content, CWM force to tear the leaf, CWM maximum adult height Hmax and CWM wood specific gravity the most important. AGBi was also a reasonable predictor of the three measures of biomass increment. In best-fit multiple regression models, CWMHmax was the most important predictor of initial standing biomass AGBi. Only leaf traits were selected in the best models for biomass increment; CWM SLA was the most important predictor, with the expected positive relationship. There were no relationships of functional variety indices to biomass increments, and AGBi was the only predictor for biomass increments from recruits. Synthesis. We found no support for the niche complementarity hypothesis and support for the green soup hypothesis only for biomass increments of recruits. We have strong support for the biomass ratio hypothesis. CWMHmax is a strong driver of ecosystem biomass and carbon storage and CWM SLA, and other CWM leaf traits are especially important for biomass increments and carbon sequestration.
    Mapping and modelling trade-offs and synergies between grazing intensity and ecosystem services in rangelands using global-scale datasets and models
    Petz, K. ; Alkemade, J.R.M. ; Bakkenes, M. ; Schulp, C.J.E. ; Velde, M. van der; Leemans, R. - \ 2014
    Global environmental change : human and policy dimensions 29 (2014). - ISSN 0959-3780 - p. 223 - 234.
    net primary production - land-use - conservation priorities - livestock production - developing-countries - production systems - biodiversity - carbon - challenges - balance
    Vast areas of rangelands across the world are grazed with increasing intensity, but interactions between livestock production, biodiversity and other ecosystem services are poorly studied. This study explicitly determines trade-offs and synergies between ecosystem services and livestock grazing intensity on rangelands. Grazing intensity and its effects on forage utilization by livestock, carbon sequestration, erosion prevention and biodiversity are quantified and mapped, using global datasets and models. Results show that on average 4% of the biomass produced annually is consumed by livestock. On average, erosion prevention is 10% lower in areas with a high grazing intensity compared to areas with a low grazing intensity, whereas carbon emissions are more than four times higher under high grazing intensity compared to low grazing intensity. Rangelands with the highest grazing intensity are located in the Sahel, Pakistan, West India, Middle East, North Africa and parts of Brazil. These high grazing intensities result in carbon emissions, low biodiversity values, low capacity for erosion prevention and unsustainable forage utilization. Although the applied models simplify the processes of ecosystem service supply, our study provides a global overview of the consequences of grazing for biodiversity and ecosystem services. The expected increasing future demand for livestock products likely increase pressures on rangelands. Global-scale models can help to identify targets and target areas for international policies aiming at sustainable future use of these rangelands.
    Global cropland monthly gross primary production in the year 2000
    Chen, T. ; Werf, G.R. van der; Gobron, N. ; Moors, E.J. ; Dolman, A.J. - \ 2014
    Biogeosciences 11 (2014). - ISSN 1726-4170 - p. 3871 - 3880.
    net primary production - light-use efficiency - ecosystem exchange - constant fraction - terrestrial gross - model - forest - modis - respiration - climate
    Croplands cover about 12% of the ice-free terrestrial land surface. Compared with natural ecosystems, croplands have distinct characteristics due to anthropogenic influences. Their global gross primary production (GPP) is not well constrained and estimates vary between 8.2 and 14.2 Pg C yr-1. We quantified global cropland GPP using a light use efficiency (LUE) model, employing satellite observations and survey data of crop types and distribution. A novel step in our analysis was to assign a maximum light use efficiency estimate (¿*GPP) to each of the 26 different crop types, instead of taking a uniform value as done in the past. These ¿*GPP values were calculated based on flux tower CO2 exchange measurements and a literature survey of field studies, and ranged from 1.20 to 2.96 g C MJ-1. Global cropland GPP was estimated to be 11.05 Pg C yr-1 in the year 2000. Maize contributed most to this (1.55 Pg C yr-1), and the continent of Asia contributed most with 38.9% of global cropland GPP. In the continental United States, annual cropland GPP (1.28 Pg C yr-1) was close to values reported previously (1.24 Pg C yr-1) constrained by harvest records, but our estimates of ¿*GPP values were considerably higher. Our results are sensitive to satellite information and survey data on crop type and extent, but provide a consistent and data-driven approach to generate a look-up table of ¿*GPP for the 26 crop types for potential use in other vegetation models.
    Temperate forest development during secondary succession: effects of soil, dominant species and management
    Bose, A.K. ; Schelhaas, M. ; Mazerolle, M.J. ; Bongers, F. - \ 2014
    European Journal of Forest Research 133 (2014)3. - ISSN 1612-4669 - p. 511 - 523.
    organic-matter accumulation - net primary production - pinus-sylvestris l. - age-related decline - land-use change - scots pine - carbon sequestration - tree height - nitrogen mineralization - practical implications
    With the increase in abandoned agricultural lands in Western Europe, knowledge on the successional pathways of newly developing forests becomes urgent. We evaluated the effect of time, soil type and dominant species type (shade tolerant or intolerant) on the development during succession of three stand attributes: above-ground biomass, stand height (HT) and stem density (SD). Additionally, we compared above-ground biomass (AGB) in natural and planted forests, using ten chronosequences (8 from the literature and 2 from this study). Both AGB and HT increased over time, whereas SD decreased. HT, SD and AGB differed among species types. For example, birch had greater HT than alder, willow and ash at a similar age and had higher SD than pine and oak at a similar age. However, birch showed lower AGB than pine. HT and AGB differed among soil types. They were higher in rich soil than in poor soils. Comparative analysis between chronosequences showed an effect of the regeneration method (natural regeneration vs plantation) on above-ground biomass. Planted sites had higher AGB than natural regeneration. Time, soil type, species and regeneration method influenced the mechanism of stand responses during secondary succession. These characteristics could be used to clarify the heterogeneity and potential productivity of such spontaneously growing temperate forest ecosystems.
    Differentiating moss from higher plants is critical in studying the carbon cycle of the boreal biome
    Yuan, W. ; Liu, S. ; Dong, W. ; Zhao, S. ; Chen, J. ; Xu, W. ; Li, X. ; Barr, A. ; Black, T.A. ; Moors, E.J. ; Molen, M.K. van der - \ 2014
    Nature Communications 5 (2014). - ISSN 2041-1723
    light-use efficiency - net primary production - leaf-area - terrestrial biosphere - forest ecosystem - climate-change - absorbed par - co2 flux - satellite - productivity
    The satellite-derived normalized difference vegetation index (NDVI), which is used for estimating gross primary production (GPP), often includes contributions from both mosses and vascular plants in boreal ecosystems. For the same NDVI, moss can generate only about one-third of the GPP that vascular plants can because of its much lower photosynthetic capacity. Here, based on eddy covariance measurements, we show that the difference in photosynthetic capacity between these two plant functional types has never been explicitly included when estimating regional GPP in the boreal region, resulting in a substantial overestimation. The magnitude of this overestimation could have important implications regarding a change from a current carbon sink to a carbon source in the boreal region. Moss abundance, associated with ecosystem disturbances, needs to be mapped and incorporated into GPP estimates in order to adequately assess the role of the boreal region in the global carbon cycle.
    Global dependence of field-observed leaf area index in woody species on climate: a systematic review
    Iio, A. ; Hikosaka, K. ; Anten, N.P.R. ; Nakagawa, Y. ; Ito, A. - \ 2014
    Global Ecology and Biogeography 23 (2014)3. - ISSN 1466-822X - p. 274 - 285.
    net primary production - nitrogen availability - forest ecosystems - plant canopy - elevated co2 - productivity - model - water - dynamics - balance
    Aim Leaf area index (LAI) is one of the key variables related to carbon, water and nutrient cycles in terrestrial ecosystems, but its global distribution patterns remain poorly understood.We evaluated the dependence of LAI on mean annual temperature (MAT) and wetness index (WI; a ratio of annual precipitation to potential evapotranspiration) for three plant functional types (PFTs: deciduous broadleaf, DB; evergreen conifer, EC; evergreen broadleaf, EB) at the global scale. Location Global. Methods We developed a new global database of unprecedented size (2606 published values) of field-observed LAI (site-specific maximum) values for vegetation of woody species. To maximize the generic applicability of our analysis, we standardized the definition of LAI, and corrected or excluded potentially erroneous data obtained from indirect optical methods. Results The global dependence of LAI on MAT showed a reverse S-shaped pattern, in which LAI peaked at around 8.9 and 25.0°C and was lowest at around -10.0 and 18.8°C. The dependence on WI followed a saturation curve levelling off at around logWI = 0.30. LAI for evergreen forests increased linearly with increasing WI, but that for DB showed a curvilinear pattern saturating at log WI = 0.03. EC forests had higher LAI values than those of DB forests under cool conditions (MAT = 8.9°C), but similar values under temperate conditions (MAT = 8.9–18.8°C). Main conclusions This analysis of global LAI-climate relationships supports the general belief that temperature limits LAI under cool conditions whereas water availability plays a predominant role under other conditions. We also found that these patterns differed significantly between PFTs, suggesting that the LAI of different PFTs may respond differently to climate change. Our study provides a broad empirical basis for predicting the global distribution of LAI and for analysing the effects of global climate change on vegetation structure and function.
    Assessing the potential of dual-purpose maize in southern Africa: A multi-level approach
    Homann-Kee Tui, S. ; Blümmel, M. ; Valbuena, D.F. ; Chirima, A. ; Maskati, P. ; Rooyen, A.F. van; Kassie, G.T. - \ 2013
    Field Crops Research 153 (2013). - ISSN 0378-4290 - p. 37 - 51.
    crop-livestock systems - net primary production - sub-saharan africa - water productivity - benefits
    This paper explores the potential and challenges of increasing production of food and feed on existing maize fields in mixed crop-livestock systems in the semi-arid areas of southern Africa. It integrates results from different sources of data and analysis: 1. Spatial stratification using secondary data for GIS layers: Maize mega-environments combined with recommendation domains for dual-purpose maize were constructed for Malawi, Mozambique and Zimbabwe, stratifying the countries by demand factors (livestock densities and human population densities) and feed availability. Relative biomass contributions to feed resources from rangelands were compared to those from croplands to explore the usefulness of global datasets for feed supply estimations. 2. Verification through farming systems analysis: the potential demand for maize residues as feed (maize cropping patterns, maize yields and uses, feed deficits) was compared at contrasting sites, based on household survey data collected on 480 households in 2010. 3. Maize cultivar analysis: Genotypic variability of maize cultivars was compared to evaluate the potential contribution (stover quantity and quality) of dual-purpose maize to reduce feed deficits. The study results illustrate high spatial variability in the demand for and supply of maize residues. Northern Malawi is characterized by high livestock density, high human population density and high feed availability. Farmers achieve maize yields of more than 2 t/ha resulting in surplus of residues. Although livestock is important, southwest Zimbabwe has low livestock densities, low human populations and low feed availability; farming systems are more integrated and farmers make greater use of maize residues to address feed shortages. Central Mozambique also has low cattle densities, low human populations and low feed availability. More rangelands are available but maize yields are very low and livestock face severe feed shortages. The investigation of 14 advanced CIMMYT maize landraces cultivars and 15 advanced hybrids revealed significant variations in grain and stover yield and fodder quality traits. Where livestock densities are high and alternative feed resources are insufficient, maize cultivars with superior residue yield and fodder quality can have substantial impact on livestock productivity. Cultivars at the higher end of the quality range can provide sufficient energy for providing livestock maintenance requirements and support about 200 g of live weight gain daily. Maize cultivars can be targeted according to primary constraints of demand domains for either stover quantity or stover fodder quality and the paper proposes an approach for this based on voluntary feed intake estimates for maize stover.
    Nested atmospheric inversion for the terrestrial carbon sources and sinks in China
    Jiang, F. ; Wang, H.W. ; Chen, J.M. ; Zhou, L.X. ; Ju, W.M. ; Peters, W. - \ 2013
    Biogeosciences 10 (2013)8. - ISSN 1726-4170 - p. 5311 - 5324.
    net primary production - interannual variability - dioxide exchange - flux inversion - north-america - co2 sources - transport - model - emissions - forests
    In this study, we establish a~nested atmospheric inversion system with a focus on China using the Bayes theory. The global surface is separated into 43 regions based on the 22 TransCom large regions, with 13 small regions in China. Monthly CO2 concentrations from 130 GlobalView sites and a Hong Kong site are used in this system. The core component of this system is atmospheric transport matrix, which is created using the TM5 model with a horizontal resolution of 3° × 2°. The net carbon fluxes over the 43 global land and ocean regions are inverted for the period from 2002 to 2009. The inverted global terrestrial carbon sinks mainly occur in Boreal Asia, South and Southeast Asia, eastern US and southern South America (SA). Most China areas appear to be carbon sinks, with strongest carbon sinks located in Northeast China. From 2002 to 2009, the global terrestrial carbon sink has an increasing trend, with the lowest carbon sink in 2002. The inter-annual variation (IAV) of the land sinks shows remarkable correlation with the El Niño Southern Oscillation (ENSO). However, no obvious trend is found for the terrestrial carbon sinks in China. The IAVs of carbon sinks in China show strong relationship with drought and temperature. The mean global and China terrestrial carbon sinks over the period 2002–2009 are -3.15 ± 1.48 and -0.21 ± 0.23 Pg C yr-1, respectively. The uncertainties in the posterior carbon flux of China are still very large, mostly due to the lack of CO2 measurement data in China.
    Spatial relationship between climatologies and changes in global vegetation activity
    Jong, R. de; Schaepman, M.E. ; Furrer, R. ; Bruin, S. de; Verburg, P.H. - \ 2013
    Global Change Biology 19 (2013)6. - ISSN 1354-1013 - p. 1953 - 1964.
    net primary production - drought-induced reduction - land-cover data - time-series - avhrr data - ndvi data - spot-vegetation - african sahel - term trends - index data
    Vegetation forms a main component of the terrestrial biosphere and plays a crucial role in land-cover and climate-related studies. Activity of vegetation systems is commonly quantified using remotely sensed vegetation indices (VI). Extensive reports on temporal trends over the past decades in time series of such indices can be found in literature. However, little remains known about the processes underlying these changes at large spatial scales. In this study, we aimed at quantifying the spatial relationship between changes in potential climatic growth constraints (i.e. temperature, precipitation and incident solar radiation) and changes in vegetation activity (1982–2008). We demonstrate an additive spatial model with 0.5° resolution, consisting of a regression component representing climate-associated effects and a spatially correlated field representing the combined influence of other factors, including land-use change. Little over 50% of the spatial variance could be attributed to changes in climatologies; conspicuously, many greening trends and browning hotspots in Argentina and Australia. The nonassociated model component may contain large-scale human interventions, feedback mechanisms or natural effects, which were not captured by the climatologies. Browning hotspots in this component were especially found in subequatorial Africa. On the scale of land-cover types, strongest relationships between climatologies and vegetation activity were found in forests, including indications for browning under warming conditions (analogous to the divergence issue discussed in dendroclimatology).
    Shifts in global vegetation activity trends
    Jong, R. de; Verbesselt, J. ; Zeileis, A. ; Schaepman, M.E. - \ 2013
    Remote Sensing 5 (2013)3. - ISSN 2072-4292 - p. 1117 - 1133.
    net primary production - drought-induced reduction - image time-series - land-surface phenology - structural-change - satellite data - terrestrial ecosystems - ols residuals - ndvi data - avhrr
    Vegetation belongs to the components of the Earth surface, which are most extensively studied using historic and present satellite records. Recently, these records exceeded a 30-year time span composed of preprocessed fortnightly observations (1981–2011). The existence of monotonic changes and trend shifts present in such records has previously been demonstrated. However, information on timing and type of such trend shifts was lacking at global scale. In this work, we detected major shifts in vegetation activity trends and their associated type (either interruptions or reversals) and timing. It appeared that the biospheric trend shifts have, over time, increased in frequency, confirming recent findings of increased turnover rates in vegetated areas. Signs of greening-to-browning reversals around the millennium transition were found in many regions (Patagonia, the Sahel, northern Kazakhstan, among others), as well as negative interruptions—“setbacks”—in greening trends (southern Africa, India, Asia Minor, among others). A minority (26%) of all significant trends appeared monotonic
    Evaluation of MODIS gross primary productivity for Africa using eddy covariance data
    Sjostrom, M. ; Zhao, M. ; Archibald, S. ; Veenendaal, E.M. - \ 2013
    Remote Sensing of Environment 131 (2013). - ISSN 0034-4257 - p. 275 - 286.
    net primary production - deciduous broadleaf forest - primary production gpp - light use efficiency - ecosystem exchange - soil-water - spatial variability - terrestrial gross - savanna ecosystem - carbon-dioxide
    MOD17A2 provides operational gross primary production (GPP) data globally at 1 km spatial resolution and 8-day temporal resolution. MOD17A2 estimates GPP according to the light use efficiency (LUE) concept assuming a fixed maximum rate of carbon assimilation per unit photosynthetically active radiation absorbed by the vegetation (emax). Minimum temperature and vapor pressure deficit derived from meteorological data down-regulate emax and constrain carbon assimilation. This data is useful for regional to global studies of the terrestrial carbon budget, climate change and natural resources. In this study we evaluated the MOD17A2 product and its driver data by using in situ measurements of meteorology and eddy covariance GPP for 12 African sites. MOD17A2 agreed well with eddy covariance GPP for wet sites. Overall, seasonality was well captured but MOD17A2 GPP was underestimated for the dry sites located in the Sahel region. Replacing the meteorological driver data derived from coarse resolution reanalysis data with tower measurements reduced MOD17A2 GPP uncertainties, however, the underestimations at the dry sites persisted. Inferred emax calculated from tower data was higher than the emax prescribed in MOD17A2. This, in addition to uncertainties in fraction of absorbed photosynthetically active radiation (FAPAR) explains some of the underestimations. The results suggest that improved quality of driver data, but primarily a readjustment of the parameters in the biome parameter look-up table (BPLUT) may be needed to better estimate GPP for African ecosystems in MOD17A2.
    Tree height integrated into pantropical forest biomass estimates
    Feldpausch, T.R. ; Lloyd, J. ; Lewis, S.L. ; Brienen, R.J.W. ; Gloor, M. ; Montegudo Mendoza, A. ; Arets, E.J.M.M. - \ 2012
    Biogeosciences 9 (2012). - ISSN 1726-4170 - p. 3381 - 3403.
    tropical rain-forest - aboveground live biomass - net primary production - land-use change - wood density - amazonian forests - carbon stocks - allometric equations - neotropical forest - secondary forests
    Aboveground tropical tree biomass and carbon storage estimates commonly ignore tree height (H). We estimate the effect of incorporating H on tropics-wide forest biomass estimates in 327 plots across four continents using 42 656 H and diameter measurements and harvested trees from 20 sites to answer the following questions: 1. What is the best H-model form and geographic unit to include in biomass models to minimise site-level uncertainty in estimates of destructive biomass? 2. To what extent does including H estimates derived in (1) reduce uncertainty in biomass estimates across all 327 plots? 3. What effect does accounting for H have on plot- and continental-scale forest biomass estimates? The mean relative error in biomass estimates of destructively harvested trees when including H (mean 0.06), was half that when excluding H (mean 0.13). Power- and Weibull-H models provided the greatest reduction in uncertainty, with regional Weibull-H models preferred because they reduce uncertainty in smaller-diameter classes (=40 cm D) that store about one-third of biomass per hectare in most forests. Propagating the relationships from destructively harvested tree biomass to each of the 327 plots from across the tropics shows that including H reduces errors from 41.8 Mg ha-1 (range 6.6 to 112.4) to 8.0 Mg ha-1 (-2.5 to 23.0). For all plots, aboveground live biomass was -52.2 Mg ha-1 (-82.0 to -20.3 bootstrapped 95% CI), or 13%, lower when including H estimates, with the greatest relative reductions in estimated biomass in forests of the Brazilian Shield, east Africa, and Australia, and relatively little change in the Guiana Shield, central Africa and southeast Asia. Appreciably different stand structure was observed among regions across the tropical continents, with some storing significantly more biomass in small diameter stems, which affects selection of the best height models to reduce uncertainty and biomass reductions due to H. After accounting for variation in H, total biomass per hectare is greatest in Australia, the Guiana Shield, Asia, central and east Africa, and lowest in east-central Amazonia, W. Africa, W. Amazonia, and the Brazilian Shield (descending order). Thus, if tropical forests span 1668 million km2 and store 285 Pg C (estimate including H), then applying our regional relationships implies that carbon storage is overestimated by 35 Pg C (31–39 bootstrapped 95% CI) if H is ignored, assuming that the sampled plots are an unbiased statistical representation of all tropical forest in terms of biomass and height factors. Our results show that tree H is an important allometric factor that needs to be included in future forest biomass estimates to reduce error in estimates of tropical carbon stocks and emissions due to deforestation.
    Trend changes in global greening and browning: Contribution of short-term trends to longer-term change
    Jong, R. de; Verbesselt, J. ; Schaepman, M.E. ; Bruin, S. de - \ 2012
    Global Change Biology 18 (2012)2. - ISSN 1354-1013 - p. 642 - 655.
    net primary production - drought-induced reduction - structural-change models - image time-series - land-cover data - terrestrial ecosystems - photosynthetic trends - environmental-change - phenological change - vegetation indexes
    Field observations and time series of vegetation greenness data from satellites provide evidence of changes in terrestrial vegetation activity over the past decades for several regions in the world. Changes in vegetation greenness over time may consist of an alternating sequence of greening and/or browning periods. This study examined this effect using detection of trend changes in normalized difference vegetation index (NDVI) satellite data between 1982 and 2008. Time series of 648 fortnightly images were analyzed using a trend breaks analysis (BFAST) procedure. Both abrupt and gradual changes were detected in large parts of the world, especially in (semi-arid) shrubland and grassland biomes where abrupt greening was often followed by gradual browning. Many abrupt changes were found around large-scale natural influences like the Mt Pinatubo eruption in 1991 and the strong 1997/98 El Niño event. The net global figure – considered over the full length of the time series – showed greening since the 1980s. This is in line with previous studies, but the change rates for individual short-term segments were found to be up to five times higher. Temporal analysis indicated that the area with browning trends increased over time while the area with greening trends decreased. The Southern Hemisphere showed the strongest evidence of browning. Here, periods of gradual browning were generally longer than periods of gradual greening. Net greening was detected in all biomes, most conspicuously in croplands and least conspicuously in needleleaf forests. For 15% of the global land area, trends were found to change between greening and browning within the analysis period. This demonstrates the importance of accounting for trend changes when analyzing long-term NDVI time series.
    Modeling the productivity of energy crops in different agro-ecological environments
    Jing, Q. ; Conijn, J.G. ; Jongschaap, R.E.E. ; Bindraban, P.S. - \ 2012
    Biomass and Bioenergy 46 (2012). - ISSN 0961-9534 - p. 618 - 633.
    miscanthus-x-giganteus - light-use efficiency - short-rotation coppice - reed canary grass - woody biomass production - phalaris-arundinacea l. - morphologically diverse varieties - radiation use efficiency - net primary production - dry-matter production
    A relatively stable biomass productivity of perennial crop after plantation establishment makes it possible to calculate their total biomass yield through predicting the annual biomass yield. The generic model LINPAC (LINTUL model for Perennial and Annual Crops) is presented to predict annual biomass yield of energy crops on large spatial scales by adding new modules to LINTUL: (1) Leaf Area Index (LAI) is simulated independent of specific leaf area; (2) a species specific daily Light Use Efficiency (LUE, g MJ-1) is modified by temperature and light intensity; (3) crop base temperature is generated by local weather conditions within crop physiological ranges. LINPAC is driven either by site-specific input data or by globally gridded weather and soil data. LINPAC was calibrated on the basis of a model sensitivity analysis of the input parameters and validated against different agro-ecological experimental data sets for two grass species Miscanthus (Miscanthus spp.) and Reed canary grass (Phalaris arundinacea L.), and for two woody species Willow (Salix spp.) and Eucalyptus (Eucalyptus spp.). LINPAC reproduced the biomass yields with a normalized root mean square error (RMSE) of 17%, comparable to the coefficient of variation (CV = 12%) of the experimental data. In the model photosynthetic pathways were differentiated by assigning higher LUE values for the C4 crop (Miscanthus) compared with the C3 crops (others), leading to higher simulated biomass yield of Miscanthus (18.8 ± 1.5 t ha-1) over Reed canary grass (10.5 ± 1.6 t ha-1) in comparable environments. LINPAC is applicable for local, regional and global estimations of biomass yield of energy crops.
    Vegetation NDVI Linked to Temperature and Precipitation in the Upper Catchments of Yellow River
    Hao, F. ; Zhang, X. ; Ouyang, W. ; Skidmore, A.K. ; Toxopeus, A.G. - \ 2012
    Environmental Modeling and Assessment 17 (2012)4. - ISSN 1420-2026 - p. 389 - 398.
    land-cover changes - qinghai-xizang plateau - net primary production - central new-mexico - tibetan plateau - modis - china - soil - climate - basin
    Vegetation in the upper catchment of Yellow River is critical for the ecological stability of the whole watershed. The dominant vegetation cover types in this region are grassland and forest, which can strongly influence the eco-environmental status of the whole watershed. The normalized difference vegetation index (NDVI) for grassland and forest has been calculated and its daily correlation models were deduced by Moderate Resolution Imaging Spectroradiometer products on 12 dates in 2000, 2003, and 2006. The responses of the NDVI values with the inter-annual grassland and forest to three climatic indices (i.e., yearly precipitation and highest and lowest temperature) were analyzed showing that, except for the lowest temperature, the yearly precipitation and highest temperature had close correlations with the NDVI values of the two vegetation communities. The value of correlation coefficients ranged from 0.815 to 0.951 (p <0.01). Furthermore, the interactions of NDVI values of vegetation with the climatic indicators at monthly interval were analyzed. The NDVI of vegetation and three climatic indices had strong positive correlations (larger than 0.733, p <0.01). The monthly correlations also provided the threshold values for the three climatic indictors, to be used for simulating vegetation growth grassland under different climate features, which is essential for the assessment of the vegetation growth and for regional environmental management.
    Quantitative mapping of global land degradation using Earth observations
    Jong, R. de; Bruin, S. de; Schaepman, M.E. ; Dent, D. - \ 2011
    International Journal of Remote Sensing 32 (2011)21. - ISSN 0143-1161 - p. 6823 - 6853.
    net primary production - time-series analysis - terrestrial primary production - difference vegetation index - noaa-avhrr data - spot-vegetation - ndvi data - interannual variability - growing-season - south-africa
    Land degradation is a global issue on par with climate change and loss of biodiversity, but its extent and severity are only roughly known and there is little detail on the immediate processes – let alone the drivers. Earth-observation methods enable monitoring of land degradation in a consistent, physical way and on a global scale by making use of vegetation productivity and/or loss as proxies. Most recent studies indicate a general greening trend, but improved data sets and analysis also show a combination of greening and browning trends. Statistically based linear trends average out these effects. Improved understanding may be expected from data-driven and process-modelling approaches: new models, model integration, enhanced statistical analysis and modern sensor imagery at medium spatial resolution should substantially improve the assessment of global land degradation
    Patterns and controls of the variability of radiation use efficiency and primary productivity across terrestrial ecosystems
    Garbulsky, M.F. ; Peñuelas, J. ; Papale, D. ; Ardö, J. ; Goulden, M.L. ; Kiely, G. ; Richardson, A.D. ; Rotenberg, E. ; Veenendaal, E.M. ; Filella, I. - \ 2010
    Global Ecology and Biogeography 19 (2010). - ISSN 1466-822X - p. 253 - 267.
    light-use efficiency - net primary production - gross primary production - carbon-dioxide exchange - comparing global-models - eddy covariance data - co2 exchange - pine forest - interannual variability - mediterranean forest
    Aim The controls of gross radiation use efficiency (RUE), the ratio between gross primary productivity (GPP) and the radiation intercepted by terrestrial vegetation, and its spatial and temporal variation are not yet fully understood. Our objectives were to analyse and synthesize the spatial variability of GPP and the spatial and temporal variability of RUE and its climatic controls for a wide range of vegetation types. Location A global range of sites from tundra to rain forest. Methods We analysed a global dataset on photosynthetic uptake and climatic variables from 35 eddy covariance (EC) flux sites spanning between 100 and 2200 mm mean annual rainfall and between -13 and 26°C mean annual temperature. RUE was calculated from the data provided by EC flux sites and remote sensing (MODIS). Results Rainfall and actual evapotranspiration (AET) positively influenced the spatial variation of annual GPP, whereas temperature only influenced the GPP of forests. Annual and maximum RUE were also positively controlled primarily by annual rainfall. The main control parameters of the growth season variation of gross RUE varied for each ecosystem type. Overall, the ratio between actual and potential evapotranspiration and a surrogate for the energy balance explained a greater proportion of the seasonal variation of RUE than the vapour pressure deficit (VPD), AET and precipitation. Temperature was important for determining the intra-annual variability of the RUE at the coldest energy-limited sites. Main conclusions Our analysis supports the idea that the annual functioning of vegetation that is adapted to its local environment is more constrained by water availability than by temperature. The spatial variability of annual and maximum RUE can be largely explained by annual precipitation, more than by vegetation type. The intra-annual variation of RUE was mainly linked to the energy balance and water availability along the climatic gradient. Furthermore, we showed that intra-annual variation of gross RUE is only weakly influenced by VPD and temperature, contrary to what is frequently assumed. Our results provide a better understanding of the spatial and temporal controls of the RUE and thus could lead to a better estimation of ecosystem carbon fixation and better modelling.
    Remote sensing of sun-induced fluorescence to improve modeling of diurnal courses of gross primary production (GPP)
    Damm, A. ; Elbers, J.A. ; Erler, A. ; Giolis, B. ; Hamdi, K. ; Hutjes, R.W.A. ; Kosvancova, M. ; Meroni, M. ; Migliettas, F. ; Moersch, A. ; Moreno, J. ; Schickling, A. ; Sonnenschein, R. ; Udelhoven, T. ; Linden, S. van der; Hostert, P. ; Rascher, U. - \ 2010
    Global Change Biology 16 (2010)1. - ISSN 1354-1013 - p. 171 - 186.
    koolstofcyclus - primaire productie - remote sensing - fluorescentie - spectroscopie - planten - fotosynthese - modelleren - carbon cycle - primary production - remote sensing - fluorescence - spectroscopy - plants - photosynthesis - modeling - light-use efficiency - induced chlorophyll fluorescence - photochemical reflectance index - net primary production - eddy covariance - photosynthetic efficiency - leaf senescence - photosystem-ii - carbon-dioxide - boreal forest
    Terrestrial gross primary production (GPP) is an important parameter to explore and quantify carbon fixation by plant ecosystems at various scales. Remote sensing (RS) offers a unique possibility to investigate GPP in a spatially explicit fashion; however, budgeting of terrestrial carbon cycles based on this approach still remains uncertain. To improve calculations, spatio-temporal variability of GPP must be investigated in more detail on local and regional scales. The overarching goal of this study is to enhance our knowledge on how environmentally induced changes of photosynthetic light-use efficiency (LUE) are linked with optical RS parameters. Diurnal courses of sun-induced fluorescence yield (FSyield) and the photochemical reflectance index of corn were derived from high-resolution spectrometric measurements and their potential as proxies for LUE was investigated. GPP was modeled using Monteith's LUE-concept and optical-based GPP and LUE values were compared with synoptically acquired eddy covariance data. It is shown that the diurnal response of complex physiological regulation of photosynthesis can be tracked reliably with the sun-induced fluorescence. Considering structural and physiological effects, this research shows for the first time that including sun-induced fluorescence into modeling approaches improves their results in predicting diurnal courses of GPP. Our results support the hypothesis that air- or spaceborne quantification of sun-induced fluorescence yield may become a powerful tool to better understand spatio-temporal variations of fluorescence yield, photosynthetic efficiency and plant stress on a global scale
    Toward a consistency cross-check of eddy covariance flux-based and biometric estimates of ecosystem carbon balance
    Luyssaert, S. ; Reichstein, M. ; Schulze, E.D. ; Janssens, I.A. ; Law, B.E. ; Papale, D. ; Dragoni, D. ; Goulden, M.L. ; Granier, A. ; Kutch, W.L. ; Linder, S. ; Matteucci, G. ; Moors, E.J. ; Munger, J.W. ; Pilegaard, K. ; Saunders, M. ; Falge, E.M. - \ 2009
    Global Biogeochemical Cycles 23 (2009). - ISSN 0886-6236 - 13
    netto ecosysteem koolstofbalans - schattingen - eddy-covariantie - primaire productie - biometrie - meetsystemen - net ecosystem carbon balance - estimates - eddy covariance - primary production - biometry - measurement systems - net primary production - gross primary production - ponderosa pine forests - mixed hardwood forest - water-vapor exchange - soil co2 efflux - european forests - beech forest - chamber measurements - spatial variability
    Quantification of an ecosystem's carbon balance and its components is pivotal for understanding both ecosystem functioning and global cycling. Several methods are being applied in parallel to estimate the different components of the CO2 balance. However, different methods are subject to different sources of error. Therefore, it is necessary that site level component estimates are cross-checked against each other before being reported. Here we present a two-step approach for testing the accuracy and consistency of eddy covariance–based gross primary production (GPP) and ecosystem respiration (Re) estimates with biometric measurements of net primary production (NPP), autotrophic (Ra) and heterotrophic (Rh) respiration. The test starts with closing the CO2 balance to account for reasonable errors in each of the component fluxes. Failure to do so within the constraints will classify the flux estimates on the site level as inconsistent. If the CO2 balance can be closed, the test continues by comparing the closed site level Ra/GPP with the Rh/GPP ratio. The consistency of these ratios is then judged against expert knowledge. Flux estimates of sites that pass both steps are considered consistent. An inconsistent ratio is not necessarily incorrect but provides a signal for careful data screening that may require further analysis to identify the possible biological reasons of the unexpected ratios. We reviewed the literature and found 16 sites, out of a total of 529 research forest sites, that met the data requirements for the consistency test. Thirteen of these sites passed both steps of the consistency cross-check. Subsequently, flux ratios (NPP/GPP, Rh/NPP, Rh/Re, and Re/GPP) were calculated for the consistent sites. Similar ratios were observed at sites which lacked information to check consistency, indicating that the flux data that are currently used for validating models and testing ecological hypotheses are largely consistent across a wide range of site productivities. Confidence in the output of flux networks could be further enhanced if the required fluxes are independently estimated at all sites for multiple years and harmonized methods are used
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