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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    Field data of "Monitoring forest phenology and leaf area index with the autonomous, low-cost transmittance sensor PASTiS-57"
    Brede, Benjamin ; Gastellu-Etchegorry, Jean Philippe ; Lauret, Nicolas ; Baret, Frederic ; Clevers, Jan ; Verbesselt, Jan ; Herold, Martin - \ 2020
    Wageningen University & Research
    forest - ground-based - Land Surface Phenology - Leaf Area Index - validation
    Land Surface Phenology (LSP) and Leaf Area Index (LAI) are important variables that describe the photosynthetically active phase and capacity of vegetation. Both are derived on the global scale from optical satellite sensors and require robust validation based on in situ sensors at high temporal resolution. This study assesses the PAI Autonomous System from Transmittance Sensors at 57? (PASTiS-57) instrument as a low-cost transmittance sensor for simultaneous monitoring of LSP and LAI in forest ecosystems. In a field experiment, spring leaf flush and autumn senescence in a Dutch beech forest were observed with PASTiS-57 and illumination independent, multi-temporal Terrestrial Laser Scanning (TLS) measurements in five plots. Both time series agreed to less than a day in Start Of Season (SOS) and End Of Season (EOS). LAI magnitude was strongly correlated with a Pearson correlation coefficient of 0.98. PASTiS-57 summer and winter LAI were on average 0.41m2m-2 and 1.43m2m-2 lower than TLS. This can be explained by previously reported overestimation of TLS. Additionally, PASTiS-57 was implemented in the Discrete Anisotropic Radiative Transfer (DART) Radiative Transfer Model (RTM) model for sensitivity analysis. This confirmed the robustness of the retrieval with respect to non-structural canopy properties and illumination conditions. Generally, PASTiS-57 fulfilled the CEOS LPV requirement of 20% accuracy in LAI for a wide range of biochemical and illumination conditions for turbid medium canopies. However, canopy non-randomness in discrete tree models led to strong biases. Overall, PASTiS-57 demonstrated the potential of autonomous devices for monitoring of phenology and LAI at daily temporal resolution as required for validation of satellite products that can be derived from ESA Copernicus’ optical missions, Sentinel-2 and -3.
    Similar factors underlie tree abundance in forests in native and alien ranges
    Sande, Masha T. van der; Bruelheide, Helge ; Dawson, Wayne ; Dengler, Jürgen ; Essl, Franz ; Field, Richard ; Haider, Sylvia ; Kleunen, Mark van; Kreft, Holger ; Pagel, Joern ; Pergl, Jan ; Purschke, Oliver ; Pyšek, Petr ; Weigelt, Patrick ; Winter, Marten ; Attorre, Fabio ; Aubin, Isabelle ; Bergmeier, Erwin ; Chytrý, Milan ; Dainese, Matteo ; Sanctis, Michele De; Fagundez, Jaime ; Golub, Valentin ; Guerin, Greg R. ; Gutiérrez, Alvaro G. ; Jandt, Ute ; Jansen, Florian ; Jiménez-Alfaro, Borja ; Kattge, Jens ; Kearsley, Elizabeth ; Klotz, Stefan ; Kramer, Koen ; Moretti, Marco ; Niinemets, Ülo ; Peet, Robert K. ; Penuelas, Josep ; Petřík, Petr ; Reich, Peter B. ; Sandel, Brody ; Schmidt, Marco ; Sibikova, Maria ; Violle, Cyrille ; Whitfeld, Timothy J.S. ; Wohlgemuth, Thomas ; Knight, Tiffany M. - \ 2020
    Global Ecology and Biogeography 29 (2020)2. - ISSN 1466-822X - p. 281 - 294.
    abundance - dissimilarity - forest - functional traits - global - plant invasion - trees

    Aim: Alien plant species can cause severe ecological and economic problems, and therefore attract a lot of research interest in biogeography and related fields. To identify potential future invasive species, we need to better understand the mechanisms underlying the abundances of invasive tree species in their new ranges, and whether these mechanisms differ between their native and alien ranges. Here, we test two hypotheses: that greater relative abundance is promoted by (a) functional difference from locally co-occurring trees, and (b) higher values than locally co-occurring trees for traits linked to competitive ability. Location: Global. Time period: Recent. Major taxa studied: Trees. Methods: We combined three global plant databases: sPlot vegetation-plot database, TRY plant trait database and Global Naturalized Alien Flora (GloNAF) database. We used a hierarchical Bayesian linear regression model to assess the factors associated with variation in local abundance, and how these relationships vary between native and alien ranges and depend on species’ traits. Results: In both ranges, species reach highest abundance if they are functionally similar to co-occurring species, yet are taller and have higher seed mass and wood density than co-occurring species. Main conclusions: Our results suggest that light limitation leads to strong environmental and biotic filtering, and that it is advantageous to be taller and have denser wood. The striking similarities in abundance between native and alien ranges imply that information from tree species’ native ranges can be used to predict in which habitats introduced species may become dominant.

    Patterns of nitrogen-fixing tree abundance in forests across Asia and America
    Menge, Duncan N.L. ; Chisholm, Ryan A. ; Davies, Stuart J. ; Abu Salim, Kamariah ; Allen, David ; Alvarez, Mauricio ; Bourg, Norm ; Brockelman, Warren Y. ; Bunyavejchewin, Sarayudh ; Butt, Nathalie ; Cao, Min ; Chanthorn, Wirong ; Chao, Wei Chun ; Clay, Keith ; Condit, Richard ; Cordell, Susan ; Silva, João Batista da; Dattaraja, H.S. ; Andrade, Ana Cristina Segalin de; Oliveira, Alexandre A. de; Ouden, Jan den; Drescher, Michael ; Fletcher, Christine ; Giardina, Christian P. ; Savitri Gunatilleke, C.V. ; Gunatilleke, I.A.U.N. ; Hau, Billy C.H. ; He, Fangliang ; Howe, Robert ; Hsieh, Chang Fu ; Hubbell, Stephen P. ; Inman-Narahari, Faith M. ; Jansen, Patrick A. ; Johnson, Daniel J. ; Kong, Lee Sing ; Král, Kamil ; Ku, Chen Chia ; Lai, Jiangshan ; Larson, Andrew J. ; Li, Xiankun ; Li, Yide ; Lin, Luxiang ; Lin, Yi Ching ; Liu, Shirong ; Lum, Shawn K.Y. ; Lutz, James A. ; Ma, Keping ; Malhi, Yadvinder ; McMahon, Sean ; McShea, William ; Mi, Xiangcheng ; Morecroft, Michael ; Myers, Jonathan A. ; Nathalang, Anuttara ; Novotny, Vojtech ; Ong, Perry ; Orwig, David A. ; Ostertag, Rebecca ; Parker, Geoffrey ; Phillips, Richard P. ; Abd. Rahman, Kassim ; Sack, Lawren ; Sang, Weiguo ; Shen, Guochun ; Shringi, Ankur ; Shue, Jessica ; Su, Sheng Hsin ; Sukumar, Raman ; Fang Sun, I. ; Suresh, H.S. ; Tan, Sylvester ; Thomas, Sean C. ; Toko, Pagi S. ; Valencia, Renato ; Vallejo, Martha I. ; Vicentini, Alberto ; Vrška, Tomáš ; Wang, Bin ; Wang, Xihua ; Weiblen, George D. ; Wolf, Amy ; Xu, Han ; Yap, Sandra ; Zhu, Li ; Fung, Tak - \ 2019
    Journal of Ecology 107 (2019)6. - ISSN 0022-0477 - p. 2598 - 2610.
    forest - legume - nitrogen fixation - nutrient limitation - Smithsonian ForestGEO - symbiosis

    Symbiotic nitrogen (N)-fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N-fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N-fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N-fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N-fixing trees were consistently rare in the forest plots we examined. Within the tropics, N-fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N-fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N-fixing tree abundance between the Asian and American tropics. Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N-fixing trees. By analysing a large dataset of ~4 million trees, we found that N-fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N-fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N-fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought.

    Resilience of tropical tree cover : The roles of climate, fire, and herbivory
    Staal, Arie ; Nes, Egbert H. van; Hantson, Stijn ; Holmgren, Milena ; Dekker, Stefan C. ; Pueyo, Salvador ; Xu, Chi ; Scheffer, Marten - \ 2018
    Global Change Biology 24 (2018)11. - ISSN 1354-1013 - p. 5096 - 5109.
    alternative stable states - bistability - forest - grasslands - livestock - model - regime shifts - remote sensing - tipping points - wildfire

    Fires and herbivores shape tropical vegetation structure, but their effects on the stability of tree cover in different climates remain elusive. Here, we integrate empirical and theoretical approaches to determine the effects of climate on fire- and herbivore-driven forest-savanna shifts. We analyzed time series of remotely sensed tree cover and fire observations with estimates of herbivore pressure across the tropics to quantify the fire–tree cover and herbivore–tree cover feedbacks along climatic gradients. From these empirical results, we developed a spatially explicit, stochastic fire-vegetation model that accounts for herbivore pressure. We find emergent alternative stable states in tree cover with hysteresis across rainfall conditions. Whereas the herbivore–tree cover feedback can maintain low tree cover below 1,100 mm mean annual rainfall, the fire–tree cover feedback can maintain low tree cover at higher rainfall levels. Interestingly, the rainfall range where fire-driven alternative vegetation states can be found depends strongly on rainfall variability. Both higher seasonal and interannual variability in rainfall increase fire frequency, but only seasonality expands the distribution of fire-maintained savannas into wetter climates. The strength of the fire–tree cover feedback depends on the spatial configuration of tree cover: Landscapes with clustered low tree-cover areas are more susceptible to cross a tipping point of fire-driven forest loss than landscapes with scattered deforested patches. Our study shows how feedbacks involving fire, herbivores, and the spatial structure of tree cover explain the resilience of tree cover across climates.

    On the relationship between fire regime and vegetation structure in the tropics
    Veenendaal, Elmar M. ; Torello-Raventos, Mireia ; Miranda, Heloisa S. ; Sato, Naomi Margarete ; Oliveras, Imma ; Langevelde, Frank van; Asner, Gregory P. ; Lloyd, Jon - \ 2018
    New Phytologist 218 (2018)1. - ISSN 0028-646X - p. 153 - 166.
    alternative stable states - feedbacks - fire ecology - forest - savannah
    We assessed data from 11 experiments examining the effects of the timing and/or frequency of fire on tropical forest and/or savanna vegetation structure over one decade or more. The initial ‘control treatment’ in many such cases consisted of previously cleared land. This is as opposed to natural vegetation subject to some sort of endogenous fire regime before the imposition of fire treatments. Effects of fire on fractional foliar cover are up to 10-fold greater when clearing pre-treatments are imposed. Moreover, because many of the ‘classic’ fire trials were initialised with applied management questions in mind, most have also used burning regimes much more frequent and/or severe than those occurring in the absence of human activity. Once these factors are taken into account, our modelling analysis shows that nonanthropogenic fire regimes serve to reduce canopy vegetative cover to a much lower extent than has previously been argued to be the case. These results call into question the notion that fire effects on tropical vegetation can be of a sufficient magnitude to maintain open-type savanna ecosystems under climatic/soil regimes otherwise sufficient to give rise to a more luxurious forest-type vegetation cover.
    Alien plant invasions in European woodlands
    Wagner, Viktoria ; Chytrý, Milan ; Jiménez-Alfaro, Borja ; Pergl, Jan ; Hennekens, Stephan ; Biurrun, Idoia ; Knollová, Ilona ; Berg, Christian ; Vassilev, Kiril ; Rodwell, John S. ; Škvorc, Željko ; Jandt, Ute ; Ewald, Jörg ; Jansen, Florian ; Tsiripidis, Ioannis ; Botta-Dukát, Zoltán ; Casella, Laura ; Attorre, Fabio ; Rašomavičius, Valerijus ; Ćušterevska, Renata ; Schaminée, Joop H.J. ; Brunet, Jörg ; Lenoir, Jonathan ; Svenning, Jens Christian ; Kącki, Zygmunt ; Petrášová-Šibíková, Mária ; Šilc, Urban ; García-Mijangos, Itziar ; Campos, Juan Antonio ; Fernández-González, Federico ; Wohlgemuth, Thomas ; Onyshchenko, Viktor ; Pyšek, Petr - \ 2017
    Diversity and Distributions 23 (2017)9. - ISSN 1366-9516 - p. 969 - 981.
    EUNIS - exotic - forest - invasive plants - life-form - neophyte - non-native - origin - tree
    Aim: Woodlands make up a third of European territory and carry out important ecosystem functions, yet a comprehensive overview of their invasion by alien plants has never been undertaken across this continent. Location: Europe. Methods: We extracted data from 251,740 vegetation plots stored in the recently compiled European Vegetation Archive. After filtering (resulting in 83,396 plots; 39 regions; 1970–2015 time period), we analysed the species pool and frequency of alien vascular plants with respect to geographic origin and life-forms, and the levels of invasion across the European Nature Information System (EUNIS) woodland habitats. Results: We found a total of 386 alien plant species (comprising 7% of all recorded vascular plants). Aliens originating from outside of and from within Europe were almost equally represented in the species pool (192 vs. 181 species) but relative frequency was skewed towards the former group (77% vs. 22%) due, to some extent, to the frequent occurrence of Impatiens parviflora (21% frequency among alien plants). Phanerophytes were the most species-rich life-form (148 species) and had the highest representation in terms of relative frequency (39%) among aliens in the dataset. Apart from Europe (181 species), North America was the most important source of alien plants (109 species). At the local scale, temperate and boreal softwood riparian woodland (5%) and mire and mountain coniferous woodland (<1%) had the highest and lowest mean relative alien species richness (percentage of alien species per plot), respectively. Main conclusions: Our results indicate that European woodlands are prone to alien plant invasions especially when exposed to disturbance, fragmentation, alien propagule pressure and high soil nutrient levels. Given the persistence of these factors in the landscape, competitive alien plant species with a broad niche, including alien trees and shrubs, are likely to persist and spread further into European woodlands.
    MODIS VCF should not be used to detect discontinuities in tree cover due to binning bias. A comment on Hanan et al. (2014) and Staver and Hansen (2015)
    Gerard, France ; Hooftman, Danny ; Langevelde, Frank van; Veenendaal, Elmar ; White, Steven M. ; Lloyd, Jon - \ 2017
    Global Ecology and Biogeography 26 (2017)7. - ISSN 1466-822X - p. 854 - 859.
    alternative stable states - forest - frequency distribution - MODIS VCF - remote sensing - savanna - tree cover

    In their recent paper, Staver and Hansen (Global Ecology and Biogeography, 2015, 24, 985–987) refute the case made by Hanan et al. (Global Ecology and Biogeography, 2014, 23, 259–263) that the use of classification and regression trees (CARTs) to predict tree cover from remotely sensed imagery (MODIS VCF) inherently introduces biases, thus making the resulting tree cover unsuitable for showing alternative stable states through tree cover frequency distribution analyses. Here we provide a new and equally fundamental argument for why the published frequency distributions should not be used for such purposes. We show that the practice of pre-average binning of tree cover values used to derive cover values to train the CART model will also introduce errors in the frequency distributions of the final product. We demonstrate that the frequency minima found at tree covers of 8–18%, 33–45% and 55–75% can be attributed to numerical biases introduced when training samples are derived from landscapes containing asymmetric tree cover distributions and/or a tree cover gradient. So it is highly likely that the CART, used to produce MODIS VCF, delivers tree cover frequency distributions that do not reflect the real world situation.

    To Tree or Not to Tree : Cultural Views from Ancient Romans to Modern Ecologists
    Holmgren, Milena ; Scheffer, Marten - \ 2017
    Ecosystems 20 (2017)1. - ISSN 1432-9840 - p. 62 - 68.
    ecosystem services - forest - grassland - land degradation - savanna - tree encroachment - visions of nature

    Few things are more defining in a landscape compared to the absence or presence of trees, both in aesthetic and in functional terms. At the same time, tree cover has been profoundly affected by humans since ancient times. It is therefore not surprising that opinions about deforestation and colonization of landscapes by trees have always been strong. Although loss of forests is often lamented, there is also profound cultural affection for open landscapes including some that have been deforested in the past. Here we take a historical view on perceptions of changing tree cover, and subsequently argue that the current ecological literature on forest-savanna-grassland transitions is not immune to value-laden perspectives. So far, ecosystem science has not done enough to analyze the effects of tree cover changes on ecosystem services and indicators of human well-being. Until these analyses are done, debates about forested versus open landscapes will be clashes of values rather than scientific evaluations. We discuss how ecosystem science may contribute to developing this field.

    The island rule of body size demonstrated on individual hosts : phytophagous click beetle species grow larger and predators smaller on phylogenetically isolated trees
    Molleman, Freerk ; Depoilly, Alexandre ; Vernon, Philippe ; Müller, Jörg ; Bailey, Richard ; Jarzabek-Müller, Andrea ; Prinzing, Andreas - \ 2016
    Journal of Biogeography 43 (2016)7. - ISSN 0305-0270 - p. 1388 - 1399.
    community ecology - dispersal selection - Elateridae - forest - island biogeography - local adaptation - microevolution - phenotypic plasticity - plant–animal interactions - vegetation diversity

    Aim: Under spatial isolation on oceanic islands, species tend to show extreme body sizes. From the point of view of many colonizers, individual hosts surrounded by phylogenetically distant neighbours are phylogenetically isolated. This study addresses for the first time how phylogenetic isolation of individual hosts affects body size of colonizers, and whether effects on body size reflect selection among colonizers established on host individuals rather than selection among colonizers dispersing toward trees or phenotypic plasticity of colonizers. Location: Rennes National Forest, Western France. Methods: We sampled click beetles (Elateridae) on individual oak trees varying in phylogenetic isolation from their neighbours and in age. We measured body size and fluctuating asymmetry (which we found to correlate to reduced body size) and related both to phylogenetic isolation and age of trees. We compared these relationships among species of different larval trophic position and adult body size, using meta-analytical approaches. Results: Within species, body size changes with phylogenetic isolation of individual host trees: root feeders tend to become larger, predators smaller. Effects were independent of mean body-size, disappeared with tree age, and were inconsistent with patterns of fluctuating asymmetry. Main conclusions: Our results are consistent with body-size selection among colonizers established on individual trees, rather than selection among colonizers dispersing toward trees or phenotypic plasticity. Overall, phenotype patterns of animals across islands in the ocean may resemble those across host individuals in a phylogenetically distant neighbourhood, suggesting micro-evolution of colonizers in response to the macro-evolutionary structure of the host community.

    Forest–climate nexus : linking adaptation and mitigation in Cameroon's climate policy process
    Chia, Eugene Loh ; Somorin, O.A. ; Sonwa, D.J. ; Bele, Y.M. ; Tiani, M.A. - \ 2015
    Climate and Development 7 (2015)1. - ISSN 1756-5529 - p. 85 - 96.
    adaptation - Cameroon - climate change - forest - mitigation - policy actors

    In Cameroon, as in other countries of the Congo basin region, policy processes and activities related to climate change have been hitherto geared mostly towards mitigation and related questions, with limited concern about adaptation issues. However, the increasing vulnerability of Cameroon to climate variability and change makes adaptation significant to its national climate-change policy. Nonetheless, it remains a challenge to make both adaptation and mitigation occupy the same policy space in Cameroon. This paper builds partly on studies carried out in two community forest carbon initiatives in the southern rainforest of Cameroon. It also argues, supported by existing literature on adaptation and mitigation, that mitigation activities have the potential to produce adaptation outcomes; a situation which avoids duplication of efforts and waste of financial and technical resources, if synergetic options are anticipated and planned. However, whether such integrated approaches succeed and are subsequently reflected in national-level climate policy depends on how actors across different sectors and at different levels engage and carry out their roles. The paper discusses these roles and how they can support each other in pursuing integrated initiatives – a context which is vital for Cameroon.

    Estimation of spruce needle-leaf chlorophyll content based on DART and PARAS canopy reflectance models
    Yanez Rausell, L. ; Malenovsky, Z. ; Rautiainen, M. ; Clevers, J.G.P.W. ; Lukes, P. ; Hanus, J. ; Schaepman, M.E. - \ 2015
    IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 8 (2015)4. - ISSN 1939-1404 - p. 1534 - 1544.
    photon recollision probability - area index - spectral invariants - forest - prospect - stands - simulations - resolution - retrieval - lai-2000
    Needle-leaf chlorophyll content (Cab) of a Norway spruce stand was estimated from CHRIS-PROBA images using the canopy reflectance simulated by the PROSPECT model coupled with two canopy reflectance models: 1) discrete anisotropic radiative transfer model (DART); and 2) PARAS. The DART model uses a detailed description of the forest scene, whereas PARAS is based on the photon recollision probability theory and uses a simplified forest structural description. Subsequently, statistically significant empirical functions between the optical indices ANCB670-720 and ANMB670-720 and the needle-leaf Cab content were established and then applied to CHRIS-PROBA data. The Cab estimating regressions using ANMB670_720 were more robust than using ANCB670-720 since the latter was more sensitive to LAI, especially in case of PARAS. Comparison between Cab estimates showed strong linear correlations between PARAS and DART retrievals, with a nearly perfect one-to-one fit when using ANMB670-720 (slope = 1.1, offset = 11 µg · cm-2). Further comparison with Cab estimated from an AISA Eagle image of the same stand showed better results for PARAS (RMSE = 2.7 µg · cm-2 for ANCB670-720; RMSE = 9.5 µg · cm-2 for ANMB670_720) than for DART (RMSE = 7.5 µg · cm-2 for ANCB670-720; RMSE = 23 µg · cm-2 for ANMB670-720). Although these results show the potential for simpler models like PARAS in estimating needle-leaf Cab from satellite imaging spectroscopy data, further analyses regarding parameterization of radiative transfer models are recommended.
    Wildlife comeback in Flanders: tracing the fault lines and dynamics of public debate
    Herzele, A. Van; Aarts, N. ; Casaer, J. - \ 2015
    European Journal of Wildlife Research 61 (2015)4. - ISSN 1612-4642 - p. 539 - 555.
    biodiversity conservation - scale frames - conflicts - forest - policy - discourse - science - europe - city
    Conflicts and debates on wildlife issues often prove intractable or resistant to resolution. This paper develops a three-layered methodological approach to identify the fault lines and dynamics, which perpetuate social division and conflict. This approach was applied to the analysis of six publicly debated events that followed the comeback of the red fox and wild boar in Flanders, Belgium. The integrated findings demonstrate that conflict was not merely a manifestation of incompatible goals and views, but was highly determined by the conduct of the debate itself. The debates evolved along a few main fault lines, most notably belonging/not belonging, opportunity/threat and control by intervention/nature controls itself. A number of dynamics were identified along these fault lines, including the convergence and alignment of arguments (in particular, dichotomisation), the linking and scaling up of issues and the stigmatisation of outgroups. These processes were largely driven by the parties’ strategies to gain credibility and support with audiences. At the same time, however, they tended to magnify the problems, polarised positions along the fault lines, and thus hampered resolution. Furthermore, part of the debate served to confirm institutional roles and identities, which, in turn, contributed to the perpetuation of conflict. Contrasting views on nature were hardly a topic of discussion. Rather they were locked into dichotomies and classifications expressed by the contending parties. Together, the findings from this paper provide useful clues for transforming the dynamics perpetuating the conflict to different dynamics that allow for more constructive relations between the parties involved.
    Spatial boundary of urban ‘acid islands’ in China
    Du, E. ; Vries, W. de; Liu, X. ; Fang, J. ; Galloway, J.N. ; Jiang, Y. - \ 2015
    Scientific Reports 5 (2015). - ISSN 2045-2322 - 9 p.
    atmospheric deposition - nitrogen deposition - air-pollution - soil acidification - emissions - canopy - forest - rain - ecosystems - cities
    Elevated emissions of sulfur dioxide, nitrogen oxides and ammonia in China have resulted in high levels of sulfur and nitrogen deposition, being contributors to soil acidification, especially in and near large cities. However, knowledge gaps still exist in the way that large cities shape spatial patterns of acid deposition. Here, we assessed the patterns of pH, sulfate, nitrate and ammonium in bulk precipitation and throughfall in southern China’s forests by synthesizing data from published literature. Concentrations and fluxes of sulfate, nitrate and ammonium in bulk precipitation and throughfall exhibited a power-law increase with a closer distance to the nearest large cities, and accordingly pH showed a logarithmic decline. Our findings indicate the occurrence of urban ‘acid islands’ with a critical radius of approximately 70¿km in southern China, receiving potential acid loads of more than 2 keq ha-1 yr-1. These urban acid islands covered an area of 0.70¿million km2, accounting for nearly 30% of the land area in southern China. Despite a significant capacity to neutralize acids in precipitation, our analysis highlights a substantial contribution of ammonium to potential acid load. Our results suggest a joint control on emissions of multiple acid precursors from urban areas in southern China
    Influence of human activities on the activity patterns of Japanese sika deer (Cervus nippon) and wild boar (Sus scrofa) in Central Japan
    Doormaal, N. van; Ohashi, H. ; Koike, S. ; Kaji, K. - \ 2015
    European Journal of Wildlife Research 61 (2015)4. - ISSN 1612-4642 - p. 517 - 527.
    agricultural landscapes - habitat selection - human disturbance - roe deer - land-use - forest - prefecture - behavior - density - damage
    Human ageing and population decline in Japan are causing agricultural field abandonment and providing new habitats for Japanese sika deer and wild boar. These species have expanded their distribution and increased in abundance across Japan and are causing increased agricultural damage. Effective countermeasures must factor in the behavioural flexibility of sika deer and wild boar. The aim of this study was to examine the effects of hunting and indirect human activities on the activity patterns of sika deer in central Japan and compare these with previous findings on wild boar. Camera traps were used to observe activity patterns of both species and that of humans. Sika deer and wild boar were most active at night during the non-hunting season. Hunting activities significantly reduced sika deer and wild boar activity patterns. In the non-hunting season, nocturnal activity of sika deer increased with decreasing distance to settlement. A similar, but weak response was also observed for wild boar. This study suggests that sika deer and wild boar avoid humans and humandominated areas by being nocturnal. The recent introduction of night hunting might help to control wildlife populations, but monitoring will be necessary to confirm this expectation.
    Estimation of Aerodynamic Roughness Length over Oasis in the Heihe River Basin by Utilizing Remote Sensing and Ground Data
    Chen, Q. ; Jia, L. ; Hutjes, R.W.A. ; Menenti, M. - \ 2015
    Remote Sensing 7 (2015)4. - ISSN 2072-4292 - p. 3690 - 3709.
    laser altimeter measurements - time-series analysis - leaf-area index - surface-roughness - vegetation - parameters - canopy - forest - lidar - displacement
    Most land surface models require information on aerodynamic roughness length and its temporal and spatial variability. This research presents a practical approach for determining the aerodynamic roughness length at fine temporal and spatial resolution over the landscape by combining remote sensing and ground measurements. The basic framework of Raupach, with the bulk surface parameters redefined by Jasinski et al., has been applied to optical remote sensing data collected by the HJ-1A/1B satellites. In addition, a method for estimating vegetation height was introduced to derive the aerodynamic roughness length, which is preferred by users over the height-normalized form. Finally, mapping different vegetation classes was validated taking advantage of the data-dense field experiments conducted in the Heihe Watershed Allied Telemetry Experimental Research (HiWATER) project. Overall, the roughness model performed well against the measurements collected at most HiWATER flux tower sites. However, deviations still occurred at some sites, which have been further analyzed.
    Satellite Earth observation data to identify anthropogenic pressures in selected protected areas
    Nagendra, H. ; Mairota, P. ; Marangi, C. ; Lucas, R. ; Dimopoulos, P. ; Honrado, J.P. ; Niphadkara, M. ; Mücher, C.A. ; Tomaselli, V. ; Panitsa, M. ; Tarantino, C. ; Manakos, I. ; Blonda, P. - \ 2015
    International Journal of applied Earth Observation and Geoinformation 37 (2015). - ISSN 0303-2434 - p. 124 - 132.
    ecosystem services - species richness - biodiversity - conservation - forest - lidar - classifications - management - predictor - invasions
    Protected areas are experiencing increased levels of human pressure. To enable appropriate conservation action, it is critical to map and monitor changes in the type and extent of land cover/use and habitat classes, which can be related to human pressures over time. Satellite Earth observation (EO) data and techniques offer the opportunity to detect such changes. Yet association with field information and expert interpretation by ecologists is required to interpret, qualify and link these changes to human pressure. There is thus an urgent need to harmonize the technical background of experts in the field of EO data analysis with the terminology of ecologists, protected area management authorities and policy makers in order to provide meaningful, context-specific value-added EO products. This paper builds on the DPSIR framework, providing a terminology to relate the concepts of state, pressures, and drivers with the application of EO analysis. The type of pressure can be inferred through the detection of changes in state (i.e. changes in land cover and/or habitat type and/or condition). Four broad categories of changes in state are identified, i.e. land cover/habitat conversion, land cover/habitat modification, habitat fragmentation and changes in landscape connectivity, and changes in plant community structure. These categories of change in state can be mapped through EO analyses, with the goal of using expert judgement to relate changes in state to causal direct anthropogenic pressures. Drawing on expert knowledge, a set of protected areas located in diverse socio-ecological contexts and subject to a variety of pressures are analysed to (a) link the four categories of changes in state of land cover/habitats to the drivers (anthropogenic pressure), as relevant to specific target land cover and habitat classes; (b) identify (for pressure mapping) the most appropriate spatial and temporal EO data sources as well as interpretations from ecologists and field data useful in connection with EO data analysis. We provide detailed examples for two protected areas, demonstrating the use of EO data for detection of land cover/habitat change, coupled with expert interpretation to relate such change to specific anthropogenic pressures. We conclude with a discussion of the limitations and feasibility of using EO data and techniques to identify anthropogenic pressures, suggesting additional research efforts required in this direction.
    Evidence for an unidentified non-photochemical ground-level source of formaldehyde in the Po Valley with potential implications for ozone production
    Kaiser, J. ; Wolfe, G.M. ; Bohn, B. ; Ganzeveld, L.N. - \ 2015
    Atmospheric Chemistry and Physics 15 (2015). - ISSN 1680-7316 - p. 1289 - 1298.
    volatile organic-compounds - exchange cafe model - total oh reactivity - tropospheric degradation - chemical mechanism - gas-phase - part - atmosphere - forest - hydrocarbons
    Ozone concentrations in the Po Valley of northern Italy often exceed international regulations. As both a source of radicals and an intermediate in the oxidation of most volatile organic compounds (VOCs), formaldehyde (HCHO) is a useful tracer for the oxidative processing of hydrocarbons that leads to ozone production. We investigate the sources of HCHO in the Po Valley using vertical profile measurements acquired from the airship Zeppelin NT over an agricultural region during the PEGASOS 2012 campaign. Using a 1-D model, the total VOC oxidation rate is examined and discussed in the context of formaldehyde and ozone production in the early morning. While model and measurement discrepancies in OH reactivity are small (on average 3.4 ± 13%), HCHO concentrations are underestimated by as much as 1.5 ppb (45%) in the convective mixed layer. A similar underestimate in HCHO was seen in the 2002–2003 FORMAT Po Valley measurements, though the additional source of HCHO was not identified. Oxidation of unmeasured VOC precursors cannot explain the missing HCHO source, as measured OH reactivity is explained by measured VOCs and their calculated oxidation products. We conclude that local direct emissions from agricultural land are the most likely source of missing HCHO. Model calculations demonstrate that radicals from degradation of this non-photochemical HCHO source increase model ozone production rates by as much as 0.6 ppb h-1 (12%) before noon.
    Tree-ring d18O in African mahogany (Entandrophragma utile) records regional precipitation and can be used for climate reconstructions
    Sleen, J.P. van der; Groenendijk, P. ; Zuidema, P. - \ 2015
    Global and Planetary Change 127 (2015). - ISSN 0921-8181 - p. 58 - 66.
    oxygen-isotope ratios - tropical atlantic - west-africa - monsoon - growth - forest - chronologies - temperature - variability - salinity
    The availability of instrumental climate data in West and Central Africa is very restricted, both in space and time. This limits the understanding of the regional climate system and the monitoring of climate change and causes a need for proxies that allow the reconstruction of paleoclimatic variability. Here we show that oxygen isotope values (d18O) in tree rings of Entandrophragma utile from North-western Cameroon correlate to precipitation on a regional to sub-continental scale (1930–2009). All found correlations were negative, following the proposed recording of the ‘amount effect’ by trees in the tropics. The capacity of E. utile to record the variability of regional precipitation is also confirmed by the significant correlation of tree-ring d18O with river discharge data (1944–1983), outgoing longwave radiation (a proxy for cloud cover; 1974–2011) and sea surface salinity in the Gulf of Guinea (1950–2011). Furthermore, the high values in the d18O chronology from 1970 onwards coincide with the Sahel drought period. Given that E. utile presents clear annual growth rings, has a wide-spread distribution in tropical Africa and is long lived (> 250 years), we argue that the analysis of oxygen isotopes in growth rings of this species is a promising tool for the study of paleoclimatic variability during the last centuries in West and Central Africa.
    Soil surface changes increase runoff and erosion risk after a low–moderate severity fire
    Stoof, C.R. ; Ferreira, A.J.D. ; Mol, W. ; Berg, J. van den; Kort, A. De; Drooger, S. ; Slingerland, E.C. ; Mansholt, A.U. ; Ritsema, C.J. - \ 2015
    Geoderma 239-240 (2015). - ISSN 0016-7061 - p. 58 - 67.
    critical shear-stress - random roughness - overland-flow - mediterranean ecosystem - physical-properties - water repellency - prescribed fire - burn severity - forest - wildfire
    Post-fire land degradation is to a large degree determined by what happens to soil properties and ground cover during and after the fire. To study fire impact in relation to fire intensity and post-fire soil exposure, a 9-ha Portuguese shrubland catchmentwas burned by experimental fire in the 2008/9 winter season. Previous studies reported on the significant increase in erosion after this fire, and discussed the role of reduced canopy interception and changed soil water repellency dynamics. Our objective was to assess whether fire-induced changes in soil physical properties and soil surface characteristics may have played an additional role in the increase in runoff and erosion observed after the fire. We sampled these properties before, immediately after, and up to one year after fire, and monitored soil temperatures during the fire using thermocouples. Despite the locally high fire intensity (N15.000kWm-1 in some places), soil physical changeswere not observed: topsoil bulk density, organic matter, porosity and saturated conductivity did not significantly change, likely because soil temperatures stayedlow with the 0.5 cm depth not exceeding 32.5 °C. Soil surface characteristics did change: Manning's n and randomroughness both decreased, increasing the risk and erosivity of overland flow. Results indicate that soil physical changes unlikely contributed to the increase in post-fire erosion observed in the catchment and that a highintensity winter burn does not necessarily lead to severe soil changes. Nevertheless, soil surface changes during and after fire contribute to an increase runoff and erosion risk in these areas
    Multi-model radiometric slope correction of SAR images of complex terrain using a two-stage semi-empirical approach
    Hoekman, D.H. ; Reiche, J. - \ 2015
    Remote Sensing of Environment 156 (2015). - ISSN 0034-4257 - p. 1 - 10.
    radar imagery - topography - forest - classification - backscatter - validation
    Practical approaches for the implementation of terrain type dependent radiometric slope correction for SAR data are introduced. Radiometric slope effects are modelled as the products of two models. The first is a simple physical model based on the assumption of a uniform opaque layer of isotropic scatterers, which is independent of terrain type, frequency and polarization. It accounts for the slope-induced variation in the number of scatterers per resolution cell. The second is a semi-empirical model, which accounts for the variation in scattering mechanisms, dependent on terrain type, frequency and polarization. PALSAR FBD (L-band, HH- and HV-polarization) data are used at two test sites in Brazil and Fiji. Results for the Brazilian area, which has slopes up to 25°, show that remaining slope effects for the multi-model case are much smaller than 0.1 dB, for all land cover types. This is much better than the best single-model approach where remaining slope effects can be very small for forests but be as large as 1.77 dB for woodland in HH-polarization. Results for the Fiji area, which has different vegetation types, are very similar. The potential large improvement, using this multi-model approach, in the accuracy of biomass estimation for transparent or open canopies is discussed. It is also shown that biomass change on slopes can be systematically under- or overestimated because of associated change in scattering mechanism.
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