What determines plant species diversity in Central Africa?
Proosdij, Andreas S.J. van - \ 2017
Wageningen University. Promotor(en): M.S.M. Sosef, co-promotor(en): N. Raes; J.J. Wieringa. - Wageningen : Wageningen University - ISBN 9789463436618 - 161
plants - biodiversity - species diversity - species - distribution - biogeography - central africa - biosystematics - tropical rain forests - modeling - planten - biodiversiteit - soortendiversiteit - soorten - distributie - biogeografie - centraal-afrika - biosystematiek - tropische regenbossen - modelleren
Planet Earth hosts an incredible biological diversity. Estimated numbers of species occurring on Earth range from 5 to 11 million eukaryotic species including 400,000-450,000 species of plants. Much of this biodiversity remains poorly known and many species have not yet been named or even been discovered. This is not surprising, as the majority of species is known to be rare and ecosystems are generally dominated by a limited number of common species.
Tropical rainforests are the most species-rich terrestrial ecosystems on Earth. The general higher level of species richness is often explained by higher levels of energy near the Equator (latitudinal diversity gradient). However, when comparing tropical rainforest biomes, African rainforests host fewer plant species than either South American or Asian ones. The Central African country of Gabon is situated in the Lower Guinean phytochorical region. It is largely covered by what is considered to be the most species-rich lowland rainforest in Africa while the government supports an active conservation program. As such, Gabon is a perfect study area to address that enigmatic question that has triggered many researchers before: “What determines botanical species richness?”.
In the past 2.5 million years, tropical rainforests have experienced 21 cycles of global glaciations. They responded to this by contracting during drier and cooler glacials into larger montane and smaller riverine forest refugia and expanding again during warmer and wetter interglacials. The current rapid global climate change coupled with change of land use poses new threats to the survival of many rainforest species. The limited availability of resources for conservation forces governments and NGOs to set priorities. Unfortunately, for many plant species, lack of data on their distribution hampers well-informed decision making in conservation.
Species distribution models (SDMs) offer opportunities to bridge at least partly this knowledge gap. SDMs are correlative models that infer the spatial distribution of species using only a limited set of known species occurrence records coupled with high resolution environmental data. SDMs are widely applied to study the past, present and future distribution of species, assess the risk of invasive species, infer patterns of species richness and identify hotspots, as well as to assess the impact of climate change. The currently available methods form a pipeline, with which data are selected and cleaned, models selected, parameterized, evaluated and projected to other areas and climatic scenarios, and biodiversity patterns are computed from these SDMs. In this thesis, SDMs of all Gabonese plant species were generated and patterns of species richness and of weighted endemism were computed (chapter 4 & 5).
Although this pipeline enables the rapid generation of SDMs and inferring of biodiversity patterns, its effective use is limited by several matters of which three are specifically addressed in this thesis. Not knowing the true distribution limits the opportunities to assess the accuracy of models and assess the impact of assumptions and limitations of SDMs. The use of simulated species has been advocated as a method to systematically assess the impact of specific matters of SDMs (virtual ecologist). Following this approach, in chapter 2, I present a novel method to simulate large numbers of species that each have their own unique niche.
One matter of SDMs that is usually ignored but has been shown to be of great impact on model accuracy is the number of species occurrence records used to train a model. In chapter 2, I quantify the effect of sample size on model accuracy for species of different range size classes. The results show that the minimum number of records required to generate accurate SDMs is not uniform for species of every range size class and that larger sample sizes are required for more widespread species. By applying a uniform minimum number of records, SDMs of narrow-ranged species are incorrectly rejected and SDMs of widespread species are incorrectly accepted. Instead, I recommend to identify and apply the unique minimum numbers of required records for each individual species. The method presented here to identify the minimum number of records for species of particular range size classes is applicable to any species group and study area.
The range size or prevalence is an important plant feature that is used in IUCN Red List classifications. It is commonly computed as the Extent Of Occurrence (EOO) and Area Of Occupancy (AOO). Currently, these metrics are computed using methods based on the spatial distribution of the known species occurrences. In chapter 3, using simulated species again, I show that methods based on the distribution of species occurrences in environmental parameter space clearly outperform those based on spatial data. In this chapter, I present a novel method that estimates the range size of a species as the fraction of raster cells within the minimum convex hull of the species occurrences, when all cells from the study area are plotted in environmental parameter space. This novel method outperforms all ten other assessed methods. Therefore, the current use of EOO and AOO based on spatial data alone for the purpose of IUCN Red List classification should be reconsidered. I recommend to use the novel method presented here to estimate the AOO and to estimate the EOO from the predicted distribution based on a thresholded SDM.
In chapter 4, I apply the currently best possible methods to generate accurate SDMs and estimate the range size of species to the large dataset of Gabonese plant species records. All significant SDMs are used here to assess the unique contribution of narrow-ranged, widespread, and randomly selected species to patterns of species richness and weighted endemism. When range sizes of species are defined based on their full range in tropical Africa, random subsets of species best represent the pattern of species richness, followed by narrow-ranged species. Narrow-ranged species best represent the weighted endemism pattern. Moreover, the results show that the applied criterion of widespread and narrow-ranged is crucial. Too often, range sizes of species are computed on their distribution within a study area defined by political borders. I recommend to use the full range size of species instead. Secondly, the use of widespread species, of which often more data are available, as an indicator of diversity patterns should be reconsidered.
The effect of global climate change on the distribution patterns of Gabonese plant species is assed in chapter 5 using SDMs projected to the year 2085 for two climate change scenarios assuming either full or no dispersal. In Gabon, predicted loss of plant species ranges from 5% assuming full dispersal to 10% assuming no dispersal. However, these numbers are likely to be substantially higher, as for many rare, narrow-ranged species no significant SDMs could be generated. Predicted species turnover is as high as 75% and species-rich areas are predicted to loose many species. The explanatory power of individual future climate anomalies to predicted future species richness patterns is quantified. Species loss is best explained by increased precipitation in the dry season. Species gain and species turnover are correlated with a shift from extreme to average values of annual temperature range.
In the final chapter, the results are placed in a wider scientific context. First, the results on the methodological aspects of SDMs and their implications of the SDM pipeline are discussed. The method presented in this thesis to simulate large numbers of species offers opportunities to systematically investigate other matters of the pipeline, some of which are discussed here. Secondly, the factors that shape the current and predicted future patterns of plant species richness in Gabon are discussed including the location of centres of species richness and of weighted endemism in relation to the hypothesized location of glacial forest refugia. Factors that may contribute to the lower species richness of African rainforests compared with South American and Asian forests are discussed. I conclude by reflecting on the conservation of the Gabonese rainforest and its plant species as well as on the opportunities SDMs offer for this in the wider socio-economic context of a changing world with growing demand for food and other ecosystem services.
Prof. Lourens Poorter over het doorgronden van het regenwoud
Poorter, L. - \ 2014
tropische regenbossen - duurzaamheid (durability) - duurzaamheidsindicatoren - klimaatverandering - biodiversiteit - bodemtypen (ecologisch) - ecologie - tropical rain forests - durability - sustainability indicators - climatic change - biodiversity - soil types (ecological) - ecology
Tropisch regenwoud is te complex om de dynamiek tussen alle afzonderlijke soorten te bepalen. Maar wel kun je aan de hand van planteigenschappen collectieve functies vaststellen, bijvoorbeeld met betrekking tot zonlicht, water en nutriënten. Daarmee ondersteunt het onderzoek van Lourens Poorter duurzaam bosgebruik en realistische klimaatmodellen.
Functional classification of spatially heterogeneous environments: the Land Cover Mosaic approach in remote sensing
Obbink, M.H. - \ 2011
Wageningen University. Promotor(en): M. Molenaar, co-promotor(en): Jan Clevers. - [S.l.] : S.n. - ISBN 9789085859956 - 304
remote sensing - heterogeniteit - tropische regenbossen - ruimtelijke variatie - classificatie - landschapsecologie - besluitvorming - remote sensing - heterogeneity - tropical rain forests - spatial variation - classification - landscape ecology - decision making
Tropical rainforest areas are difficult to classify in the digital analysis of remote sensing data because of spatial heterogeneity. Often many technical solutions are adopted to reduce the ‘problem’ of spatial heterogeneity. This thesis describes theory and methods that now use this heterogeneity during the digital image classification. With spatial heterogeneity, spatial aggregation levels such as patches,patch-mosaics and landscapes can be distinguished. Consequently, vegetation patterns can be related to functional management units at different decision-levels. The developed theory and methods thus save two birds with one stone: (a) the classification is completely digitally, and (b) the classification provides information on deforestation that meets the needs of decision-makers. This thesis further recommends approaching all land cover classifications from a heterogeneous perspective for understanding and controlling environmental processes on a global level. This can enhance a sustainable development of tropical rainforest areas for the benefit of future generations.
Impact of severe dry season on net ecosystem exchange in the Neotropical rainforest of French Guiana
Bonal, D. ; Bosc, A. ; Ponton, S. ; Goret, J. ; Burban, B. ; Gross, P. ; Bonnefonds, J.M. ; Elbers, J.A. ; Longdoz, B. ; Epron, D. ; Guehl, J. ; Granier, A. - \ 2008
Global Change Biology 14 (2008)8. - ISSN 1354-1013 - p. 1917 - 1933.
ecosystemen - droog seizoen - tropische regenbossen - eddy-covariantie - netto ecosysteem koolstofbalans - atmosferische grenslaag - droogte - frans-guyana - ecosystems - dry season - tropical rain forests - eddy covariance - net ecosystem carbon balance - atmospheric boundary-layer - drought - french guiana - transitional tropical forest - carbon-dioxide uptake - soil co2 efflux - european forests - amazonian ecosystems - respiration - climate - fluxes
The lack of information on the ways seasonal drought modifies the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to precisely predict how these ecosystems will respond as global environmental changes force them to face increasingly contrasting conditions in the future. To address this issue, seasonal variations in daily net ecosystem productivity (NEPd) and two main components of this productivity, daily total ecosystem respiration (REd) and daily gross ecosystem productivity (GEPd), were estimated over 2 years at a flux tower site in French Guiana, South America (5 °16'54"N, 52 °54'44"W). We compared seasonal variations between wet and dry periods and between dry periods of contrasting levels of intensity (i.e. mild vs. severe) during equivalent 93-day periods. During the wet periods, the ecosystem was almost in balance with the atmosphere (storage of 9.0 g C m¿2). Seasonal dry periods, regardless of their severity, are associated with higher incident radiation and lower REd combined with reduced soil respiration associated with low soil water availability. During the mild dry period, as is normally the case in this region, the amount of carbon stored in the ecosystem was 32.7 g C m¿2. Severe drought conditions resulted in even lower REd, whereas the photosynthetic activity was only moderately reduced and no change in canopy structure was observed. Thus, the severe dry period was characterized by greater carbon storage (64.6 g C m¿2), emphasizing that environmental conditions, such as during a severe drought, modify the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and potentially the resulting carbon balance
Spaceborne radar monitoring of forest fires and forest cover change : a case study in Kalimantan
Sugardiman, R.A. - \ 2007
Wageningen University. Promotor(en): Reinder Feddes, co-promotor(en): Dirk Hoekman. - [S.l.] : S.n. - ISBN 9789085046042 - 190
tropische regenbossen - regenbossen - bosbranden - kroondak - remote sensing - radar - monitoring - digitaal terreinmodel - kalimantan - tropical rain forests - rain forests - forest fires - canopy - remote sensing - radar - monitoring - digital elevation model - kalimantan
The devastation of tropical rain forests has been proven to have a significant effect on global climate change. The sustainability of these forests becomes a major concern for the international community. The Indonesian Ministry of Forestry (MOF) is eager to carry on forest inventory activities and to generate forest resources information.Advanced spaceborne radar techniques are a very promising tool to monitor forests. This technique is complementary with the existing spaceborne optical imagery which suffers too much from cloud cover. Radar provide reliable information on a regular basis and has been applied in various types of applications e.g. forest classification.The approach presented in this thesis includes. Firstly, multi-temporal classification of spaceborne Synthetic Aperture Radar (SAR) data using Iterated Conditional Modes which is proposed as a fast step of Maximum Likelihood classification in order to circumvent the slow image segmentation step. Secondly, slope correction dealing with steep slopes that considerable has geometric distortion. Thirdly, textural analysis has been applied to derive additional information layers in multi-temporal classification from fine structures in the radar images.The study focuses on three test site areas i.e. Sungai Wain test site area, the Gunung Meratustest site area and the NASA AirSAR PacRim-II test site area.This area experienced long drought periods associated with the El Niño Southern Oscillation (ENSO)phenomenon. For this study the severe ENSO event of 1997 - 1998 is of particular interest.
|Land Use, Nature Conservation and the Stability of Rainforest Margins in Southeast Asia
Gerold, G. ; Fremery, M. ; Guhardja, E. ; Claassen, N. ; Priess, J. ; Rheenen, T. van; Waltert, M. ; Zeller, M. - \ 2004
Berlin : Springer Science + Business Media (Environmental science ) - ISBN 9783540006039 - 534
tropische regenbossen - landgebruik - natuurbescherming - ontbossing - bosbestanden - bosbedrijfsvoering - biodiversiteit - zuidoost-azië - tropical rain forests - land use - nature conservation - deforestation - forest resources - forest management - biodiversity - south east asia
This book contains a selection of contributions presented at an international symposium on "Land Use, Nature Conservation and the Stability of Rainforest Margins in Southeast Asia," in Bogor, Indonesia, October 2002. It highlights the critical issue of rainforest preservation from an interdisciplinary perspective, comprising input from scientists in socio-economic, biological, geographical, agrarian and forestry disciplines.
Plant diversity in a central African rain forest, implications for biodiversity conservation in Cameroon
Tchouto, M.G.P. - \ 2004
Wageningen University. Promotor(en): Jos van der Maesen; A.M. Cleef, co-promotor(en): Fred de Boer. - Wageningen : S.n. - ISBN 9789051130683 - 210
vegetatie - biodiversiteit - soortendiversiteit - tropische regenbossen - natuurbescherming - bosecologie - kameroen - centraal-afrika - vegetation - biodiversity - species diversity - tropical rain forests - nature conservation - forest ecology - cameroon - central africa
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.
The importance of seed mass for early regeneration in tropical forest: a review
Rose, S.A. ; Poorter, L. - \ 2003
In: Long-term changes in tropical tree diversity: Studies from the Guiana Shield, Africa, Borneo and Melanesia / ter Steege, H., Wageningen : Tropenbos - p. 19 - 35.
tropische regenbossen - regeneratievermogen - schaduw - zaden - bosecologie - tropical rain forests - regenerative ability - shade - seeds - forest ecology
Seed mass is an important component of the shade tolerance of rain forest tree species. Using a metaanalysis this article evaluates till what extent seed mass affects the survival, initial size, and growth of seedlings in light environments that are typical of forest gaps and understory
Scatterhoarding and tree regeneration : ecology of nut dispersal in a Neotropical rainforest
Jansen, P.A. - \ 2003
Wageningen University. Promotor(en): Frans Bongers; Herbert Prins, co-promotor(en): Sip van Wieren. - [S.I.] : s.n. - ISBN 9789058087775
zaadverspreiding - noten - carapa procera - knaagdieren - natuurlijke verjonging - zaadpredatie - zaadgrootte - natuurlijke selectie - tropische regenbossen - seed dispersal - nuts - carapa procera - rodents - natural regeneration - seed predation - seed size - natural selection - tropical rain forests - cum laude
cum laude graduation (with distinction)
ENVISAT forest monitoring Indonesia
Hoekman, D.H. ; Vissers, M.A.M. ; Sugardiman, R.A. ; Vargas, J. - \ 2002
The RADARSAT International (RSI) RADARSAT-2 e-Newsletter 2 (2002)7. - p. 68 - 68.
remote sensing - radar - tropische regenbossen - geografische informatiesystemen - landclassificatie - vegetatie - bosbranden - monitoring - kalimantan - indonesië - remote sensing - radar - tropical rain forests - geographical information systems - land classification - vegetation - forest fires - monitoring - kalimantan - indonesia
To support the introduction of operational radar forest monitoring systems in Indonesian a demonstration is executed at the Tropenbos study area in East-Kalimantan. Interest focuses on fulfilling information needs relating to land cover change, fire risk and fire damage monitoring, with main emphasis on early detection.
Progress on forest certification in Malaysia
Diemont, W.H. ; Siepel, H. - \ 2001
Wageningen : Alterra (Alterra-rapport 331) - 38
hout - certificering - maleisië - tropische regenbossen - bossen - wood - certification - malaysia - tropical rain forests - forests
|Nouragues Dynamics and Plant-Animal Interactions in a Neotropical Rainforest
Bongers, F. ; Charles-Dominique, P. ; Forget, P.M. ; Théry, M. - \ 2001
Dordrecht [etc.] : Kluwer Academic Publishers - ISBN 9781402001239 - 421
tropische regenbossen - vegetatie - onderzoeksinstituten - frans-guyana - ecologie - tropen - dieren - planten - interacties - flora - fauna - tropical rain forests - vegetation - research institutes - french guiana - ecology - tropics - animals - plants - interactions
Observation of Tropical Rain Forest Trees by Airborne High-Resolution Interferometric Radar
Hoekman, D.H. ; Varekamp, C. - \ 2001
IEEE Transactions on Geoscience and Remote Sensing 39 (2001)3. - ISSN 0196-2892 - p. 584 - 594.
tropische regenbossen - remote sensing - radar - tropical rain forests - remote sensing - radar
The Indonesian Radar Experiment (INDREX) Campaign was executed in Indonesia to study the potential of high-resolution interferometric airborne radar in support of sustainable tropical forest management. Severe cloud cover limits the use of aerial photography, which is currently applied on a routine basis to extract information at the tree level. Interferometric radar images may be a viable alternative once radar imaging at the tree level is sufficiently understood. It is shown that interferometric height images can contain large height and displacement errors for individual trees but that this problem can be solved to a large extent using models for the vertical distribution of backscatter intensity and an extension of the Van Cittert-Zernike theorem. The predicted loss of coherence in lay-over regions of emergent trees is shown to be in good agreement with the loss of coherence as observed in the high resolution radar data (Pierson correlation coefficient=0.94). Several correction methods for height and displacement errors are proposed. It is shown that a simple approach already gives a good correction. Semi-empirical correction models, which can be calibrated for forest structure, perform even better
|DGIS-WWF tropical forest portfolio 1996-2001 : midterm evaluation - interregional component
Hillegers, P.J.M. ; Conradi, M.K. - \ 2000
Wageningen : Alterra - 99
tropische regenbossen - conservering - bosbedrijfsvoering - duurzaamheid (sustainability) - plattelandsgemeenschappen - participatie - bosbeleid - hulpbronnenbeheer - opleiding - biodiversiteit - ecologie - natuurbehoud - regenwoud - tropen - Afrika - Azië - Amerika - Ethiopië - Gabon - Filipijnen - Pakistan - Ecuador - Honduras - tropical rain forests - conservation - forest management - sustainability - rural communities - participation - forest policy - resource management - training - Gabon - Pakistan - Ecuador - Honduras
|Biophysical suitability classification of forest land in the Bipindi - Akom II - Lolodorf region, South Cameroon
Hazeu, G.W. ; Gemerden, B.S. van; Hommel, P.W.F.M. ; Kekem, A.J. van - \ 2000
Wageningen : Alterra (Tropenbos-Cameroon Doc 4) - 130
landschapsecologie - tropische regenbossen - landevaluatie - landgebruik - natuurbescherming - bosbouw - landbouw - kameroen - bosproducten anders dan hout - landscape ecology - tropical rain forests - land evaluation - land use - nature conservation - forestry - agriculture - cameroon - non-wood forest products
|The social dimension of rainforest management in Cameroon : Issues for co-management
Berg, J. van den; Biesbrouck, K. - \ 2000
Kribi : The Tropenbos-Cameroon Programme - ISBN 9789051130430 - 99
bosbedrijfsvoering - bosbouw - tropische regenbossen - bedrijfsvoering - regenbossen - gemeenschappen - bosbestanden - bosproducten - wetgeving - participatie - plaatselijke bevolking - kameroen - forest management - forestry - tropical rain forests - management - rain forests - communities - forest resources - forest products - legislation - participation - local population - cameroon
Leaf function in tropical rain forest canopy trees : the effect of light on leaf morphology and physiology in different-sized trees
Rijkers, T. - \ 2000
Agricultural University. Promotor(en): G.M.J. Mohren; F. Bongers; T.L. Pons. - S.l. : S.n. - ISBN 9789058083142 - 116
goupia glabra - pourouma - dicorynia guianensis - duguetia - tropische regenbossen - fotosynthese - bladleeftijd - bladeren - plantenmorfologie - bomen - planthoogte - licht - lichtregiem - schaduw - tolerantie - frans-guyana - goupia glabra - pourouma - dicorynia guianensis - duguetia - tropical rain forests - photosynthesis - leaf age - leaves - plant morphology - trees - plant height - light - light regime - shade - tolerance - french guiana
In this thesis the effect of constant and fluctuating light availability on several leaf traits was studied for naturally growing trees of different sizes, i.e . from sapling to adult canopy tree, of five species in a tropical rain forest in French Guiana. Leaf acclimation responses were examined throughout the life time of leaves in order to evaluate whether leaves can profit from these adjustments in terms of carbon gain. The five species, arranged in order from most shade-tolerant to pioneer, were: Duguetia surinamensis , Vouacapoua americana , Dicorynia guianensis , Pourouma bicolor spp. digitata , and Goupia glabra .
For Duguetia , Vouacapoua , Dicorynia and Goupia , it was shown that tree height and light availability had independent effects on photosynthesis and other features of leaf function. Direction and magnitude of the variation in leaf variables tended to be similar among species. The morphological variable leaf mass per unit area seemed to be a key variable as it determined most of the variation in other leaf variables.
The time needed to increase the photosynthetic rate (up to 90% of its capacity) to a sudden increase in light was between 7 to 11 min for shade and sun growing saplings of Vouacapoua , Dicorynia and Pourouma . The readiness to exploit the next lightfleck was substantial in these plants as the induction loss was moderate to low, except in gap saplings of Dicorynia . The time needed to reach 75% of the maximum carboxylation efficiency (V cmax ) was used to separate the relative importance of biochemical and stomatal limitation during the time course of photosynthetic induction.
The mean leaf life span of different-sized trees for Vouacapoua was 61 months (range 27-101) and for Dicorynia 32 months (range 17-54). The variation in traits in response to leaf age was low. Photosynthetic capacity and nitrogen concentration were relatively constant with time; leaf mass per unit area increased during the first 18 months. Simulations of the daily carbon gain with a low- and highlight regime showed differences among both sun- and shade-leaves and trees of different sizes. Leaf construction cost was independent of leaf life span. Leaf payback time was relatively short (4 to 40 days); it was constant during a wide range of irradiance, but increased sharply in a narrow range of low light. The rate of net return on carbon investment was slow in long-lived leaves of Vouacapoua . Leaf mass per area decreased with increased leaf life span, which could be explained by a light- and height-dependent selection pressure for leaf life span and leaf mass per area.
The integration of the results with those at higher organisation levels, such as branch and tree crown, is briefly discussed, and the applicability in silvicultural systems in which light is manipulated to enhance growth and production of timber species is evaluated.
Key-words: tropical rain forest, leaf morphology, photosynthesis, leaf age, tree height, shade tolerance, leaf construction costs, leaf payback time, ecophysiology.
TROPFOMS, a decision support model for sustainabele management of south Cameroon's rainforests
Eba'a Atyi, R. - \ 2000
Agricultural University. Promotor(en): A. van Maaren; W.B.J. Jonkers. - S.l. : S.n. - ISBN 9789058081940 - 203
tropische regenbossen - oerbossen - bosbedrijfsvoering - duurzaamheid (sustainability) - bosbestanden - houtkap - conservering - kameroen - beslissingsondersteunende systemen - tropical rain forests - virgin forests - forest management - sustainability - forest resources - logging - conservation - cameroon - decision support systems
Natural forests play an important role in the economy of Cameroon, at both the national and local levels. Unfortunately, there is still a general sense that in Cameroon, like in most tropical countries, forests are not managed in a sustainable way. The poor forest management practices, which still prevail in Cameroon, result from both an inadequate institutional context and insufficient scientific and technical knowledge. For the last few decades important research efforts have been made in tropical forestry. However, these efforts concentrate mostly on developing silvicultural systems and more and more on predicting growth and yield of forest stands. Research on supporting decision-making for forest has been negligible in tropical forestry. The research presented here confronts the problem of how to assist decision-making in tropical forest management using the best available scientific information gathered in different disciplines. The specific objectives of the research were:
A methodological tool was developed to support decision making with respect to tropical forest management. The system was given the acronym of TROPFOMS (TROPical Forest Management support System). The management items to which TROPFOMS provides support for decision making include:
The target steady state growing stock characteristics, mainly the structure in terms of number of trees per size class to be found both before and after harvest and the species composition of the stand
TROPFOMS consists of four modules including a mathematical programming module, a growth and yield module, and economic module and a constraint definition module. TROPFOMS was developed using mostly quantitative techniques and methods such as transition matrices, cluster analysis, logistic regression analysis, mathematical programming and stumpage prices derivation. The outcomes show that the optimal cutting cycle is about 30 years, for a harvest of 13.4 m 3/ha for the species currently commercialized in south Cameroon. In addition it would require about 120 year to convert the current forest of the Tropenbos Cameroon research site to a regulated forest. TROPFOMS has shown a great deal of sensitivity to hypotheses concerning growth and yield and timber value. Research needs for the improvement of the outcomes of TROPFOMS include: Costs and returns of silvicultural operations, relationships between growth and yield and density of forest stands, reproductive maturity of different tree species, logging efficiency, costs and damage, the utilization of the forest by local population, royalties.
Diversity and dynamics of mycorrhizal associations in tropical rain forests with different disturbance regimes in South Cameroon
Onguene, N.A. - \ 2000
Agricultural University. Promotor(en): L. Brussaard; T.W. Kuyper. - S.l. : S.n. - ISBN 9789058082930 - 167
mycorrhizae - mycorrhizaschimmels - ectomycorrhiza - vesiculair-arbusculaire mycorrhizae - symbiose - bosecologie - regenbossen - tropische regenbossen - bosbedrijfsvoering - bosschade - entstofdichtheid - kameroen - mycorrhizas - mycorrhizal fungi - ectomycorrhizas - vesicular arbuscular mycorrhizas - symbiosis - forest ecology - rain forests - tropical rain forests - forest management - forest damage - inoculum density - cameroon
The present study documents the occurrence of mycorrhizal associations in the rain forests of south Cameroon. All species investigated are mycorrhizal. Most timber species form arbuscular mycorrhiza, but some timber species, which usually occur in clumps, form ectomycorrhiza. Species diversity of ectomycorrhizal fungi in the undisturbed rain forest is substantial, with more than 125 species having been recorded. Inoculum potential of arbuscular mycorrhizal and ectomycorrhizal fungi is high in the undisturbed rain forest. The shifting cultivation cycle increases inoculum potential of arbuscular mycorrhizal fungi, but lowers inoculum potential of ectomycorrhizal fungi to various extent.
On sites of forestry practices (skid trails, landings) inoculum potential of arbuscular mycorrhizal and ectomycorrhizal fungi is very substantially reduced and recovery rates are low. Mycorrhizal colonisation and seedling growth are positively correlated with mycorrhiza inoculum potential. Inoculum potential of arbuscular mycorrhizal fungi and performance of seedlings of arbuscular mycorrhizal trees can be boosted after inoculum addition. Both inoculum quantity and inoculum quality are important criteria for inoculation practices. Ectomycorrhizal inoculum potential cannot be increased through inoculum addition and management of the intact ectomycorrhizal network is necessary for maintenance of the ectomycorrhizal tree species.
Key words : Arbuscular mycorrhiza, ectomycorrhiza, disturbance, rain forest, diversity, inoculum potential, Cameroon, forestry practices