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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    Supplementary material from "Interactive effects of tree size, crown exposure and logging on drought-induced mortality"
    Shenkin, Alexander ; Bolker, Benjamin ; Pena Claros, Marielos ; Licona, Juan Carlos ; Ascarrunz, Nataly ; Putz, Francis E. - \ 2018
    University of Florida
    drought - tree mortality - climate change - tropical forest - logging - forest structure - resilience - climate adaptation
    Large trees in the tropics are reportedly more vulnerable to droughts than their smaller neighbours. This pattern is of interest due to what it portends for forest structure, timber production, carbon sequestration and multiple other values given that intensified El Niño Southern Oscillation (ENSO) events are expected to increase the frequency and intensity of droughts in the Amazon region. What remains unclear is what characteristics of large trees renders them especially vulnerable to drought-induced mortality and how this vulnerability changes with forest degradation. Using a large-scale, long-term silvicultural experiment in a transitional Amazonian forest in Bolivia, we disentangle the effects of stem diameter, tree height, crown exposure and logging-induced degradation on risks of drought-induced mortality during the 2004/2005 ENSO event. Overall, tree mortality increased in response to drought in both logged and unlogged plots. Tree height was a much stronger predictor of mortality than stem diameter. In unlogged plots, tree height but not crown exposure was positively associated with drought-induced mortality, whereas in logged plots, neither tree height nor crown exposure was associated with drought-induced mortality. Our results suggest that at the scale of a site, hydraulic factors related to tree height, not air humidity, are a cause of elevated drought-induced mortality of large trees in unlogged plots.This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Nino on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.
    Interactive effects of tree size, crown exposure and logging on drought-induced mortality
    Shenkin, Alexander ; Bolker, Benjamin ; Peña-Claros, Marielos ; Licona, Juan Carlos ; Ascarrunz, Nataly ; Putz, Francis E. - \ 2018
    Philosophical Transactions of the Royal Society B. Biological sciences 373 (2018)1760. - ISSN 0962-8436 - 10 p.
    climate change - drought - logging - resilience - tree mortality - tropical forest

    Large trees in the tropics are reportedly more vulnerable to droughts than their smaller neighbours. This pattern is of interest due to what it portends for forest structure, timber production, carbon sequestration and multiple other values given that intensified El Niño Southern Oscillation (ENSO) events are expected to increase the frequency and intensity of droughts in the Amazon region. What remains unclear is what characteristics of large trees render them especially vulnerable to drought-induced mortality and how this vulnerability changes with forest degradation. Using a large-scale, long-term silvicultural experiment in a transitional Amazonian forest in Bolivia, we disentangle the effects of stem diameter, tree height, crown exposure and logging-induced degradation on risks of drought-induced mortality during the 2004/2005 ENSO event. Overall, tree mortality increased in response to drought in both logged and unlogged plots. Tree height was a much stronger predictor of mortality than stem diameter. In unlogged plots, tree height but not crown exposure was positively associated with drought-induced mortality, whereas in logged plots, neither tree height nor crown exposure was associated with drought-induced mortality. Our results suggest that, at the scale of a site, hydraulic factors related to tree height, not air humidity, are a cause of elevated drought-induced mortality of large trees in unlogged plots.This article is part of a discussion meeting issue 'The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.

    Plan van aanpak voor houtmobilisatie bij particuliere boseigenaren
    Clerkx, A.P.P.M. ; Reumerman, Patrick ; Schelhaas, M. ; Raa, Rik te - \ 2016
    Enschede : BTG Biomass Technology Group - 28
    bosbezit - particulier eigendom - hout - bosproducten - houtkap - twente - forest ownership - private ownership - wood - forest products - logging - twente
    In Nederland bestaat 11% van het oppervlak uit bossen. Deze bossen vervullen belangrijke functies, zoals recreatie, bron van biodiversiteit en leverancier van grondstoffen voor bioenergie en de bioeconomie. Daarnaast passen bossen in de cultuur en tradities van Nederland. De houtoogst in Nederland is laag – ongeveer de helft van de jaarlijkse bijgroei – en redelijk constant. Diverse (overheids)acties in de afgelopen 20 jaar hebben hier geen verandering in gebracht. Het is belangrijk om de houtoogst te verhogen vanwege de positieve effecten op de staat van het Nederlandse bos en vanwege de toekomstige grotere vraag naar hout. Uit een recente enquête onder particuliere boseigenaren in Twente is gebleken dat de helft van deze eigenaren – goed voor 2/5 van het bos in Twente – niet oogst. Daarnaast is ook gebleken dat een belangrijk deel van deze eigenaren bereid is te oogsten als de omstandigheden zouden verbeteren. In dit Plan van Aanpak zijn een aantal acties opgesteld met als doel de houtmobilisatie onder particuliere eigenaren te verhogen.
    Stelling : "we moeten ons meer richten op houtproductie hier in Nederland om de bossen elders op de wereld te beschermen"
    Prins, Herbert - \ 2016
    forest administration - woody plants - logging - timber production - biodiversity - natural value - netherlands - international cooperation - discussion
    Oogsten van tak- en tophout in bossen
    Jong, J.J. de; Spijker, J.H. - \ 2014
    Vakblad Natuur Bos Landschap 11 (2014)108. - ISSN 1572-7610 - p. 26 - 28.
    houtkap - takken - bossen voor brandhout - mechanisch oogsten - biomassa - bosbeheer - bio-energie - biomassa productie - biobased economy - logging - branches - fuel plantations - mechanical harvesting - biomass - forest administration - bioenergy - biomass production - biobased economy
    Nederlandse bossen zijn aangelegd voor de houtproductie. Vanaf de jaren zeventig is deze functie wat naar de achtergrond geschoven. De overheid en veel beheerders vonden natuur en recreatie steeds belangrijker. Tegenwoordig komt er weer meer aandacht voor de productie van hout. In 2013 hebben Staatsbosbeheer, Natuurmonumenten, de 12Landschappen, Federatie Particulier grondbezit het houtconvenant ondertekend, waarin ze aangeven meer stamhout te willen oogsten. Een ander doel is om meer energiehout uit bossen te halen, bijvoorbeeld door de oogst van tak- en tophout dat nu meestal blijft liggen. Deze oogst kan helpen om de ambitieuze doelen van het Energieakkoord te halen. Dergelijke oogst dient echter wel aantrekkelijk te zijn voor de boseigenaar.
    Costs and benefits of a more sustainable production of tropical timber
    Arets, E.J.M.M. ; Veeneklaas, F.R. - \ 2014
    Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-technical report 10) - 57
    houtkap - houtproductie - kosten-batenanalyse - bosbeheer - tropische bossen - duurzaamheid (sustainability) - tropisch hout - ecosysteemdiensten - biobased economy - zuid-amerika - zuidoost-azië - logging - timber production - cost benefit analysis - forest administration - tropical forests - sustainability - tropical timbers - ecosystem services - biobased economy - south america - south east asia
    This study is part of the TEEB (The Economics of Ecosystems and Biodiversity) study of trade chains, and assessed the impact of harvesting tropical timber on ecosystem services and the costs and benefits of more sustainable production. The costs of implementation and the benefits from increased ecosystem services levels were assessed for two alternatives to conventional selective logging (CL), sustainable forest management (SFM) and forest plantation. The SFM alternative involves certified forest management implementing reduced impact logging techniques. The forest plantation alternative involves high-yield plantations that have a larger impact on ecosystem services than CL on the actual plantation area, but require only an equivalent of 11-42% of the CL area due to the higher yields per unit of area, and thus allows a larger area of primary forest to be conserved. The majority of Dutch imports of tropical timbers are from South America and South East Asia. We conducted separate analyses for South America and South East Asia to account for regional differences in terms of logging practices, timber yields and the extent and value of ecosystem services
    "Interactief kappen": Staatsbosbeheer en de maatschappelijke acceptie van houtoogst
    Arts, B.J.M. ; Buijs, A.E. ; Elands, B.H.M. ; Groot, M. de; Hoogstra-Klein, M.A. ; Kamphorst, D.A. ; Turnhout, E. - \ 2014
    Wageningen : Alterra - ISBN 9789462570511 - 45
    bosbeheer - houtkap - maatschappelijk draagvlak - forest administration - logging - public support
    In dit essau aandacht voor het vernieuwende natuurbeleid van de kabinetten Rutte I en II, de daaruit voortvloeiende consequenties voor Staatsbosbeheer, de bijgestelde bosbeheervisie van de organisatie en de wijze waarop Nederlandse burgers - gemiddeld genomen - op de kap van bome reageren. Daarna komen vijf gebieden / aandachtspunten aan bod uit het recente verleden en heden van Staatsbosbeheer. Dit zijn: Drents Friese Woud, Heiderijk, Baarnse Bos, Westerkwartier en het project Kap & Verjonging. Directe aanleiding is de interactie tussen Staatsbosbeheer, belangengroepen en burgers, vrom en aand van die interactie, wederzijdse beeldvorming en uiteindelijk het leerproces
    Aanzet voor een adviessysteem voor oogst uit het bos : voor een evenwichtige nutriëntenbalans en een goede functievervulling van het bos
    Jong, J.J. de; Briel, J. van den; Vries, W. de; Spijker, J.H. - \ 2014
    Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2494) - 52
    bosexploitatie - bodembescherming - bodemchemie - houtkap - voedingsstoffen - biomassa - habitats - natuurbeheer - biobased economy - forest exploitation - soil conservation - soil chemistry - logging - nutrients - biomass - habitats - nature management - biobased economy
    In Nederland zijn afspraken gemaakt om meer biomassa uit het bos te oogsten. Hierdoor kan de beschikbaarheid van voedingsstoffen afnemen. Dit rapport geeft een overzicht over de in andere landen bestaande systemen om uitputting van bosbodems tegen te gaan. Verder wordt een analyse gemaakt van de beschikbaarheid van gegevens om nutriëntenbalansen voor het Nederlandse bos op te stellen en worden eerste indicaties van de balanstermen en voorraden voedingsstoffen gegeven. Afsluitend wordt een aanzet gegeven voor een adviessysteem dat geschikt is voor praktisch gebruik door terreinbeheerders om eraan bij te dragen dat oogst van biomassa uit het bos kan plaatsvinden zonder dat dit tot ongewenste uitputting van nutriënten in de bodem leidt.
    The Multi-Stakeholder Dialogue in Ghana : Towards a negotiated solution to illegal chainsaw milling
    Mckeown, J.P. ; Rozemeijer, N. ; Wit, M. - \ 2013
    Wageningen : Tropenbos International - ISBN 9789051131147 - 44
    ontbossing - houtkap - illegale kap - ghana - deforestation - logging - illicit felling - ghana
    Forest management and regeneration of tree species in the Eastern Amazon
    Schwartz, G. - \ 2013
    Wageningen University. Promotor(en): Frits Mohren; Bas Arts, co-promotor(en): Marielos Pena Claros; J.C.A. Lopes. - S.l. : s.n. - ISBN 9789461734662 - 132
    bosbedrijfsvoering - bomen - soorten - verjonging - houtkap - houtteelt - amazonia - forest management - trees - species - regeneration - logging - silviculture - amazonia

    Forest management for timber production applied in the Brazilian Amazon follows a polycyclic silvicultural system where harvesting is done through reduced-impact logging (RIL). In this study the short- and medium-term effects of RIL on the regeneration of commercial tree species were assessed in the Tapajós National Forest, Eastern Amazon, Brazil. Besides, post-harvesting silvicultural techniques such as enrichment planting using commercial tree species and tending naturally established individuals in gaps created by RIL were tested in Jari Valley, Eastern Amazon, Brazil in order to improve forest management for ensuring sustainable timber production. Finally the profitability of the tested post-harvesting silvicultural treatments was evaluated. Results showed that RIL did not have a destructive effect on the regeneration of the investigated species. In the short-term RIL caused unevenly spatially distributed disturbances over the forest, which tended to increase recruitment and growth rates of seedlings and saplings in the medium-term. The silvicultural techniques proved to be efficient to decrease mortality and increase growth rates of commercial tree species but are not profitable under the current timber prices and harvesting operation costs in the Brazilian Amazon. Although not profitable, enrichment planting in logging gaps showed to be an important tool for conserving rare species.

    Environmental life cycle assessment to enhance the sustainability of the timber sector in Ghana
    Eshun, J.F. - \ 2012
    Wageningen University. Promotor(en): Rik Leemans, co-promotor(en): Jose Potting. - S.l. : s.n. - ISBN 9789461732118 - 115
    houtproductie - bos- en houtproductenindustrieën - levenscyclusanalyse - duurzaamheid (sustainability) - milieueffect - houtkap - ghana - timber production - forest products industries - life cycle assessment - sustainability - environmental impact - logging - ghana

    The timber sector, i.e. forestry and timber industry, is an important industry in Ghana. It provides a significant contribution to Ghana’s foreign exchange earnings through wood products export, provides jobs and incomes for numerous local economies and communities. The timber production in Ghana is associated with an increasing environmental burden in terms of use of resources, and production of emissions and waste. The overall objective of this thesis was to quantify the environmental performance of the sector and to explore the possible options and strategies to sustain and improve the environmental performance of the timber sector in Ghana. To achieve this objective, the following research questions are addressed in successive chapters: (1) Is the timber sector in Ghana sustainable?, (2) What is the most dominant environmental pressure for the five major production lines in the Ghanaian timber industry, and what is the influence of the choice of functional unit?, (3) What does the most dominant environmental pressure contribute to the life cycle impact of the timber sector in Ghana?, and (4) Which potentials improvement options and strategies are available for reducing the major environmental impact in the timber sector in Ghana?

    The research for question 1 identified a sustainability gap that has been created as a result of aggressive competition between the informal and formal timber sectors for raw material supply. The subsequent life cycle assessment (LCA), in response to research question 2 and 3, showed land use and wood waste as the most dominant environmental pressure for five major production lines (air dried lumber, kiln dried lumber, plywood, veneer and furniture parts). Land use and wood waste pressures will eventually lead to complete deforestation in the year 2025 if major policies are not implemented. The LCA results were sensitive to the choice of the functional unit (1m3, 1kg and 1euro). The money-based functional unit, that was seen as more appropriate, favors the value-added products. This holds a promising future in terms of sustainability for the timber industry in Ghana. The impact assessment results showed a strong correlation between wood waste and land use as proxy for biodiversity loss, and also positive correlations between wood waste and the other five impacts results. Wood waste production was concluded as a major driving force for biodiversity loss, and a sufficiently good single indicator for all other environmental impact in the timber sector of Ghana. The research for question 4 showed that combining technological changes, good operational practices and recycling measures could reduce wood waste by approximately 50%.

    This thesis presents a first step in exploring the possible options and strategies to sustain and improve the environmental performance of the timber sector in Ghana. The understanding of the link between sustainability and environmental assessment can help to design and implement good and working sustainability policies in Africa. The presented research therefore contributes to the development of integrated policy support approaches, which aim at strengthening the sustainable management of the timber sector in Ghana. This research may serve as a guide for policy-makers as well as for companies in elaborating measures to sustain and reduce environmental impacts in terms of possible future developments in the timber sector in Africa and particularly Ghana.

    Global wood production : assessment of industrial round wood supply from forest management systems in different global regions
    Arets, E.J.M.M. ; Meer, P.J. van der; Verwer, C.C. ; Hengeveld, G.M. ; Tolkamp, G.W. ; Nabuurs, G.J. ; Oorschot, M. van - \ 2011
    Wageningen : Alterra, Wageningen-UR (Alterra-report 1808)
    bosbouw - houtkap - velling - kaalslag - modellen - forestry - logging - felling - clear felling - models
    To meet the global demand for wood the old forest management module of the IMAGE integrated assessment model (Bouwman et al. 2006) only applied clear felling. As a consequence in whole gird cells the forest was completely harvested. In reality, however, there many different ways to produce wood, ranging from selective logging to clear felling and forestry plantations. Each of these logging systems will have different effects on the area needed for wood production and impact on remaining forest and diversity patterns. The global biodiversity model GLOBIO (Alkemade et al. 2009), which is coupled to the IMAGE model, however, needs more precise information on area needed and differentiates in impact of different forest management types. In this report an overview is given of different forest management types (clear felling, selective felling, reduced impact logging and forest plantations) and the associated wood production and harvest losses on an area base in different climate zones (boreal, temperate and tropical). The data were collected form scientific and grey literature for a sample of 20 important wood producing countries across most world regions that are distinguished within the IMAGE model. Together these example countries covered 81.5% of the global industrial round wood production in 2005.
    Social safeguards in the Ghana-EU Voluntary Partnership Agreement (VPA); Triggering improved forest governance or an afterthought?
    Arts, B.J.M. ; Wiersum, K.F. ; Aggrey, J. ; Owusu, B. ; Oijen, D.C.C. van; Nketiah, S. ; Wit, M. ; Zagt, R. ; Vellema, H. ; Rozemeijer, N. - \ 2010
    Wageningen : Wageningen Universiteit and Research Centre - ISBN 9789085859703 - 12
    bosbedrijfsvoering - houtkap - houthandel - middelen van bestaan - sociaal beleid - rechtshandhaving - ghana - forest management - logging - timber trade - livelihoods - social policy - law enforcement - ghana
    Implementing FLEGT: Impacts on local people
    Wiersum, K.F. ; Oijen, D.C.C. van - \ 2010
    Wageningen, the Netherlands : Wageningen University and Research Centre - ISBN 9789085858966 - 19
    houtkap - houthandel - illegale kap - participatie - middelen van bestaan - logging - timber trade - illicit felling - participation - livelihoods
    A landscape approach guiding a multiple stakeholder process to find alternatives for illegal chainsaw lumbering in Ghana - enhanced effectiveness or more confusion?
    Rozemeijer, N.G. - \ 2008
    Wageningen : Wageningen International - 16
    landschapsbescherming - landschapsecologie - houtkap - bosbedrijfsvoering - ghana - multi-stakeholder processen - landscape conservation - landscape ecology - logging - forest management - ghana - multi-stakeholder processes
    Dinámica de la biomasa en áreas de manejo forestal sujetas a diferentes intensidades de aprovechamiento.
    Mostacedo, B. ; Villegas, Z. ; Licona, J.C. ; Alarcón, A. ; Leaño, C. ; Peña-Claros, M. ; Poorter, L. - \ 2008
    Santa Cruz de la Sierra, Bolivia : Instituto Boliviano de Investigación Forestal (Documento t├®cnico / Instituto Boliviano de Investigacion Forestal (IBIF) 3)
    biomassa - tropische bossen - groei - houtkap - bosmonitoring - biomass - tropical forests - growth - logging - forest monitoring
    Optimising multi-functional forest use
    Meer, Peter van der - \ 2008
    forestry - forest management - logging - sustainability - optimization - yields - ecosystems - land use planning - awareness - decision making - methodology
    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.
    Lianas and logging in West Africa
    Parren, M.P.E. - \ 2003
    Wageningen University. Promotor(en): Frans Bongers; Frits Mohren. - Wageningen : Wageningen Universiteit - ISBN 9789058088710 - 168
    klimplanten - houtkap - snijden - gaten in het kroondak - houtteelt - tropische bossen - bosbedrijfsvoering - bosecologie - west-afrika - climbing plants - logging - cutting - canopy gaps - silviculture - tropical forests - forest management - forest ecology - west africa
    The role of lianas in relation to logging activities is analysed in a lowland moist forest in Cameroon. Lianas are an abundant, diverse, and conspicuous growth form in nearly all tropical forests. Lianas are mostly seen as a nuisance by foresters. Cutting of liana stems is an important operation in forest management practices. Pre-harvest liana cutting is aimed at a reduction of logging damage, an improved precision of felling, an enhancement of the development of the growing tree stock and a reduction of the regrowth capacity of lianas. Lianas were very abundant: on average nearly 5000 individuals per ha of which over 100 large ones (³ 5 cm dbh). Felling gap sizes, tree mortality and damage were not significantly affected by pre-harvest liana cutting. However, this intervention significantly reduced the number of lianas and also the number of liana-infested trees in logging gaps. Cut lianas were monitored and proved that certain species were extremely vulnerable while others hardly. To avoid problems related to the negative impacts that both liana cutting and fire can have on liana species, which are vulnerable to these interventions, it is recommended to apply this treatment only selectively. Spatially, treatments should be limited to zones where lianas are heavily interfering with trees to be felled. Treatments also should be species-specific, by limiting liana cutting to those species, which cause most of the damage.
    Houtoogst: natuurlijk?! : impressie van het 2de Nationale Bosdebat
    Bartelink, H.H. ; Vries, J. de; Houtzagers, M.R. ; Baaij, G.B.J. de - \ 2003
    Nederlands Bosbouwtijdschrift 75 (2003)4. - ISSN 0028-2057 - p. 20 - 22.
    bossen - bosbeheer - bosbedrijfsvoering - bosbouw - houtteelt - oogsten - natuurbescherming - houtkap - forests - forest administration - forest management - forestry - silviculture - harvesting - nature conservation - logging
    Verslag van het tweede Nationale Bosdebat, met als onderwerp 'Houtoogst: natuurlijk?!' (7 mei 2003, Alterra, Wageningen). Houtproductie en houtoogst in Nederlandse bosssen moet kunnen en hoort niet in het beklaagdenbankje. Het kan zelfs met vergroting van natuurwaarde en -beleving. Kwaliteit moet bij de productie voorop staan, en de bosbouwsector moet nut en noodzaak van de houtoogst beter communiceren naar de maatschappij toe
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