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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.

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    Anthropogenic soils in central Amazonia: farmers’ practices, agrobiodiversity and land-use patterns
    Braga Junqueira, A. - \ 2015
    Wageningen University. Promotor(en): Paul Struik, co-promotor(en): Tjeerd-Jan Stomph; Conny Almekinders; C.R. Clement. - Wageningen : Wageningen University - ISBN 9789462574472 - 163
    antropogene horizonten - bodem - agro-ecologie - biodiversiteit - landgebruik - zwerflandbouw - intensivering - diversificatie - amazonia - anthropogenic horizons - soil - agroecology - biodiversity - land use - shifting cultivation - intensification - diversification - amazonia

    Keywords: Terra Preta; Amazonian Dark Earths; Shifting cultivation; Homegardens; Intensification; Diversification; Smallholder farming.

    André Braga Junqueira (2015). Anthropogenic soils in central Amazonia: farmers’ practices, agrobiodiversity and land-use patterns. PhD thesis, Wageningen University, The Netherlands, with summary in English, 163 pp.

    Rural Amazonia is increasingly experiencing environmental and socio-economic changes that directly affect smallholder farmers, with potential negative effects for environmental quality, agrobiodiversity and livelihoods. In this dynamic context, there is an urgent need to support pathways for smallholder agriculture that guarantee farmers’ economic and food security while maintaining and enhancing ecosystem functions. Amazonian Dark Earths (ADE, or Terra Preta) are anthropogenic soils created by pre-Columbian populations. Due to their high carbon content and enhanced fertility, ADE have been considered models for sustainable agriculture, based on the idea that transforming soils by mimicking some of the properties of ADE would benefit farmers, sequester carbon and reduce pressure on forests. Investigating the current use of ADE and surrounding soils by smallholder farmers allows us to evaluate the relevance of anthropogenic soils and of soil heterogeneity for smallholder farming in Amazonia, and to identify opportunities and constraints associated with the cultivation of fertile soils. The main objective of this thesis is to understand how ADE are understood and cultivated by smallholder farmers in Central Amazonia, and how these soils influence cultivation systems, agrobiodiversity and land-use patterns.

    Ethnographic data indicated that farmers’ understanding of ADE – and of soils in general – is based on their historical and shared knowledge about soil variation across the landscape, on physical attributes of the soil, and mainly on the recognition of different soil-vegetation interactions. A widespread perception about ADE is that these soils are suitable for the cultivation of ‘almost everything’ and always produce decent yields, but they require much more weeding during cultivation. Farmers’ decision-making in shifting cultivation is grounded in this differential understanding of soil-vegetation relationships, and weighed against the labor demands. Soil and vegetation inventories in swiddens used for shifting cultivation showed that the soil fertility gradient between surrounding soils and ADE was associated with more intensive cultivation (shorter fallow periods, shorter and more frequent cultivation cycles, higher labor requirements) and with changes in the crop assemblages, but with similar or larger numbers of species cultivated. In homegardens, vegetation structure and crop diversity were mainly influenced by natural variation in soil texture (homegardens on sandier soils being denser and more diverse), while the soil fertility gradient between ADE and adjacent soils influenced mainly the crop assemblages. At the farm level, the relationship between farmers’ use of ADE and the need to open areas for shifting cultivation was strongly dependent on the labor availability of the household. Instead of driving specific trends in land use, fertile soils are incorporated into local livelihoods as part of an extensive repertoire of resource management activities; most often, farmers with enough available labor manage multiple plots, combining more intensive cultivation on ADE with typical long-fallow shifting cultivation on poorer soils. Farmers’ access to increased soil fertility, therefore, does not necessarily lead to reduced pressure on forests.

    This thesis has shown that cultivation systems on ADE are associated with specific knowledge, practices and agrobiodiversity, providing increased opportunities for farmers to diversify their cultivation systems and grow a greater diversity of crops. Despite these advantages, ADE can also be associated with conventional intensification practices that can lead to environmental degradation and pose threats to local livelihoods. It cannot be assumed, therefore, that the use of more fertile soils will be associated with sustainable cultivation, neither that it will reduce pressure on forests. Initiatives aiming to promote sustainable pathways for agriculture in Amazonia should promote (and make use of) the heterogeneity of soils and of cultivation strategies, and should aim at increasing and not narrowing farmers’ opportunities for resource use and management.

    Loss of secondary-forest resilience by land-use intensification in the Amazon
    Jakovac, A.C. ; Pena Claros, M. ; Kuijper, T.W.M. ; Bongers, F. - \ 2015
    Journal of Ecology 103 (2015)1. - ISSN 0022-0477 - p. 67 - 77.
    slash-and-burn - alternative successional pathways - bornean rain-forest - shifting cultivation - tropical forest - fallow period - species composition - soil fertility - costa-rica - agriculture
    Understanding how land-use intensification affects forest resilience is a key for elucidating the mechanisms underlying regeneration processes and for planning more sustainable land-use systems. Here, we evaluate how the intensification of a swidden cultivation system affects secondary-forest resilience in the Amazon. Along a gradient of land-use intensity, we analysed the relative role of management intensity, soil properties and landscape configuration in determining the resilience of early secondary forests (SFs). We assessed resilience as the recovery level of forest structure and species diversity achieved by SFs 5 years after abandonment. We used as a reference the recovery level achieved by SFs subjected to the lowest intensity of use, given that these SFs are part of a dynamic system and may not develop to old-growth forests. Therefore, we interpreted a deviation from this reference level as a change in forest resilience. The recovery of forest structure was determined by management intensity, while the recovery of species diversity was driven by landscape configuration. With increasing number of cycles and weeding frequency along with decreasing fallow period and patch area, SF basal area and canopy height decreased, regeneration shifted from a seed- to sprout-dependent strategy, and liana infestation on trees increased. With decreasing area covered by old-growth forest, species richness and Shannon diversity decreased. Secondary-forest resilience decreased with land-use intensification, mainly mediated by the effect of management intensity upon regeneration strategies. Our findings demonstrate the – many times overlooked – importance of previous management intensity in determining the structure of SFs and highlight the importance of regeneration strategy for forest resilience. Synthesis. Swidden cultivation supports people's livelihoods and transforms landscapes in the tropics. The sustainability of this system depends on ecosystem services provided by SFs that develop during the fallow period. Land-use intensification reduces the resilience of SFs and ultimately may drive the system towards an arrested succession state that holds a lower potential to deliver ecosystem services to the Amazonian people. Under an intensification scenario, the adaptation of management practices is needed to guarantee the resilience of swidden cultivation systems.
    Implementing REDD+ (Reducing Emissions from Deforestation and Degradation): evidence on governance, evaluation and impacts from the REDD-ALERT project
    Matthews, R.B. ; Noordwijk, M. van; Lambin, E. ; Meyfroidt, P. ; Gupta, J. ; Verschot, L. ; Hergoualc'h, K. ; Veldkamp, E. - \ 2014
    Mitigation and Adaptation Strategies for Global Change 19 (2014)6. - ISSN 1381-2386 - p. 907 - 925.
    land-use - agricultural intensification - environmental services - avoided deforestation - shifting cultivation - developing-world - food security - carbon - payments - costs
    Abstract The REDD-ALERT (Reducing Emissions from Deforestation and Degradation from Alternative Land Uses in the Rainforests of the Tropics) project started in 2009 and finished in 2012, and had the aim of evaluating mechanisms that translate international-level agreements into instruments that would help change the behaviour of land users while minimising adverse repercussions on their livelihoods. Findings showed that some developing tropical countries have recently been through a forest transition, thus shifting from declining to expanding forests at a national scale. However, in most of these (e.g. Vietnam), a significant part of the recent increase in national forest cover is associated with an increase in importation of food and timber products from abroad, representing leakage of carbon stocks across international borders. Avoiding deforestation and restoring forests will require a mixture of regulatory approaches, emerging market-based instruments, suasive options, and hybrid management measures. Policy analysis and modelling work showed the high degree of complexity at local levels and highlighted the need to take this heterogeneity into account—it is unlikely that there will be a one size fits all approach to make Reducing Emissions from Deforestation and Degradation (REDD+) work. Significant progress was made in the quantification of carbon and greenhouse gas (GHG) fluxes following land-use change in the tropics, contributing to narrower confidence intervals on peat-based emissions and their reporting standards. There are indications that there is only a short and relatively small window of opportunity of making REDD+ work—these included the fact that forest-related emissions as a fraction of total global GHG emissions have been decreasing over time due to the increase in fossil fuel emissions, and that the cost efficiency of REDD+ may be much less than originally thought due to the need to factor in safeguard costs, transaction costs and monitoring costs. Nevertheless, REDD+ has raised global awareness of the world’s forests and the factors affecting them, and future developments should contribute to the emergence of new landscape-based approaches to protecting a wider range of ecosystem services. Keywords Reducing Emissions from Deforestation and Degradation . REDD+ . Indonesia . Vietnam. Cameroon . Peru . Peatlands . Carbon stocks .Greenhouse gases . GHGs
    A methodology for digital soil mapping in poorly-accessible areas
    Cambule, A. ; Rossiter, D.G. ; Stoorvogel, J.J. - \ 2013
    Geoderma 192 (2013). - ISSN 0016-7061 - p. 341 - 353.
    residual maximum-likelihood - reflectance spectroscopy - shifting cultivation - terrain attributes - spatial prediction - organic-matter - carbon - variogram - scales - geostatistics
    Effective soil management requires knowledge of the spatial patterns of soil variation within the landscape to enable wise land use decisions. This is typically obtained through time-consuming and costly surveys. The aim of this study was to develop a cost-efficient methodology for digital soil mapping in poorly-accessible areas. The methodology uses a spatial model calibrated on the basis of limited soil sampling and explanatory covariables related to soil-forming factors, developed from readily available secondary information from accessible areas. The model is subsequently applied in the poorly-accessible areas. This can only be done if the environmental conditions in the poorly-accessible areas are also found in the accessible areas in which the model is developed. This study illustrates the methodology in an exercise to predict soil organic carbon (SOC) concentration in the Limpopo National Park, Mozambique. Readily-available secondary data was used as explanatory variables representing the soil-forming factors. Conditions in the accessible and poorly-accessible areas corresponded sufficiently to allow the extrapolation of the spatial model into the latter. The spatial variation of SOC in the accessible area was mostly described by the sampling cluster (71.5%) and the landscape unit (46.3%). Therefore ordinary (punctual) kriging (OK) and kriging with external drift (KED) based on the landscape unit were used to predict SOC. A linear regression (LM) model using only landscape stratification was used as control. All models were independently validated with test sets collected in both accessible and poorly-accessible areas. In the former the root mean squared error of prediction (RMSEP) was 0.42–0.50% SOC. The ratio between the RMSEP in the poorly-accessible and accessible areas was 0.67–0.72, showing that the methodology can be applied to predict SOC in poorly-accessible areas as successful as in accessible areas. The methodology is thus recommended for areas with similar access problems, especially for baseline studies and for sample design in two-stage surveys
    Carbon outcomes of major land-cover transitions in SE Asia: great uncertainties and REDD+ policy implications
    Ziegler, A.D. ; Phelps, J. ; Yuen, J.Q. ; Webb, E.L. ; Lawrence, D. ; Fox, J.M. ; Bruun, T.B. ; Leisz, S.J. ; Ryan, C.M. ; Dressler, W.H. ; Mertz, O. ; Pascual, U. ; Padoch, C. ; Koh, L.P. - \ 2012
    Global Change Biology 18 (2012)10. - ISSN 1354-1013 - p. 3087 - 3099.
    tropical forest biomass - slash-and-burn - southeast-asia - shifting cultivation - rain-forest - swidden cultivation - agricultural land - soil carbon - tm data - environmental consequences
    Policy makers across the tropics propose that carbon finance could provide incentives for forest frontier communities to transition away from swidden agriculture (slash-and-burn or shifting cultivation) to other systems that potentially reduce emissions and/or increase carbon sequestration. However, there is little certainty regarding the carbon outcomes of many key land-use transitions at the center of current policy debates. Our meta-analysis of over 250 studies reporting above- and below-ground carbon estimates for different land-use types indicates great uncertainty in the net total ecosystem carbon changes that can be expected from many transitions, including the replacement of various types of swidden agriculture with oil palm, rubber, or some other types of agroforestry systems. These transitions are underway throughout Southeast Asia, and are at the heart of REDD+ debates. Exceptions of unambiguous carbon outcomes are the abandonment of any type of agriculture to allow forest regeneration (a certain positive carbon outcome) and expansion of agriculture into mature forest (a certain negative carbon outcome). With respect to swiddening, our meta-analysis supports a reassessment of policies that encourage land-cover conversion away from these [especially long-fallow] systems to other more cash-crop-oriented systems producing ambiguous carbon stock changes – including oil palm and rubber. In some instances, lengthening fallow periods of an existing swidden system may produce substantial carbon benefits, as would conversion from intensely cultivated lands to high-biomass plantations and some other types of agroforestry. More field studies are needed to provide better data of above- and below-ground carbon stocks before informed recommendations or policy decisions can be made regarding which land-use regimes optimize or increase carbon sequestration. As some transitions may negatively impact other ecosystem services, food security, and local livelihoods, the entire carbon and noncarbon benefit stream should also be taken into account before prescribing transitions with ambiguous carbon benefits.
    Jhum Meets IFOAM: Introducing Organic Agriculture in a Tribal Society
    Eernstman, N. ; Wals, A.E.J. - \ 2009
    International Journal of Agricultural Sustainability 7 (2009)2. - ISSN 1473-5903 - p. 95 - 106.
    agroforestry - inheemse kennis - biologische landbouw - kennissystemen - duurzaam bodemgebruik - natuur- en milieueducatie - agroforestry - indigenous knowledge - organic farming - knowledge systems - sustainable land use - nature and environmental education - shifting cultivation
    Worldwide organic agriculture (OA) is seen by many as a promising alternative for the present `unsustainable' farming systems. The conversion to `organic' is often accompanied by the introduction of universal principles and standards that allow for certification. This study explores the interface between two knowledge systems: organic agriculture as interpreted by the International Federation of Organic Agriculture Movements (IFOAM) and the slash-and-burn-based Naga shifting cultivation system (Jhum) as it still functions today in the Northeast of India. The study demonstrates that in some cases the introduction of a universal knowledge system such as IFOAM may actually be counteractive in the development of contextually appropriate and workable sustainable land management (SLM) systems. Instead of imposing OA on local communities, in a well-meant attempt to establish a more sustainable agriculture system, the authors conclude that alternative paths towards sustainable development are needed, paths which take into account differing perceptions of what `sustainable land use' means in a specific context.
    Invasion of Piper aduncum in the shifting cultivation systems of Papua New Guinea: Foreword by David Pimentel
    Hartemink, A.E. - \ 2006
    Wageningen : ISRIC - World Soil Information - ISBN 9789081062817 - 234
    piper aduncum - invasies - zwerflandbouw - ecologie - invasie - papoea-nieuw-guinea - piper aduncum - invasions - shifting cultivation - ecology - invasion - papua new guinea
    Piper aduncum, a shrub native to Central America, arrived in Papua New Guinea before the mid-1930s possibly from West Papua. From the 1970s it started to dominate the secondary fallow vegetation in many parts of the humid lowlands. It invaded grassland areas and it also appeared in the highlands up to 2100 m. The combination of its small and abundant seeds, its high growth rates, and the accidental or intentional spreading has resulted in its presence in most provinces of Papua New Guinea. The spread will continue.
    Analysis of the effects of rotational woodlots on the nutrition and yield of maize following trees in western Tanzania
    Nyadzi, G.I. ; Janssen, B.H. ; Oenema, O. - \ 2006
    Agriculture, Ecosystems and Environment 116 (2006)1-2. - ISSN 0167-8809 - p. 93 - 103.
    shifting cultivation - soil fertility - nitrogen - fallow - agroforestry - management - vegetation - nutrients - africa - quefts
    Farmers in western Tanzania are establishing rotations of trees and crops in an attempt to overcome the shortage of wood, reverse deforestation of natural forests and improve soil fertility for food security enhancement. We compared fallows of Acacia crassicarpa, A. julifera, A. leptocarpa, Leucaena pallida and Senna siamea, with traditional bush fallow and continuous sole maize (Zea mays L.). The aim of the study was to analyze the effectiveness of fallow types in terms of N, P and K use by maize. Trees were intercropped with maize for the first 3 years. After 5 years, trees were harvested, wood components were removed, and leaves, twigs and grasses were incorporated into the soil. Factorial N, P, K trials were carried out with maize grown after the fallow types. Parameters studied were grain yield, uptake of N, P and K, and nutrient use efficiency. The effects of fertiliser were much stronger than the effects of fallow types. There was no clear effect of tree fallows on nutrient use efficiency of the following maize. Non-fertilized maize yielded more after acacia than after the other trees and natural fallow. Upon fertiliser application the influences of fallow types became weaker. Fertiliser N improved maize yields more than fertiliser P, and there was a positive NP interaction. Fertilizer K did not bring about clear effects. N recovery efficiency was improved by the application of P and vice versa. When fertilisers were applied, differences in average maize grain yields between tree fallows and natural fallow varied from 300 kg ha¿1 (for A. julifera) to minus 250 kg ha¿1 (for S. siamea). A yield increase of 300 kg maize grain could also be obtained by application of 10 kg fertiliser N or 8 kg fertiliser P. The best fallow type for soil fertility improvement was Acacia julifera suggesting that this acacia is mining the soil for P and K. In conclusion, benefits of rotational woodlots seem larger in terms of wood production than in terms of soil fertility restoration
    Soil macrofauna community structure along a gradient of land use intensification in the humid forest zone of southern Cameroon.
    Madong à Birang, - \ 2004
    Wageningen University. Promotor(en): Lijbert Brussaard, co-promotor(en): W.A.M. Didden; S. Hauser. - Wageningen : S.n. - ISBN 9789085040316 - 200
    bodemfauna - bodeminvertebraten - aardwormen - formicidae - isoptera - zwerflandbouw - landgebruik - bossen - humide klimaatzones - kameroen - macrofauna - soil fauna - soil invertebrates - earthworms - formicidae - isoptera - shifting cultivation - land use - forests - humid zones - cameroon - macrofauna
    The impact of land use systems on soil macrofauna community structures is described as well as their relationships with the vegetation and soil parameters in the humid forest zone of southernCameroon. 36 Earthworm species were found. A completely different earthworm assemblage was found at high LUI while low and medium LUI blocks had species in common in the various functional groups. Earthworm surface casting decreased when fallow plots were converted to cultivated fields. This reduction depended on the type of fallow. 223 Termite species were recorded.There was no significant effect of LUI but in contrast, a strong effect of LUS on termite species richness and abundance. 80 Ant species were found. LUI and LUS had striking effects on ant communities with highest richness in the low LUI block. Ant species assemblages were location specific.Soil macrofaunal species richness was more responsive to soil and vegetation parameters than macrofaunal abundances.The knowledge gathered on the present state of earthworm, termite and ant communities and the effects of land use change on these macrofauna in southernCameroonconstitutes the baseline information necessary for the design and /or implementation of measures of conservation in which farmers should play a pivotal role.
    Slash and burn agriculture in the humid forest zone of southern Cameroon
    Kanmegne, J. - \ 2004
    Wageningen University. Promotor(en): Lijbert Brussaard; E.M.A. Smaling. - Wageningen : s.n. - ISBN 9789051130706 - 184
    inga edulis - zwerflandbouw - gewasopbrengst - wormhoopjes - landgebruik - verbeterde braak - ontbossing - voedingsstoffen - humide klimaatzones - bossen - kameroen - inga edulis - shifting cultivation - crop yield - worm casts - land use - improved fallow - deforestation - nutrients - humid zones - forests - cameroon
    Keywords: crop yields, earthworm cast, Inga edulis , land use, nutrient flows, nutrient stocks, nutrient management, slash and burn

    A field study was conducted on acid soils in the humid forest zone of Southern Cameroon, to characterize the traditional slash-and-burn land uses, assess the major effects of land use change on soil nutrient stocks, flows, and soil biological quality, and to explore alternatives for sustainable land management. The typical land use chronosequence in the area after forest felling includes essep (cucumber-based), banana, and afup (groundnut/cassava-based), and is interrupted by short (after banana) and long (after afup) fallows. Moreover, farmers have cocoa farms where many shade trees are kept. Yield declines in farmers' fields were attributed to diseases and weed infestation (56%) and soil properties (44%).  Burning is practiced prior to essep, and prior to afup. It reduces the weed seed-bank, cleans the field and improves short-term soil fertility, but, together with changing land use, it strongly reduces standing biomass, carbon and nutrient stocks in the vegetation. The forest carbon stock decreased from 199 Mg.ha -1 to 102 Mg.ha -1 in essep , and to 64 Mg.ha -1 in banana farm. Nutrient stocks showed the same trend, but Chromolaena short fallow, that followed banana, recovered most of the P. The cocoa plantation had 53 % of the carbon stocks of the original forest. Soil carbon stock was less affected than vegetation stocks.Burning increased P, K, Ca and Mg available stocks in essep and afup . Lowest 'system' C and N occurred in afup , which is followed by a long fallow to restore soil fertility. The nutrient balance at farm level was strongly negative, i.e., -72.6 kg N, -4.8 kg P and -38.2 kg K ha -1 yr -1 , showing its 'no external input' character, where food and wood are derived from natural stocks. Major losseswere dueto burning, leaching and the non-recycling of farm residues. Only the cocoa farm had a positive nutrient balance: +9.6 kg N, +1.4 kg P and +7.6 kg K ha -1 .yr -1 , as burning is absent, leachingmodest,and deep capture by shade trees providing inputs to the productive system. Simple scenarios showed that recycling farm residues is able to redress the P and K balance, and avoiding burning could even turn the entire nutrient balance positive. Burning also negatively affected earthworm density and casting activities. Up to 95% loss in density was recorded, and casting activity was inhibited during 14 and 19 months in land use systems following afup and essep respectively. Inga fallow proved to favour rapid and intensive casting just as the forest ecosystem. Total cast production was: 5.9 Mg.ha -1 in afup , 3.2 Mg.ha -1 in forest and Inga , and 2.9 Mg.ha -1 in essep after two years, but although the casts were richer in nutrients than the topsoil, the nutrients recycled from casts alone were insufficient for sustained crop production.   Inga edulis was found to be a suitable planted fallow, providing several benefits to farmers and follow-up crops.   Inga fallows produce more biomass (between 44.5 and 62 Mg ha -1 ), and accumulate more C and N than natural fallow. Maize following Inga fallow yielded 800 to 2200 kg.ha -1, against a mere 200-400 kg.ha -1 after natural fallow.  Burning Inga residues gave ngon (cucumber) productionof 300 kg.ha -1 ,which is similar to yields obtained in essep following natural forest. Mulching instead of burning, however, only gave50 kg.ha -1. An innovative on-farm approach was used in the development and implementation of planted fallows, ensuring highadoption. Inga edulis planted fallow can play a leading role among strategies to fight the gradual process of land degradation in the land use chronosequence, providing wood and fruits, and mimicking the natural forest to a considerable extent.
    Disturbance, diversity and distributions in Central African rain forest
    Gemerden, B.S. van - \ 2004
    Wageningen University. Promotor(en): A.M. Cleef; Marc Sosef, co-promotor(en): H. Olff. - - 199
    tropical rain forests - biodiversity - rehabilitation - plant succession - conservation - forest ecology - logging - shifting cultivation - central africa - human impact - disturbance - tropische regenbossen - biodiversiteit - herstel - plantensuccessie - conservering - bosecologie - houtkap - zwerflandbouw - centraal-afrika - menselijke invloed - verstoring
    The aim of this study is to gain insight in the impact of human land use on plant community composition, diversity and levels of endemism in Central African rain forest. Human disturbance in this region is causing large-scale habitat degradation. The two most widespread forms of land use are selective logging and shifting cultivation. Assessment of the long-term effects of these land uses on plant species composition will provide elements for the identification of effective conservation measures and sustainable forms of forest use.

    Disturbances are relatively discrete events in time that cause high mortality of biomass and change the structure of populations, communities or ecosystems. Individual plants and species differ in their ability to claim the previously utilised space and resources, and therefore disturbance events may cause (temporary) shifts in species composition and diversity. In large parts of the African rain forest biome, the most important natural disturbance regime is gap-phase dynamics in which relatively small canopy openings are made by falling branches or trees. Larger-scale disturbances such as landslides, volcanic activity and large-scale river dynamics, have been extremely rare during the last millennia. Therefore, the present set of species is likely to be adapted to disturbance regimes characterised by frequent small-scale disturbances. Analogous to gap-phase dynamics, human land use can be considered as a disturbance. However, human induced disturbances are generally larger, more frequent and more severe. As a result, human land use may have long-term impacts on plant species composition and diversity.

    The fieldwork for this thesis was conducted in the main research site of the Tropenbos-Cameroon Programme; an area of 2000 km 2 of forestland in South Cameroon Vegetation was sampled in old growth forest, logging gaps of 5, 14 and 27 years old, and in abandoned shifting cultivation fields of 10-20, 30-40 and 50-60 years old. Within plots, all terrestrial vascular plants (including all growth forms) were recorded. In total 10.1 ha was surveyed allowing the detailed analysis of human impact on full plant species composition. Much effort was devoted to plant identification and in total some 11 000 herbarium vouchers were collected, processed and sent to specialists for identification. Voucher material was stored in theNationaalHerbarium Nederland - WageningenUniversity branch and in the IRAD/TropenbosField Herbarium inKribi. Some 75% of the plants in the survey identified to species level and an additional 20% was systematically categorised asmorphospecies. In total 1264 species were identified to species level. These included 261 species with ranges restricted to Lower Guinea (South Nigeria - Gabon) of which 51 are confined to the rain forest region of Cameroon.

    Tropical rain forests are often regarded as being undisturbed by humans. In Chapter 2, we analyse the disturbance history of 16 ha of structurally complex and species-rich 'old growth' rain forest (data collected by forestry research project of theTropenbos-Cameroon Programme). The recruitment preference of tree species along a disturbance gradient, ranging from shifting cultivation fields, to canopy gaps and old growth forest, was compared to present-day tree species composition. In nine plots out of 16, older (larger) trees preferred shifting cultivation fields for recruitment while younger trees recruited in small canopy gaps and under closed canopy. These results indicate that these plots once experienced a disturbance regime that included larger-scale disturbances. Combined, the pattern of disturbed and undisturbed plots, the high frequency of charcoal in the forest soil and anthropological data strongly suggest that humans caused these disturbances. The estimated date of these disturbances is 300-400 years ago. Surprisingly, species richness at larger scales was found to be lower in historically disturbed sites compared to undisturbed sites. Therefore, present-day species composition and diversity of old growth forests still reflects historical human impacts.

    Outside protected areas, forests are subject to logging and shifting cultivation and secondary forests are therefore becoming important in many Central African landscapes. Chapter 3 examines the potential of secondary vegetation to contribute to biodiversity conservation. The results indicate that vegetation recovery in logging plots and abandoned shifting cultivation fields is relatively quick, and in most aspects surprisingly complete. A notable exception is the poor recovery of endemics in shifting cultivation fields. We found that even after 60 years the proportion of endemic species was still significantly lower than in old growth forest. In light of the fast recovery of all other vegetation characteristics (including species richness and floristic composition), we conclude that secondary vegetation can contribute biodiversity conservation e.g. as buffer zones around protected areas.

    In Chapter 4, we analyse the relative importance of local and regional processes for structuring species composition during succession. Local processes refer to the ability of species to compete successfully with other species and avoid predation and pathogen attack. Regional processes refer to dispersal and colonisation. Both processes have been suggested to explain the typically high species richness in tropical rain forests. Our results indicate that local processes are especially important during the early stages of succession, whereas regional processes are especially important during the later stages. However, large differences were observed between different species groups. Regional processes mainly governed composition of large tree species (maximum height ≥ 15 m). A similar but smaller effect was observed in small tree species (3-15 m) and shrub species. Local processes structured composition of terrestrial herb species. In general, woody and non-woody climbers were widely distributed generalists with a very similar set of species occurring in all landscape mosaics and in all succession stages. The differences between species groups implies that effective conservation management requires insight in the importance of local and regional processes for the recruitment of target species (e.g. endemic species). A blanket conservation treatment for all species is unlikely to address adequately the specific sensitivity of species with high conservation value to habitat quality and habitat fragmentation.

    The general lack of information on biodiversity patterns is a serious problem for conservation planning in most tropical rain forest regions. With ongoing habitat destruction, conservation priorities must be identified quickly. Therefore optimal use should be made of all currently available sources of information. However, direct comparison of results is problematic if assessment methods differ. In Chapter 5, we make a first attempt to reconcile different assessments by taking into account their methodological differences. The key factors affecting the general shape and position of the species-area curve found through partial sampling are (1) the total extent in which observations are made, (2) the spatial distribution of the observations, (3) the proportion of the total extent sampled, (4) the proportion of the individuals in the sampled area that was included in the survey, and (5) the proportion of the included individuals that was successfully identified. Through simulations, the effects of partial sampling of these factors on observed species richness was identified. To test the method, we compared four botanical surveys conducted in the same area of lowland old growth rain forest. The surveys included were (1) reconnaissance scale vegetation survey, (2) detailed botanical assessment (100% individuals), (3) incomplete botanical assessment (10% individuals), and (4) herbarium collections. Correcting for partial sampling and scaling the results to extent greatly increased the comparability between assessments. This first attempt to reconcile methodologically different surveys suggests that species -area relations can be reconstructed from incomplete sample data if the key characteristics of the methods can be statistically described. The study provides an outline for optimising the use of existing datasets in the evaluation of conservation needs in tropical rain forest areas.

    In Chapter 6, I present an overview of the main effects of human land use on plant diversity in Central African forest. Rain forests are highly dynamic on all spatial and temporal scales. Present-day species composition and diversity reflects their cumulativebiogeographicalhistory. Therefore both present-day and historical disturbance regimes should be considered to understand current patterns of diversity and to predict its responses to future disturbances. The biotic andabioticprocesses that influence diversity vary with the scale of organisation of biological and ecological systems (i.e. community, ecosystem, landscape,region). While human land use obviously disrupts local communities, the impact of humans is also evident on much larger scales. As a result of large-scale forest degradation, fragmentation and global climate change, species composition of most Central African rain forests is likely to undergo changes in the near future. Conservation management should aim at increasing the survival chances of endemic species and species with poor dispersal capacity. In light of the present ecological insights and the uncertainty of the upcoming climate changes, it seems wise to invest in large networks of protected areas. Moreover, it is unlikely that areas managed for timber production will be beneficial for the conservation of characteristic plant diversity unless damage control is rigid. The expected increase in seasonality in large parts of Central Africa, combined with forest fragmentation and canopy opening, is likely to increase the abundance of pioneer species while species of concern to conservation are likely to decline. To increase the effectiveness of conservation management, insight is required in the mechanisms that make species and forest systems vulnerable to human induced disturbances, including global climate change.
    Sweet potato yields and nutrient dynamics after short-term fallows in the humid lowlands of Papua New Guinea
    Hartemink, A.E. - \ 2003
    Netherlands Journal of Agricultural Science 50 (2003)3-4. - ISSN 0028-2928 - p. 297 - 319.
    ipomoea batatas - zwerflandbouw - verbeterde braak - piper aduncum - gliricidia sepium - imperata cylindrica - gewasopbrengst - papoea-nieuw-guinea - bodemvruchtbaarheid - voedingsstoffenbalans - zoete aardappelen - sweet potatoes - ipomoea batatas - shifting cultivation - improved fallow - piper aduncum - gliricidia sepium - imperata cylindrica - soil fertility - nutrient balance - crop yield - papua new guinea - ipomoea-batatas - imperata-cylindrica - gliricidia-sepium - piper-aduncum - use efficiency - nitrogen - soil - cultivation - growth - fertilization
    Shifting cultivation is common in the humid lowlands of Papua New Guinea but little is known about the effect of different fallows on sweet potato (Ipomoea batatas) yield and nutrient flows and pools in these systems. An experiment was conducted in which two woody fallow species (Piper aduncum and Gliricidia sepium) and a non-woody fallow species (Imperata cylindrica) were planted and slashed after one year. Sweet potato was grown for two consecutive seasons (1 year) after which the fallows and yields were compared with yields from continuously cropped plots. The experiment was conducted on a high base status soil (Typic Eutropepts). In the first season, marketable sweet potato yield after piper and imperata was about 11 t ha-1 but yields after gliricidia and under continuous cropping were significantly lower. Vine yield was similar for the continuously cropped plots and for the sweet potato after piper and gliricidia, but significantly lower than after imperata. The effects of the fallows on sweet potato yield lasted only one season. In the second season after the fallow, sweet potato yields were higher, which was contributed to lower rainfall. Nutrient budgets showed that the three fallow species (piper, gliricidia and imperata) added insufficient amounts of nitrogen, phosphorus and potassium for the removal of these nutrients by two consecutive seasons of sweet potato. From a yield point of view there seems no benefit in having a nitrogen-fixing fallow species like Gliricidia sepium in sweet potato based systems on high base status soils.
    Sustainable Management of African Rain Forest Part I: Workshops
    Foahom, B. ; Jonkers, W.B.J. ; Nkwi, P.N. ; Schmidt, P. ; Tchatat, M. - \ 2001
    Wageningen : The Tropenbos Foundation - ISBN 9789051130478 - 274
    regenbossen - bosbedrijfsvoering - duurzaamheid (sustainability) - landgebruiksplanning - plattelandsgemeenschappen - participatie - biodiversiteit - houtteelt - zwerflandbouw - houtkap - kameroen - rain forests - forest management - sustainability - land use planning - rural communities - participation - biodiversity - silviculture - shifting cultivation - logging - cameroon
    Sustainable Management of African Rain Forest. Part II: Symposium
    Jonkers, W.B.J. ; Foahom, B. ; Schmidt, P. - \ 2001
    Wageningen : The Tropenbos Foundation - ISBN 9789051130515 - 159
    regenbossen - bosbedrijfsvoering - duurzaamheid (sustainability) - landgebruiksplanning - plattelandsgemeenschappen - participatie - biodiversiteit - houtteelt - zwerflandbouw - houtkap - kameroen - rain forests - forest management - sustainability - land use planning - rural communities - participation - biodiversity - silviculture - shifting cultivation - logging - cameroon
    Improving soil fertility in Africa: nutrient networks & stakeholder perceptions' NUTNET
    Hilhorst, Th. ; Hassink, J. - \ 1999
    Wageningen : AB-DLO - 23
    bodemvruchtbaarheid - zwerflandbouw - plantenvoeding - afrika - internationale samenwerking - planning - soil fertility - shifting cultivation - plant nutrition - africa - international cooperation
    Chinantec shifting cultivation : InTERAcTIVE landuse : a case-study in the Chinantla, Mexico, on secondary vegetation, soils and crop performance under indigenous shifting cultivation
    Wal, H. van der - \ 1999
    Agricultural University. Promotor(en): R.A.A. Oldeman. - S.l. : s.n. - ISBN 9789058081315 - 162
    zwerflandbouw - vegetatietypen - bosbouw - agroforestry - landgebruik - vegetatie - herbegroeiing - vegetatiebeheer - secundaire bossen - mexico - shifting cultivation - vegetation types - forestry - agroforestry - land use - vegetation - revegetation - vegetation management - secondary forests - mexico - cum laude

    The development of secondary vegetation, soils and crop performance was studied in local variants of shifting cultivation in two villages in the Chinantla, Mexico. In Chapter 1, the institutional, social and political context of the research are presented and the reader is advertised that the scope of the study is limited to the interaction between ecological-productive aspects and the landuse pattern as practiced by the farmers.

    In Chapter 2 a conceptual framework is presented. Indigenous shifting cultivation is defined as a general form of landuse, characterized by the continuous recontextualization of a many-sided relation between man and nature, the continuous recreation of knowledge and the making and use of dynamic fields according to a landuse pattern. A great specificity of indigenous shifting cultivation in response to local environmental and socio-economical factors is observed.

    The ecology of secondary vegetation is reviewed, paying attention to mountain areas such as the Chinantla. The development of forest eco-units is not a simple, unilinear process, but, on the contrary, a process that can take one of many possible courses, influenced by environmental factors and the use-history of the land. Soils develop as an integral part of eco-units, as has been observed by comparing the soil in hurricane tracts and eco-units of different ages. The development of secondary vegetation and soils, as related to the landuse pattern for shifting cultivation, leads to variation in the ecological conditions within the mosaic of fields. Consequently, the performance of crops may vary within the mosaic of fields.

    In the Chinantla region a large variation in climate occurs due to a wide altitudinal range (Chapter 3). As a consequence, several vegetation types occur. Soils in the area have developed from limestone or sandstone/metamorphic rocks. Chapter 4 describes the variants of shifting cultivation and the landuse pattern in the Chinantec communities Santa Cruz Tepetotutla and Santiago Tlatepusco. Three variants of shifting cultivation were distinguished: shifting cultivation in the area of 'selva alta perennifolia de montaña' (the most widely practised), shifting cultivation in the limestone area, and shifting cultivation in the Quercus -forests. In all variants maize is the principal crop.

    In Chapter 5 the development of secondary vegetation as related to the use-history of fields is studied, concentrating on secondary vegetation in the area of 'selva alta perennifolia de montaña'. Secondary regrowths were sampled in 28 fields. Ages of regrowths varied from 5 to 50 years, and orders of regrowths (first-order regrowths develop after cutting primary or old secondary vegetation; second-order regrowths after cutting a first-order regrowth) varied from 1 to 4. On each field, data on the trees and shrubs with a diameter at breast-height of more than 2 cm were recorded in four transects, each of 100 m 2surface area, which were all laid out on steep slopes.

    A total of 5691 trees and shrubs, belonging to 229 species, were found on the sampled area. Thirty-seven species comprised 90% of all sampled individuals. Cluster and ordination analysis showed variation of the species composition of secondary vegetation with age, altitude, geographic location, lithology and order of regrowth. Analysis of farmers' information on the relation between order of regrowth and species composition confirmed the results of sampling.

    Structural parameters, species composition, tree development and eco-unit development varied between orders of regrowth. Basal area, number of trees and crown area index were high in first- and second-order regrowths, but fell sharply in subsequent regrowths. First-order regrowths were dominated by one or two species. In several second-order regrowths, Hedyosmum mexicanum was the single dominant. In other second-order and in later-order regrowths polydominance was observed. Analysis of height-diameter relations in frequent species also indicated a relation between the order of regrowth and the development of the trees of a certain species, demonstrating the flexibility of trees in responding to a changing environment. Whereas first- and second-order regrowths were composed of few eco-units, third- and fourth-order regrowths showed fragmentation of eco-units from early phases of development onwards. The results indicate that the number of consecutive eco-units per time unit diminishes with increasing order of regrowth.

    Changes in soils during one cropping season were studied by comparing soil parameters in samples obtained after slashing the vegetation (May), after burning (June) and at harvest (October-November). No significant differences in bases, pH, nitrogen and carbon were found between May- and June-samples on limestone-derived soils. Between burning and harvest, pH and the sum of exchangeable bases increased slightly. In the area of 'selva alta perennifolia de montaña' pH and exchangeable bases increased significantly between May and June. During the cropping season (June to October-November), the sum of exchangeable bases declined slightly. No relation of these changes with the use-history of fields was found, possibly due to the small number of sampled fields and burns being partial and heterogenous in the year of sampling (1993).

    Sampling of soils in a chronosequence of fields in the area of 'selva alta perennifolia de montaña' gave strong indications of an increase of pH and exchangeable bases in the course of several decades, from the cutting of primary or old secondary vegetation onwards. The strongest increase was observed in the quantity of exchangeable calcium. Correlations between use-history parameters and carbon, nitrogen and phosphorus were not significant. A mechanism of soil change based on a combination of physical and biological processes is proposed, wherein an initial increase in pH through the addition of bases triggers of an increased biological activity resulting in a more hospitable soil.

    The performance of maize crops in a chronosequence of fields was studied in 1994 by determining several parameters referring to the crops (Chapter 7). Crop performance varied strongly between fields, both in the limestone area and in the area of 'selva alta perennifolia de montaña'. In the limestone area, yield per square meter sloping surface diminished with increasing number of burns; there was no relation between yield and any of the measured soil parameters. In the area of 'selva alta perennifolia de montaña', yields were not significantly correlated with any of the parameters applied to characterize the use-history of fields. However, yields per square meter sloping surface were correlated with several soil parameters: CEC-BaCl 2 , exchangeable calcium, total phosphorus and the C/N-ratio. At values smaller than 3.9 also pH-KCl was positively correlated with yields. In fertilization experiments, the combined application of nitrogen and phosphorus improved yield on a field where without fertilization a low yield was obtained; fertilization had no effect where high yields were obtained without fertilization.

    The development of secondary vegetation, soils and crop performance in indigenous shifting cultivation in two villages in the Chinantla, Mexico, illustrates the interactive and iterative character of this form of agriculture. This character should be taken as the point of departure for its redesign in such a way that the production of a variety of goods is combined with the production of a variety of services in a complex mosaic of eco-units.

    Treemail Publishers
    all rights reserved - ISBN 90-804443-4-0
    for information on all Treebooks visithttp://www.treemail.nl

    Nutrients in food crop cultivation in southwest Côte d'Ivoire.
    Reuler, H. van - \ 1996
    Meststoffen : Dutch/English annual on fertilizers and fertilization (1996). - ISSN 0169-2267 - p. 81 - 88.
    akkerbouw - ivoorkust - extensieve landbouw - agrarische bedrijfsvoering - kunstmeststoffen - veldgewassen - innovaties - mest - plantenvoeding - zwerflandbouw - arable farming - cote d'ivoire - extensive farming - farm management - fertilizers - field crops - innovations - manures - plant nutrition - shifting cultivation
    Nutrient management over extended cropping periods in the shifting cultivation system of south-west Cote d'Ivoire
    Reuler, H. van - \ 1996
    Agricultural University. Promotor(en): A. van Diest; B.H. Janssen. - S.l. : Reuler - ISBN 9789054854869 - 189
    bodemvruchtbaarheid - zwerflandbouw - plantenvoeding - kunstmeststoffen - mest - extensieve landbouw - agrarische bedrijfsvoering - innovaties - ivoorkust - soil fertility - shifting cultivation - plant nutrition - fertilizers - manures - extensive farming - farm management - innovations - cote d'ivoire

    Intensification of food crop production in shifting cultivation systems can contribute to protection of tropical forest. For such an intensification knowledge of soil fertility and its dynamics is essential. It was tested whether intensification could be achieved by extending the cropping period in on-farm field trials with controlled management. These trials were conducted on locations along catenas ranging from the crest to the fringe of the valley bottom. On the (moderately) well drained soils P proved to be the yield-limiting nutrient. In extended cropping systems with alternately rice and maize, applications of N, P and K were not sufficient to maintain the yield level obtained in the first season after clearing. Yield decline was much less pronounced for maize than for rice. In the eighth season after clearing yields of over 4 ton of maize per ha were still obtained. Data on the efficiency of utilization of absorbed P indicate that factors other than P deficiency caused the yield decline. A probable cause is deterioration of soil physical properties. Fertilizer recommendations (N,P,K) are formulated for the well drained soils of the upper/middle slopes and for the moderately well drained soils of the lower slope.
    Low-external-input alternatives to shifting cultivation in S. Sumatera : brief description of an Indonesian - Dutch project on environment and development
    Noordwijk, M. van; Guritno, B. - \ 1992
    Haren (Gr.) : DLO-Instituut voor Bodemvruchtbaarheid (Nota / DLO-Instituut voor Bodemvruchtbaarheid 251) - 24
    alternatieve landbouw - tussenteelt - tussenplanting - gemengde teelt - meervoudige teelt - biologische landbouw - zwerflandbouw - zelfvoorzieningslandbouw - sumatra - alternative farming - intercropping - interplanting - mixed cropping - multiple cropping - organic farming - shifting cultivation - subsistence farming
    Rice, weeds and shifting cultivation in a tropical rain forest : a study of vegetation dynamics
    Rouw, A. de - \ 1991
    Agricultural University. Promotor(en): I.S. Zonneveld; R.A.A. Oldeman. - S.l. : S.n. - 263
    bosbouw - zwerflandbouw - rijst - oryza sativa - onkruiden - plantensuccessie - periodiciteit - vegetatie - plantengemeenschappen - onderzoek - planten - flora - tropen - forestry - shifting cultivation - rice - oryza sativa - weeds - plant succession - periodicity - vegetation - plant communities - research - plants - flora - tropics

    The study deals with the rain forest area in south-west Côte d'lvoire (Taï National Park). Descriptions are given of the area's history, agricultural practices, geology, geomorphology, soils, flora and vegetation. The shifting cultivation system based on upland rice was studied as it is practiced without land shortage and under constraints. Possible adaptations of the system to the increasing population pressure have been tested on the fields of local farmers. Special attention was paid to the dynamics of the weed population and to the competition between rice and weeds. The classifications of primary forest, secondary forest and field vegetations are based on their complete floristic composition and was carried out by tabular comparison of plot-data.

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