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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    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 - fauna - 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.
    Coniferous needle-leaves, shots and canopies : a remote sensing approach
    Yanez Rausell, L. - \ 2014
    Wageningen University. Promotor(en): Michael Schaepman, co-promotor(en): Z. Malenovsky; Jan Clevers. - Wageningen : Wageningen University - ISBN 9789461738684 - 154
    remote sensing - naaldbossen - pinopsida - naalden, coniferen - bladeren - optische eigenschappen - modellen - remote sensing - coniferous forests - pinopsida - conifer needles - leaves - optical properties - models

    Coniferous forests are important in the regulation of the Earth’s climate and thus continuous monitoring of these ecosystems is crucial to better understand potential responses to climate change. Optical remote sensing (RS) provides powerful methods for the estimation of essential climate variables and for global forest monitoring. However, coniferous forests represent challenging targets for RS methods, mainly due to structural features specific for coniferous trees (e.g. narrow needle leaves, shoot clumping) whose effects on the RS signal are not yet known or not yet fully understood.

    Recognizing the need for a better adaptation of RS methods to such spatially heterogeneous and structurally complex canopies, this thesis contributes to improving the interpretation of the remotely sensed optical signal reflected from coniferous stands by focusing on specific knowledge gaps identified in the RS methods at different scales of the coniferous canopies. In addition, it explores the application of approaches that simplify the way the structural complexity of such an environment is tackled when using canopy-level radiative transfer approaches. Three main levels based on the identified gaps were defined for the analysis: (needle) leaf level (chapter 2 and 3); shoot level (chapter 4) and canopy level (chapter 5).

    At leaf levelthis thesis contributes to minimizing the uncertainties and errors related to leaf optical measuring methods adapted for needle leaves. Although optical properties of coniferous leaves are extensively used in RS approaches (i.e. as input or as validation data), there is only a limited number of techniques available for measuring coniferous leaves. The first focus of this thesis was to review the shortcomings and uncertainties of such methods in order to identify application limits and potential improvements (chapter 2). A review showed that a more standardized measuring protocol was needed, for which measurement uncertainties and errors had to be identified, quantified and preferably removed or minimized. Thus, an experimental set-up improving the original method of Mesarch et al. (1999) was presented (chapter 3), which focused on analyzing uncertainties caused by the presence of the sample holder and by the multiple scattering triggered by both the shape of the specific needle cross-section, and the distance between the needles composing a sample. Results showed that both the sample holder and the multiple scattering, triggered specially by the shape of the non-flat cross section of the coniferous needle-leaves, had a non-negligible effect on the optical signal when measured using a standard spectroradiometer coupled to a single-beam integrating sphere and following the method suggested by Mesarch. Thus, approaches designed to measure optical properties of non-flat coniferous needle samples more comprehensively should take into account these effects in their current signal correction algorithms.

    Needle clumping into shoots quickly transforms the optical signal making the description of the canopy radiative transfer a complex task and encouraging the search for simplified yet robust approaches. Thus, subsequent steps in this thesis focus on one such simplified approach, known as the recollision probability theory (“p-theory”), applied at two hierarchical levels, i.e., shoots (Chapter 4) and the whole canopy (Chapter 5).At shoot level, an empirical verification of the relationship between the photon recollision probability and a structural parameter called STAR was investigated. The approach allows upscaling needle albedo to shoot albedo and was previously theoretically tested only (chapter 4). For this analysis empirical optical measurements of Scots pine needles and shoots were used. Results showed that the approach works well for the VIS and SWIR spectral regions. However, it was less accurate for the NIR and also for sparse shoots (STAR <0.15) with an uneven distribution of photon–needle interactions and a larger influence of the twig bark.

    Finally, accurate modelling of the reflectance signal at canopy levelfor coniferous canopies requires realistic representations of the forest stands, which in general implies a large number of input parameters and computationally demanding algorithms. Radiative transfer modelling based on the photon recollision probability offers an alternative for a simplified definition of the forest canopy structure. The performance of such approach for estimation of the leaf chlorophyll content from satellite imaging spectroscopy data acquired by the CHRIS-PROBA sensor was investigated. The approach was compared to a computationally more demanding one based on a detailed 3D structural description of a forest (chapter 5). For this purposes two canopy models, PARAS and DART, representing the first and second approach respectively, were used. Top-of-canopy bidirectional reflectance factors (BRF) were simulated for both models and used to calculate two optical indices, ANCB670–720 and ANMB670–720.Subsequently, the empirical relationships established between the optical indices and the needle-leaf chlorophyll content (Cab) were applied to the CHRIS-PROBA image of a Norway spruce forest stand to retrieve a map of Cab estimates. Results showed that for the spatial resolution of CHRIS-PROBA (17 m), the simpler model PARAS can be applied to retrieve plausible needle-leaf Cab estimates from satellite imaging spectroscopy data with less intensive model parameterization and reduced computational powerthan when using a model like DART. The ANMB670–720 optical indexwas more robust andresulted in a linear relationship between the Cab estimated by both models. This relationship showed, however, a systematic offset that is potentially caused by differences in the implementation of woody elements in each model or by a different parameterization of leaf optical properties. Thus, further investigation on the impact of parameterization differences related to the needle optical properties and the implementation of woody elements in such a model is recommended.

    Imaging spectroscopy for ecological analysis in forest and grassland ecosystems
    Homolova, L. - \ 2014
    Wageningen University. Promotor(en): Michael Schaepman, co-promotor(en): Jan Clevers. - Wageningen : Wageningen University - ISBN 9789461738240 - 177
    remote sensing - naaldbossen - alpenweiden - picea abies - bladoppervlakte - ecofysiologie - ecosysteemdiensten - vegetatie - chlorofyl - cartografie - beeldvormende spectroscopie - remote sensing - coniferous forests - alpine grasslands - picea abies - leaf area - ecophysiology - ecosystem services - vegetation - chlorophyll - mapping - imaging spectroscopy

    Terrestrial vegetation is an important component of the Earth’s biosphere and therefore playing an essential role in climate regulation, carbon sequestration, and it provides large variety of services to humans. For a sustainable management of terrestrial ecosystems it is essential to understand vegetation responses to various pressures, to monitor and to predict the spatial extent and the rate of ecosystem changes. Remote sensing (RS) therefore offers a unique opportunity for spatially continuous, and for some type of RS data, also frequent monitoring of terrestrial ecosystems.

    RS of vegetation is a broad research field, where a lot of progress has been made in the last three decades. However, the complexity of interactions between vegetation and solar radiation, constantly modulated by environmental factors, offers room for deeper investigation. Rather than solving one big research problem, this thesis built a few bridges on a way leading towards better understanding of using airborne imaging spectroscopy for ecological analysis in temperate coniferous forests and subalpine grasslands. The research was divided into a theoretical and an applied part. The theoretical part contributed to a critical evaluation of research achievements and challenges in optical RS of plant traits (Chapter 2). The applied part addressed three research topics: i) investigating variability of total to projected leaf area ratio in spruce canopies and its implications on RS of chlorophyll content (Chapter 3), ii) testing chlorophyll retrieval methods based on continuum removal in spruce canopies (Chapter 4), and iii) exploring potentials of imaging spectroscopy to map ecosystem properties and the capacity of subalpine grasslands in providing ecosystem services in comparison with a plant trait-based modelling approach (Chapter 5).

    In Chapter 2, we reviewed achievements and challenges in RS estimation of key plant traits and we concentrated our discussion on eight traits with the strongest potential to be mapped using RS (plant growth and life forms, flammability properties, photosynthetic pathways and photosynthesis activity, plant height, leaf lifespan and phenology, specific leaf area, leaf nitrogen and phosphorous). The review indicated that imaging spectroscopy facilitates better retrievals of plant traits related to leaf biochemistry, photosynthesis and phenology rather than traits related to vegetations structure. Estimation of the canopy structure related traits (e.g. plant height) can certainly benefit from increasing synergies between imaging spectroscopy and active RS (radar or laser scanning). One of major challenges in RS of plant traits is to effectively suppress the negative influences of water absorption and canopy structure, which would facilitate more accurate retrievals of biochemical and photosynthesis-related traits. Secondly, a successful integration of RS and plant ecology concepts would require careful matching of spatial scales of in-situ trait data with RS observations.

    In Chapter 3, measurement methods and variability of total to projected leaf area within spruce crowns were investigated. Comparison of six laboratory methods revealed that methods using an elliptic approximation of a needle shape underestimated total leaf area compared to methods using a parallelepiped approximation. The variability in total to projected leaf area was primarily driven by the vertical sampling position and less by needle age or forest stand age. We found that total leaf area estimation has an important implication on RS of leaf chlorophyll content. An error associated with biased estimates of total leaf area can reach up to 30% of the expected chlorophyll range commonly found in forest canopies and therefore negatively influences the validation of RS-based chlorophyll maps. In Chapter 4, potentials of the continuum removal transformation for mapping of chlorophyll content in spruce canopies were investigated. We tested two methods based on continuum removal: artificial neural networks and an optical index. The optical index was newly designed here and it was based on the spectral continuum between 650 and 720 nm. Both continuum removal based methods exhibited superior accuracy in chlorophyll retrieval compared to commonly used narrow-band vegetation indices (e.g. NDVI, TCARI/OSAVI). The newly designed index was equally accurate, but certainly provided a more operational approach as compared to the neural network.

    In Chapter 5, mapping of ecosystem properties that underline ecosystem services provided by subalpine grasslands using RS methods was tested and further compared with a statistical plant trait-based modelling approach. Imaging spectroscopy in combination with empirical retrieval methods was partly successful to map ecosystem properties. The prediction accuracy at the calibration phase was comparable to the trait-based modelling approach. Spatial comparison between the two approaches revealed rather small agreement. The average fuzzy similarity between the approaches was around 20% for ecosystem properties, but in case of the total ecosystem service supply it decreased below 10%. However, the RS approach detected more variability in ecosystem properties and thereby in services, which was driven by local topography and microclimatic conditions, which could not be detected by the plant trait-based approach. Especially Chapters 2 and 5 indicated that one of the future RS research directions may be in spatial ecology, i.e. spatially explicit mapping of plant traits, ecosystem properties and ecosystem services. High quality RS data are certainly essential building elements for spatial ecology. But in order to address the effects of climate and land use changes on biodiversity and ecosystems, their properties and services, the integration of in-situ and RS data will be ultimately required. Therefore, more coherent experiments, where in-situ and RS data are measured simultaneously at different spatial scales, are needed in the future.

    Naaldbossen en paddenstoelen: op zoek naar ecologische criteria voor waardering
    Bijlsma, R.J. - \ 2011
    Coolia 54 (2011)1. - ISSN 0929-7839 - p. 9 - 15.
    bosbeheer - naaldbossen - habitats - paddestoelen - ecosystemen - mycologie - forest administration - coniferous forests - mushrooms - ecosystems - mycology
    Najaar 2010 verscheen de fraai uitgevoerde NMV-brochure ‘Naaldbossen in Nederland. Bedreigde levensgemeenschappen’ (Chrispijn & Arnolds, 2010). Aanleiding voor deze uitgave is het streven van bosbeheerders naar een groter aandeel inheems loofbos ten koste van naaldbos. Deze maatregel wordt aangeduid met de term (bos)omvorming. De NMV is van mening dat naaldbossen ‘zomaar worden opgeofferd’ en dat ‘het anders moet, niet alleen ten behoeve van paddenstoelen, maar ook voor talrijke karakteristieke planten en dieren van naaldbossen en voor het behoud van biodiversiteit op landschapsschaal’.
    Monitoring proefprojecten plaggen in naaldbos van de arme zandgronden : eindrapportage 2011
    Kemmers, R.H. ; Delft, S.P.J. van; Boxman, A.W. ; Veerkamp, M.T. - \ 2011
    Den Haag : Directie Kennis en Innovatie, Ministerie van Economische Zaken, Landbouw en Innovatie (Rapport / DKI nr. 2011/OBN153-DZ) - 116
    plaggen steken - herstelbeheer - zandgronden - bossen - naaldbossen - bodemchemie - humusvormen - bosecologie - natura 2000 - sod cutting - restoration management - sandy soils - forests - coniferous forests - soil chemistry - humus forms - forest ecology - natura 2000
    In het kader van Ontwikkeling en Beheer Natuurkwaliteit (OBN) heeft de Unie van Bosgroepen het proefproject “Plaggen in naaldbos op arme zandgronden” in uitvoering genomen. Omdat een dergelijke proefmaatregel monitoringplichtig is, werd in 2005 opdracht gegeven in een aantal bosopstanden het effect van de maatregelen te monitoren. Doel van het plaggen is de ruwe humus- en strooisellaag (L-, F- en H-horizont), met de grote hoeveelheden stikstof die zich daarin hebben geaccumuleerd, te verwijderen, waardoor de veel nutriëntarmere, open, minerale bodem aan het oppervlak komt. De vraag is of deze veranderingen in de abiotische omstandigheden leiden tot een herstel van de bosvitaliteit en de kenmerkende vegetatie met een grote soortenrijkdom van mossen, korstmossen en mycorrhiza-paddenstoelen
    Paddestoelen in naaldbossen
    Kuyper, T.W. ; Arnolds, E.J.M. ; Berg, A. van den; Chrispijn, R. ; Jalink, L. ; Veerkamp, M.T. - \ 2006
    De Levende Natuur 107 (2006)6. - ISSN 0024-1520 - p. 228 - 232.
    mycologie - naaldbossen - inventarisaties - mycology - coniferous forests - inventories
    In Nederland komen ten minste 3500 soorten paddestoelen voor volgens het "Overzicht van de paddestoelen in Nederland"; ongeveer 450 soorten komen uitsluitend voor bij naaldbomen. In dit artikel aandacht voor het belang van de bossen voor de Nederlandse paddestoel
    Effecten van brand in een voedselarm dennenbos
    Kemmers, R.H. ; Dirkse, G.M. ; Mekkink, P. - \ 2005
    Vakblad Natuur Bos Landschap 2 (2005)3. - ISSN 1572-7610 - p. 6 - 10.
    naaldbossen - zandgronden - bosbranden - vegetatie - bodemchemie - nitraten - coniferous forests - sandy soils - forest fires - vegetation - soil chemistry - nitrates
    Door atmosferische stikstofdepositie zijn veel dennenbossen van de arme zandgronden vermest en in hun successie verstoord. Bij Kootwijk is in een voedselarm dennenbos onderzocht of de overmaat aan stikstof die in de strooisellaag lag opgeslagen door brand kan worden teruggedrongen en de bosontwikkeling zo kan worden teruggezet naar een voedselarme pionierfase. Op grond van de resultaten lijkt het twijfelachting dat brand effectief is als maatregel tegen vermesting. Hoofdlijnen uit Alterra rapport 1028; gevolgd door de visie van de beheerder (Staatsbosbeheer) in de persoon van Klein Lebbink
    Effecten van brand op bodem en vegetatie in dennenbossen van voedselarme zandgronden bij Kootwijk
    Kemmers, R.H. ; Dirkse, G.M. ; Hille, M.G. ; Mekkink, P. - \ 2005
    Wageningen : Alterra (Alterra-rapport 1028) - 57
    naaldbossen - bossen - verbranden - bodem - vegetatie - zandgronden - bosbranden - stikstof - verrijking - natuurgebieden - veluwe - gelderland - coniferous forests - forests - burning - soil - vegetation - sandy soils - forest fires - nitrogen - enrichment - natural areas - veluwe - gelderland
    Door atmosferische stikstofdepositie zijn veel bossen van de arme zandgronden vermest en in hun verdere successie verstoord. In een voedselarm dennenbos op zandgrond is onderzocht of door brand de overmaat aan stikstof die in de strooisellaag ligt opgeslagen kan worden teruggedrongen en de bosontwikkeling kan worden teruggezet naar een voedselarme pionierfase. Het onderzoek werd uitgevoerd bij Kootwijk waar in 1995 een bosbrand woedde. De vegetatie- en bodemkundige toestand van voor de brand, één en negen jaar na de brand werd geanalyseerd. Een belangrijke conclusie is dat brand eerder tot een verrijking van de bodem leidt dan tot een verschraling. Door brand vindt een verplaatsing van elementen van ectorganische naar endorganische horizonten plaats. Weliswaar verdwijnt er in zijn totaliteit stikstof, maar direct na de brand is de bodem sterk verrijkt met kalium, ammonium en fosfaat en in zuurgraad gedaald. Bovendien wordt het beschikbaar gekomen ammonium door micro-organismen vastgelegd in organische stof wat daardoor een rijk karakter krijgt. Dit effect is negen jaar na de brand nog steeds aanwezig. Het laten staan van de necromassa na de brand, zoals in Kootwijk plaatsvond, draagt niet bij aan het terugzetten van de vegetatiesuccessie naar een initieel schraal stadium, maar wel aan de diversiteit van bodemeigenschappen
    Omvormingsbeheer naaldbos en herstel duinroosjesvegetatie Amsterdamse Waterleidingduinen; de bodemkundige uitgangstoestand
    Kemmers, R.H. ; Mekkink, P. - \ 2002
    Wageningen : Alterra (Alterra-rapport 483) - 37
    vegetatie - naaldbossen - herstel - duinplanten - duinen - duingraslanden - rosa pimpinellifolia - bodemchemie - ligstro - bedrijfsvoering - nederland - bodemkunde - bosbeheer - humusprofiel - Noord-Holland - vegetation - coniferous forests - rehabilitation - duneland plants - dunes - dune grasslands - rosa pimpinellifolia - soil chemistry - litter - management - netherlands
    In de Amsterdamse Waterleidingduinen wordt een experiment uitgevoerd om te onderzoeken welke beheersvorm het meest geschikt is voor de omvorming van naaldbos naar vegetaties met duinroosjes. Inrichtingsmaatregelen betreffen kappen, kappen en strooiselverwijdering, en kappen en plaggen. Na de inrichtingsmaatregelen is de bodemkundige uitgangsituatie van de verschillende proefvlakken vastgelegd. Het humusprofiel is beschreven, waarna de horizonten bemonsterd werden. De monsters zijn chemisch geanalyseerd om de basen- en nutriëntentoestand te bepalen. Na bepaling van elementgehalten zijn elementvoorraden in het profiel berekend. De resultaten zijn met een variantieanalyse getoetst op verschillen tussen de behandelingen en binnen de replica's van de behandelingen.
    Radar modelling of coniferous forest using a tree growth model
    Woodhouse, I.H. ; Hoekman, D.H. - \ 2000
    International Journal of Remote Sensing 21 (2000)8. - ISSN 0143-1161 - p. 1725 - 1737.
    remote sensing - microgolfstraling - groeimodellen - naaldbossen - remote sensing - microwave radiation - growth models - coniferous forests
    Subantarctic forest ecology : case study of a conifer-broadleaved stand in Patagonia, Argentina
    Dezzotti, A. - \ 2000
    Agricultural University. Promotor(en): R.A.A. Oldeman; L.A. Sancholuz. - S.l. : S.n. - ISBN 9789058082169 - 140
    bosbouw - ecologie - bosecologie - naaldbossen - loofhout - gemengde bossen - populaties - opstandsstructuur - gebieden - seksuele dimorfie - forestry - ecology - forest ecology - coniferous forests - broadleaves - mixed forests - populations - stand structure - areas - sexual dimorphism

    In the temperate rainforests of southern South America, the tree genus Nothofagus (Nothofagaceae) is the dominant in extension and abundance on zonal soils at different latitudes and altitudes, as well as on intrazonal (e.g., wetlands) and azonal soils (e.g., morrenic and fluvioglacial deposits). Although concern on the global role of this biome is currently important, the existing level of ecological knowledge on its functioning is still inadequate to design a sound management to maintain or enhance forest values, services, and commodities. Vegetation misuse triggers severe biota and physical deterioration, particularly in the intrinsically fragile Andean Patagonic region characterised by seasonality of high rainfall levels, low temperature, strong intensity and frequency of winds, and extensive and deep mountain slopes. In Argentina, at low and mid elevations between 38° and 43°S and the annual isohyets of 1,500 to 2,000mm, the forest is composed of the xeric cypress Austrocedrus chilensis ("ciprés", Cupressaceae) and the mesic southern beech Nothofagus dombeyi ("coihue"). The effect of the strong east - west environmental gradient, caused by the Andes' rain shadow, on community composition and dynamics is striking. This is reflected in a clear vegetational zonation, whose edges are the sparse A.chilensis woodland surrounded by the Patagonian steppe towards the east and the Valdivian rainforest co-dominated by N.dombeyi towards the west. Both communities are separated only by tens of kilometres. The conifer-angiosperm association, characterised by two groups of plants with contrasting evolutionary histories and ecological adaptations, has received little scientific attention.

    At 41°11'S and 71°25'W, a mixed, virgin, post-fire stand, located on a dry north-facing slope was examined regarding regeneration, size, age, and spatial structures, and stand and tree growth. Inferences on community dynamics were made. The minimum area of the community was also estimated. Density, basal area, and volume of adult trees is calculated in 658 ind ha -1(66.6% of A.chilensis ), 72.1 m 2ha -1(65.6%), and 608.7m 3ha -1(51.2%), respectively. Total density of saplings and seedlings is 2,991 (27.1% of A.chilensis ) and 7,143 ind ha -1(34.3%), respectively. Stand growth is estimated in 7.3m 3ha -1yr -1(42.5% of A.chilensis ) and 3.7 t ha -1yr -1(32.4%). Between species, individual increments significantly differ within development stages. Adults A.chilensis and N.dombeyi grow in diameter at an individual rate of 0.36 and 0.57cm yr -1, respectively, while in height at a rate of 15.8 and 29.3cm yr -1, respectively. Saplings of A.chilensis and N.dombeyi grow in diameter at a rate of 0.11 and 0.21cm yr -1, respectively, while in height at a rate of 7.8 and 17.2cm yr -1, respectively. Within species, adults grow in diameter at rates between 2.7 (in N.dombeyi ) and 3.2 (in A.chilensis ) times significantly faster than their respective saplings, and also old trees show significantly larger diameter increments than young trees. Within species, adults grow in height at rates between 0 (in N.dombeyi ) - 2.0 (in A.chilensis ) times faster than their respective saplings. In A.chilensis , old trees grow in height at significantly higher rates than young trees, whereas this is not the case for N.dombeyi . For each A.chilensis tree, a negative relationship is found between individual diameter (range= 0.22 to 0.42cm yr -1) and height growth (12 to 21cm yr -1), and the number of neighbour trees (0 to > = 7) taller than itself within a 5m distance. Contrarily, for N.dombeyi no relationship is observed between these variables. In A.chilensis , individual growth rates do not differ significantly between sex classes: for males, mean and current diameter, and height growth rate is 0.360, 0.132, and 17.6cm yr -1, respectively, while for females is 0.348, 0.124, and 17.2cm yr -1, respectively.

    The inherently inferior growth capacity of A.chilensis over N.dombeyi is explained by its lower leaf photosynthetic rate. Conifers from the northern hemisphere show a primary productivity similar to their mostly associated deciduous angiosperms. However, southern hemisphere conifers show a lower productivity than broadleaved. This is probably because they cannot benefit differentially from an extended period of net photosynthesis as they co-exist mainly with broadleaved evergreen species. The greater growth disadvantage of A.chilensis in comparison to N.dombeyi during the juvenile stage is consistent with the same trend observed in gymnosperms as a group: seedling represents the ontogenetic phase of slowest growing, caused by multiple factors related to leaf productivity and carbohydrate allocation. This constraint has been used to explain the decline and retreat of gymnosperms along evolutionary scales. Within species, the dependence of growth to age and crowding is indicative of one-sided, asymmetric competition for light: trees that arrived earlier to the site have pre-empt resources, developed a larger size, and therefore at present they interfere asymmetrically with those arriving later. However, contrasting responses are found according to species and growth variables: i) In N.dombeyi , the independence of individual growth to crowding, and of height growth to age/development stage of trees suggests that this species is rather insensitive to this competition type. On the contrary, A.chilensis is highly susceptible judging from the dependence between growth to age and taller neighbours. ii) In comparison to diameter growth, height growth differs slightly between age classes/stages, which reflect the common priority that trees give to height during development. Lack of gender-related growth differences in the dioecious A.chilensis would be masked by the low reproductive development exhibited in the sampled individuals. If trees in structurally well-developed stand are unable to express the reproductive potential as observed in isolated trees, then its incidence on the individual energetic budget would be marginal and marked intersexual growth contrasts would not be expected. This hypothesis would explain the incongruence with previously results suggesting a trade-off between vegetative and reproductive investments, and needs to be tested during future studies given the ecological and silvicultural relevance of this issue.

    In 1860, both tree species began to colonize a heterogeneous site, following a fire that eliminated the original vegetation. This first regenerative pulse lasted 60 to 70 years after which recruitment ceased probably in response to canopy closure, resulting in the present even-aged clustered adult tree populations. Because of its lower density and higher growth rates, N.dombeyi constitutes widely spaced, big emergent trees of the stand. The build-up of the A.chilensis -dominated mixed stand probably improved autogenously local moisture conditions, encouraging establishment of N.dombeyi seedlings and defining a second continuous regenerative pulse starting ca.1930. In the understorey, the sapling population dominated by N.dombeyi represents a third regenerative pulse with ages between 1 to 10 years. The current-day stand structure is represented by a young population dominated primarily by N.dombeyi , and a mature overstorey dominated primarily by A.chilensis . In absence of large-scale impacts, changes in forest structure over time would be accounted for interspecific differences in recruitment, growth rate, and sensitivity to competition, probably resulting in a local decline of the conifer component. However, the combination of a great longevity and a light-demanding temperament of A.chilensis implies that frequent to very infrequent large-scale impacts would be sufficient to maintain its abundance in the landscape. These results, together with others described in literature, suggest that divergent development patterns occur in the A.chilensis - N.dombeyi stands, probably because these forests grow under a spatially varied environment and their responses differ consequently.

    Based on the concept of "quantitative minimum area", the statistically optimum plot size for the ecological study of a temperate forest was examined. Changes in the estimated tree density (N), basal area (G), stemwood volume (V), and volume growth rate (I v ) per area unit, in relation to the increase of sample plot size (X), were analysed. Means of N, G, V, and I v fluctuated considerably within a range of small plot sizes, showing stability at X >= 1,000m 2. The accuracy of the parameters estimates measured as relative error (RE) increases as long as the plot size is enlarged. For X= 1,000m 2, ER varies between ± 30% and ± 49%, and for X= 2,500m 2, RE varies between ± 20% and ± 32%. Around X= 5,000m 2should be sampled to obtain RE < = ± 20% in all variables, according to the developed regressions RE= f (X) (P<0.05). This estimated plot size is larger than those often recommended in literature for ecological studies of temperate forests.

    Het voorkomen van intersteriele groepen van de wortelzwam in Nederland
    Schuring, W. - \ 1999
    Nederlands Bosbouwtijdschrift 71 (1999)3. - ISSN 0028-2057 - p. 144 - 147.
    heterobasidion annosum - schimmels - plantenziekteverwekkende schimmels - bosplagen - plantenplagen - schimmelziekten - pinopsida - naaldbossen - bossen - bosbouw - bosschade - ziektebestrijdende teeltmaatregelen - schimmelbestrijding - steriliteit - mycologie - gastheer parasiet relaties - gastheerspecificiteit - bosbescherming - heterobasidion annosum - fungi - plant pathogenic fungi - forest pests - plant pests - fungal diseases - pinopsida - coniferous forests - forests - forestry - forest damage - cultural control - fungus control - sterility - mycology - host parasite relationships - host specificity - protection of forests
    Resultaten van een enquete onder bosbeheerders naar problemen met de wortelzwam of dennemoorder (Heterobasidion annosum), en van kruisingsproeven met paddestoelen verzameld in verschillende boswachterijen. In Nederland blijkt alleen de P-groep (grove den) van de wortelzwam voor tekomen; dit betekent dat aangetaste naaldhoutopstanden in principe alleen omgevormd kunnen worden tot loofhout
    Exchange processes between a coniferous forest and the atmosphere
    Bosveld, F.C. - \ 1999
    Agricultural University. Promotor(en): A.A.M. Holtslag; W. Bouten. - S.l. : S.n. - ISBN 9789058081117 - 181
    bossen - naaldbossen - kroondak - lagenstructuur - oppervlakteruwheid - transpiratie - evaporatie - atmosfeer - nederland - energie-uitwisseling - straling - warmteuitwisseling - forests - coniferous forests - canopy - layer structure - surface roughness - transpiration - evaporation - atmosphere - netherlands - energy exchange - radiation - heat exchange

    This thesis deals with the research question: which processes are relevant in controlling the exchange fluxes between the forest and the atmosphere and how can this control be quantified? Answering this question is relevant for research in the fields of air pollution, weather and climate and remote sensing. To answer this question a measurement program has been performed over and in a dense Douglas fir forest (Speulderbos), near the village of Garderen, the Netherlands. Variables were monitored related to, the state of the atmosphere, the state of soil water and the state of the trees. Forest response was determined by measuring outgoing radiation fluxes and the surface fluxes of momentum, sensible and latent heat. Well-known concepts from micro-meteorology and hydrology were used for the interpretation of the measurement. At times, these concepts had to be adapted for the specific forest situation. One concept is surface layer similarity theory, which enables to categorise observations in a convenient way. A second concept, related to surface layer similarity, is on resistances relating spatial differences in variables to their corresponding fluxes. A third concept is the Penman-Monteith equation, which enables the discrimination between atmospheric control and plant control on transpiration.

    Turbulent exchange within the roughness sublayer is investigated. The importance of terrain inhomogeneity is studied with footprint analysis and with an inhomogeneous surface layer model. A windspeed dependence of roughness length for momentum and displacement height is found. Surface layer similarity theory is extended to describe the roughness-sublayer influence. This involves the introduction of an additional length scale related to the geometry of the forest. It is found that well- defined flux profile relations exist for momentum and sensible heat in the roughness layer of the current forest. In the roughness layer the exchange of temperature is more efficient than the exchange of momentum. This is in contrast to results for the surface layer, but in concord with previous findings for dense forests.

    The scalar excess resistance, which describes the difference between momentum transport and scalar transport at the surface/atmosphere interface, is investigated by using measurements of infrared surface temperature. Surface radiation temperature and aerodynamic surface temperature, obtained by extrapolating the air-temperature profile to the surface, are not necessarily equal. By assuming equality between the two, it is shown that a consistent description of the relation between sensible heat flux and temperature difference between the surface and the atmosphere is obtained, at least for daytime cases. The excess resistance for the current forest is much smaller than values found for low vegetation. It is shown that the enhanced exchange efficiency of heat, relative to momentum, in the roughness sublayer attributes to this low value. An alternative analysis is presented to separate this roughness layer effect from the transfer resistance at the forest/atmosphere interface. The value found for this alternative excess resistance, is more in line with low vegetation values. For neutral cases the two methods give the same results for temperature differences between the surface and the surface layer. It is shown that stability effects give rise to a discrepancy between the two methods. The observations show some evidence in favour of the alternative method. The difference between forest interior air temperature and air temperature at canopy height is related to storage heat flux and sensible heat flux by applying the concepts of gust penetration and surface renewal. The analysis suggests that the renewal of interior air caused by gust penetration is slow due to the presence of a very dense crown layer.

    For night-time cases, the equality between aerodynamic and radiation surface temperature breaks down when wind speeds are low and longwave cooling is high. The analysis shows that forest air becomes decoupled from the air aloft. Longwave cooling at the crown layer triggers canopy convection which transports cooled air from the crown layer to the forest interior. The existence of a convective surface temperature in the crown layer is deduced from the measurements. A two-layer radiation/energy balance model is constructed. The model explains the difference between radiation- and aerodynamic surface temperature in terms of the distribution of storage heat and sensible heat over the two model layers.

    Transpiration for dry conditions is investigated by using the Penman-Monteith equation with a Jarvis type of formulation for the surface resistance. First the closure of the surface energy balance is checked. Overall closure is within the range of estimated measurement error. However, at times deviations occur which can be attributed to wind direction. With respect to transpiration it is found that surface resistance reacts strongly to water vapour deficit changes. This is related to the good aerodynamic coupling of the rough forest to the atmosphere. In spring, a clear increase in transpiration is observed after shoot growth. Soil water response is clearly present before mid summer, after that the forest seems less susceptible to draught. Probably the root system adapts to the dry situation. An analysis of residuals between observed and modelled transpiration shows that deviations occurred at the same wind direction where the energy balance closure broke down. The variance in the residuals appears to be two times larger than estimated from atmospheric statistics.

    Important contributions to this variance are correlated over periods of one day. This suggests that standard statistical techniques lead to an underestimation of the confidence intervals of estimated model parameters. Two other models are evaluated. A new formulation suggested by Monteith, where stomatal response to moisture deficit is replaced by a response to transpiration itself, is investigated. This formulation appears to be equivalent to the Jarvis formulation with an atmospheric moisture deficit response. The Priestley-Taylor formula is adapted to include soil water response. It performs reasonably well given the simple nature of the formulation.

    Interception measurements and xylem sapflow measurements are exploited to investigate the interaction between evaporation and transpiration in a partially wet forest. The Penman-Monteith equation is generalised to describe this interaction. Explicit expressions are obtained for evaporation and transpiration. After optimisation the model is capable of describing both evaporation and transpiration reduction fairly well. Due to parameter interdependency, error bounds on individual parameter estimates, related to evaporation, are large. Independent estimates of the parameters, although crude, are shown to be within the confidence region of the optimisation results. It is shown that evaporation rates are smaller than the frequently used formula: wet fraction times potential evaporation. Most of the transpiration reduction comes from energy consumption by the process of evaporation and the impact of the humidity conditions close to the needles. Only a small amount of stomatal blocking due to intercepted water is needed to explain the remaining reduction. This is in concord with the observation that stomata of the Douglas fir are at the lower side of the needle, which is only partially wetted during rain.

    The response of the forest to external forcings can be described by a number of parameters related to model descriptions of various processes. The results for the current dense Douglas-fir forest are compared with other forest studies. A good agreement is found for the relation between the geometric parameters, canopy height, displacement height and roughness length for momentum. The exchange coefficients in the roughness layer for momentum and heat agree qualitatively with typical values found for other dense forests. Quantitatively significant and as yet unexplained differences remain. The very small scalar excess resistance found for the current forest is in agreement with the only other comparable dense forest study, which appeared recently in the literature. Transpiration rates as a function of external conditions are broadly in line with results found at other forest sites in the temperate climate.

    New in this thesis are the results on; the estimation of displacement height; the difference between aerodynamic surface temperature and radiation surface temperature at night time; night time convection; changing transpiration response to soil water stress during the season; and the interaction between evaporation and transpiration reduction during wet conditions.

    Primaire Grove-dennenbossen in stuifzandgebieden als refugia voor zeldzame mycorrhizapaddestoelen.
    Ozinga, W. ; Baar, J. - \ 1997
    De Levende Natuur 98 (1997). - ISSN 0024-1520 - p. 129 - 133.
    schimmels - mycologie - naaldbossen - plantengemeenschappen - vegetatie - onderzoek - nederland - fungi - mycology - coniferous forests - plant communities - vegetation - research - netherlands
    Vegetatietypen in Nederlandse naaldhoutbossen
    Bannink, J.F. ; Leijs, H.N. ; Zonneveld, I.S. - \ 1968
    Wageningen : STIBOKA - 32
    naaldbossen - coniferous forests
    Vegetatieonderzoek Stiboka
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