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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    A Bayesian approach to combine Landsat and ALOS PALSAR time series for near real-time deforestation detection
    Reiche, J. ; Bruin, S. de; Hoekman, D.H. ; Verbesselt, J. ; Herold, M. - \ 2015
    Remote Sensing 7 (2015). - ISSN 2072-4292 - p. 4973 - 4996.
    conditional-probability networks - remotely-sensed images - forest cover loss - tropical deforestation - brazilian amazon - accuracy assessment - classification - sar - disturbance - fusion
    To address the need for timely information on newly deforested areas at medium resolution scale, we introduce a Bayesian approach to combine SAR and optical time series for near real-time deforestation detection. Once a new image of either of the input time series is available, the conditional probability of deforestation is computed using Bayesian updating, and deforestation events are indicated. Future observations are used to update the conditional probability of deforestation and, thus, to confirm or reject an indicated deforestation event. A proof of concept was demonstrated using Landsat NDVI and ALOS PALSAR time series acquired at an evergreen forest plantation in Fiji. We emulated a near real-time scenario and assessed the deforestation detection accuracies using three-monthly reference data covering the entire study site. Spatial and temporal accuracies for the fused Landsat-PALSAR case (overall accuracy = 87.4%; mean time lag of detected deforestation = 1.3 months) were consistently higher than those of the Landsat- and PALSAR-only cases. The improvement maintained even for increasing missing data in the Landsat time series.
    Disturbance Level Determines the Regeneration of Commercial Tree Species in the Eastern Amazon
    Schwartz, G. ; Lopes, J.C. ; Kanashiro, M. ; Mohren, G.M.J. ; Pena Claros, M. - \ 2014
    Biotropica 46 (2014)2. - ISSN 0006-3606 - p. 148 - 156.
    mahogany swietenia-macrophylla - bolivian tropical forest - reduced-impact - brazilian amazon - natural regeneration - logging damage - silvicultural treatments - carapa-guianensis - timber production - gaps
    The effects of reduced-impact logging (RIL) on the regeneration of commercial tree species were investigated, as long-term timber yields depend partly on the availability of seedlings in a managed forest. On four occasions during a 20-month period in the Tapajós National Forest (Eastern Amazon, Brazil), seven commercial tree species were assessed as follows: the long-lived pioneers Bagassa guianensis and Jacaranda copaia; the partially shade-tolerant Hymenaea courbaril, Dipteryx odorata, and Carapa guianensis; and the totally shade-tolerant Symphonia globulifera and Manilkara huberi. In 2439 10 × 10 m plots, all individuals <20 cm diameter at breast height (dbh) were assessed over three intervals, before, during, and after the forest being logged. Before logging, the density of seedlings and saplings of the seven species did not change. Logged trees were spatially aggregated, with 9.2 percent of the plots being heavily impacted by logging. After logging, the recruitment rate increased more than the mortality rate, so that post-harvesting densities of seedlings and saplings increased. The increase in density was concentrated in logged plots with more disturbances. It is concluded that post-harvesting heterogeneity of micro-environments created by RIL may be an important component to be taken into account for sustainable forest management and conservation of commercial species.
    Integrating Stand and Soil Properties to Understand Foliar Nutrient Dynamics during Forest Succession Following Slash-and-Burn Agriculture in the Bolivian Amazon
    Broadbent, E.N. ; Zambrano, A.M.A. ; Asner, G.P. ; Soriano, M. ; Field, C.B. ; Souza, H.R. de; Pena Claros, M. ; Adams, R.I. ; Dirzo, R. ; Giles, L. - \ 2014
    PLoS ONE 9 (2014)2. - ISSN 1932-6203 - 23 p.
    carbon-isotope discrimination - tropical rain-forests - n-15 natural-abundance - northeastern costa-rica - below-ground carbon - land-use change - n-p ratios - secondary forest - organic-matter - brazilian amazon
    Secondary forests cover large areas of the tropics and play an important role in the global carbon cycle. During secondary forest succession, simultaneous changes occur among stand structural attributes, soil properties, and species composition. Most studies classify tree species into categories based on their regeneration requirements. We use a high-resolution secondary forest chronosequence to assign trees to a continuous gradient in species successional status assigned according to their distribution across the chronosequence. Species successional status, not stand age or differences in stand structure or soil properties, was found to be the best predictor of leaf trait variation. Foliar d13C had a significant positive relationship with species successional status, indicating changes in foliar physiology related to growth and competitive strategy, but was not correlated with stand age, whereas soil d13C dynamics were largely constrained by plant species composition. Foliar d15N had a significant negative correlation with both stand age and species successional status, – most likely resulting from a large initial biomass-burning enrichment in soil 15N and 13C and not closure of the nitrogen cycle. Foliar %C was neither correlated with stand age nor species successional status but was found to display significant phylogenetic signal. Results from this study are relevant to understanding the dynamics of tree species growth and competition during forest succession and highlight possibilities of, and potentially confounding signals affecting, the utility of leaf traits to understand community and species dynamics during secondary forest succession.
    Options for a national framework for benefit distribution and their relation to community-based and national REDD+ monitoring
    Skutsch, M. ; Turnhout, E. ; Vijge, M.J. ; Herold, M. ; Wits, T. ; Besten, J.W. den; Balderas Torres, A. - \ 2014
    Forests 5 (2014)7. - ISSN 1999-4907 - p. 1596 - 1617.
    environmental services - brazilian amazon - payments - deforestation - conservation - carbon - challenges - poverty - mexico - biodiversity
    Monitoring is a central element in the implementation of national REDD+ and may be essential in providing the data needed to support benefit distribution. We discuss the options for benefit sharing systems in terms of technical feasibility and political acceptability in respect of equity considerations, and the kind of data that would be needed for the different options. We contrast output-based distribution systems, in which rewards are distributed according to performance measured in terms of carbon impacts, with input-based systems in which performance is measured in term of compliance with prescribed REDD+ activities. Output-based systems, which would require regular community carbon inventories to produce Tier 3 data locally, face various challenges particularly for the case of assessing avoided deforestation, and they may not be perceived as equitable. Input-based systems would require data on activities undertaken rather than change in stocks; this information could come from community-acquired data. We also consider how community monitored data could support national forest monitoring systems and the further development of national REDD+
    Age and light effects on seedling growth in two alternative secondary successions in central Amazonia
    Jakovac, A.C. ; Bentos, T.V. ; Mesquita, R.C.G. ; Williamson, G.B. - \ 2014
    Plant Ecology & Diversity 7 (2014)1-2. - ISSN 1755-0874 - p. 349 - 358.
    mahogany swietenia-macrophylla - cacao theobroma-cacao - tropical rain-forest - abandoned pastures - brazilian amazon - costa-rica - regeneration - communities - responses - environments
    Background : In central Amazonia, previous low intensity land use engenders succession dominated by Cecropia spp. which proceeds at high rates; however, at higher intensity of use succession is arrested and dominated by Vismia spp. over the long-term. Factors driving these two successional pathways are unknown. Aims : We aimed to elucidate seedling growth under the two alternative successional pathways. Methods : We experimentally determined the effects of successional age and photosynthetically active radiation (PAR) on relative height growth (RHG) of nine species of shade-tolerant tree seedlings in secondary forests dominated by Cecropia and Vismia, varying in age from 1–20 years. Results : In Cecropia-dominated successions, seedling RHG decreased with increasing successional age and with associated decreasing PAR. In Vismia-dominated successions, RHG was independent of successional age and PAR, and PAR did not change with successional age, being always higher than in Cecropia stands. The RHG of seedlings was lower in Vismia- than in Cecropia-dominated stands for similar PAR levels. Conclusions : Successional age and light availability affect seedlings growth differently in the two successional pathways. Unlike in Cecropia-dominated successions, in Vismia-dominated secondary forests seedling growth is limited by factors other than light. In a scenario of increasing land use intensity, constraints to seedling development in secondary forests can reduce species diversity in human-altered landscapes
    Post-harvesting silvicultural treatments in logging gaps: A comparison between enrichment planting and tending of natural regeneration
    Schwartz, G. ; Lopes, J.C.A. ; Mohren, G.M.J. ; Peña-Claros, M. - \ 2013
    Forest Ecology and Management 293 (2013). - ISSN 0378-1127 - p. 57 - 64.
    bolivian tropical forests - neotropical rain-forest - long-term impacts - reduced-impact - eastern amazon - brazilian amazon - dry forest - management - growth - canopy
    Despite greatly improved forest management in recent decades, long-term assessments show that if current harvesting volumes and cutting cycles are maintained, future volume yields of commercial species will decrease. A possible solution is to apply post-harvesting silvicultural treatments to increase the number of valuable trees. In this study we compared during 4 years two treatments: tending naturally established seedlings/saplings of commercial species in logging gaps, and enrichment planting + tending seedlings of commercial species. In both treatments, competition was artificially reduced by liberating each focal seedling/sapling from competitors (i.e. other tree seedlings/saplings, lianas, or herbs). The experiment was carried out in an area of ombrophilous dense forest managed by the Orsa Florestal forestry company in Jari Valley, eastern Amazon, Brazil (01°09'S and 52°38'W). The company applies reduced-impact logging in a polycyclic silvicultural system. We sampled 64 2-year-old logging gaps (average area 427.2 m2). Thirty-four gaps were used for the planting + tending, 15 gaps underwent the tending treatment, and there were 15 gaps in the control treatment (i.e. no intervention). The tending treatment showed lower mortality rate, faster growth rate, and required less liberation from overstorey plants and lianas than the other two treatments. Half of the species responded positively to tending: the long-lived pioneers Goupia glabra and Laetia procera, and the partially shade-tolerant Dinizia excelsa, Tachigali myrmecophila, and Trattinnickia sp. Similarly to tending, individuals subjected to the enrichment planting + tending treatment also presented higher growth rates. Based on these results we recommend tending be applied to areas with sufficient natural regeneration of commercial species. Enrichment planting + tending should be applied when regeneration of commercial species is scare, ideally using species that have high initial growth rates, and high commercial or conservation value.
    Livelihood strategies and forest dependence: New insights from Bolivian forest communities
    Zenteno, M. ; Zuidema, P.A. ; Jong, W. de; Boot, R.G.A. - \ 2013
    Forest Policy and Economics 26 (2013). - ISSN 1389-9341 - p. 12 - 21.
    brazilian amazon - developing-countries - conservation - products - household - deforestation - management - resources - framework - peasants
    Total income and income from forest resources among rural dwellers in tropical forest regions are influenced not only by market access, prices, but also organizational, institutional, and social factors. These factors influence the diversity of resources to which the poor have access and result in specializations in livelihood strategies. We analyzed the relation between forest dependence and livelihood strategies in the Bolivian Amazon, applying the SLF. We tested for the differences across strategies with respect to financial, human, physical, social, and natural livelihood assets. Results show that forest income is highly related to cash income from Brazil nut, while income from agriculture and timber exploitation is associated with higher levels of education. Brazil nuts serve as a safety net and start-up capital for certain livelihood strategies in our study region. Livelihood strategies that are based on the commercialization of multiple products from forests and agriculture and services inside and outside communities depend less on forests. Livelihoods can be supported by investing in sustainable livelihood asset endowments. Our results demonstrate that activities that aim to support community forest management and to enhance household income should explicitly consider a differentiated support for different strategies. This will result in a more effective outcome of development efforts from which the poorest people would benefit most.
    Interannual variability of carbon monoxide emission estimates over South America from 2006 to 2010
    Hooghiemstra, P.B. ; Krol, M.C. ; Leeuwen, T.T. van; Werf, G.R. van der; Novelli, P.C. ; Deeter, M.N. ; Aben, I. ; Rockmann, T. - \ 2012
    Journal of Geophysical Research: Atmospheres 117 (2012). - ISSN 2169-897X
    variational data assimilation - land-use change - climate-change - co emissions - amazon deforestation - brazilian amazon - fire emissions - model tm5 - mopitt - inversion
    We present the first inverse modeling study to estimate CO emissions constrained by both surface and satellite observations. Our 4D-Var system assimilates National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) surface and Measurements Of Pollution In The Troposphere (MOPITT) satellite observations jointly by fitting a bias correction scheme. This approach leads to the identification of a positive bias of maximum 5 ppb in MOPITT column-averaged CO mixing ratios in the remote Southern Hemisphere (SH). The 4D-Var system is used to estimate CO emissions over South America in the period 2006-2010 and to analyze the interannual variability (IAV) of these emissions. We infer robust, high spatial resolution CO emission estimates that show slightly smaller IAV due to fires compared to the Global Fire Emissions Database (GFED3) prior emissions. South American dry season (August and September) biomass burning emission estimates amount to 60, 92, 42, 16 and 93 Tg CO/yr for 2006 to 2010, respectively. Moreover, CO emissions probably associated with pre-harvest burning of sugar cane plantations in Sao Paulo state are underestimated in current inventories by 50-100%. We conclude that climatic conditions (such as the widespread drought in 2010) seem the most likely cause for the IAV in biomass burning CO emissions. However, socio-economic factors (such as the growing global demand for soy, beef and sugar cane ethanol) and associated deforestation fires, are also likely as drivers for the IAV of CO emissions, but are difficult to link directly to CO emissions.
    Mid-term effects of reduced-impact logging on the regeneration of seven tree commercial species in the Eastern Amazon
    Schwartz, G. ; Peña-Claros, M. ; Lopes, J.C.A. ; Mohren, G.M.J. ; Kanashiro, M. - \ 2012
    Forest Ecology and Management 274 (2012). - ISSN 0378-1127 - p. 116 - 125.
    bolivian tropical forest - brazilian amazon - natural regeneration - population-structure - carapa-guianensis - rain-forest - gaps - management - diversity - recovery
    Reduced-impact logging (RIL) is a set of techniques aimed to maintain forest structure and functions of the harvested forest as similar as possible to pre-logging status, while reducing adverse impacts from logging activity on the remaining forest. We analysed the mid-term effects of RIL on the regeneration of the long-lived pioneers (LLP) Bagassa guianensis and Jacaranda copaia; the partially shade tolerant (PST) Hymenaea courbaril, Dipteryx odorata, and Carapa guianensis and the total shade tolerant species (TST) Symphonia globulifera and Manilkara huberi. This study was carried out in an intensive study plot in the 600,000-ha Tapajós National Forest, Eastern Amazon – Brazil (03°02'S and 54°56'W). Three transects split in 10 × 10 m plots, adding up to 2.37 ha were sampled in an area where RIL was applied, and compared with a same size sampling in an unlogged area. The regeneration of individuals 20 cm in dbh was inventoried and measured before logging in 2003 and three times after logging (2004, 2006, and 2009). RIL modified the forest structure creating more gap-phase plots, with the consequences of such disturbance still remaining after 6 years. Densities of B. guianensis, J. copaia, and S. globulifera increased, while C. guianensis diminished. The positive effect on the density of LLP species was, however, ephemeral and disappeared 2 years after logging. RIL had a positive effect on the height growth rate of S. globulifera and on the dbh growth rate of C. guianensis. Plants growing in the gap-phase plots had higher height growth rates (ANOVA, F2;2980 = 33.3, p <0.001) than plants growing in other phases, but the same difference was not observed for dbh growth rates (ANOVA, F1;364 = 0.9, p = 0.33). Crown position had positive effects on height and dbh growth rates: the higher the crown position, the faster the plant grows in height (ANOVA, F3;2979 = 148.4, p <0.001) and dbh (ANOVA, F3;362 = 26.1, p <0.001). The application of RIL following the Brazilian regulations, may be considered a silvicultural technique for increasing density and growth rates of commercial species, but additional silvicultural interventions, as liberation for example, might be required for maintaining the ecological outcomes of RIL in the long run
    Do Anthropogenic Dark Earths Occur in the Interior of Borneo? Some Initial Observations from East Kalimantan
    Sheil, D. ; Basuki, I. ; German, L. ; Kuyper, T.W. ; Limberg, G. ; Puri, R.K. ; Sellato, B. ; Noordwijk, M. van - \ 2012
    Forests 3 (2012)2. - ISSN 1999-4907 - p. 207 - 229.
    soil organic-matter - terra-preta - carbon sequestration - brazilian amazon - sustainable agriculture - phosphorus availability - black earth - land-use - forest - indonesia
    Anthropogenic soils of the Amazon Basin (Terra Preta, Terra Mulata) reveal that pre-Colombian peoples made lasting improvements in the agricultural potential of nutrient-poor soils. Some have argued that applying similar techniques could improve agriculture over much of the humid tropics, enhancing local livelihoods and food security, while also sequestering large quantities of carbon to mitigate climate change. Here, we present preliminary evidence for Anthropogenic Dark Earths (ADEs) in tropical Asia. Our surveys in East Kalimantan (Indonesian Borneo) identified several sites where soils possess an anthropogenic development and context similar in several respects to the Amazon’s ADEs. Similarities include riverside locations, presence of useful fruit trees, spatial extent as well as soil characteristics such as dark color, high carbon content (in some cases), high phosphorus levels, and improved apparent fertility in comparison to neighboring soils. Local people value these soils for cultivation but are unaware of their origins. We discuss these soils in the context of local history and land-use and identify numerous unknowns. Incomplete biomass burning appears key to these modified soils. More study is required to clarify soil transformations in Borneo and to determine under what circumstances such soil improvements might remain ongoing.
    Capabilities and limitations of Landsat and land cover data for aboveground woody biomass estimation of Uganda
    Avitabile, V. ; Baccini, A. ; Friedl, M.A. ; Schmullius, C. - \ 2012
    Remote Sensing of Environment 117 (2012). - ISSN 0034-4257 - p. 366 - 380.
    tropical forest biomass - thematic mapper data - inventory data - tm data - brazilian amazon - satellite estimation - stand structure - carbon balance - etm+ data - imagery
    Aboveground woody biomass for circa-2000 is mapped at national scale in Uganda at 30-m spatial resolution on the basis of Landsat ETM + images, a National land cover dataset and field data using an object-oriented approach. A regression tree-based model (Random Forest) produces good results (cross-validated R² 0.81, RMSE 13 T/ha) when trained with a sufficient number of field plots representative of the vegetation variability at national scale. The Random Forest model captures non-linear relationships between satellite data and biomass density, and is able to use categorical data (land cover) in the regression to improve the results. Biomass estimates were strongly correlated (r = 0.90 and r = 0.83) with independent LiDAR measurements. In this study, we demonstrate that in certain contexts Landsat data provide the capability to spatialize field biomass measurements and produce accurate and detailed estimates of biomass distribution at national scale. We also investigate limitations of this approach, which tend to provide conservative biomass estimates. Specific limitations are mainly related to saturation of the optical signal at high biomass density and cloud cover, which hinders the compilation of a radiometrically consistent multi-temporal dataset. As a result, a Landsat mosaic created for Uganda with images acquired in the dry season during 1999–2003 does not contain phenological information useful for discriminating some vegetation types, such as deciduous formations. The addition of land cover data increases the model performance because it provides information on vegetation phenology. We note that Landsat data present higher spatial and thematic resolution compared to land cover and allow detailed and spatially continuous biomass estimates to be mapped. Fusion of satellite and ancillary data may improve biomass predictions but, to avoid error propagation, accurate, detailed and up-to-date land cover or other ancillary data are necessary. --------------------------------------------------------------------------------
    Ecology of Anopheles darlingi Root with respect to vector importance: a review
    Hiwat, H. ; Bretas, G. - \ 2011
    Parasites & Vectors 4 (2011). - ISSN 1756-3305 - 13 p.
    malaria vector - plasmodium-falciparum - brazilian amazon - central-america - south-america - rain-forest - diptera-culicidae - age-composition - breeding sites - population-structure
    Anopheles darlingi is one of the most important malaria vectors in the Americas. In this era of new tools and strategies for malaria and vector control it is essential to have knowledge on the ecology and behavior of vectors in order to evaluate appropriateness and impact of control measures. This paper aims to provide information on the importance, ecology and behavior of An. darlingi. It reviews publications that addressed ecological and behavioral aspects that are important to understand the role and importance of An. darlingi in the transmission of malaria throughout its area of distribution. The results show that Anopheles darlingi is especially important for malaria transmission in the Amazon region. Although numerous studies exist, many aspects determining the vectorial capacity of An. darlingi, i.e. its relation to seasons and environmental conditions, its gonotrophic cycle and longevity, and its feeding behavior and biting preferences, are still unknown. The vector shows a high degree of variability in behavioral traits. This makes it difficult to predict the impact of ongoing changes in the environment on the mosquito populations. Recent studies indicate a good ability of An. darlingi to adapt to environments modified by human development. This allows the vector to establish populations in areas where it previously did not exist or had been controlled to date. The behavioral variability of the vector, its adaptability, and our limited knowledge of these impede the establishment of effective control strategies. Increasing our knowledge of An. darlingi is necessary.
    Estimating carbon stock in secondary forests: decisions and uncertainties associated with allometric biomass models.
    Breugel, M. van; Ransijn, J. ; Craven, D. ; Bongers, F. ; Hall, J. - \ 2011
    Forest Ecology and Management 262 (2011)8. - ISSN 0378-1127 - p. 1648 - 1657.
    aboveground tree biomass - tropical rain-forest - wood density - climate-change - functional-groups - brazilian amazon - landscape-scale - land-use - deforestation - equations
    Secondary forests are a major terrestrial carbon sink and reliable estimates of their carbon stocks are pivotal for understanding the global carbon balance and initiatives to mitigate CO2 emissions through forest management and reforestation. A common method to quantify carbon stocks in forests is the use of allometric regression models to convert forest inventory data to estimates of aboveground biomass (AGB). The use of allometric models implies decisions on the selection of extant models or the development of a local model, the predictor variables included in the selected model, and the number of trees and species for destructive biomass measurements. We assess uncertainties associated with these decisions using data from 94 secondary forest plots in central Panama and 244 harvested trees belonging to 26 locally abundant species. AGB estimates from species-specific models were used to assess relative errors of estimates from multispecies models. To reduce uncertainty in the estimation of plot AGB, including wood specific gravity (WSG) in the model was more important than the number of trees used for model fitting. However, decreasing the number of trees increased uncertainty of landscape-level AGB estimates substantially, while including WSG had limited effects on the accuracy of the landscape-level estimates. Predictions of stand and landscape AGB varied strongly among models, making model choice an important source of uncertainty. Local models provided more accurate AGB estimates than foreign models, but high variability in carbon stocks across the landscape implies that developing local models is only justified when landscape sampling is sufficiently intensive. --------------------------------------------------------------------------------
    Effects of malathion and carbendazim on Amazonian freshwater organisms: comparison of tropical and temperate species sensitivity distributions and water quality criteria
    Rico Artero, A. ; Waichman, A.V. ; Geber-Correa, R. ; Brink, P.J. van den - \ 2011
    Ecotoxicology 20 (2011)4. - ISSN 0963-9292 - p. 625 - 634.
    aquatic ecosystems - brazilian amazon - risk-assessment - rainbow-trout - pesticides - toxicity - invertebrates - macroinvertebrates - ecotoxicology - environment
    The risk assessment of pesticides for freshwater ecosystems in the Amazon has relied on the use of toxicity data and water quality criteria derived for temperate regions due to a lack of ecotoxicological studies performed with indigenous species. This leaves an unknown margin of uncertainty for the protection of Amazonian ecosystems, as differences in environmental conditions and species sensitivity are not taken into account. To address this issue, the acute toxic effects of malathion (an organophosphorus insecticide) and carbendazim (a benzimidazole fungicide) were assessed on five fish and five freshwater invertebrates endemic to the Amazonian region. Subsequently, the intrinsic sensitivity of Amazonian and temperate freshwater species was compared using the species sensitivity distribution (SSD) concept. Amazonian species sensitivity to malathion was found to be similar to that of their temperate counterparts, with LC50 values ranging between 111 and 1507 g/l for fish species and 2.1426 g/l for arthropod species. However, Amazonian fish appeared to be slightly less sensitive for carbendazim than temperate fish with LC50 values ranging between 1648 and 4238 g/l, and Amazonian invertebrates were found to be significantly more resistant than their temperate counterparts, with LC50 values higher than 16000 g/l. The results of this study suggest that for these compounds, the use of water quality criteria derived with laboratory toxicity data for temperate species will result in a sufficient protection level for Amazonian freshwater organisms. Recommendations for further research include the validation of threshold concentrations derived with temperate standard test species and with the SSD model with semi-field experiments considering larger assemblages of indigenous species under local environmental conditions.
    Evaluation of Methods for Sampling the Malaria Vector Anopheles darlingi (Diptera, Culicidae) in Suriname and the Relation With Its Biting Behavior
    Hiwat-van Laar, H. ; Rijk, M. de; Andriessen, R. ; Koenraadt, C.J.M. ; Takken, W. - \ 2011
    Journal of Medical Entomology 48 (2011)5. - ISSN 0022-2585 - p. 1039 - 1046.
    carbon-dioxide - light-traps - differential attractiveness - mosquitos diptera - brazilian amazon - field-evaluation - sensu-stricto - endemic area - gambiae - tanzania
    The effectiveness of CO2-baited and human-baited mosquito traps for the sampling of Anopheles darlingi Root was evaluated and compared with human landing collections in Suriname. Biting preferences of this mosquito on a human host were studied and related to trapping data. Traps used were the Centers for Disease Control and Prevention Miniature Light trap, the BG Sentinel mosquito trap, the Mosquito Magnet Liberty Plus mosquito trap (MM-Plus), and a custom-designed trap. Carbon dioxide and humans protected by a bed net were used as bait in the studies. The number of An. darlingi collected was greater with human landing collections than with all other collection methods. An. darlingi did not show a preference for protected humans over CO2 bait. The BG Sentinel mosquito trap with CO2 or human odor as bait and the MM-Plus proved the best alternative sampling tools for An. darlingi. The BG Sentinel mosquito trap with CO2 or human odor as bait was also very efficient at collecting Culex spp. In a field study on biting preferences of wild An. darlingi, the females showed directional biting behavior (P <0.001), with a majority of females (93.3%) biting the lower legs and feet when approaching a seated human host. Higher efficiency of the closer-to-the-ground collecting MM-Plus and BG Sentinel mosquito trap when compared with the other trapping methods may be a result of a possible preference of this mosquito species for low-level biting. It is concluded that odor-baited sampling systems can reliably collect An. darlingi, but the odor bait needs to be improved, for instance, by including host-specific volatiles, to match live human baits.
    Drivers of land use change and household determinants of sustainability in smallholder farming systems of Eastern Uganda
    Ebanyat, P. ; Ridder, N. de; Jager, A. de; Delve, R.J. ; Bekunda, M. ; Giller, K.E. - \ 2010
    Population and Environment 31 (2010)6. - ISSN 0199-0039 - p. 474 - 506.
    soil fertility management - sub-saharan africa - cover change - nutrient balances - brazilian amazon - level evidence - southern mali - use patterns - dynamics - agriculture
    Smallholder farming systems in sub-Saharan Africa have undergone changes in land use, productivity and sustainability. Understanding of the drivers that have led to changes in land use in these systems and factors that influence the systems’ sustainability is useful to guide appropriate targeting of intervention strategies for improvement. We studied low input Teso farming systems in eastern Uganda from 1960 to 2001 in a place-based analysis combined with a comparative analysis of similar low input systems in southern Mali. This study showed that policy-institutional factors next to population growth have driven land use changes in the Teso systems, and that nutrient balances of farm households are useful indicators to identify their sustainability. During the period of analysis, the fraction of land under cultivation increased from 46 to 78%, and communal grazing lands nearly completely disappeared. Cropping diversified over time; cassava overtook cotton and millet in importance, and rice emerged as an alternative cash crop. Impacts of political instability, such as the collapse of cotton marketing and land management institutions, of communal labour arrangements and aggravation of cattle rustling were linked to the changes. Crop productivity in the farming systems is poor and nutrient balances differed between farm types. Balances of N, P and K were all positive for larger farms (LF) that had more cattle and derived a larger proportion of their income from off-farm activities, whereas on the medium farms (MF), small farms with cattle (SF1) and without cattle (SF2) balances were mostly negative. Sustainability of the farming system is driven by livestock, crop production, labour and access to off-farm income. Building private public partnerships around market-oriented crops can be an entry point for encouraging investment in use of external nutrient inputs to boost productivity in such African farming systems. However, intervention strategies should recognise the diversity and heterogeneity between farms to ensure efficient use of these external inputs.
    Silvicultural treatments enhance growth rates of future crop trees in a tropical dry forest
    Villegas, Z. ; Peña-Claros, M. ; Mostacedo, B. ; Alarcón, A. ; Licona, J.C. ; Leaño, C. ; Pariona, W. ; Choque, U. - \ 2009
    Forest Ecology and Management 258 (2009)6. - ISSN 0378-1127 - p. 971 - 977.
    rain-forest - timber production - brazilian amazon - eastern amazon - management - sustainability - performance - bolivia - yield
    Silvicultural treatments are often needed in selectively logged tropical forest to enhance the growth rates of many commercial tree species and, consequently, for recovering a larger proportion of the initial volume harvested over the next cutting cycle. The available data in the literature suggest, however, that the effect of silvicultural treatments on tree growth is smaller in dry forests than in humid forest tree species. In this study, we analyze the effect of logging and application of additional silvicultural treatments (liana cutting and girdling of competing trees) on the growth rates of future crop trees (FCTs; i.e., trees of current and potentially commercial timber species with adequate form and apparent growth potential). The study was carried out in a tropical dry forest in Bolivia where a set of 21.25-ha plots were monitored for 4 years post-logging. Plots received one of four treatments that varied in intensity of both logging and silvicultural treatments as follows: normal (reduced-impact) logging; normal logging and low-intensity silviculture; increased logging intensity and high-intensity silviculture; and, unlogged controls. The silvicultural treatments applied to FCTs involved liberation from lianas and overtopping trees. Results showed that rates of FCT stem diameter growth increased with light availability, logging intensity, and intensity of silvicultural treatments, and decrease with liana infestation degree. Growth rate increment was larger in the light and intensive silvicultural treatment (22¿27%). Long-lived pioneer species showed the strongest response to intensive silviculture (50% increase) followed by total shade-tolerant species (24%) and partial shade-tolerant species (10%). While reduced-impact logging is often not sufficient to guarantee the sustainability of timber yields, application of silvicultural treatments that substantially enhanced the growth rates of FCTs will help move the management of these forests closer to the goal of sustained yield
    Downscaling time series of MERIS full resolution data to monitor vegetation seasonal dynamics
    Zurita Milla, R. ; Kaiser, G. ; Clevers, J.G.P.W. ; Schneider, W. ; Schaepman, M.E. - \ 2009
    Remote Sensing of Environment 113 (2009)9. - ISSN 0034-4257 - p. 1874 - 1885.
    multiresolution image fusion - land-cover - species richness - brazilian amazon - cloud-cover - tm images - index - avhrr - model - sensor
    Monitoring vegetation dynamics is fundamental for improving Earth system models and for increasing our understanding of the terrestrial carbon cycle and the interactions between biosphere and climate. Medium spatial resolution sensors, like MERIS, exhibit a significant potential to study these dynamics over large areas because of their spatial, spectral and temporal resolution. However, the spatial resolution provided by MERIS (300 m in full resolution mode) is not appropriate to monitor heterogeneous landscapes, where typical length scales of these dynamics rarely reach 300 m. We, therefore, motivate the use of data fusion techniques to downscale medium spatial resolution data (MERIS full resolution, FR) to a Landsat-like spatial resolution (25 m). An unmixing-based data fusion approach was applied to a time series of MERIS FR images acquired over The Netherlands. The selected data fusion approach is based on the linear mixing model and uses a high spatial resolution land use database to produce images having the spectral and temporal resolution as provided by MERIS, but a Landsat-like spatial resolution. A quantitative assessment of the quality of the fused images was done in order to test the validity of the proposed method and to evaluate the radiometric characteristics of the MERIS fused images. The resulting series of fused images was subsequently used to compute two vegetation indices specifically designed for MERIS: the MERIS terrestrial chlorophyll index (MTCI) and the MERIS global vegetation index (MGVI). These indices represent continuous fields of canopy chlorophyll (MTCI) and of the fraction of photosynthetically active radiation absorbed by the canopy (MGVI). Results indicate that the selected data fusion approach can be successfully used to downscale MERIS data and, therefore, to monitor vegetation dynamics at Landsat-like spatial, and MERIS-like spectral and temporal resolution.
    Mapping soil carbon stocks of Central Africa using SOTER
    Batjes, N.H. - \ 2008
    Geoderma 146 (2008)1-2. - ISSN 0016-7061 - p. 58 - 65.
    land-use change - organic-carbon - subtropical soils - brazilian amazon - tropical africa - food security - sequestration - emissions - world - management
    Little is known about the soil carbon stocks of Central Africa although such baseline data are needed for research and policy development on soil carbon changes. Estimates are presented based on a 1:2 million scale soil and terrain (SOTER) database for Burundi, the Democratic Republic of Congo, and Rwanda (hereafter referred to as Central Africa). Each SOTER map unit consists of up to six soil components, characterized by a representative soil profile extracted from survey data. Gaps in the measured soil analytical data were filled using consistent, taxonomy-based pedotransfer procedures. Natural variation in individual soil components was simulated to put bounds on regional-scale carbon stocks rather than a single figure. The 95% confidence interval for the median stock of soil organic carbon (SOC) to 1 m is 19.3 to 19.6 Pg C; this corresponds with some 11% of African and about 1% of worldwide SOC stocks to that depth. The area-weighted SOC content is largest in the cool, humid mountains (22.1¿22.7 kg C m¿ 2) in part due to the presence of soils formed on volcanic parent materials, and smallest for the warm savannah region (7.6¿7.7 kg C m¿ 2). Local differences in SOC content are related to type and texture of parent material, soil drainage conditions, and land use/vegetation. Less than 1% of the region consists of soil units that contain secondary carbonates (~ 0.19 Pg C), accounting for ~ 0.8% of the total carbon stock to 2 m in the soils of Central Africa. About 45% of the SOC stock to 2 m is held in the upper 30 cm; much of this would be released to the atmosphere as CO2 upon forest clearance.
    Beyond reduced-impact logging: silvicultural treatments to increase growth rates of tropical trees
    Peña-Claros, M. ; Fredericksen, T.S. ; Alarcón, A. ; Blate, G.M. ; Choque, U. ; Leaño, C. ; Licona, J.C. ; Mostacedo, B. ; Pariona, W. ; Villegas, Z. ; Putz, F.E. - \ 2008
    Forest Ecology and Management 256 (2008)7. - ISSN 0378-1127 - p. 1458 - 1467.
    rain-forest - timber production - eastern amazon - sustainable forestry - brazilian amazon - dry forest - trade-offs - regeneration - management - bolivia
    Use of reduced-impact logging (RIL) techniques has repeatedly been shown to reduce damage caused by logging. Unfortunately, these techniques do not necessarily ameliorate the low growth rates of many commercial species or otherwise assure recovery of the initial volume harvested during the next cutting cycle. In this study, we analyze the effect of logging and application of additional silvicultural treatments (liana cutting and girdling of competing trees) on the growth rates on trees in general and on of future crop trees (FCTs) of 24 commercial timber species. The study was carried out in a moist tropical forest in Bolivia, where we monitored twelve 27-ha plots for 4 years. Plots received one of four treatments in which logging intensity and silvicultural treatments were varied: control (no logging); normal (reduced-impact) logging; normal logging and low-intensity silviculture; and, increased logging intensity and high-intensity silviculture. Tree growth rates increased with intensity of logging and silvicultural treatments. The growth rates of FCTs of commercial species were 50¿60% higher in plots that received silvicultural treatments than in the normal logging and control plots. Responses to silvicultural treatments varied among functional groups. The largest increase in growth rates was observed in FCTs belonging to the partially shade-tolerant and the shade-tolerant groups. These results indicate that silvicultural treatments, in addition to the use of RIL techniques, are more likely to result in a higher percentage of timber volume being recovered after the first cutting cycle than RIL alone.
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