Auditory - Visual Matching in Learning Disabilities : Intervention Studies from Finland and Sweden

The present thesis discusses relevant issues in education: 1) learning disabilities including the role of comorbidity in LDs, and 2) the use of research-based interventions. This thesis consists of a series of four studies (three articles), which deepens the knowledge of the field of special education. Intervention studies (N=242) aimed to examine whether training using a nonverbal auditory-visual matching computer program had a remedial effect in different learning disabilities, such as developmental dyslexia, Attention Deficit Disorder (ADD) and Specific Language Impairment (SLI). These studies were conducted in both Finland and Sweden. The intervention’s non-verbal character made an international perspective possible. The results of the intervention studies confirmed, that the auditory-visual matching computer program, called Audilex had positive intervention effects. In Study I of children with developmental dyslexia there were also improvements in reading skills, specifically in reading nonsense words and reading speed. These improvements in tasks, which are thought to rely on phonological processing, suggest that such reading difficulties in dyslexia may stem in part from more basic perceptual difficulties, including those required to manage the visual and auditory components of the decoding task. In Study II the intervention had a positive effect on children with dyslexia; older students with dyslexia and surprisingly, students with ADD also benefited from this intervention. In conclusion, the role of comorbidity was apparent. An intervention effect was evident also in students’ school behavior. Study III showed that children with SLI experience difficulties very similar to those of children with dyslexia in auditory-visual matching. Children with language-based learning disabilities, such as dyslexia and SLI benefited from the auditory-visual matching intervention. Also comorbidity was evident among these children; in addition to formal diagnoses, comorbidity was explored with an assessment inventory, which was developed for this thesis. Interestingly, an overview of the data of this thesis shows positive intervention effects in all studies despite learning disability, language, gender or age. These findings have been described by a concept inter-modal transpose. Self-evidently these issues need further studies. In learning disabilities the aim in the future will also be to identify individuals at risk rather than by deficit; this aim can be achieved by using research-based interventions, intensified support in general education and inclusive special education. Keywords: learning disabilities, developmental dyslexia, attention deficit disorder, specific language impairment, language-based learning disabilities, comorbidity, auditory-visual matching, research-based interventions, inter-modal transpose

A comparison of alternative plant mixes for conservation bio-control by native beneficial arthropods in vegetable cropping systems in Queensland Australia.

Cucurbit crops host a range of serious sap-sucking insect pests, including silverleaf whitefly (SLW) and aphids, which potentially represent considerable risk to the Australian horticulture industry. These pests are extremely polyphagous with a wide host range. Chemical control is made difficult due to resistance and pollution, and other side-effects are associated with insecticide use. Consequently, there is much interest in maximising the role of biological control in the management of these sap-sucking insect pests. This study aimed to evaluate companion cropping alongside cucurbit crops in a tropical setting as a means to increase the populations of beneficial insects and spiders so as to control the major sap-sucking insect pests. The Population of beneficial and harmful insects, with a focus on SLW and aphids, and other invertebrates were sampled weekly oil four different crops which could be used for habitat manipulation: Goodbug Mix (GBM; a proprietary seed Mixture including self-sowing annual and perennial herbaceous flower species); lablab (Lablab purpureus L. Sweet); lucerne (Medicago sativa L.); and niger (Guizotia abyssinica (L.f.) Cass.). Lablab hosted the highest numbers of beneficial insects (larvae and adults of lacewing (Mallada signata (Schneider)), ladybird beetles (Coccinella transversalis Fabricius) and spiders) while GBM hosted the highest numbers of European bees (Apis mellifera Linnaeus) and spiders. Lucerne and niger showed little promise in hosting beneficial insects, but lucerne hosted significantly more spiders (double the numbers) than niger. Lucerne hosted significantly more of the harmful insect species of aphids (Aphis gossypii (Glover)) and Myzus persicae (Sulzer)) and heliothis (Heliothis armigera Hubner). Niger hosted significantly more vegetable weevils (Listroderes difficillis (Germar)) than the other three species. Therefore, lablab and GBM appear to be viable options to grow within cucurbits or as field boundary crops to attract and increase beneficial insects and spiders for the control of sap-sucking insect pests. Use of these bio-control strategies affords the opportunity to minimise pesticide usage and the risks associated with pollution.

Self-Concept and School Achievement of Pupils with Cleft Lip, Cleft Palate or Both : A longitudinal study

The goal of this research was to survey the self-concept and school achievement of pupils with cleft lip, cleft palate or both from juvenile age to adolescence. Longitudinal researches of self-concept and school achievement among pupils with cleft lip, cleft palate or both are uncommon. This research was the first longitudinal research ever conducted in Finland among this population. This research can be considered to be a special educational study because of the target group involved. Self-concept consists of the person s entire personality. Personality is biological and deterministic. Self-concept includes concepts, attitudes and feelings that the person has about him or her qualities, abilities and relations to the environment. The individual associates experiences to this personality with earlier observations through the social interaction. The individual will have the consciousness of the person s existence and action. The target group in this study consisted of Finnish children with clefts, who were comprised of four different age groups. The questionnaire was sent to all subjects (N1 = 419) both times. A total of 74 % of children returned the questionnaire in 1988 (N2=305). 48 % of children returned the questionnaire in 1993 (N3=203). 42% of children returned the questionnaire both times (N4=175) . These 175 children formed the research subjects. The survey was conducted in 1988, and again in 1993. In 1988, the pupils surveyed were 9 to 12 years of age, while in 1993 they were between 14 and 17 years old. The data was collected through the use of a questionnaire, which consisted of common questions and a personality inventory test that was developed for Finnish students by professor Maija-Liisa Rauste-von Wright. Quantitative analysis methods were used to examine the structure of self-concept and school achievement. Structures found in this research were observed in relation to disorder, gender and maturation. According to these results, structures of self-concepts and school achievement are in fact stable. Basic self-concept elements are seen to be formed at an early age. The developmental aspects of self-concept following puberty are observed as the stability of self-concept and as the forming of a general self. The level of school achievement is stable, but the structure of school achievement changes. From these results, it is possible to state that the gender of the child has a statistical significance regarding self-concept and school achievement. However, the experienced disorder does not have statistical significance as regards to self-concept and school achievement. Results of self-concept support the research of self-concept conducted earlier in Finland.

Epidemiological data of seasonal variation in mood and behaviour

The aim of this study was to measure seasonal variation in mood and behaviour. The dual vulnerability and latitude effect hypothesis, the risk of increased appetite, weight and other seasonal symptoms to develop metabolic syndrome, and perception of low illumination in quality of life and mental well-being were assessed. These variations are prevalent in persons who live in high latitudes and need balancing of metabolic processes to adapt to environmental changes due to seasons. A randomized sample of 8028 adults aged 30 and over (55% women) participated in an epidemiological health examination study, The Health 2000, applying the probability proportional to population size method for a range of socio-demographic characteristics. They were present in a face-to-face interview at home and health status examination. The questionnaires included the modified versions of the Seasonal Pattern Assessment Questionnaire (SPAQ) and Beck Depression Inventory (BDI), the Health Related Quality of Life (HRQoL) instrument 15D, and the General Health Questionnaire (GHQ). The structured and computerized Munich Composite International Diagnostic Interview (M-CIDI) as part of the interview was used to assess diagnoses of mental disorders, and, the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATPIII) criteria were assessed using all the available information to detect metabolic syndrome. A key finding was that 85% of this nationwide representative sample had seasonal variation in mood and behaviour. Approximately 9% of the study population presented combined seasonal and depressive symptoms with a significant association between their scores, and 2.6% had symptoms that corresponded to Seasonal Affective Disorder (SAD) in severity. Seasonal variations in weight and appetite are two important components that increase the risk of metabolic syndrome. Other factors such as waist circumference and major depressive disorder contributed to the metabolic syndrome as well. Persons reported of having seasonal symptoms were associated with a poorer quality of life and compromised mental well-being, especially if indoors illumination at home and/or at work was experienced as being low. Seasonal and circadian misalignments are suggested to associate with metabolic disorders, and could be remarked if individuals perceive low illumination levels at home and/or at work that affect the health-related quality of life and mental well-being. Keywords: depression, health-related quality of life, illumination, latitude, mental well-being, metabolic syndrome, seasonal variation, winter.

Robustness of the partitions in grouping multi-item inventories

A recent work obtained closed-form solutions to the.problem of optimally grouping a multi-item inventory into subgroups with a common order cycle per group, when the distribution by value of the inventory could be described by a Pareto function. This paper studies the sensitivity of the optimal subgroup boundaries so obtained. Closed-form expressions have been developed to find intervals for the subgroup boundaries for any given level of suboptimality. Graphs have been provided to aid the user in selecting a cost-effective level of aggregation and choosing appropriate subgroup boundaries for a whole range of inventory distributions. The results of sensitivity analyses demonstrate the availability of flexibility in the partition boundaries and the cost-effectiveness of any stock control system through three groups, and thus also provide a theoretical support to the intuitive ABC system of classifying the items.

The genetic association between personality and major depression or bipolar disorder. A polygenic score analysis using genome-wide association data

The relationship between major depressive disorder (MDD) and bipolar disorder (BD) remains controversial. Previous research has reported differences and similarities in risk factors for MDD and BD, such as predisposing personality traits. For example, high neuroticism is related to both disorders, whereas openness to experience is specific for BD. This study examined the genetic association between personality and MDD and BD by applying polygenic scores for neuroticism, extraversion, openness to experience, agreeableness and conscientiousness to both disorders. Polygenic scores reflect the weighted sum of multiple single-nucleotide polymorphism alleles associated with the trait for an individual and were based on a meta-analysis of genome-wide association studies for personality traits including 13,835 subjects. Polygenic scores were tested for MDD in the combined Genetic Association Information Network (GAIN-MDD) and MDD2000+ samples (N=8921) and for BD in the combined Systematic Treatment Enhancement Program for Bipolar Disorder and Wellcome Trust Case-Control Consortium samples (N=6329) using logistic regression analyses. At the phenotypic level, personality dimensions were associated with MDD and BD. Polygenic neuroticism scores were significantly positively associated with MDD, whereas polygenic extraversion scores were significantly positively associated with BD. The explained variance of MDD and BD, approximately 0.1%, was highly comparable to the variance explained by the polygenic personality scores in the corresponding personality traits themselves (between 0.1 and 0.4%). This indicates that the proportions of variance explained in mood disorders are at the upper limit of what could have been expected. This study suggests shared genetic risk factors for neuroticism and MDD on the one hand and for extraversion and BD on the other.

Kohti hyvää suometsien hoitoa : harvennusten ja kunnostusojitusten vaikutus ojitusaluemänniköiden puuntuotokseen ja metsänkasvatuksen taloustulokseen

This thesis examines the impacts of silvicultural activities on productivity and financial returns of Scots pine (Pinus sylvestris L.) stands on drained peatlands in Finland. The effects of ditch network maintenance operations (DNM) and thinnings, with different timings and intensities, were studied. Based on stand development simulations, the best regimes for different types of stands according to site type, climatic area, and stand silvicultural status were defined from the viewpoint of both wood production and financial profitability. Certain aspects affecting the management outcomes, such as the timing of the first thinning, were examined using data from thinning experiments. Long-term predictions of the impacts of different management regimes were carried out by simulating the development of well-representative model-stands which were composed from appropriate inventory data sets. The MOTTI stand simulator used to perform the simulations enables the predictions by utilizing specific models for drained peatland stands. In addition to natural stand dynamics, these models describe the effects of silvicultural treatments on the development of a given stand. The mean annual increment of merchantable wood (MAImerch) was used as the measure of wood productivity, and the financial feasibility of the regimes was compared using net present value (NPV) analysis. Silvicultural treatments, when applied to appropriately match stand condition, increased both the productivity and financial returns of stand management. Applying DNM resulted in a small increase in MAImerch. When thinning was introduced along with DNM, their combined effect on wood productivity was considerable. According to current operational practices, DNM is generally combined with thinning. In some cases, e.g., in sites of low productivity, the need for DNM may become apparent prior to the thinning stage. As for profitability, thinnings proved to be crucial. The regimes with heavy and late thinnings were generally more profitable than those with normal thinnings. Further, early thinning (relative to stand volume) lacked appeal when seeking a financially profitable removal from the first thinning. In young stands with an initially poor silvicultural condition, however, applying even a low-yielding first thinning considerably increased the NPV when compared to a regime with no thinning at all. Generally, the regimes resulting in the best profitability included heavier thinnings and fewer DNM and thinning treatments than did the regimes resulting in the best yield results. This study demonstrates considerable potential for profitable wood production-oriented management in pine stands on drained peatlands despite their challenging circumstances and long rotations. The results can be used for defining new and more site-specific silvicultural guidelines for various types of drained, pine-dominated peatland stands within the entire range of boreal conditions.

Nuorten männiköiden kehitys - taimikonhoito ja ensiharvennus

The aim of this study was to investigate the effects of location, site type, regeneration method and precommercial thinning on the characteristics and development of young, even-aged, pure Scots pine stands. In addition, the effects of timing and intensity of first commercial thinning on the yield and profitability during the rotation period were also studied. The stand characteristics and external quality of young Scots pine stands and stand-level growth models were based on extensive inventory data of the Finnish Forest Research Institute for young Scots pine stands (3 measurement times, 192 stands). The effect of precommercial thinning on stand development was examined on the basis of long-term experiments (13 stands, 169 plots). The effect of timing and intensity of the first commercial thinning on yield and profitability were based on measurements made in first commercial thinnings (27 stands of Metsähallitus), and the further stand development was modeled using the MOTTI simulator. The thesis was based on four articles and a summary. Stand level growth models were developed for young, even-aged Scots pine stands. The models reliably predicted the development up until the first commercial thinning stage. The stand density of young Scots pine stands in Finland was moderately low compared to the target values. In addition, the external quality of pines was low on average. The low stand density and poor external quality will result in the need for quality tree selection in thinnings, if high quality sawn timber is required. In Northern Finland, only 20% of the dominant trees were classified as normal. This will lead to the situation where external quality will remain relatively poor up until the end of rotation. Early and light precommercial thinning (Hdom 3 m, to a density of 3000 trees per hectare) increased the thinning removal by 40% compared to late and more intensive precommercial thinning (at 7 meters to a density of 2000 trees per hectare). A model for the effect of precommercial thinning on merchantable thinning removal at the first commercial thinning was developed for forest management planning purposes. When the recommended time of first commercial thinning was delayed from a dominant height of 12 m to 16 m, or by ten years, the yield of merchantable wood was doubled. Simultaneously, the current value of the stumpage revenues (with 4% interest rate) was increased on the average by 65% (330 € per hectare). Variation in stumpage prices or interest rates did not have any effect on the final results. Without exception, delaying the first commercial thinning by ten years seemed to be the most profitable method. This presupposes that precommercial thinning has been carried out at the right time and that tree quality aspects do not be specially considered. Furthermore, the wood yield and economic outcome from the entire rotation were similar regardless of whether the first thinning was performed at the time currently recommended or ten years later.

Management of multi-scale forest resource data over time

During the last decades there has been a global shift in forest management from a focus solely on timber management to ecosystem management that endorses all aspects of forest functions: ecological, economic and social. This has resulted in a shift in paradigm from sustained yield to sustained diversity of values, goods and benefits obtained at the same time, introducing new temporal and spatial scales into forest resource management. The purpose of the present dissertation was to develop methods that would enable spatial and temporal scales to be introduced into the storage, processing, access and utilization of forest resource data. The methods developed are based on a conceptual view of a forest as a hierarchically nested collection of objects that can have a dynamically changing set of attributes. The temporal aspect of the methods consists of lifetime management for the objects and their attributes and of a temporal succession linking the objects together. Development of the forest resource data processing method concentrated on the extensibility and configurability of the data content and model calculations, allowing for a diverse set of processing operations to be executed using the same framework. The contribution of this dissertation to the utilisation of multi-scale forest resource data lies in the development of a reference data generation method to support forest inventory methods in approaching single-tree resolution.

Genome-wide linkage analysis of multiple measures of neuroticism of 2 large cohorts from Australia and the Netherlands

CONTEXT People meeting diagnostic criteria for anxiety or depressive disorders tend to score high on the personality scale of neuroticism. Studying this personality dimension can give insights into the etiology of these important psychiatric disorders. OBJECTIVES To undertake a comprehensive genome-wide linkage study of neuroticism using large study samples that have been measured multiple times and to compare the results between countries for replication and across time within countries for consistency. DESIGN Genome-wide linkage scan. SETTING Twin individuals and their family members from Australia and the Netherlands. PARTICIPANTS Nineteen thousand six hundred thirty-five sibling pairs completed self-report questionnaires for neuroticism up to 5 times over a period of up to 22 years. Five thousand sixty-nine sibling pairs were genotyped with microsatellite markers. METHODS Nonparametric linkage analyses were conducted in MERLIN-REGRESS for the mean neuroticism scores averaged across time. Additional analyses were conducted for the time-specific measures of neuroticism from each country to investigate consistency of linkage results. RESULTS Three chromosomal regions exceeded empirically derived thresholds for suggestive linkage using mean neuroticism scores: 10p 5 Kosambi cM (cM) (Dutch study sample), 14q 103 cM (Dutch study sample), and 18q 117 cM (combined Australian and Dutch study sample), but only 14q retained significance after correction for multiple testing. These regions all showed evidence for linkage in individual time-specific measures of neuroticism and 1 (18q) showed some evidence for replication between countries. Linkage intervals for these regions all overlap with regions identified in other studies of neuroticism or related traits and/or in studies of anxiety in mice. CONCLUSIONS Our results demonstrate the value of the availability of multiple measures over time and add to the optimism reported in recent reviews for replication of linkage regions for neuroticism. These regions are likely to harbor causal variants for neuroticism and its related psychiatric disorders and can inform prioritization of results from genome-wide association studies.

Development of a productivity asessment toll for native spotted gum forest on private land based on estimates of forest growth on Crown land.

Reliable estimates of forest productivity are essential for improved predictions of timber yields for the private native spotted gum resource in southern Qld and northern NSW. The aim of this research was to estimate the potential productivity of native spotted gum forests on private land by making use of available inventory data collated from Qld and northern NSW for spotted gum forest on Crown land (i.e. state forests). We measured a range of site-related factors to determine their relative importance in predicting productivity of spotted gum forest. While measures such as stand height and height-diameter relationships are known to be useful predictors of productivity, we aimed to determine productivity for a site where this information was not available. Through estimation of stand growth rates we developed a spotted gum productivity assessment tool (SPAT) for use by landholders and extension officers. We aimed to develop a tool to allow private landholders to see the benefits of maintaining their timber resource. This paper summarises the information used to develop the SPAT with a particular focus on forest growth relationships.

Landscape-scale soil erosion modelling and ecological restoration for a mountainous watershed in Sichuan, China

Sichuanissa Tiibetin ylängön metsäkato on pysähtynyt mutta eroosio-ongelmat jatkuvat Viikin tropiikki-instituutin tutkija Ping ZHOU kartoitti trooppisen metsänhoidon alaan kuuluvassa väitöskirjatyössään maaperän eroosioalttiutta ja sen riippuvuutta metsäkasvillisuudesta Jangtsen tärkeää sivuhaaraa Min-jokea ympäröivällä n. 7400 neliökilometrin suuruisella valuma-alueella Sichuanin Aba-piirikunnassa. Aineistonaan hän käytti muun muassa satelliittikartoitustietoja ja mittaustuloksia yli 600 maastokoealalta. Tutkimuksen nimi suomeksi on "Maaperän eroosion mallinnus ja vuoristoisen valuma-alueen ekologinen ennallistaminen Sichuanissa Kiinassa". Aikaisempien tutkimusten perusteella oli tiedossa että metsien häviäminen tällä alueella pysähtyi jo 1980-luvun alussa. Sen jälkeen on metsien pinta-ala hitaasti kasvanut etupäässä sen vuoksi, että teollinen puunhakkuu luonnonmetsissä kiellettiin kokonaan v. 1998 ja 25 astetta jyrkemmillä rinteillä myös maatalouden harjoittaminen on saatu lopetetuksi viljelijöille tarjottujen taloudellisten houkuttimien avulla. Täten myös pelto- ja laidunmaata on voitu ennallistaa metsäksi. Ping Zhou pystyi jakamaan 5700 metrin korkeuteen saakka kohoavan vuoristoalueen eroosioalttiudeltaan erilaisiin vyöhykkeisiin rinteen kaltevuuden, sademäärän, kasvipeitteen ja maalajin perusteella. Noin 15 prosentilla tutkitun valuma-alueen pinta-alasta, lähinnä Min-joen pääuomaa ympäröivillä jyrkillä rinteillä, eroosioriski oli suuri tai erittäin suuri. Eri tyyppisellä kasvillisuudella oli hyvin erilainen vaikutus eroosioalttiuteen, ja myös alueen sijainti vuoriston eri korkeuksilla vaikutti eroosioon. Säästyneet lähes luonnontilaiset havumetsät, joita on etupäässä vuoriston ylimmissä osissa 2600-4000 metrin korkeudella, edistävät tehokkaasti metsän luontaista uudistumista ja levittäytymistä vaurioituneille alueille. Säilyneiden metsien puulajikoostumus antoi tutkimuksessa mahdollisuuden ennustaa metsien tulevaa kehitystä koko tutkitulla valuma-alueella sen eri korkeusvyöhykkeissä ja eri maaperätyypeillä. Ennallistamisen kannalta ongelmallisimpia olivat alueet joilta metsäpeite oli lähinnä puiden teollisen hakkuun vuoksi kokonaan hävinnyt ja joilla maaperä yleisesti oli eroosion pahoin kuluttama. Näillä alueilla ei ole tehty juuri mitään uudistamis- tai ennallistamistoimenpiteitä. Niillä metsien ennallistaminen vaatii myös puiden tai pensaiden istuttamista. Tähän sopivia ovat erityisesti ilmakehän typpeä sitovat lajit, joista alueella kasvaa luontaisena mm. sama tyrnilaji joka esiintyy myös Suomessa. Työssä tutkittiin yli kahdeksankymmenen paikallisen luontaisen puulajin (joista peräti noin kolmannes on havupuulajeja) ekologisia ominaisuuksia ja soveltuvuutta metsien ennallistamiseen. Avainasemassa työn onnistumisen kannalta ovat nyt paikalliset asukkaat, joiden maankäytön muutokset ovat jo selvästi edistänet luonnonmetsän ennalleen palautumista. Suomen Akatemia rahoitti vuosina 2004-2006 VITRI:n tutkimushanketta, josta Ping Zhou'n väitöskirjatyö muodosti keskeisen osan. Kenttätyö Sichuanissa avasi mahdollisuuden hedelmälliseen monitieteiseen yhteistyöhön ja tutkijavaihtoon Kiinan tiedeakatemian alaisen Chengdun biologiainstituutin (CIB) kanssa; tämä tieteellinen kanssakäyminen jatkuu edelleen.

Soil carbon modelling as a tool for carbon balance studies in forestry

Soils represent a remarkable stock of carbon, and forest soils are estimated to hold half of the global stock of soil carbon. Topical concern about the effects of climate change and forest management on soil carbon as well as practical reporting requirements set by climate conventions have created a need to assess soil carbon stock changes reliably and transparently. The large spatial variability of soil carbon commensurate with relatively slow changes in stocks hinders the assessment of soil carbon stocks and their changes by direct measurements. Models therefore widely serve to estimate carbon stocks and stock changes in soils. This dissertation aimed to develop the soil carbon model YASSO for upland forest soils. The model was aimed to take into account the most important processes controlling the decomposition in soils, yet remain simple enough to ensure its practical applicability in different applications. The model structure and assumptions were presented and the model parameters were defined with empirical measurements. The model was evaluated by studying the sensitivities of the model results to parameter values, by estimating the precision of the results with an uncertainty analysis, and by assessing the accuracy of the model by comparing the predictions against measured data and to the results of an alternative model. The model was applied to study the effects of intensified biomass extraction on the forest carbon balance and to estimate the effects of soil carbon deficit on net greenhouse gas emissions of energy use of forest residues. The model was also applied in an inventory based method to assess the national scale forest carbon balance for Finland’s forests from 1922 to 2004. YASSO managed to describe sufficiently the effects of both the variable litter and climatic conditions on decomposition. When combined with the stand models or other systems providing litter information, the dynamic approach of the model proved to be powerful for estimating changes in soil carbon stocks on different scales. The climate dependency of the model, the effects of nitrogen on decomposition and forest growth as well as the effects of soil texture on soil carbon stock dynamics are areas for development when considering the applicability of the model to different research questions, different land use types and wider geographic regions. Intensified biomass extraction affects soil carbon stocks, and these changes in stocks should be taken into account when considering the net effects of forest residue utilisation as energy. On a national scale, soil carbon stocks play an important role in forest carbon balances.

Uncertainty in forest simulators and forest planning systems

The forest simulator is a computerized model for predicting forest growth and future development as well as effects of forest harvests and treatments. The forest planning system is a decision support tool, usually including a forest simulator and an optimisation model, for finding the optimal forest management actions. The information produced by forest simulators and forest planning systems is used for various analytical purposes and in support of decision making. However, the quality and reliability of this information can often be questioned. Natural variation in forest growth and estimation errors in forest inventory, among other things, cause uncertainty in predictions of forest growth and development. This uncertainty stemming from different sources has various undesirable effects. In many cases outcomes of decisions based on uncertain information are something else than desired. The objective of this thesis was to study various sources of uncertainty and their effects in forest simulators and forest planning systems. The study focused on three notable sources of uncertainty: errors in forest growth predictions, errors in forest inventory data, and stochastic fluctuation of timber assortment prices. Effects of uncertainty were studied using two types of forest growth models, individual tree-level models and stand-level models, and with various error simulation methods. New method for simulating more realistic forest inventory errors was introduced and tested. Also, three notable sources of uncertainty were combined and their joint effects on stand-level net present value estimates were simulated. According to the results, the various sources of uncertainty can have distinct effects in different forest growth simulators. The new forest inventory error simulation method proved to produce more realistic errors. The analysis on the joint effects of various sources of uncertainty provided interesting knowledge about uncertainty in forest simulators.