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Analys av drivkrafter bakom skogsutnyttjandet i Polen, Litauen och Lettland
Get PDFThis work is a part of international research that was carried out in Latvia, Lithuania and Poland, in order to investigate policy drivers behind the harvesting level in these countries. This thesis was focused on Lithuania. However, a comparative analysis of future tendencies for possible harvesting levels in Latvia, Lithuania and Poland was done as well. First of all, it is necessary to point out the importance of a social system and social changes that are of great importance to forestry (Shanz 1999) and have a decisive impact on a harvesting level, especially when a society moves from socialist planning system to market economy. Further, the harvesting level is influenced by interests of stakeholders and their games of power in the decision making process. The interests of stakeholders are formed by ecological, economic and social factors (Krott 2005). These factors form the basis of stakeholders' knowledge that gives directions for further actions (Krott 2005).
The understanding of policy drivers for the harvesting level in Lithuania is not possible without the understanding of Lithuanian stakeholders' interests and their power in the national decision-making process. For defining policy drivers in Lithuania, methodological triangulation (Denscombe 1998), combining literature and inventory data analysis with questionnaire and expert interview methods, was used. The questionnaire and expert interview methods were based on a qualitative research approach and in total thirty-five top administrators of different stakeholders, five from each stakeholder group, were interviewed. However, the questionnaire was made of qualitative, open-ended questions as well as quantitative questions.
The analysis of ecological factors, such as gross annual increment, the total volume, the volume and area of mature woods, total forest area, distribution in the age classes showed, that at the end of the period 1988 – 2006, the harvesting level was higher as compared with the beginning of the same period. However, species composition did not become better, a fact, that can be illustrated by the loss of pine by 2% and increase of grey alder by 1%. Additionally, analysing forest ownership was found that forests, left for restitution, without a proper supervision, significantly decreased the harvesting level. Forest diseases, drought and beetle outbreak increased the harvesting level in 1992 – 1996, but it was done at the expense of losses in the future harvesting.
Literature analysis and the opinion of interviewed experts revealed, that market demand for wood is increasing. However, as the survey and literature analysis showed, the society and forest management traditions were more favourable to a lower harvesting level. According to the respondents, the Ministry of Environment and its Department of Forests, as well as Inventory bodies are the most powerful stakeholders today. Yet, the opinion of the respondents, concerning the power of the stakeholders after 10 years, was that the power of the Ministry of Environment and its Department of Forests as well as inventory bodies will decrease, while the power of wood industry and Non-Governmental Organizations (further NGOs) will increase. This shows that in the future the process of the approval of a harvesting level will be more corporative. In addition, the dominant part of the most important stakeholders in Lithuanian forestry would like the harvesting/increment ratio to increase from 41- 80% to 61 – 100%.
The main goal of the comparative part was to compare the possible future harvesting tendencies in Latvia, Lithuania and Poland. In order to achieve this goal, it was necessary to address the following issues: 1. Ecological, social and economic factors, that create the interests of various groups of stakeholders, 2. Expected harvesting level in the future, 3. The changes of different groups of stakeholders' power in the future, 4. Relations between stakeholders. When completing the second part of the study, the same methodology as in the previous part was used. The results for Latvia and Poland were taken from the theses, written in those countries, and prepared by the colleagues of the work team. After carrying out the research, the following results were obtained.
According to the respondents from different countries, after 10 years power of the Ministry of Environment in Poland and Lithuania, and the Ministry of Agriculture in Latvia, as well as power of inventory bodies in all the three countries will decrease. However, power of wood industry will increase significantly in Latvia, Lithuania and Poland. In addition, according to the respondents, NGOs will become more powerful as well. The analysis of the opinions on the future harvesting /increment ratio showed that the groups of stakeholders would like the harvesting level in all countries to increase from 41 - 80% to 61 – 100%. According to the respondents, economic factors, such as the need for bio fuel as a resource of renewable energy and raw material for wood industry, as well as the importance of wood industries to national economies, will contribute to the increase of the harvesting level. Yet, ecological and social factors, according to the opinion of the respondents, will have a contrary effect.
Referring to the results, presented above, the following conclusion can be made. In all countries, the harvesting level has a tendency to increase; however, in order to make more reliable predictions on the exact level of increase, some additional research is necessary. It is obvious, that the harvesting level will depend on the future development of ecological, economic and social factors as well as on power of different stakeholders.
According to the respondents, the most important future factors will be: the increase of the role of wood industry, mostly by lobbing through politicians, changes in private sector, development of usage of renewable resources, possibility to import wood, labour costs and larger range of non-productive forest functions will continuously generate higher expenditures of state forests. Keeping to the rule of self-sufficiency (in Lithuania and Poland) will require more harvesting in order to cover increasing costs. Ecological requirements should become softer and more rational, and decrease in number. Among the main biological factors, that determine a future harvesting level, the enlargement of total growing stock and distribution in age classes are listed.
To summarize, it is expected, that power of wood industry as well as power of protective organizations will increase in all countries in the future. However, according to the respondents, wood industry will be more powerful than NGOs
Single Tree Level Simulator for Lituanian Pine Forests
Get PDFZiele
Die Forsteinrichtung in Litauen war in den vergangenen Jahrzehnten vom Leitgedanken geprägt, die Optimierung der Bestandsdichte und die Maximierung der Produktivität in jeder Phase der Bestandsentwicklung als gleichrangige Ziele zu betrachten. Deshalb wurden große Anstrengungen in die Herleitung von Bestandswuchsmodellen für gleichaltrige Kiefern- oder Fichtenreinbestände gelegt. Bei der Anwendung dieser Modelle auf gemischte oder in der Umwandlung befindliche Wälder sind allerdings nur ungenaue Resultate zu erzielen. Um den Erfordernissen einer zeitgemäßen Forstwirtschaft gerecht zu werden, sind geeignete Instrumente zur Prognose von Wachstum und Ertrag strukturreicher Wälder vonnöten. Das Hauptziel dieser Arbeit bestand deshalb in der Neuparametrisierung des Einzelbaumwachstumssimulators BWINPro-S (entwickelt für sächsische Wuchsverhältnisse) für Kiefernwälder auf mineralischen Standorten in Litauen.
Zur Zielerreichung dienten folgende Schritte:
• Schaffung und Evaluierung einer Datengrundlage für die Modellierung.
• Abschätzung der Effekte von Konkurrenz um Wuchsraum auf den Durchmesser-, Grundflächen- und Höhenzuwachs von Einzelbäumen.
• Entwicklung eines Durchmesser-Zuwachsmodells sowie Neuparametrisierung der Grundflächen- und Höhenwachstumsmodelle.
• Bestimmung der Einzelbaummortalität durch Konkurrenz um Wuchsraum.
• Entwicklung eines ersten Ansatzes für einen Einzelbaumwachstumssimulator für Kiefer in Litauen.
Hypothesen:
1. Die Standorteigenschaften sind der prägende Faktor für Wachstum und Ertrag von Waldbeständen.
2. Distanzabhängige Konkurrenzindizes zeigen höhere partielle Korrelationen zu Grundflächen- und Höhenzuwachs der Einzelbäume als distanzunabhängige Konkurrenzindizes.
3. Im Vergleich zum Ursprungsmodell BWINPro-S kann durch die Neuparametrisierung eine bessere Anpassung an die Wachstumswirklichkeit in Litauen erzielt werden (in Bezug auf Durchmesser-, Grundflächen- und Höhenzuwachs sowie Mortalitätsschätzung).
4. Ein Einzelbaumwachstumssimulator unterstützt die Entscheidungsträger und Forstplaner in Litauen bei der Optimierung der Waldbewirtschaftung ganz wesentlich.
Material und Methoden
Der Forschungsansatz gliederte sich wie folgt:
1) Vervollständigung der Datengrundlage.
2) Analyse der Konkurrenzverhältnisse.
3) Modellierung des Einzelbaumwachstums.
4) Validierung der neuentwickelten bzw. neuparametrisierten Modelle.
Die Datengrundlage bestand aus Messwerten von 18 Dauerversuchsflächen (PEP) und zwei Validierungsflächen (VP), von denen letztere nur zur Modellüberprüfung herangezogen wurden. Auf allen Flächen stocken vorwiegend aus Naturverjüngung hervorgegangene, einschichtige Kiefernbestände auf kieferntypischen Standorteinheiten. Die Vervollständigung der Datengrundlage erforderte (a) die Erzeugung der Ausgangsdatenbasis, (b) Berechnung fehlender Werte, und (c) Evaluierung der vervollständigten Datengrundlage. Dabei lag das Hauptaugenmerk auf:
• Stichprobenumfang und Schätzung der Populationsmittelwerte.
• Schätzung des potentiellen Standort-Leistungsvermögens.
• Analyse der Beziehung zwischen dem potentiellen Standort-Leistungsvermögen und dem tatsächlichen Waldertrag.
Zur Abschätzung der Effekte von Konkurrenz um Wuchsraum auf den Durchmesser-, Grundflächen- und Höhenzuwachs von Einzelbäumen diente folgendes Vorgehen: Zur Konkurrentenidentifikation wurde ein inverser Lichtkegel mit einem Öffnungswinkel von 60 und 80 Grad konstruiert, dessen nach unten gerichtete Spitze (a) an der Kronenansatzhöhe, (b) an der Höhe der größten Kronenbreite, und (c) am Stammfuß des Zentralbaumes ansetzte. Zur Quantifizierung des Konkurrenzdrucks wurden mit Hilfe der partiellen Korrelationsanalyse 20 Konkurrenzindizes geprüft, von denen letztendlich sechs distanzabhängige und zwei distanzunabhängige Indizes in der weiteren Auswertung Berücksichtigung fanden. Die Modellierung des Einzelbaumwachstums erfolgte in drei Schritten: (a) Entwicklung eines originären Einzelbaum-Durchmesserzuwachsmodells, (b) Neuparametrisierung des Grundflächen- und Höhenzuwachsmodells, und (c) Entwicklung und Neuparametrisierung von Mortalitätsmodellen.
Zur Bewertung einfacher linearer Regressionsmodelle wurden die statistische Signifikanz und das Bestimmtheitsmaß herangezogen. Bei multiplen linearen Regressionsmodellen wurde die Signifikanz jeder unabhängigen Variablen gesondert geprüft (hinsichtlich Normalverteilung, Varianzhomogenität der Residuen und Multikollinearität). Zur Bewertung einfacher nichtlinearer Regressionsmodelle diente in erster Linie das korrigierte Bestimmtheitsmaß, bei multiplen nichtlinearen Regressionsmodellen fanden darüber hinaus Q-Q-Plots (Quantil-Quantil-Diagramme) und die Prüfung auf Varianzhomogenität der Residuen Verwendung.
Die Evaluierung multipler logistischer Regressionsmodelle erfolgte mit Pearsons Chi-Quadrat-Test, die Signifikanz jedes Modellparameters wurde mit der Wald-Statistik geprüft. Die Anpassungsgüte wurde mit Hilfe der Log-Likelihood-Funktion, Cox & Snell- bzw. Nagelkerke-Bestimmtheitsmaßen, Klassifikationstabellen und ROC-Kurven bewertet.
Zur Prüfung der neuparametrisierten Grundflächen- und Höhenzuwachsmodelle wurden die modellierten Werte gegen die Messwerte und darüber hinaus die Residuen gegen die Modellwerte geplottet. Außerdem wurden zur Beurteilung die Verzerrung, die Präzision und die Treffgenauigkeit (sowohl als Absolut- als auch als Relativwerte) herangezogen.
Ergebnisse und Schlussfolgerungen
Die Wachstumsmodelle des Simulators BWINPro-S konnten erfolgreich an die Bedingungen in Litauen angepasst werden. Daraus lassen sich folgende Schlussfolgerungen ableiten:
1. Der stehende Vorrat und die Gesamtwuchsleistung von Kiefernbeständen werden nur z. T. vom standörtlichen Leistungsvermögen determiniert. Die Standorteigenschaften bestimmen das theoretische Leistungsvermögen von Beständen. Ob dieses Potential auch tatsächlich ausgeschöpft werden kann, hängt weitgehend von der Bewirtschaftungsart ab, die geprägt ist durch Beginn, Häufigkeit und Stärke der Durchforstungseingriffe.
2. In Kiefernreinbeständen eignen sich distanzabhängige Konkurrenzindizes besser zur Prognose des mittleren Grundflächenzuwachses als distanzunabhängige Indizes. Zur Beschreibung des Einzelbaum-Durchmesserzuwachses hat sich der Index nach BIGING & DOBBERTIN (1992, in dieser Arbeit als Index CI4 bezeichnet) in Kombination mit der Konkurrentenidentifikationsmethode „Suchkegelansatz in Kronenansatzhöhe, Öffnungswinkel 80 Grad“ als der bestgeeignetste Ansatz erweisen.
3. Der distanzunabhängige Konkurrenzindex nach HEGYI (1974) erreichte die höchsten partiellen Korrelationskoeffizienten mit den mittleren Einzelbaum-Höhenzuwächsen und ergab etwas bessere Resultate bei der Wachstumsprognose als distanzabhängige Indizes. Allerdings waren die Beziehungen zwischen den Konkurrenzindizes und den Einzelbaum-Höhenzuwächsen nur schwach ausgeprägt.
4. Konkurrenz wirkt sich dämpfend auf den Einzelbaum-Durchmesserzuwachs aus, bei zunehmender Konkurrenz sinkt der Zuwachs kontinuierlich ab. Im Gegensatz dazu beschleunigt leichte Konkurrenz das Einzelbaum-Höhenwachstum, bei starker Konkurrenz jedoch wird auch der Höhenzuwachs negativ beeinflusst.
5. Das im Rahmen dieser Arbeit hergeleitete nichtlineare Durchmesserzuwachsmodell ist zur Prognose des Kiefernwachstums bestens geeignet, das Bestimmtheitsmaß beträgt 0,483, die Residuen waren normalverteilt.
6. Die Neuparametrisierung des Grundflächen- und Höhenzuwachsmodells verbesserte die Anpassung an die Wuchsbedingungen in Litauen bedeutend. Eine erste Validierung, durchgeführt für eine Wachstumsprognose über einen 30-jährigen Zeitraum, ergab zufriedenstellende Ergebnisse.
7. Die zwei im Rahmen dieser Arbeit hergeleiteten Mortalitätsschätzer sind zur Vorhersage der natürlichen Absterbeprozesse in den Kiefernbeständen gut geeignet. Beide Ansätze klassifizierten lebende und tote Bäume mit einer Treffgenauigkeit von über 83%, während der in BWINPro-S enthaltene Schätzer nur 77% der Bäume korrekt zuordnete.
8. Der für litauische Verhältnisse neuparametrisierte Wachstumssimulator BWINPro-S ist ein wichtiges Instrument zur Entscheidungsunterstützung für Forstplaner in Litauen.Objectives
In Lithuania, during the most recent decades, the leading theory in forest management and planning combined optimization of forest stand density and maximal productivity at every time point of stand development. Thus, great effort was spent in creating stand level models that are highly effective in managing even-aged monocultures of pine or spruce forests. But these models produce significant errors in mixed or converted forests. In order to meet the requirements of contemporary forestry, appropriate forest management tools are required that would be capable to predict the growth and yield of more structured forests.
Thus, the overall objective for this study was to re-parameterise the single tree level simulator BWINPro-S (developed for forests in Saxony/Germany) for Lithuanian pine forests that grow on mineral sites.
To reach this goal, the following tasks were set:
• To create, and to evaluate, a database for modelling.
• To estimate the impact of competition for growing space on diameter, basal area and height growth of trees.
• To develop a tree diameter model, and re-parameterise basal area and height growth models.
• To assess natural tree mortality induced by competition between trees for growing space.
• To develop the first approach of STLS for pine in Lithuania.
Hypotheses
1. Site quality is the most important factor that affects forest growth and yield.
2. Distance dependent Competition Indices had higher partial correlation with tree basal area and height increment than distance independent Competition Indices.
3. The re-parameterised model based on Lithuanian data fits better under Lithuanian conditions (regarding diameter, basal area, height increment and mortality) than the original model BWINPro-S.
4. A single tree level simulator provides valuable support for decision makers and forest managers to improve forest management in Lithuania.
Materials and methods
To reach the main goals of this study, the research was structured to four sections: 1) Database completion, 2) Analysis of competition, 3) Modelling tree growth, 4) Validation of developed models.
The database consisted of analytical data from 18 permanent experimental plots (PEPs) and 2 Validation Plots (VP) that were used only for the validation of the models. All plots (PEPs and VP) represent mainly naturally regenerated, single layer pine stands that grow on very typical pine sites. Database completion involved (a) establishment of the initial database, (b) modelling of missing data values and (c) evaluation of the complete database, which focused on:
• Sample size and estimation of the population’s mean
• Estimation of potential site productivity
• Estimation of relationship between potential site productivity and forest yield
In order to estimate the impact of competition for growing space on diameter, basal area and height growth of trees the following methods were used. To select the competitors, this study focuses on three separate positions for setting the inverse cone: a) at the height of the crown base, b) at the height of widest crown width, and c) at the stem base. The opening angle of the search cone was either 60 or 80 degrees. To estimate the competition, the study by partial correlation analysis evaluated a total of 20 competition indices, of which six distance dependent and two distance independent CIs were applied in the research programme. Modelling of tree growth was divided into three parts: a) development of an original tree diameter increment model, b) re-parameterisation of basal area and height increment models, and c) development of new natural mortality models and re-parameterisation of natural mortality models.
Simple linear regression models were evaluated by estimating each model’s statistical significance and coefficient of determination. Statistical analysis of multiple linear regression models was enlarged by conducting further tests: statistical significance was checked for each independent variable: regression assumptions (concerning normal distribution and homogeneity of variance of the models’s residuals, and multicollinearity of the independent variables) were checked.
Simple nonlinear regression models were evaluated mainly by adjusted coefficient of determination. For multiple nonlinear regression models, regression assumptions were also checked by producing normal Q-Q plots and by checking homogeneity of variance of model’s residuals.
Multiple logistic regression models were evaluated by estimating each model’s statistical significance with Pearson’s chi square statistics and the statistical significance of each model’s parameters with Wald statistics. Goodness of fit was estimated by using log likelihood function values, Cox-Snell and Nagelkerkle’s coefficients of determination, classification tables and ROC curves.
The re-parameterised basal area and height increment models were validated by plotting each model’s predicted values against observed values. Also each model’s residuals were plotted against predicted values. Bias, relative bias, precision, relative precision, accuracy and relative accuracy when comparing predicted and observed values were estimated as well.
Results and Conclusions
The growth models used in the BWINPro-S simulator were successfully re-parameterised for Lithuanian growth conditions. Thus the study may state these conclusions:
1. The accumulated standing volumes and overall productivity of pine stands only partially depends on the productivity potential of sites. Site quality defines the growth potential that could be reached in a stand. The realization of growth potential largely depends on the growing regime in the stand that is defined by the beginning, frequency and intensity of thinning.
2. In pure pine stands, distance dependent competition indices show greater capabilities to predict mean annual basal area increment than distance independent indices. Competition index (coded as CI4 in this study) proposed by BIGING & DOBBERTIN (1992) combined with the selection method height to crown base with opening angle of 80 degrees is recommended as the most efficient for describing the individual diameter growth of trees.
3. HEGYI\\\'S (1974) distance independent competition index scored the highest partial correlation coefficients and produced slightly better results than distance dependent competition indices in predicting mean annual height increment for individual trees. Yet, the generally poor performance of competition indices to predict height increment of individual pine trees was also recorded.
4. Competition has a purely negative impact on tree diameter growth. Increasing competition leads to steady decreases in diameter increment. Nevertheless, although a small amount of competition does stimulate tree height growth, stronger competition has a lasting negative impact on tree height growth.
5. The nonlinear diameter increment model, developed by this study, has high capabilities to predict growth of pine trees. The model’s coefficient of determination value was equal to 0.483. The distribution of the model’s residuals fulfilled the requirements of regression assumptions.
6. The re-parameterisation of the BWINPro-S basal area and height increment models for use in Lithuanian permanent experimental plots, increased their performance. During the first validation procedure, based on 30 years growth simulation, the re-parameterised models produced reliable results.
7. Two individual mortality models, developed by this study, showed very high capabilities to predict the natural mortality of pine trees. The distance dependent natural mortality model scored slightly better results. Both models managed to correctly classify dead and living trees, slightly more than 83% of the time. The re-parameterisation of the BWINPro-S natural mortality model increased its ability to predict the natural mortality of pine trees in Lithuania. Correctly classifying growing and dead trees increased by 6%, from 77 to 83%.
8. BWINPro-S simulator with re-parameterised growth models for Lithuanian conditions is a valuable support tool for decision makers and forest managers in Lithuania.Darbo tikslai
Lietuvoje ilgą laiką ūkininkavimas miškuose buvo grindžiamas medynų tankumo optimizavimu ir maksimalaus medynų produktyvumo siekimu visose medynų vystymosi stadijose. Mokslininkai dėjo daug pastangų kurdami medyno lygmens našumo modelius. Šie modeliai buvo patikimi ūkininkaujant vienaamžiuose medynuose. Tačiau jie yra sunkiai pritaikomi mišriuose medynuose. Siekiant patenkinti šiuolaikinio miškininkavimo poreikius, kai vis didesnis dėmesys skiriamas mišrių medynų su keliais ardais auginimui, reikalingi nauji modeliai, kurie sėkmingai prognozuotų mišrių medynų augimą, jų našumą bei reakcijas į įvairias ūkines priemones.
Todėl pagrindinis šio darbo tikslas yra parametrizuoti iš naujo BWINPro-S medžio lygio stimuliatorių sukurtą Vokietijos rytinėje žemėje Saksonijoje taip pritaikant jį Lietuvos sąlygoms.
Šiam tikslui pasiekti, buvo suformuluoti sekantys uždaviniai:
• Paruošti ir įvertinti duomenų bazę reikalingą modeliavimui.
• Įvertinti medžių tarpusavio konkurencijos įtaką medžių skersmens, skerspločių sumos ir aukščio prieaugiui.
• Sukurti naują medžio skersmens prieaugio modelį ir parametrizuoti iš naujo skerspločių sumos bei aukščio modelius.
• Įvertinti pušynų savaiminio retinimosi dėsningumus atsižvelgiant į medžių tarpusavio konkurenciją dėl augimo erdvės.
Tikrintinos hipotezės:
1. Medyno augavietė yra svarbiausias veiksnys, lemiantis medynų našumą ir produktyvumą.
2. Konkurencijos indeksai, įvertinantys atstumą tarp medžių, turi didesnes dalinės koreliacijos reikšmes su medžių skerspločių sumos, skersmens ir aukščio prieaugiais lyginant su konkurencijos indeksais, neįvertinančiais atstumo tarp medžių.
3. Parametrizuoti naujai, panaudojant Lietuvoje augančių pušynų duomenis, modeliai geriau tinka Lietuvos sąlygoms (pagal skersmens, skerspločių sumos ir aukščio prieaugį bei savaiminį retinimąsi) lyginant su modeliais, sukurtais Vokietijos sąlygoms.
4. Medžio lygmens augimo simuliatorius yra naudinga priemonė miškų valdytojams siekiant pagerinti ūkininkavimo kokybę Lietuvoje.
Darbo metodai
Šis darbas buvo suskirstytas į keturias pagrindines dalis: 1) duomenų bazės suformavimas, 2) konkurencijos indeksų analizė, 3) medžių augimo modeliavimas, 4) augimo modelių patikrinimas.
Duomenų bazę sudarė 20 pastovių tyrimo barelių, iš kurių 18 buvo skirti modelių kūrimui ir 2 modelių patikrinimui. Tyrimo bareliai buvo įsteigti natūraliai atsikūrusiuose vienaardžiuose pušynuose, augančiuose tipingose pušiai augavietėse. Duomenų bazės įvertinimas buvo atliekamas tokiais etapais: (a) pirminės duomenų bazės suformavimas, (b) trūkstamų matavimų modeliavimas ir (c) duomenų bazės įvertinimas yra grindžiamas:
• Imties dydžiu ir populiacijos vidurkio nustatymo tikslumu.
• Potencialaus medynų našumo įvertinimu.
• Ryšių tarp potencialaus medynų našumo ir medynų našumo bei produktyvumo įvertinimu.
Vertinant konkurencijos įtaką medžių skersmens, skerspločių sumos ir aukščio prieaugiui, buvo naudoti konkurentų parinkimo ir konkurencijos įvertinimo metodai.
Konkuruojantys medžiai buvo atrenkami pagal apversto kūgio viršūnę, sutapatintą su tiriamojo medžio a) lajos pradžia, b) plačiausia lajos vieta, ir c) medžio šaknies kakleliu. Kūgio kampas buvo keičiamas nuo 60 iki 80 laipsnių. Iš viso buvo tiriama dvidešimt konkurencijos indeksų (du konkurencijos indeksai, nepriklausantys nuo atstumo tarp medžių ir aštuoniolika konkurencijos indeksų, priklausančių nuo atstumo tarp medžių). Konkurencijos indeksai vertinti taikant dalinės koreliacijos metodus.
Medžių augimo modeliavimas buvo atliekamas trim etapais: a) originalaus medžių skersmens prieaugio modelio sukūrimas, b) medžių skerspločių sumos ir medžių aukščio prieaugio modelių parametrizavimas naujai, c) sukūrimas originalių ir parametrizavimas naujai jau esamų natūralaus retinimosi modelių.
Paprastieji tiesinės regresijos modeliai buvo vertinami naudojant jų statistinį reikšmingumą ir skaičiuojant determinacijos koeficientą. Daugialypių tiesinės regresijos modelių statistinė analizė buvo išplėsta papildomais testais: statistinis reikšmingumas tiriamas kiekvienam nepriklausomam kintamajam, taip pat vertinama ar modelis tenkina pagrindines regresijos sąlygas (nepriklausomi kintamieji nėra tarpusavyje susieti, modelio liekanos turi normalųjį skirstinį, yra tolygiai išsidėstę).
Paprastieji netiesinės regresijos modeliai buvo vertinami skaičiuojant koreguotąjį determinacijos koeficientą. Atliekant daugialypių netiesinės regresijos modelių analizę taip pat buvo tikrinama ar tenkinamos regresijos sąlygos. Logistiniai savaiminio retinimosi modeliai buvo vertinami naudojant šiuos statistinius parametrus: modelio X2 suderinamumo kriterijų, Voldo kriterijų, didžiausio tikėtinumo funkcijos vertę, Kokso-Snelo ir Nagelkerkės pseudodeterminacijos koeficientus, klasifikavimo lenteles ir klasifikatoriaus jautrumo ir specifiškumo (ROC) kreives.
Parametrizuoti naujai medžių skerspločių sumos ir medžių aukščio prieaugių modeliai buvo tikrinami lyginant modeliuotas medžių skersmens ir aukščio reikšmes su realiai išmatuotomis reikšmėmis analizuojamo periodo pabaigoje. Taip pat buvo tiriamas modelių liekanų išsidėstymas modeliuojamų verčių atžvilgiu. Galiausiai, poslinkio, santykinio poslinkio, tikslumo, santykinio tikslumo, tikslumo be poslinkio ir santykinio tikslumo be poslinkio buvo naudojami vertinant modelių prognozes.
Rezultatai ir išvados
Augimo modeliai, naudojami BWINPro-S medžio lygio simuliatoriuje, buvo sė
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Linking forest policy issues and decision support tools in Europe
No full textWhile very many decision-support (DS) tools (i.e. models and decision support systems (DSS)) have been developed to address forest management problems in Europe, the use of such tools in supporting forest policy processes remains limited. Additionally, while there has been very limited sharing of these tools between European countries, there may be an untapped potential for both users and developers in this area.
This paper focuses on improving understanding and capacities in the use of forest DS tools for decision making by identifying major forest policy areas, tools available to support them, compatibility of existing tools with the requirements of forest policy areas, potential areas where tools may be shared between countries and factors limiting the use of DS tools in forest policy.
Data collection was based on expert interviews. The questionnaire, which comprised a combination of open- and close-ended questions, was forwarded to experts via email. Expert interviews were completed via Skype with the input of one policy specialist and one modeller/decision support specialist from each country.
This study categorised key forest policy areas and the DS tools available to support them. Almost one third of these forest policy areas were not addressed by any DS tool. The analysis also revealed that DS tools are mainly developed to assist scientists and policy decision makers to address smaller spatial scales, that they are more orientated to single decision makers with a predominant focus on market wood products. In addition, through an attribute-matching exercise, the DS tools that could potentially be used in other countries to support similar forest policy areas were also identified.
Interviews highlighted some of the reasons why DS tools are seldom used in policy making processes; these include a lack of trust in the actual use of the tools as well as a perception of inadequacy for the specifics of real policy process. This research provides a detailed overview of existing DS tools and the forest policy areas that they address. It further provides information on how to address or reduce the gap between DS tools functionalities and requirements from policy makers
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Policy drivers behind forest utilisation in Lithuania in 1986-2007
Get PDFAfter regaining the independence, Lithuania was in the process of making transition to the market economy, yet radical societal shifts only moderately affected Lithuanian forestry. This study evaluates the main drivers that stimulated or decreased forest utilisation. Review of numerous sources reveals that the major drivers towards increased utilisation were the economic transition and changes in the resource base. These have been counterbalanced primarily by deeply-rooted normativism, increasing environmental restrictions, economic model of State forestry and sluggish land reform. The study shows that seeking to understand the dynamics of forest utilisation, it is insufficient to focus solely on the available forest inventory as is typically done in forecasts of timber removals. Instead, a holistic analysis is needed, taking into account, inter alia, institutional norms and developments outside the forest sector
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