Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 21 - 40 / 196

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    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.
    The fate of populations of Euterpe oleracea harvested for palm heart in Colombia
    Vallejo, M.I. ; Galeano, G. ; Bernal, R. ; Zuidema, P. - \ 2014
    Forest Ecology and Management 318 (2014). - ISSN 0378-1127 - p. 274 - 284.
    understory palm - leaf harvest - forest - extraction - management - demography - dynamics - sustainability - arecaceae - responses
    Palm heart is an important non-timber forest product obtained from various palm species in tropical forests. We studied the effect of four decades of palm heart extraction from the clonal palm Euterpe oleracea at the southern Pacific coast of Colombia. We monitored populations that had been subject to a range of harvest intensities and used measured vital rates (survival, growth, sexual and clonal reproduction) to construct population matrix models. We then used these models to simulate several harvest scenarios and to project the population dynamics for the next 50 years. Our projections suggest that the currently implemented intensive harvest regimes - which involve up to four harvests per year - result in dramatic demographic changes, primarily affecting seedlings and adults. In addition, current harvest regimes affect the future supply of palm heart, which is projected to drop sharply during the first years following harvest and fails to recover unless a number of stems are spared. Our simulations indicate that the most sustainable scenarios involve annual harvest between 50% and 75% of all harvestable stems, without any removal of small shoots from the clumps. Implementation of this regime must be accompanied by other management practices, including planning harvestable areas, marking the stems to be cut during subsequent harvests, assigning harvesters to specific areas, and leaving harvest residues as mulch around clumps. The degradation of populations of E. oleracea directly affects livelihoods of local people, by reducing cash income from palm heart sales and by reducing availability of palm fruits, a locally important food resource. (C) 2014 Elsevier B.V. All rights reserved.
    Does phenology distinguish bitter and sweet African bush mango trees (Irvingia spp., Irvingiaceae)?
    Vihotogbe, R. ; Berg, R.G. van den; Bongers, F. ; Sinsin, B. ; Sosef, M.S.M. - \ 2014
    Trees-Structure and Function 28 (2014)6. - ISSN 0931-1890 - p. 1777 - 1791.
    genetic diversity - dahomey gap - west-africa - phenotypic variation - conservation status - gabonensis - domestication - forest - cameroon - fruits
    Key message This phenological analysis of bitter and sweet bush mango trees is part of their biosystematics. It supports the species distinction hypothesis postulated by Harris (Bull J Bot Nat Belg 65(1-2):143-196, 1996 ) and Lowe et al. (Mol Ecol 9:831-841, 2000 ). African Bush Mango trees are priority food trees in Sub-Saharan Africa. The unclear distinction between bitter and sweet fruited trees is still subject to taxonomic debate. This hinders their effective use and conservation programmes. This study investigates differences in phenological behaviour between bitter and sweet fruited populations and their taxonomic implications. Monthly phenological description data on seven populations of bitter or sweet bush mangos across Benin and Togo were used to assess within and between mango type phenological diversity, to discriminate bitter and sweet trees and to evaluate their responses to environmental factors. The phenological states differentiating bitter and sweet trees were identified and individual trees were classified based on the discriminating phenological characters. Finally, phenological variation was analyzed with time of the year, soil type, type of bush mango tree, and climatic zone. Phenological diversity varies significantly among populations. Bitter and sweet trees have consistently different phenological states. Bitter trees have a lower phenological diversity for all phenological phases throughout the year compared to sweet trees, possibly due to their limited distribution range in the study area. The tree types also differ in their reproductive responses to environmental factors, but did not respond differently to soils. These results support the hypothesis that bitter and sweet trees represent different taxa and we suggest for efficient conservation purpose to consider them as different species.
    Vegetation dynamics prior to wildlife reintroductions in southern umfurudzi park, Zimbabwe
    Muposhi, V. ; Ndlovu, N. ; Gandiwa, E. ; Muvengwi, J. ; Muboko, N. - \ 2014
    The JAPS 24 (2014)6. - ISSN 1018-7081 - p. 1680 - 1690.
    gonarezhou national-park - tree species-diversity - woody vegetation - miombo woodlands - tanzania - forest - size - herbivores - elephants - savannas
    Vegetation assessments are critical in the status and success of reintroduction programs and are an important aspect in ecological restoration. Vegetation structure and composition influences the suitability and availability of unique habitats for different wildlife species. The objectives of this study were to (1) establish the vegetation structure and composition, and (2) determine the soil-vegetation associations in southern Umfurudzi Park, Zimbabwe, prior to the reintroduction of wildlife species. Using a stratified random design, 15 rectangular plots from three strata were assessed in April and May 2012. A total of 23 woody plants from 58 tree and 68 shrub families as well as 30 grass species were recorded. Tree basal area, canopy cover, tree density, tree and grass species diversity, and tree height for the riverine strata were significantly different from the miombo and vlei strata. The influence of soil properties on the occurrence and diversity of woody and grass species was evident across the three strata. Long-term changes in the vegetation dynamics and primary productivity in southern Umfurudzi Park due to the reintroduced mega-herbivores is recommended for the success of the restoration program.
    Evaluating a non-destructive method for calibrating tree biomass equations derived from tree branching architecture
    MacFarlane, D.W. ; Kuyah, S. ; Mulia, R. ; Dietz, J. ; Muthuri, C. ; Noordwijk, M. van - \ 2014
    Trees-Structure and Function 28 (2014)3. - ISSN 0931-1890 - p. 807 - 817.
    aboveground biomass - root architecture - fractal analysis - model - agroforestry - allometry - systems - forest - size
    Functional branch analysis (FBA) is a promising non-destructive alternative to the standard destructive method of tree biomass equation development. In FBA, a theoretical model of tree branching architecture is calibrated with measurements of tree stems and branches to estimate the coefficients of the biomass equation. In this study, species-specific and mixed-species tree biomass equations were derived from destructive sampling of trees in Western Kenya and compared to tree biomass equations derived non-destructively from FBA. The results indicated that the non-destructive FBA method can produce biomass equations that are similar to, but less accurate than, those derived from standard methods. FBA biomass prediction bias was attributed to the fact that real trees diverged from fractal branching architecture due to highly variable length–diameter relationships of stems and branches and inaccurate scaling relationships for the lengths of tree crowns and trunks assumed under the FBA model.
    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.
    Spatio-temporal trends of nitrogen deposition and climate effects on Sphagnum productivity in European peatlands
    Granath, G. ; Limpens, J. ; Posch, M. ; Mücher, S. ; Vries, W. de - \ 2014
    Environmental Pollution 187 (2014). - ISSN 0269-7491 - p. 73 - 80.
    carbon accumulation - n deposition - boreal mire - bogs - growth - vegetation - impact - mosses - forest - emissions
    To quantify potential nitrogen (N) deposition impacts on peatland carbon (C) uptake, we explored temporal and spatial trends in N deposition and climate impacts on the production of the key peat forming functional group (Sphagnum mosses) across European peatlands for the period 1900–2050. Using a modelling approach we estimated that between 1900 and 1950 N deposition impacts remained limited irrespective of geographical position. Between 1950 and 2000 N deposition depressed production between 0 and 25% relative to 1900, particularly in temperate regions. Future scenarios indicate this trend will continue and become more pronounced with climate warming. At the European scale, the consequences for Sphagnum net C-uptake remained small relative to 1900 due to the low peatland cover in high-N areas. The predicted impacts of likely changes in N deposition on Sphagnum productivity appeared to be less than those of climate. Nevertheless, current critical loads for peatlands are likely to hold under a future climate.
    Negative density dependence of seed dispersal and seedling recruitment in a Neotropical palm
    Jansen, P.A. ; Visser, M.D. ; Joseph Wright, S. ; Rutten, G. ; Muller-Landau, H.C. - \ 2014
    Ecology Letters 17 (2014)9. - ISSN 1461-023X - p. 1111 - 1120.
    scatter-hoarding rodent - tropical tree - spatial-patterns - plant diversity - forest - competition - removal - consequences - mechanisms - herbivores
    Negative density dependence (NDD) of recruitment is pervasive in tropical tree species. We tested the hypotheses that seed dispersal is NDD, due to intraspecific competition for dispersers, and that this contributes to NDD of recruitment. We compared dispersal in the palm Attalea butyracea across a wide range of population density on Barro Colorado Island in Panama and assessed its consequences for seed distributions. We found that frugivore visitation, seed removal and dispersal distance all declined with population density of A. butyracea, demonstrating NDD of seed dispersal due to competition for dispersers. Furthermore, as population density increased, the distances of seeds from the nearest adult decreased, conspecific seed crowding increased and seedling recruitment success decreased, all patterns expected under poorer dispersal. Unexpectedly, however, our analyses showed that NDD of dispersal did not contribute substantially to these changes in the quality of the seed distribution; patterns with population density were dominated by effects due solely to increasing adult and seed density.
    Why trees and shrubs but rarely trubs?
    Scheffer, M. ; Vergnon, R.O.H. ; Cornelissen, J.H.C. ; Hantson, S. ; Holmgren, M. ; Nes, E.H. van; Xu, C. - \ 2014
    Trends in Ecology and Evolution 29 (2014)8. - ISSN 0169-5347 - p. 433 - 434.
    savanna - forest - transitions - height
    An analysis of the maximum height of woody plant species across the globe reveals that an intermediate size is remarkably rare. We speculate that this may be due to intrinsic suboptimality or to ecosystem bistability with open landscapes favouring shrubs, and closed canopies propelling trees to excessive tallness.
    Traditional land use and reconsideration of environmental zoning in the Hawf Protected Area, south-eastern Yemen
    Slecht, E. ; Zaballos, L.G.H. ; Quiroz Villarreal, D.K. ; Scholte, P. ; Buerkert, A. - \ 2014
    Journal of Arid Environments 109 (2014). - ISSN 0140-1963 - p. 92 - 102.
    monsoonal fog oases - arabian peninsula - mountain pastures - genetic-structure - conservation - goats - populations - forest - kenya
    The Al Hawf area at the Yemen–Oman border hosts a unique fog-derived ecosystem which, due to its high diversity of plant and animal species, merits protection. Given the area's remoteness, poor infrastructure, high population growth and limited exchanges across the Omani border, the local livelihoods strongly rely on the exploitation of natural marine and terrestrial resources. Since quantitative data on the intensity of anthropogenic pressure on the terrestrial ecosystem are lacking, the present study analysed the impact of agricultural and pastoral land use on the vegetation of the designated Hawf Protected Area (HPA). To this end structured interviews, village walks and other rural appraisal tools were combined with vegetation surveys and GPS-based monitoring of pasturing livestock herds. The loss of traditional herding systems that regulated selective management of fragile grazing grounds along the altitude gradient in the HPA, particularly for camels, the overexploitation of woody perennials for construction purposes, and the resettlement of former migrant workers are major constraints for the successful implementation of the government-designed management plan. Implementation could be improved by better taking into account the vegetation composition in the area, current and traditional grazing schemes and local people's needs for off-farm income
    Relative growth rate variation of evergreen and deciduous savanna tree species is driven by different traits
    Tomlinson, K.W. ; Poorter, L. ; Bongers, F. ; Borghetti, F. ; Jacobs, L. ; Langevelde, F. van - \ 2014
    Annals of Botany 114 (2014)2. - ISSN 0305-7364 - p. 315 - 324.
    phylogenetically independent contrasts - adaptive significance - carbohydrate storage - shade tolerance - seedling shade - woody-plants - allocation - biomass - forest - strategies
    Background and Aims Plant relative growth rate (RGR) depends on biomass allocation to leaves (leaf mass fraction, LMF), efficient construction of leaf surface area (specific leaf area, SLA) and biomass growth per unit leaf area (net assimilation rate, NAR). Functional groups of species may differ in any of these traits, potentially resulting in (1) differences in mean RGR of groups, and (2) differences in the traits driving RGR variation within each group. We tested these predictions by comparing deciduous and evergreen savanna trees. Methods RGR, changes to biomass allocation and leaf morphology, and root non-structural carbohydrate reserves were evaluated for juveniles of 51 savanna species (34 deciduous, 17 evergreen) grown in a common garden experiment. It was anticipated that drivers ofRGRwould differ between leaf habit groups because deciduous species have to allocate carbohydrates to storage in roots to be able to flush leaves again, which directly compromises their LMF, whereas evergreen species are not subject to this constraint. Key Results Evergreen species had greaterLMFandRGRthan deciduous species. Amongdeciduous speciesLMF explained 27% of RGR variation (SLA 34% and NAR 29 %), whereas among evergreen species LMF explained between 2 and 17% of RGR variation (SLA 32–35% and NAR 38–62 %). RGR and LMF were (negatively) related to carbohydrate storage only among deciduous species. Conclusions Trade-offs between investment in carbohydrate reserves and growth occurred only among deciduous species, leading to differences in relative contribution made by the underlying components of RGR between the leaf habit groups. The results suggest that differences in drivers ofRGRoccur among savanna species because these have different selected strategies for coping with fire disturbance in savannas. It is expected that variation in the drivers of RGR will be found in other functional types that respond differently to particular disturbances.
    Social Networks of Corruption in the Vietnamese and Lao Cross-Border Timber Trade
    To, P.X. ; Mahanty, S. ; Dressler, W.H. - \ 2014
    Anthropological Forum : a journal of social anthropology and comparative sociology 24 (2014)2. - ISSN 0066-4677 - p. 154 - 174.
    forest - politics
    Although corruption is a core issue in discourses on Southeast Asian states and the region's illegal timber trade, its specific meanings, characteristics, and role are poorly understood. Our ethnographic study of corruption and timber trade in the lower Mekong uncovers the relationships, dealings, and networks that enable illegal timber flows. We follow the disputed case of a shipment of high-value timber that originated in Laos and was seized by Vietnamese seaport customs officials in 2011. By examining the actors involved and their efforts to obtain the release of the timber, we reveal the complex and networked nature of relationships from local to national levels that enable illicit rosewood trade from Laos to Vietnam and onward from Vietnamese ports. At the same time, interactions between timber traders and state officials highlight the recursive relationship between ‘private’ and ‘state’ actors, and the scope for mobility between these categories. Our analysis challenges the current international and national emphasis on law enforcement as a means to tackle illegal logging. Instead, policy would be better founded on a more holistic and nuanced understanding of the socio-political relationships that characterise and perpetuate corruption across these multiple scales.
    Rapid characterisation of vegetation structure to predict refugia and climate change impacts across a global biodiversity hotspot
    Schut, A.G.T. ; Wardell-Johnson, G.W. ; Yates, C.J. ; Keppel, G. ; Baran, I. ; Franklin, S.E. ; Hopper, S.D. ; Niel, K.P. Van; Mucina, L. ; Byrne, M. - \ 2014
    PLoS ONE 9 (2014)1. - ISSN 1932-6203 - 15 p.
    australian floristic region - western-australia - conservation - forest - fire - future - scale - distributions - microrefugia - inselbergs
    Identification of refugia is an increasingly important adaptation strategy in conservation planning under rapid anthropogenic climate change. Granite outcrops (GOs) provide extraordinary diversity, including a wide range of taxa, vegetation types and habitats in the Southwest Australian Floristic Region (SWAFR). However, poor characterization of GOs limits the capacity of conservation planning for refugia under climate change. A novel means for the rapid identification of potential refugia is presented, based on the assessment of local-scale environment and vegetation structure in a wider region. This approach was tested on GOs across the SWAFR. Airborne discrete return Light Detection And Ranging (LiDAR) data and Red Green and Blue (RGB) imagery were acquired. Vertical vegetation profiles were used to derive 54 structural classes. Structural vegetation types were described in three areas for supervised classification of a further 13 GOs across the region. Habitat descriptions based on 494 vegetation plots on and around these GOs were used to quantify relationships between environmental variables, ground cover and canopy height. The vegetation surrounding GOs is strongly related to structural vegetation types (Kappa = 0.8) and to its spatial context. Water gaining sites around GOs are characterized by taller and denser vegetation in all areas. The strong relationship between rainfall, soil-depth, and vegetation structure (R2 of 0.8–0.9) allowed comparisons of vegetation structure between current and future climate. Significant shifts in vegetation structural types were predicted and mapped for future climates. Water gaining areas below granite outcrops were identified as important putative refugia. A reduction in rainfall may be offset by the occurrence of deeper soil elsewhere on the outcrop. However, climate change interactions with fire and water table declines may render our conclusions conservative. The LiDAR-based mapping approach presented enables the integration of site-based biotic assessment with structural vegetation types for the rapid delineation and prioritization of key refugia.
    Tipping points in tropical tree cover: linking theory to data
    Nes, E.H. van; Hirota, M. ; Holmgren, M. ; Scheffer, M. - \ 2014
    Global Change Biology 20 (2014)3. - ISSN 1354-1013 - p. 1016 - 1021.
    critical transitions - global resilience - climate-change - stable states - savanna - fire - forest - ecosystems - amazon - deforestation
    It has recently been found that the frequency distribution of remotely sensed tree cover in the tropics has three distinct modes, which seem to correspond to forest, savanna and treeless states. This pattern has been suggested to imply that these states represent alternative attractors, and that the response of these systems to climate change would be characterized by critical transitions and hysteresis. Here, we show how this inference is contingent upon mechanisms at play. We present a simple dynamical model that can generate three alternative tree cover states (forest, savanna and a treeless state), based on known mechanisms, and use this model to simulate patterns of tree cover under different scenarios. We use these synthetic data to show that the hysteresis inferred from remotely sensed tree cover patterns will be inflated by spatial heterogeneity of environmental conditions. On the other hand, we show that the hysteresis inferred from satellite data may actually underestimate real hysteresis in response to climate change if there exists a positive feedback between regional tree cover and precipitation. Our results also indicate that such positive feedback between vegetation and climate should cause direct shifts between forest and a treeless state (rather than through an intermediate savanna-state) to become more likely. Lastly, we show how directionality of historical change in conditions may bias the observed relationship between tree cover and environmental conditions.
    Diversity and dynamics of management of gum and resin resources in Ethiopia: a trade-off between domestication and degradation
    Lemenih, M. ; Wiersum, K.F. ; Teshale Woldeamanuel Habebo, Teshale ; Bongers, F. - \ 2014
    Land Degradation and Development 25 (2014)2. - ISSN 1085-3278 - p. 130 - 142.
    papyrifera del. hochst - boswellia-papyrifera - biodiversity conservation - northern ethiopia - forest - frankincense - acacia - restoration - environment - landscapes
    Although the human domestication of forest and tree resources is often considered to result in resource degradation, it may also lead to improved resource potentials. This paper assesses the nature and dynamics of gum and resin focused woodland exploitation and management systems in Ethiopia in the context of degradation and domestication processes. In three sites with commercial gum resin producing woodlands and production history, we studied variation in (i) woodland management and gum resin production systems and (ii) socio-economic and biophysical factors that condition the management and production systems. On the basis of their organizational features, we formulated nine production models and related them to different phases of domestication and different degrees of ecosystem degradation. The production systems gradually evolved from the extraction of wild trees to production in an adapted forest system. However, domesticated woodlands with an adapted forest structure and composition and increased provisioning services are still little developed despite decades of production history. Many of these woodlands are undergoing serious degradation because of low quality management practices. This is mainly attributable to existing land use practices and the social arrangements for the production of and trade in the gums and resins. The findings illustrate that domestication involves not only a change in ecological and production systems but also the development of social arrangements for production and trade. We conclude that the status of domestication in a social sense determines whether forests and/or specific forest resources are degraded or aggraded in the sense of resource enrichment
    On the variation of regional CO2 exchange over temperate and boreal North America
    Zhang, X. ; Gurney, K.R. ; Peylin, P. ; Chevallier, F. ; Law, R.M. ; Patra, P.K. ; Rayner, P.J. ; Roedenbeck, C. ; Krol, M.C. - \ 2013
    Global Biogeochemical Cycles 27 (2013)4. - ISSN 0886-6236 - p. 991 - 1000.
    atmospheric carbon-dioxide - terrestrial ecosystems - united-states - interannual variability - climate - forest - trends - drought - fluxes - land
    Inverse-estimated net carbon exchange time series spanning two decades for six North American regions are analyzed to examine long-term trends and relationships to temperature and precipitation variations. Results reveal intensification of carbon uptake in eastern boreal North America (0.1 PgC/decade) and the Midwest United States (0.08 PgC/decade). Seasonal cross-correlation analysis shows a significant relationship between net carbon exchange and temperature/precipitation anomalies during the western United States growing season with warmer, dryer conditions leading reduced carbon uptake. This relationship is consistent with global change-type drought dynamics which drive increased vegetation mortality, increases in dry woody material, and increased wildfire occurrence. This finding supports the contention that future climate change may increase carbon loss in this region. Similarly, higher temperatures and reduced precipitation are accompanied by decreased net carbon uptake in the Midwestern United States toward the end of the growing season. Additionally, intensified net carbon uptake during the eastern boreal North America growing season is led by increased precipitation anomalies in the previous year, suggesting the influence of climate memory carried by regional snowmelt water. The two regions of boreal North America exhibit opposing seasonal carbon-temperature relationships with the eastern half experiencing a net carbon loss with near coincident increases in temperature and the western half showing increased net carbon uptake. The carbon response in the boreal west region lags the temperature anomalies by roughly 6months. This opposing carbon-temperature relationship in boreal North America may be a combination of different dominant vegetation types, the amount and timing of snowfall, and temperature anomaly differences across boreal North America.
    Soil organic matter dynamics in Mediterranean A-horizons-The use of analytical pyrolysis to ascertain land-use history
    Schellekens, J. ; Barbera, G.G. ; Buurman, P. ; Perez-Jorda, G. ; Martinez-Cortizas, A. - \ 2013
    Journal of Analytical and Applied Pyrolysis 104 (2013). - ISSN 0165-2370 - p. 287 - 298.
    chromatography-mass-spectrometry - black carbon - fractionation methods - calcareous soils - nw spain - gc/ms - turnover - biomass - lignin - forest
    In archaeology and nature conservation studies, knowledge about (pre)historical land-use is important. The molecular composition of soil organic matter (SOM) supplies information about its history, as its composition is controlled by input material and decay processes. In this study, the molecular composition of SOM of calcareous A-horizons from SE Spain was studied with pyrolysis gas chromatography/mass spectrometry (pyrolysis-GC/MS). The effect of vegetation type (Pinus halepensis forest and Stipa tenacissima grassland), land-use (cultivation with cereals and olive trees) and wildfire were examined. In addition, former grassland and agricultural soils that had been reforested with P. halepensis (35 yr) were selected. Three locations were sampled for each vegetation type, except for the olive tree (two) and cereal (six) fields, resulting in a total of 26 samples. Each sample was a composite of ten sub-samples taken from a plot of I ha. After removal of weakly or non-decomposed particulate OM, two OM fractions were obtained; (i) sodium hydroxide (NaOH) extractable OM and (ii) the OM that remained after extraction, which was isolated after dissolution of minerals by repeated hydrofluoric acid (HF) treatment. The NaOH-extractable fraction is generally used in soil chemistry (i.e. humic acid), but surprisingly little is known about the SOM that remains in the residue (i.e. humin plus minerals). Comparison of the two SOM fractions (by factor analyses applied to 82 quantified pyrolysis products) provided insight into soil OM dynamics. Polyaromatic pyrolysis products were more prominent in the extractable OM, while a relative enrichment of aliphatic compounds was found in the non-extractable OM. Although some pyrolysis products were associated with one vegetation type in both SOM fractions (C-3-naphthalene, dimethylphenanthrene and 2,3,5-trimethylphenanthrene, retene, and monoterpenes for both burnt and unburnt P. halepensis forest: benzene, naphthalene and C-1-naphthalene for burnt and unburnt S. tenacissima grassland), lignin content and composition highly differed between agricultural soils and soils under native vegetation in both SOM fractions. These differences were mainly decay characteristics, reinforced by cultivation. In reforested soils it was still possible to identify their former land-use, decades after the vegetation change. The probability of the sites to be correctly attributed to its present land-use was P > 0.7 for grassland and pine forest, while most of the cultivated sites had a P > 0.5 to be assigned correctly. The results obtained suggest that the molecular composition of SOM has a large potential for reconstructing land-use history, at least at the scale of decades/centuries. (C) 2013 Elsevier B.V. All rights reserved.
    Are the mangroves in the Galle-Unawatuna area (Sri Lanka) at risk? A social-ecological approach involving local stakeholders for a better conservation policy
    Satyanarayana, B. ; Mulder, S. ; Jayatissa, L.P. ; Dahdouh-Guebas, F. - \ 2013
    Ocean & Coastal Management 71 (2013). - ISSN 0964-5691 - p. 225 - 237.
    indian-ocean tsunami - coastal vegetation - environmental-change - socioeconomic data - natural disasters - human-populations - ecosystems - forest - protection - perceptions
    Despite the known ecological and economic importance of mangrove ecosystems, research is still lacking as to what extent local populations depends on various forest products, or how this might be related to their economic status (i.e. poor, middle and rich), age, or gender (male and female) relations. In the present study, the percentage of people depending on such resources in the Galle-Unawatuna area (Sri Lanka) for their subsistence needs was assessed through a survey. The results indicated that local people rely on mangroves to a greater extent for fishery products, fuelwood, and edible plants, than for house/boat construction material, medicinal and other non-timber forest products. All people under the poor, middle and rich categories use mangrove resources, although greater dependency of the poor is common. In relation to age, the mangrove resources utilization was high among old (>60 years) people. A gendered division of labor indicating the men involved in fishery-related activities and women in edible plant collection was observed. In addition, the use of mangrove resources is not necessarily poverty-driven: preference and tradition also play important roles. However, the physical infrastructure developments (i.e. construction of a cement factory, dam and road) have had several negative impacts ranging from water quality deterioration and dynamic shifts in mangrove vegetation to reduced fish production in the vicinity. Given our results, possible amendments to the existing rules governing forest conservation are recommended in order to provide long-term benefits for local livelihoods as well as ecosystem. (C) 2012 Elsevier Ltd. All rights reserved.
    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.
    An institutional analysis of deforestation processes in protected areas: The case of the transboundary Mt. Elgon, Uganda and Kenya
    Petursson, J.G. ; Vedeld, P. ; Sassen, M. - \ 2013
    Forest Policy and Economics 26 (2013). - ISSN 1389-9341 - p. 22 - 33.
    mount-elgon - forest - conservation - management - biodiversity - livelihoods - tropics - parks
    Protected areas (PAs) are a country's key strategy to conserve and manage forest resources. In sub-Saharan Africa, the effectiveness and efficiency of PA institutions in delivering sustainable outcomes is debated, however, and deforestation has not been avoided within such formal regimes. This paper analyzes the processes that led to deforestation within the PAs on the transboundary Mt. Elgon, Uganda-Kenya, employing institutional theory. Landsat satellite imagery helped identify and quantify forest loss over time. The study showed how, since 1973, about a third of all forests within the PAs on Elgon have been cleared in successive processes. Within formal protected area regimes, complex political and institutional factors drive forest loss. We argue, therefore, that policies to counter deforestation using a PA model have to be considered and understood against the broader background of these factors, originating both inside and outside the PA regimes. (C) 2012 Elsevier B.V. All rights reserved.
    Check title to add to marked list

    Show 20 50 100 records per page

     
    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.