I addressed how light availability influences sexual and clonal offspring production, demographic performance and contribution to population dynamics by studying the Neotropical understory herb Calathea marantifolia across a light gradient in Costa Rica. To understand how demographic performance was influenced by light availability I conducted a transplant experiment in the field. Both seedlings and clonal offspring grew best when planted in high light areas, but seedlings showed a faster and more dramatic response. Survival of seedlings was greatest in high light sites but clonal offspring survival was greatest where light availability was low. To examine the demographic consequences of physiological integration between parent plants and their clonal offspring I combined an isotope tracing study with a severing experiment in natural populations. Very little water was transported between parent and offspring. Severing the connections between parent and offspring did not influence the demographic performance of parent plants, but clonal offspring were negatively affected, especially prior to rooting. I investigated the demographic cost of sexual reproduction by manipulating the sexual reproductive effort of plants in the field. Increasing the sexual reproductive effort of plants did not reduce their future demographic performance. However, subsequently produced clonal offspring displayed a small reduction in size due to their parent's increased reproduction. To understand the contribution of both reproductive modes for population growth rate I used field data collected in plots with high and low light. Data from the first census interval were used to develop a new size-structured integral projection model that includes both sexual and clonal recruitment. Population growth rate was faster in high light than in low light and a life table response experiment revealed that this difference was primarily due to improved survival and growth at large sizes and increased clonal reproduction in high light. By removing reproductive modes from the model, I found that sexual reproduction contributes more to population growth than clonal reproduction. When only sexual reproduction is included in the model population growth rate is fastest in high light environments. By contrast, when only clonal reproduction is included in the model population growth rate is fastest low light.

Bottomland hardwood stands managed as greentree reservoirs (GTRs) provide critical habitat for numerous wildlife species. The oak component in GTRs is of critical importance to wildlife managers since oaks produce high energy foods during the winter. However, GTR management warrants concern since it has been linked to increased mortality and insufficient regeneration of desirable species. This project evaluates willow oak acorn production and the effects of flooding and midstory control on the survival and growth of planted willow oak seedlings. Winter flooding reduced survival of seedlings inundated in early October but did not reduce survival of seedlings inundated in mid-November. Midstory control did not produce desired light levels for the future survival of underplanted seedlings. Acorn production was good for both years. Trees with DBH between 55 and 65 cm produced the majority of sound acorns. Acorn production was likely adequate to support foraging waterfowl and natural regeneration.

No description available.

På grund av hårt skogsbruk har den generella skogsstrukturen i Sverige förändrats, vilket har påverkat ljusklimatet i skogsvattendrag. Övergången från gammal skog till yngre produktiv skog i kantzonen längs vattendrag har lett till ett strukturellt skifte mot mer enskiktade krontak som förmodligen lämnar lite utrymmer för ljus att tränga igenom. Ljus är en fundamental faktor som möjliggör många ekologiska processer i skogsvattendrag, vilket gör det till en viktig aspekt att undersöka för att kunna upprätthålla ett hållbart skogsbruk. Denna studie avsåg att undersöka ljusklimatet i skogsvattendrag, med syftet att utreda om det fanns skillnader i förhållande till skogens ålder. Studien utfördes i augusti 2020 i Stockholms län, och innefattade fem vattendrag i medelåldrig skog (40 – 80 år) samt fem i gammal skog (>140 år). Krontakstäckning uppskattades genom hemisfäriska foton tagna med en fish-eye lins vid åtta punkter i varje provlokal, och analyserades med hjälp av en mobilapplikation (GLAMA). En inventering av träd i kantzonerna utfördes enligt point-centered quarter method, och datan användes för att beräkna träddensitet, artrikedom samt absolut densitet för varje påträffad art. Resultaten visade en liten men icke-signifikant skillnad i krontakstäckning mellan ålderskategorierna, med en något högre medelprocent i gammal skog. Både medelåldrig och gammal skog dominerades av gran, och artsammansättningen var lika oavsett ålderskategori. Träddensiteten skilde sig något mellan kategorierna, med indikationer på en högre medeldensitet i gammal skog. Ytterligare studier krävs för att minska osäkerheter samt vidare öka kunskaperna om skogsbrukets effekter för att kunna bevara de akvatiska och terrestra miljöerna i skogsekosystem. / Due to intensive forestry, the general stand structure in Swedish forests has changed, which in turn has affected light availability in forest streams. The transformation from old growth to younger productive forests in the riparian zone has led to a structural shift towards a higher density and single-leveled canopies that limits light penetration. Light is a fundamental factor promoting many ecological processes in forest streams, which makes it an important feature to examine in a sustainable forestry context. This study investigated the light climate in forest streams, with the purpose to look for differences in relation to forest age. The study was conducted in August 2020 in Stockholm County, and consisted of five streams in middle stage forests (40 – 80 years) and five in old growth forests (>140 years). Canopy closure was estimated using hemispherical photos taken with a fish-eye lens at eight sample points within each site and analyzed with a mobile app (GLAMA). An inventory of trees in the riparian zone was carried out according to the point-centered quarter method, and the data were used to measure tree density, species richness and absolute density of each observed species. The results showed small non-significant differences in canopy closure between age categories, with a higher mean percentage in old growth forests. Both middle stage and old growth forests were dominated by spruce, and the species richness was the same regardless of age category. The tree density differed slightly between categories, with a tendency for a higher mean density in old growth forests. Further research is needed to reduce uncertainty and expand on the effects of forestry if we are to sustain the aquatic and terrestrial environments in forest ecosystems.

Dynamics of carbon and phosphorus flows in arbuscular mycorrhizal symbiosis Mgr. Tereza Konvalinková (doctoral thesis) Abstract Arbuscular mycorrhizal fungi (AMF) are widespread and highly specialized root symbionts, which gain all of their carbon (C) from the hosts, supplying plants with mineral nutrients (particularly with phosphorus, P) in return. This thesis focuses on the size and flexibility of C and P flows in arbuscular mycorrhiza in relation to environmental conditions, in particular to light and P availability. The indications that the symbiotic flows are regulated actively by both partners are discussed. The main findings are presented as a compilation of separate scientific works (two research articles, one review and one book section). A glasshouse experiment has shown that both mycorrhizal benefits and mycorrhizal colonization of medic (Medicago truncatula) by an AMF species (R. irregularis) decline along the gradient of decreasing light intensity. Interestingly, morphological adaptation of medic to the long-term light deprivation was boosted by mycorrhiza, probably because of C demand of AMF and due to the improved nutrition of the mycorrhizal plants. On the other hand, sudden 6-day shading caused rapid decline of shoot P content of mycorrhizal plants, accompanied with the accumulation of P...

Un des principaux challenges pour prédire la composition, la structure et la dynamique des communautés végétales est de déterminer comment l’environnement biotique et abiotique va modifier la direction et l’amplitude des interactions entre plantes. L’objectif de ma thèse est de mettre en évidence le rôle prépondérant des interactions complexes (impliquant plus de deux compartiments biotiques) dans la dynamique forestière et plus particulièrement dans la dynamique de régénération des ligneux d’intérêt sylvicole tel que le chêne sessile. Les résultats soulignent l’importance de prendre en compte : (i) l’effet des cervidés sur les patrons de réponses des interactions entre plantes le long des gradients de ressources, (ii) les interactions indirectes et notamment la facilitation indirecte, (iii) des paramètres démographiques différents en relation avec la phénologie des espèces en présence, (iv) la séparation des mécanismes sous-jacents à une interaction écologique multiple via un suivi des conditions environnementales. Ainsi, ma thèse appuie l’idée que les gestions se focalisant sur une unique pression et ignorant les autres pressions ne sont pas capables de maintenir des populations d’espèces cibles car elles ne tiennent pas compte des interactions multiples. Ceci souligne l’importance d’utiliser des stratégies complémentaires pour permettre la pérennité des écosystèmes forestiers et notamment une régénération suffisante dans le cadre des changements globaux que sont le changement climatique et la surabondance de cervidés. / One of the main challenges to predict vegetation dynamics and plant community composition is to identify how biotic and abiotic factors modify the nature and magnitude of plant-plant interactions. The objective of my thesis is to highlight the leading role of multiple interactions (involving more than two biotic compartments) in forest understory dynamics and more specifically regeneration dynamics of target species such as sessile oak. The results emphasize the importance of: (i) effects of deer on response patterns of plant-plant interactions along resource gradients, (ii) indirect interactions, in particular indirect facilitation, (iii) demographic parameters in relation to species phenology, (iv) distinguishing among underlying mechanisms of multiple interactions thanks to environmental monitoring. Thus, my thesis supports the idea that management practices focusing on a single pressure, while ignoring others, are unable to conserve populations of target species because they don’t consider multiple interactions. This highlights the importance to use complementary management strategies to achieve sustainability in the context of global changes (climatic change and deer overabundance).