• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 164
  • 53
  • 31
  • 30
  • 20
  • 11
  • 7
  • 6
  • 4
  • 4
  • 4
  • 3
  • 3
  • 3
  • 3
  • Tagged with
  • 437
  • 58
  • 47
  • 43
  • 35
  • 27
  • 26
  • 21
  • 20
  • 19
  • 18
  • 16
  • 16
  • 15
  • 15
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
311

Juridictionnalisation de la répression pénale et institution du ministère public : étude comparative France-Angleterre / Juridicial nature of repression and Public Prosecutor : comparative analysis France-England

Jeanne, Nicolas 11 March 2015 (has links)
En France comme en Angleterre, le ministère public a historiquement vocation à garantir la forme juridictionnelle de la répression-pénale. A l'inverse, la juridictionnalisation de la répression pénale constitue une limite traditionnelle aux prérogatives du ministère public. Ainsi, alors que le premier rend toujours possible la juridictionnalisation et légitime la répression, la seconde limite légitimement le champ des possibles offerts au ministère public. Pourtant, la liaison qui paraît si évidente entre la juridictionnalisation de la répression pénale et l'institution du ministère public s'efface progressivement en nuances. Les législateurs français et anglais, encouragés par la jurisprudence, ont considérablement renforcé les pouvoirs d’enquête et de traitement infrajuridictionnels du ministère public évinçant par là la juridictionnalisation de la répression. Et même si la juridictionnalisation peut paraître préservée lorsqu'il s'agit pour le ministère public d'obtenir une coercition et une rétribution ultimes, celle-ci s'avère en réalité sans substance. Le contrôle à priori du juge de l'autorisation des pouvoirs d'enquête juridictionnalisés est souvent purement formel et ne peut permettre de contredire la nécessité d'ordonner tel ou tel acte qui serait requis par le ministère public, alors que le contrôle a posteriori du juge de l'annulation des actes d'enquête est lui déficient et aléatoire. La garantie d'un usage régulier des pouvoirs d'enquête et de traitement des infractions ne saurait pourtant venir d'une juridictionnalisation de l'institution du ministère public. La comparaison de l'organisation des ministères publics français et anglais laisse apparaître que les solutions qui sont envisagées l'indépendance et impartialité du ministère public français ne seraient pas suffisantes. C'est une restauration de la juridictionalisation des fonctions de l'institution, conforme à sa ratio profonde qu'il convient de mettre en œuvre. / In France, like in England, the Public Prosecutor is historically intended to ensure the judicial nature of criminal justice. Reciprocally, the strengthening of the judicial nature of the criminal justice traditionally restricts the prerogatives of the Public Prosecutor's Office. However, the link between the reinforcement of the judicial nature of the criminal justice and the existence of the Public Prosecutor, albeit obvious, evaporates slowly in multiple shades. The French and the English lawmakers, supported by case law, have come to considerably strengthen the Public Prosecutor's investigation and pre-trial powers, thus ousting the judicial nature of the criminal justice. Although it may seem that the judicial nature of repression is preserved when the Public Prosecutor is required to obtain coercive measures or ultimate retribution, it turns out to be deprived of substance. An a priori control by a judge who grants judicial investigative powers to the Public Prosecutor is always formalistic, whereas an a posteriori control by a judge who may annul decisions taken during the investigation is flawed and random. However, a guarantee of a regular use of investigative powers and of treatment of offenses cannot come out of the strengthening of judicial nature of the Public Prosecutor. A comparative analysis of the structure of the Public Prosecutor’s Office in France and in England reveals that the dues that are to be considered -independence and impartiality of the French Public Prosecutor -do not suffice. It is a reestablishment of the judicial functions of the body, coherent with its true ratio, that should be implemented.
312

Tree and oil palm water use: scaling, spatial heterogeneity and temporal dynamics (Sumatra, Indonesia)

Ahongshangbam, Joyson 08 October 2020 (has links)
No description available.
313

Influência do tratamento de superfície em diferentes substratos na resistência de união à cimento resinoso autoadesivo /

Almeida, Cláudia Cristina Miranda de Souza. January 2019 (has links)
Orientador: Paula Carolina Komori de Carvalho / Coorientador: Rodrigo Othávio de Assunção e Souza / Banca: Carolina Machado Martinelli Lobo / Banca: Eduardo Miyashita / Resumo: As reabilitações orais com próteses fixas na Odontologia passaram por grande evolução ao serem estabelecidos e firmados os conceitos de adesão química. A alta demanda estética desses tratamentos faz com que as cerâmicas que são materiais altamente biocompatíveis e com ótimas propriedades mecânicas, sejam amplamente utilizadas nas reabilitações orais. Nas próteses sobre implantes, o processo de cimentação de restaurações cerâmicas acontece sobre conexões metálicas em titânio (Ti), cobalto-cromo (CoCr) ou infra-estruturas personalizadas em zircônia (Zr). O processo de cimentação necessita de algumas etapas para promover o tratamento de superfície das restaurações indiretas e variam de acordo com a especificidade de cada substrato. O objetivo deste estudo foi avaliar a influência do tratamento de superfície em diferentes substratos de conexões protéticas utilizando primer e sistema adesivo universal contento o monômero funcional 10-MDP na resistência de união à cimento resinoso autoadesivo, por meio de teste mecânico de cisalhamento. Foram confeccionadas 120 amostras (n= 40 de Ti, CoCr e Zr) as quais foram incluidas em blocos de resina acrílica. As amostras foram subdivididas em 12 grupos (n=10), 3 grupos representam o controle e não tiveram a superfície tratada, os demais grupos tiveram a superfície tratada com primer monocomponente ou sistema adesivo universal contendo 10-MDP. Em seguida foi confeccionado um cilíndro de cimento resinoso (2mm de altura X 2,37mm de diâmetro) com... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Oral rehabilitations with fixed prostheses in Dentistry had grown with great evolution when the concepts of chemical adhesion were established and signed. The high aesthetic demand of these treatments makes Ceramics, that are highly biocompatible materials and with good mechanical properties, widely used in oral rehabilitation. In implant prostheses, the process of cementation happens between ceramic restorations on metallic connections in titanium (Ti) and / or cobalt chromium (CoCr) or custom zirconia (Zr) infrastructures. During the cementing process of ceramic restorations some surface treatment steps are required, these steps varying according to the type of specific ceramics. The aim of this study was to evaluate the influence of surface treatment on different substrates of prosthetic connections using primer and universal adhesive system containing 10-MDP functional monomer on bond strength to self-adhesive resin cement by mechanical shear test. One hundred and twenty samples (n = 40 Ti, CoCr and Zr) were made and included in blocks of acrylic resin. The samples were subdivided into 12 groups (n = 10), 3 groups represent the control and did not have the surface treated, the other groups had the surface treated with single component primer or universal adhesive system containing 10-MDP. Then a resin cement cylinder (2mm height X 2,37mm diameter) was made with the aid of a teflon device to measure the exact dimensions. Twenty four hours after the cylinders were made, the... (Complete abstract click electronic access below) / Mestre
314

Longevity of Crown Margin Repairs Using Glass Ionomer: A Retrospective Study

Watson, Justin I. January 2020 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Objectives: Repair of crown margins may extend the functional life of existing crowns. However, the longevity of such treatment is unknown. This study determined the survival time of crown margin repairs (CMR) with glass-ionomer (GI) and resin-modified glass-ionomer cements. Methods: We queried axiUm (Exan Group, Coquitlam, BC, Canada) database for permanent teeth that underwent CMR in the Graduate Operative Dentistry Clinic, Indiana University School of Dentistry (IUSD), Indianapolis, Ind., USA, from January 1, 2006 through January 1, 2018. Since there is no CDT code for the CMR procedure, CDT codes for resin-composite and GI restorations (D23XX) were queried; these patients also had treatment notes that indicated CMR. The final data set included patient ID, birth date, gender, dates of treatments, CDT codes, tooth type, tooth surface and existing findings. Two examiners developed guidelines for record review and manually reviewed the clinical notes of patient records to confirm CMR. Only records that were confirmed with the presence of CMR were retained in the final dataset for survival analysis. Survival time was calculated by Kaplan-Meier statistics and a Cox Proportional Hazards model was performed to assess the influence of selected variables (p < 0.05). Results: 214 teeth (115 patients) with CMR were evaluated. Patient average age was 69.4  11.7 years old. Posterior teeth accounted for 78.5 percent (n = 168) of teeth treated. CMRs using GI had a projected 5-year survival rate of 62.9 percent (K-M Analysis) and an 8.9 percent annual failure rate. Cox Proportional Hazards Regression analysis revealed that none of the factors examined (age, gender, tooth type) affected time to failure. Conclusion: CMRs may extend the longevity of crowns with defective margins. Larger EHR studies or case control studies are needed to investigate other variables, such as the caries risk status or the severity of defects that may affect the survival rate of CMRs.
315

Ett svenskt kronvittnessystem? Att vara eller inte vara ett kronvittne

Markusson, Caroline January 2014 (has links)
Kronvittnessystem har vid ett flertal tillfällen diskuterats i svensk politik som en möjlig åtgärd i arbetet mot organiserad brottslighet. Ett kronvittne är en person som vittnar om sin egen eller andras brottslighet och på grund av detta erhåller ett mildare straff för sina brott. Flera andra länder använder sig av kronvittnessystem på grund av de nyttor som finns med det, men forskning visar att det även finns problem med systemet. Syftet med denna studie är att besvara frågan vad kriminella personer har för uppfattning om att kronvittna i ett kronvittnessystem. Kvalitativa intervjuer genomfördes med före detta kriminella med erfarenhet av organiserad brottslighet. Resultaten visade att det fanns många aspekter av att kronvittna som skulle leda till problem. Det mest framträdande resultatet var bilden av det hot och våld som blir en effekt mot den person som kronvittnar, samt mot denna persons familj och vänner. Det rådde stor konsensus om att ett kronvittnessystem är farligt för människor och för med sig svåra konsekvenser. Resultaten pekar på att kriminella personer inte vill se ett kronvittnessystem införas i Sverige. / Crown witness systems have previously been discussed in Swedish politics as a possible way to fight organized crime. A crown witness, or supergrass, is a person who in return for giving information about his or her own crime or another person’s crime, is rewarded with a penalty discount. Many other countries use crown witness methods because of the positive things with doing so, but studies also show that there are problems with such a procedure. The purpose of this study is to answer the question what opinions criminals have about being a crown witness/accomplice witness within a crown witness system. The method that was used was interviews with former criminals who had experience regarding organized crime. The results showed that there are many aspects of testifying as a crown witness that would lead to problems. The most important result was that the crown witness and its family and friends would as an affect of the testimony be subjects of threats and violence against them. It was agreed that a crown witness system is dangerous for people and lead to severe consequences. The results indicate that criminals do not want to see a crown witness system be incorporated in Sweden.
316

Automated Tree Crown Discrimination Using Three-Dimensional Shape Signatures Derived from LiDAR Point Clouds

Sadeghinaeenifard, Fariba 05 1900 (has links)
Discrimination of different tree crowns based on their 3D shapes is essential for a wide range of forestry applications, and, due to its complexity, is a significant challenge. This study presents a modified 3D shape descriptor for the perception of different tree crown shapes in discrete-return LiDAR point clouds. The proposed methodology comprises of five main components, including definition of a local coordinate system, learning salient points, generation of simulated LiDAR point clouds with geometrical shapes, shape signature generation (from simulated LiDAR points as reference shape signature and actual LiDAR point clouds as evaluated shape signature), and finally, similarity assessment of shape signatures in order to extract the shape of a real tree. The first component represents a proposed strategy to define a local coordinate system relating to each tree to normalize 3D point clouds. In the second component, a learning approach is used to categorize all 3D point clouds into two ranks to identify interesting or salient points on each tree. The third component discusses generation of simulated LiDAR point clouds for two geometrical shapes, including a hemisphere and a half-ellipsoid. Then, the operator extracts 3D LiDAR point clouds of actual trees, either deciduous or evergreen. In the fourth component, a longitude-latitude transformation is applied to simulated and actual LiDAR point clouds to generate 3D shape signatures of tree crowns. A critical step is transformation of LiDAR points from their exact positions to their longitude and latitude positions using the longitude-latitude transformation, which is different from the geographic longitude and latitude coordinates, and labeled by their pre-assigned ranks. Then, natural neighbor interpolation converts the point maps to raster datasets. The generated shape signatures from simulated and actual LiDAR points are called reference and evaluated shape signatures, respectively. Lastly, the fifth component determines the similarity between evaluated and reference shape signatures to extract the shape of each examined tree. The entire process is automated by ArcGIS toolboxes through Python programming for further evaluation using more tree crowns in different study areas. Results from LiDAR points captured for 43 trees in the City of Surrey, British Columbia (Canada) suggest that the modified shape descriptor is a promising method for separating different shapes of tree crowns using LiDAR point cloud data. Experimental results also indicate that the modified longitude-latitude shape descriptor fulfills all desired properties of a suitable shape descriptor proposed in computer science along with leaf-off, leaf-on invariance, which makes this process autonomous from the acquisition date of LiDAR data. In summary, the modified longitude-latitude shape descriptor is a promising method for discriminating different shapes of tree crowns using LiDAR point cloud data.
317

PLANTING DEPTH OF TREES - A SURVEY OF FIELD DEPTH, EFFECT OF DEEP PLANTING, AND REMEDIATION

Rathjens, Richard G. 03 September 2009 (has links)
No description available.
318

Host-Guest Systems Based on Crown Ether, Cryptand, and Pseudocryptand Hosts with Paraquat, Diquat, Secondary Ammonium, and Monopyridinium Salt Guests

Huang, Feihe 25 March 2005 (has links)
Supramolecular host-guest chemistry is a topic of great current interest. However, the further development of host-guest chemistry is still limited by the number of available host-guest recognition motifs. This makes it necessary and valuable to find new host-guest recognition motifs and apply known host-guest recognition motifs in the preparation of novel supramolecular systems. By comparing the crystal structures of the host and its taco complex, we proved that folding is a necessary step during the formation of taco complexes. Based on the known bis(m-phenylene)-32-crown-10/paraquat recognition motif, the first solid-state supramolecular poly(taco complex) was prepared. We demonstrate not only that bis(m-phenylene)-32-crown-10-based cryptands are powerful hosts for paraquat derivatives compared with the simple crown ether, but also that cooperative complexation can be obtained with the cryptand structure. It was shown that the significant improvement in complexation was the result of the combination of the preorganization of the cryptand hosts and the introduction of additional and optimized binding sites. Furthermore, it was demonstrated that improved complexation of bis(secondary ammonium) and bisparaquat salts could also be achieved by the formation of the pseudocryptand structure. We also prepared two dimers of inclusion cryptand/paraquat complexes driven by dipole-dipole and face-to-face p-stacking interactions. An interesting complex based on dibenzo-24-crown-10 and diquat was prepared. In its crystal structure the diquat guest lies in the concave cavity provided by two dibenzo-24-crown-8 hosts. Monopyridinium-based [2]- and [3]-pseudorotaxanes were prepared based on the newly discovered bis(m-phenylene)-32-crown-10/monopyridinium salt and cryptand/monopyridinium salt recognition motifs. Inspired by the formation of solid-state taco complexes between bis(m-phenylene)-32-crown-10 and paraquat derivatives, we designed and synthesized the first cylindrical bis(crown ether) host for paraquat derivatives and studied its complexation with paraquat. We prepared three slow-exchange C3-symmetric inclusion complexes based on a newly discovered cryptand/trispyridinium recognition motif, in which 1,3,5-trispyridiniumbenzene salts act as guests. Finally the application of several new and known recognition motifs in the preparation of a supramolecular poly[3]pseudrotaxane, and the first pseudorotaxane-type supramolecular star-shaped polymer, and the first supramolecular hyperbranched polymer was discussed. / Ph. D.
319

​ Soilborne Pathogens Of Strawberry In The Central Coast Region Of California: ​ Survey And Cover Cropping With Wheat For Management Of Macrophomina Phaseolina

Steele, Mary 01 June 2023 (has links) (PDF)
Surveys of the four major soilborne pathogens of strawberry (Fusarium oxysporum f. sp. fragariae, Macrophomina phaseolina, Phytophthora spp., and Verticillium dahliae) to determine their relative prevalence were conducted in Watsonville-Salinas, CA in 2021 and in Santa Maria, CA in 2022. All four major pathogens were detected at relatively similar prevalence in Watsonville-Salinas, between 22% and 31% of sampled fields. In Santa Maria, M. phaseolina was far more prevalent at 52% of sampled fields, the other three falling between 14% and 17%. Additionally replicated greenhouse and field trials were conducted to evaluate the effects of wheat as a single season cover crop on Macrophomina root rot of strawberry and the soil microbiome. Greenhouse trials and the first year of the field trial are described here and demonstrate a lack of substantial disease mitigation or pathogen reduction in the soil following wheat growth compared to no-treatment control. Significant changes were seen in the soil microbiome following wheat growth, including the significant amplification of several bacterial species known to be antagonistic to plant-pathogenic fungi.
320

Evolution of Plants : a mathematical perspective

Lindh, Magnus January 2016 (has links)
The Earth harbors around 300 000 plant species. The rich and complex environment provided by plants is considered a key factor for the extraordinary diversity of the terrestrial fauna by, for example, providing food and shelter. This thesis contributes to the understanding of these questions by investigating how the interplay of physiology, demography, and evolution gives rise to variation and diversity in fundamental plant traits. This will help us answer questions such as: How has this amazing diversity of plant species emerged? Which mechanisms maintain diversity? How are plant strategies and plant diversity influenced by variations in the environment? A plant faces multiple problems to survive and reproduce successfully. These problems can be modeled by considering traits, trade-offs and a fitness measure. For example: How to maximize growth rate, while maximizing structural stability? I will investigate four plant models in order to understand the function of plants, and mechanisms promoting diversity.  Paper I: We study how annual plants with and without growth constraints should optimize their flowering time when productivity or season length changes. With a dynamic ontogenetic growth model and optimal control theory we prove that a bang-bang reproductive control is optimal under constrained growth and constant mortality rate. We find that growth constraints can flip the direction of optimal phenological response for increasing productivity. The reason is that the growth rate of vegetative mass saturates at high productivity and therefore it is better to flower earlier and take advantage of a longer reproductive period. If season length extends equally both in the beginning and the end of the season, growth constraints control the direction of the optimal response as well. Our theory can help explaining phenological patterns along productivity gradients, and can be linked to empirical observations made on a calendar scale. Paper II: We introduce a new measure of tree crown-rise efficiency based on the loss of biomass of the tree during growth. The more mass the tree looses during growth, the less crown-rise efficient it is. Top-heavy shapes loose more biomass than bottom-heavy shapes. Light-use efficiency is defined as the mean light assimilation of the leaves in the crown times the ratio of leaf mass and total mass. We then study the trade-off between light-use efficiency to crown-rise efficiency for tree crown shapes. We assume that the total tree mass is constant, and a constant vertical light gradient represent the shading from a surrounding forest. We find large differences in crown shapes at intermediate vertical light gradient, when both self-shading and mean-field shading are important, suggesting light-use vs crown-rise efficiency as a new trade-off that can explain tree diversity. Our crown-rise efficiency measure could easily be integrated into existing forest models. Paper III: We extend an evolutionary tree crown model, where trees with different heights compete for light, with drought-induced mortality rates depending on ground-water availability and the depth of an optional taproot. The model does not include competition for ground water. Our model explains how ground-water availability can shape plant communities, when taproot and non-taproot strategies can coexist, and when only one of these strategies can persist. We investigate how emerging plant diversity varies with water table depth, soil water gradient and drought-induced mortality rate. The taproot enables plants to reach deep water, thus reducing mortality, but also carries a construction cost, thus inducing a trade-off. We find that taproots maintain plant diversity under increasing drought mortality, and that taproots evolve when groundwater is accessible at low depths. There are no viable strategies at high drought mortality and deep water table. Red Queen evolutionary dynamics appear at intermediate drought mortality in mixed communities with and without taproots, as the community never reaches a final evolutionarily stable composition. Paper IV: We extend a size-structured plant model, with self-shading and two evolving traits, crown top-heaviness and crown width-to-height ratio. The model allows us to identify salient trade-offs for the crown shape. The most important trade-off for top-heaviness is light-use efficiency vs crownrise efficiency, and the most important trade-off for width-to-height ratio is self-shading vs branch costs. We find that when the two traits coevolve; the outcome is a single common evolutionarily stable strategy (ESS), far away from the highest net primary production (NPP). When only sun angle is decreasing with increasing latitude both the crown width-to-height ratio and crown top-heaviness decrease. However, when light response in addition to the sun angle decreases with increasing latitude, the crown width-to-height ratio is nearly invariant of latitude except at low site productivity when the ratio decreases with latitude. Top-heaviness is always decreasing with increasing latitude. Finally, we find that crown top-heaviness increases with the NPP or leaf-area index (LAI) at ESS, but crown width-to-height ratio is maximal at an intermediate NPP or LAI. / Artikel I: Arters reproduktionsframgång (fitness), till exempel antal avkommor eller frön som produceras under livet, är ofta avgörande för huruvida de är evolutionärt framgångsrika eller inte. Här undersöker vi hur ettåriga växter med eller utan tillväxtbegränsningar ska optimera sin blomningstid när produktivitet eller säsongslängd ändras. Det är optimalt att gå direkt från tillväxt till blomning när tillväxten är begränsad och dödligheten är konstant. Vid ökad produktivitet sker blomningen tidigare med tillväxtbegränsningar men senare utan tillväxtbegränsningar, vilket beror på att med tillväxtbegränsningar ökar den vegetativa massan långsamt. Därför är det bättre att blomma tidigare och ta tillvara på en längre reproduktionsperiod. Vi får samma resultat om säsongslängden ökar lika mycket i början och slutet av säsongen. Vår teori kan bidra till att förutsäga blomningstider vid produktivitetsförändringar och säsongsförändringar. Artikel II: Tillväxten hos träd kan begränsas av brist på ljus, vatten, och näring, men också genom förlust av grenar. Vi introducerar ett nytt mått på tillväxteffektiviteten hos trädkronor baserat på förlust av biomassa under trädets tillväxt. Ju mer massa trädet förlorar under tillväxt, desto mindre tillväxteffektiva är de. Topptunga former förlorar mer biomassa än bottentunga former. Vi studerar avvägningar mellan ljuseffektivitet och tillväxteffektivitet för trädformer, där ljuseffektiviteten definieras som medelljusupptaget för löven i kronan. Vi antar en konstant totalmassa, och en statisk vertikal skuggning som representerar skuggningen från en omgivande skog. Vi hittar stora skillnader i kronformer vid en medelhög skuggning, då både självskuggningen och medelskuggningen har betydelse. Vårt mått för tillväxteffektivitet kan enkelt integreras i existerande skogsmodeller. Studien visar att avvägningar mellan tillväxteffektivitet och ljuseffektivitetet kan vara viktig för mångfalden av trädformer i en skog. En överraskande upptäckt är att konformade eller sfäriska trädkronor aldrig är effektiva, men däremot timglasformade kronor. Artikel III: Växter kan försvara sig på olika sätt mot torka, till exempel genom att rulla ihop bladen eller genom att reproducera tidigare och därigenom undvika uttdragen torka. Här undersöker vi fördelarna med en pålrot vid torka. En pålrot är en rot som växer nedåt för att nå djupliggande grundvatten. Vi utvidgar en evolutionär modell av trädkronor med grundvatten och en pålrot, där träd med olika höjd konkurrerar om ljus. Det finns ingen konkurrens om vatten. Vi undersöker hur mångfalden hos träden beror på vattendjup, vattengradient och dödlighet orsakad av torka. Med hjälp av pålroten kan träden nå djupt vatten och därigenom minska dödligheten, men den medför också en kostnad, så en avvägning måste göras. Vi ser att pålrötter upprätthåller mångfalden hos växterna vid ökad mortalitet, och att pålrötter uppstår när grundvattnet är grunt. Det finns inga strategier som kan överleva om grundvattnet är djupt och dödligheten är hög. Vår modell kan förklara hur grundvatten kan förändra sammansättningen på trädsamhällen, när träd med och utan pålrot kan samexistera, och under vilka förutsättningar endast en av strategierna förväntas dominera. Artikel IV: Träd som växer upp i en skog måste konkurrera med andra träd om ljus, framförallt större träd. Detta ger upphov till en asymmetrisk ljuskonkurrens, där de små träden hämmas av större träd. Små träd har därmed små chanser att överleva utom då skogen nyligen störts och det öppnas upp en glänta. Vid denna ljuskonkurrens kan man anta att trädkronans form har stor betydelse för trädets framgång. Frågan är hur de evolutionärt fördelaktiga kronformerna beror på latituden och produktiviteten. Vi antar att latituden påverkar solens genomsnittliga vinkel och ljusrespons. Vi utvidgar en storleksstrukturerad trädmodell med självskuggning där två evolverande egenskaper beskriver kronans topptyngd och bredd. Med modellen kan vi undersöka vilka strategiska avvägningar som bestämmer om kronans form blir konkurrenskraftig. En topptung krona har högt ljusupptag eftersom det finns mest ljus högt upp i grenverket. Å andra sidan har den en låg tillväxteffektivitet eftersom topptunga kronor måste tappa mycket grenar för att behålla sin form. En bred krona har en låg självskuggning eftersom bladen är utspridda. Å andra sidan har den höga kostnader för de långa grenar som krävs. Vi finner att när dessa egenskaper evolverar tillsammans så finns endast en evolutionärt stabil strategi (ESS), långt från den högsta nettoproduktionen. När endast solvinkeln minskar med ökande latitud minskar både kronans bredd och topptyngd, men när både solvinkel och ljusrespons minskar med ökande latitud så är bredden nästan oförändrad utom vid låg produktivitet då den minskar med latituden. Kronans topptyngd minskar alltid med latituden. Slutligen ser vi hur kronans topptyngd alltid ökar med nettoproduktionen vid ESS, medan kronans bredd har ett maxium för ett mellanvärde hos nettoproduktionen vid ESS.

Page generated in 0.0351 seconds