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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    Socio-ecological analysis of multiple-use forest management in the Bolivian Amazon
    Soriano Candia, Marlene - \ 2017
    Wageningen University. Promotor(en): G.M.J. Mohren, co-promotor(en): M. Peña Claros; N. Ascarrunz. - Wageningen : Wageningen University - ISBN 9789463436557 - 220
    forest management - timber production - nuts - multiple use - bertholletia excelsa - forest ecology - amazonia - sustainability - community forestry - bosbedrijfsvoering - houtproductie - noten - meervoudig gebruik - bertholletia excelsa - bosecologie - amazonia - duurzaamheid (sustainability) - gemeenschapsbosbouw

    Community families throughout tropical regions derive an important share of their income from multiple forest products, with generally positive outcomes on their livelihoods. The production of these products in a multiple-use forest management scheme (MFM, the production of multiple forest products within a single management unit) encompasses many (yet) unknown socioeconomic and ecological feedbacks. In particular, MFM entailing timber and non-timber production may be affecting the future availability of valuable timber and non-timber tree species due to the extraction of vital plant components, which may have undesired outcomes on the income that community families derive from forests. In this thesis, I evaluated the social, economic, and ecological viability of an important MFM scheme widely practiced by community households in the Bolivian Amazon: the production of Amazon or Brazil nut (Bertholletia excelsa) and timber from other tree species. Data was obtained from a two-year (2014 and 2015) survey questionnaires of 24 community households in six campesino communities with community forest management plans (CFMPs) and from ecological surveys of 72 2 ha permanent research transects (three transects per household forest) harvested at varying Amazon nut and logging intensities. A CFMP entails the planning and execution of logging activities in compliance with formal rules intended to secure the long-term provision of timber at community-owned forest. Household-level decisions to harvest Amazon nut and to log timber allowed us to account for household forest as our sampling unit. We used multi-model inference and structural equation modelling techniques to determine the impact of socio-ecological factors on the income that community families derived from Amazon nut and timber (chapter 2), and regression and matrix modelling techniques to determine the impact of Amazon nut harvest and logging intensity on Bertholletia (chapter 3) and commercial timber species (chapter 4).

    In general, we found that few socioeconomic and biophysical factors of community households, together with a general positive response of studied species to timber logging and customary silvicultural intervention, make the production of Amazon nut and timber production of other tree species viable in a MFM scheme. In chapter 2, we found that community households could reduce their dependency on forest resources by increasing income opportunities from other existing livelihood activities. Amazon nut represented the largest source of household income (44% of the total household net income); and off-farm (salary, business and gifts; 21%), husbandry (generally subsistence agriculture, animal rising, and agroforestry; 21%), and timber (9%) incomes were complementary to their livelihood. Increased skills and ecological knowledge of community households enhanced household income derived from forest products. For example, an increase in the number of management practices reduced the need for timber income by increasing Amazon nut production; decreasing further pressure on timber of other tree species.

    In chapter 3, logging intensity was found to increase Bertholletia’s seedlings and saplings growth rate, and liana cutting was found to increase Amazon nut production rate. Both, logging and liana cutting intensities played a key role on Bertholletia population growth rate. Increased logging and liana cutting intensities counteracted the negative impact of Amazon nut harvesting intensity on the number of new recruits (i.e., due to nut harvest), indicating a trade-off between logging, liana cutting and Amazon nut harvesting intensities.

    Considering the overall stem density of commercial timber species (chapter 4), we found that 17% of the species present at unlogged sites (3 species out of 17: Swietenia macrophylla, Tabebuia impetiginosa and Terminalia sp.) were not present at sites six years after logging; and a larger percentage (71%) of the species present at unlogged sites in the harvestable size (trees>minimum diameter cutting – MDC) were not present at sites six years after logging, e.g., Cedrela spp. Stem density and timber volume of five of the eight most abundant commercial timber species under study differed among community-owned forests, after accounting for the effects of logging intensity and time since logging as indicated by our best models; whereas, potentially harvestable and harvestable timber volume differed between communities for only two and three species, respectively. Best models indicated that logging intensity increased either stem density or timber volume of Apuleia leiocarpa, Cedrela odorata, Dipteryx micrantha and Hymenaea parvifolia, decreased potentially harvestable timber volume of T. serratifolia, and had no effect on the other three species investigated. We also investigated the impact of logging intensity on congeneric species given that lumping congeneric species for logging is a common simplification during forest inventories and censuses, and is accepted in CFMPs assuming that closely related species respond to timber logging in a similar way. However, logging intensity had a differentiated effect on congeneric species. Logging intensity favoured growth rate of C. odorata trees >10 cm DBH and had no effects on Cedrela fissilis. Regarding Hymenaea congeneric species, logging intensity favoured H. parvifolia survival of individuals <10 cm DBH, but decreased growth rates of H. courbaril trees >10 cm DBH.

    In conclusion, Amazon nut harvest and timber logging of other tree species are compatible under certain socioeconomic and biophysical conditions, and as long as commercial timber species differential response to harvesting are accounted for in managing these species in a MFM scheme. This compatibility is due to existing socioeconomic complementarity of both activities and to the positive impact of logging intensity levels as practiced in the region on Amazon nut production and on most commercial timber species. Community families’ better negotiation skills to obtain better prices for Amazon nut, and increased implementation of management practices to increase Amazon nut production (e.g., liana cutting) helped families to increase their income and also decrease pressure on timber. These results highlight the need to look at both socioeconomic and ecological aspects when assessing the long-term sustainability of MFM schemes.

    Results of this research have important implications for policy to support the sustainable development of community forestry in the Bolivian Amazon. The compatibility found between Amazon nut and timber production calls for the investigation of the compatibility of timber production with other valuable NTFPs commonly harvested by community families throughout the tropics. We argue that management needs to be done at species-specific level, rather than at the level of products or at the level of species groups. This may result prohibitively expensive for communities and smallholders. Thus, we urge governments and the international community to revalorize local ecological knowledge of community people to manage their forests, while supporting the development of technologies, such as the ones based on hyperspectral LiDAR technology, to develop tools that could help reduce management costs of tropical forests at the required level. Such policies need to be accompanied by capacity building programs on different management tasks and negotiation skills to enhance the income obtained from MFM schemes. The research approaches used here could be used in other contexts and scales involving natural resources management to get a better understanding of the systems.

    Vochtige bossen, tussen verdrogen en nat gaan : OBN deskundigenteam Nat zandlandschap
    Burg, A. van den; Bijlsma, R.J. ; Brouwer, E. ; Waal, R.W. de - \ 2016
    VBNE, Vereniging van Bos- en Natuurterreineigenaren - 36
    bosbeheer - waterbeheer - bossen - bosecologie - ecohydrologie - grondwater - grondwaterstand - beekdalen - forest administration - water management - forests - forest ecology - ecohydrology - groundwater - groundwater level - brook valleys
    Deze brochure is geschreven voor bos- en waterbeheerders, landschapsecologen en provinciale beleidsambtenaren, om hen te stimuleren de vochtige bossen met meer aandacht te bekijken. De brochure beschrijft om welke bostypen het gaat, hoe je deze kunt herkennen, in welke landschappen ze voorkomen en hoe ze functioneren.
    Terug naar de basis
    Willems, Arno ; Schreppers, Harrie ; Jans, Rino ; Klingen, Simon ; Ouden, J. den; Schoonderwoerd, Henny ; Wijdeven, Sander ; Staak, Erik van der - \ 2016
    Vakblad Natuur Bos Landschap 13 (2016)127. - ISSN 1572-7610 - p. 40 - 41.
    bosbeheer - houtachtige planten - duurzaamheid (sustainability) - bosgronden - bodemuitputting - bosecologie - voedingsstoffenbalans - verzuring - bodemverdichting - mechanisatie - forest administration - woody plants - sustainability - forest soils - soil exhaustion - forest ecology - nutrient balance - acidification - soil compaction - mechanization
    Als bosbeheerders gaan we er prat op dat we het begrip duurzaamheid hebben uitgevonden. Dat is inderdaad iets om trots op te zijn en bewijst dat we als sector gewend zijn ver vooruit te kijken en te denken. Het is echter de vraag of we onze bossen nog wel volgens de principes van duurzaamheid beheren. Met name over de mogelijke uitputting van de bodem en de invloed van de exploitatie op de bodem bestaan veel vragen waarvan de antwoorden niet voor het oprapen liggen. Op 17 mei 2016 ging de Studiekring van de KNBV terug naar de basis: de bosbodem.
    Biodiversity and the functioning of tropical forests
    Sande, M.T. van der - \ 2016
    Wageningen University. Promotor(en): Lourens Poorter, co-promotor(en): Marielos Pena Claros; Eric Arets. - Wageningen : Wageningen University - ISBN 9789462578029 - 282
    tropical forests - biodiversity - forest ecology - forest management - climatic change - tropische bossen - biodiversiteit - bosecologie - bosbedrijfsvoering - klimaatverandering

    Tropical forests are the most diverse terrestrial ecosystems. Moreover, their capacity for removal of carbon from the atmosphere makes them important for climate change mitigation. Theories predict that species use resources in a different way, and therefore high species diversity would result in more efficient resource use and higher total carbon removal. These theories, however, have yet not been clearly demonstrated for tropical forests. In this thesis, I evaluated how biodiversity of plants and their traits influenced carbon removal. I used data collected in different tropical forest types and at different spatial and temporal scales. I found that biodiversity was important for carbon removal especially at large spatial scales (e.g. the Amazon) where biodiversity varies strongly, and at long temporal scales (e.g. >200 years) where high biodiversity functions as a buffer for changing environmental conditions. In this way biodiversity contributes to long-term stable forests and a safe climate.

    Ghana's high forests : trends, scenarios and pathways for future developments
    Oduro, K.A. - \ 2016
    Wageningen University. Promotor(en): Frits Mohren; Bas Arts, co-promotor(en): B. Kyereh. - Wageningen : Wageningen University - ISBN 9789462577824 - 171
    forests - forest ecology - forest management - high forest system - forest resources - forestry - ghana - bossen - bosecologie - bosbedrijfsvoering - hoog opgaand bos - bosbestanden - bosbouw - ghana

    Deforestation and forest degradation in the tropics have been receiving both scientific and political attention in recent decades due to its impacts on the environment and on human livelihoods. In Ghana, the continuous decline of forest resources and the high demand for timber have raised stakeholders concerns about the future timber production prospects in the country. The principal drivers of deforestation and forest degradation in Ghana are agricultural expansion (50%), wood harvesting (35%), population and development pressures (10%), and mining and mineral exploitation (5%). Various measures are being pursued that are targeted at addressing the drivers of deforestation and forest degradation and at increasing the forest resource base. Understanding the key driving forces behind current forest resource development trends will help to gain insights into the possible courses of action to take to improve the developments of the resources, especially where actions that are being taken today will have an impact on the forest resources for many years to come.

    In this thesis, I used interdisciplinary research methods to provide insights into the current status of the forest resource base in Ghana and into its likely and possible future developments. I addressed 5 research questions: (1) What are the trends and changes associated with the growing stock in the timber production areas? (2) What driving forces account for current trends and future developments of timber resources in Ghana? (3) What different scenarios can be identified and how will these affect future developments of timber resources in the high forest zone? (4) What factors motivate farmers to engage in on-farm tree planting and management? (5) To what extent do the current trends of forest resources drive forest transition in Ghana?

    National forest inventory data, timber harvesting data and forest plantation establishment data showed that the growing stock in both on- and off-reserve production areas have been declining since 1990. Ghana’s average forest growing stock of 40m3 per ha is much lower than the 195 m3 per ha for the Western and Central Africa sub-region. Timber harvesting records also indicate that, in recent decades, total timber harvests have mostly been substantially higher than the annual allowable cut, resulting in an increasing gap between national timber demand and supply, which drives illegal logging. Current plantation establishment efforts are not sufficient to bridge the gap between demand and supply of timber, partly due to low establishment rates and lack of appropriate management of newly established plantations. Forest governance system and resource demand are the two key driving forces that affect the current trends and future developments of forest resources in the high forest zone of Ghana. Four scenarios were developed: (1) legal forestry scenario with emphasis on improving the resource base to meet high demand; (2) forest degradation, which implies a business-as-usual scenario; (3) forest transition, with emphasis on expanding the resource base in response to environmental concerns; and (4) timber substitution scenario seeking to provide wood substitutes to conserve the resource base. Across two on-farm tree planting schemes, I found that financial benefits, educational campaigns by project teams, knowledge about current environmental issues, ownership of timber for family use and access to land, grants, farming inputs, seedlings, capacity building, and market for agricultural produce are the factors that motivated farmers to engage in on-farm tree planting and management. Currently, there is no strong force toward a forest transition through any of the five generic pathways (economic development; forest scarcity; globalization; state forest policy; and smallholder, tree-based land use intensification). This is because the existing trends of forest resources developments are either too small-scale or too ineffective. In order to accelerate a forest transition in Ghana, policy and management options should target measures that reduce current degradation of natural forests, increase the area and productivity of commercial forest plantations, promote sustainable forest management, and support and encourage forest conservation and integration of trees into farming systems.

    Arme bossen verdienen beter : OBN Deskundigenteam Droog zandlandschap
    Burg, A. Van den; Bijlsma, R.J. ; Bobbink, R. - \ 2015
    VBNE, Vereniging van Bos- en Natuurterreineigenaren - 24
    bossen - bosbeheer - zandgronden - zure regen - voedingsstoffenbeschikbaarheid - biodiversiteit - verzuring - voedingsstoffenbalans - verstoorde bossen - bosecologie - forests - forest administration - sandy soils - acid rain - nutrient availability - biodiversity - acidification - nutrient balance - disturbed forests - forest ecology
    Bossen van het droog zandlandschap van Noordwest- Europa staan bekend als ‘arme bossen’. Het landschap waarin ze voorkomen was tot in de 20ste eeuw overwegend een heidelandschap. Op de voedselarme heide- en stuifzandbodems zijn vanaf 1900 vooral naaldbossen geplant. Inmiddels zijn in deze voormalige plantages volop kenmerken aanwezig van oudere, meer natuurlijke bossen, zoals dikke levende en dode bomen, natuurlijke verjonging van inheemse loofbomen en een gevarieerd lichtklimaat. Veel soorten hebben sterk geprofiteerd van deze natuurlijke ontwikkeling die nog steeds doorzet. In de loop van 20ste eeuw zijn echter eerst zwaveldepositie (‘zure regen’) en later ook stikstofdepositie een grote negatieve invloed gaan uitoefenen op het landschap. Dit raakt niet alleen de biodiversiteit, maar ook de hout- en biomassaproductie en daarmee de duurzaamheid van het bosgebruik. We hebben directe gevolgen vastgesteld voor soorten en nutriëntenvoorraden in de bodem en indirecte effecten op concurrentieverhoudingen en voedselketens. Er zijn echter ook onzekerheden en belangrijke kennisleemten waar het gaat om de precieze mechanismen, het experimenteel vastleggen van oorzaak-gevolg relaties en mogelijke oplossingsrichtingen. De achtergronden van deze problematiek in droge bossen staan centraal in deze brochure.
    Bosmuizen verlicht [door studenten / promovendi]
    Sindram, Janneke - \ 2015
    De Levende Natuur 116 (2015)2. - ISSN 0024-1520 - p. 71 - 72.
    forest ecology - artificial light - fauna - mice - adverse effects - bosecologie - kunstlicht - fauna - muizen - nadelige gevolgen
    Kunstlicht heeft op allerlei dieren invloed. Daar zijn veel voorbeelden van te verzinnen. Gecombineerd met het feit dat het in Europa 's nachts steeds lichter is geworden, mag de conclusie getrokken worden dat de natuur hier veel gevolgen van ondervindt. Nader onderzoek wordt verricht door Janneke Sandram, begeleid vanuit Wageningen Universiteit en NIOO.
    Tropical forests in a changing world
    Zuidema, P.A. - \ 2015
    Wageningen : Wageningen University - ISBN 9789462573765 - 24
    tropical forests - forests - forest ecology - climatic change - forest management - tropische bossen - bossen - bosecologie - klimaatverandering - bosbedrijfsvoering
    Inauguratie Koen Kramer
    Kramer, K. - \ 2015
    Wageningen UR
    adaptatie - genetische diversiteit - bossen - modelleren - klimaatverandering - bosbescherming - bosproducten - bosecologie - adaptation - genetic diversity - forests - modeling - climatic change - protection of forests - forest products - forest ecology
    Nieuwe en bestaande bossen kunnen door gebruik te maken van de genetische diversiteit van bomen hun functionaliteit behouden bij klimaatverandering. Dat stelt prof. dr. Koen Kramer bij zijn oratie als buitengewoon hoogleraar Kwantitatieve bosgenetica aan Wageningen University op donderdag 8 oktober
    Resilience of Amazonian landscapes to agricultural intensification
    Jakovac, C.C. - \ 2015
    Wageningen University. Promotor(en): Frans Bongers; Thomas Kuijper, co-promotor(en): Marielos Pena Claros; R.C.G. Mesquita. - Wageningen : Wageningen University - ISBN 9789462574434 - 172
    landschap - landschapsecologie - veerkracht van de natuur - intensivering - landbouw - landgebruik - bosecologie - amazonia - landscape - landscape ecology - resilience of nature - intensification - agriculture - land use - forest ecology - amazonia

    ISBN: 978-94-6257-443-4

    Author: Catarina C. Jakovac

    Title: Resilience of Amazonian landscapes to agricultural intensification

    Swidden cultivation is the traditional agricultural system in riverine Amazonia, which supports local livelihoods and transforms landscapes. In the last decades, riverine Amazonia has been undergoing important transformations related to population migration and market integration. In this study I investigated whether these socio-economic transformations could be inducing agricultural intensification and what are the consequences of such intensification for the resilience of the swidden cultivation systems in the region of the middle-Amazonas river, Brazil. This region is one of the largest producers of cassava flour (farinha in Portuguese) in the Brazilian Amazon, which is the local staple food. By combining information from field surveys, farmers interviews and remote sensing time-series, I investigated how agricultural intensification is taking place at the landscape level, and what are the consequences for secondary forests (fallows) regrowth and swiddens productivity.

    The results of this study show that swidden cultivation has been intensified in the last three decades, evidenced by an increase in the frequency of swidden-fallow cycles and a decrease in the length of the fallow period, from 9 to 5 years on average. I also found that agricultural intensification was associated to land accessibility and market orientation. Across the region, swiddens are dominated by a single cassava variety that is preferred by the market, reducing the possibilities for adaptation to pests outbreaks and environmental variations. At the field level, repeated swidden-fallow cycles under a short-fallow-period regime (of 5 yrs) leads to a decrease in the recovery capacity of secondary forests (reduced regrowth rate, lower species alpha- and beta-diversity, and changed species composition). Intensification also leads to a reduction in the labour productivity of swiddens (reduced cassava yield and higher weeding labour demand), and consequently in household income.

    I found that management-environment feedbacks play a key role in the decrease of swiddens and fallows productivity. The sprouting and persistent species favoured by cutting, burning and weeding practices are slow growing and form secondary forests with limited potential to fertilize the next cropping field and to suppress weeds. This results in a higher demand for weeding, which in itself will further favour strong-sprouting species. Such feedbacks reinforce the adverse effects of intensification on the environment and for livelihoods. Although farmers recognize thresholds for managing resilience, such as the formation of tired lands (terras cansadas in Portuguese), the combination of a low-nutrient-requiring crop, increasing farinha prices and shortage of accessible land, is encouraging farmers to keep on cultivating in already exhausted lands, and is pushing the system over such threshold.

    To enhance the resilience of swidden cultivation systems in the context of riverine Amazonia, management-environment feedbacks should be broken and market opportunities should be broadened beyond cassava, to include forest products that can be harvested within the swidden-fallow landscape, such as nuts, fruits and timber from fast-growing species. Thus, the proper management of secondary succession is key for assuring resilience to swidden-fallow landscapes and for promoting the integration of production and nature conservation in human modified landscapes.

    Insecten schadelijk voor naaldhout, vroeger en nu
    Hoopen, Jan ten; Moraal, L.G. ; Smits, J. - \ 2015
    Entomologische Berichten 75 (2015)3. - ISSN 0013-8827 - p. 86 - 96.
    bosecologie - naaldbossen - insect-plant relaties - fauna - historische ecologie - forest ecology - coniferous forests - insect plant relations - historical ecology
    In het eerste deel van de Entomologische Berichten besteedt Arie Brants in 1904 aandacht aan de door Staatsbosbeheer in 1903 uitgebrachte plaat 'Insecten schadelijk voor naaldhout'. Wij beschrijven in dit artikel hoe sommige van deze insecten nog steeds als de meest schadelijke in de Europese bosbouw worden beschouwd, maar in Nederland nauwelijks meer een rol spelen. Ook bespreken wij hoe veranderend bosbeheer en veranderend klimaat een verschuiving van plagen liet zien.
    Ecologie van bosbodems : een verkennende studie naar ecologisch functioneren van bosbodems op zandgronden
    Jong, J.J. de; Bloem, J. ; Delft, S.P.J. van; Hommel, P.W.F.M. ; Oosterbaan, A. ; Waal, R.W. de - \ 2015
    Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2657) - 89
    bosecologie - bodemecologie - bodemvruchtbaarheid - humus - organische stof - zandgronden - forest ecology - soil ecology - soil fertility - organic matter - sandy soils
    De bodem van een bos is bepalend voor het functioneren van het bos als productie- en ecosysteem. Het is het substraat waar organismen in leven en waar planten in wortelen. De bodem houdt vocht en nutriënten vast en levert deze aan planten en het bodemleven, terwijl planten organische stof aan de bodem leveren. De wijze waarop dit allemaal gebeurt, bepaalt in grote mate welke organismen er in en op voor kunnen komen en hoe die functioneren. De bodemorganismen en voedingstoestand van de bodem worden beïnvloed door beheer en externe factoren, zoals depositie. Kennis van de onderlinge relaties tussen de factoren die de bodemvruchtbaarheid bepalen of door de bodemvruchtbaarheid bepaald worden, is daarom van groot belang voor een duurzaam bosbeheer. Dit rapport bevat een verkenning van de kennis die er aanwezig is op dat gebied.
    Houtoogst en bodemvruchtbaarheid : een modelstudie naar duurzaamheid van houtoogst op Nederlandse bosgroeiplaatsen
    Bonten, L.T.C. ; Bijlsma, R.J. ; Delft, S.P.J. van; Jong, J.J. de; Spijker, J.H. ; Vries, W. de - \ 2015
    Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2618)
    bosecologie - bodemvruchtbaarheid - bepaling van groeiplaatshoedanigheden - opbrengstregeling - nutrientenbeheer - bodemchemie - forest ecology - soil fertility - site class assessment - yield regulation - nutrient management - soil chemistry
    Dit rapport brengt met een modelstudie de duurzaamheid van houtoogstscenario’s in beeld ten aanzien van nutriëntenbalansen op verschillende Nederlandse bosgroeiplaatsen. Tegelijkertijd geeft de studie aan waar (nog aanzienlijke) onzekerheden liggen bij de vertaling naar een adviessysteem voor houtoogst. De voor houtoogst relevante groeiplaatsen zijn gekarakteriseerd met 11 typen. Voor elk van deze groeiplaatstypen is met een model nagegaan in welke mate combinaties van boomsoort, groeiklasse (groeiverwachting) en oogstscenario leiden tot een negatieve nutriëntenbalans voor calcium (Ca), magnesium (Mg), kalium (K) en fosfor (P). Ook is nagegaan hoe snel de bosbodem wordt uitgeput.
    Long-term trends in tropical tree growth: a pantropical study
    Groenendijk, P. - \ 2015
    Wageningen University. Promotor(en): Pieter Zuidema; Frans Bongers. - Wageningen : Wageningen University - ISBN 9789462572362 - 244
    bosbomen - tropische bossen - bomen - groei - jaarringen - bosecologie - bosbedrijfsvoering - centraal-afrika - forest trees - tropical forests - trees - growth - growth rings - forest ecology - forest management - central africa

    Tropical forests cover only 7% of the earth’s land surface, but harbour almost half of the world’s biodiversity. These forests also provide many ecosystem services, such as the storage of carbon and the regulation of local and regional climate, and many goods such as timber and fruits. Furthermore, tropical forests contribute disproportionately to the global carbon cycle, storing an estimated 25% of the carbon stocks on land and accounting for a third of the terrestrial net primary productivity. Therefore, changes in forest cover or in the net uptake or loss of carbon by forests directly influences the global carbon cycle. Tropical forests are under increasing anthropogenic pressure and are undergoing rapid changes due to deforestation, conversion to other land uses and logging. Additionally, there is evidence that pristine and intact tropical forests are undergoing changes due to the effects of climate change. Concerted increases in biomass and tree growth have been found in studies monitoring intact tropical forests, suggesting that they acted as considerable carbon sinks over the past decades. On the other hand, decreasing or fluctuating forest growth and biomass have also been noted. These different changes have been attributed to different climatic drivers: growth increases have been suggested to arise from growth stimulation by increasing atmospheric CO2 concentrations, while growth decreases have been interpreted to reflect the limiting effects of increased temperature on growth. As monitoring plots usually cover only a few decades, it is still unclear whether these changes are pervasive or whether they simply reflect the effect of short-term climatic fluctuations on tree growth. Assessing whether changes have occurred over centennial scales is thus crucial to understanding whether and how tropical forests are reacting to climatic changes.

    In this thesis we apply tree-ring analysis on a pantropical study to assess longterm changes in growth of tropical forest trees. Tree-ring analysis was used to measure long-term growth rates of ~1350 trees of different species coming from three sites across the tropics. Trends in growth over the last two centuries were then analysed using an established an a new trend-detection method. Additionally, we applied the long-term growth data from rings to improve the evaluation of forest management practices in Cameroon. All samples were collected and measured within the TROFOCLIM project led by Pieter Zuidema. The project also includes two other PhD theses and sample collection was divided among the three PhD projects and the three sites: in Bolivia (samples collected by Peter van der Sleen), Cameroon (by me) and in Thailand (by Mart Vlam). The main objectives of this thesis were: (1) to assess the potential for using treerings in a wet tropical forest in Central Africa; (2) to project timber yields in the next logging round for four Cameroonian tree species; (3) to evaluate the sensitivity and accuracy of four commonly used methods to detect long-term trends in tree-ring data; and (4) to detect whether growth rates of tropical forest trees have changed over the past ~150 years.

    In Chapter 2 of this dissertation, we evaluated whether growth rings are formed annually in the wood of tree species growing under very high levels of precipitation (>4000 mm) in an African tropical forest. For this purpose, we assessed whether ring structures are formed in the wood of the 22 commercially exploited tree species and found that ring structures are indeed formed by more than half of these species (in 14 species), though with varying ring clarity. On four species we proved the annual character of ring formation using radiocarbon bomb-peak dating. That rings are formed under such high levels of precipitation is surprising, as these conditions are considered improper to induce ring formation. These results suggest that the potential of tree-rings analysis is more or less similar across the tropics. Based on our results and that of other studies, we estimate that tree rings can be used to measure tree growth and ages for around a quarter to a third of tropical tree species.

    Worldwide, over 400 million hectares of tropical forests are set aside for timber production. Attaining sustainable use of these forests is very important, in the light of the important role of tropical forests in retaining biodiversity and storing carbon. Ensuring that timber species are not overexploited is key to ensure that forest use is sustainable and entails finding a balance between economic gains and the (ecological) sustainability of logging operations. In Chapter 3, we integrated growth data from tree-rings with logging inventory data to forecast whether timber yields can be sustained in the next harvest round for four timber species in Cameroon. Under current logging practices, future logging yields were predicted to reduce moderately to strongly for all species. These yield reductions are worrisome for forest conservation, as loss of economic value may lead to conversion of forests to other land uses. We recommend that such calculations are needed for more species and argue that these simulations should include the effects of logging and eventual silvicultural measures on the growth and survival of trees.

    Lifetime tree growth data – as acquired by tree-ring analysis – contains longterm trends in growth that reflect the ontogenetic development of an individual or species, i.e., these data contains an age/size signal in growth. In Chapter 4 we evaluate the sensitivity, accuracy and reliability to detect long-term trends in growth of four methods that are commonly used to disentangle these age/size trends from long-term growth trends. We applied these growth-trend detection methods to measured growth data from tree rings and to simulated growth trajectories on which increasing an decreasing trends were imposed. The results revealed that the choice of method influences results of growth-trend studies. We recommend applying two methods simultaneously when analysing long-term trends – the Regional Curve Standardization and Size Class Isolation – as these methods are complementary and showed the highest reliability to detecting long-term growth changes.

    In Chapter 5, we analysed long-term growth trends in tropical forest trees using a pantropical approach applying the two recommended growth-trend detection methods. We showed that growth rates for most of the 13 tropical tree species, from the three sites across the tropics, decreased over the last centuries. These species-level changes may have important demographic consequences and may eventually lead to shifts in the species composition of tropical forests. We found no strong growth changes when analysing trends aggregated per site or across sites: only weak growth reductions were detected for the Thai site and across sites. These findings contrast growth increases that would be expected if tree growth is stimulated by increased ambient CO2. These growth reductions suggest worsening growth conditions for several tropical tree species, and could result from the negative effect of temperature increases on tree growth, or reflect the effect of large-scale disturbances on these forests.

    If one image becomes clear from this thesis it is that long-term data are crucial to enhance the management of tropical forests and to quantify changes happening in these forests. Tree-ring analysis provides this long-term perspective for tree growth and is thus a great tool to evaluate changes in the growth of trees, including for tropical species. One of the most important finding of this thesis is that many tropical species show long-term decreases in growth. These results suggest that the commonly assumed growth increases tropical forests, based on measurements over the last couple of decades, may be incorrect. This discrepancy in results could have strong consequences, among others leading to erroneous predictions of the carbon dynamics of tropical forests under future climate change. Combining monitoring plot data (to analyse short-term changes in growth and species composition) with remotely sensed data (to accurately determine forest land cover) and with the long-term growth data from tree rings is probably the best way forward to relate recent findings of short-term changes in tree growth and forest biomass to changes over the past centuries. Such integrative approaches are needed to better quantify and understand the effects of climate change on tropical forests.

    Dood hout en insecten
    Moraal, L.G. - \ 2015
    Vakblad Natuur Bos Landschap 111 (2015). - ISSN 1572-7610 - p. 20 - 22.
    bosecologie - dood hout - natuurwaarde - fauna - inventarisaties - forest ecology - dead wood - natural value - inventories
    Dood hout is een belangrijke drager van natuurwaarden in het bos. Dat inzicht wordt in het bosbeheer breed gedeeld. Toch is het in tijden van een naar hout hongerende economie met een groeiende behoefte aan biomassa uit bos, goed om dit uitgangspunt nog eens nader te belichten. Dit artikel is gebaseerd op een eerder artikel uit Entomologische Berichten (2014), p. 28-41
    Het Nederlandse bos in cijfers : resultaten van de 6e Nederlandse Bosinventarisatie
    Schelhaas, M. ; Clerkx, A.P.P.M. - \ 2015
    Vakblad Natuur Bos Landschap 12 (2015)111. - ISSN 1572-7610 - p. 23 - 27.
    bosecologie - bossen - bosbeheer - inventarisaties - nederland - forest ecology - forests - forest administration - inventories - netherlands
    In 2012 is begonnen met de metingen van de 6e Nederlandse Bosinventarisatie. Twee jaar later en 85.000 bomen verder zit het werk erop en is het tijd om te kijken wat al dat meten opgeleverd heeft.
    Beïnvloeden zwijnen de overlevingskans van rode bosmieren?
    Mabelis, A.A. - \ 2014
    De Levende Natuur 115 (2014)5. - ISSN 0024-1520 - p. 212 - 214.
    fauna - bosecologie - formicidae - habitats - nadelige gevolgen - sus scrofa - natuurgebieden - fauna - forest ecology - formicidae - habitats - adverse effects - sus scrofa - natural areas
    Rode bosmieren zijn ondergebracht in de categorie "bijna begreifd (IUCN list of threatened anmilams, 1996). Bosmiervolken zijn kwetsbaar, omdat hun nesten nogal eens worden vernield en de mieren lang niet altijd in staat zijn de schade te herstellen. In verscheidene Europese landen worden maatregelen getroffen om bosmiernesten tegen wilde zwijnen te beschermen. In Nederland is dit niet gebruikelijk. Monitoring is noodzakelijk om te weten of dit noodzakelijk is.
    Het mooiste landgoed van Noord-Brabant; Verslag van de excursie op Landgoed Baest
    Laar, J.N. van; Sande, G. van de - \ 2014
    Vakblad Natuur Bos Landschap 11 (2014)10. - ISSN 1572-7610 - p. 24 - 25.
    landgoederen - bosecologie - historische ecologie - noord-brabant - estates - forest ecology - historical ecology
    Op 2 oktober 2014 vond de najaarsexcursie van de Commissie Bosgeschiedenis plaats op Landgoed Baest. Het thema betrof het maken van keuzes in het beheer van groene cultuurhistorische elementen in het bos. Ruim 25 personen waren op deze bijeenkomst afgekomen.
    Paddenstoelen: diversiteit verhogend beheer. infoblad veldwerkplaats
    Terhürne, R.L. ; Ozinga, W.A. ; Keizer, P.J. - \ 2014
    Vereniging van Bos- en Natuurterreineigenaren
    vegetatiebeheer - paddestoelen - bosecologie - habitats - natuurbeheer - veldwerk - vegetation management - mushrooms - forest ecology - nature management - field work
    Paddenstoelen zijn een groot deel van het jaar onzichtbaar, maar ze spelen in vele ecosystemen een belangrijke rol. Schimmels behoren tot de ecologisch functionele groep van de reducenten, d.w.z. ze verzorgen de afbraak van organisch materiaal dat door groene planten is opgebouwd. Doordat paddenstoelen andere eisen aan hun standplaats stellen dan planten, profiteren ze niet automatisch van beheer gericht op planten. Wat zijn de mogelijkheden om met het beheer meer op het behoud en herstel van de diversiteit aan paddenstoelen in te spelen?
    Zesde Nederlandse bosinventarisatie, 2012-2013
    Schelhaas, M. ; Clerkx, A.P.P.M. - \ 2014
    Wageningen : Alterra
    bosecologie - bossen - bosbeheer - inventarisaties - nederland - forest ecology - forests - forest administration - inventories - netherlands
    Brochure met enkele cijfers uit de zesde bosinventarisatie.
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